Power conversion device

Abstract

This power conversion device comprises a power converter (10) that has a plurality of arms serially connecting a plurality of unit converter groups (120) connecting a plurality of unit converters (122), and a control device (20), wherein the unit converters (122) include switching elements (SWp, SWn), and the unit converter groups (120) include a gate control unit (126) having a carrier wave generation unit (1262) and compare a modulation command (kref) from the control device (20) with carrier waves (kcar) to perform on / off control on the switching elements (SWp, SWn). In the carrier waves (kcar), the phases corresponding to the unit converters (122) are shifted by a first phase shift amount obtained by dividing one cycle (2π) of a carrier wave (kcar) by the number (M) of unit converters (122) of the unit converter groups (120), and are shifted by a second phase shift amount (φb) between unit converter groups within the arms, the second phase shift amount being obtained by dividing the first phase shift amount (φa) by the number of the unit converter groups within the arms.

Description

Power Conversion Device

[0001] The present application relates to a power conversion device.

[0002] Modular multilevel converters are known as self-commutated power conversion devices used in DC transmission systems. Modular multilevel converters are used for converting three-phase AC to DC or vice versa. These modular multilevel converters include multiple submodules, each of which has a plurality of series-connected cells, each of which has a capacitor and a switching element. If the voltage and current of the AC voltage system to which the modular multilevel converter is connected contain a large number of harmonic components, the voltage balance of the capacitors is disrupted, resulting in significant waveform distortion of the synthesized AC voltage.

[0003] In response to this, it is known that a carrier wave for controlling the on / off operation of the switching elements in each cell is generated based on the phase information of multiple cells and the cell's unique information, and the switching elements of the cells that make up each submodule perform on / off operations using carrier waves with different phases (see, for example, Patent Document 1).

[0004] In the technology disclosed in Patent Document 1, cells in a single submodule, in which multiple cells are connected in series, are turned on and off based on carrier waves with different phases, which makes it possible to reduce waveform distortion. Furthermore, since carrier waves can be generated with a phase shift, the configuration of the control device can be simplified, contributing to the miniaturization of the device.

[0005] JP 2019-75844 A

[0006] Meanwhile, modular multilevel converters are known that accommodate large-capacity power conversion, with submodules each having a cell group in which cells are connected in series. In Patent Document 1, a carrier wave is generated for each cell group in a submodule, and carrier waves with different phases are transmitted to multiple cell groups within the submodule (see Embodiment 3 of Patent Document 1). By making the carrier waves for each cell in a cell group equal, the amount of data is reduced. However, there is a risk of increased harmonic distortion due to the presence of carrier waves with the same phase within a single submodule and switching elements operating with the carrier waves with the same phase. To solve this problem, it has been considered to generate carrier waves with different phases for each cell in the submodule, but this approach poses the problem of increasing the size of the control device due to the increased data volume of the carrier waves and the increased amount of calculations required.

[0007] The present application discloses a technology for solving the above-mentioned problems, and aims to provide a power conversion device equipped with a modular multilevel converter that is compatible with large-capacity power conversion, and that is capable of outputting voltage and current with little harmonic distortion with a simple configuration without increasing the size of the control device.

[0008] The power conversion device disclosed in the present application is a power conversion device comprising: a power converter having a plurality of arms in which a plurality of converter unit groups, each of which is connected in series, are connected; and a control device that controls the power converter, wherein the converter unit has a series body in which two switching elements are connected in series, and a capacitor connected in parallel to the series body, the converter unit group has a gate control unit that generates gate signals that control the on / off of the plurality of switching elements in the converter unit group, and the gate control unit has a carrier wave generation unit that generates a plurality of carrier waves corresponding to the number of converter unit groups in the converter unit, and a gate signal generation unit that compares a modulation command received from the control device with the carrier wave generated by the carrier wave generation unit and generates a gate signal based on the result of the comparison, The multiple carrier waves generated by the carrier wave generation unit are configured so that the phase of each carrier wave is shifted by a first phase shift amount, which is a value obtained by dividing one period of the carrier wave equally by the number of unit converters in the unit converter group, based on the carrier wave reference phase received from the control device, and between the unit converter groups within the arm, the carrier waves are generated by shifting the first phase shift amount by a second phase shift amount, which is a value obtained by dividing the first phase shift amount equally by the number of unit converter groups in the arm, based on the carrier wave reference phase received from the control device.

[0009] According to the power conversion device of the present disclosure, it is possible to output voltage and current with little harmonic distortion with a simple configuration without increasing the size of the control device.

[0010] FIG. 1 is a schematic diagram showing the configuration of a power conversion device according to embodiment 1. FIG. 2 is a schematic configuration diagram of one arm that constitutes the power conversion device according to embodiment 1. FIG. 3 is a diagram showing the configuration of a unit converter. FIG. 4 is a configuration diagram showing an example of a unit converter group that constitutes an arm. FIG. 5 is another configuration diagram showing an example of a unit converter group that constitutes an arm. FIG. 6 is yet another configuration diagram showing an example of a unit converter group that constitutes an arm. FIG. 7 is a diagram showing the configuration of a gate control unit that a unit converter group is equipped with. FIG. 8 is a diagram showing another configuration of a gate control unit that a unit converter group is equipped with. FIG. 9 is a diagram for explaining a phase shift of a carrier wave in a unit converter group. FIG. 10 is a diagram for explaining a phase shift of a carrier wave between unit converter groups in one arm. FIG. 11 is a diagram for explaining a carrier wave in a power conversion device according to embodiment 2. FIG. 12 is a diagram showing the configuration of a gate control unit according to embodiment 2. FIG. 13 is a configuration diagram showing an example of a unit converter group that constitutes an arm according to embodiment 2. FIG. 14 is a hardware configuration diagram that is an example of a control device and a gate control unit according to each embodiment.

[0011] Hereinafter, the present embodiment will be described with reference to the drawings. Note that the same reference numerals in each drawing indicate the same or corresponding parts. Hereinafter, the embodiment of the present disclosure will be described in detail with reference to the drawings.

[0012] First Embodiment. A power conversion apparatus according to the first embodiment will be described below with reference to the drawings. <Configuration of the Power Conversion Apparatus> FIG. 1 is a diagram showing a schematic configuration of a power conversion apparatus called an MMC (Modular Multilevel Converter) according to the first embodiment. In FIG. 1, the power conversion apparatus includes a power converter 10 and a control device 20 that controls the power converter 10, and performs power conversion between AC and DC. The power converter 10 is connected between an AC power source 1, which is a three-phase AC system, and a power device, a DC power source, or another power converter, etc., to which DC power is supplied via a positive DC terminal 6P and a negative DC terminal 6N, which are a DC system. Note that the power device, DC power source, other power converter, etc., to which DC power is supplied are not shown. A current sensor 2, a voltage sensor 3, a transformer 4, etc. are connected between the AC power source 1 and the power converter 10, and an AC current Iac detected by the current sensor 2 and an AC voltage Vac detected by the voltage sensor 3 are output to the control device 20. The DC system is also provided with voltage sensors 14p and 14n for detecting a DC voltage Vdc.

[0013] The power converter 10 has three leg circuits corresponding to the u-phase, v-phase, and w-phase of the three-phase AC, and the three leg circuits are connected in parallel between the positive-side DC terminal 6P and the negative-side DC terminal 6N. The u-phase leg circuit is configured by connecting a positive-side u-phase arm 12pu and a negative-side u-phase arm 12nu in series. One end of the positive-side u-phase arm 12pu is connected to the positive-side DC terminal 6P, one end of the negative-side u-phase arm 12nu is connected to the negative-side DC terminal 6N, and the junction u between the positive-side u-phase arm 12pu and the negative u-phase arm 12nu is connected to the u-phase terminal of the transformer 4.

[0014] The V-phase leg circuit is configured by connecting a positive V-phase arm 12pv and a negative V-phase arm 12nv in series. One end of the positive V-phase arm 12pv is connected to the positive DC terminal 6P, one end of the negative V-phase arm 12nv is connected to the negative DC terminal 6N, and the junction point V between the positive V-phase arm 12pv and the negative V-phase arm 12nv is connected to the V-phase terminal of the transformer 4.

[0015] The w-phase leg circuit is configured by connecting a positive-side w-phase arm 12pw and a negative-side w-phase arm 12nw in series. One end of the positive-side w-phase arm 12pw is connected to the positive-side DC terminal 6P, one end of the negative-side w-phase arm 12nw is connected to the negative-side DC terminal 6N, and the junction point w between the positive-side w-phase arm 12pw and the negative w-phase arm 12nw is connected to the w-phase terminal of the transformer 4.

[0016] <Configuration of Arm 12> Next, the configuration of each arm of the power converter 10 will be described with reference to Fig. 2. Fig. 2 is a diagram showing a schematic configuration of the arm 12 (referred to as arm 12 when referring to the arms collectively or when describing one arm as an example). In the figure, the arm 12 is one of the six arms shown in Fig. 1.

[0017] 2, the arm 12 includes N (N is an integer of 2 or more) switching element groups 120_1, ..., 120_k, ..., 120_N (switching element groups are collectively referred to as switching element groups 120) connected in series, a reactor 12L connected in series thereto, and a current i ａｒｍ When the arm 12 is the positive side u-phase arm 12pu in FIG. 1, one end of the switching element group 120_1 is connected to the positive side DC terminal 6P, and the other end is connected to the switching element group 120_2. Also, one end of the switching element group 120_N is connected to the switching element group 120_N-1, and the other end is connected to the reactor 12L, the current i ａｒｍ is connected to the connection point u via a current sensor 12di that detects

[0018] The voltage value vc of the capacitors of the unit converters that make up the unit converter group 120 described below or the total value Σvc of the capacitor voltage values ​​of the unit converters in the unit converter group 120, and a signal to turn on the bypass switch provided in the unit converter group 120 described below are transmitted from the unit converter group 120 to the control device 20.

[0019] In addition, the control device 20 sends an arm modulation command k ｒｅｆ , the average capacitor voltage in the arm vc ａｒｍ , arm current detection value i ａｒｍ, carrier reference phase θc, and carrier frequency fc are transmitted.

[0020] <Configuration of Unit Converter> Next, the configuration of the unit converter included in the unit converter group 120 will be described using Fig. 3. Fig. 3 is a circuit diagram showing an example of the configuration of a unit converter, which has a series body in which semiconductor switching elements SWp and SWn, for example, are connected in series as switching elements, and a DC capacitor as an energy storage element connected in parallel to this series body. Although not shown, the unit converter further includes a voltage sensor that detects the voltage vc of the DC capacitor, which will be described later, and a gate driver that controls the on / off of the P-side semiconductor switching element SWp and the N-side semiconductor switching element SWn.

[0021] <Configuration of the switching element group 120> Next, the configuration of the switching element group 120 will be described with reference to Fig. 4 to Fig. 6. Fig. 4 to Fig. 6 are configuration diagrams showing examples of switching element groups that make up each arm, and in all of these examples the number M (M is an integer of 2 or greater) of switching elements in the switching element group is 4.

[0022] 4, the unit converter group 120A has four unit converters 122_1, 122_2, 122_3, and 122_4 connected in series (when referring to the unit converters collectively, they are referred to as unit converters 122), and each unit converter 122 has a voltage sensor 124_1, 124_2, 124_3, and 124_4 (when referring to the voltage sensors collectively, they are referred to as voltage sensors 124) that detects a voltage vci (i is an integer from 1 to M, where M is 4, and vci is the voltage of the capacitor included in the i-th unit converter) that it has. The unit converter group 120A also has a gate control unit 126 that receives as input the capacitor voltage vci detected by each voltage sensor 124 and generates gate signals for driving the semiconductor switching elements SWpi, SWni included in each unit converter 122. One gate control section 126 is provided for each unit converter group.

[0023] The AC terminal of the unit converter 122_1 located at one end of the unit converter group 120A is one terminal of the unit converter group 120A. The N terminal of the unit converter 122_1 is connected to the AC terminal of the unit converter 122_2, the N terminal of the unit converter 122_2 is connected to the AC terminal of the unit converter 122_3, and the N terminal of the unit converter 122_3 is connected to the AC terminal of the unit converter 122_4. The N terminal of the unit converter 122_4 located at the other end of the unit converter group 120A is the other terminal of the unit converter group 120A. A bypass switch 128 is provided between the terminals of the unit converter group 120A, i.e., between the AC terminal of the unit converter 122_1 and the N terminal of the unit converter 122_4. In the event of a failure of the unit converter group 120A, for example, by activating (closing) the bypass switch 128, no current flows through the unit converter group 120A, making it possible to disconnect it from the power conversion device.

[0024] The semiconductor switching elements SWpi and SWni of the unit converter 122_i are provided with gate drivers GDpi and GDni, respectively, which receive gate signals giP and giN transmitted from the gate control unit 126 and perform on / off control of the semiconductor switching elements SWpi and SWni. Through the on / off control, the voltage output by the unit converter 122_i becomes the capacitor voltage vci or 0.

[0025] 2. Configuration of the unit converter group 120B Although the reference numerals for the individual unit converters are omitted in Fig. 5, four unit converters 122_1, 122_2, 122_3, and 122_4 are connected in series in Fig. 5 as well. The difference from the configuration in Fig. 4 is the connection points between the unit converters. In Fig. 5, the P terminal of unit converter 122_1 located at one end of the unit converter group 120B is one terminal of the unit converter group 120B. The AC terminal of unit converter 122_1 is connected to the P terminal of unit converter 122_2, the AC terminal of unit converter 122_2 is connected to the P terminal of unit converter 122_3, and the AC terminal of unit converter 122_3 is connected to the P terminal of unit converter 122_4. The AC terminal of unit converter 122_4 located at the other end of the unit converter group 120B is the other terminal of the unit converter group 120B. Similar to FIG. 4, a bypass switch 128 is provided between the terminals of the switching element group 120B, that is, between the P terminal of the switching element 122_1 and the AC terminal of the switching element 122_4.

[0026] 6 differs from the configurations in FIGS. 4 and 5 in the connections between the unit converters. In FIG. 6, the AC terminal of the unit converter 122_1 located at one end of the unit converter group 120C is one terminal of the unit converter group 120C. The N terminal of the unit converter 122_1 is connected to the P terminal of the unit converter 122_2, the AC terminal of the unit converter 122_2 is connected to the AC terminal of the unit converter 122_3, and the N terminal of the unit converter 122_3 is connected to the P terminal of the unit converter 122_4. The AC terminal of the unit converter 122_4 located at the other end of the unit converter group 120C is the other terminal of the unit converter group 120C. Similar to FIGS. 4 and 5, a bypass switch 128 is provided between the terminals of the unit converter group 120C, i.e., between the AC terminal of the unit converter 122_1 and the AC terminal of the unit converter 122_4.

[0027] The converter unit group 120_k constituting the arm 12 shown in FIG. 2 is composed of any one of the converter unit groups A, B, and C shown in FIGS. 4 to 6, and it is desirable that the same type and number of converter unit groups are configured within the arm 12 and the power conversion device.

[0028] <Configuration of Gate Control Unit 126> Next, the gate control unit 126 provided in the unit converter group 120 will be described. FIG. 7 is a functional block diagram showing the configuration of the gate control unit 126 according to the first embodiment. The gate control unit 126 includes gate signal generation units 1264 (each gate signal generation unit is referred to as a gate signal generation unit 1264_i, collectively referred to as a gate signal generation unit 1264) corresponding to each of the M unit converters 122 in the unit converter group, and carrier wave generation units 1262 (each carrier wave generation unit is referred to as a carrier wave generation unit 1262_i, collectively referred to as a carrier wave generation unit 1262) that generate carrier waves for generating gate signals. The ith gate signal generation unit 1264_i generates gate signals giP, giN to be transmitted to the gate drivers GDpi, GDni of the ith unit converter 122_i, respectively, and the ith carrier wave generation unit 1262_i transmits a triangular wave carrier k to the ith gate signal generation unit 1264_i. ｃａｒ Send i.

[0029] The i-th carrier wave generating unit 1262 — i generates a triangular wave carrier k based on the carrier frequency fc and the carrier reference phase θc received from the control device 20. ｃａｒ An adder 1261 is provided in front of each of the second carrier generation unit 1262_2 to the M-th carrier generation unit 1262_M. The adder 1261_2 inputs a carrier reference phase θc+2π / M to the second carrier generation unit 1262_2, and therefore generates a triangular wave carrier k with a phase delayed by 2π / M from the first carrier generation unit 1262_1. ｃａｒ 2. Triangular wave carrier k with phases shifted by 2π / M in succession is generated. ｃａｒ That is, the M unit converters 122 in the unit converter group 120 all generate triangular wave carriers k ｃａｒ Hereinafter, generating carrier waves with phases shifted by 2π / M will be referred to as phase shift.

[0030] The i-th gate signal generator 1264_i receives the arm modulation command k from the control device 20. ｒｅｆ and the triangular wave carrier k received from the i-th carrier wave generation unit 1262 — i ｃａｒ i and the arm modulation command k ｒｅｆis larger, the arm modulation command k is set so that the voltage output from the i-th unit converter 122_i becomes the capacitor voltage vci. ｒｅｆ is smaller, gate signals giP and giN are output to the gate drivers GDpi and GDni, respectively, so that the voltage output by the i-th unit converter 122_i becomes zero.

[0031] That is, for the unit converters 122_1, 122_2, 122_3, and 122_4 of the unit converter group 120A shown in FIG. 4 and the unit converters 122_1 and 122_3 of the unit converter group 120C shown in FIG. 6, the i-th gate signal generator 1264_i generates the arm modulation command k ｒｅｆ and the triangular wave carrier k received from the i-th carrier wave generation unit 1262 — i ｃａｒ i and the arm modulation command k ｒｅｆ is larger, a gate signal giP is output to the gate driver GDpi so as to turn on the P-side semiconductor switching element of the i-th unit converter 122_i. On the other hand, the arm modulation command k ｒｅｆ is smaller, a gate signal giN is output to the gate driver GDni so as to turn on the N-side semiconductor switching element of the i-th unit converter 122_i.

[0032] For each of the unit converters 122_1, 122_2, 122_3, and 122_4 of the unit converter group 120B shown in FIG. 5 and the unit converters 122_2 and 122_4 of the unit converter group 120C shown in FIG. 6, the i-th gate signal generator 1264_i generates an arm modulation command k ｒｅｆ and the triangular wave carrier k received from the i-th carrier wave generation unit 1262 — i ｃａｒ i and the arm modulation command k ｒｅｆ is larger, a gate signal giN is output to the gate driver GDni so as to turn on the N-side semiconductor switching element of the i-th unit converter 122_i. On the other hand, the arm modulation command k ｒｅｆ is smaller, a gate signal giP is output to the gate driver GDpi so as to turn on the P-side semiconductor switching element of the i-th unit converter 122_i.

[0033] The gate control unit 126 shown in FIG. 7 is based on the premise that the variation in the capacitor voltage vci of each of the unit converters 122 included in the unit converter group 120 is small, and ｒｅｆ When the capacitor voltage vci of each unit converter 122 included in the unit converter group 120 varies, the capacitor voltage vci is set to the average capacitor voltage vc in the arm. ａｒｍ The capacitor voltage vci and the average capacitor voltage vc in the arm are adjusted so as to approach ａｒｍ deviation from the arm current detection value i ａｒｍ Using the arm modulation command k ｒｅｆ and modulating command k of each unit converter. ｒｅｆ It is desirable to output the signal as i to each gate signal generator 1264_i.

[0034] 8 is a functional block diagram showing the configuration of another gate control unit 126 according to the first embodiment. In FIG. 8, the gate control unit 126 further includes a balance control unit 1266. The i-th balance control unit 1266_i receives an arm modulation command k ｒｅｆ , the average capacitor voltage in the arm vc ａｒｍ and arm current detection value i ａｒｍ is input, and the capacitor voltage vci received from each unit converter 122_i is input. Then, the capacitor voltage vci is calculated as the average capacitor voltage vc in the arm. ａｒｍ The modulation command balance correction amount corresponding to each unit converter is calculated so that the arm modulation command k ｒｅｆ The corrected arm modulation command is added to the modulation command k of each unit converter. ｒｅｆ i to the i-th gate signal generator 1264 — i. Here, the balance controllers 1266 are provided in the same number as the converter elements 122 corresponding to the converter elements 122 in the converter element group 120 .

[0035] In FIG. 8, the i-th gate signal generator 1264 — i receives a modulation command k transmitted from the i-th balance controller 1266 — i. ｒｅｆ i and the triangular wave carrier k transmitted from the i-th carrier wave generation unit 1262_i ｃａｒAs explained in FIG. 7, the arm modulation command k ｒｅｆ is larger, the arm modulation command k is set so that the voltage output from the i-th unit converter 122_i becomes the capacitor voltage vci. ｒｅｆ is smaller, gate signals giP and giN are output to the gate drivers GDpi and GDni, respectively, so that the voltage output by the i-th unit converter 122_i becomes zero.

[0036] Since a gate control unit 126 is provided for each converter group 120, the arm modulation command k ｒｅｆ , arm current detection value i ａｒｍ and the average capacitor voltage vc in the arm ａｒｍ This makes it possible to reduce the amount of data transmitted compared to the past, since the data only needs to be transmitted for each converter unit group 120. In other words, the amount of data can be significantly reduced compared to transmitting the data for each gate driver of each converter unit.

[0037] <Explanation of Operation Due to Phase Shift> Next, the phase shift of the carrier wave input to the gate signal generation unit 1264 will be described. The number of unit converters M in the unit converter group 120 is predetermined and does not change during operation of the power conversion device. For this reason, a value of 2π / M [rad] is stored in advance in the gate control unit 126, and each carrier wave generation unit 1262 can generate a reference phase of each carrier wave based on the carrier wave reference phase θc received from the control device 20. 2π / M is the value obtained by dividing one period (2π) of the carrier wave by the number M of unit converters in the unit converter group 120, that is, π / M is the value obtained by equally dividing one period (2π) of the carrier wave by the number M of unit converters in the unit converter group 120.

[0038] FIG. 9 shows the phase shift of the triangular wave carrier k for explaining the phase shift of the carrier when the number of unit converters in the unit converter group is M=4. ｃａｒ In FIG. 9, each triangular wave carrier k ｃａｒ The triangular wave carrier generated by the first carrier generation unit 1262_1 is assigned i=1, and the symbols are sequentially assigned up to i=4. As described above, the i-th carrier generation unit 1262_i generates the triangular wave carrier k based on the carrier frequency fc and the carrier reference phase θc received from the control device 20.ｃａｒ i, and each triangular wave carrier k ｃａｒ The phase difference φa of each triangular wave carrier k is 2π / M. ｃａｒ Since the value of i is 2π / M [rad] stored in advance in the gate control unit 126 based on the number M of unit converters in the unit converter group 120, each carrier wave generation unit 1262 can easily generate a reference phase for each carrier wave based on the carrier wave reference phase θc received from the control device 20. This makes it possible to reduce the amount of data transmitted from the control device 20.

[0039] Next, the phase shift of the carrier wave when there are three switching element groups 120 in the arm 12 (N=3) will be described with reference to Fig. 10. Fig. 10 shows the phase shift of the carrier wave when the number of switching element groups N in the arm 12 is 3. ｃａｒ In the waveform diagram of i, each switching element group has four switching elements, similar to Fig. 9. From the top, the triangular wave carrier k in the first switching element group 120_1, the second switching element group 120_2, and the third switching element group 120_3 are ｃａｒ 1 is a waveform diagram of a triangular wave carrier k generated by the first carrier wave generating unit of each converter group. ｃａｒ Focusing on the waveform of 1, the phase difference between the switching element groups is φb. This phase difference φb is a value obtained by dividing the first phase shift amount φa (=2π / M [rad]) in the switching element group by the number N of switching element groups in the arm, and is a value obtained by equally dividing φa by N. In other words, the triangular wave carrier k generated by the carrier wave generating unit in the arm ｃａｒ i has a phase difference obtained by equally dividing 360° (=2π) by the total number of unit converters in the arm (M×N), and the generation of harmonics due to carrier waves being in phase can be suppressed.

[0040] Furthermore, the number N of converter unit groups in an arm is also determined in advance and does not change during operation of the power conversion device. Therefore, if the second phase shift amount φb (=φa / N [rad]) is stored in advance in the gate control unit 126 along with the value of the first phase shift amount φa (=2π / M [rad]), each carrier wave generation unit 1262 in the arm can generate a reference phase for each carrier wave based on the carrier wave reference phase θc received from the control device 20. This makes it possible to reduce the amount of data transmitted from the control device 20.

[0041] Furthermore, if a failure or abnormality occurs in any of the converter unit groups 120, or if a failure or abnormality occurs in any of the converter unit 122 within the converter unit group 120 and the bypass switch 128 of the converter unit group including the failed or abnormal converter unit 122 is turned on, it is only necessary to change the phase shift amount between the converter unit groups, taking into account the number of converter unit groups for which the bypass switch 128 has been turned on. In other words, if the number of converter unit groups for which the bypass switch 128 has been turned on is 1, the new φb can be simply changed by φa / (N-1). At this time, there is no need to change the first phase shift amount φa within the converter unit group, and therefore the amount of data to be changed can be reduced.

[0042] As described above, according to the power conversion device of the first embodiment, in an MMC having a gate control unit 126 for each of the converter unit groups 120 to which a plurality (M) of converter unit groups 122 are connected, and a power converter 10 having a plurality of arms to which a plurality (N) of converter unit groups 120 are connected in series, and a control device 20 that controls the power converter 10, a triangular wave carrier k ｃａｒ Since the phases of the triangular wave carriers k i are all shifted relative to the semiconductor switching elements of the multiple converter elements 122 that make up the arms, it is possible to output voltage and current with little harmonic distortion. Within the converter element group 120, each carrier wave generating unit 1262 of the gate control unit 126 can easily generate reference phases that are sequentially shifted by 2π / M based on the carrier reference phase θc received from the control device 20, and triangular wave carriers k i that are shifted in phase by 2π / M are generated.ｃａｒ i are sequentially transmitted to the gate signal generator 1264. Between the switching element groups 120, a reference phase is generated that is shifted by a phase obtained by dividing 2π / M by the number N of switching element groups. Therefore, if the control device 20 transmits a carrier reference phase θc for each arm, and based on that, using the predetermined number M of switching element 122 and the number N of switching element groups 120, triangular wave carriers of different phases can be generated for the switching element groups in the arms with a small number of signals. Therefore, it is possible to output voltages and currents with little harmonic distortion with a simple configuration, without increasing the size of the control device 20.

[0043] The number of signals to be reduced is not limited to the carrier reference phase θc. Since a gate control unit 126 is provided for each converter group 120, the arm modulation command k ｒｅｆ , arm current detection value i ａｒｍ and the average capacitor voltage vc in the arm ａｒｍ This makes it possible to reduce the amount of data transmitted compared to the past, since the data only needs to be sent for each unit converter group 120. In other words, the amount of data can be significantly reduced compared to sending data for each gate driver of each unit converter, and the occurrence of data delays and the like can also be reduced.

[0044] Furthermore, since a gate control section 126 is provided for each switching element group 120, maintenance and testing can be carried out for each switching element group 120.

[0045] Furthermore, in the explanation of FIGS. 9 and 10, the carrier wave is a triangular wave, but it is not limited to a triangular wave and may be a sawtooth wave or the like.

[0046] Second Embodiment A power conversion device according to a second embodiment will be described below with reference to the drawings. In the power conversion device according to the second embodiment, a method of generating a carrier wave and a configuration of the unit converter group that are different from those of the first embodiment will be described for an example in which the number of unit converters included in the unit converter group is two (M=2).

[0047] FIG. 11 shows the phase shift of the triangular wave carrier k for explaining the phase shift of the carrier when the number of unit converters M in the unit converter group 120 is 2. ｃａｒ11 is a waveform diagram of the first carrier k. FIG. 11 corresponds to the diagram in FIG. 9 where M=2. When the number of unit converters M=2, the two carriers become triangular wave carriers with a phase difference of 180° (π), which is a half cycle. Therefore, the first carrier k is ｃａｌ By subtracting the value of 1, the second carrier k ｃａｒ 2 can be generated.

[0048] Fig. 12 is a diagram showing the configuration of a gate control unit 126 in a converter unit group 120 in a power conversion device according to embodiment 2. In comparison with Figs. 7 and 8, in Fig. 12, the converter unit group does not have two carrier wave generation units, the same number as the number of converter unit M, but only has one carrier wave generation unit 1262. In Fig. 12, the carrier wave generation unit 1262 generates a triangular wave carrier k based on the carrier frequency fc and carrier reference phase θc transmitted from the control device 20. ｃａｒ Generate 1. Generated triangular wave carrier k ｃａｒ The triangular wave carrier k output from the adder 1268 is then sent to the first gate signal generator 1264_1 and input to the adder 1268, where it is subtracted from the value of the apex CarTop of the triangular wave carrier. ｃａｒ 2 is the triangular wave carrier k ｃａｒ The phase of the signal is shifted by 180° from that of the signal 1 and is sent to the second gate signal generating unit 1264_2.

[0049] In the second embodiment, when the capacitor voltage vci of each unit converter 122 in the unit converter group 120 varies, the capacitor voltage vci is set to the average capacitor voltage vc ａｒｍ The capacitor voltage vci and the average capacitor voltage vc in the arm are adjusted so as to approach ａｒｍ deviation from the arm current detection value i ａｒｍ Using the arm modulation command k ｒｅｆ and modulating command k of each unit converter. ｒｅｆ 12 may also be configured to use the balance control section 1266 as in FIG.

[0050] Next, an example in which the number of unit converters included in the unit converter group is two (M=2), and the configuration of the unit converter group different from that shown in the first embodiment will be described with reference to FIG.

[0051] 13, in the switching element group 120D, the N terminal of switching element 122_1 is connected to the P terminal of switching element 122_2, as shown by the dashed oval. In other words, the potential is shared in the portion that is not an AC terminal, making it possible to miniaturize the device. The rest of the configuration is the same as in FIGS. 4 to 6 of embodiment 1, so a description thereof will be omitted.

[0052] As described above, according to the power conversion device of embodiment 2, in addition to the effects of embodiment 1, when the number of unit converters 122 in the unit converter group 120 is two, there is no need to provide two carrier wave generating units 1262 in the gate control unit 126 of each unit converter group 120, the same number as the unit converters 122, and only one is required, and calculations can be performed using the adder 1268, which simplifies the device configuration and reduces the amount of calculations.

[0053] Furthermore, when the number of unit converters in a unit converter group is two (M=2), the potential can be shared in the parts that are not AC terminals in the configuration within the unit converter group, further contributing to the miniaturization of the device. Therefore, it is possible to provide a power conversion device equipped with a modular multilevel converter (MMC) that supports large-capacity power conversion, and that is capable of outputting voltage and current with little harmonic distortion with a simple configuration without increasing the size of the control device.

[0054] An example of the hardware configuration of the control device 20 in the first and second embodiments is shown in Fig. 14. As shown in Fig. 14, the control device 20 includes, for example, a processor 1000 and a storage device 1100 as processing circuits. The processor 1000 may include a central processing unit (CPU), an application specific integrated circuit (ASIC), an integrated circuit (IC), a field programmable gate array (FPGA), various logic circuits, various signal processing circuits, etc. Furthermore, a plurality of processors 1000 of the same type or different types may be provided, and each process may be shared and executed. The storage device 1100 includes a RAM (Random Access Memory) configured to be able to read and write data from the processor 1000, and a ROM (Read Only Memory) configured to be able to read data from the processor 1000. The processor 1000 executes a program input from the storage device 1100 such as a ROM.

[0055] Similarly to the control device 20, the gate control section 126 also has the hardware configuration shown in FIG. 14, and executes a program for generating signals for driving and controlling the gates.

[0056] <Other Embodiments> (1) Although the semiconductor switching elements SWp and SWn constituting the unit converter 122 are IGBTs (Insulated Gate Bipolar Transistors) as an example of the switching elements, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) may also be used.

[0057] (2) The semiconductor switching element is not limited to one made of a silicon (Si) semiconductor, but may be made of a wide bandgap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN). Wide bandgap semiconductors are suitable for application to MMCs due to their characteristics such as faster switching speeds, high temperature operation, and high dielectric breakdown field strength.

[0058] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0059] 1: AC power supply, 2: Current sensor, 3: Voltage sensor, 4: Transformer, 6P: Positive DC terminal, 6N: Negative DC terminal, 10: Power converter, 12, 12pu, 12nu, 12pv, 12nv, 12pw, 12nw: Arm, 14p, 14n: Voltage sensor, 20: Control device, 12L: Reactor, 12di: Current sensor, 120, 120_1, 120_2, 120_3, 120_k, 120_N, 120A, 120B, 120C, 120D: Unit converter group, 122, 122_1, 122_2, 122_3, 122_4, 122_i: Unit converter, 124, 124_1: Voltage sensor, 126: Gate control unit, 128: Bypass switch, 1261, 1261_2, 1268: Adders, 1262, 1262_1, 1262_2, 1262_i, 1262_M: Carrier wave generating units, 1264, 1264_1, 1264_2, 1264_i: Gate signal generating units, 1266, 1266_i: Balance control units, 1000: Processor, 1100: Storage device, Vac: AC voltage, Vdc: DC voltage, Iac: AC current, vc: Capacitor voltage value, k ｒｅｆ , k ｒｅｆi: arm modulation command, vc ａｒｍ : average capacitor voltage in arm, i ａｒｍ : arm current detection value, θc: carrier reference phase, fc: carrier frequency, k ｃａｒ 1, k ｃａｒ 2, k ｃａｒ i: triangular wave carrier; GDpi, GDni: gate drivers; giP, giN: gate signals; SWp, SWpi, SWn, SWni: semiconductor switching elements; u, v, w: connection points; φa: first phase shift amount; φb: second phase shift amount.

Claims

1. A power converter including a plurality of arms in which a plurality of unit converter groups are connected in series, and a control device that controls the power converter, the unit converter includes a series body in which two switching elements are connected in series, and a capacitor connected in parallel to the series body, the switching element group has a gate control unit that generates a gate signal that controls on / off of a plurality of the switching elements in the switching element group, the gate control unit includes a carrier wave generation unit that generates a plurality of carrier waves corresponding to the number of the unit converters in the unit converter group, and a gate signal generation unit that compares a modulation command received from the control device with the carrier wave generated by the carrier wave generation unit and generates a gate signal based on the comparison result; a power conversion device in which the phases of the multiple carrier waves generated by the carrier wave generating unit are shifted by a first phase shift amount, which is a value obtained by equally dividing one period of the carrier wave by the number of unit converters in the unit converter group, based on a carrier reference phase received from the control device, and between the unit converter groups in the arm, the first phase shift amount is shifted by a second phase shift amount, which is a value obtained by equally dividing the first phase shift amount by the number of unit converter groups in the arm, based on the carrier reference phase received from the control device.

2. Each of the converter units has one bypass switch, The bypass switch is connected between a terminal of the unit converter located at one end of the unit converter group and a terminal of the unit converter located at the other end, When a failure or abnormality occurs in any of the unit converters in the unit converter group, turning on the bypass switch of the unit converter group including the unit converter in which the failure or abnormality occurs; 2. The power conversion device according to claim 1, wherein the second phase shift amount is calculated using a number obtained by subtracting the number of the converter unit groups in which the bypass switch is closed from the number of the converter unit groups in the arm.

3. The unit converter group includes two of the unit converters, a first carrier wave, which is one of the two carrier waves generated by the carrier wave generating unit, is a triangular wave generated based on the carrier wave reference phase and a carrier wave frequency received from the control device; The power conversion device according to claim 1 , wherein a second carrier wave that is the other carrier wave is generated by subtracting a value of the first carrier wave from a peak value of the first carrier wave.

4. The unit converter group has two of the unit converters, a first carrier wave, which is one of the two carrier waves generated by the carrier wave generating unit, is a triangular wave generated based on the carrier wave reference phase and a carrier wave frequency received from the control device; The power conversion device according to claim 2 , wherein a second carrier wave that is the other carrier wave is generated by subtracting a value of the first carrier wave from a peak value of the first carrier wave.

5. The power conversion device according to claim 3 or 4, wherein the group of unit converters includes two unit converters, an N terminal of one of the unit converters and a P terminal of the other of the unit converters being connected as a common terminal.

6. The unit converter includes a voltage sensor for detecting a voltage of a capacitor included in the unit converter, the gate control unit further includes balance control units, the number of which corresponds to the number of the converter units included in the converter unit group, Each of the balance control units is outputting a modulation command balance correction amount obtained by comparing the voltage of the capacitor of the unit converter with the average voltage value of the capacitor in the arm in correspondence with the unit converter, and calculating a corrected modulation command obtained by adding the modulation command balance correction amount to the modulation command received from the control device; the gate signal generation unit compares the corrected modulation command with the carrier wave and outputs the gate signal based on the result of the comparison. The power conversion device according to claim 1 .

7. The power conversion device according to claim 1 , wherein the gate control section is provided for each of the converter unit groups.

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