JP5860720B2 - Power converter, DC substation, DC power transmission system, and method for controlling power converter - Google Patents

Description

  The present invention relates to a power converter, a DC substation, a DC power transmission system, and a method for controlling the power converter, and more particularly, to a power converter, a DC substation, a DC power transmission system, and a power converter suitable for improving reliability. It relates to a control method.

  In recent years, a technique for converting power from alternating current to direct current or from direct current to alternating current has been widely used. A switching element that can be turned on / off, such as an IGBT (Insulated Gate Bipolar Transistor), is used for this power conversion device.

  Among such techniques, a so-called MMC circuit system having an arm in which unit converters are connected in cascade is known and disclosed in Non-Patent Document 1. According to Non-Patent Document 1, an arm composed of one or a plurality of unit converters connected in series (cascade) is connected.

  Each unit converter is, for example, a bidirectional chopper circuit, and includes a switching element and a DC capacitor. Each unit converter is connected to the outside through a terminal, and is controlled to a voltage of a DC capacitor of the unit converter or zero.

  In application, half of the arms are connected to the positive DC bus and the other half are connected to the negative DC bus. Each arm is connected to a reactor, and the connection point between each positive arm and reactor in series and the negative arm and reactor in series is an AC terminal. Power conversion is performed by PWM (Pulse-Width Modulation) control of each unit converter. In particular, application to a direct current power transmission system (HVDC), a reactive power compensator (STATCOM), a motor drive inverter, and the like is expected.

JP 2010-503979 gazette

Makoto Sugawara and Yasufumi Akagi: “PWM control method and operation verification of modular multilevel converter (MMC)”, IEEJ Transactions D, Vol. 128, No. 7, pp. 957-965.

  In a power conversion device, for example, a short-circuit current may flow under the influence of a DC accident or the like. In general, this short-circuit current is often an excessive current, and when this overcurrent flows through the switching circuit constituting the power conversion device, for example, a conductive member near the switching element is melted or arc discharge occurs. Problems occur.

  An object of the present invention is to provide a power conversion device, a DC substation, a DC power transmission system, and a control method for the power conversion device that can suppress / prevent fusing or arcing of a conductive member.

In order to achieve the above object, the present invention includes a unit converter, and the unit converter includes a terminal, at least a first switching element, a second switching element, and a DC capacitor, and The voltage of the capacitor can be output to the terminal by conduction / cutoff of one switching element and the second switching element, and one or a plurality of the unit converters are connected in cascade to form an arm . In the power converter, when a thyristor is connected in parallel with at least one of the DC capacitors of the unit converter, and the thyristor is in a conductive state, a current having a current increase rate higher than the current increase rate withstand capability of the thyristor. So that the inductance of the discharge path from the DC capacitor through the thyristor Chest <configured so as to satisfy the condition of the current increase rate capability of the DC capacitor rated voltage / pressure-contact type thyristor.

  According to the present invention, it is possible to suppress / prevent melting of the conductive member and generation of an arc.

The lineblock diagram of the power converter connected to the system of the present invention. FIG. 2 is a schematic diagram of a unit converter according to the first embodiment. The block diagram inside an IGBT module. FIG. 3 is a mounting schematic diagram of a main part of a unit converter according to the first embodiment. FIG. 4 is a mounting schematic comparison diagram of main parts of the unit converter according to the first embodiment. FIG. 3 is an explanatory diagram in the first embodiment. FIG. 3 is an explanatory diagram in the first embodiment. FIG. 6 is a schematic diagram of a unit converter in Embodiment 2. FIG. 6 is a schematic diagram of a unit converter in Embodiment 3. FIG. 6 is a schematic diagram of a unit converter in Embodiment 4. FIG. 10 is a schematic diagram of a unit converter in the fifth embodiment. FIG. 10 is a schematic diagram of a unit converter in Embodiment 6. FIG. 10 is a schematic diagram of a unit converter according to a seventh embodiment. The current waveform in Example 1. FIG. The current waveform in Example 1. FIG. The current waveform in Example 1. FIG. The current waveform in Example 3. The current waveform in Example 4. The current waveform in Example 4. The current waveform in Example 5.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following examples show one form of the present invention, and the present invention includes other forms unless departing from the gist.

  Currently, IGBT modules are widely used as semiconductor modules. Therefore, hereinafter, the semiconductor module is referred to as an IGBT module, but the present invention is not limited to the IGBT module. The semiconductor may be a power MOS-FET or the like.

  FIG. 1 shows a configuration diagram of a power conversion device 1 according to an embodiment of the present invention. In general, the MMC technique related to the invention of panicle cancer is configured by connecting arms configured by one or a plurality of unit converters connected in series (cascade) in a bridge shape. Half of the arms are connected to the positive DC bus of the MMC, and the other half are connected to the negative DC bus of the MMC. In this specification, an arm connected to the positive DC bus is called a positive arm, and an arm connected to the negative DC bus is called a negative arm.

  The power conversion device 1 has a configuration in which unit converters 2 are cascade-connected, and the power conversion device 1 is connected to an AC system 7 via a connection reactor (transformer) 6. The power conversion device 1 includes a unit converter 2, a control device 3, a signal line 4 for transmitting a control signal from the control device 3 to each unit converter, and a buffer reactor 5. 2_U, 2_V, 2_W, 2_u, 2_v, and 2_w are obtained by connecting a plurality of unit converters 2 in cascade, and are defined as arms. The upper arms 2_U, 2_V, 2_W are referred to as the U-phase positive arm, the V-phase positive arm, and the W-phase positive arm, respectively, and the lower arms 2_u, 2_v, and 2_w are the U-phase negative arm and the V-phase, respectively. This is called the negative arm and the W-phase negative arm. Each upper arm (U-phase positive arm, V-phase positive arm, W-phase positive arm) and each lower arm (U-phase negative arm, V-phase negative arm, W-phase negative arm) are each a buffer reactor. 5, the connection point between each positive arm and the serial body of the buffer reactor 5, and each negative arm and the serial body of the buffer reactor 5 is an AC output of the power converter 1, and the AC output and the AC system An interconnected reactor (system impedance) 6 is connected between 7 and 7.

  Each of the arms 2_U, 2_V, 2_W, 2_u, 2_v, and 2_w outputs a total voltage of the output voltages of the unit converters 2 constituting each arm. Further, when any one of the unit converters 2 constituting the arm is opened, it is impossible to pass a current through the arm.

  The configuration of the unit converter 2 will be described with reference to FIG. The unit converter 2 has an IGBT leg in which an IGBT module 11a and an IGBT module B are connected in series. The IGBT leg, which is a series body of the IGBT module 11a and the IGBT module 11b, is connected to the DC capacitor 12.

  The output terminal 22p of the unit converter 2 is connected to the connection point between the IGBT module 11a and the IGBT module 11b, and the output terminal 22n of the unit converter 2 is connected to the emitter of the IGBT module 11b.

  Each IGBT module 11 a and IGBT module 11 b are driven by a gate driver 16. Usually, the IGBT module 11a and the IGBT module 11b are driven complementarily. In this embodiment, the power of the gate driver 16 is supplied from a self-supplied power source 17 connected to the DC capacitor 12. The gate signal is supplied from the unit converter control circuit 15, and the unit converter control circuit 15 is supplied with a gate signal or a signal used for calculation of the gate signal from the central controller. Usually, the AC fundamental wave frequency output from the unit converter 2 in each arm is substantially the same, but by shifting the pulse timing, each arm 2_U, 2_V, 2_W, 2_u, 2_v, 2_w is a sine wave, respectively. A voltage in which a direct current is superimposed on a sine wave can be output.

Next, problems to be solved by the present invention will be described.
As described above, since the IGBT module 11a and the IGBT module 11b are complementarily switched, when either the IGBT module 11a or the IGBT module 11b is short-circuited, the IGBT module 11a and the IGBT module are switched from the DC capacitor 12 when the other is turned on. A short-circuit current flows through 11b.

  Since the path from the DC capacitor 12 to the IGBT module 11a and the IGBT module 11b has very little impedance in addition to the parasitic inductance (inductance) 60, the short-circuit current has an excessive current value.

  FIG. 3 shows the internal structure of the IGBT module. A metal collector electrode 101 is formed on the insulating substrate 11s, and an IGBT chip 11i and a diode chip 11d are mounted thereon. In the example of FIG. 3 (or each IGBT module element of the IGBT is composed of an IGBT chip), the collector of 11a is on the lower side and the emitter is on the upper side. Although the gate electrode is also formed on the top surface of the IGBT chip, it is omitted in FIG. The cathode of the diode chip 11d is the lower side, and the anode is the upper surface. Conductive wires 77 connect the emitter of the IGBT chip 11i and the anode of the diode chip 11d to the emitter electrode 102 formed on the insulating substrate 11s.

  If the excessive short-circuit current flows in the IGBT module, the conductive wire 77 may generate heat and melt. If all of the conductive wires 77 of the IGBT chip 11i having the short-circuit failure are melted, there is a problem that an arc is generated between the emitter electrode 102 and the IGBT chip 11i having the short-circuit failure.

  Next, the points of the present invention will be described with reference to FIG. One of the features is that a pressure contact thyristor 80 is connected in parallel to the DC capacitor 12. The pressure contact thyristor 80 is connected between the branch 88p and the branch 88n. The pressure contact thyristor 80 is driven by a thyristor driving circuit 82. The thyristor driving circuit 82 detects the current flowing from the DC capacitor 12 in the direction of the IGBT module 11a with the current detector 85, and turns on the pressure contact thyristor 80 when the detected current value exceeds a specified value.

  When the IGBT leg composed of the IGBT module (module IGBT) 11a and the IGBT module (module IGBT) 11b is short-circuited due to some malfunction or failure, a discharge current flows from the DC capacitor 12 to the IGBT leg. In the present invention, the discharge current is detected by the current detector 85, and the thyristor driving circuit 82 turns on the pressure contact type thyristor 80 to shunt the discharge current. By shunting the discharge current, the current flowing through the IGBT module 11a and the IGBT module 11b is suppressed, so that the conductive wire 77 is prevented from fusing and the arc is prevented from being generated.

  In general, a thyristor has a withstand capability for a current increase rate at turn-on, and if a current with an increase rate exceeding the withstand capability flows, the thyristor may break down and fail. The maximum value of the current increase rate of a commercially available thyristor is usually several tens A / μs to several hundreds A / μs.

  In the unit converter having the configuration shown in FIG. 2, the current increase rate di / dt when the pressure contact thyristor 80 is turned on is the inductance Ls of the path connecting the pressure contact thyristor 80 from the DC capacitor 12 and the steady voltage of the DC capacitor 12. It can design using Formula (1) from Vc.

di / dt = Vc / Ls (1)
One feature of the present invention is that the inductance value of Ls is set so that the thyristor current increase rate di / dt after turn-on of the pressure contact thyristor 80 is sufficiently larger than the withstand capability of the current increase rate of the pressure contact thyristor 80. It is.

The operation of this embodiment will be described in more detail.
It is assumed that the IGBT module 11a and the IGBT module 11b are simultaneously conducted / short-circuited due to some malfunction or failure.

  When the IGBT module 11a and the IGBT module 11b are short-circuited, a discharge current flows from the DC capacitor 12 via the IGBT module 11a and the IGBT module 11b. Assuming that the main impedance of the discharge path is a parasitic inductance (inductance) 60, the discharge current increases in current value due to the current increase rate determined by the voltage of the parasitic inductance 60 and the DC capacitor 12. When the current detection value of the current detector 85p exceeds the threshold value, the thyristor drive circuit 82 turns on the pressure contact thyristor 80. As described above, when the inductance Ls of the bypass discharge path from the DC capacitor 12 via the pressure contact thyristor 80 is sufficiently small, a current exceeding the withstand capability of the current rise rate is passed through the pressure contact thyristor, and the pressure contact thyristor is passed. Breaks down and causes a short circuit failure. In the pressure contact type thyristor, the semiconductor is pressurized with the conductor interposed therebetween, so that a conductive path to the short-circuited portion can be secured and current can continue to flow.

  If the thyristor is not a pressure contact type thyristor and the conductor and the semiconductor are connected by solder or the like, the temperature may rise at the short-circuit point, and the solder bonding surface may be peeled off, resulting in electrical release.

  After the pressure contact thyristor 80 is turned on, the discharge current flowing from the DC capacitor 12 is shunted by the inverse ratio of the impedance of the discharge path passing through the IGBT module 11a and the IGBT module 11b and the impedance of the discharge path passing through the pressure contact thyristor 80. Therefore, when the impedance of the pressure contact thyristor 80, the IGBT module 11a, and the IGBT module 11b is sufficiently small, if Ls is sufficiently smaller than the parasitic inductance (inductance) 60, most of the discharge current flowing through the IGBT module 11a and the IGBT module 11b is reduced. Since the current can be diverted to the pressure contact type thyristor 80, the current flowing through the IGBT module 11a and the IGBT module 11b can be reduced, the fusing of the conductive wire 77 can be prevented, and the occurrence of an arc can be prevented.

  In the pressure contact thyristor 80, since the thyristor is short-circuited before the ignition region is expanded from the gate, the conductive portion is limited to the vicinity of the gate. Therefore, the current can be more effectively diverted to the thyristor 80 when the plurality of gates are provided in the pressure contact thyristor 80.

  The mounting structure is also important for suppressing the current flowing through the IGBT module 11a and the IGBT module 11b more effectively. A point on the mounting structure, which is one of the features of the present invention, will be described by comparing FIG. 4 and FIG.

  First, the configurations of FIGS. 4 and 5 will be described. 4 and 5 show the mounting structure of the main circuit portion of the unit converter 2 shown in FIG.

  In FIG. 4, the high voltage side terminal 12p of the DC capacitor 12 is connected to the stack electrode 94k via the circuit conductor 220cp. The stack electrode 94k is electrically connected to the circuit conductor 220ip from the side opposite to the circuit conductor 220cp, and the circuit conductor 220ip is electrically connected to the collector terminal of the IGBT module 11a. The emitter terminal of the IGBT module 11 a and the collector terminal of the IGBT module 11 b are electrically connected to one output terminal 22 p of the unit converter 2. The emitter terminal of the IGBT module 11b is electrically connected to the other output terminal 22n of the unit converter 2. Further, the emitter terminal of the IGBT module 11b is connected to the stack electrode 94k electrically connected to the cathode of the pressure contact thyristor 80 through the circuit conductor 220in. The stack electrode 94k is connected to the circuit conductor 220cp on the side opposite to the connection point with the circuit conductor 220in, and is connected to the low voltage side terminal 12n of the DC capacitor 12.

  Next, the configuration of the pressure-contact stack 99 that pressurizes the pressure-type thyristor 80 will be described. A spring 90 is installed inside the stacking support 93, and the spring 90 and an insulator 91 adjacent to the spring, a cathode-side stack electrode 94k, a pressure contact thyristor 80, and an insulator 91 are stacked. The pressure of the spring 90 is pressed.

Next, the configuration of FIG. 5 will be described.
The configuration of the pressure welding stack 99 is the same as that of the pressure welding stack 99 of FIG.
In FIG. 4, the circuit conductor 220ip connected to the IGBT module and the circuit conductor 220cp connecting the high-voltage side terminal of the DC capacitor 12 and the stack electrode 94a are branched by the stack electrode 94a, whereas in FIG. 12 branches at the high voltage side terminal 12p. The branch of the circuit conductor 220in and the circuit conductor 220cn is also branched at the low voltage side terminal 12n of the DC capacitor 12 in FIG. That is, the branch 88P and the branch 88N are the stack electrode 94a and the stack electrode 94k in FIG. 4, whereas in FIG. 5, they are the DC capacitor high-voltage side terminal 12p and the DC capacitor low-voltage side terminal 12n.

  The configuration of FIG. 5 will be described in more detail. The high-voltage side terminal 12p of the DC capacitor 12 is connected to the stack electrode 94a electrically connected to the anode of the pressure contact thyristor 80 through the circuit conductor 220cp. Further, the high voltage side terminal 12 of the DC capacitor 12 is connected to the collector terminal of the IGBT module 11a via the circuit conductor 220ip. The emitter terminal of the IGBT module 11 a and the collector terminal of the IGBT module 11 b are electrically connected to one output terminal 22 p of the unit converter 2. The emitter terminal of the IGBT module 11b is electrically connected to the other output terminal 22n of the unit converter 2. Furthermore, the emitter terminal of the IGBT module 11b is connected to the low voltage side terminal 12n of the DC capacitor 12 via the circuit conductor 220in. The low voltage side terminal 12n of the DC capacitor 12 is connected to a stack electrode 94k electrically connected to the pressure contact thyristor 80 via a circuit conductor 220cn.

  FIGS. 6 and 7 are diagrams in which the paths of the discharge current from the branch 88P to the branch 88N are added to FIGS. 4 and 5, respectively.

However, in order to make the figure easier to see, some leader lines and numbers were deleted.
6 and 7, the discharge path of the route from the branch 88p via the IGBT module 11p and the IGBT module 11n is represented by a solid line as 300i, and the discharge path is bypassed from the branch 88p via the pressure welding thyristor 80 and returned to the branch 88n. Is indicated by a dotted line as 300 s.

  As shown in FIG. 7, when the high-voltage side terminal 12p and the low-voltage side terminal 12n of the DC capacitor 12 are branch points and the conductor electrode is drawn from the branch point to the pressure contact thyristor 80, the parasitic inductance of the conductor electrode portion is It is difficult to reduce the impedance of the discharge path 300s passing through the thyristor. Therefore, the current shunted to the pressure contact thyristor 80 is limited.

  FIG. 14 shows a current waveform flowing into the IGBT module 11a when the pressure contact thyristor 80 is not turned on.

  FIG. 15 shows a current shunting to the pressure contact thyristor 80 and a current flowing to the IGBT module 11a in the mounting configuration of FIG. 5 and FIG. The current flowing into the IGBT module 11a is smaller than that in FIG. 14, and the reduction effect is about 40%.

  On the other hand, one of the mounting features of the present invention is to connect a pressure contact thyristor 80 in the middle of the wiring from the DC capacitor 12 to the IGBT modules 11a and 11b, as shown in FIGS.

  In general, since the gate of the thyristor exists in the center portion, when the pressure contact thyristor is broken down at a high current rise rate di / dt, a short-circuit path is often formed in the center portion. Therefore, when FIG. 4 and FIG. 6 are connected, the branch 88p and the branch 88n become points that are close to the center of the pressure contact thyristor 80. Since the length of the discharge path 300s from one branch 88p to the other branch 88n via the pressure contact thyristor 80 is about the thickness of the pressure contact thyristor 80, the inductance can be extremely reduced.

  FIG. 16 shows the current shunting to the pressure contact thyristor 80 and the current flowing to the IGBT module 11a in the mounting configuration of FIG. 4 and FIG. Compared to FIG. 15, it can be seen that the current diverted to the pressure contact thyristor 80 is increased, and the current flowing to the IGBT module 11a is reduced by about half.

  Therefore, it is possible to extremely increase the current diverted to the pressure contact thyristor 80, and to reduce the current flowing to the IGBT module 11a and the IGBT module 11b.

  In the first embodiment, when the current detection value of the current detector 85 exceeds the threshold value, the thyristor driving circuit 82 turns on the pressure contact thyristor 80, whereas in the second embodiment, the current detector 85p The point that the thyristor driving circuit 82 turns on the pressure contact type thyristor 80 when the direction of flow of the detected current of the current detector 85n is the direction of flow from the collector terminal of the IGBT module 11a to the emitter terminal of the IGBT module 11b. Different.

  In the current detection method of FIG. 2, the distinction between the current during steady operation and the short-circuit current when the IGBT module 11 a and the IGBT module 11 b are short-circuited cannot be determined in the flow direction, but is determined based on the current value that flows. Become.

  When the IGBT module 11a is turned on while a current is flowing through the diode of the IGBT module 11b during steady operation, the current flows from the high-voltage side terminal 12p of the DC capacitor 12 toward the IGBT module 11a. This has the same direction as the short-circuit current that flows when the IGBT module 11a and the IGBT module 11b are short-circuited.

  Therefore, it is necessary to set the threshold value of the thyristor driving circuit 82 high so that the turn-on current of the IGBT module 11a that flows during steady operation is erroneously detected and the pressure contact thyristor 80 is not turned on. However, if the threshold value of the current detection value for turning on the pressure contact thyristor 80 is increased, the timing for turning on the pressure contact thyristor 80 is delayed.

  Therefore, as shown in FIG. 8, the unit converter 2 of the present embodiment includes a current detector 85p that detects a current flowing through the IGBT module 11a and a current detector 85n that detects a current flowing through the IGBT module 11b.

  In the thyristor drive circuit 82 of the present embodiment, when the flow direction of the current detected by the current detector 85p and the current detection 85n is both the flow direction from the collector terminal of the IGBT module 11a to the emitter terminal of the IGBT module 11b, The thyristor driving circuit 82 turns on the pressure contact thyristor 80.

  During steady operation, in principle, no current flows from the collector terminal of the IGBT module 11a to the emitter terminal of the IGBT module 11b, so the threshold value can be made smaller than the threshold value of the first current detection value.

  However, when the diodes of the IGBT module 11a and the IGBT module 11b are recovered, a current flows instantaneously from the collector terminal of the IGBT module 11a to the emitter terminal of the IGBT module 11b. Since the recovery period is usually as extremely small as 1 μs, the recovery period can be dealt with by masking current detection.

  This embodiment has an effect that the current detection threshold value can be reduced and the pressure contact thyristor can be quickly turned on.

The configuration of the third embodiment is shown in FIG.
The third embodiment differs from the first embodiment in that a small-capacitance capacitor 12c and an inductance 61 are provided.

  In order to increase the current shunted to the pressure contact thyristor 80, the inductance of the path from the branch 88p to the branch 88n via the IGBT module 11a and the IGBT module 11b may be increased.

  Therefore, in the third embodiment, the inductance 61 is installed on the path from the branch 88p to the branch 88n via the IGBT module 11a and the IGBT module 11b.

  However, since the jumping voltage when the IGBT module 11a and the IGBT module 11b are turned off during normal operation may be increased, the capacitor 12c is provided for the suppression.

  FIG. 17 shows a current waveform that flows into the IGBT module 11a when the IGBT module 11a and the IGBT module 11b are short-circuited.

  Compared with FIG. 16, it turns out that the electric current which flows into IGBT module 11a can be suppressed.

  The present embodiment has an effect that the current from the DC capacitor 12 to the IGBT module 11a and the IGBT module 11b can be suppressed as compared with the first embodiment.

The configuration of the fourth embodiment is shown in FIG.
The fourth embodiment is different from the third embodiment in that a diode 69 and a resistor 68 connected to the small-capacitance capacitor 12c are provided.

  In the third embodiment, when the IGBT module 11a and the IGBT module 11b are short-circuited, there is a problem that the discharge current flows from the small-capacitance capacitor 12c to the IGBT module 11a and the IGBT module 11b.

  FIG. 18 shows a current waveform flowing out from the small-capacitance capacitor. It can be seen that the current waveform is oscillating.

  FIG. 10 shows a configuration in which a resistor 68 and a diode 69 are added to FIG. The resistor 68 and the diode 69 are installed between the small capacitor 12 c and the inductance 61. When the IGBT module 11a or the IGBT module 11b is turned off, the energy stored in the inductance 61 can be converted into electrostatic energy by passing a current through the small-capacitance capacitor 12c via the diode 69. Therefore, the IGBT module 11a is turned off. And the surge voltage applied to the IGBT module 11b can be suppressed.

  On the other hand, when the IGBT module 11a and the IGBT module 11b are short-circuited, the small-capacitance capacitor 12c is discharged and attempts to flow current to the IGBT module 11a and the IGBT module 11b, but the resistor 68 suppresses the current.

  FIG. 19 shows a current waveform flowing into the IGBT module. The vibration waveform seen in FIG. 17 is not recognized.

  This embodiment has an effect that the current flowing from the small-capacitance capacitor 12c to the IGBT module 11a and the IGBT module 11b can be suppressed as compared with the third embodiment.

  In this embodiment, the current discharged from the DC capacitor 12 to the IGBT module 11a and the IGBT module 11b can be suppressed more than the first embodiment, and the discharge current of the small-capacitance capacitor 12c can also be suppressed. Therefore, the short circuit current which flows into IGBT module 11a and IGBT module 11b can be controlled rather than the 1st example.

The configuration of the fifth embodiment is shown in FIG.
The fifth embodiment is characterized in that a pressure contact thyristor 80i is added to the fourth embodiment.

  In the fourth embodiment, the IGBT module 11a and the IGBT module 11b are connected via the inductance 61 and the parasitic inductance (inductance) 60 after the IGBT module 11a and the IGBT module 11b are short-circuited until the press-contact thyristor 80 is turned on. Current is passed through.

  Even if the pressure-contact thyristor 80 is turned on, the parasitic inductance 60 and the inductance 61 try to continuously pass the current through the IGBT module 11a and the IGBT module 11b, and the current is electromagnetic energy stored in the parasitic inductance 60 and the inductance 61. Continue until becomes zero. The current flowing into the IGBT module 11 a and the IGBT module 11 b due to the parasitic inductance 60 and the inductance 61 cannot be processed by the pressure contact thyristor 80.

  FIG. 11 shows a configuration in which a pressure contact thyristor 80i is added to FIG. The pressure contact thyristor 80 i is turned on by a thyristor driving circuit 82. The turn-on conditions of the pressure contact thyristor 80 and the pressure contact thyristor 80i are substantially the same. However, it is not indispensable to arrange the turn-on conditions.

  The pressure contact thyristor 80i is connected in proximity to the IGBT module 11a and the IGBT module 11b so as not to include the parasitic inductance 60 as much as possible. By connecting in this way, when the pressure contact thyristor 80i is turned on, the current that the parasitic inductance 60 and the inductance 61 try to flow is shunted to the pressure contact thyristor 80i, and flows to the IGBT module 11a and the IGBT module 11b. The current can be reduced.

  In order to more effectively divide the current into the pressure contact thyristor 80i, it is preferable to have a plurality of gates in the pressure contact thyristor 80i. The reason is that when a plurality of gates are provided, a plurality of conduction paths are formed, and the impedance of the thyristor can be reduced.

  FIG. 20 shows a current flowing into the IGBT module 11a. As compared with FIG. 19, it can be confirmed that the current flowing into the IGBT module 11a can be further suppressed.

  The main feature of the sixth embodiment is that a short-circuit switch 71 is added to the output terminal of the unit converter 2 and a break-over thyristor 72 for driving the short-circuit switch is added to the first embodiment. It is.

  The configuration of FIG. 12 will be described. FIG. 12 is different from FIG. 2 in that a short-circuit switch 71, a diode 90, a breakover thyristor 72, and a capacitor 12b are added, and the self-supply power source (self-supply circuit) 17 is connected to the capacitor 12b instead of the DC capacitor 12.

  The present embodiment aims to close the short-circuit switch 71 when the IGBT module 11a and the IGBT module 11b are short-circuited to ensure a conductive path to the other unit converter 2.

  When the IGBT module 11a and the IGBT module 11b are short-circuited, the charge of the DC capacitor 12 is discharged, and the voltage of the DC capacitor 12 decreases. On the other hand, since the capacitor 12b is connected through the diode 90, the electric charge of the capacitor 12b is not discharged and the voltage of the capacitor 12b does not decrease. Therefore, when the IGBT module 11a and the IGBT module 11b are short-circuited, a potential difference is generated between the high-voltage side terminal of the DC capacitor 12 and the high-voltage side terminal of the capacitor 12b. In FIG. 12, a drive coil for a short-circuit switch is connected from the capacitor 12 b via the breakover thyristor 72 and connected to the high-voltage side terminal of the DC capacitor 12. The breakover thyristor 72 is an element that turns on when a predetermined breakover voltage is exceeded. When the voltage of the DC capacitor 12 decreases, a voltage is applied to the breakover thyristor 72. When the applied voltage exceeds the breakover voltage, the breakover thyristor 72 is turned on and current flows through the coil portion of the short-circuit switch 71. Thus, the short circuit switch 71 can be closed. Here, the capacitor 12 b needs to store sufficient electrostatic energy to drive the short-circuit switch 71.

  The breakover voltage needs to be sufficiently larger than the fluctuation of the DC capacitor 12 during normal operation or the like.

  The first embodiment is characterized in that the unit converter 2 has a chopper configuration, whereas the seventh embodiment is a full bridge circuit.

  The configuration of the seventh embodiment is shown in FIG. In FIG. 2, the IGBT leg is only one leg composed of the IGBT module 11a and the IGBT module 11b, whereas in FIG. 13, the IGBT leg composed of the IGBT module 11ca and the IGBT module 11cb, and the IGBT module 11da and IGBT. This is different from the point formed by two IGBT legs of the IGBT leg composed of the module 11db. Further, in FIG. 2, the output terminal 22n of the unit converter is in electrical conduction with the low voltage side terminal of the DC capacitor 12, whereas in FIG. 13, the output terminals 22p and 22n of the unit converter 2 are respectively IGBT leg. Is the midpoint and the conduction potential.

  The unit converter output terminal 22p is the conductivity of the emitter of the IGBT module 11ca and the collector of the IGBT module 11cb, and the unit converter output terminal 22n is the conductivity of the emitter of the IGBT module 11da and the collector of the IGBT module 11db.

  In the normal operation, the unit converter output terminal 22n can output only the zero voltage or the voltage of the high voltage side terminal of the DC capacitor 12 with the unit converter output terminal 22n as the reference potential in the configuration of FIG. On the other hand, in the configuration of FIG. 13, the unit converter output terminal 22n can be used as a reference potential to output a zero voltage, a voltage on the high voltage side of the DC capacitor 12, and a voltage having a polarity opposite to that on the high voltage side of the DC capacitor 12. That is, three types of voltages, zero voltage, positive voltage, and negative voltage, can be output.

  For example, when the IGBT module 11ca is on, the IGBT module 11cb is off, the IGBT module 11da is off, and the IGBT module 11db is on, the output voltage of the unit converter 2 is based on the unit converter output terminal 22n as a DC capacitor 12a. When the IGBT module 11ca is on, the IGBT module 11cb is off, the IGBT module 11da is on, and the IGBT module 11db is off, the output voltage of the unit converter 2 is the unit converter output terminal. The output voltage of the unit converter 2 is output when the IGBT module 11ca is turned off, the IGBT module 11cb is turned on, the IGBT module 11da is turned on, and the IGBT module 11db is turned off. Terminal 22p Since the unit converter output terminal 22n outputs the voltage of the high-voltage side terminal of the DC capacitor 12 as a reference, when the unit converter output terminal 22n is used as a reference, a voltage having a polarity opposite to that of the high-voltage side of the DC capacitor 12, that is, Output negative voltage.

Next, the point of the present invention will be described assuming that the IGBT leg is short-circuited.
It is assumed that the IGBT module 11ca and the IGBT module 11cb are simultaneously conducted / short-circuited due to some malfunction or failure. When the IGBT module 11ca and the IGBT module 11cb are short-circuited, a discharge current flows from the DC capacitor 12 via the IGBT module 11ca and the IGBT module 11cb. Assuming that the main impedance of the discharge path is a parasitic inductance (inductance) 60, the discharge current rises at a current increase rate determined by the voltage of the parasitic inductance 60 and the DC capacitor 12. When the current detection value of the current detector 85p exceeds the threshold value, the thyristor drive circuit 82 turns on the pressure contact thyristor 80. As described above, when the inductance Ls of the bypass discharge path from the DC capacitor 12 via the pressure contact thyristor 80 is sufficiently small, a current exceeding the di / dt tolerance is passed through the pressure contact thyristor. Breaks down and causes a short circuit failure. In the pressure contact type thyristor, since the silicon wafer is pressurized with the metal sandwiched therebetween, a conductive path to the short-circuited portion can be secured, so that a current can continue to flow.

  The discharge current flowing from the DC capacitor 12 after the pressure contact type thyris 80 is turned on is shunted by the inverse ratio of the impedance of the discharge path passing through the IGBT module 11ca and the IGBT module 11cb and the impedance of the discharge path passing through the pressure contact thyristor 80. Therefore, when the impedance of the pressure contact type thyristor 80, the IGBT module 11ca, and the IGBT module 11cb is sufficiently small, if Ls is sufficiently smaller than the parasitic inductance (inductance) 60, most of the discharge current flowing through the IGBT module 11ca and the IGBT module 11cb is increased. Since the current can be diverted to the pressure contact type thyristor 80, the current flowing through the IGBT module 11ca and the IGBT module 11cb can be reduced, the fusing of the conductive wire 77 can be prevented, and the occurrence of an arc can be prevented.

  Similarly, it is assumed that the IGBT module 11da and the IGBT module 11db are simultaneously connected and short-circuited due to some malfunction or failure. When the IGBT module 11da and the IGBT module 11db are short-circuited, a discharge current flows from the DC capacitor 12 via the IGBT module 11da and the IGBT module 11db. Assuming that the main impedance of the discharge path is a parasitic inductance (inductance) 60, the discharge current rises at a current increase rate determined by the voltage of the parasitic inductance 60 and the DC capacitor 12. When the current detection value of the current detector 85p exceeds the threshold value, the thyristor drive circuit 82 turns on the pressure contact thyristor 80. As described above, when the inductance Ls of the bypass discharge path from the DC capacitor 12 via the pressure contact thyristor 80 is sufficiently small, a current exceeding the di / dt tolerance is passed through the pressure contact thyristor. Breaks down and causes a short circuit failure. In the pressure contact type thyristor, since the silicon wafer is pressurized with the metal sandwiched therebetween, a conductive path to the short-circuited portion can be secured, so that a current can continue to flow.

  The discharge current flowing from the DC capacitor 12 after the pressure contact type thyris 80 is turned on is shunted by an inverse ratio of the impedance of the discharge path passing through the IGBT module 11da and the IGBT module 11db and the impedance of the discharge path passing through the pressure contact thyristor 80. Therefore, when the impedance of the pressure contact thyristor 80, the IGBT module 11da, and the IGBT module 11db is sufficiently small, if Ls is sufficiently smaller than the parasitic inductance (inductance) 60, most of the discharge current flowing through the IGBT module 11da and the IGBT module 11db is largely consumed. Since the current can be diverted to the pressure contact thyristor 80, the current flowing through the IGBT module 11da and the IGBT module 11db can be reduced, the fusing of the conductive wire 77 can be prevented, and the occurrence of an arc can be prevented.

The power conversion devices 1 according to the first to seventh embodiments are likely to continue operation because there is a low possibility that a failure of the IGBT module affects other unit converters 2.
Moreover, it can be said that the substation and power transmission system using the power converter are also highly reliable.

DESCRIPTION OF SYMBOLS 1 Power converter 2 Unit converter 2_U U-phase positive side arm 2_V V-phase positive side arm 2_W W-phase positive side arm 2_u U-phase negative side arm 2_v V-phase negative side arm 2_w W-phase negative side arm 3 Controller 4 Signal line 5 Buffer reactor 6 Interconnection reactor 7 AC system 8 Each phase voltage command generator 9 Synchronous signal generator 10 Carrier wave generator 11a, 11b, 11ca, 11cb, 11da, 11db IGBT module 12 DC capacitor 12p DC capacitor high voltage side terminal 12n DC Capacitor low voltage side terminal 15 Unit converter control circuit 16 Gate driver 17 Self-supplied power supply 22p, 22n Unit converter output terminal 60 Parasitic inductance 71 Short-circuit switch 72 Breakover thyristor 80 Pressure contact thyristor 85, 85p, 85n Current detector 88p, 88n Branch 91 Insulator, short-circuit switch HI 93 Stack support 94a, 94k Stack electrode 99 Pressure stack 220ip, 220in, 220cp, 220cn Circuit conductor 300i, 300s Discharge path 666 Semiconductor of press pack element 777 Electrode conductor of press pack element 999 Press pack element

Claims (24)

A unit converter, the unit converter including a terminal, at least a first switching element, a second switching element, and a direct current capacitor, wherein the first switching element and the second switching element the connection / disconnection, the being configured to output a voltage of the capacitor to the terminal, the power converter to configure the arm and the one unit converters or multiple cascaded, at least of the unit converters A thyristor is connected in parallel with one of the DC capacitors, and when the thyristor is in a conductive state, the DC capacitor is configured to allow a current with a current increase rate higher than the withstand capability of the current increase rate of the thyristor to flow. To the inductance of the discharge path through the thyristor,
Inductance <power conversion equipment which is characterized by being configured so as to satisfy the condition of the current increase rate capability of the DC capacitor rated voltage / pressure-contact type thyristor.   2. The power conversion device according to claim 1, wherein the power conversion device has a chopper configuration including the first switching element and the second switching element. 3.   2. The power conversion device according to claim 1, wherein the power conversion device has a full bridge configuration including the first switching element and the second switching element. 3.   4. The power conversion device according to claim 1, wherein the thyristor is a pressure contact type. 5.   5. The power conversion device according to claim 1, wherein the thyristor is connected in parallel to another pressure contact thyristor via an inductance. 6. Be any power converter according to claim 1 to claim 4, said arm constitutes a leg with at least two connections, at least one unit converter, a conductive path from the DC capacitor to said leg power conversion apparatus characterized by having a structure in which the branch point is inserted between the thyristor and the front sharp Tsu grayed in the middle of. 7. The power converter according to claim 6 , wherein a branch of a conductive path from the DC capacitor to the leg and a conductive path from the DC capacitor to the thyristor sandwiches the thyristor in at least one unit converter. A power conversion device characterized by being a stack electrode. The power conversion device according to claim 7 , wherein at least one unit converter has a function of detecting that at least one leg is short-circuited. The power conversion device according to claim 8, wherein at least one unit converter has a function of detecting a current discharged from the DC capacitor to the leg, and when the detected current exceeds a predetermined current value, A power conversion device having a function of turning on the thyristor. 10. The power conversion device according to claim 9, wherein at least one unit converter has a function of detecting a current of an upper arm and a current of a lower arm of each leg, and each current detector is moved downward from the upper arm. A power conversion device having a function of turning on the thyristor when a current of a polarity flowing through the arm is detected.   The power conversion device according to claim 10, wherein at least one unit converter has a time when each current detector detects a current having a polarity flowing from the upper arm to the lower arm for a predetermined time or longer. A power converter having a function of turning on the pressure contact thyristor. 12. The power converter according to claim 11, wherein at least one unit converter has a reactor inserted in a conductive path from the DC capacitor to the leg.   The power conversion device according to claim 12, wherein a capacitor is inserted in parallel with the leg on the leg side of the reactor. A power converter according to claim 1 2, the power conversion device characterized in that said leg is constructed as a semiconductor leg. A power converter according to claim 1 2, the power conversion apparatus characterized by CRD snubber is inserted in parallel with the legs on the leg side of the reactor.   The power conversion device according to any one of claims 1 to 15, wherein a short-circuit switch is connected between output terminals of at least one unit converter.   17. The power converter according to claim 16, wherein the at least one unit converter includes a capacitor for storing energy for driving a coil of the short-circuit switch separately from the DC capacitor. 18. The power conversion device according to claim 17, wherein the at least one unit converter includes a diode between a capacitor for storing energy for driving the coil of the short-circuit switch and the DC capacitor, and the diode is connected from the DC capacitor side. power conversion apparatus characterized by being connected in a direction that can charging toward the storage capacitor. The power conversion device according to claim 17 , wherein at least one unit converter includes a diode between a capacitor for storing energy for driving a coil of the short-circuit switch and a DC capacitor, and the diode is connected to the DC capacitor side. The power converter is connected in a direction that can be charged only from the storage capacitor toward the storage capacitor.   20. The power conversion device according to claim 19, wherein at least one unit converter is connected from the high voltage terminal of the storage capacitor to the high voltage side terminal of the DC capacitor via the break switch thyristor and the coil of the short circuit switch. A power converter having a configuration.   21. The power conversion device according to claim 1, wherein the switching element is stored as a semiconductor module, and the semiconductor module is an IGBT module. A unit converter, the unit converter including a terminal, at least a first switching element, a second switching element, and a direct current capacitor, wherein the first switching element and the second switching element The voltage of the capacitor can be output to the terminal by conduction / cutoff, one or a plurality of unit converters are connected in cascade to form an arm, and at least two arms are connected to form a leg . In a DC substation that converts power between AC and DC using a power converter that configures,
When a thyristor is connected in parallel with at least one of the DC capacitors of the unit converter and the thyristor is in a conducting state, a current having a current increase rate higher than the current increase rate withstand capability of the thyristor can flow. Thus, the inductance of the discharge path from the DC capacitor via the thyristor,
Inductance <DC capacitor rated voltage / DC substation characterized by satisfying the condition of withstand current rise rate withstand voltage type thyristor. A unit converter, the unit converter including a terminal, at least a first switching element, a second switching element, and a direct current capacitor, wherein the first switching element and the second switching element The voltage of the capacitor can be output to the terminal by conduction / cutoff, one or a plurality of unit converters are connected in cascade to form an arm, and at least two arms are connected to form a leg . In a DC substation system that converts power between AC and DC using a power conversion device that constitutes,
When a thyristor is connected in parallel with at least one of the DC capacitors of the unit converter and the thyristor is in a conducting state, a current having a current increase rate higher than the current increase rate withstand capability of the thyristor can flow. Thus, the inductance of the discharge path from the DC capacitor via the thyristor,
Inductance <DC capacitor rated voltage / DC contact type thyristor configured to satisfy the conditions of withstand current rise rate thyristor. A unit converter, the unit converter including a terminal, at least a first switching element, a second switching element, and a direct current capacitor, wherein the first switching element and the second switching element The voltage of the capacitor can be output to the terminal by conduction / cutoff, and one or a plurality of the unit converters are connected in cascade to form an arm, and at least one DC capacitor of the unit converter In the control method of the power conversion device, in which the thyristor is connected in parallel, and the power conversion device configured to connect the at least two arms to configure the leg ,
The inductance of the discharge path from the DC capacitor through the thyristor is selected so as to satisfy the condition of inductance <DC capacitor rated voltage / current rise rate withstand capability of the pressure contact thyristor,
A control method for a power conversion device, wherein when the thyristor is in a conductive state, a current having a current increase rate higher than a withstand current increase rate of the thyristor is passed.