Power conversion device

Abstract

To provide a power conversion device capable of reducing a discharge time of a charge storage element of each converter without increasing the loss during normal operation.SOLUTION: A power conversion device includes a main circuit unit that includes a plurality of converters connected in series and converts power through operation of the plurality of converters, and a control device that controls operation of the main circuit unit. Each of the converters includes a pair of connection terminals, a plurality of switching elements, a charge storage element connected in parallel with the plurality of switching elements, and a plurality of drive circuits that switches on and off states of the plurality of switching elements. When the operation of the converter is stopped or the converter in which the abnormality occurs is protected, the plurality of drive circuits short-circuits the charge storage element with at least one switching element in a state in which the ON resistance is higher than the ON state, thereby discharging the charge storage element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] There is known a power conversion device including a main circuit section that performs at least one of conversion from AC power to DC power and conversion from DC power to AC power, and a control device that controls the operation of the main circuit section. In such a power conversion device, a multi-stage main circuit section in which a plurality of converters are connected in series is used. A power conversion device including a multi-stage main circuit section is used, for example, in a DC power transmission system that converts AC power to DC power and transmits the power.

[0003] Each converter has a plurality of switching elements and a charge storage element connected in parallel to the plurality of switching elements, and each converter has a pair of connection terminals and is connected in series via the pair of connection terminals.

[0004] In the power conversion device as described above, when the operation is stopped for maintenance inspection, it may take a long time for the charge storage element of each converter to discharge. If the discharge time is long, for example, the time from the operation stop to the actual start of the maintenance inspection will be long. This will result in, for example, a longer time required for the maintenance inspection, leading to an increase in the labor required for the maintenance inspection. It is possible to shorten the discharge time by providing a resistive element or the like in the discharge path of the charge storage element, but in this case, there is a concern that the loss of each converter during normal operation will increase.

[0005] For this reason, in a power conversion device in which multiple converters are connected in series, it is desirable to be able to shorten the discharge time of the charge storage elements of each converter without increasing losses during normal operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-140738 A Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An embodiment of the present invention provides a power conversion apparatus that can reduce the discharge time of the charge storage element of each converter without increasing losses during normal operation. [Means for solving the problem]

[0008] According to an embodiment of the present invention, there is provided a power conversion device comprising: a main circuit unit having a plurality of converters connected in series and converting power by operation of the plurality of converters; and a control device controlling the operation of the main circuit unit, wherein each of the plurality of converters has a pair of connection terminals, a plurality of switching elements, a charge storage element connected in parallel to the plurality of switching elements, and a plurality of drive circuits switching between an on state and an off state of the plurality of switching elements, and are connected in series via the pair of connection terminals, and are capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals is conductive, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements, and wherein when stopping the operation of the converter or protecting the converter in which an abnormality has occurred, the plurality of drive circuits set at least one of the plurality of switching elements to an intermediate state between the on state and the off state, and short-circuit the charge storage element with at least one of the switching elements in a state having a higher on-resistance than the on state, thereby discharging the charge storage element. Effect of the Invention

[0009] A power conversion device is provided that can shorten the discharge time of the charge storage element of each converter without increasing the loss during normal operation. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram illustrating a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a block diagram illustrating a converter. [Diagram 3] FIG. 2 is a block diagram illustrating a drive circuit. [Figure 4] FIG. 13 is a block diagram illustrating a modified example of a drive circuit. [Diagram 5] FIG. 13 is a block diagram illustrating a modified example of the converter. [Figure 6] FIG. 13 is a block diagram illustrating a modified example of the converter.

[0011] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0012] FIG. 1 is a block diagram that illustrates a power conversion device according to an embodiment. 1, the power conversion device 10 includes a main circuit unit 12 and a control device 14. The power conversion device 10 is used, for example, in a DC power transmission system. The power conversion device 10 is connected to an AC power system 2 and a pair of DC transmission lines 3 and 4 in the DC power transmission system.

[0013] The DC transmission system has, for example, a transformer 6. The main circuit section 12 of the power conversion device 10 is connected to the AC power system 2 via the transformer 6. The AC power of the AC power system 2 is three-phase AC power. More specifically, it is symmetrical three-phase AC power. The transformer 6 converts the three-phase AC power of the AC power system 2 into AC power corresponding to the main circuit section 12. The transformer 6 changes the effective value of each phase of the three-phase AC power in accordance with the main circuit section 12. The transformer 6 is a three-phase transformer. The transformer 6 is provided as necessary and can be omitted. The three-phase AC power of the AC power system 2 may be directly supplied to the main circuit section 12.

[0014] The power conversion device 10 converts three-phase AC power supplied from the AC power system 2 into DC power, and supplies the converted DC power to the DC transmission lines 3 and 4. The power conversion device 10 also converts DC power supplied from the DC transmission lines 3 and 4 into three-phase AC power, and supplies the converted three-phase AC power to the AC power system 2. In this manner, the power conversion device 10 performs AC-DC conversion from AC to DC, and DC-DC conversion from DC to AC. In this example, the AC power system 2 is shown as an AC circuit, and the DC transmission lines 3 and 4 are shown as DC circuits. The AC circuit may be, for example, an AC load or an AC power source. The DC circuit may be, for example, a DC load or a DC power source.

[0015] For example, the DC transmission line 3 is a high-voltage side transmission line of DC power, and the DC transmission line 4 is a low-voltage side transmission line of DC power. The power conversion device 10 outputs converted DC power to the DC transmission lines 3 and 4 so that the DC transmission line 3 side is high voltage and the DC transmission line 4 side is low voltage.

[0016] The main circuit unit 12 is provided between the AC power system 2 and each of the DC transmission lines 3 and 4. The main circuit unit 12 converts three-phase AC power to DC power and converts DC power to three-phase AC power. The main circuit unit 12 is, for example, a multilevel power converter having a plurality of converters connected in series. The main circuit unit 12 is, for example, an MMC (Modular Multilevel Converter) type power converter. The MMC type main circuit unit 12 has a plurality of converters connected in series. Each converter has a plurality of switching elements connected in half-bridge connection or full-bridge connection, and a charge storage element connected in parallel to each switching element. The main circuit unit 12 converts power by the operation of the plurality of converters. The main circuit unit 12 converts AC to DC by, for example, switching each switching element of the plurality of converters.

[0017] The control device 14 is connected to the main circuit section 12. The control device 14 controls the on / off of each switching element to control the conversion from three-phase AC power to DC power and the conversion from DC power to three-phase AC power by the main circuit section 12.

[0018] The main circuit portion 12 has a pair of first and second DC terminals 20a, 20b, three AC terminals (first to third) 21a to 21c, and six arm portions (first to sixth) 22a to 22f.

[0019] The first DC terminal 20a is connected to the high-voltage side DC transmission line 3. The second DC terminal 20b is connected to the low-voltage side DC transmission line 4. As a result, DC power converted by the main circuit unit 12 is supplied to the DC transmission lines 3 and 4, and DC power supplied from the DC transmission lines 3 and 4 is input to the main circuit unit 12.

[0020] The first arm portion 22a is connected to the first DC terminal 20a. The second arm portion 22b is connected between the first arm portion 22a and the second DC terminal 20b. The first arm portion 22a and the second arm portion 22b are connected in series between the DC terminals 20a, 20b.

[0021] The third arm portion 22c is connected to the first DC terminal 20a. The fourth arm portion 22d is connected between the third arm portion 22c and the second DC terminal 20b. The third arm portion 22c and the fourth arm portion 22d are connected in parallel to the first arm portion 22a and the second arm portion 22b.

[0022] The fifth arm portion 22e is connected to the first DC terminal 20a. The sixth arm portion 22f is connected between the fifth arm portion 22e and the second DC terminal 20b. That is, the fifth arm portion 22e and the sixth arm portion 22f are connected in parallel to the first arm portion 22a and the second arm portion 22b, and are connected in parallel to the third arm portion 22c and the fourth arm portion 22d.

[0023] In the main circuit unit 12, the first leg LG1 is formed by the first arm portion 22a and the second arm portion 22b, the second leg LG2 is formed by the third arm portion 22c and the fourth arm portion 22d, and the third leg LG3 is formed by the fifth arm portion 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-phase inverter with three legs and six arms. In other words, the main circuit unit 12 has a plurality of bridge-connected arm portions 22a to 22f. In this example, the main circuit unit 12 has six three-phase bridge-connected arm portions 22a to 22f.

[0024] The first arm portion 22a, the third arm portion 22c, and the fifth arm portion 22e are upper arms. The second arm portion 22b, the fourth arm portion 22d, and the sixth arm portion 22f are lower arms. In this manner, the main circuit portion 12 has a plurality of arms and a plurality of legs each formed by a plurality of switching elements. The main circuit portion 12 may be, for example, a two-leg or four-arm single-phase inverter. The number of arms and legs is not limited to the above and may be any number.

[0025] The first arm section 22a has a plurality of converters UP1, UP2...UPM1 connected in series. The second arm section 22b has a plurality of converters UN1, UN2...UNM2 connected in series. The third arm section 22c has a plurality of converters VP1, VP2...VPM3 connected in series. The fourth arm section 22d has a plurality of converters VN1, VN2...VNM4 connected in series. The fifth arm section 22e has a plurality of converters WP1, WP2...WPM5 connected in series. The sixth arm section 22f has a plurality of converters WN1, WN2...WNM6 connected in series.

[0026] However, in the following, when the converters UP1, UP2...UPM1, UN1, UN2...UNM2, VP1, VP2...VPM3, VN1, VN2...VNM4, WP1, WP2...WPM5, WN1, WN2...WNM6 are referred to collectively as the "converter CEL."

[0027] In each of the arm sections 22a to 22f, M1, M2, M3, M4, M5, and M6 represent the number of converters CEL connected in series. In each of the arm sections 22a to 22f, the number of converters CEL connected in series is, for example, about 100 to 120. However, the number of converters CEL connected in series is not limited to this and may be any number.

[0028] The number of converters CEL provided in each of the arm sections 22a to 22f is substantially the same. For example, when a large number of converters CEL are connected, the number of converters CEL provided in each of the arm sections 22a to 22f may differ within a range that does not affect the operation of the main circuit section 12. For example, when 100 converters CEL are connected in series to one arm section, the number of converters CEL provided in another arm section may differ by one or two.

[0029] The arm sections 22a to 22f further include buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f, respectively. The power conversion device 10 further includes a voltage detection section 25.

[0030] The buffer reactors 23a to 23f are connected in series to the converters CEL in the arm sections 22a to 22f, respectively. The buffer reactor 23a of the first arm section 22a is provided between the converter UP1 and a connection point between the AC terminal 21a and the first arm section 22a and the second arm section 22b. The buffer reactor 23b of the second arm section 22b is provided between the converter UN1 and a connection point between the AC terminal 21a and the first arm section 22a and the second arm section 22b. The buffer reactor 23c of the third arm section 22c is provided between the converter VP1 and a connection point between the AC terminal 21b and the third arm section 22c and the fourth arm section 22d. The buffer reactor 23d of the fourth arm section 22d is provided between the converter VN1 and a connection point between the AC terminal 21b and the third arm section 22c and the fourth arm section 22d. The buffer reactor 23e of the fifth arm portion 22e is provided between the converter WP1 and a connection point between the AC terminal 21c and the fifth arm portion 22e and the sixth arm portion 22f. The buffer reactor 23f of the sixth arm portion 22f is provided between the converter WN1 and a connection point between the AC terminal 21c and the fifth arm portion 22e and the sixth arm portion 22f.

[0031] The current detector 24a is provided in the first arm portion 22a and detects a current flowing through the first arm portion 22a. That is, the current detector 24a detects an arm current of the first arm portion 22a. The current detector 24a is connected to the control device 14 via wiring or the like (not shown). The current detector 24a inputs the detected current value of the first arm portion 22a to the control device 14. As a result, the current value of the first arm portion 22a is input to the control device 14.

[0032] Similarly, current detector 24b detects the current flowing through the second arm portion 22b and inputs the detected current value to the control device 14. Current detector 24c detects the current flowing through the third arm portion 22c and inputs the detected current value to the control device 14. Current detector 24d detects the current flowing through the fourth arm portion 22d and inputs the detected current value to the control device 14. Current detector 24e detects the current flowing through the fifth arm portion 22e and inputs the detected current value to the control device 14. Current detector 24f detects the current flowing through the sixth arm portion 22f and inputs the detected current value to the control device 14.

[0033] The voltage detection unit 25 detects the AC voltage (phase voltage) of each phase of the AC power system 2, and inputs the detected value to the control device 14. The voltage detection unit 25 may be connected to the primary side or the secondary side of the transformer 6.

[0034] In the main circuit section 12, the connection point between the first arm section 22a and the second arm section 22b, the connection point between the third arm section 22c and the fourth arm section 22d, and the connection point between the fifth arm section 22e and the sixth arm section 22f are each an AC output point.

[0035] The first AC terminal 21a is connected to a connection point between the first arm portion 22a and the second arm portion 22b. The second AC terminal 21b is connected to a connection point between the third arm portion 22c and the fourth arm portion 22d. The third AC terminal 21c is connected to a connection point between the fifth arm portion 22e and the sixth arm portion 22f. Each of the AC terminals 21a to 21c is connected to a transformer 6, for example.

[0036] Each converter CEL is connected to the control device 14, for example, via a signal line 26. The control device 14 controls the operation of the converter CEL by inputting a control signal to the converter CEL via the signal line 26. In addition, the converter CEL inputs, for example, a control signal and a protection signal related to the control and operational protection of the converter CEL to the control device 14 via another signal line (not shown).

[0037] The communication method between the control device 14 and each converter CEL is not limited to the above. For example, a plurality of converters CEL connected in series may be connected in a daisy chain, and the control device 14 may communicate only with the converter CEL at one end of the daisy chain and the converter CEL at the other end. The communication method between the control device 14 and each converter CEL may be any communication method that can appropriately communicate between the control device 14 and each converter CEL.

[0038] FIG. 2 is a block diagram that illustrates a schematic representation of a converter. As shown in FIG. 2, the converter CEL includes a plurality of switching elements 41, 42, a plurality of rectifying elements 51, 52, a charge storage element 60, a pair of connection terminals 61, 62, a power supply circuit 64, and a plurality of drive circuits 71, 72.

[0039] Each of the switching elements 41, 42 has a pair of main terminals and a control terminal. The control terminal controls a current flowing between the pair of main terminals. A self-extinguishing element such as an IGBT is used for each of the switching elements 41, 42. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate.

[0040] Each of the switching elements 41, 42 switches between an on state that allows current to flow between a pair of main terminals and an off state that blocks the current flowing between the pair of main terminals. The off state is not limited to a state in which no current flows between the pair of main terminals, but may be, for example, a state in which a weak current that does not affect the operation of the converter CEL flows between the pair of main terminals. In other words, the off state is a state in which the current flowing between the pair of main terminals is sufficiently small.

[0041] Each of the switching elements 41, 42 is, for example, a normally-off type semiconductor element. Each of the switching elements 41, 42 is in an on state when the voltage of the control terminal is high, and in an off state when the voltage of the control terminal is low. Each of the switching elements 41, 42 is in an off state when the voltage of the control terminal is lower than the on state. Each of the switching elements 41, 42 is in an on state when a positive voltage is applied to the control terminal, and in an off state when the voltage of the control terminal is set to 0 V or a negative voltage is applied to the control terminal.

[0042] A pair of main terminals of the switching element 42 are connected in series to a pair of main terminals of the switching element 41. In this example, the converter CEL has two switching elements 41, 42 connected in series. In other words, the converter CEL has two switching elements 41, 42 connected in half-bridge configuration. In this example, the converter CEL is a converter with a half-bridge configuration.

[0043] The rectifier element 51 is connected in anti-parallel to a pair of main terminals of the switching element 41. The forward direction of the rectifier element 51 is opposite to the direction of the current flowing between the pair of main terminals of the switching element 41. Similarly, the rectifier element 52 is connected in anti-parallel to the pair of main terminals of the switching element 42. The rectifier elements 51 and 52 are so-called freewheel diodes.

[0044] The connection terminal 61 is connected between the switching element 41 and the switching element 42. The connection terminal 62 is connected to a main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42.

[0045] The multiple converters CEL in the same arm portion are connected in series via a pair of connection terminals 61, 62. Power is supplied to the converters CEL via each of the connection terminals 61, 62. The switching element 41 is a so-called low-side switch, and the switching element 42 is a so-called high-side switch.

[0046] The multiple drive circuits 71, 72 are provided corresponding to the multiple switching elements 41, 42, respectively. In this example, the converter CEL has two drive circuits 71, 72 corresponding to the two switching elements 41, 42, respectively. The drive circuit 71 is connected to a control terminal of the switching element 41. The drive circuit 72 is connected to a control terminal of the switching element 42. In this manner, the multiple drive circuits 71, 72 are connected to the control terminals of the corresponding switching elements of the multiple switching elements 41, 42.

[0047] The multiple drive circuits 71, 72 communicate with the control device 14 via a signal line 26 and a transmission circuit (not shown). The control device 14 transmits drive commands for switching the on and off states of the switching elements 41, 42 to each converter CEL via the signal line 26. The drive commands are, in other words, control signals for controlling the switching of the switching elements 41, 42.

[0048] Each drive circuit 71, 72 switches the on and off states of each switching element 41, 42 based on a drive command received from the control device 14. This controls the on / off of each switching element 41, 42 in response to the drive command from the control device 14. The control device 14 generates a drive command for each converter CEL and controls the on / off of each switching element 41, 42 of each converter CEL. In this way, the control device 14 controls the power conversion by the main circuit unit 12.

[0049] The charge storage element 60 is connected in parallel to the switching element 41 and the switching element 42. The charge storage element 60 is, for example, a capacitor.

[0050] When the switching element 41 is in the off state and the switching element 42 is in the on state, the voltage of the charge storage element 60 appears between the connection terminals 61, 62. When the switching element 41 is in the on state and the switching element 42 is in the off state, the connection terminals 61, 62 are conductive, and the voltage between the connection terminals 61, 62 becomes substantially zero.

[0051] In this way, the converter CEL switches between an output state in which the voltage of the charge storage element 60 is output between the connection terminals 61, 62, a bypass state in which the connection terminals 61, 62 are conductive, and a stop state in which the switching elements 41, 42 are turned off, by switching the switching elements 41, 42 based on a drive command from the control device 14. The converter CEL is brought into the bypass state by turning on the lower switching element 41 of the two half-bridge connected switching elements 41, 42.

[0052] In each of the arm sections 22a to 22f, the total voltage of the converters CEL in the output state becomes the voltage of the arm section 22a to 22f. The main circuit section 12 and the control device 14 perform multi-level power conversion by controlling the number of converters CEL in the output state.

[0053] When both switching elements 41, 42 are in the off state (when converter CEL is in the stopped state), the voltage between each connection terminal 61, 62 is determined by the direction of the arm current. For example, when the arm current flows from connection terminal 62 to connection terminal 61, rectifier element 51 turns on, and the voltage between each connection terminal 61, 62 becomes substantially zero. Conversely, when the arm current flows from connection terminal 61 to connection terminal 62, rectifier element 52 turns on, charge storage element 60 is charged, and the voltage of charge storage element 60 appears between each connection terminal 61, 62.

[0054] The power supply circuit 64 is connected in parallel to the charge storage element 60. The power supply circuit 64 generates drive power for each of the drive circuits 71, 72 based on the charge stored in the charge storage element 60, and supplies the generated drive power to each of the drive circuits 71, 72. Each of the drive circuits 71, 72 operates in response to the supply of drive power from the power supply circuit 64.

[0055] The method of supplying power to each of the drive circuits 71, 72 is not limited to the above. For example, power may be supplied to each of the drive circuits 71, 72 from a power source separate from the charge storage element 60. The method of supplying power to each of the drive circuits 71, 72 may be any method that can appropriately supply power to each of the drive circuits 71, 72. The power supply circuit 64 is provided as necessary and can be omitted. However, as described above, by supplying power to each of the drive circuits 71, 72 from the power supply circuit 64 based on the charge stored in the charge storage element 60, the configuration such as insulation can be simplified, and power can be supplied to each of the drive circuits 71, 72 with a simple configuration.

[0056] The control device 14 transmits a drive command and a discharge command to each converter CEL via the signal line 26. The discharge command is a command for causing each converter CEL to discharge the charge storage element 60. When stopping the operation of any converter CEL among the multiple converters CEL, the control device 14 transmits a discharge command to the converter CEL to be stopped. For example, the control device 14 transmits a discharge command to each converter CEL when stopping the power conversion operation of the main circuit unit 12. In other words, the control device 14 transmits a discharge command to each converter CEL when the operation of the main circuit unit 12 (power conversion device 10) is stopped.

[0057] In response to receiving a discharge command from the control device 14, each of the drive circuits 71, 72 sets each of the switching elements 41, 42 to an intermediate state between the on state and the off state, and shorts the charge storage element 60 with each of the switching elements 41, 42 in a state in which the on resistance is higher than that in the on state. If the normal on state is defined as the first on state, the intermediate state is a second on state having a higher on resistance than the first on state. In each of the switching elements 41, 42, the second on resistance in the second on state is higher than the first on resistance in the first on state.

[0058] In this way, when the operation of the converter CEL in which each drive circuit 71 and 72 is provided is stopped, the drive circuits 71 and 72 set the switching elements 41 and 42 to the intermediate state in response to receiving a discharge command from the control device 14, and short-circuit the charge storage element 60 with the switching elements 41 and 42 in a state in which the on-resistance is higher than that in the on-state. When the power conversion operation by the main circuit unit 12 is stopped, for example, the drive circuits 71 and 72 set the switching elements 41 and 42 to the intermediate state in response to receiving a discharge command from the control device 14, and short-circuit the charge storage element 60 with the switching elements 41 and 42 in a state in which the on-resistance is higher than that in the on-state. This allows the energy stored in the charge storage element 60 to be consumed by the switching elements 41 and 42. Therefore, for example, compared to the case in which the switching elements 41 and 42 are turned off in response to the stop of the power conversion operation, it is easier to consume the energy stored in the charge storage element 60, and the discharge time of the charge storage element 60 can be shortened. For example, the time from when the main circuit unit 12 stops operating until the voltage of the charge storage element 60 drops to a predetermined voltage or lower can be shortened.

[0059] For example, each of the drive circuits 71, 72 switches each of the switching elements 41, 42 to the off state in response to the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage. In other words, each of the drive circuits 71, 72 switches the converter CEL to the stopped state in response to the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage. For example, the converter CEL may be stopped by the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage and the supply of drive power from the power supply circuit 64 being stopped.

[0060] FIG. 3 is a block diagram illustrating a schematic configuration of the drive circuit. 3, the drive circuit 71 includes switching elements 101 to 103, resistive elements 111 to 113, a first power supply circuit 121 to a third power supply circuit 123, a NAND circuit 131, an AND circuit 132, and NOT gates 141 and 142. The configuration of the drive circuit 72 can be substantially the same as the configuration of the drive circuit 71, and therefore a detailed description thereof will be omitted.

[0061] The switching elements 101 to 103 each have a pair of main terminals and a control terminal. For example, a MOSFET or a bipolar transistor is used for the switching elements 101 to 103. In this example, the switching elements 101 and 103 are P-channel MOSFETs. The switching element 102 is an N-channel MOSFET. The switching elements 101 and 103 are turned on when the voltage of the control terminal is less than a threshold voltage, and turned off when the voltage is equal to or greater than the threshold voltage. Conversely, the switching element 102 is turned on when the voltage of the control terminal is equal to or greater than the threshold voltage, and turned off when the voltage is less than the threshold voltage. The first power supply circuit 121 to the third power supply circuit 123 supply DC voltages. In other words, the first power supply circuit 121 to the third power supply circuit 123 are DC power supply circuits.

[0062] A high potential side main terminal of the switching element 101 is connected to a high potential side terminal of a first power supply circuit 121. A low potential side main terminal of the switching element 101 is connected to a control terminal of the switching element 41 via a resistive element 111. A low potential side terminal of the first power supply circuit 121 is connected to the low potential side main terminal of the switching element 41.

[0063] A high-potential side main terminal of the switching element 102 is connected to a control terminal of the switching element 41 via a resistive element 112. A low-potential side main terminal of the switching element 102 is connected to a low-potential side terminal of a second power supply circuit 122. A high-potential side terminal of the second power supply circuit 122 is connected to a low-potential side main terminal of the switching element 41.

[0064] A high potential side main terminal of the switching element 103 is connected to a high potential side terminal of the third power supply circuit 123. A low potential side main terminal of the switching element 103 is connected to a control terminal of the switching element 41 via a resistive element 113. A discharge command is input to the control terminal of the switching element 103 via a NOT gate 142. A low potential side terminal of the third power supply circuit 123 is connected to the low potential side main terminal of the switching element 41.

[0065] A drive command is input to one input terminal of the NAND circuit 131. A discharge command is input to the other input terminal of the NAND circuit 131 via a NOT gate 142. An output terminal of the NAND circuit 131 is connected to the control terminal of the switching element 101.

[0066] A drive command is input to one input terminal of the AND circuit 132 via a NOT gate 141. A discharge command is input to the other input terminal of the AND circuit 132 via a NOT gate 142. An output terminal of the AND circuit 132 is connected to the control terminal of the switching element 102.

[0067] The drive command has a state for turning on the switching element 41 and a state for turning off the switching element 41. The discharge command has a state for instructing to perform discharge and a state for instructing to stop discharge. The drive command and the discharge command are, for example, digital signals. The drive command is, for example, a digital signal (pulse signal) in which a high voltage state (high state) corresponds to a state for turning on the switching element 41 and a low voltage state (low state) corresponds to a state for turning off the switching element 41. The discharge command is, for example, a digital signal (pulse signal) in which a high voltage state (high state) corresponds to a state for instructing to perform discharge and a low voltage state (low state) corresponds to a state for instructing to stop discharge.

[0068] When switching the switching element 41 between the on state and the off state, the control device 14 sets the discharge command to a state (low) instructing the end of discharge. In this case, the logic of the discharge command is inverted by the NOT gate 142, so that a high is input to the control terminal of the switching element 103, and the switching element 103 is turned off. In this case, the logic of the discharge command is also inverted by the NOT gate 142, so that a high is input to one input terminal of each of the NAND circuit 131 and the AND circuit 132.

[0069] When the drive command is in a state (high) that turns on the switching element 41, a high signal corresponding to the drive command is input to the other input terminal of the NAND circuit 131. As a result, the output of the NAND circuit 131 becomes low. When the output of the NAND circuit 131 becomes low, a low signal is input to the control terminal of the switching element 101, and the switching element 101 becomes on.

[0070] On the other hand, when the drive command is in a state (high) that turns on the switching element 41, the logic of the drive command is inverted by the NOT gate 141, and a low signal is input to the other input terminal of the AND circuit 132. As a result, the output of the AND circuit 132 becomes low. When the output of the AND circuit 132 becomes low, a low signal is input to the control terminal of the switching element 102, and the switching element 102 becomes off.

[0071] In this way, when the switching element 101 is in the ON state, the switching element 102 is in the OFF state, and the switching element 103 is in the OFF state, the voltage Von1 of the first power supply circuit 121 is applied to the control terminal of the switching element 41. The voltage Von1 of the first power supply circuit 121 is a voltage for setting the switching element 41 to the ON state. In other words, the first power supply circuit 121 supplies the voltage Von1 for setting the corresponding switching element 41 to the ON state. The voltage Von1 is, for example, +15 V. As a result, the switching element 41 is turned on in response to the drive command.

[0072] When the drive command is in a state (low) that turns the switching element 41 off, a low signal corresponding to the drive command is input to the other input terminal of the NAND circuit 131. As a result, the output of the NAND circuit 131 becomes high. When the output of the NAND circuit 131 becomes high, a high signal is input to the control terminal of the switching element 101, and the switching element 101 turns off.

[0073] On the other hand, when the drive command is in a state (low) that turns off the switching element 41, the logic of the drive command is inverted by the NOT gate 141, and a high signal is input to the other input terminal of the AND circuit 132. As a result, the output of the AND circuit 132 becomes high. When the output of the AND circuit 132 becomes high, a high signal is input to the control terminal of the switching element 102, and the switching element 102 becomes on.

[0074] In this way, when the switching element 101 is in the OFF state, the switching element 102 is in the ON state, and the switching element 103 is in the OFF state, the voltage Voff of the second power supply circuit 122 is applied to the control terminal of the switching element 41. At this time, the potential of the control terminal of the switching element 41 becomes lower than the potential of the low potential side of the switching element 41. A negative bias is applied to the control terminal of the switching element 41. The voltage Voff of the second power supply circuit 122 is a voltage for setting the switching element 41 to the OFF state. In other words, the second power supply circuit 122 supplies the voltage Voff for setting the corresponding switching element 41 to the OFF state. The voltage Voff is, for example, +15V. In this case, -15V is applied to the control terminal of the switching element 41. As a result, the switching element 41 is turned to the OFF state in response to the drive command.

[0075] When the control device 14 stops the operation of the converter CEL and causes the corresponding converter CEL to discharge the charge storage element 60, it sets a drive command to a state in which the switching element 41 is turned off, and sets a discharge command to a state (high) instructing the execution of discharge. In this case, the logic of the discharge command is inverted by the NOT gate 142, so that a low signal is input to the control terminal of the switching element 103, and the switching element 103 is turned on. In this case, the logic of the discharge command is inverted by the NOT gate 142, and a low signal is input to one input terminal of each of the NAND circuit 131 and the AND circuit 132. Therefore, the output of the NAND circuit 131 becomes high, the output of the AND circuit 132 becomes low, and both the switching elements 101 and 102 are turned off.

[0076] In this way, when the switching element 101 is in the OFF state, the switching element 102 is in the OFF state, and the switching element 103 is in the ON state, the voltage Von2 of the third power supply circuit 123 is applied to the control terminal of the switching element 41. The voltage Von2 of the third power supply circuit 123 is a voltage for setting the switching element 41 to an intermediate state. In other words, the third power supply circuit 123 supplies the voltage Von2 for setting the corresponding switching element 41 to an intermediate state. The voltage Von2 is set lower than the voltage Von1 of the first power supply circuit 121. Also, for example, when the switching element 41 is an IGBT, the voltage Von2 is set to be equal to or higher than the mirror voltage of the switching element 41. This allows the switching element 41 to be set to an intermediate state (a second ON state having a higher ON resistance than the first ON state) in response to a discharge command.

[0077] As described above, the configuration of the drive circuit 72 is substantially the same as that of the drive circuit 71. The multiple drive circuits 71, 72 selectively apply any one of the voltage Von1 of the first power supply circuit 121, the voltage Voff of the second power supply circuit 122, and the voltage Von2 of the third power supply circuit 123 to the control terminals of the corresponding switching elements 41, 42, thereby switching the corresponding switching elements 41, 42 between the on state, the off state, and the intermediate state. As a result, as described above, when stopping the operation of the converter CEL, in response to receiving a discharge command from the control device 14, each drive circuit 71, 72 sets each switching element 41, 42 to the intermediate state, and can short-circuit the charge storage element 60 with each switching element 41, 42 in a state in which the on-resistance is higher than that in the on state.

[0078] As described above, in the power conversion device 10 according to the present embodiment, when the drive circuits 71, 72 stop the operation of the converter CEL, they set the switching elements 41, 42 to an intermediate state in response to receiving a discharge command from the control device 14, and short-circuit the charge storage element 60 with the switching elements 41, 42 in a state with a higher on-resistance than in the on-state. This makes it easier to consume the energy stored in the charge storage element 60, and shortens the discharge time of the charge storage element 60, compared to a case in which the switching elements 41, 42 are turned off in response to the stop of the operation of the converter CEL. In addition, there is no increase in the loss of each converter CEL during normal operation, as in the case in which a resistive element or the like is provided in the discharge path of the charge storage element 60 to shorten the discharge time.

[0079] Therefore, in the power conversion device 10 according to this embodiment, the discharge time of the charge storage element 60 of each converter CEL can be shortened without increasing the loss during normal operation. For example, when the operation of the main circuit unit 12 is stopped for maintenance and inspection, the time required for the maintenance and inspection can be prevented from becoming longer, and the number of steps required for the maintenance and inspection can be prevented from increasing.

[0080] Furthermore, there is no need to add new parts for discharging the charge storage elements 60, and it is possible to suppress an increase in the number of parts in each converter CEL and to suppress the configuration of each converter CEL from becoming complicated. In the power conversion device 10 according to the present embodiment, it is possible to achieve a reduction in the discharge time of the charge storage elements 60 of each converter CEL with a simple configuration.

[0081] In the main circuit section 12 having a plurality of converters CEL connected in series, for example, even when abnormalities occur in a predetermined number or less of the converters CEL in each of the arm sections 22a to 22f, the operation can be continued with the remaining normal converters CEL by placing the abnormal converters CEL in a bypass state. For example, when the control device 14 detects an overvoltage in the charge storage element 60 of a predetermined converter CEL, the control device 14 protects the converter CEL in which the overvoltage is detected by setting the converter CEL in which the overvoltage is detected in a bypass state.

[0082] For example, when protecting the converter CEL in which an overvoltage has been detected, the control device 14 may send a discharge command to each drive circuit 71, 72, thereby setting the converter CEL to a bypass state via the switching element 41 set to an intermediate state and discharging the charge storage element 60, thereby protecting the charge storage element 60 from overvoltage.

[0083] In this way, the timing when the control device 14 transmits a discharge command to the converter CEL is not limited to the timing when the power conversion operation by the main circuit unit 12 is stopped. For example, as described above, the control device 14 may transmit a discharge command to the converter CEL when protecting the charge storage element 60 from overvoltage. The control device 14 may transmit a discharge command to the converter CEL when detecting another abnormality in the converter CEL, not limited to when detecting an overvoltage in the charge storage element 60.

[0084] In addition, the detection of an abnormality of the converter CEL may be performed on the side of each converter CEL, not limited to the control device 14. The converter CEL may further include a voltage detector or the like to detect an overvoltage of the charge storage element 60, and automatically cause each drive circuit 71, 72 to discharge the charge storage element 60 in response to the detection of the overvoltage. After discharging the charge storage element 60, each drive circuit 71, 72 may stop discharging the charge storage element 60 in response to the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage, and switch the converter CEL to a bypass state. Each drive circuit 71, 72 may switch each converter CEL to a stop state (may stop the main circuit unit 12 due to an abnormality) in response to the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage, for example. In addition, the converter CEL may determine that the abnormality has been eliminated in response to the voltage of the charge storage element 60 becoming equal to or lower than a predetermined voltage, and may return to normal operation.

[0085] In this way, the timing at which the multiple drive circuits 71, 72 discharge the charge storage element 60 is not limited to the timing at which the power conversion operation by the main circuit unit 12 is stopped, but may also be the timing at which an abnormality occurs in the converter CEL in which the multiple drive circuits 71, 72 are provided and the converter CEL in which the abnormality has occurred is protected. When stopping the operation of the converter CEL or protecting the converter CEL in which an abnormality has occurred, the multiple drive circuits 71, 72 set at least one of the multiple switching elements 41, 42 to an intermediate state between the on state and the off state, and short-circuit the charge storage element 60 with at least one of the switching elements in a state with a higher on-resistance than the on state, thereby discharging the charge storage element 60.

[0086] FIG. 4 is a block diagram showing a schematic diagram of a modified example of the driving circuit. As shown in Fig. 4, in the drive circuit 71 of this example, the third power supply circuit 123 is omitted and a resistive element 114 is added, compared to the example shown in Fig. 3. Note that the same reference numerals are used for components that are substantially the same in function and configuration as those in the above embodiment, and detailed description thereof will be omitted.

[0087] In this example, the high potential side main terminal of the switching element 103 is connected to the high potential side terminal of the first power supply circuit 121. The resistive element 114 is provided between the control terminal of the switching element 41 and the low potential side main terminal.

[0088] As a result, in the drive circuit 71 of this example, when the discharge command is set to a state (low) instructing the stop of discharge and the drive command is set to a state (high) for turning on the switching element 41, so that the switching element 101 is in the on state and the switching elements 102 and 103 are in the off state, a voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 by the resistance elements 111 and 114 is applied to the control terminal of the switching element 41. The voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 by the resistance elements 111 and 114 is a voltage for setting the switching element 41 to the on state. As a result, also in this example, the switching element 41 is turned on in response to the drive command.

[0089] In addition, in the drive circuit 71 of this example, when the drive command is set to a state (low) that turns the switching element 41 off and the discharge command is set to a state (high) that instructs the execution of discharge, so that the switching elements 101 and 102 are in the off state and the switching element 103 is in the on state, a voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 by the resistance elements 113 and 114 is applied to the control terminal of the switching element 41.

[0090] In this example, the resistance value of the resistive element 111 is set to be sufficiently smaller than the resistance value of the resistive element 114. The resistance value of the resistive element 113 is set to be larger than the resistance value of the resistive element 111. As a result, the voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 between the resistive elements 113 and 114 becomes lower than the voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 between the resistive elements 111 and 114. The voltage obtained by dividing the voltage Von1 of the first power supply circuit 121 between the resistive elements 113 and 114 is a voltage for setting the switching element 41 to an intermediate state.

[0091] In other words, the resistive elements 113 and 114 are resistive elements that convert the voltage Von1 of the first power supply circuit 121 into a voltage for setting the corresponding switching element 41 to an intermediate state. In this example, the drive circuit 71, in other words, selectively applies any one of the voltage Von1 of the first power supply circuit 121, the voltage Voff of the second power supply circuit 122, and the voltage converted by the resistive elements 113 and 114 to the control terminal of the corresponding switching element 41, thereby switching the on state, off state, and intermediate state of the corresponding switching element 41. As a result, even in this example, the switching element 41 can be set to an intermediate state (a second on state having an on resistance higher than the first on state) in response to a discharge command.

[0092] In this way, the configuration of the drive circuits 71 and 72 may be a configuration having the first power supply circuit 121 and the third power supply circuit 123, and switching the switching elements 41 and 42 between the on state and the intermediate state based on the voltages of the first power supply circuit 121 and the third power supply circuit 123, or a configuration having the resistance elements 111, 113, and 114, and switching the switching elements 41 and 42 between the on state and the intermediate state based on the voltage division ratio of the resistance elements 111, 113, and 114. The configuration of the drive circuits 71 and 72 is not limited to the above, and may be any configuration that can appropriately switch the switching elements 41 and 42 between the on state, the off state, and the intermediate state. The resistance element that converts the voltage Von1 of the first power supply circuit 121 into a voltage for setting the corresponding switching element 41 to the intermediate state may be, for example, a resistance element that converts the voltage Von1 of the first power supply circuit 121 into a voltage for setting the corresponding switching element 41 to the intermediate state by stepping down the voltage Von1.

[0093] FIG. 5 is a block diagram showing a schematic diagram of a modified example of the converter. As shown in FIG. 5, in this example, the control device 14 transmits a discharge release command to each converter CEL instead of a discharge command. The discharge release command is a command for causing each converter CEL to stop discharging the charge storage element 60. When causing any of the multiple converters CEL to operate, the control device 14 transmits a discharge release command to the converter CEL to be operated. For example, the control device 14 transmits a discharge release command to each converter CEL when causing the main circuit unit 12 to perform a power conversion operation. In other words, the control device 14 transmits a discharge release command to each converter CEL when the main circuit unit 12 (power conversion device 10) is operating.

[0094] When not receiving a discharge release command from the control device 14, each of the drive circuits 71, 72 sets each of the switching elements 41, 42 to an intermediate state, and shorts the charge storage element 60 with each of the switching elements 41, 42 in a state with a higher on-resistance than in the on state, thereby discharging the charge storage element 60. Then, in response to receiving a discharge release command from the control device 14, each of the drive circuits 71, 72 stops discharging the charge storage element 60 by each of the switching elements 41, 42 in the intermediate state, and switches between the on state and the off state of each of the switching elements 41, 42 based on the drive command received from the control device 14.

[0095] The discharge release command is, for example, a digital signal (pulse signal) in which a low voltage state (low state) corresponds to a state instructing to execute discharge and a high voltage state (high state) corresponds to a state instructing to stop discharge (release of discharge). When a discharge release command has not been received, in other words, it is a time when the discharge release command is instructing to execute discharge. When a discharge release command has been received, in other words, it is a time when the discharge release command is instructing to stop discharge.

[0096] In this example, when the control device 14 stops the power conversion operation, it stops sending the discharge release command to each of the drive circuits 71, 72. In other words, when the control device 14 stops the power conversion operation, it switches the discharge release command to a state (low) that instructs the execution of discharge.

[0097] When the power conversion operation is stopped, each drive circuit 71, 72 sets each switching element 41, 42 to an intermediate state in response to the stopping of the discharge release command from the control device 14 (switching of the discharge release command to a state instructing the execution of discharge), and shorts out the charge storage element 60 with each switching element 41, 42 in a state with a higher on-resistance than in the on-state.

[0098] In the example shown in FIG. 2, each of the drive circuits 71 and 72 is normally in a state where the charge storage element 60 is not discharged, and only when a discharge command is received from the control device 14, the switching elements 41 and 42 are set to an intermediate state to discharge the charge storage element 60. Without being limited thereto, as in the example shown in FIG. 5, each of the drive circuits 71 and 72 may normally set each of the switching elements 41 and 42 to an intermediate state to discharge the charge storage element 60, and only when a discharge release command is received from the control device 14, the discharge of the charge storage element 60 may be stopped. In the example shown in FIG. 5, as in the example shown in FIG. 2, the discharge time of the charge storage element 60 can be shortened when the power conversion operation is stopped.

[0099] When each part of each converter CEL including each drive circuit 71, 72 receives power from the power supply circuit 64, for example, a transmission circuit that communicates with the control device 14 has a higher operating voltage than the drive circuits 71, 72 and may stop operating before the drive circuits 71, 72. For this reason, in a configuration in which the charge storage element 60 is discharged only when a discharge command is received from the control device 14 as in the example shown in Fig. 2, even if the drive circuits 71, 72 are still in a state where they can discharge the charge storage element 60, the discharge of the charge storage element 60 may be stopped due to a breakdown in communication with the control device 14.

[0100] In contrast, in the example shown in Fig. 5, by discharging the charge storage element 60 when a discharge release command is not received from the control device 14, even if communication with the control device 14 is interrupted due to the stop of operation of the transmission circuit or the like, the charge storage element 60 can be discharged to a voltage at which the drive circuits 71 and 72 can operate. Thus, in the example shown in Fig. 5, when power is being supplied from the power supply circuit 64 to each unit, it is possible that the charge storage element 60 can be discharged more appropriately than in the example shown in Fig. 2. For example, it is possible that the voltage of the charge storage element 60 can be discharged to a lower voltage when the operation of the main circuit unit 12 is stopped.

[0101] The trigger for each of the drive circuits 71, 72 to start discharging the charge storage elements 60 is not limited to a discharge command or a discharge release command from the control device 14, and may be any trigger. For example, each converter CEL may detect the stop of operation of the main circuit unit 12 based on the voltage values ​​of the AC terminals 21a-21c, the voltage values ​​of the DC terminals 20a, 20b, or the operation of a switch connecting the main circuit unit 12 to the AC power system 2 or the DC transmission lines 3, 4, and may cause each of the drive circuits 71, 72 to start discharging the charge storage elements 60 in response to the detection of the stop of operation of the main circuit unit 12.

[0102] The configuration of each driving circuit 71, 72 may be any configuration that allows discharging of the charge storage element 60 by setting each switching element 41, 42 to an intermediate state when stopping the operation of the converter CEL or protecting a converter CEL in which an abnormality has occurred, and shorting the charge storage element 60 with each switching element 41, 42 in a state with a higher on-resistance than in the on state.

[0103] FIG. 6 is a block diagram showing a schematic diagram of a modified example of the converter. 6, in this example, the converter CEL further includes switching elements 43 and 44, rectifying elements 53 and 54, and driving circuits 73 and 74. For the switching elements 43 and 44, substantially the same elements as the switching elements 41 and 42 are used.

[0104] A pair of main terminals of the switching element 44 are connected in series to a pair of main terminals of the switching element 43. Moreover, the switching elements 43 and 44 are connected in parallel to the switching elements 41 and 42. The charge storage element 60 is connected in parallel to the switching elements 41 and 42, and is also connected in parallel to the switching elements 43 and 44.

[0105] The rectifying element 53 is connected in anti-parallel to a pair of main terminals of the switching element 43. The rectifying element 54 is connected in anti-parallel to a pair of main terminals of the switching element 44.

[0106] In this example, the connection terminal 61 is connected between the switching element 41 and the switching element 42. The connection terminal 62 is connected between the switching element 43 and the switching element 44. The connection terminal 62 is connected via the switching element 43 to a main terminal of the switching element 41 opposite to the main terminal connected to the switching element 42. That is, in this example, the switching elements 41 to 44 are full-bridge connected. In this example, the converter CEL is a full-bridge circuit.

[0107] The drive circuit 73 is connected to a control terminal of the switching element 43. The drive circuit 74 is connected to a control terminal of the switching element 44. Like the drive circuits 71 and 72, the drive circuits 73 and 74 communicate with the control device 14 via the signal line 26 and a transmission circuit (not shown). Each of the drive circuits 71-74 switches the on and off states of each of the switching elements 41-44 based on a drive command received from the control device 14. As a result, even in the converter CEL of the full bridge circuit, the on / off of each of the switching elements 41-44 is controlled in response to the drive command from the control device 14.

[0108] In this manner, the converter CEL used in the MMC type main circuit unit 12 may be a half-bridge circuit or a full-bridge circuit.

[0109] In the converter CEL of the full-bridge circuit, +Vc is output between each of the connection terminals 61, 62 when the switching element 42 and the switching element 43 are turned on and the switching element 41 and the switching element 44 are turned off.

[0110] When the switching elements 41 and 44 are turned on and the switching elements 42 and 43 are turned off, −Vc is output between the connection terminals 61 and 62 .

[0111] When switching elements 41 and 43 are turned on and switching elements 42 and 44 are turned off, or when switching elements 42 and 44 are turned on and switching elements 41 and 43 are turned off, substantially 0 V is output between each connection terminal 61, 62.

[0112] In this way, the converter CEL of the full-bridge circuit can output three levels of power, +Vc, 0, and -Vc, by combining the switching elements 41 to 44 that are turned on and off.

[0113] In the converter CEL of the full bridge circuit, for example, a state in which +Vc is output is a first output state, a state in which -Vc is output is a second output state, a state in which 0V is output is a bypass state, and a state in which each of the switching elements 41 to 44 is in an off state is a stopped state. This converter CEL is in the bypass state by turning on the upper two switching elements 42, 44 or the lower two switching elements 41, 43 of the four full bridge connected switching elements 41 to 44. The switching of each state of this converter CEL can be realized, for example, by making the drive command a ternary signal corresponding to three levels.

[0114] When the power conversion operation is stopped, each of the drive circuits 71-74 sets each of the switching elements 41-44 to an intermediate state, and shorts the charge storage element 60 with each of the switching elements 41-44 in a state with a higher on-resistance than in the on state, thereby discharging the charge storage element 60. As a result, in the converter CEL of the full-bridge circuit as well, like the converter CEL of the half-bridge circuit, the discharge time of the charge storage element 60 can be shortened when the power conversion operation is stopped.

[0115] In the full-bridge converter CEL, the charge storage element 60 may be short-circuited by setting each of the four switching elements 41 to 44 to an intermediate state, or the charge storage element 60 may be short-circuited by setting only the switching elements 41 and 42 to an intermediate state, or the charge storage element 60 may be short-circuited by setting only the switching elements 43 and 44 to an intermediate state.

[0116] In this manner, the multiple drive circuits 71-74 may be configured to set at least one of the multiple switching elements 41-44 to an intermediate state when stopping the operation of the converter CEL or protecting the converter CEL in which an abnormality has occurred, and to discharge the charge storage element 60 by shorting the charge storage element 60 with at least one of the switching elements in a state having a higher on-resistance than the on-state. The combination of switching elements to be set to the intermediate state may be any combination that can short-circuit the charge storage element 60. The combination of switching elements to be set to the intermediate state may be appropriately set depending on the configuration of the multiple switching elements, etc.

[0117] In the converter CEL of the full-bridge circuit, power may be supplied to each of the drive circuits 71 to 74 and other components by the power supply circuit 64 or from a separate power source.

[0118] The configuration of the converter CEL is not limited to the above, but may be any configuration that can switch between an output state in which the voltage of the charge storage element 60 is output between a pair of connection terminals 61, 62, a bypass state in which the pair of connection terminals 61, 62 is conductive, and a stop state in which the multiple switching elements are in an off state by switching multiple switching elements, and that can short-circuit the charge storage element 60 by setting at least one of the multiple switching elements to an intermediate state.

[0119] In each of the above embodiments, an MMC type power converter is used for the main circuit unit 12. The main circuit unit 12 is not limited to the MMC type, and may be, for example, a power converter of another type in which a plurality of converters CEL are connected in series, such as an MV (Medium Voltage) type power converter.

[0120] The power conversion device is not limited to a DC transmission system, but may be applied to any other system that requires conversion from AC to DC and from DC to AC. The AC / DC conversion by the power conversion device is not limited to both AC to DC and DC to AC, but may be only AC to DC or DC to AC.

[0121] The present embodiment includes the following aspects. (Appendix 1) A main circuit unit includes a plurality of converters connected in series, and converts power by the operation of the plurality of converters; A control device for controlling the operation of the main circuit unit; Equipped with Each of the plurality of converters comprises: A pair of connection terminals; A plurality of switching elements; a charge storage element connected in parallel to the plurality of switching elements; a plurality of drive circuits for switching the plurality of switching elements between an on state and an off state; and the charge storage element is connected in series via the pair of connection terminals, and is capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are electrically connected, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements; The power conversion device includes a plurality of driving circuits that, when stopping the operation of the converter or protecting the converter in the event of an abnormality, set at least one of the plurality of switching elements to an intermediate state between the on state and the off state, and discharge the charge storage element by short-circuiting the charge storage element with at least one of the switching elements that has a higher on-resistance than the on state.

[0122] (Appendix 2) The control device transmits a discharge command to the converter to be stopped or protected when stopping operation of any of the converters among the plurality of converters or protecting the converter; 2. The power conversion device according to claim 1, wherein the plurality of drive circuits discharge the charge storage elements in response to receiving the discharge command from the control device.

[0123] (Appendix 3) The control device transmits a discharge release command to the converter to be operated when the converter is to be operated. 2. The power conversion device according to claim 1, wherein the plurality of drive circuits discharge the charge storage elements when the discharge release command is not received from the control device, and stop discharging the charge storage elements in response to receiving the discharge release command from the control device.

[0124] (Appendix 4) the plurality of converters each have a power supply circuit that generates a drive power supply for the plurality of drive circuits based on the charge stored in the charge storage element and supplies the generated drive power supply to the plurality of drive circuits; 4. The power conversion device according to claim 1, wherein the plurality of drive circuits operate in response to the supply of the drive power from the power supply circuit.

[0125] (Appendix 5) The plurality of switching elements each have a pair of main terminals and a control terminal, The plurality of drive circuits are connected to the control terminals of corresponding switching elements among the plurality of switching elements, and include a first power supply circuit that supplies a voltage for setting the corresponding switching element to the on state, a second power supply circuit that supplies a voltage for setting the corresponding switching element to the off state, and a third power supply circuit that supplies a voltage for setting the corresponding switching element to the intermediate state, and the power conversion device described in any one of appendixes 1 to 4 switches the on state, off state, and intermediate state of the corresponding switching element by selectively applying one of the voltages of the first power supply circuit, the second power supply circuit, and the third power supply circuit to the control terminal of the corresponding switching element.

[0126] (Appendix 6) The plurality of switching elements each have a pair of main terminals and a control terminal, The plurality of drive circuits are connected to the control terminals of corresponding switching elements among the plurality of switching elements, and include a first power supply circuit that supplies a voltage for setting the corresponding switching element to the on state, a second power supply circuit that supplies a voltage for setting the corresponding switching element to the off state, and a resistive element that converts the voltage of the first power supply circuit into a voltage for setting the corresponding switching element to the intermediate state, and the power conversion device described in any one of appendixes 1 to 4 switches the on state, off state, and intermediate state of the corresponding switching element by selectively applying one of the voltage of the first power supply circuit, the voltage of the second power supply circuit, and the voltage converted by the resistive element to the control terminal of the corresponding switching element.

[0127] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0128] 2...AC power system, 3, 4...DC transmission line, 6...transformer, 10...power conversion device, 12...main circuit section, 14...control device, 20a, 20b...DC terminals, 21a-21c...first to third AC terminals, 22a-22f...first to sixth arm sections, 23a-23f...buffer reactors, 24a-24f...current detectors, 25...voltage detectors, 26...signal lines, 41-44...switching elements, 51-54...rectifier elements, 60...charge storage elements, 61, 62...connection terminals, 64...power supply circuit, 71-74...drive circuits, 101-103...switching elements, 111-114...resistance elements, 121...first power supply circuit, 122...second power supply circuit, 123...third power supply circuit, 131...NAND circuit, 132...AND circuit, 141, 142...NOT gate, CEL...converter

Claims

1. A main circuit unit includes a plurality of converters connected in series, and converts power by the operation of the plurality of converters; A control device for controlling the operation of the main circuit unit; Equipped with Each of the plurality of converters comprises: A pair of connection terminals; A plurality of switching elements; a charge storage element connected in parallel to the plurality of switching elements; a plurality of drive circuits for switching the plurality of switching elements between an on state and an off state; and the charge storage element is connected in series via the pair of connection terminals, and is capable of switching between an output state in which a voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are electrically connected, and a stop state in which the plurality of switching elements are in an off state by switching the plurality of switching elements; The power conversion device includes a plurality of driving circuits that, when stopping the operation of the converter or protecting the converter in the event of an abnormality, set at least one of the plurality of switching elements to an intermediate state between the on state and the off state, and discharge the charge storage element by short-circuiting the charge storage element with at least one of the switching elements that has a higher on-resistance than the on state.

2. The control device transmits a discharge command to the converter to be stopped or protected when stopping operation of any of the converters among the plurality of converters or protecting the converter; The power conversion device according to claim 1 , wherein the plurality of drive circuits discharge the charge storage elements in response to receiving the discharge command from the control device.

3. The control device transmits a discharge release command to the converter to be operated when the converter is to be operated.

2. The power conversion device according to claim 1, wherein the plurality of drive circuits discharge the charge storage elements when the discharge release command is not received from the control device, and stop discharging the charge storage elements in response to receiving the discharge release command from the control device.

4. the plurality of converters each have a power supply circuit that generates a drive power supply for the plurality of drive circuits based on the charge stored in the charge storage element and supplies the generated drive power supply to the plurality of drive circuits; The power conversion device according to claim 1 , wherein the plurality of drive circuits operate in response to the supply of the drive power from the power supply circuit.

5. The plurality of switching elements each have a pair of main terminals and a control terminal, 2. The power conversion device according to claim 1, wherein the plurality of drive circuits are connected to the control terminals of corresponding switching elements among the plurality of switching elements, and include a first power supply circuit that supplies a voltage for setting the corresponding switching element to the on state, a second power supply circuit that supplies a voltage for setting the corresponding switching element to the off state, and a third power supply circuit that supplies a voltage for setting the corresponding switching element to the intermediate state, and the corresponding switching element is switched between the on state, the off state, and the intermediate state by selectively applying one of the voltages of the first power supply circuit, the second power supply circuit, and the third power supply circuit to the control terminal of the corresponding switching element.

6. The plurality of switching elements each have a pair of main terminals and a control terminal, 2. The power conversion device according to claim 1, wherein the plurality of drive circuits are connected to the control terminals of corresponding switching elements among the plurality of switching elements, and include a first power supply circuit that supplies a voltage for setting the corresponding switching element to the on state, a second power supply circuit that supplies a voltage for setting the corresponding switching element to the off state, and a resistive element that converts the voltage of the first power supply circuit into a voltage for setting the corresponding switching element to the intermediate state, and the corresponding switching element is switched between the on state, the off state, and the intermediate state by selectively applying to the control terminals of the corresponding switching elements the voltage of the first power supply circuit, the voltage of the second power supply circuit, or the voltage converted by the resistive element.

Images