DE2730010A1 - Reactive current generator - has static converter bridge circuits connected on DC side in series in ring - Google Patents

Abstract

The generated current intensity and shape vary quickly. The generator has a rectifier transformer connected to the three-phase network to be influenced, and a rectifier control element, by which controllable rectifier diodes are looped in the same secondary windings of the rectifier transformer, or they are bypassed in a free-running operation. A three-phase capacitor battery is connected in parallel with the three-phase network in order to provide a specified compensation reactive power, and a control device is provided. Network voltage controlled static convertor bridge circuits are used as the convertor control element, connected to secondary windings (1-4) of each secondary winding system. They are connected with each other of the d.c. side, and in series with a smoothing inductor (10, 20, 30, 40). D.c. circuits of all secondary systems are connected in the same sence in series in a closed ring.

Description

"Circuit arrangement for generating according to size and curve shape

quickly changeable reactive currents and control and regulation equipment for the same "The invention relates to a circuit arrangement for generating Reactive currents that can be quickly changed in terms of size and curve shape with one to be influenced three-phase AC network lying converter transformer and a converter actuator, by means of its controllable converter valves the same secondary windings of the converter transformer looped in or bypassed in freewheeling mode, as well as with a / parallel Three-phase capacitor bank connected to the AC network for provision a predetermined compensation reactive power, also a control and regulation direction for regulating this circuit arrangement.

The invention finds application in power electronics, in particular for converter-fed drives with inductive loads.

Such a known circuit arrangement for balancing asymmetrical Active power load in supply networks and to compensate of reactive power load points to the connection or disconnection of the secondary windings of the converter transformer forcibly commutated semiconductor valves open (DT-OS 23 29 287). The converter transformer is designed as a leakage transformer. Advantageous In the known case, therefore, the primary supply voltage is once through the scattering transport converter is converted into a voltage of relatively low magnitude to be switched by the controller, and on the other hand, the leakage transformer is used to generate an inductive current component.

Quickly changing reactive currents for compensation and balancing an arrangement has also already been proposed (P 26 44 682.2) that consists of a self-guided converter called a four-quadrant converter, and one three-phase capacitor, which is preferably dimensioned so that the currents of the three capacitor phases are each about half the size of the largest in the relevant Phase consumer current to be compensated. According to the older proposal, the active component the currents of the converter compensation actuator through its conductance setpoint certainly. As a setpoint for the reactive currents of the compensation actuator the total instantaneous values of the loads and currents directly and without delay a three-phase capacitor parallel to this and measured by the active component of the positive sequence system of the consumer currents is reduced, the active component by means of a Conductivity converter by automatically multiplying one of the effective conductance of the consumer proportional size with sizes that correspond to the time course of the voltages of the three-phase network are proportional to 'generated. The size of the setpoints for the conductance of the compensation actuator or that for the compensation actuator used Vierquadrantent steller is through a device to regulate the mean voltage on the direct current side of the four-quadrant controller certainly. The transducer required for this circuit arrangement is in another older suggestion given (P 26 57 168.6).

To build a self-commutated converter are called controllable Converter valves thyristors with particularly short release times required, which are only produced in comparatively small quantities. For It can therefore be advantageous to use grid-commutated compensation systems with high performance To use power converters, because then the requirements for the release time of the Thyristors are considerably lower.

It is already known, with two mains-commutated controllable bridge converters, which are connected in series on the DC side via two inductors and of which the one bridge converter in the rectifier area, e.g. B. with a control angle of t = 750, and the other converter in the inverter area, for example with a control angle «= 1050, a certain desired reactive power works to an alternating + current network and thereby also the harmonic content through delivery to reduce the corresponding currents (DT-AS 22 01 800).

In this known case, too, one is connected in parallel to the alternating current network Connected three-phase capacitor battery, capacitive reactive power available. In the known case, the converter valves are directly connected to the alternating current network connected so that they are to be dimensioned accordingly.

The object of the invention is based on a circuit arrangement with converter transformer and the other features described above, controllable converter valves, in particular thyristors, to be able to use their Free times do not have to be extremely short. It should continue to do so the Circuit arrangement allow reactive currents to be generated with an adjustable curve shape.

The solution to this problem is that according to the invention as a converter actuator power converter bridge circuits connected to the mains to the secondary windings 3 of the secondary winding system are connected, the DC side with each other and with a smoothing choke coil are connected in series, with the DC circuits of all secondary systems in the same direction are connected in series to form a closed circuit.

Two embodiments are possible: In a first embodiment a single-phase bridge circuit is connected to a secondary winding in each case.

In a second embodiment, the phase conductors of each are connected to of the secondary three-phase winding systems, each in a star connection connected, a stroke rectifier valve set connected in a three-phase bridge circuit, which additionally has a fourth pair of valve branches, whose AC connection is connected to the zero point of the associated winding system j.

It is advantageous with both embodiments with the converter bridge circuits in connection with the three-phase capacitor battery and the corresponding control device possible to deliver reactive currents that meet a specified setpoint quickly and with follow a good approximation.

For the delivery of power oscillations of twice the net frequency it is advisable to use a parallel resonance circuit made up of a parallel resonance circuit that is cut to this frequency Choke coil and a capacitor added to the DC circuit.

The invention is also based on the object of a control and Specify control device for the circuit arrangements described above, which the The aforementioned conditions for the delivery of the reactive currents are met. This tax and control device represents the low-voltage component of the circuit arrangement and it is to be assumed as known that the device according to DT-OS 23 29 287 a control or regulating device to compensate for the reactive power load having.

For the solution of this task, reference is made to the older one mentioned above Patent application P 26 44 682.2 pointed out. The solution is that according to the invention a setpoint generator and a device for valve monitoring and control are provided are where the three currents of the transformer primary windings are independent of each other predetermined setpoints are approximated by multi-stage control that the number the switching stages of one polarity with the number of secondary systems of the converter transformer agrees that when a positive switching limit is exceeded or when it is undershot a negative switching limit due to the current setpoint a valve stretch over the Device for valve monitoring and control is ignited with the transformer secondary winding the associated phase is connected and at which the reverse voltage is straight in the forward direction takes effect when the sign of the mains voltage and the time derivative of the current setpoint to match.

Further refinements of the control and regulating device according to the invention Circuit arrangements are characterized in the preceding claims 6 to 11. In addition to the reactive current control described above, a direct current control loop is preferred intended.

The invention is illustrated below with reference to the in the drawing Embodiments explained in more detail. 1 shows a circuit arrangement with single-phase bridge circuit and control and regulating device, whereby only the execution for one phase is shown, Fig. 2 time courses of the currents and voltages in the circuit according to FIG. 1, FIG. 3 an embodiment the circuit arrangement with three-phase secondary windings in star connection and with three-phase bridge circuits connected to the same and FIG. 4 time courses of currents and voltages of the circuit arrangement according to FIG. 3.

In Fig. 1, a phase of the circuit arrangement is shown, wherein a converter transformer, for example, four identical secondary windings 1 to 4 and a primary winding 5.

The primary winding 5 lies with the other primary windings, not shown of the converter transformer in delta connection. Parallel to the primary winding a capacitor 6, which is dimensioned so that when connected to the mains voltage results in a current whose peak value is about as large as the greatest instantaneous value of the current to be compensated. Preferably the same secondary windings 1 to 4, four valve sets are connected in a single-phase bridge circuit with converter valves the valve sections 11; 13; 14; 16 and 21; 23; 24; 26; and 31; 33; 34; 36 and 41; 43; 44; 46. Four of the same on the direct current side of the single-phase converter connected ge / smoothing choke windings 10; 20; 30 and 40 can share a common iron core to be ordered. All four single-phase converters are connected in series on the DC side switched and together form a short circuit.

The interruption device for this circuit arrangement consists of a setpoint generator 50, the output 50a of which with the output signal with a comparison point 51 is connected. The comparison junction 51 is on the output side connected to a device for valve monitoring and control 54. These Einrich-54 via a measuring device 55 device / monitors / current and voltage each Valve section, e.g.

Inputs 11a and 11b, and forms on the other hand via a corresponding one Tax rate the control commands for the valves 11, 13, 14, 16 and 21, 23, 24, 26 and 31, 33, 34, 36 and 41, 43, 44, 46. Such facilities are in other contexts generally known, e.g. from DT-OS 24 41 962 a device for monitoring the reverse voltage, but only in connection with thyristor protection a HGU facility.

Furthermore, a control loop with a direct current regulator 60 is provided, which keeps constant the direct current id detected by a transducer 61 and in the event of differences between target - Idsoll and Ist5sert id of the direct current before? jeichenrich tig specifies an active current setpoint iwsoll that is derived from the reactive current control Setpoint iqsoll for the current in the primary winding 5 of the converter transformer will be added. The value of the Gleiohstromes is to be chosen so large that with symmetrical From control of all valve sections 11 .. 46 the current i in the primary winding 5 about q is as large as the peak value of the capacitor current.

The following is the mode of operation of the entire circuit arrangement in the approximate generation of a desired reactive current curve using the example of Fig. 2 will be explained in more detail.

Curve 1 shows the sinusoidal voltage URS, Curve 2 the setpoint predetermined by the superordinate compensation control device 50 lqsoll of the current to be absorbed by the transformer winding 5. Flows with one Converter bridge of the direct current id via two diagonally opposite valves * e.g. 13 and 11, the direct current id also flows through the associated secondary winding, e.g. 1, of the transformer, resulting in a corresponding current iq in the primary winding 5 has the consequence. On the other hand, if the direct current id flows in so-called free-running mode via two adjacent valves connected to the same transformer connection, e.g. 13 and 14, the associated transformer winding, e.g. 1, remains de-energized and therefore makes no contribution to the primary current iq. With constant direct current id are therefore nine different values of, taking into account the sign - 100% to + 100% for the current iq of the primary winding 5 possible, depending on how many of the four bridges are currently in freewheel mode. Should be in the primary winding 5 the greatest current iq, denoted by 100%, must flow, no bridge must be free-running work. On the other hand, if all bridges work in freewheeling mode, the primary current is 0%.

In Fig. 2, the possible values of the primary current i are shown as thin parallels entered on the timeline. At the beginning of the displayed time * tervaisi the current setpoint q should only be small.

The actual current value (strongly drawn out step curve 3) is 0%; Everyone Bridges work in freewheeling mode, the valves 13 are conductive; 14 and 23; 24 and 33; 34 and 43; 44. In the lower part of Fig. 2 is the conductive state of a valve indicated by a solid line. Beginning and end of the leading state are highlighted by dashes. At time a, the target value is exceeded i qsoll of the primary current iq the switching limit + 12.5% the middle between the possible Actual values of the primary current i of 0% and 25%. This can be done through the comparator 51, to which the variable iqsoll is given, or by various means Threshold members (not shown). In a well-known way, this will be Exceed the switching value is detected by the control device 54, which then ignites the Valve path 11 causes. With the help of the mains voltage, which is positive at that moment uRs ko lut benefits the direct current from valve 14 to valve 11, the direct current id now flows through the secondary winding 1 of the transformer, the primary current i now has the value + 25%.

Correspondingly, in moments b and c, the valves 21 and 31 ignited, after time c the primary current iq has the value 75%. Because the setpoint iqsoll does not exceed the limit of 87.5%, the fourth bridge remains in Free running. At time d, the setpoint iqsol1 falls below the limit of 62.5%, the bridge connected to winding 1 is activated by igniting the valve 16 brought back into freewheeling mode. The direct current commutates with the help of the Voltage uRS from valve 13 to valve 16, which has meanwhile become negative, applies accordingly happens at times e and f; from f to g all bridges are again in the freewheeling state.

At the point in time g, the direct current id is generated by the ignition of the valve 46 out in the negative direction via the winding 4, the primary current takes the value - 25% on. The valves 11 ... 46 to be ignited are selected as follows Rule: If the primary current 19 q is to be increased while observing the sign, i.e. increase in positive direction, then a valve with an odd number must be used be ignited. At this point in time there are several valves with an odd number de-energized, the valve that has been de-energized the longest is ignited. Should he Primary flow are reduced, a valve with an even number is healthy In order to keep the direct current id constant, the direct current regulator 60 an active current setpoint iwsoll is formed in a known manner, which corresponds to the reactive current setpoint iq80ll * of the primary stream is added. As shown in FIG. 2, the actual value follows iq of the primary current quickly and with little error its resulting setpoint iq50ll. The active part of the Primary current i arises at the described arrangement independently in such a way that all losses in the transformer, Chokes and valves are covered.

The explained on the arrangement shown in FIG. 1 single-phase Mode of operation does not change when the converter bridges all three phases - the usually three-phase arrangement - to a single DC circuit in Can be connected in series. It is useful to start with three bridges, which are in different phases, connect directly in series z #, so that the total voltage that of a six-pulse converter. If the total voltage of all converter bridges If the values are not too high, this can affect the distribution of the smoothing inductor windings be waived. The primary windings 5 of the three-phase arrangements are like already mentioned, operated in delta connection.

In order to reduce the complexity of the three-phase arrangement, a Proposed continuation of the inventive concept instead of the single-phase converter to use a special form of a three-phase converter. This possibility is shown in FIG. 3. In parallel with a three-phase capacitor bank 6 is the delta connected primary winding 5 of a three-phase transformer, of the four identical secondary windings 1 ... 4. The secondary windings are star-connected. The conductors connected to the winding ends are labeled R, S, T, the Neutral point conductor with N. The four conductors of each secondary winding 1 ... 4 are each a converter valve set connected in four-phase bridge circuit, the circuit can also be referred to as a three-phase block with two controlled neutral anodes. The affiliation of the valves to the different branches is indicated by the letters R, S, T and N marked, the affiliation to the 8 different commutation groups through the Digits 11; 12; 21; 22; 31; 32; 41; 42. DC side all four bridge circuits are connected in series, the circuit still contains a power choke coil 9 and a parallel resonance circuit with a choke coil 7 and a capacitor 8. The resonance frequency of the parallel resonant circuit is the same of twice the network frequency. The control device corresponds to that based on of Fig. 1 described, in addition to the measuring devices 55 for detecting the No current of the valves corresponding to the zero valves.

Fig. 4 shows how it is possible with this arrangement, the currents the primary winding 5 of the transformer a predetermined target value quickly and adapt with comparatively little error. In Fig. 4, the thinly drawn out, continuously running curves the setpoints iRsoll, iSsollg iTsoll of the primary side Winding currents, the stair-shaped curves show the actual values iR is, iT of these currents. The lead times of the individual valves 12 .. 41 go from the lower one Part of Fig. 4 emerges. The four different branches R, S, T, N are through different types of lines marked, the eight different commutation groups by the assigned digits 11 ... 42. The individual valves are ignited according to the following rules: 1. Should be the amount of a primary current with a positive instantaneous value are enlarged, one is connected to a phase conductor of the relevant phase To ignite a valve from a commutation group with an odd number. If several valves of this type are de-energized at this point in time, the valve becomes the one Eommutation group ignited, the zero anode valve of which has the longest burning time.

2. Should the amount of a primary current iR, iS or iT be positive If the instantaneous value is reduced, it is connected to a neutral conductor To ignite the valve of an eommutation group with an odd number.

If several valves of this type are de-energized at this point in time, will the valve of that commutation group is ignited, the phase in question associated valve has the longest burning time. For primary currents with even negative The same rules apply to instantaneous values, only that instead of the commutation group with odd designation digits to select those with even designation digits are. The example in Fig. 4 shows a system of primary winding currents with strong asymmetry.

With a symmetrical voltage system, the co-components form of the asymmetrical current system a constant power over time, the counter-components an alternating power that oscillates at twice the line frequency.

The parallel resonance circuit makes it possible to use this alternating power to supply the direct current circuit 7, 8 without noticeable pulsation of the direct current id.

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Claims (11)

Claims: 1. Circuit arrangement for generating according to size and Waveform of quickly variable reactive currents with a three-phase to be influenced AC power converter transformer and a converter actuator, by means of the sen controllable converter valves the same secondary windings of the converter transformer looped in or in freewheeling mode5Dwegr§n, with one parallel to the alternating current network connected three-phase capacitor bank to provide a predetermined Compensation reactive power and with a control or regulating device, thereby characterized in that as a converter actuator to the secondary windings (1 to 4) Line-commutated converter bridge circuits for every secondary winding system are connected, the DC side with each other and with a smoothing choke coil (10, 20, 30, 40; 9) are connected in series, with the DC circuits of all Secondary systems are connected in the same direction in series to form a closed circuit. 2. Circuit arrangement according to claim 1, characterized in that A single-phase bridge circuit is connected to each secondary winding (1 to 4) is. 3. Circuit arrangement according to claim 1, characterized in that to the phase conductors of each of the secondary three-phase winding systems (1st up to 4), which are each connected in star connection, a converter valve set (11, 12; 21, 22; 31, 32; 41, 42) is connected in a rotary current bridge circuit, which additionally has a fourth two-pair valve, its AC connection connected to the zero point of the associated secondary winding system (1, 2, 3 or 4) is. 4. Circuit arrangement according to Claim 1 or the following, characterized in that that for the delivery of power oscillations £ 'cn of double the network frequency on this frequency offset parallel resonance circuit is inserted into the direct current circuit is which consists of a choke coil (7) and a capacitor (8). 5. Circuit arrangement according to Claim 1 or the following, characterized in that that a Sollvertgeber (50), a comparator (51) and a device (54) for valve monitoring and control are provided, the three currents of the transformer primary windings (5) approximated setpoint values independently of one another by means of multi-stage control that the number of control stages has a polarity with the number of secondary systems (1 to 4) of the Stritrichtertransformators agrees that when one is exceeded positive switching limit or when falling below a negative switching limit the current setpoint by means of a comparator (51) a valve path over the device for valve monitoring and control (54) is ignited with the transformer secondary winding (1, 2, 3 or 4) of the associated phase is connected and at the time of comparison positive reverse voltage is when the sign of the mains voltage and the time Derive the current setpoint via agree. 6. Circuit arrangement according to claims 1, 2, 4 and 5, characterized characterized that when falling below a positive switching limit or when exceeding a negative switching limit through the current setpoint by means of an upstream Comparator (51) via the control device (54) the ignition of the valve path is caused to be associated with a transformer winding (1, 2, 3 or 4) Phase is connected and the reverse voltage is positive at the time of comparison, if the sign of the mains voltage and the time derivative of the current setpoint to match. 7. Circuit arrangement according to claims 1, 2 and 5, characterized by measuring devices (55), the duration of the currentlessness of each valve section detect and via the control device (54) dieJenige with positive reverse voltage Find the stressed valve section (11 .. 46) which has the greatest measured value for the time that shows no electricity 8. Circuit arrangement according to claims 1, 3 and 5, characterized in that when falling below a positive switching limit or when a negative switching limit is exceeded by the current setpoint using of the comparator (51) via the affected control device (54) the ignition of the Valve path is caused, which is connected to a neutral point of the transformer systems and is at the positive reverse voltage if the sign of the mains voltage and the time derivative of the current setpoint match. 9. Circuit arrangement according to claim 8, characterized by measuring devices (55), the duration of the current flow of the valve branches connected to the phase conductors detect and the ignition of those with positive reverse voltage stressed valve path that belongs to the muting group in which the valve is sized MeB-who for the power supply of all valves of the relevant phase lies. 10. Circuit arrangement according to claim 8 or the following, characterized by measuring devices that determine the duration of the current carrying to the neutral point conductors Detect connected valve branches and the ignition of those with positive reverse voltage cause the stressed valve section that belongs to the commutation group, in which the zero valve with the largest measured value for the current conduction is located. 11. Circuit arrangement according to claim 5 or the following, gekeniizeichnet by a direct current regulator (60), which keeps the direct current id constant and at Differences between the setpoint and actual value of the direct current with the correct sign Active current setpoint iwsoll specifies that derived from the reactive current control 1 Setpoint iqsoll for the current in the primary winding (5) of the converter transformer will be added.