JP2020010564A - Electric power conversion device - Google Patents

Abstract

To provide an electric power conversion device capable of suppressing variations of a voltage of an electric charging storage element of each converter while suppressing the increase of a loss or a space.SOLUTION: An electric power conversion device comprises: a main circuit part having a plurality of converters connected in serial; and a control device that controls an operation of each converter. Each converter includes: a first switching element; a second switching element connected serially to the first switching element; an electric charge storage element connected in parallel to the first and second switching elements; a control part that controls ON/OFF of the first and second switching elements; and a constant power load connected in parallel to the electric charge storage element. The control device executes temporally an operation control for turning on/off the first and second switching elements at a prescribed timing in an operation standby mode that sets the first and second switching elements to an off state.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a power converter.

  There is a multi-stage power converter including a plurality of converters connected in series and a control device for controlling the operation of each converter. Each converter includes a plurality of switching elements, a charge storage element connected in parallel to each switching element, a control unit for controlling ON / OFF of each switching element, and a control unit from a main circuit side such as the charge storage element. And a power supply circuit for supplying control power to the power supply.

  The main circuit power supply load such as the control unit is a constant power load. In addition, variations occur in the load of the main circuit power supply due to individual differences and the like. For this reason, in the operation standby state where each switching element of each converter is turned off, there is a possibility that the voltage of the charge storage element of each converter varies.

  The variation in the voltage of the charge storage element of each converter increases with time. For this reason, the voltage of the charge storage element of a specific converter rises and reaches an overvoltage level, or conversely, the voltage of the charge storage element of a specific converter decreases and reaches an undervoltage level, The system may be stopped.

  As a method of balancing the voltage of the charge storage element of each converter, it has been proposed to connect a resistive load that consumes more power than a constant power load fed by the main circuit. However, adding a resistive load for balancing increases the loss of the converter and increases the space and cost for adding the resistive load.

  For this reason, in the power converter, it is desired to be able to suppress the variation in the voltage of the charge storage element of each converter while suppressing the loss and the increase in the space.

JP 2014-18028 A

  Embodiments of the present invention provide a power conversion device capable of suppressing a variation in voltage of a charge storage element of each converter while suppressing a loss and an increase in space.

  According to an embodiment of the present invention, it has a plurality of converters connected in series, and the operation of the plurality of converters converts AC power to DC power and DC power to AC power. And a control device that controls the operation of the plurality of converters, wherein each of the plurality of converters includes a first switching element and a first switching element. A second switching element connected in series to the first switching element, a charge storage element connected in parallel to the first switching element and the second switching element, and an on state of the first switching element and the second switching element. A control unit that controls off, and a constant power load connected in parallel to the charge storage element, wherein the control device includes the first switching element and the second switching element In operation standby state for the device in the OFF state, the power conversion device on and off controls the operation of the first switching element and the second switching element is temporarily performed at a predetermined timing is provided.

  Provided is a power conversion device capable of suppressing a variation in voltage of a charge storage element of each converter while suppressing a loss and an increase in space.

1 is a block diagram schematically illustrating a power conversion device according to an embodiment. It is a block diagram which represents a converter typically. FIG. 4 is a graph schematically illustrating an example of an operation of the control device. It is a flowchart which shows an example of operation | movement of a power converter schematically. FIG. 4 is a graph schematically illustrating an example of an operation of the power conversion device. FIG. 4 is an equivalent circuit diagram schematically illustrating a first arm unit in a driving standby state. It is a flowchart which represents an example of another operation | movement of a power converter schematically. FIGS. 8A to 8C are graphs schematically illustrating a modification example based on voltage. It is a block diagram showing the modification of a converter typically.

Hereinafter, each embodiment will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and the width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. In addition, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
In the specification and the drawings, the same reference numerals are given to the same components as those described above with respect to the already-explained drawings, and the detailed description will be appropriately omitted.

FIG. 1 is a block diagram schematically illustrating a power conversion device according to the embodiment.
As illustrated in FIG. 1, the power conversion device 10 includes a main circuit unit 12 and a control device 14. The power converter 10 is used, for example, in a DC power transmission system. The power converter 10 is connected to the AC power system 2 and the pair of DC transmission lines 3 and 4 in the DC power transmission system.

  The DC power transmission system has, for example, a transformer 6. Main circuit section 12 of power converter 10 is connected to AC power system 2 via transformer 6. The AC power of the AC power system 2 is three-phase AC power. More specifically, symmetric 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 unit 12. The transformer 6 changes the effective value of each phase of the three-phase AC power in accordance with the main circuit unit 12. Transformer 6 is a three-phase transformer. The transformer 6 is provided as needed and can be omitted. The three-phase AC power of the AC power system 2 may be directly supplied to the main circuit unit 12.

  The power converter 10 converts the 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 converter 10 converts the 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. Thus, the power conversion device 10 performs AC / DC conversion from AC to DC and DC / AC conversion from DC to AC.

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

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

  The control device 14 is connected to the main circuit unit 12. The control device 14 controls the conversion of the three-phase AC power to the DC power and the conversion of the DC power to the three-phase AC power by the main circuit unit 12 by controlling ON / OFF of each switching element.

  The main circuit section 12 includes a first and second pair of DC terminals 20a and 20b, first to third AC terminals 21a to 21c, first to sixth six arm sections 22a to 22f, And

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

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

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

  The fifth arm 22e is connected to the first DC terminal 20a. The sixth arm 22f is connected between the fifth arm 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 to the third arm portion 22c and the fourth arm portion 22d. Connected in parallel.

  In the main circuit section 12, a first leg LG1 is formed by the first arm section 22a and the second arm section 22b, a second leg LG2 is formed by the third arm section 22c and the fourth arm section 22d, and a fifth arm section is formed. The third leg LG3 is configured by the 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-leg, six-arm three-phase inverter. 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.

The first arm portion 22a has a plurality of transducers UP1, UP2 ... UPM ₁ connected in series. The second arm portion 22b has a plurality of transducers UN1, UN2 ... UNM ₂ connected in series. The third arm portion 22c has a plurality of transducers VP1, VP2 ... VPM ₃ connected in series. The fourth arm portion 22d includes a plurality of transducers VN1, VN2 ... VNM ₄ connected in series. The fifth arm portion 22e has a plurality of transducers WP1, WP2 ... WPM ₅ connected in series. The sixth arm portion 22f includes a plurality of transducers WN1, WN2 ... WNM ₆ connected in series.

However, in the following, each transducer _{UP1, UP2 ... UPM 1, UN1} , UN2 ... UNM 2, VP1, VP2 ... VPM 3, VN1, VN2 ... VNM 4, WP1, WP2 ... WPM 5, WN1, WN2 ... WNM 6 When referred to collectively, it is referred to as a "converter CELL".

In each of the arm portions _{22a~22f, M 1, M 2,} M 3, M 4, M 5, M 6 represents the number of series-connected transducers CELL. In each of the arm units 22a to 22f, the number of converters CELL connected in series is, for example, about 100 to 120 units. However, the number of converters CELL connected in series is not limited to this, and may be any number.

  The number of converters CELL provided in each of the arms 22a to 22f is substantially the same. For example, when a large number of converters CELL are connected, the number of converters CELL provided in each of the arm units 22a to 22f may be different as long as the operation of the main circuit unit 12 is not affected. For example, when 100 converters CELL are connected in series to one arm, the number of converters CELL provided in another arm may be different from one to two.

  Each of the arm portions 22a to 22f further includes buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f. The power conversion device 10 further includes a voltage detection unit 25.

  Each of the buffer reactors 23a to 23f is connected in series to each of the converters CELL in each of the arm portions 22a to 22f. The buffer reactor 23a of the first arm unit 22a is provided between a connection point between the AC terminal 21a and the first arm unit 22a and the second arm unit 22b and the converter UP1. The buffer reactor 23b of the second arm 22b is provided between a connection point between the AC terminal 21a and the first arm 22a and the second arm 22b and the converter UN1. The buffer reactor 23c of the third arm 22c is provided between a connection point between the AC terminal 21b and the third arm 22c and the fourth arm 22d and the converter VP1. The buffer reactor 23d of the fourth arm 22d is provided between a connection point between the AC terminal 21b and the third arm 22c and the fourth arm 22d and the converter VN1. The buffer reactor 23e of the fifth arm 22e is provided between a connection point between the AC terminal 21c and the fifth arm 22e and the sixth arm 22f and the converter WP1. The buffer reactor 23f of the sixth arm 22f is provided between a connection point between the AC terminal 21c and the fifth arm 22e and the sixth arm 22f and the converter WN1.

  The current detector 24a is provided on the first arm 22a and detects a current flowing through the first arm 22a. That is, the current detector 24a detects an arm current of the first arm unit 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 22a to the control device 14. Thereby, the current value of the first arm portion 22a is input to the control device 14.

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

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

  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 fifth arm section 22e and the sixth arm section Each connection point with 22f is an AC output point.

  The first AC terminal 21a is connected to a connection point between the first arm 22a and the second arm 22b. The second AC terminal 21b is connected to a connection point between the third arm 22c and the fourth arm 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, for example, the transformer 6.

  Each converter CELL is connected to the control device 14 via a signal line 26. The control device 14 controls the operation of the converter CELL by inputting a control signal to the converter CELL via the signal line 26. The converter CELL inputs, for example, a control signal and a protection signal relating to control and operation protection of the converter CELL to the control device 14 via another signal line (not shown).

FIG. 2 is a block diagram schematically showing the converter.
As shown in FIG. 2, the converter CELL includes a chopper circuit 40, a control unit 42, a power supply circuit 44, and a voltage detector 46.

  The chopper circuit 40 has a first connection terminal 50a, a second connection terminal 50b, a first switching element 51, a second switching element 52, and a charge storage element 55. Each of the switching elements 51 and 52 includes a pair of main terminals and a control terminal. The control terminal controls a current flowing between the pair of main terminals. For each of the switching elements 51 and 52, for example, a self-extinguishing element such as an IGBT is used. The pair of main terminals are, for example, an emitter and a collector, and the control terminal is, for example, a gate. For example, a normally-off type semiconductor element is used for each of the switching elements 51 and 52.

  The pair of main terminals of the second switching element 52 are connected in series to the pair of main terminals of the first switching element 51. The charge storage element 55 is connected in parallel to the first switching element 51 and the second switching element 52. The charge storage element 55 is, for example, a capacitor. The first connection terminal 50a is connected between the first switching element 51 and the second switching element 52. The second connection terminal 50b is connected to a main terminal of the first switching element 51 opposite to the main terminal connected to the second switching element 52.

  In addition, a rectifying element 51d is connected to the first switching element 51 in antiparallel to a pair of main terminals. The forward direction of the rectifying element 51d is opposite to the direction of the current flowing between the pair of main terminals of the first switching element 51. Similarly, a rectifying element 52d is connected to the second switching element 52 in antiparallel to the pair of main terminals. The rectifiers 51d and 52d are so-called reflux diodes.

  The supply of power to the chopper circuit 40 is performed via the connection terminals 50a and 50b. In the chopper circuit 40, the switching elements 51 and 52 are half-bridge connected. The first switching element 51 is a so-called low-side switch, and the second switching element 52 is a so-called high-side switch.

  The control unit 42 controls on / off of each of the switching elements 51 and 52. The control unit 42 includes a gate control circuit 60 and gate drive circuits 61 and 62. The gate control circuit 60 is connected to the control device 14 via the signal line 26. The control device 14 transmits a control signal for controlling on / off of each of the switching elements 51 and 52 to the gate control circuit 60 via the signal line 26. The gate control circuit 60 inputs a drive signal for switching on / off of each of the switching elements 51 and 52 to the gate drive circuits 61 and 62 based on the input control signal.

  The gate drive circuit 61 is connected to a control terminal of the first switching element 51. The gate drive circuit 62 is connected to a control terminal of the second switching element 52. The gate drive circuits 61 and 62 switch on / off of the switching elements 51 and 52 based on the drive signal input from the gate control circuit 60. Thus, the ON / OFF of each of the switching elements 51 and 52 is controlled according to the control signal from the control device 14. The control device 14 generates a control signal for each converter CELL and controls on / off of each switching element 51, 52 of each converter CELL. Thereby, the control device 14 controls the power conversion by the main circuit unit 12. The configuration of the control unit 42 is not limited to the above, and may be any configuration that can control on / off of each of the switching elements 51 and 52.

  The power supply circuit 44 is connected in parallel to the charge storage element 55 of the chopper circuit 40. The power supply circuit 44 generates a control power supply for the control unit 42 based on the charge stored in the charge storage element 55, and supplies the generated control power supply to the control unit 42. The power supply circuit 44 generates a control power supply corresponding to each of the gate control circuit 60 and the gate drive circuits 61 and 62, and supplies a control power supply corresponding to each of the gate control circuit 60 and the gate drive circuits 61 and 62. . The control unit 42 operates according to the supply of control power from the power supply circuit 44.

  The voltage detector 46 is electrically connected to the charge storage element 55. The voltage detector 46 is connected to the control device 14 via the signal line 26, for example. The voltage detector 46 detects the voltage Vc of the charge storage element 55, and inputs the detection result to the control device 14.

FIG. 3 is a graph diagram schematically illustrating an example of the operation of the control device.
As shown in FIG. 3, the control device 14 controls on / off of each of the switching elements 51 and 52 based on the voltage reference VR and the carrier signal CW. The control device 14 sets the voltage reference VR and the carrier signal CW for each converter CELL. When N converters CELL are connected in series to one arm, the control device 14 sets N voltage references VR and carrier signals CW for each converter CELL.

  The voltage reference VR is, for example, sinusoidal. The controller 14 adjusts the amplitude and phase of the voltage reference VR for each converter CELL. The frequency of voltage reference VR is set according to the frequency of the AC power of AC power system 2. That is, the frequency is set according to the actual use condition. The frequency of the voltage reference VR is, for example, 50 Hz or 60 Hz. The carrier signal CW has, for example, a triangular waveform. The carrier signal CW may be a sawtooth wave or the like. The frequency of the carrier signal CW is higher than the frequency of the voltage reference VR.

  The controller 14 shifts the phase of the voltage reference VR of each converter CELL. The control device 14 sets, for example, a voltage reference VR whose phase is shifted by 360 / N (degrees) for each converter CELL in one arm unit.

  Control device 14 compares voltage reference VR with carrier signal CW. The controller 14 turns on the first switching element 51 and turns off the second switching element 52 when the voltage reference VR is lower than the carrier signal CW. In this case, the connection terminals 50a and 50b are short-circuited by the first switching element 51, and the voltage between the connection terminals 50a and 50b becomes substantially 0V. Then, when the voltage reference VR is equal to or higher than the carrier signal CW, the control device 14 turns off the first switching element 51 and turns on the second switching element 52. In this case, the voltage Vc of the charge storage element 55 appears between the connection terminals 50a and 50b.

  As described above, the converter CELL outputs two levels of power of + Vc and 0 by turning on and off the switching elements 51 and 52. The converter CELL may be called, for example, a power cell.

  In the main circuit section 12, the sum of the output voltages of the converters CELL connected in series is the voltage of each of the arm sections 22a to 22f. This allows the main circuit unit 12 to perform multi-level power conversion according to the number of serially connected converters CELL.

FIG. 4 is a flowchart schematically illustrating an example of the operation of the power conversion device.
FIG. 5 is a graph diagram schematically illustrating an example of the operation of the power conversion device.
In FIG. 5, the voltage Vc1 of the charge storage element 55 of one converter CELL and the voltage Vc2 of the charge storage element 55 of another converter CELL among the voltage Vc of the charge storage element 55 of each converter CELL. , As an example.

  When the power conversion device 10 starts operation, the power storage device 55 of each converter CELL is initially charged by an initial charging circuit (not shown) or the like (timing t1 to t2 in FIG. 5).

  The control device 14 disconnects (bypasses) the initial charging circuit, for example, and shifts to an operation standby state. At this time, each switching element 51, 52 of each converter CELL is gate-blocked (GB), and each switching element 51, 52 is off. (Steps S1 and S2 in FIG. 4, timing t2 in FIG. 5).

  When the switching elements 51 and 52 are gate-blocked, the control device 14 determines whether or not the first time TM1 has elapsed from the time of transition to the operation standby state (step S3 in FIG. 4, timing t2 in FIG. 5). t3).

  When the control device 14 determines that the first time TM1 has elapsed, the control device 14 performs an operation control to deblock (DEB) each of the switching elements 51 and 52 of each converter CELL and to turn on and off each of the switching elements 51 and 52. (Step S4 in FIG. 4 and timing t3 in FIG. 5).

  The control device 14 controls on / off of each of the switching elements 51 and 52 so that a circulating current circulating in each of the arm portions 22a to 22f flows, for example. That is, the control device 14 turns on and off the switching elements 51 and 52 so that the current flows only in the main circuit unit 12 without flowing the current to the AC power system 2 side or the DC transmission lines 3 and 4 side. Control off.

  When the switching devices 51 and 52 are deblocked, the control device 14 determines whether or not the second time TM2 has elapsed since the deblocking (step S5 in FIG. 4 and timings t3 to t4 in FIG. 5). The second time TM2 is shorter than the first time TM1 in the gate block. In the second time period TM2, for example, the voltage Vc of the charge storage element 55 of each converter CELL is equalized by controlling on / off of each of the switching elements 51 and 52 and flowing a circulating current to each of the arms 22a to 22f. It is set to a time that can be changed. In other words, the second time TM2 is set, for example, to a time during which each voltage Vc of each converter CELL can be set to a rated value.

  When determining that the second time TM2 has elapsed, the control device 14 returns to the process of step S2, and gate-blocks the switching elements 51 and 52 again (timing t4 in FIG. 5).

  On the other hand, when determining that the second time TM2 has not elapsed, the control device 14 subsequently determines whether or not an operation has been instructed by a higher-level controller or the like (step S6 in FIG. 4). When the driving has not been instructed, the control device 14 returns to the process of step S4. Then, when the operation is instructed during the deblocking of each of the switching elements 51 and 52, the control device 14 converts each of the switching elements 51 and 52 so as to perform conversion from AC to DC or conversion from DC to AC. On / off is controlled to bring the main circuit section 12 into a normal operation state (timing t5 in FIG. 5).

  When it is determined in step S3 that the first time TM1 has not elapsed, similarly to the case of the second time TM2, the control device 14 determines whether an operation has been instructed (step S3 in FIG. 4). S7). When the driving has not been instructed, control device 14 returns to the process of step S2.

  When the operation is instructed during the gate block of each of the switching elements 51 and 52, the control device 14 deblocks each of the switching elements 51 and 52 (step S8 in FIG. 4). Then, the control device 14 controls ON / OFF of each of the switching elements 51 and 52 so as to perform conversion from AC to DC or from DC to AC, and brings the main circuit unit 12 into a normal operation state. (Timing t5 in FIG. 5). Hereinafter, the control device 14 repeats the above-described processing when instructed to wait for operation.

  As shown at timings t2 to t3 in FIG. 5, in the operation standby state in which the switching elements 51 and 52 of each converter CELL are turned off, each converter CELL is caused by an individual difference of the load of the control unit 42 and the like. There is a possibility that the voltage Vc of the charge storage element 55 varies.

  The variation of the voltage Vc of the charge storage element 55 of each converter CELL increases with time. FIG. 5 schematically illustrates an example in which the voltage Vc1 increases with time and the voltage Vc2 decreases with time.

  Therefore, if the switching elements 51 and 52 are gate-blocked for a long time, the voltage Vc becomes higher than the overvoltage detection level (upper limit) or lower than the main circuit power supply probability level (lower limit). Or the system may be stopped.

  In the power conversion device 10 according to the present embodiment, in the operation standby state, the control device 14 temporarily executes operation control for turning on / off each of the switching elements 51 and 52 at a predetermined timing. In this example, the control device 14 periodically executes the operation control according to the elapse of a predetermined time (first time TM1). Thus, the voltage Vc of the charge storage element 55 of each converter CELL can be equalized. For example, after performing the operation control for a predetermined time (second time TM2), the control device 14 returns to the operation standby state. Without being limited to this, for example, when the voltage Vc of the charge storage element 55 of each converter CELL has returned to a predetermined range, the operation may return to the operation standby state.

  Therefore, as compared with a case where a resistive load for balance is added, it is possible to suppress a variation in the voltage Vc of the charge storage element 55 of each converter CELL while suppressing an increase in loss and space.

  The first time TM1 is set to a time during which the voltage Vc of the charge storage element 55 of each converter CELL does not reach the overvoltage detection level or the main circuit power supply probability level. The first time TM1 can be obtained, for example, by simulation or the like. The first time TM1 may be adjusted on-site by confirming, for example, the variation of the voltage Vc when the main circuit unit 12 is actually operated.

FIG. 6 is an equivalent circuit diagram schematically illustrating the first arm unit in the operation standby state.
As shown in FIG. 6, in the driving standby state in which the switching elements 51 and 52 is turned off, the first arm portion 22a, each rectifying element 52d and the charge storage element 55 of each transducer UP1～UPM ₁ And can be expressed as a circuit in which are connected in series.

Controller 14, when executing the operation control at a predetermined timing in the operation standby state, as shown in FIG. 6, the sum of the voltage Vc of the charge storage element 55 of each transducer UP1～UPM _1, AC It charges higher than the power supply voltage supplied from the power system 2. More specifically, control device 14 charges the total value of voltages Vc higher than the maximum value of the power supply voltage. The power supply voltage supplied from the AC power system 2 is, in other words, a voltage between the first AC terminal 21a and the second AC terminal 21b and a voltage between the first AC terminal 21a and the third AC terminal 21c. Voltage. The control device 14 also charges the charge storage elements 55 of the respective converters CELL for the other arm units 22b to 22f, similarly to the first arm unit 22a. Accordingly, after the switching elements 51 and 52 are gate-blocked, the operation is only to be discharged in each converter CELL, and the overvoltage of the voltage Vc can be more appropriately suppressed. The risk of system shutdown can be further reduced.

FIG. 7 is a flowchart schematically illustrating another example of the operation of the power conversion device.
As illustrated in FIG. 7, in this example, the control device 14 gates the switching elements 51 and 52 of each converter CELL in response to an operation standby instruction or the like from a higher-level controller, and then controls each converter CELL. It is determined whether any of the voltages Vc of the charge storage elements 55 of the converters CELL has exceeded the first range based on the detection result of the voltage detector 46 (steps S11 to S13 in FIG. 7).

  The first range is set between the overvoltage detection level (upper limit) of the voltage Vc and the main circuit power supply probability level (lower limit). That is, the upper threshold of the first range is set lower than the overvoltage detection level, and the lower threshold of the first range is set higher than the main circuit power supply probability level. As a result, before the system is stopped, the fluctuation of the voltage Vc can be detected.

  When the control device 14 determines that the voltage Vc has exceeded the first range in any one of the converters CELL, the control device 14 deblocks the switching elements 51 and 52 of the converters CELL and sets the switching elements 51 and 52 to Operation control for turning on and off is executed (step S14 in FIG. 7).

  When the switching elements 51 and 52 are deblocked, the control device 14 determines whether or not the voltage Vc of the charge storage element 55 of each converter CELL has returned to the second range (Step S15 in FIG. 7). When the control device 14 determines that the voltages Vc of all the converters CELL have returned within the second range, the process returns to step S12, and the switching elements 51 and 52 are gate-blocked again.

  The second range is set narrower than the first range. That is, the upper threshold of the second range is set lower than the upper threshold of the first range, and the lower threshold of the second range is set higher than the lower threshold of the first range. . Thus, it is possible to prevent the determination that the switching elements 51 and 52 have exceeded the first range immediately after the gate blocks. That is, it is possible to prevent the gate block and the deblock from being repeated in a short time.

  The processing in steps S16 to S18 in FIG. 7 is the same as the processing in steps S6 to S8 described with reference to FIG. 4, and thus detailed description is omitted.

  As described above, the control device 14 executes the operation control when any one of the voltages Vc of the charge storage elements 55 of the converters CELL exceeds a predetermined range (first range), thereby controlling each converter CELL. The voltage Vc of the charge storage element 55 of CELL may be equalized. Also in this case, similarly to the above-described embodiment, it is possible to suppress the variation in the voltage Vc of the charge storage element 55 of each converter CELL while suppressing the loss and the increase in the space. In this example, the control device 14 returns to the operation standby state when the voltages Vc of all the converters CELL return to within the second range. Without being limited to this, the control device 14 may return to the operation standby state after performing the operation control for a predetermined time, for example.

FIGS. 8A to 8C are graphs schematically illustrating a modification example based on voltage.
The voltage reference VRa shown in FIG. 8A is substantially the same as the voltage reference VR described with reference to FIG. 3, and is a sine-wave voltage reference set according to the frequency of the AC power of the AC power system 2. is there.

  The voltage reference VRb shown in FIG. 8B is a sinusoidal voltage reference having a frequency twice as high as the voltage reference VRa. That is, when the frequency of the voltage reference VRa is 50 Hz, the frequency of the voltage reference VRb is 100 Hz. The amplitude of the voltage reference VRb is, for example, substantially the same as the amplitude of the voltage reference VRa.

  The voltage reference VRc illustrated in FIG. 8C is a composite wave voltage reference in which the voltage reference VRb is superimposed on the voltage reference VRa.

  Control device 14 has the same frequency as the frequency of the AC power of AC power system 2 shown in FIG. 3 or FIG. 8A in a normal operation state in which the conversion from AC to DC or from DC to AC is performed. On / off control of each of the switching elements 51 and 52 is performed using a voltage reference VR (VRa) having a frequency.

  The control device 14 uses the voltage reference VRc shown in FIG. 8C to execute the operation control for turning on / off each of the switching elements 51 and 52 in the operation standby state. 52 is turned on and off.

  As described above, at the time of the operation control in the operation standby state, the control of each of the switching elements 51 and 52 is performed based on the carrier signal CW and the voltage reference VRc using the voltage reference VRc on which the double frequency component is superimposed. Do. This makes it more difficult for the current to flow out to the AC power system 2 side and the DC transmission lines 3 and 4 side. A circulating current can more appropriately flow through each of the arms 22a to 22f. The frequency of the voltage reference VRb to be superimposed is not limited to two times, but may be four times or six times. The frequency of the voltage reference VRb may be an even multiple of the frequency of the voltage reference VRa.

FIG. 9 is a block diagram schematically illustrating a modified example of the converter.
As shown in FIG. 9, in the converter CELL of this example, the chopper circuit 40 is replaced with a full bridge circuit 48. The full bridge circuit 48 has a first switching element 51 and a second switching element 52, and further has a third switching element 53 and a fourth switching element 54. As the third switching element 53 and the fourth switching element 54, substantially the same elements as the first switching element 51 and the second switching element 52 are used.

  The pair of main terminals of the fourth switching element 54 are connected in series to the pair of main terminals of the third switching element 53. The third switching element 53 and the fourth switching element 54 are connected in parallel to the first switching element 51 and the second switching element 52. The charge storage element 55 is connected in parallel to the first switching element 51 and the second switching element 52, and is connected in parallel to the third switching element 53 and the fourth switching element 54.

  A rectifying element 53d is connected to the third switching element 53 in antiparallel to the pair of main terminals. A rectifying element 54d is connected to the fourth switching element 54 in antiparallel to the pair of main terminals.

  The first connection terminal 50a of the converter CELL is connected between the first switching element 51 and the second switching element 52. The second connection terminal 50b is connected between the third switching element 53 and the fourth switching element 54. In this example, the second connection terminal 50b is connected via the third switching element 53 to a main terminal of the first switching element 51 opposite to the main terminal connected to the second switching element 52.

  In the converter CELL, the first switching element 51 and the fourth switching element 54 are turned on, and the second switching element 52 and the third switching element 53 are turned off, thereby connecting between the connection terminals 50a and 50b. A voltage of + Vc appears.

  Further, by turning on the second switching element 52 and the third switching element 53 and turning off the first switching element 51 and the fourth switching element 54, the -Vc voltage between the connection terminals 50a and 50b is reduced. Voltage appears.

  Further, the first switching element 51 and the third switching element 53 on the low side are turned on, and the second switching element 52 and the fourth switching element 54 on the high side are turned off. Alternatively, the second switching element 52 and the fourth switching element 54 on the high side are turned on, and the first switching element 51 and the third switching element 53 on the low side are turned off. As a result, conduction is established between the connection terminals 50a and 50b, and substantially 0 V appears between the connection terminals 50a and 50b. Thus, the converter CELL can output three levels of voltages of + Vc, 0, and -Vc between the connection terminals 50a and 50b.

  Although not shown in FIG. 9 for the sake of convenience, the third switching element 53 and the fourth switching element 54 are connected to the control unit 42, like the first switching element 51 and the second switching element 52. ON / OFF is controlled by the control unit 42. The control unit 42 has, for example, four gate drive circuits corresponding to each of the switching elements 51 to 54. The gate control circuit 60 controls the operation of each gate drive circuit based on a control signal input from the control device 14. Thereby, ON / OFF of each of the switching elements 51 to 54 is controlled.

  As described above, the converter used in the MMC-type power converter 10 may be the chopper circuit 40 or the full bridge circuit 48.

  In each of the above embodiments, an MMC type power converter is used for the main circuit unit 12. The main circuit section 12 is not limited to the MMC type, and may be another type of power converter in which a plurality of converters CELL are connected in series.

  The power conversion device 10 is not limited to a DC power transmission system, and 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 converter 10 is not limited to both AC to DC and DC to AC, but may be only one of AC to DC or DC to AC. The AC power converted by the power converter 10 is not limited to three-phase AC power, but may be single-phase AC power, two-phase AC power, or the like.

  While some embodiments of the invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  2 ... AC power system 3, 4 ... DC transmission line, 6 ... Transformer, 10 ... Power conversion device, 12 ... Main circuit part, 14 ... Control device, 20a, 20b ... DC terminal, 21a-21c ... First to first Third AC terminals, 22a to 22f: first to sixth arms, 23a to 23f: buffer reactors, 24a to 24f: current detectors, 25: voltage detectors, 26: signal lines, 40: chopper circuits, 42 ... Control unit, 44: power supply circuit, 46: voltage detector, 48: full bridge circuit, 51 to 54: first to fourth switching elements, 55: charge storage element, 60: gate control circuit, 61, 62: gate drive circuit

Claims (9)

A main circuit unit having a plurality of converters connected in series, and performing at least one of conversion from AC power to DC power and conversion from DC power to AC power by the operation of the plurality of converters. ,
A control device for controlling the operation of the plurality of converters,
With
Each of the plurality of converters,
A first switching element;
A second switching element connected in series with the first switching element;
A charge storage element connected in parallel to the first switching element and the second switching element;
A control unit that controls on / off of the first switching element and the second switching element;
A constant power load connected in parallel to the charge storage element;
Has,
In the operation standby state in which the first switching element and the second switching element are turned off, the control device temporarily performs operation control for turning on and off the first switching element and the second switching element at a predetermined timing. Power conversion device to be executed.   2. The power supply according to claim 1, wherein the constant power load is a power supply circuit that generates a control power supply for the control unit based on the charge stored in the charge storage element and supplies the generated control power supply to the control unit. 3. Conversion device.   The power converter according to claim 1, wherein the control device periodically executes the operation control as the first time elapses.   The power converter according to claim 3, wherein the control device returns to the operation standby state after performing the operation control for a second time shorter than the first time. Each of the plurality of converters further includes a voltage detector that detects a voltage of the charge storage element and inputs a detection result to the control device,
3. The power converter according to claim 1, wherein the control device executes the operation control when any one of the voltages of the charge storage elements of the plurality of converters exceeds a first range. 4.   6. The control device according to claim 5, wherein the control device returns to the operation standby state when the voltage of each of the charge storage elements of the plurality of converters returns within a second range narrower than the first range. Power converter. The main circuit unit includes:
A first DC terminal;
A second DC terminal;
A first arm connected to the first DC terminal;
A second arm connected between the first arm and the second DC terminal;
A third arm connected to the first DC terminal;
A fourth arm connected between the third arm and the second DC terminal;
A first AC terminal connected to a connection point between the first arm and the second arm;
A second AC terminal connected to a connection point between the third arm and the fourth arm;
Has,
Each of the first arm unit, the second arm unit, the third arm unit, and the fourth arm unit includes the plurality of converters connected in series,
The control device may include, in the operation control, the first switching unit so that a circulating current that circulates through each of the first arm unit, the second arm unit, the third arm unit, and the fourth arm unit flows. The power converter according to any one of claims 1 to 6, which controls on / off of an element and the second switching element. The control device is configured to control the first switching element and the second switching element based on a triangular carrier signal and a voltage reference set for each of the plurality of converters during the operation control. Control on / off,
The power converter according to claim 7, wherein the voltage reference is a composite wave in which a sine wave of an even multiple of the frequency of the AC power is superimposed on a sine wave of the frequency of the AC power.   The plurality of converters connected in series in each of the first arm unit, the second arm unit, the third arm unit, and the fourth arm unit during the operation control. 9. The power conversion device according to claim 7, wherein a total value of the voltages of the charge storage elements is charged higher than a power supply voltage supplied from the AC power side.

Images