CA2267304A1 - System interconnection device and distributed power supply device including the same having instantaneous voltage drop counter-measure function - Google Patents
System interconnection device and distributed power supply device including the same having instantaneous voltage drop counter-measure function Download PDFInfo
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- CA2267304A1 CA2267304A1 CA002267304A CA2267304A CA2267304A1 CA 2267304 A1 CA2267304 A1 CA 2267304A1 CA 002267304 A CA002267304 A CA 002267304A CA 2267304 A CA2267304 A CA 2267304A CA 2267304 A1 CA2267304 A1 CA 2267304A1
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- power supply
- voltage drop
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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Abstract
A system interconnecting device (21) is interposed between two power systems, such as a power receiving bus (22) for receiving electric power through a commercial power line (25) and a cogeneration bus (23) for receiving electric power from a private power generator (27). The device (21) is provided with thyristors (TH1 and TH2), diodes (D1 and D2), and a DC reactor (L). The thyristors (TH1 and TH2) are connected to the AC terminal (AC1), the diodes (D1 and D2) are connected to the AC terminals (AC2), the thyristor (TH1) and diode (D1) are connected to the DC terminal (DC1), and the thyristor (TH2) and the diode (D2) are connected to the DC terminal (DC2). The reactor (L) is connected between the DC terminals (DC1 and DC2). Therefore, when a fault occurs in a distribution line (26), the commercial power line (25), etc., power failure due to the overload of the power generator (27) can be prevented and instantaneous voltage drop in a distribution line (28) connected with an important load can be suppressed by the current limiting action of the reactor (L).
Description
SYSTEM INTERCONNECTION DEVICE AND
DISTRIBUTED POWER SUPPLY DEVICE INCLUDING THE SAME
HAVING INSTANTANEOUS VOLTAGE DROP COUNTER-MEASURE
FUNCTION
FIELD OF THE INVENTION
The present invention relates to a system interconnection device for interconnecting two power systems, for example, a commercial power supply system and domestic power generation system, especially a system interconnection device having a capability to cope with an instantaneous voltage drop due to a short circuit and other reasons, and also refer to a distributed power supply device having an instantaneous voltage drop counter-measure function operated by the system interconnection device in interconnection with a commercial power supply system.
DISTRIBUTED POWER SUPPLY DEVICE INCLUDING THE SAME
HAVING INSTANTANEOUS VOLTAGE DROP COUNTER-MEASURE
FUNCTION
FIELD OF THE INVENTION
The present invention relates to a system interconnection device for interconnecting two power systems, for example, a commercial power supply system and domestic power generation system, especially a system interconnection device having a capability to cope with an instantaneous voltage drop due to a short circuit and other reasons, and also refer to a distributed power supply device having an instantaneous voltage drop counter-measure function operated by the system interconnection device in interconnection with a commercial power supply system.
BACKGROUND OF THE INVENTION
Figure 9 illustrates an arrangement of a basic interconnection of an above-mentioned commercial power supply system and domestic power generation system. A
commercial power supply line 1 extends into a place where necessary and is connected to a receptor bus line 2 therein. The receptor bus line 2 is then connected to many distribution lines 3 which is connected to general loads.
Meanwhile, a cogenerator bus line 5 is connected to a domestic power generator 6 via a power supply line 9 and is also connected to, for example, distribution lines 4 extending to essential loads that make up of about 60%
to 70% of the domestic power generation capacity. The receptor bus line 2 and the cogenerator bus line 5 are mutually connected via a bus line connecting line 8 along which a breaker 7 is provided. The breaker 7 is actuated by a relay (not shown) provided to the side of the commercial power supply line 1 so as to break the bus line connecting line 8 when there occurs a malfunction including a short circuit, grounding, and opening of a receiving system.
However, with the interconnection thus arranged, when, for example, there occurs an aforementioned malfunction to the receptor bus line 2 or the v distribution line 3, it takes about 5 to 10 cycles (100msec to 200msec at 50 Hz) for the breaker 7 to be actuated, causing the essential loads connected to the distribution lines 4 to suffer a voltage drop for a long period of time. Also, since it takes a long period of time for the breaker 7 to be actuated in this manner, when a breaker (not shown) of a power supply line for the commercial power supply line 1 is opened, the domestic power generator 6 must operate while being connected to loads of the place. The loads, which typically amount to a several times larger than the capacity of the domestic power generator 6, constitute an overload for the domestic power generator 6, and are blacked out at last.
Figure 10 shows a typical system interconnection device 11 using conventional technologies to address such a problem. Here, for convenience, members shown in Figure that have similar, corresponding functions as members shown in Figure 9 are indicated by the same reference numerals and description thereof is omitted.
The system interconnection device 11 includes two thyristors 12 and 13 connected in reverse parallel. When an interconnection is established between the bus lines 2 and 5, the gates of the thyristors 12 and 13 are driven by the output of the aforementioned relay to keep the thyristors 12 and 13 energised. When there is an , , aforementioned malfunction, the gates of the thyristors 12 and 13 are blocked, and the thyristors 12 and 13 are opened.
Malfunction detection when the thyristors 12 and 13 are driven is carried out at, for example, half-cycle intervals, and the thyristors 12 and 13 become ready to drive opening at the zero cross point in the immediately subsequent half cycle. Therefore, taking a direct offset current as an example, the bus lines 2 and 5 can be opened within one cycle (20 msec at 50 Hz) after the occurrence of the malfunction. However, before the opening, the arrangement is still incapable of stopping a complete short-circuit current from flowing and of avoiding a great voltage drop from occurring across the cogenerator bus line 5.
As explained so far, in comparison to interconnection by the breaker 7, the system interconnection device 11 cuts short the time required to break the connection between the bus lines 2 and 5 and avoids the domestic power generator 6 from coming to a halt. However, the system interconnection device 11 is still short of eliminating an instantaneous voltage drop, and negatively affects the loads connected to the cogenerator bus line 5 of, for example, a computer.
Figure 11 shows an arrangement of a conventional t distributed power supply device establishing an interconnection with a system by the breaker 7. Here, for convenience, members shown in Figure 11 that have similar, corresponding functions as members shown in Figure 9 are indicated by the same reference numerals.
The distributed power supply device includes, for example, a diesel-fueled power generator or gas-fueled power generator as the domestic power generator 6 constituting a cogeneration system, which is an example of so-called new energy supply, and operates on an alternative current in interconnection in parallel to a commercial power supply system including a power supply 13. Essential loads that make up of about 60o to 70% of the domestic power generation capacity are connected to the distribution line 4 connected to the cogenerator bus line 5 of the distributed power supply system.
There are diverse alternative choices to be adopted as the domestic power generator 6 other than the diesel-fueled power generator and the gas-fueled power generator, including a secondary cell, fuel cell, photovoltaic power generation system, flywheel, wind power generation system, and UPS (Uninterruptible Power Supply) .
The breaker 7 is provided in the distributed power supply system to operate the interconnected distributed power supply system and commercial power supply system.
In some cases, where necessary, a countermeasure is taken to cope with a short-circuit current such as a reactor in accordance with guidelines of the interconnection.
However, if there occurs a malfunction to the commercial power supply system, such as a grounding and phase-to-phase short circuit, shown by reference number 15, a malfunction current flows from the distributed power supply system, causing a voltage drop in the distributed power supply system.
As a counter-measure to such a malfunction, the arrangement is made such that a voltage transformer detects the voltage of the commercial power supply line 1, an undervoltage relay judges according to a detected result whether it is possible or not to lower the voltage, and, when a voltage drop having a value not larger than a preselected number is judged, the breaker 7 is driven to open. Another arrangement may be made such that a current transformer detects an interconnection current, an overcurrent relay judges according to a detected result whether it is possible or not to increase the current, and the breaker 7 is driven to open when there is detected an overcurrent having a value not smaller than a preselected number.
However, the voltage of the distributed power supply _.7 _ system remains dropped until the breaker 7 opens (3 kinds of cycles, i.e., 2, 3, and 5 cycles, according to the JEC
2300 standards). Figure 12 shows a compensable region for the voltage drop and the region of the presence of the effect of an instantaneous voltage drop on the load when a vacuum breaker is used as the breaker 7. Figure 12 shows a threshold value of each load where the effect appears in relation to the voltage drop rate and the period of time during which the voltage remains dropped.
A reference denotation M1 shows a compensable region for the voltage drop in the aforementioned vacuum breaker.
As shown in Figure 12, most of the loads connected to the distribution line 4 fall out of the compensable region, being vulnerable to a voltage drop. In other words, although having successfully developed a countermeasure against a blackout of the essential loads by interconnecting the distributed power supply to the system, the distributed power supply device shown in Figure 11 completely fails to satisfy the demand for a countermeasure against the instantaneous voltage drop.
For these reasons, conventionally, a UPS (Uninterruptible Power Supply) is provided to some essential loads as indicated by the reference denotation 16.
The UPS AC/DC-converts, rectifies, and smooths the electric power fed from the cogenerator bus line 5, saves _g_ the DC power in an accumulator with a charger, and sends out, after conversion from DC to AC, the electric power saved in the accumulator to a load. Therefore, the UPS
has following problems: a semiconductor switching element and other components are indispensable, the costs are high, and there occurs a large loss in conversion. The UPS consequently is only used for aforementioned some essential loads. This leaves most of the loads having a widely used electromagnetic switch unprotected against an instantaneous voltage drop.
For these reasons, the system interconnection device 11 shown in Figure 10 is more and more commonly used as shown in Figure 13 to interconnect the distributed power supply device to a commercial power supply system. Here, for convenience, members shown in Figure 13 that have similar, corresponding functions as members shown in Figure 10 or 11 are indicated by the same reference numerals and description thereof is omitted. However, in some cases, the system interconnection device 11 still consumes a total time period of one cycle for the detection of a voltage drop and the passing of the zero cross where the thyristors 12 and 13 can be arc-removed.
Thus, the system interconnection device 11 using the thyristors 12 and 13 can compensate for a voltage drop in a region denoted by a reference denotation M2 in Figure r _9_ 12. This compensates many operations of office automation equipment and medical electric appliances, but still falls short of eliminating the effect on an electromagnetic switch provided to a distribution line extending essential loads and velocity variable motor contained in essential loads.
Therefore, the UPS 16 is necessary to essential loads among those loads incompensable even by the system interconnection device 11 using the thyristors 12 and 13 (those which fall out of the region shown by the reference denotation M2 in Figure 12).
If the distributed power supply system is interconnected to the commercial power supply system, there is an increase in the short-circuit capacity, and occurs a need for the breaker in the load side to be replaced by a breaker with a larger momentary break capacity, and also a need for the cable connected to the breaker to be replaced by a cable with a larger current capacity. Another problem is that if a malfunction occurs and it takes time for the system to be disconnected, the domestic power generator 6 stops operating and the distributed power supply system comes to a complete halt.
An object of the present invention is to offer a system interconnection device capable of restraining an instantaneous voltage drop when a malfunction occurs in t interconnection of two power systems, for example, a commercial power system and a domestic power supply generation system, provide a distributed power and to supply device having an instantaneous voltage drop counter-measure function equipped with such a system interconnection device.
DISCLOSURE OF THE INVENTION
The system interconnection device in accordance with claim 1 of the present invention is a system interconnection device, disposed between two power systems, for making an adaptable use of electric power by interconnecting the two power systems with each other, and is characterised in that it includes:
a single phase rectifier circuit arranged so that a pair of rectifying switching elements are connected to one of two a.c. terminals connected so as to link phase interconnecting terminals of the two power systems and that a pair of rectifying elements are connected to the other one of the two a.c. terminals; and a d.c. reactor connected so as to link two d.c.
terminals that are connecting points of the rectifying switching elements to the rectifying elements.
According to the above arrangement, when connecting the two power systems with each other, the d.c. reactor is connected so as to link the d.c. terminals of the single phase rectifier circuit constituted by the two rectifying switching elements realised by thyristors or other members and the two rectifying elements realised by diodes, thyristors, or other members, and the a.c.
terminals are connected to the respective power systems.
The circuit has following functions:
(i) under normal operation, the impedance viewed from the a.c. side is substantially zero, (ii) when a short-circuit occurs, a high impedance is produced instantaneously and restrains a short-circuit current, and (iii) the rectifying switching elements can cut off the two systems quickly.
The following will discuss functions (i) to (iii) in this order.
(i) The d.c, reactor, viewed from the a.c. terminal, can have an impedance which is substantially zero under normal operation and which is large only when a malfunction occurs.
(ii) Even if such a malfunction occurs, a current sustaining function by the d.c. reactor increases the inter-terminal voltage of the d.c. reactor and can restrain an instantaneous drop in power supply voltage applied across essential loads in the power system side which should be separated. Furthermore, the current sustaining function by the d.c. reactor can realise a current limiting function that restrains a malfunction current from flowing through a distribution line where the malfunction is happening, and restrain the short-circuit capacity of the two power systems.
(iii) When a malfunction occurs, the rectifying switching elements can cut off and separate the two systems quickly. Therefore, a generator provided in the power system to be separated does not stop its operation due to an overload, and a blackout can be avoided.
In the system interconnection device in accordance with claim 2 of the present invention, since by setting a current attenuation time constant determined by a reactance component and resistance component of the d.c.
reactor and a rectifier circuit including the rectifying switching elements and rectifying elements to not less than 2.5 times a system frequency cycle of the power system, a threshold current at which the d.c. reactor starts a current limiting function is specified, there is no need for a special power supply.
To put it differently, Figure 2 shows a relationship between the current attenuation time constant and an equivalent impedance produced across the a.c. terminals of the system interconnection device. Typically, the d.c.
reactance is selected so as to restrain a malfunction current during a system short-circuit malfunction to approximately 3 times the rated current.
Meanwhile, under normal operation, it is preferable to reduce the equivalent impedance as much as possible.
Practically, since the requirement is met if the equivalent impedance is not larger than 3% of the rated current, or in other words, as shown in Figure 2, not larger than 0.09pu (=30/33%) the a.c. impedance produced by the d.c. reactor L, from Figure 2, if the current attenuation time constant is not less than 2.5 times the system frequency cycle of the power system, there is no regular loss, and a current limiting function can be carried out when a system malfunction causes a current not less than the threshold current to flow.
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 3 of the present invention is a distributed power supply device with an instantaneous voltage drop counter-measure function, having a single power supply or a plurality of power supplies, connected to an essential load which should avoid an instantaneous voltage drop and blackout, and operated in a.c. parallel interconnection to a commercial power supply system by the system interconnection device as defined in any of claims 1 and 2, and is characterised in that an inductance of the d.c. reactor is formed to have a reactance larger than (1-A)/A times an equivalent inductance corresponding to an internal impedance of a distributed power supply system where A is a voltage drop ratio acceptable to the distributed power supply system when a malfunctions occurs in the commercial power supply system.
With the arrangement, when a malfunction occurs, the system interconnection device in accordance with claim 1 or 2 disposed between the bus lines of the two systems restrains voltage drop in the distributed power supply system and the short-circuit current by the large reactor of the impedance. While voltage drop is restrained, a protective relay arc-removes the semiconductor switching element, and breaks the distributed power supply system off the commercial power supply system.
In a distributed power supply system arranged in this manner, if a malfunction occurs in the commercial power supply system, the bus line voltage in the distributed power supply system equals a value of the system voltage divided between the equivalent inductance of the distributed power supply system and the inductance of the d.c. reactor. Therefore, from the acceptable voltage drop ratio A, a choice is made so as to satisfy Ldc /Ls > (1-A)/A where Ldc is the inductance of the d.c.
reactor and Ls is the equivalent inductance of the distributed power supply system. In other words, when the voltage drop ratio A is, for example, 50%, by equalising the inductance Ldc of the d.c. reactor to the equivalent inductance Ls of the distributed power supply system, the voltage drop ratio can be restrained within the above range A. In addition, when the voltage drop ratio A is, for example, 250, from (1-0.25)/0.25, the inductance Ldc of the d.c. reactor only needs be set to 3 times the equivalent inductance Ls of the distributed power supply system.
Simply by setting the inductance Ldc of the d.c.
reactor according to the voltage drop ratio A acceptable to the distributed power supply system when a malfunction occurs and to the equivalent inductance Ls of the distributed power supply system, even without using a UPS, the operation is assured of devices that are prone to instantaneous voltage drop such as an electromagnetic switch that are connected to essential loads, variable velocity motor, and other devices. As a result of this, the operation of the interconnection is more reliable, and the stress on the distributed power supply system can be reduced. Further, since the short-circuit current is restrained owing to the current limiting function of the d.c. reactor, breakers and cables in the load side do not need be replaced by those having undesirably large capacities for interconnection.
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 4 of the present invention is characterised in that the power supply in the distributed power supply system is a rotary machine.
With the above arrangement, if the rotary machine is used as a power supply in a distributed power supply system, during a short-circuit malfunction, although a high short-circuit current is running, the circuit .voltage, i.e. the output voltage of a generator of the rotary machine, becomes zero, the stress between that generator and a motor of the rotary machine is released, and a mechanical vibration occurs to the shaft, and when the short-circuit malfunction is solved, the generator of the rotary machine carries an excessive load above the capacity thereof , an abrupt braking torque occurs to that generator, and an excessive vibration torque occurs to the shaft . While a stress (e . g. a share-pin split in a case of a turbine-driven generator) results, as explained here, from an temporary release of overcurrent from the generator of the rotary machine when a short-circuit malfunction occurs, the stress can be avoided by restraining the short-circuit current as explained earlier..
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 5 of the present invention is characterised in that the power supply in the distributed power supply system is of a stationary model using an inverter.
With the arrangement, since the stationary model power supply has no inertia unlike a rotary machine, halts soon, and results in a blackout, the present invention can be embodied in a especially preferable manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a drawing illustrating a system interconnection device of an embodiment in accordance with the present invention.
Figure 2 is a graph showing a relationship between a current attenuation time constant with respect to an a.c. power supply cycle and an equivalent impedance.
Figure 3(a) through Figure 3(c) are drawings showing a possible arrangement example of a current limiting device as such and that when the current limiting device is used as a system interconnection device.
Figure 4(a) through Figure 4(h) are waveform charts illustrating operations of the system interconnection device shown in Figure 1.
Figure 5(a) through Figure 5(h) are waveform charts illustrating operations of the system interconnection device shown in Figure 3.
Figure 6 is a single phase schematic of a power system of another embodiment in accordance with the present invention, illustrating a distributed power supply device incorporating the system interconnection device shown in Figure 1.
Figure 7(a) and Figure 7(b) are simulation waveform charts illustrating operations of the distributed power supply device shown in Figure 6.
Figure 8(a) and Figure 8(b) are simulation waveform charts illustrating operations of a conventional distributed power supply device shown in Figure 13.
Figure 9 is a drawing illustrating a basic arrangement of system interconnection.
Figure 10 is a drawing illustrating a typical conventional system interconnection device.
_1_g_ Figure 11 is a single phase schematic of a power system, illustrating a typical conventional distributed power supply device.
Figure 12 is a graph illustrating examples of effect by an instantaneous voltage drop on a load device and a compensable region of various devices in accordance with the present invention and conventional technologies.
Figure 13 is a single phase schematic of a power system, illustrating another conventional distributed power supply device.
BEST MODES OF CARRYING OUT THE INVENTION
The following will discuss an embodiment in accordance with the present invention in reference to Figure 1 through Figure 5.
Figure 1 is a drawing illustrating a system interconnection device 21 of an embodiment in accordance with the present invention. The system interconnection device 21 is disposed along a bus connecting line 24 connecting a receptor bus line 22 to a cogenerator bus line 23 in a place where necessary. The receptor bus line 22 is connected to a commercial power supply line 25 and to distribution lines 26 which are connected to many general loads. The cogenerator bus line 23 is connected to a domestic power generator 27 and to distribution lines 28 which are connected to essential loads, such as computers.
The system interconnection device 21 is realised by a pair of thyristors TH1 and TH2 that are rectifying switching elements, a pair of diodes D1 and D2 that are rectifying elements, and a d.c. reactor L. It should be noted in the present invention that the pair of thyristors TH1 and TH2 are connected to one of a pair of a.c. terminals AC1 and AC2 connected to the bus connecting line 24, while the pair of diodes D1 and D2 are connected to the other one of the pair of the a . c .
terminals AC1 and AC2 (In an example shown in Figure 1, the thyristors TH1 and TH2 are connected to the a.c.
terminal AC1, and the diodes Dl and D2 are connected to the a.c. terminal AC2). Meanwhile, the d.c. reactor L is connected so as to link d.c. terminals DC1 and DC2.
In the system interconnection device 21, between an equivalent impedance viewed from the power system side, and a current attenuation time constant determined by a rectifier circuit constituted by the thyristors THl and TH2, the diodes D1 and D2 and a reactance component and resistance component of the d.c. reactor L, there is a relationship shown in Figure 2; the equivalent impedance decreases with a larger current attenuation time constant. Meanwhile, the device impedance is preferably as small as possible under normal operation. Therefore, in the present invention, the current attenuation time constant is selected so as to be 2.5 or more times the system frequency cycle of the power system.
In the system interconnection device 21 arranged in the above manner, under normal conditions, the gates of the thyristors TH1 and TH2 are driven to energise the thyristors TH1 and TH2, permitting a current to flow along either a path denoted by a reference denotation il or a path denoted by a reference denotation i2.
Therefore, the direction and amplitude of the current flowing through the d.c. reactor L are constant, and the d.c. reactor L has an impedance Z (=c~L) of 0, causing no loss.
By contrast, if an overcurrent is about to flow from the cogenerator bus line 23 side to the receptor bus line 22 side due to, for example, a short-circuit or grounding of the distribution lines 26 or an opening of a receptor system, the d.c. reactor L immediately increases the impedance Z thereof and increases the inter-terminal voltage, so as to retain the current between the terminals at a constant level.
With this, the impedance viewed from the a. c.
terminals AC1 and AC2 side increases, and a current limiting function can be realised that restrains the current flowing from the cogenerator bus line 23 side to the receptor bus line 22 side via the bus connecting line 24. During the time, the gates of the thyristors TH1 and TH2 are blocked by an output of a short-circuit or ground relay, and the cogenerator bus line 23 is cut off from the receptor bus line 22 surely and quickly within a single cycle. Therefore, the domestic power generator 27 can be prevented from being overloaded.
In this manner, a malfunction in the receptor bus line 22 side can be prevented from halting the operation of the domestic power generator 27, and a likely blackout can be thus prevented. In addition, the malfunction is prevented by an increased inter-terminal voltage of the d. c . reactor L from causing an instant voltage drop in the cogenerator bus line 23. The reliability of the cogeneration system can be thus improved. Furthermore, by achieving the current limiting function mentioned above, the short-circuit capacities in both the cogenerator bus line 23 side and the receptor bus line 22 side can be restricted.
The following describes an example of a single phase mixed bridge rectifier circuit applied to a current limiting device (Japanese Laid-Open Patent Application No. 49-50448/1974 (Tokukaisho 49-50448/1974)) shown in Figure 3(a). The current limiting device 31 is constituted by a mixed bridge rectifier circuit 32 and a current limiting reactor L2 that are disposed in parallel with each other and in series with an a.c. line 33.
The mixed bridge rectifier circuit 32 is constituted by a pair of thyristors thl and th2, a pair of diodes dl and d2, a d.c. reactor L1, and a d.c. power supply B
connected in series to the d.c. reactor L1. It should be noted that the thyristor thl and diode dl are connected to one of a.c. terminals, i.e. an a.c. terminal AC1, and that the thyristor th2 and diode d2 are connected to the other one of the a.c. terminals, i.e. an a.c. terminal AC2. Therefore, the thyristors thl and th2 are connected to the d.c. terminal DC1, the diodes dl and d2 are connected to the d.c. terminal DC2, a d.c. circuit constituted by the d.c. reactor L and the d. c. power supply B is provided between the d.c. terminals DC1 and DC2.
In the current limiting device 31 arranged as above, the thyristors thl and th2 are energised under normal conditions, and the line current bypasses the current limiting reactor L2 and flows via the mixed bridge rectifier circuit 32. By contrast, when a malfunction occurs, a current exceeding the current value set by the d . c . power supply B is restrained by the d . c . reactor L1, effecting a current limiting function. Thereafter, the thyristors thl and th2 are opened. By the opening of the thyristors thl and th2, an undesirable overvoltage is generated between the a.c. terminals AC1 and AC2.
Therefore, a side path circuit is formed between the a.c.
terminals AC1 and AC2 from the current limiting reactor L2 for restraining the overvoltage. The presence of the current limiting reactor L2 does not permit application to a system interconnection device for the purpose of separation of systems.
Let us suppose that the mixed bridge rectifier circuit 32 arranged as above is applied to a system interconnection device as in the present invention with no current limiting reactor L2 and no d. c. power supply B which determines a threshold current for operation of the d.c. reactor L1. Figure 3(b) shows such a system interconnection device 41. Members of the system interconnection device 41 corresponding to those of system interconnection device 21 in accordance with the present invention are indicated by the same reference numerals and description thereof is omitted.
It should be noted that in the system interconnection device 41, the thyristor THla and diode Dla are connected to one of a.c. terminals, i.e. an a.c.
terminal AC1, and that the thyristor TH2a and diode D2a are connected to the other one of the a.c. terminals, i.e. an a.c. terminal AC2. Therefore, the thyristors TH1 and TH2 are connected to the d.c. terminal DC1, the diodes Dla and D2a are connected to the d.c. terminal DC2, and the d.c. reactor L is provided between the d.c.
terminals DC1 and DC2.
In other words, the system interconnection device 41 differs from the system interconnection device 21 in accordance with the present invention in how the thyristors and diodes are connected in the single phase bridge rectifier circuit.
Figures 4 and 5 show simulation waveform of various parts when the system interconnection devices 21 and 41 are opened. Conditions for simulation are such that the percentage impedance of the commercial power supply is set to 100, the reactance of the power supply thereof is set to l.Opu, the power supply frequency is set to 50Hz, and the reactance of the d.c. reactor L is set to 4.Opu.
As shown in Figures 4 (a) and 5 (a) , the current flowing through the thyristors TH1 and THla are such that the arc is removed temporarily when crossing zero after a half cycle during which the a.c. terminal AC1 is at a high level lapses and that no current flows thereafter.
As a result of this, referring to Figure 4(c), the current flowing through the diode D2 changes into a current, denoted by a reference denotation al, which corresponds to the current flowing through the thyristor TH1 and a current, denoted by a reference denotation a2, caused by energy released by the d.c. reactor L. By contrast, referring to Figure 5(c), the current flowing through the diode D2a changes into a current, denoted by a reference denotation ail, which corresponds to the current flowing through the thyristor THla and currents, denoted by reference denotations ,Q2, ~i3, (34, etc., added by energy released by the d.c. reactor L. As shown by the reference denotation i3 in Figure 3(b), the phenomenon occurs since the thyristor TH2a cannot remove the arc due to a current circulated by the opening of the thyristor THla, and the current thus increases.
Therefore, as shown in Figure 4(b), the current flowing through the thyristor TH2 removes the arc after only a half cycle during which the a.c. terminal AC2 is at a high level . By contrast, as shown in Figure 5 (b) , the current flowing through the thyristor TH2a increases at every one cycle. As a result of this, as shown in Figure 4(d), the current flowing through the diode D1 equals the sum of the current flowing through the thyristor TH2 shown in Figure 4(b) and the current, denoted by a reference denotation a2 in Figure 4(c), caused by the release by the d.c. reactor L, whereas the current flowing through the diode Dla, as shown in Figure 5(d), increases at every one cycle similarly to the current flowing through the diode D2a shown in Figure (c) .
Further, as a result of this, in the system interconnection devices 21 and 41, Figures 4(e) and 5(e) show the current flowing through the d.c. reactor L, Figures 4 ( f ) and 5 ( f ) show the voltage of the cogenerator bus line 23, Figures 4 (g) and 5 (g) show the voltage of the receptor bus line 22, and Figures 4(h) and 5(h) show a malfunction current flowing from the cogenerator bus line 23 side to the receptor bus line 22 side.
The current flowing through the d.c. reactor L
converges to a substantially constant value in the system interconnection device 21 in accordance with the present invention as shown in Figure 4(e), but increases at every cycle in the system interconnection device 41 as shown in Figure 5(e). Corresponding to this, the malfunction current also is quickly and surely cut off in one cycle in the system interconnection device 21 in accordance with the present invention as shown in Figure 4(h), but increases at every cycle in the system interconnection device 41 as shown in Figure 5(h).
Therefore, although the system interconnection device 41 does function as a current limiting device, the system interconnection device 41 falls short of arc-removing either one of the thyristors THla and TH2a, and therefore cannot be used as a system interconnection device.
In this respect, when a malfunction occurs, the system interconnection device 21 in accordance with the present invention can surely cut off a malfunction current by carrying out a current limiting function with the d.c. reactor L and opening the thyristors TH1 and TH2. As a result of this, a great improvement can be made on an instantaneous voltage drop, and the UPS that was conventionally provided to each essential load such as a computer can be omitted. In addition, a quick break becomes possible, the domestic power generator 27 can be prevented from being overloaded, and undesirable incidents can be surely avoided such as a blackout due to a halt of the operation of the domestic power generator 27 and an excessive torque load on a generator shaft of a rotary machine due to an abrupt overload. Moreover, it becomes possible to restrain, to a low value, the short-circuit capacity in both the cogenerator bus line 23 side and the receptor bus line 22 side.
Japanese Laid-Open Patent Application No. 49-50448/1974 (Tokukaisho 49-50448/1974) mentioned above also discloses an example of a thyristor pure bridge rectifier circuit applied as a current limiting device.
Figure 3(c) shows such an example. A pure bridge rectifier circuit 32a of a current limiting device 31a is a circuit for limiting current in a similar manner as in the above arrangement shown in Figure 3(a), such that a current always runs through thyristors thl through th4 by means of effect of a d.c. power supply B and that if the current of an a.c. circuit is not larger than the value of that current, the impedance viewed from the a.c. side is zero, and if the current becomes equal to, or larger than, the value of the current, a current limiting function is carried out.
The addition of the d.c. power supply B having the above-mentioned purpose makes it technically and economically difficult to realise the arrangement shown in Figure 3(c). The system interconnection device 21 in accordance with the present invention can dispense with such a d.c. power supply B, as mentioned above, by selecting the current attenuation time constant determined by the reactance component and resistance component of the d.c. reactor L, and the rectifier circuit constituted by the thyristors TH1 and TH2 and diodes D1 and D2 to not smaller than 2.5 times the system frequency cycle of the power system, which is of a totally different arrangement from the technology disclosed in Japanese Laid-Open Patent Application No.
49-50448/l974 (Tokukaisho 49-50448/1974).
Referring to Figure 6 through Figure 8 and aforementioned Figure 12, the following describes another embodiment of the present invention.
Figure 6 is a single phase schematic of a power system, illustrating a distributed power supply device of the other embodiment in accordance with the present invention. A system interconnection device 51 incorporated in the distributed power supply device, having the same arrangement as the system interconnection device 21, connects a receptor bus line 54 to a cogeneration bus line 56 to enable a commercial power supply system and a distributed power supply system to operate in interconnection.
A commercial power supply line 53 extending from a power supply 52 of a commercial power supply system into a place where necessary is connected to the receptor bus line 54. To the receptor bus line 54 are connected many distribution lines 55 which are connected to general loads. The cogenerator bus line 56 of a distributed power supply system is connected via a power supply line 57 to a power supply 58 such as a cogeneration system. To the cogenerator bus line 56 are connected many distribution lines 60 which are connected to essential loads.
The system interconnection device 51 is constituted by a breaker 61, a single phase rectifier circuit 62, and a d.c. reactor 63. The single phase rectifier circuit 62 is made to be connected to a pair of thyristors TH1 and TH2 at at least one of two a.c. terminals (in the breaker 61 side in the example shown in Figure 6) and is constituted by a bridge circuit including the thyristors TH1 and TH2 and a pair of diodes D1 and D2. Thus, it becomes possible to drive opening within half a cycle (lOmsec at 50Hz) when a malfunction occurs, and the breaker 61 opens thereafter. One of the two a.c.
terminals of the single phase rectifier circuit 62 is connected to the cogenerator bus line 56, while the other is connected to the receptor bus line 54 via the breaker 61 . The d. c . reactor 63 connects two d. c . terminals of the single phase rectifier circuit 62 similarly to the above case.
The voltages of the power supply lines 53 and 57 are detected by undercurrent voltage relays 67 and 68 via voltage transformers 65 and 66 respectively. The undercurrent voltage relays 67 and 68 assumes that a malfunction has occurred if the voltages of the power supply lines 53 and 57 are of a predetermined set value, for example, 85% or less, of a rated voltage, arc-removes the thyristors TH1 and TH2, and drives to open the breaker 61.
In a distributed power supply device arranged in this manner, the system impedance in the power supply 58 side looks almost L, and the inductance Ldc of the d.c.
reactor 63 is selected in the present invention so as to meet the relationship with respect to the equivalent inductance Ls of the distributed power supply system:
Ldc / Ls > (1-A) / A ...(1) where Ls is the equivalent inductance corresponding to the internal impedance of the power supply 58 and A is the voltage drop ratio acceptable to the distributed power supply system.
Here, as shown by a reference denotation 69, when considering a case where a grounding malfunction occurs in the commercial power supply system, the voltage of the cogenerator bus line 56 equals a value, of the voltage V
of the power supply 58, divided between the equivalent inductance Ls and the inductance Ldc of the d.c. reactor 63. Therefore, the system voltage V' after the occurrence of the malfunction can be obtained as:
V' - Ldc / ( Ldc + Ls ) x V . . . ( 2 ) Therefore, when the acceptable voltage drop ratio A
is 50%, from Equation 1, by equalising the inductance Ldc to the inductance of the power supply 58 that is substantially equal to the equivalent inductance Ls, in a case where a malfunction occurs in the commercial power supply system as shown by the reference denotation 69, the voltage drop in the cogenerator bus line 56 of the distributed power supply system can be restrained so much as to 50% of the voltage V of the power supply 58. In addition, for example, when the acceptable voltage drop ratio A is 25%, from Equation 1, the multiple Ldc / Ls becomes 3 or larger, and, by setting the inductance Ldc of the d.c. reactor 63 to 3 times the inductance of the power supply 58, the voltage drop in the cogenerator bus line 56 can be restrained so much as to 75% of the voltage V of the power supply 58.
As clearly understood from the foregoing equation, to the larger value the inductance Ldc of the d.c.
reactor 63 is set, to the smaller value the voltage drop can be restrained. Preferably, the voltage obtained when a malfunction occurs is not larger than the set value of the undercurrent voltage relay 68.
Figures 7 and 8 show results of analysis of operations of the distributed power supply system of the present invention and of the distributed power supply system shown in aforementioned Figure 13 when a malfunction occurs. Figure 7(a) shows the bus line voltage of the cogenerator bus line 56, Figure 7(b) shows the interconnection current flowing through the system interconnection device 51, Figure 8(a) shows the bus line voltage of the cogenerator bus line 5, and Figure 8(b) shows the interconnection current flowing through the system interconnection device 11. Note that it is presumed that the grounding malfunction occurs at the zero cross point, and that the inductance Ldc of the d.c.
reactor 63 in the system interconnection device 51 of the present invention is set to be equal to the equivalent inductance Ls of the power supply 58.
In the present invention, clearly from comparison of Figures 7(a) and 8(a), the voltage drop is restrained so much as to 50% or less; further, clearly from comparison of Figures 7(b) and 8(b), the interconnection current is restrained to half or less.
In such a distributed power supply device in accordance with the present invention, the voltage drop when a malfunction occurs in a commercial power supply system can be restrained to a desired level by setting the inductance Ldc of the d.c. reactor 63 in the system interconnection device 51 according to the acceptable voltage drop ratio A and equivalent inductance Ls.
For example, when the acceptable voltage drop ratio A is set to 50%, the compensable region for the voltage drop is such that shown by reference denotation M3 in Figure 12, and assures stable operation with a power-electronics-applied variable velocity motor, electromagnetic switch 59 (see Figure 6) to which essential loads are connected, and other devices.
As a result of this, without using a UPS, the operation is assured of the variable velocity motor, electromagnetic switch, and other devices with little loss and low costs. As a result of this, operation of the interconnection is more reliable, and stress on the distributed power supply system can be reduced. Further, owing to the current limiting function of the d.c.
reactor 63 and quick current breaking function of the thyristors, the short-circuit capacity of the electromagnetic switch 59 in the load side does not need be unnecessarily excessively large, and the need is eliminated for replacement of the distribution lines 60 and the electromagnetic switch 59 thereof when the distributed power supply system is interconnected to a commercial power supply system.
Incidentally, it should be noted the system interconnection devices 21 and 51 are not necessarily an aforementioned mixed bridge constituted by thyristors and diodes, and can be arranged using a thyristor pure bridge. It should be also noted that the breaker 61 can be omitted in the system interconnection device 51.
INDUSTRIAL APPLICABILITY
As mentioned above, with the system interconnection device in accordance with the present invention, when a malfunction occurs, the rectifying switching element quickly opens so as to separate the two power systems, and even when the malfunction occurs, an instantaneous power supply voltage drop on essential loads that should be separated can be restrained by the current sustaining function of a d.c. reactor. For these reasons, the system interconnection device can be suitably applied as a system interconnection device for making an adaptable use of electric power by interconnecting two power supply systems with each other.
Moreover, as mentioned above, since the distributed power supply device having an instantaneous voltage drop counter-measure function in accordance with the present invention interconnects a commercial power supply system by using the above system interconnection device, and, when a malfunction occurs in the commercial power supply, changes, to a value that is acceptable to the distributed power supply system, a bus line voltage, of the distributed power supply system, which equals a value of the system voltage divided between an equivalent inductance Ls and an inductance Ldc of a d.c. reactor, the distributed power supply device assures operation of essential loads with little loss and at low costs without using a UPS device and can be suitably applied as a distributed power supply device.
Figure 9 illustrates an arrangement of a basic interconnection of an above-mentioned commercial power supply system and domestic power generation system. A
commercial power supply line 1 extends into a place where necessary and is connected to a receptor bus line 2 therein. The receptor bus line 2 is then connected to many distribution lines 3 which is connected to general loads.
Meanwhile, a cogenerator bus line 5 is connected to a domestic power generator 6 via a power supply line 9 and is also connected to, for example, distribution lines 4 extending to essential loads that make up of about 60%
to 70% of the domestic power generation capacity. The receptor bus line 2 and the cogenerator bus line 5 are mutually connected via a bus line connecting line 8 along which a breaker 7 is provided. The breaker 7 is actuated by a relay (not shown) provided to the side of the commercial power supply line 1 so as to break the bus line connecting line 8 when there occurs a malfunction including a short circuit, grounding, and opening of a receiving system.
However, with the interconnection thus arranged, when, for example, there occurs an aforementioned malfunction to the receptor bus line 2 or the v distribution line 3, it takes about 5 to 10 cycles (100msec to 200msec at 50 Hz) for the breaker 7 to be actuated, causing the essential loads connected to the distribution lines 4 to suffer a voltage drop for a long period of time. Also, since it takes a long period of time for the breaker 7 to be actuated in this manner, when a breaker (not shown) of a power supply line for the commercial power supply line 1 is opened, the domestic power generator 6 must operate while being connected to loads of the place. The loads, which typically amount to a several times larger than the capacity of the domestic power generator 6, constitute an overload for the domestic power generator 6, and are blacked out at last.
Figure 10 shows a typical system interconnection device 11 using conventional technologies to address such a problem. Here, for convenience, members shown in Figure that have similar, corresponding functions as members shown in Figure 9 are indicated by the same reference numerals and description thereof is omitted.
The system interconnection device 11 includes two thyristors 12 and 13 connected in reverse parallel. When an interconnection is established between the bus lines 2 and 5, the gates of the thyristors 12 and 13 are driven by the output of the aforementioned relay to keep the thyristors 12 and 13 energised. When there is an , , aforementioned malfunction, the gates of the thyristors 12 and 13 are blocked, and the thyristors 12 and 13 are opened.
Malfunction detection when the thyristors 12 and 13 are driven is carried out at, for example, half-cycle intervals, and the thyristors 12 and 13 become ready to drive opening at the zero cross point in the immediately subsequent half cycle. Therefore, taking a direct offset current as an example, the bus lines 2 and 5 can be opened within one cycle (20 msec at 50 Hz) after the occurrence of the malfunction. However, before the opening, the arrangement is still incapable of stopping a complete short-circuit current from flowing and of avoiding a great voltage drop from occurring across the cogenerator bus line 5.
As explained so far, in comparison to interconnection by the breaker 7, the system interconnection device 11 cuts short the time required to break the connection between the bus lines 2 and 5 and avoids the domestic power generator 6 from coming to a halt. However, the system interconnection device 11 is still short of eliminating an instantaneous voltage drop, and negatively affects the loads connected to the cogenerator bus line 5 of, for example, a computer.
Figure 11 shows an arrangement of a conventional t distributed power supply device establishing an interconnection with a system by the breaker 7. Here, for convenience, members shown in Figure 11 that have similar, corresponding functions as members shown in Figure 9 are indicated by the same reference numerals.
The distributed power supply device includes, for example, a diesel-fueled power generator or gas-fueled power generator as the domestic power generator 6 constituting a cogeneration system, which is an example of so-called new energy supply, and operates on an alternative current in interconnection in parallel to a commercial power supply system including a power supply 13. Essential loads that make up of about 60o to 70% of the domestic power generation capacity are connected to the distribution line 4 connected to the cogenerator bus line 5 of the distributed power supply system.
There are diverse alternative choices to be adopted as the domestic power generator 6 other than the diesel-fueled power generator and the gas-fueled power generator, including a secondary cell, fuel cell, photovoltaic power generation system, flywheel, wind power generation system, and UPS (Uninterruptible Power Supply) .
The breaker 7 is provided in the distributed power supply system to operate the interconnected distributed power supply system and commercial power supply system.
In some cases, where necessary, a countermeasure is taken to cope with a short-circuit current such as a reactor in accordance with guidelines of the interconnection.
However, if there occurs a malfunction to the commercial power supply system, such as a grounding and phase-to-phase short circuit, shown by reference number 15, a malfunction current flows from the distributed power supply system, causing a voltage drop in the distributed power supply system.
As a counter-measure to such a malfunction, the arrangement is made such that a voltage transformer detects the voltage of the commercial power supply line 1, an undervoltage relay judges according to a detected result whether it is possible or not to lower the voltage, and, when a voltage drop having a value not larger than a preselected number is judged, the breaker 7 is driven to open. Another arrangement may be made such that a current transformer detects an interconnection current, an overcurrent relay judges according to a detected result whether it is possible or not to increase the current, and the breaker 7 is driven to open when there is detected an overcurrent having a value not smaller than a preselected number.
However, the voltage of the distributed power supply _.7 _ system remains dropped until the breaker 7 opens (3 kinds of cycles, i.e., 2, 3, and 5 cycles, according to the JEC
2300 standards). Figure 12 shows a compensable region for the voltage drop and the region of the presence of the effect of an instantaneous voltage drop on the load when a vacuum breaker is used as the breaker 7. Figure 12 shows a threshold value of each load where the effect appears in relation to the voltage drop rate and the period of time during which the voltage remains dropped.
A reference denotation M1 shows a compensable region for the voltage drop in the aforementioned vacuum breaker.
As shown in Figure 12, most of the loads connected to the distribution line 4 fall out of the compensable region, being vulnerable to a voltage drop. In other words, although having successfully developed a countermeasure against a blackout of the essential loads by interconnecting the distributed power supply to the system, the distributed power supply device shown in Figure 11 completely fails to satisfy the demand for a countermeasure against the instantaneous voltage drop.
For these reasons, conventionally, a UPS (Uninterruptible Power Supply) is provided to some essential loads as indicated by the reference denotation 16.
The UPS AC/DC-converts, rectifies, and smooths the electric power fed from the cogenerator bus line 5, saves _g_ the DC power in an accumulator with a charger, and sends out, after conversion from DC to AC, the electric power saved in the accumulator to a load. Therefore, the UPS
has following problems: a semiconductor switching element and other components are indispensable, the costs are high, and there occurs a large loss in conversion. The UPS consequently is only used for aforementioned some essential loads. This leaves most of the loads having a widely used electromagnetic switch unprotected against an instantaneous voltage drop.
For these reasons, the system interconnection device 11 shown in Figure 10 is more and more commonly used as shown in Figure 13 to interconnect the distributed power supply device to a commercial power supply system. Here, for convenience, members shown in Figure 13 that have similar, corresponding functions as members shown in Figure 10 or 11 are indicated by the same reference numerals and description thereof is omitted. However, in some cases, the system interconnection device 11 still consumes a total time period of one cycle for the detection of a voltage drop and the passing of the zero cross where the thyristors 12 and 13 can be arc-removed.
Thus, the system interconnection device 11 using the thyristors 12 and 13 can compensate for a voltage drop in a region denoted by a reference denotation M2 in Figure r _9_ 12. This compensates many operations of office automation equipment and medical electric appliances, but still falls short of eliminating the effect on an electromagnetic switch provided to a distribution line extending essential loads and velocity variable motor contained in essential loads.
Therefore, the UPS 16 is necessary to essential loads among those loads incompensable even by the system interconnection device 11 using the thyristors 12 and 13 (those which fall out of the region shown by the reference denotation M2 in Figure 12).
If the distributed power supply system is interconnected to the commercial power supply system, there is an increase in the short-circuit capacity, and occurs a need for the breaker in the load side to be replaced by a breaker with a larger momentary break capacity, and also a need for the cable connected to the breaker to be replaced by a cable with a larger current capacity. Another problem is that if a malfunction occurs and it takes time for the system to be disconnected, the domestic power generator 6 stops operating and the distributed power supply system comes to a complete halt.
An object of the present invention is to offer a system interconnection device capable of restraining an instantaneous voltage drop when a malfunction occurs in t interconnection of two power systems, for example, a commercial power system and a domestic power supply generation system, provide a distributed power and to supply device having an instantaneous voltage drop counter-measure function equipped with such a system interconnection device.
DISCLOSURE OF THE INVENTION
The system interconnection device in accordance with claim 1 of the present invention is a system interconnection device, disposed between two power systems, for making an adaptable use of electric power by interconnecting the two power systems with each other, and is characterised in that it includes:
a single phase rectifier circuit arranged so that a pair of rectifying switching elements are connected to one of two a.c. terminals connected so as to link phase interconnecting terminals of the two power systems and that a pair of rectifying elements are connected to the other one of the two a.c. terminals; and a d.c. reactor connected so as to link two d.c.
terminals that are connecting points of the rectifying switching elements to the rectifying elements.
According to the above arrangement, when connecting the two power systems with each other, the d.c. reactor is connected so as to link the d.c. terminals of the single phase rectifier circuit constituted by the two rectifying switching elements realised by thyristors or other members and the two rectifying elements realised by diodes, thyristors, or other members, and the a.c.
terminals are connected to the respective power systems.
The circuit has following functions:
(i) under normal operation, the impedance viewed from the a.c. side is substantially zero, (ii) when a short-circuit occurs, a high impedance is produced instantaneously and restrains a short-circuit current, and (iii) the rectifying switching elements can cut off the two systems quickly.
The following will discuss functions (i) to (iii) in this order.
(i) The d.c, reactor, viewed from the a.c. terminal, can have an impedance which is substantially zero under normal operation and which is large only when a malfunction occurs.
(ii) Even if such a malfunction occurs, a current sustaining function by the d.c. reactor increases the inter-terminal voltage of the d.c. reactor and can restrain an instantaneous drop in power supply voltage applied across essential loads in the power system side which should be separated. Furthermore, the current sustaining function by the d.c. reactor can realise a current limiting function that restrains a malfunction current from flowing through a distribution line where the malfunction is happening, and restrain the short-circuit capacity of the two power systems.
(iii) When a malfunction occurs, the rectifying switching elements can cut off and separate the two systems quickly. Therefore, a generator provided in the power system to be separated does not stop its operation due to an overload, and a blackout can be avoided.
In the system interconnection device in accordance with claim 2 of the present invention, since by setting a current attenuation time constant determined by a reactance component and resistance component of the d.c.
reactor and a rectifier circuit including the rectifying switching elements and rectifying elements to not less than 2.5 times a system frequency cycle of the power system, a threshold current at which the d.c. reactor starts a current limiting function is specified, there is no need for a special power supply.
To put it differently, Figure 2 shows a relationship between the current attenuation time constant and an equivalent impedance produced across the a.c. terminals of the system interconnection device. Typically, the d.c.
reactance is selected so as to restrain a malfunction current during a system short-circuit malfunction to approximately 3 times the rated current.
Meanwhile, under normal operation, it is preferable to reduce the equivalent impedance as much as possible.
Practically, since the requirement is met if the equivalent impedance is not larger than 3% of the rated current, or in other words, as shown in Figure 2, not larger than 0.09pu (=30/33%) the a.c. impedance produced by the d.c. reactor L, from Figure 2, if the current attenuation time constant is not less than 2.5 times the system frequency cycle of the power system, there is no regular loss, and a current limiting function can be carried out when a system malfunction causes a current not less than the threshold current to flow.
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 3 of the present invention is a distributed power supply device with an instantaneous voltage drop counter-measure function, having a single power supply or a plurality of power supplies, connected to an essential load which should avoid an instantaneous voltage drop and blackout, and operated in a.c. parallel interconnection to a commercial power supply system by the system interconnection device as defined in any of claims 1 and 2, and is characterised in that an inductance of the d.c. reactor is formed to have a reactance larger than (1-A)/A times an equivalent inductance corresponding to an internal impedance of a distributed power supply system where A is a voltage drop ratio acceptable to the distributed power supply system when a malfunctions occurs in the commercial power supply system.
With the arrangement, when a malfunction occurs, the system interconnection device in accordance with claim 1 or 2 disposed between the bus lines of the two systems restrains voltage drop in the distributed power supply system and the short-circuit current by the large reactor of the impedance. While voltage drop is restrained, a protective relay arc-removes the semiconductor switching element, and breaks the distributed power supply system off the commercial power supply system.
In a distributed power supply system arranged in this manner, if a malfunction occurs in the commercial power supply system, the bus line voltage in the distributed power supply system equals a value of the system voltage divided between the equivalent inductance of the distributed power supply system and the inductance of the d.c. reactor. Therefore, from the acceptable voltage drop ratio A, a choice is made so as to satisfy Ldc /Ls > (1-A)/A where Ldc is the inductance of the d.c.
reactor and Ls is the equivalent inductance of the distributed power supply system. In other words, when the voltage drop ratio A is, for example, 50%, by equalising the inductance Ldc of the d.c. reactor to the equivalent inductance Ls of the distributed power supply system, the voltage drop ratio can be restrained within the above range A. In addition, when the voltage drop ratio A is, for example, 250, from (1-0.25)/0.25, the inductance Ldc of the d.c. reactor only needs be set to 3 times the equivalent inductance Ls of the distributed power supply system.
Simply by setting the inductance Ldc of the d.c.
reactor according to the voltage drop ratio A acceptable to the distributed power supply system when a malfunction occurs and to the equivalent inductance Ls of the distributed power supply system, even without using a UPS, the operation is assured of devices that are prone to instantaneous voltage drop such as an electromagnetic switch that are connected to essential loads, variable velocity motor, and other devices. As a result of this, the operation of the interconnection is more reliable, and the stress on the distributed power supply system can be reduced. Further, since the short-circuit current is restrained owing to the current limiting function of the d.c. reactor, breakers and cables in the load side do not need be replaced by those having undesirably large capacities for interconnection.
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 4 of the present invention is characterised in that the power supply in the distributed power supply system is a rotary machine.
With the above arrangement, if the rotary machine is used as a power supply in a distributed power supply system, during a short-circuit malfunction, although a high short-circuit current is running, the circuit .voltage, i.e. the output voltage of a generator of the rotary machine, becomes zero, the stress between that generator and a motor of the rotary machine is released, and a mechanical vibration occurs to the shaft, and when the short-circuit malfunction is solved, the generator of the rotary machine carries an excessive load above the capacity thereof , an abrupt braking torque occurs to that generator, and an excessive vibration torque occurs to the shaft . While a stress (e . g. a share-pin split in a case of a turbine-driven generator) results, as explained here, from an temporary release of overcurrent from the generator of the rotary machine when a short-circuit malfunction occurs, the stress can be avoided by restraining the short-circuit current as explained earlier..
The distributed power supply device with an instantaneous voltage drop counter-measure function in accordance with claim 5 of the present invention is characterised in that the power supply in the distributed power supply system is of a stationary model using an inverter.
With the arrangement, since the stationary model power supply has no inertia unlike a rotary machine, halts soon, and results in a blackout, the present invention can be embodied in a especially preferable manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a drawing illustrating a system interconnection device of an embodiment in accordance with the present invention.
Figure 2 is a graph showing a relationship between a current attenuation time constant with respect to an a.c. power supply cycle and an equivalent impedance.
Figure 3(a) through Figure 3(c) are drawings showing a possible arrangement example of a current limiting device as such and that when the current limiting device is used as a system interconnection device.
Figure 4(a) through Figure 4(h) are waveform charts illustrating operations of the system interconnection device shown in Figure 1.
Figure 5(a) through Figure 5(h) are waveform charts illustrating operations of the system interconnection device shown in Figure 3.
Figure 6 is a single phase schematic of a power system of another embodiment in accordance with the present invention, illustrating a distributed power supply device incorporating the system interconnection device shown in Figure 1.
Figure 7(a) and Figure 7(b) are simulation waveform charts illustrating operations of the distributed power supply device shown in Figure 6.
Figure 8(a) and Figure 8(b) are simulation waveform charts illustrating operations of a conventional distributed power supply device shown in Figure 13.
Figure 9 is a drawing illustrating a basic arrangement of system interconnection.
Figure 10 is a drawing illustrating a typical conventional system interconnection device.
_1_g_ Figure 11 is a single phase schematic of a power system, illustrating a typical conventional distributed power supply device.
Figure 12 is a graph illustrating examples of effect by an instantaneous voltage drop on a load device and a compensable region of various devices in accordance with the present invention and conventional technologies.
Figure 13 is a single phase schematic of a power system, illustrating another conventional distributed power supply device.
BEST MODES OF CARRYING OUT THE INVENTION
The following will discuss an embodiment in accordance with the present invention in reference to Figure 1 through Figure 5.
Figure 1 is a drawing illustrating a system interconnection device 21 of an embodiment in accordance with the present invention. The system interconnection device 21 is disposed along a bus connecting line 24 connecting a receptor bus line 22 to a cogenerator bus line 23 in a place where necessary. The receptor bus line 22 is connected to a commercial power supply line 25 and to distribution lines 26 which are connected to many general loads. The cogenerator bus line 23 is connected to a domestic power generator 27 and to distribution lines 28 which are connected to essential loads, such as computers.
The system interconnection device 21 is realised by a pair of thyristors TH1 and TH2 that are rectifying switching elements, a pair of diodes D1 and D2 that are rectifying elements, and a d.c. reactor L. It should be noted in the present invention that the pair of thyristors TH1 and TH2 are connected to one of a pair of a.c. terminals AC1 and AC2 connected to the bus connecting line 24, while the pair of diodes D1 and D2 are connected to the other one of the pair of the a . c .
terminals AC1 and AC2 (In an example shown in Figure 1, the thyristors TH1 and TH2 are connected to the a.c.
terminal AC1, and the diodes Dl and D2 are connected to the a.c. terminal AC2). Meanwhile, the d.c. reactor L is connected so as to link d.c. terminals DC1 and DC2.
In the system interconnection device 21, between an equivalent impedance viewed from the power system side, and a current attenuation time constant determined by a rectifier circuit constituted by the thyristors THl and TH2, the diodes D1 and D2 and a reactance component and resistance component of the d.c. reactor L, there is a relationship shown in Figure 2; the equivalent impedance decreases with a larger current attenuation time constant. Meanwhile, the device impedance is preferably as small as possible under normal operation. Therefore, in the present invention, the current attenuation time constant is selected so as to be 2.5 or more times the system frequency cycle of the power system.
In the system interconnection device 21 arranged in the above manner, under normal conditions, the gates of the thyristors TH1 and TH2 are driven to energise the thyristors TH1 and TH2, permitting a current to flow along either a path denoted by a reference denotation il or a path denoted by a reference denotation i2.
Therefore, the direction and amplitude of the current flowing through the d.c. reactor L are constant, and the d.c. reactor L has an impedance Z (=c~L) of 0, causing no loss.
By contrast, if an overcurrent is about to flow from the cogenerator bus line 23 side to the receptor bus line 22 side due to, for example, a short-circuit or grounding of the distribution lines 26 or an opening of a receptor system, the d.c. reactor L immediately increases the impedance Z thereof and increases the inter-terminal voltage, so as to retain the current between the terminals at a constant level.
With this, the impedance viewed from the a. c.
terminals AC1 and AC2 side increases, and a current limiting function can be realised that restrains the current flowing from the cogenerator bus line 23 side to the receptor bus line 22 side via the bus connecting line 24. During the time, the gates of the thyristors TH1 and TH2 are blocked by an output of a short-circuit or ground relay, and the cogenerator bus line 23 is cut off from the receptor bus line 22 surely and quickly within a single cycle. Therefore, the domestic power generator 27 can be prevented from being overloaded.
In this manner, a malfunction in the receptor bus line 22 side can be prevented from halting the operation of the domestic power generator 27, and a likely blackout can be thus prevented. In addition, the malfunction is prevented by an increased inter-terminal voltage of the d. c . reactor L from causing an instant voltage drop in the cogenerator bus line 23. The reliability of the cogeneration system can be thus improved. Furthermore, by achieving the current limiting function mentioned above, the short-circuit capacities in both the cogenerator bus line 23 side and the receptor bus line 22 side can be restricted.
The following describes an example of a single phase mixed bridge rectifier circuit applied to a current limiting device (Japanese Laid-Open Patent Application No. 49-50448/1974 (Tokukaisho 49-50448/1974)) shown in Figure 3(a). The current limiting device 31 is constituted by a mixed bridge rectifier circuit 32 and a current limiting reactor L2 that are disposed in parallel with each other and in series with an a.c. line 33.
The mixed bridge rectifier circuit 32 is constituted by a pair of thyristors thl and th2, a pair of diodes dl and d2, a d.c. reactor L1, and a d.c. power supply B
connected in series to the d.c. reactor L1. It should be noted that the thyristor thl and diode dl are connected to one of a.c. terminals, i.e. an a.c. terminal AC1, and that the thyristor th2 and diode d2 are connected to the other one of the a.c. terminals, i.e. an a.c. terminal AC2. Therefore, the thyristors thl and th2 are connected to the d.c. terminal DC1, the diodes dl and d2 are connected to the d.c. terminal DC2, a d.c. circuit constituted by the d.c. reactor L and the d. c. power supply B is provided between the d.c. terminals DC1 and DC2.
In the current limiting device 31 arranged as above, the thyristors thl and th2 are energised under normal conditions, and the line current bypasses the current limiting reactor L2 and flows via the mixed bridge rectifier circuit 32. By contrast, when a malfunction occurs, a current exceeding the current value set by the d . c . power supply B is restrained by the d . c . reactor L1, effecting a current limiting function. Thereafter, the thyristors thl and th2 are opened. By the opening of the thyristors thl and th2, an undesirable overvoltage is generated between the a.c. terminals AC1 and AC2.
Therefore, a side path circuit is formed between the a.c.
terminals AC1 and AC2 from the current limiting reactor L2 for restraining the overvoltage. The presence of the current limiting reactor L2 does not permit application to a system interconnection device for the purpose of separation of systems.
Let us suppose that the mixed bridge rectifier circuit 32 arranged as above is applied to a system interconnection device as in the present invention with no current limiting reactor L2 and no d. c. power supply B which determines a threshold current for operation of the d.c. reactor L1. Figure 3(b) shows such a system interconnection device 41. Members of the system interconnection device 41 corresponding to those of system interconnection device 21 in accordance with the present invention are indicated by the same reference numerals and description thereof is omitted.
It should be noted that in the system interconnection device 41, the thyristor THla and diode Dla are connected to one of a.c. terminals, i.e. an a.c.
terminal AC1, and that the thyristor TH2a and diode D2a are connected to the other one of the a.c. terminals, i.e. an a.c. terminal AC2. Therefore, the thyristors TH1 and TH2 are connected to the d.c. terminal DC1, the diodes Dla and D2a are connected to the d.c. terminal DC2, and the d.c. reactor L is provided between the d.c.
terminals DC1 and DC2.
In other words, the system interconnection device 41 differs from the system interconnection device 21 in accordance with the present invention in how the thyristors and diodes are connected in the single phase bridge rectifier circuit.
Figures 4 and 5 show simulation waveform of various parts when the system interconnection devices 21 and 41 are opened. Conditions for simulation are such that the percentage impedance of the commercial power supply is set to 100, the reactance of the power supply thereof is set to l.Opu, the power supply frequency is set to 50Hz, and the reactance of the d.c. reactor L is set to 4.Opu.
As shown in Figures 4 (a) and 5 (a) , the current flowing through the thyristors TH1 and THla are such that the arc is removed temporarily when crossing zero after a half cycle during which the a.c. terminal AC1 is at a high level lapses and that no current flows thereafter.
As a result of this, referring to Figure 4(c), the current flowing through the diode D2 changes into a current, denoted by a reference denotation al, which corresponds to the current flowing through the thyristor TH1 and a current, denoted by a reference denotation a2, caused by energy released by the d.c. reactor L. By contrast, referring to Figure 5(c), the current flowing through the diode D2a changes into a current, denoted by a reference denotation ail, which corresponds to the current flowing through the thyristor THla and currents, denoted by reference denotations ,Q2, ~i3, (34, etc., added by energy released by the d.c. reactor L. As shown by the reference denotation i3 in Figure 3(b), the phenomenon occurs since the thyristor TH2a cannot remove the arc due to a current circulated by the opening of the thyristor THla, and the current thus increases.
Therefore, as shown in Figure 4(b), the current flowing through the thyristor TH2 removes the arc after only a half cycle during which the a.c. terminal AC2 is at a high level . By contrast, as shown in Figure 5 (b) , the current flowing through the thyristor TH2a increases at every one cycle. As a result of this, as shown in Figure 4(d), the current flowing through the diode D1 equals the sum of the current flowing through the thyristor TH2 shown in Figure 4(b) and the current, denoted by a reference denotation a2 in Figure 4(c), caused by the release by the d.c. reactor L, whereas the current flowing through the diode Dla, as shown in Figure 5(d), increases at every one cycle similarly to the current flowing through the diode D2a shown in Figure (c) .
Further, as a result of this, in the system interconnection devices 21 and 41, Figures 4(e) and 5(e) show the current flowing through the d.c. reactor L, Figures 4 ( f ) and 5 ( f ) show the voltage of the cogenerator bus line 23, Figures 4 (g) and 5 (g) show the voltage of the receptor bus line 22, and Figures 4(h) and 5(h) show a malfunction current flowing from the cogenerator bus line 23 side to the receptor bus line 22 side.
The current flowing through the d.c. reactor L
converges to a substantially constant value in the system interconnection device 21 in accordance with the present invention as shown in Figure 4(e), but increases at every cycle in the system interconnection device 41 as shown in Figure 5(e). Corresponding to this, the malfunction current also is quickly and surely cut off in one cycle in the system interconnection device 21 in accordance with the present invention as shown in Figure 4(h), but increases at every cycle in the system interconnection device 41 as shown in Figure 5(h).
Therefore, although the system interconnection device 41 does function as a current limiting device, the system interconnection device 41 falls short of arc-removing either one of the thyristors THla and TH2a, and therefore cannot be used as a system interconnection device.
In this respect, when a malfunction occurs, the system interconnection device 21 in accordance with the present invention can surely cut off a malfunction current by carrying out a current limiting function with the d.c. reactor L and opening the thyristors TH1 and TH2. As a result of this, a great improvement can be made on an instantaneous voltage drop, and the UPS that was conventionally provided to each essential load such as a computer can be omitted. In addition, a quick break becomes possible, the domestic power generator 27 can be prevented from being overloaded, and undesirable incidents can be surely avoided such as a blackout due to a halt of the operation of the domestic power generator 27 and an excessive torque load on a generator shaft of a rotary machine due to an abrupt overload. Moreover, it becomes possible to restrain, to a low value, the short-circuit capacity in both the cogenerator bus line 23 side and the receptor bus line 22 side.
Japanese Laid-Open Patent Application No. 49-50448/1974 (Tokukaisho 49-50448/1974) mentioned above also discloses an example of a thyristor pure bridge rectifier circuit applied as a current limiting device.
Figure 3(c) shows such an example. A pure bridge rectifier circuit 32a of a current limiting device 31a is a circuit for limiting current in a similar manner as in the above arrangement shown in Figure 3(a), such that a current always runs through thyristors thl through th4 by means of effect of a d.c. power supply B and that if the current of an a.c. circuit is not larger than the value of that current, the impedance viewed from the a.c. side is zero, and if the current becomes equal to, or larger than, the value of the current, a current limiting function is carried out.
The addition of the d.c. power supply B having the above-mentioned purpose makes it technically and economically difficult to realise the arrangement shown in Figure 3(c). The system interconnection device 21 in accordance with the present invention can dispense with such a d.c. power supply B, as mentioned above, by selecting the current attenuation time constant determined by the reactance component and resistance component of the d.c. reactor L, and the rectifier circuit constituted by the thyristors TH1 and TH2 and diodes D1 and D2 to not smaller than 2.5 times the system frequency cycle of the power system, which is of a totally different arrangement from the technology disclosed in Japanese Laid-Open Patent Application No.
49-50448/l974 (Tokukaisho 49-50448/1974).
Referring to Figure 6 through Figure 8 and aforementioned Figure 12, the following describes another embodiment of the present invention.
Figure 6 is a single phase schematic of a power system, illustrating a distributed power supply device of the other embodiment in accordance with the present invention. A system interconnection device 51 incorporated in the distributed power supply device, having the same arrangement as the system interconnection device 21, connects a receptor bus line 54 to a cogeneration bus line 56 to enable a commercial power supply system and a distributed power supply system to operate in interconnection.
A commercial power supply line 53 extending from a power supply 52 of a commercial power supply system into a place where necessary is connected to the receptor bus line 54. To the receptor bus line 54 are connected many distribution lines 55 which are connected to general loads. The cogenerator bus line 56 of a distributed power supply system is connected via a power supply line 57 to a power supply 58 such as a cogeneration system. To the cogenerator bus line 56 are connected many distribution lines 60 which are connected to essential loads.
The system interconnection device 51 is constituted by a breaker 61, a single phase rectifier circuit 62, and a d.c. reactor 63. The single phase rectifier circuit 62 is made to be connected to a pair of thyristors TH1 and TH2 at at least one of two a.c. terminals (in the breaker 61 side in the example shown in Figure 6) and is constituted by a bridge circuit including the thyristors TH1 and TH2 and a pair of diodes D1 and D2. Thus, it becomes possible to drive opening within half a cycle (lOmsec at 50Hz) when a malfunction occurs, and the breaker 61 opens thereafter. One of the two a.c.
terminals of the single phase rectifier circuit 62 is connected to the cogenerator bus line 56, while the other is connected to the receptor bus line 54 via the breaker 61 . The d. c . reactor 63 connects two d. c . terminals of the single phase rectifier circuit 62 similarly to the above case.
The voltages of the power supply lines 53 and 57 are detected by undercurrent voltage relays 67 and 68 via voltage transformers 65 and 66 respectively. The undercurrent voltage relays 67 and 68 assumes that a malfunction has occurred if the voltages of the power supply lines 53 and 57 are of a predetermined set value, for example, 85% or less, of a rated voltage, arc-removes the thyristors TH1 and TH2, and drives to open the breaker 61.
In a distributed power supply device arranged in this manner, the system impedance in the power supply 58 side looks almost L, and the inductance Ldc of the d.c.
reactor 63 is selected in the present invention so as to meet the relationship with respect to the equivalent inductance Ls of the distributed power supply system:
Ldc / Ls > (1-A) / A ...(1) where Ls is the equivalent inductance corresponding to the internal impedance of the power supply 58 and A is the voltage drop ratio acceptable to the distributed power supply system.
Here, as shown by a reference denotation 69, when considering a case where a grounding malfunction occurs in the commercial power supply system, the voltage of the cogenerator bus line 56 equals a value, of the voltage V
of the power supply 58, divided between the equivalent inductance Ls and the inductance Ldc of the d.c. reactor 63. Therefore, the system voltage V' after the occurrence of the malfunction can be obtained as:
V' - Ldc / ( Ldc + Ls ) x V . . . ( 2 ) Therefore, when the acceptable voltage drop ratio A
is 50%, from Equation 1, by equalising the inductance Ldc to the inductance of the power supply 58 that is substantially equal to the equivalent inductance Ls, in a case where a malfunction occurs in the commercial power supply system as shown by the reference denotation 69, the voltage drop in the cogenerator bus line 56 of the distributed power supply system can be restrained so much as to 50% of the voltage V of the power supply 58. In addition, for example, when the acceptable voltage drop ratio A is 25%, from Equation 1, the multiple Ldc / Ls becomes 3 or larger, and, by setting the inductance Ldc of the d.c. reactor 63 to 3 times the inductance of the power supply 58, the voltage drop in the cogenerator bus line 56 can be restrained so much as to 75% of the voltage V of the power supply 58.
As clearly understood from the foregoing equation, to the larger value the inductance Ldc of the d.c.
reactor 63 is set, to the smaller value the voltage drop can be restrained. Preferably, the voltage obtained when a malfunction occurs is not larger than the set value of the undercurrent voltage relay 68.
Figures 7 and 8 show results of analysis of operations of the distributed power supply system of the present invention and of the distributed power supply system shown in aforementioned Figure 13 when a malfunction occurs. Figure 7(a) shows the bus line voltage of the cogenerator bus line 56, Figure 7(b) shows the interconnection current flowing through the system interconnection device 51, Figure 8(a) shows the bus line voltage of the cogenerator bus line 5, and Figure 8(b) shows the interconnection current flowing through the system interconnection device 11. Note that it is presumed that the grounding malfunction occurs at the zero cross point, and that the inductance Ldc of the d.c.
reactor 63 in the system interconnection device 51 of the present invention is set to be equal to the equivalent inductance Ls of the power supply 58.
In the present invention, clearly from comparison of Figures 7(a) and 8(a), the voltage drop is restrained so much as to 50% or less; further, clearly from comparison of Figures 7(b) and 8(b), the interconnection current is restrained to half or less.
In such a distributed power supply device in accordance with the present invention, the voltage drop when a malfunction occurs in a commercial power supply system can be restrained to a desired level by setting the inductance Ldc of the d.c. reactor 63 in the system interconnection device 51 according to the acceptable voltage drop ratio A and equivalent inductance Ls.
For example, when the acceptable voltage drop ratio A is set to 50%, the compensable region for the voltage drop is such that shown by reference denotation M3 in Figure 12, and assures stable operation with a power-electronics-applied variable velocity motor, electromagnetic switch 59 (see Figure 6) to which essential loads are connected, and other devices.
As a result of this, without using a UPS, the operation is assured of the variable velocity motor, electromagnetic switch, and other devices with little loss and low costs. As a result of this, operation of the interconnection is more reliable, and stress on the distributed power supply system can be reduced. Further, owing to the current limiting function of the d.c.
reactor 63 and quick current breaking function of the thyristors, the short-circuit capacity of the electromagnetic switch 59 in the load side does not need be unnecessarily excessively large, and the need is eliminated for replacement of the distribution lines 60 and the electromagnetic switch 59 thereof when the distributed power supply system is interconnected to a commercial power supply system.
Incidentally, it should be noted the system interconnection devices 21 and 51 are not necessarily an aforementioned mixed bridge constituted by thyristors and diodes, and can be arranged using a thyristor pure bridge. It should be also noted that the breaker 61 can be omitted in the system interconnection device 51.
INDUSTRIAL APPLICABILITY
As mentioned above, with the system interconnection device in accordance with the present invention, when a malfunction occurs, the rectifying switching element quickly opens so as to separate the two power systems, and even when the malfunction occurs, an instantaneous power supply voltage drop on essential loads that should be separated can be restrained by the current sustaining function of a d.c. reactor. For these reasons, the system interconnection device can be suitably applied as a system interconnection device for making an adaptable use of electric power by interconnecting two power supply systems with each other.
Moreover, as mentioned above, since the distributed power supply device having an instantaneous voltage drop counter-measure function in accordance with the present invention interconnects a commercial power supply system by using the above system interconnection device, and, when a malfunction occurs in the commercial power supply, changes, to a value that is acceptable to the distributed power supply system, a bus line voltage, of the distributed power supply system, which equals a value of the system voltage divided between an equivalent inductance Ls and an inductance Ldc of a d.c. reactor, the distributed power supply device assures operation of essential loads with little loss and at low costs without using a UPS device and can be suitably applied as a distributed power supply device.
Claims (5)
1. A system interconnection device, disposed between two power systems, for making an adaptable use of electric power by interconnecting the two power systems with each other, said system interconnection device being characterised in that it comprises:
a single phase rectifier circuit arranged so that a pair of rectifying switching elements are connected to one of two a.c. terminals connected so as to link phase interconnecting terminals of the two power systems and that a pair of rectifying elements are connected to the other one of the two a.c. terminals; and a d.c. reactor connected so as to link two d.c.
terminals that are connecting points of the rectifying switching elements to the rectifying elements.
a single phase rectifier circuit arranged so that a pair of rectifying switching elements are connected to one of two a.c. terminals connected so as to link phase interconnecting terminals of the two power systems and that a pair of rectifying elements are connected to the other one of the two a.c. terminals; and a d.c. reactor connected so as to link two d.c.
terminals that are connecting points of the rectifying switching elements to the rectifying elements.
2. The system interconnection device as defined in claim 1, being characterised in that a current attenuation time constant determined by a reactance component and resistance component of the d.c.
reactor and a rectifier circuit including the rectifying switching elements and rectifying elements is not less than 2.5 times a system frequency cycle of the power system.
reactor and a rectifier circuit including the rectifying switching elements and rectifying elements is not less than 2.5 times a system frequency cycle of the power system.
3. A distributed power supply device with an instantaneous voltage drop counter-measure function, having a single power supply or a plurality of power supplies, connected to an essential load which should avoid an instantaneous voltage drop and blackout, and operated in a.c. parallel interconnection to a commercial power supply system by the system interconnection device as defined in any of claims 1 and 2, said distributed power supply device being characterised in that an inductance of the d.c. reactor is formed to have a reactance larger than (1-A)/A times an equivalent inductance corresponding to an internal impedance of a distributed power supply system where A is a voltage drop ratio acceptable to the distributed power supply system when a malfunctions occurs in the commercial power supply system.
4. The distributed power supply device with an instantaneous voltage drop counter-measure function as defined in claim 3, being characterised in that the power supply in the distributed power supply system is a rotary machine.
5. The distributed power supply device with an instantaneous voltage drop counter-measure function as defined in claim 3, being characterised in that the power supply in the distributed power supply system is of a stationary model using an inverter.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9222737A JP2998711B2 (en) | 1997-08-19 | 1997-08-19 | Distributed power supply with sag protection |
| JP9-222737 | 1997-08-19 | ||
| PCT/JP1997/003758 WO1999009631A1 (en) | 1997-08-19 | 1997-10-17 | System interconnecting device and decentralized power supply equipped with the same and having instantaneous voltage drop preventing function |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2267304A1 true CA2267304A1 (en) | 1999-02-25 |
Family
ID=16787119
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002267304A Abandoned CA2267304A1 (en) | 1997-08-19 | 1997-10-17 | System interconnection device and distributed power supply device including the same having instantaneous voltage drop counter-measure function |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP2998711B2 (en) |
| CA (1) | CA2267304A1 (en) |
| WO (1) | WO1999009631A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107819357A (en) * | 2016-09-13 | 2018-03-20 | 通用电气公司 | Isolation parallel UPS system with abort situation detection |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2947261B1 (en) * | 1998-04-08 | 1999-09-13 | 日新電機株式会社 | System interconnection device and its design method |
| WO2001061838A1 (en) * | 2000-02-17 | 2001-08-23 | Powerline Ges Pty Ltd | An energy generating and supply system |
| CN100370667C (en) * | 2002-12-19 | 2008-02-20 | 中国科学院电工研究所 | Fault current limiting circuit |
| CN100370668C (en) * | 2002-12-19 | 2008-02-20 | 中国科学院电工研究所 | Current-limiting circuit |
| CN100433490C (en) * | 2002-12-19 | 2008-11-12 | 中国科学院电工研究所 | Fault current-limiting circuit for transmission and distribution electric network |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55131280A (en) * | 1979-03-29 | 1980-10-11 | Fuji Electric Co Ltd | Inverter |
| JPS5826533A (en) * | 1981-08-10 | 1983-02-17 | 株式会社明電舎 | Load balancing device for power system |
-
1997
- 1997-08-19 JP JP9222737A patent/JP2998711B2/en not_active Expired - Fee Related
- 1997-10-17 WO PCT/JP1997/003758 patent/WO1999009631A1/en active Application Filing
- 1997-10-17 CA CA002267304A patent/CA2267304A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107819357A (en) * | 2016-09-13 | 2018-03-20 | 通用电气公司 | Isolation parallel UPS system with abort situation detection |
| CN107819357B (en) * | 2016-09-13 | 2023-01-24 | Abb瑞士股份有限公司 | Isolated parallel UPS system with fault location detection |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2998711B2 (en) | 2000-01-11 |
| WO1999009631A1 (en) | 1999-02-25 |
| JPH1169664A (en) | 1999-03-09 |
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