Power converter

Abstract

This electric power conversion apparatus (2) comprises an electric power converter (3) and a control device (4). The control device (4) comprises: a first electric current command calculation unit (24) that calculates a first electric current command value on the basis of voltage representative values and DC voltage command values of all electric power storage elements (10); an electric power calculation unit (23) that calculates unbalanced components of the output electric power from arms; a first electric power command calculation unit (27) that calculates unbalanced component command values so that the voltage values of the electric power storage elements are balanced among the arms; a phase electric current command calculation unit (28) that generates an electric current command value for each phase on the basis of the unbalanced components and the unbalanced component command values; a second electric current command calculation unit (30) that calculates a second electric current command value on the basis of the output voltage representative values and the electric current command value for each phase; a voltage command generation unit (35) that generates an output voltage command value for each unit converter on the basis of the output electric current, the first electric current command value, and the second electric current command value; and a gate signal generation unit (70) that generates a control signal for each switching element, on the basis of the output voltage command value.

Description

Technical Field

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

Background Art

[0002] As a large-capacity power conversion device installed in a power system, a modular multilevel converter (MMC) is known. The MMC is composed of arms in which a plurality of unit converters called cells are cascade-connected. Each cell includes a plurality of semiconductor switches and a DC capacitor, and by turning on and off the semiconductor switches, the voltage across the DC capacitor or zero voltage is output.

[0003] One of the methods for configuring the arm connection of a three-phase MMC is the delta connection method. A three-phase MMC with a delta connection cascade method (hereinafter also referred to as "delta connection MMC") has a configuration in which a plurality of cells are cascade-connected and the arms with reactors connected in series are delta-connected.

[0004] In the delta connection MMC, in order to keep the voltage of the energy storage element within a certain range, the first voltage control for keeping the representative voltage value of the energy storage elements of all cells constant and the second voltage control for suppressing the variation of the representative voltage value of the energy storage elements of the cells included in each arm between the arms are performed.

[0005] However, when the voltage of the three-phase AC power supply fluctuates or the three-phase AC voltage is unbalanced, the first voltage control and the second voltage control interfere with each other, which may prevent the stable operation of the delta connection MMC. In Patent Document 1 (International Publication No. 2018 / 211624), it is considered to make the first voltage control and the second voltage control non-interfering by removing the control amount of the first voltage control from the control amount of the second voltage control.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, when the voltage of the three-phase AC power supply fluctuates or the three-phase AC voltage is unbalanced, there is a problem in the first voltage control and the second voltage control where interference occurs in the active power output generated by the output current controlled according to the current command value, which is the respective manipulated variable.

[0008] Specifically, active power is output through the interaction between the output current, which follows a three-phase balanced current command value, and the three-phase unbalanced voltage, controlled by the first voltage control (i.e., control that maintains a constant voltage representative value for the energy storage elements of all cells). This active power corresponds to the "unbalanced active power between each arm" that the second voltage control is trying to control, and therefore becomes a disturbance to the second voltage control.

[0009] Furthermore, the second voltage control (i.e., a control that suppresses variations in the typical voltage values ​​of the energy storage elements in the cells included in each arm) outputs active power through the interaction between the output current, which follows the three-phase unbalanced current command value, and the three-phase unbalanced voltage. This active power corresponds to the "active power common to each arm" that the first voltage control is trying to control, and therefore becomes a disturbance to the first voltage control.

[0010] One objective in a part of this disclosure is to ensure stable operation of a three-phase MMC in a power converter equipped with a delta-connected cascade configuration when there are voltage fluctuations in the three-phase AC power supply or when the three-phase AC voltage is unbalanced. [Means for solving the problem]

[0011] According to one embodiment, a power converter connected to a three-phase AC power supply is provided. The power converter comprises a power converter including three delta-connected arms and a control device for controlling the power converter. Each of the three arms is configured by connecting a plurality of unit converters in series. Each of the plurality of unit converters includes a plurality of switching elements and energy storage elements connected to the plurality of switching elements. The control device includes a first current command calculation unit that calculates a first current command value for the power converter based on a voltage representative value and a DC voltage command value that represent the voltage values ​​of all the energy storage elements included in the power converter; a power calculation unit that calculates the unbalanced component of the output power of each of the three arms based on the output current representative value and output voltage representative value of the cell group including each unit converter included in the arm; a first power command calculation unit that calculates an unbalanced component command value of the output power of each arm so that the voltage values ​​of the energy storage elements are balanced among the three arms; and the unbalanced component of the output power of each arm and each arm The power converter includes: a phase current command calculation unit that generates current command values ​​for each phase based on the unbalanced component command value of the output power; a second current command calculation unit that calculates a second current command value for the power converter based on the representative output voltage value of the cell group included in each arm and the current command value of each phase; a voltage command generation unit that generates an output voltage command value for controlling the output voltage of each unit converter based on the output current of the power converter and the current command value calculated from the first current command value and the second current command value; and a gate signal generation unit that generates control signals for each switching element included in the power converter based on the output voltage command value. [Effects of the Invention]

[0012] According to this disclosure, in a power converter equipped with a delta-connected cascade type three-phase MMC, the operation of the three-phase MMC can be made stable even when there are voltage fluctuations in the three-phase AC power supply or when the three-phase AC voltage is unbalanced. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram illustrating an example of the overall configuration of a power conversion device. [Figure 2] This figure shows an example of the arm configuration. [Figure 3] It is a diagram showing a configuration example of a cell. [Figure 4] It is a block diagram showing an example of the functional configuration of a control device. [Figure 5] It is a block diagram showing a configuration example of a DC voltage control unit 20 according to Embodiment 1. [Figure 6] It is a block diagram showing a configuration example of an output power calculation unit. [Figure 7] It is a block diagram showing a configuration example of a total control power command calculation unit. [Figure 8] It is a block diagram showing a configuration example of a phase control power command calculation unit. [Figure 9] It is a block diagram showing a configuration example of a phase control current command calculation unit. [Figure 10] It is a block diagram showing a configuration example of a current command conversion unit. [Figure 11] It is a block diagram showing a configuration example of a current command calculation unit. [[ID=z7]] [Figure 12] It is a block diagram showing a configuration example of a current control unit. [Figure 13] It is a block diagram showing a configuration example of a phase voltage command calculation unit. [Figure 14] It is a block diagram showing a configuration example of a cell DC voltage control unit. [Figure 15] It is a block diagram showing a configuration example of a DC voltage control unit according to Embodiment 2. [Figure 16] It is a block diagram showing a configuration example of an output power calculation unit according to Embodiment 2. [Figure 17] It is a block diagram showing a configuration example of a total control current command calculation unit according to Embodiment 2. [Figure 18] It is a diagram showing a configuration example of a phase control current command calculation unit according to Embodiment 3. [Figure 19] It is a diagram showing a configuration example of a phase control current command calculation unit according to a modification of Embodiment 3.

Modes for Carrying Out the Invention

[0014] This embodiment will be described below with reference to the drawings. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0015] [Basic configuration of each embodiment] <Overall Structure> Figure 1 is a diagram illustrating an example of the overall configuration of the power converter 2. The power converter 2 is connected to a three-phase AC power supply 1. The power converter 2 includes a power converter 3 configured as an MMC and a control device 4 for controlling the power converter 3. The power converter 3 includes a transformer 5a, a voltage detector 5s, current detectors 6uv, 6vw, 6wu, and three arms 7uv, 7vw, 7wu (hereinafter sometimes collectively referred to as "arm 7"). Each arm 7 is configured by connecting multiple unit converters in series.

[0016] One three-phase terminal of transformer 5a is connected to the three-phase AC power supply 1, and the other three-phase terminal of transformer 5a is connected to one terminal of power lines L2u, L2v, and L2w.

[0017] Arm 7uv is connected between the other terminal of power line L2u and the other terminal of power line L2v. Arm 7vw is connected between the other terminal of power line L2v and the other terminal of power line L2w. Arm 7wu is connected between the other terminal of power line L2w and the other terminal of power line L2u. Thus, arms 7uv, 7vw, and 7wu are connected in a delta connection.

[0018] The voltage detector 5s detects the voltages Vuv, Vvw, and Vwu of the three-phase AC power supply 1. The current detector 6uv is located on the power line L2u and detects the current flowing through arm 7uv (hereinafter referred to as "arm current Iuv"). The current detector 6vw is located on the power line L2v and detects the current flowing through arm 7vw (hereinafter referred to as "arm current Ivw"). The current detector 6wu is located on the power line L2w and detects the current flowing through arm 7wu (hereinafter referred to as "arm current Iwu"). The detected voltages Vuv, Vvw, and Vwu, and arm currents Iuv, Ivw, and Iwu are input to the control device 4.

[0019] In Figure 1, the power converter 3 is connected to the three-phase AC power supply 1 via a transformer 5a, but it may also be configured to be connected to the three-phase AC power supply 1 via an interconnection reactor instead of the transformer 5a.

[0020] Figure 2 shows an example of the arm configuration. Since the configurations of arms 7uv, 7vw, and 7wu are similar, we will refer to one arm as arm 7 for explanation.

[0021] Referring to Figure 2, arm 7 is connected between two terminals 7a and 7b. Arm 7 has multiple cells 9 connected in series. Each of the multiple cells 9 performs bidirectional power conversion according to the gate signal Sg from the control device 4. In this embodiment, n cells 9 (where n is an integer of 2 or more) are connected in series in each of the three arms 7uv, 7vw, and 7wu. Therefore, the total number of cells 9 included in the power converter 3 is 3n. Note that the number of cells 9 included in each of arms 7uv, 7vw, and 7wu does not need to be equal; it is sufficient if there are more than the minimum number required for the operation of the power converter 2. Therefore, the total number of cells 9 included in the power converter 3 is not limited to 3n.

[0022] Arm 7 further includes a reactor 8 connected in series with multiple cells 9. The reactor 8 is positioned to suppress circulating currents flowing within the delta connection. Thus, arm 7 is composed of a group of cells including multiple cells 9 and the reactor 8.

[0023] Figure 2 shows a configuration in which the reactor 8 is inserted between output terminal 9a and terminal 7a, but the configuration is not limited to this. The reactor 8 can be connected in series at any position in the power line connecting terminals 7a, 7b and the n cells 9. Also, although the example in Figure 2 shows a configuration in which one reactor 8 is included for one arm 7, the reactor 8 can be connected to at least one of the arms 7uv, 7vw, and 7wu, and the arm to which it is connected can be arbitrarily selected.

[0024] Figure 3 shows an example of a cell configuration. Referring to Figure 3, cell 9 according to the first configuration example has a so-called full-bridge configuration. Specifically, cell 9 includes an energy storage element 10, a voltage detector 11, switching elements Q1 to Q4, diodes D1 to D4, and a pair of output terminals 9a and 9b.

[0025] One terminal and the other terminal of the energy storage element 10 are connected to a positive electrode wire 10P and a negative electrode wire 10N, respectively. The energy storage element 10 is, for example, a capacitor that stores DC power. The voltage detector 11 detects the DC voltage between the terminals of the energy storage element 10 (hereinafter also simply referred to as "voltage Vdccell") and outputs a signal indicating the detected voltage Vdccell to the control device 4.

[0026] The switching elements Q1 to Q4 are self-extinguishing power semiconductor elements, such as IGBTs (Insulated Gate Bipolar Transistors). The switching elements Q1 to Q4 are connected to the energy storage element 10 via a positive electrode wire 10P and a negative electrode wire 10N.

[0027] Switching elements Q1 and Q2 are connected in series between the power line pair (i.e., the positive terminal 10P and the negative terminal 10N). Switching elements Q3 and Q4 are connected in series between the power line pair. Specifically, one terminal of switching elements Q1 and Q3 is connected to the positive terminal 10P, and the other terminals of switching elements Q1 and Q3 are connected to output terminals 9a and 9b, respectively. One terminal of switching elements Q2 and Q4 is connected to the negative terminal 10N, and the other terminals of switching elements Q2 and Q4 are connected to output terminals 9a and 9b, respectively. Diodes D1 to D4 are connected in antiparallel to switching elements Q1 to Q4, respectively.

[0028] Cell 9 controls the on and off (i.e., switching operation) of switching elements Q1 to Q4 based on the gate signal Sg from the control device 4. Depending on the switching operation of switching elements Q1 to Q4, Cell 9 outputs a voltage with the same polarity as the voltage of the energy storage element 10, a voltage with the opposite polarity, or zero voltage as the cell voltage Vcell between output terminals 9a and 9b.

[0029] Cell 9 according to the second configuration example has a so-called half-bridge configuration, rather than the full-bridge configuration shown in Figure 3. Cell 9 according to the second configuration example has the switching elements Q3 and Q4 and diodes D3 and D4 removed from cell 9 according to the first configuration example shown in Figure 3, and the connection position of output terminal 9b has been changed to the negative terminal line 10N. Cell 9 according to the second configuration example controls the on and off (i.e., switching operation) of switching elements Q1 and Q2 based on the gate signal Sg, thereby outputting a voltage with the same polarity as the voltage of the energy storage element 10, or a zero voltage, as the cell voltage Vcell between output terminals 9a and 9b.

[0030] The configuration of cell 9 shown in Figure 2 is not limited to the first and second configuration examples. The configuration of cell 9 is limited to a series circuit of multiple (for example, two) switching elements and a capacitor connected in parallel to this series circuit, and is configured to selectively output voltages between output terminals 9a and 9b according to the switching operation of the multiple switching elements.

[0031] Referring again to Figure 1, the control device 4 controls the operation of arms 7uv, 7vw, and 7wu (i.e., each of the 3n cells 9) using commands from a higher-level device (not shown) and detection signals input from each detector.

[0032] The control device 4 can be configured, for example, with a microcomputer. As an example, the control device 4 may include a memory and CPU (C) (not shown). entral Processing Unit) The following control operations can be performed through software processing, where the CPU executes a program pre-stored in memory.

[0033] Furthermore, it is also possible to configure at least a portion of the control device 4 using circuits such as FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit).

[0034] <Functional Configuration of Control Device> Figure 4 is a block diagram showing an example of the functional configuration of the control device. The functions of each block shown in Figure 4 can be realized by software processing and / or hardware processing by the control device 4.

[0035] Referring to Figure 4, the control device 4 receives inputs of voltages Vuv, Vvw, Vwu detected by the voltage detector 5s, arm currents Iuv, Ivw, Iwu detected by the current detectors 6uv, 6vw, 6wu, and the voltage Vdccell of the energy storage element 10 detected by the voltage detector 11. The control device 4 calculates the gate signal Sg using the control calculations shown in Figure 4 and outputs it to the cell 9. Note that there are voltages Vdccell and gate signals Sg corresponding to each cell 9, and the number of signals is equal to the number of cells 9 (for example, 3n). Specifically, the control device 4 includes a DC voltage control unit 20, a current command calculation unit 30, a voltage command generation unit 35, and a gate signal generation unit 70.

[0036] The DC voltage control unit 20 accepts inputs of voltages Vcuv, Vcvw, Vcwu, currents Icuv, Icvw, Icwu, ​​voltage Vdccell, and DC voltage command value Vdc*. Based on each of the input parameters, the DC voltage control unit 20 calculates the first q-axis current command value I1q*, the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz*.

[0037] Voltages Vcuv, Vcvw, and Vcwu are representative output voltage values ​​of the cell groups included in arms 7uv, 7vw, and 7wu, respectively. For example, voltages Vcuv, Vcvw, and Vcwu are voltages Vuv, Vvw, and Vwu, respectively. Alternatively, voltages Vcuv, Vcvw, and Vcwu may be the voltages Vuv, Vvw, and Vwu plus the voltage drop due to components of power converter 2 other than the cell groups, which is calculated from at least a portion of the current command values ​​I0d*, I0q*, I1q*, I2d*, I2q*, and Iz*.

[0038] The currents Icuv, Icvw, and Icwu are representative output current values ​​for the cell groups included in arms 7uv, 7vw, and 7wu, respectively. For example, currents Icuv, Icvw, and Icwu are arm currents Iuv, Ivw, and Iwu, respectively. Alternatively, currents Icuv, Icvw, and Icwu may be values ​​calculated from at least some of the current command values ​​I0d*, I0q*, I1q*, I2d*, I2q*, and Iz*.

[0039] The DC voltage command value Vdc* may be input from a higher-level device (not shown), may be predetermined in the control device 4, or may be obtained from a prescribed calculation by a DC voltage command calculation unit (not shown).

[0040] The current command calculation unit 30 calculates the d-axis current command value Idr* and the q-axis current command value Iqr* of the power converter 3 based on the reference d-axis current command value I0d*, the reference q-axis current command value I0q*, the first q-axis current command value I1q*, the second d-axis current command value I2d*, and the second q-axis current command value I2q*.

[0041] The reference d-axis current command value I0d* and reference q-axis current command value I0q* are the reference command values ​​for the d-axis current and q-axis current output from the power converter 3. The reference d-axis current command value I0d* and reference q-axis current command value I0q* may be input from a higher-level device (not shown) or may be predetermined in the control device 4. Alternatively, the reference d-axis current command value I0d* and reference q-axis current command value I0q* may be obtained from prescribed calculations performed by a d-axis current calculation unit and a q-axis current calculation unit (not shown), respectively. Note that if the control of active power exchange with the three-phase AC power supply 1 is not included in the use of the power converter 2, except for the purpose of maintaining the voltage Vdccell of the energy storage element 10 within a certain range, the reference q-axis current command value I0q* may not be used.

[0042] The voltage command generation unit 35 generates cell voltage command values ​​Vcell* for controlling the output voltage of each cell 9. Specifically, the voltage command generation unit 35 includes a current control unit 40, a phase voltage command calculation unit 50, and a DC voltage control unit 60 for each cell.

[0043] The current control unit 40 calculates the d-axis voltage command value Vd*, the q-axis voltage command value Vq*, and the zero-sequence voltage command value Vz* based on the d-axis current command value Idr*, the q-axis current command value Iqr*, the zero-sequence current command value Iz*, the voltages Vuv, Vvw, Vwu, and the arm currents Iuv, Ivw, Iwu.

[0044] The phase voltage command calculation unit 50 calculates the phase voltage command values ​​Vuv*, Vvw*, and Vwu* based on the d-axis voltage command value Vd*, the q-axis voltage command value Vq*, and the zero-sequence voltage command value Vz*.

[0045] The cell DC voltage control unit 60 calculates the cell voltage command value Vcell* for each cell 9 included in the power converter 3 based on the phase voltage command values ​​Vuv*, Vvw*, Vwu*, the arm currents Iuv, Ivw, Iwu, and the voltage Vdccell of each energy storage element 10.

[0046] The gate signal generation unit 70 generates a gate signal Sg based on the cell voltage command value Vcell* of each cell 9. Specifically, the gate signal generation unit 70 performs PWM control based on each of the 3n cell voltage command values ​​Vcell* calculated by the DC voltage control unit 60 for each cell, and generates a gate signal Sg to control the on / off state of the switching elements Q1 to Q4 of each cell 9 included in the power converter 3.

[0047] The configurations of the DC voltage control unit 20, the current command calculation unit 30, and the voltage command generation unit 35 will be described in more detail below.

[0048] Embodiment 1. <DC Voltage Control Unit> Figure 5 is a block diagram showing an example configuration of a DC voltage control unit 20 according to Embodiment 1. Referring to Figure 5, the DC voltage control unit 20 includes an output power calculation unit 23, a total control power command calculation unit 24, a phase control power command calculation unit 27, a phase control current command calculation unit 28, and a current command conversion unit 29.

[0049] The output power calculation unit 23 calculates the unbalanced components P2uv, P2vw, P2wu of the output power (i.e., active power) of arms 7uv, 7vw, 7wu based on the currents Icuv, Icvw, Icwu and the voltages Vcuv, Vcvw, Vcwu.

[0050] Figure 6 is a block diagram showing an example configuration of the output power calculation unit. Referring to Figure 6, the output power calculation unit 23 includes multipliers 231u, 231v, 231w, filters 232u, 232v, 232w, adder 233, arithmetic unit 233a, and subtractors 234u, 234v, 234w.

[0051] Multiplier 231u outputs the product of the input voltage Vcuv and current Icuv. Filter 232u outputs Pcuv, which is the output value of multiplier 231u minus the frequency component 2f, which is twice the voltage frequency of the three-phase AC power supply 1. Multiplier 231v outputs the product of the input voltage Vcvw and current Icvw. Filter 232v outputs Pcvw, which is the output value of multiplier 231v minus the frequency component 2f. Multiplier 231w outputs the product of the input voltage Vcwu and current Icwu. Filter 232w outputs Pcwu, which is the output value of multiplier 231w minus the frequency component 2f. Moving average filters with a period of half the voltage period of the three-phase AC power supply 1 can be used as filters 232u, 232v, and 232w.

[0052] The adder 233 calculates the sum of the values ​​Pcuv, Pcvw, and Pcwu. The arithmetic unit 233a calculates the average value Pcav of the values ​​Pcuv, Pcvw, and Pcwu by multiplying the sum by 1 / 3.

[0053] Subtractor 234u calculates the unbalanced component P2uv by subtracting the average value Pcav from the value Pcuv. Subtractor 234v calculates the unbalanced component P2vw by subtracting the average value Pcav from the value Pcvw. Subtractor 234w calculates the unbalanced component P2wu by subtracting the average value Pcav from the value Pcwu.

[0054] In this way, the output power calculation unit 23 calculates the unbalanced component of the output power of each of the three arms 7uv, 7vw, and 7wu (e.g., P2uv, P2vw, P2wu) based on the typical output voltage values ​​(e.g., voltage Vcuv, Vcvw, Vcwu) and typical output current values ​​(e.g., current Icuv, Icvw, Icwu) of the cell group included in that arm.

[0055] Referring again to Figure 5, the total control power command calculation unit 24 calculates the total phase active power command value Pall* based on the voltage Vdccell and the DC voltage command value Vdc*. In Embodiment 1, the total control power command calculation unit 24 outputs the total phase active power command value Pall* as the first q-axis current command value I1q*. The total control power command calculation unit 24 according to Embodiment 1 functions as a "first current command calculation unit" that calculates the first q-axis current command value I1q*.

[0056] Figure 7 is a block diagram showing an example configuration of the total control power command calculation unit 24. Referring to Figure 7, the total control power command calculation unit 24 includes a representative value calculation unit 241, a subtractor 242, and a controller 243.

[0057] The representative value calculation unit 241 calculates a representative voltage value Vdccell that represents the voltage of all cells 9 included in each arm 7uv, 7vw, 7wu (i.e., the 3n cells 9 included in the power converter 3). The representative voltage value can be set to, for example, the average, maximum, or minimum value of the voltage Vdccell of all cells 9.

[0058] The subtractor 242 outputs a value obtained by subtracting the voltage representative value from the DC voltage command value Vdc* (i.e., the deviation between Vdc* and the voltage representative value). The controller 243 performs a control calculation to make this deviation zero (i.e., so that the voltage representative value follows the DC voltage command value Vdc*), calculates the all-phase active power command value Pall*, and outputs this as the first q-axis current command value I1q*.

[0059] In this way, the total control power command calculation unit 24 performs a first voltage control to keep the typical voltage value of all cells 9, Vdccell, constant (for example, to make the typical voltage value follow the DC voltage command value Vdc*), and generates the total phase active power command value Pall* (here, the first q-axis current command value I1q*). That is, the total control power command calculation unit 24 generates the first q-axis current command value I1q* to keep the typical voltage value constant.

[0060] Referring again to Figure 5, the phase control power command calculation unit 27 calculates the unbalanced component command values ​​P2uv*, P2vw*, and P2wu* of the output power of arms 7uv, 7vw, and 7wu based on the voltage Vdccell. Specifically, the phase control power command calculation unit 27 calculates the unbalanced component command values ​​P2uv*, P2vw*, and P2wu* so that the voltage Vdccell of the energy storage element 10 is balanced among the three arms 7uv, 7vw, and 7wu.

[0061] Figure 8 is a block diagram showing an example configuration of the phase control power command calculation unit 27. Referring to Figure 8, the phase control power command calculation unit 27 includes a representative value calculation unit 271, subtractors 272u, 272v, 272w, and controllers 273u, 273v, 273w.

[0062] The representative value calculation unit 271 performs a prescribed representative value calculation to calculate the representative value Vdcuv of the voltage Vdccell of each cell 9 included in arm 7uv, the representative value Vdcvw of the voltage Vdccell of each cell 9 included in arm 7vw, and the representative value Vdcwu of the voltage Vdccell of each cell 9 included in arm 7wu. As an example, the calculation method for the representative value Vdcuv will be described. The representative value calculation unit 271 calculates the average, maximum, or minimum value of the voltage Vdccell of each cell 9 included in arm 7uv, and calculates the representative value Vdcuv by removing the fluctuation from the calculated value. The process of removing the fluctuation from the calculated value uses a moving average filter with a period of 1 / 2 the voltage period of the three-phase AC power supply 1. The same method is used for calculating the representative values ​​Vdcvw and Vdcwu.

[0063] Furthermore, the representative value calculation unit 271 calculates the three-phase equilibrium component Vdcall of the representative values ​​Vdcuv, Vdcvw, and Vdcwu. The three-phase equilibrium component Vdcall is, for example, the average value of the representative values ​​Vdcuv, Vdcvw, and Vdcwu.

[0064] The subtractor 272u calculates the deviation between the three-phase balanced component Vdcall and the representative value Vdcuv (i.e., Vdcall - Vdcuv). The controller 273u performs a control operation to make the deviation calculated by the subtractor 272u zero (i.e., so that the representative value Vdcuv follows the three-phase balanced component Vdcall) and calculates the unbalanced component command value P2uv*.

[0065] The subtractor 272v calculates the deviation between the three-phase equilibrium component Vdcall and the representative value Vdcvw (i.e., Vdcall - Vdcvw). The controller 273v performs a control calculation to set the deviation calculated by the subtractor 272v to zero, and calculates the unequilibrium component command value P2vw*.

[0066] decrease The calculator 272w calculates the deviation between the three-phase equilibrium component Vdcall and the representative value Vdcwu (i.e., Vdcall - Vdcwu). The controller 273w performs a control calculation to zero out the deviation calculated by the subtractor 272w and calculates the unequilibrium component command value P2wu*.

[0067] In this way, the phase control power command calculation unit 27 performs a second voltage control to suppress variations between arms in the representative value of the voltage Vdccell of each cell 9 included in each arm 7 (for example, by making the representative values ​​Vdcuv, Vdcvw, Vdcwu follow the three-phase balanced component Vdcall), and generates unbalanced component command values ​​P2uv*, P2vw*, P2wu*.

[0068] Referring again to Figure 5, the phase control current command calculation unit 28 calculates the current command values ​​I2uv*, I2vw*, I2wu* for each phase based on the unbalanced components P2uv, P2vw, P2wu of the output power of arms 7uv, 7vw, 7wu and the unbalanced component command values ​​P2uv*, P2vw*, P2wu*. Specifically, for each of the three arms 7uv, 7vw, 7wu, the phase control current command calculation unit 28 calculates the current command value for the phase corresponding to that arm so that the unbalanced component of that arm follows the unbalanced component command value of that arm.

[0069] Figure 9 is a block diagram showing an example configuration of the phase control current command calculation unit 28. Referring to Figure 9, the phase control current command calculation unit 28 includes subtractors 281u, 281v, 281w and controllers 283u, 283v, 283w.

[0070] The subtractor 281u calculates the deviation between the unbalanced component command value P2uv* and the unbalanced component P2uv (i.e., P2uv* - P2uv). The controller 283u performs a control operation to make the deviation calculated by the subtractor 281u zero (i.e., so that the unbalanced component P2uv follows the unbalanced component command value P2uv*) and calculates the current command value I2uv*. More specifically, the controller 283u calculates the current command value I2uv* by, for example, feedback control to make the deviation zero. The feedback control is, for example, P control or PI control. However, the feedback control may be configured by appropriately combining proportional control, integral control, differential control, etc. This is also true for controllers 283v and 283w.

[0071] The subtractor 281v calculates the deviation between the unbalanced component command value P2vw* and the unbalanced component P2vw (i.e., P2vw* - P2vw). The controller 283v performs a control calculation to set the deviation calculated by the subtractor 281v to zero, and calculates the current command value I2vw*.

[0072] The subtractor 281w calculates the deviation between the unbalanced component command value P2wu* and the unbalanced component P2wu (i.e., P2wu* - P2wu). The controller 283w performs a control calculation to set the deviation calculated by the subtractor 281w to zero, and calculates the current command value I2wu*.

[0073] In this manner, the phase control current command calculation unit 28 performs control calculations to compensate for the deviation between the unbalanced component command values ​​P2uv*, P2vw*, P2wu* generated by the phase control power command calculation unit 27 and the unbalanced components P2uv, P2vw, P2wu.

[0074] Referring again to Figure 5, the current command conversion unit 29 calculates the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz* of the power converter 3 based on the current command values ​​I2uv*, I2vw*, I2wu* for each phase and the voltages Vcuv, Vcvw, Vcwu. The current command conversion unit 29 functions as a "second current command calculation unit" that calculates the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz*.

[0075] Figure 10 is a block diagram showing an example configuration of the current command conversion unit 29. Referring to Figure 10, the current command conversion unit 29 includes multipliers 291u, 291v, 291w, a coordinate transformation unit 292, filters 293d, 293q, and subtractors 294d, 294q.

[0076] Multiplier 291u calculates the product of the current command value I2uv* and the voltage Vcuv. Note that instead of the voltage Vcuv, a sine wave that is in phase with the voltage Vcuv and has an amplitude of 1 may be input to multiplier 291u. Multiplier 291v calculates the product of the current command value I2vw* and the voltage Vcvw. Note that instead of the voltage Vcvw, a sine wave that is in phase with the voltage Vcvw and has an amplitude of 1 may be input to multiplier 291v. Multiplier 291w calculates the product of the current command value I2wu* and the voltage Vcwu. Note that instead of the voltage Vcwu, a sine wave that is in phase with the voltage Vcwu and has an amplitude of 1 may be input to multiplier 291w.

[0077] The coordinate transformation unit 292 converts the multiplication values ​​of the multipliers 291u, 291v, and 291w, which are three-phase inputs, into values ​​in the dq0 axis coordinate system synchronized with the three-phase AC power supply 1, thereby generating the d-axis output value, q-axis output value, and zero-sequence output value. The generated zero-sequence output value is output as the zero-sequence current command value Iz*.

[0078] Filter 293d outputs a value obtained by subtracting a frequency component 2f, which is twice the voltage frequency of the three-phase AC power supply 1, from the d-axis output value of the coordinate transformation unit 292. Filter 293d is composed of, for example, a notch filter. Subtractor 294d outputs a value obtained by subtracting the output value of filter 293d from the d-axis output value of the coordinate transformation unit 292 as the second d-axis current command value I2d*. That is, the second d-axis current command value I2d* is the frequency component 2f extracted from the d-axis output value of the coordinate transformation unit 292.

[0079] Filter 293q outputs a value obtained by subtracting the frequency component 2f from the q-axis output value of the coordinate transformation unit 292. Filter 293q is composed of, for example, a notch filter. Subtractor 294q outputs a value obtained by subtracting the output value of filter 293q from the q-axis output value as the second q-axis current command value I2q*. In other words, the second q-axis current command value I2q* is the frequency component 2f extracted from the q-axis output value.

[0080] <Current command calculation section> Figure 11 is a block diagram showing an example configuration of the current command calculation unit 30. Referring to Figure 11, the current command calculation unit 30 includes adders 31q, 32d, and 32q.

[0081] Adder 31q outputs the sum of the first q-axis current command value I1q* and the second q-axis current command value I2q*. Adder 32d calculates the sum of the reference d-axis current command value I0d* and the second d-axis current command value I2d* as the d-axis current command value Idr*. Adder 32q calculates the sum of the reference q-axis current command value I0q* and the output value of adder 31q as the q-axis current command value Iqr*.

[0082] <Voltage Command Generation Unit> Referring again to Figure 4, the voltage command generation unit 35 generates cell voltage command values ​​Vcell* for controlling the output voltage of each cell 9 based on the output currents of the power converter 3 (e.g., arm currents Iuv, Ivw, Iwu), the d-axis current command value Idr*, the q-axis current command value Iqr*, and the zero-sequence current command value Iz*. The configurations of the current control unit 40, the phase voltage command calculation unit 50, and the DC voltage control units 60 for each cell, which are included in the voltage command generation unit 35, will be described in detail below.

[0083] <Current Control Unit> Figure 12 is a block diagram showing an example configuration of the current control unit 40. Referring to Figure 12, the current control unit 40 includes coordinate transformation units 41 and 44, subtractors 42d, 42q, and 42z, controllers 43d, 43q, and 43z, and adders 45d and 45q.

[0084] The coordinate transformation unit 41 converts the arm currents Iuv, Ivw, Iwu as three-phase inputs into values ​​in the dq0 axis coordinate system synchronized with the three-phase AC power supply 1, and generates d-axis output values, q-axis output values, and zero-sequence output values. The coordinate transformation unit 44 converts the voltages Vuv, Vvw, Vwu as three-phase inputs into values ​​in the dq axis coordinate system, and generates d-axis output values ​​and q-axis output values.

[0085] The subtractor 42d calculates the deviation between the d-axis current command value Idr* and the d-axis output of the coordinate transformation unit 41 (i.e., Idr* - d-axis output value). The controller 43d performs a control calculation to make the deviation calculated by the subtractor 42d zero (i.e., so that the d-axis output value follows the d-axis current command value Idr*) and outputs a control calculation value. The adder 45d calculates the sum of the control calculation value from the controller 43d and the d-axis output value of the coordinate transformation unit 44 as the d-axis voltage command value Vd*.

[0086] The subtractor 42q calculates the deviation between the q-axis current command value Iqr* and the q-axis output of the coordinate transformation unit 41 (i.e., Iqr* - q-axis output value). The controller 43q performs a control calculation to make the deviation calculated by the subtractor 42q zero (i.e., so that the q-axis output value follows the q-axis current command value Iqr*) and outputs a control calculation value. The adder 45q calculates the sum of the control calculation value of the controller 43q and the q-axis output value of the coordinate transformation unit 44 as the q-axis voltage command value Vq*.

[0087] The subtractor 42z calculates the difference between the zero-sequence current command value Iz* and the zero-sequence output value of the coordinate transformation unit 41 (i.e., Iz* - zero-sequence output value). The controller 43z performs a control operation to make the difference calculated by the subtractor 42z zero (i.e., so that the zero-sequence output value follows the zero-sequence current command value Iz*) and calculates the zero-sequence voltage command value Vz*.

[0088] <Phase Voltage Command Calculation Unit> Figure 13 is a block diagram showing an example configuration of the phase voltage command calculation unit 50. Referring to Figure 13, the phase voltage command calculation unit 50 includes a coordinate transformation unit 51. The coordinate transformation unit 51 transforms the d-axis voltage command value Vd*, the q-axis voltage command value Vq*, and the zero-sequence voltage command value Vz* as dq0 axis inputs to calculate the respective phase voltage command values ​​Vuv*, Vvw*, and Vwu*.

[0089] <Cell DC Voltage Control Unit> Figure 14 is a block diagram showing an example configuration of a cell DC voltage control unit 60. Referring to Figure 14, each cell DC voltage control unit 60 contains 3n cell control units 600, corresponding to the total number of cells. Each of the 3n cell control units 600 is configured to generate the cell voltage command value Vcell* for the corresponding cell 9. Since the configurations of the 3n cell control units 600 are the same as those of one another, the configuration of a cell control unit 600 corresponding to one cell 9 will be described.

[0090] The cell control unit 600 includes a voltage command selection unit 61, a representative value calculation unit 62, a cell voltage extraction unit 63, a filter 64, subtractors 65 and 69, a controller 66, an arm current selection unit 67, and a multiplier 68.

[0091] The voltage command selection unit 61 selects and outputs one of the phase voltage command values ​​Vuv*, Vvw*, and Vwu* according to the phase of the arm 7 that contains the cell 9 to be controlled.

[0092] The representative value calculation unit 62 calculates a representative value Vdccellx of the voltage Vdccell of n energy storage elements 10 included in the arm 7 which contains the cell 9 to be controlled. The representative value Vdccellx can be the average, maximum, or minimum value of the n voltage Vdccells. The cell voltage extraction unit 63 extracts the voltage Vdccell of the corresponding cell 9 from the 3n voltage Vdccells.

[0093] Filter 64 outputs a value Vdccellf obtained by removing the frequency component with the same frequency as the voltage of the three-phase AC power supply 1 from the voltage Vdccell extracted by the cell voltage extraction unit 63. Filter 64 is, for example, a moving average filter with a period equal to the period of the voltage of the three-phase AC power supply 1. Subtractor 65 calculates the deviation between the voltage Vdccellx and the value Vdccellf (i.e., Vdccellx - Vdccellf).

[0094] The controller 66 performs a control calculation to make the deviation calculated by the subtractor 65 zero, and outputs the manipulated variable as a result of the control calculation. The arm current selection unit 67 selects and outputs one of the arm currents Iuv, Ivw, or Iwu according to the phase of the arm 7 that contains the cell 9 to be controlled. The multiplier 68 multiplies the manipulated variable output from the controller 66 by the arm current selected by the arm current selection unit 67.

[0095] The subtractor 69 calculates the cell voltage command value Vcell* of the controlled cell 9 by subtracting the multiplication value output from the multiplier 68 from the voltage command value selected by the voltage command selection unit 61.

[0096] <Advantages> During voltage fluctuations in the three-phase AC power supply or when the three-phase AC voltage is unbalanced, the output current of the power converter 3, which follows a three-phase balanced current command value (i.e., the first q-axis current command value I1q*) generated by the first voltage control by the full control power command calculation unit 24 (i.e., control that keeps the representative value of the voltage Vdccell of all cells 9 constant), and the voltage of the three-phase unbalanced three-phase AC power supply 1 result in the output of active power (i.e., three-phase unbalanced power) that is unbalanced between each arm. This active power can disturb the second voltage control by the phase control power command calculation unit 27 (i.e., control that suppresses variations between arms in the representative value of the voltage Vdccell of each cell 9 included in each arm 7).

[0097] However, in Embodiment 1, the three-phase unbalanced power is calculated by the output power calculation unit 23 as unbalanced components P2uv, P2vw, and P2wu, and these unbalanced components P2uv, P2vw, and P2wu are input to the phase control current command calculation unit 28. Subsequently, the phase control current command calculation unit 28 performs a control calculation to compensate for the deviation between the unbalanced component command values ​​P2uv*, P2vw*, and P2wu* generated by the phase control power command calculation unit 27 and the unbalanced components P2uv, P2vw, and P2wu. The current command values ​​I2uv*, I2vw*, and I2wu* generated by this control calculation are reflected in the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz*. The power converter 3 then outputs currents according to the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz*.

[0098] With the above configuration, the three-phase unbalanced power that could become a disturbance in the phase-controlled power command calculation unit 27 is compensated for by the phase-controlled current command calculation unit 28. Therefore, when the three-phase AC power supply 1 is three-phase unbalanced, interference between the total control power command calculation unit 24 and the phase-controlled power command calculation unit 27 can be prevented, and the operational continuity of the power converter 2 can be improved.

[0099] Embodiment 2. Embodiment 2 describes other configurations of the DC voltage control unit 20 of Embodiment 1, as shown in Figure 5. The configurations other than the DC voltage control unit 20 in Embodiment 2 are the same as those in Embodiment 1.

[0100] <DC Voltage Control Unit> Figure 15 is a block diagram showing an example configuration of the DC voltage control unit 20A according to Embodiment 2. The DC voltage control unit 20A corresponds to the DC voltage control unit 20 in Figure 4, but for convenience, it is denoted with the letter "A" to distinguish it from the DC voltage control unit 20 according to Embodiment 1.

[0101] Referring to Figure 15, the DC voltage control unit 20A includes an output power calculation unit 23A, a total control power command calculation unit 24, a total control current command calculation unit 25, a phase control power command calculation unit 27, a phase control current command calculation unit 28, and a current command conversion unit 29. In other words, the DC voltage control unit 20A is configured by adding a total control current command calculation unit 25 to the DC voltage control unit 20 of Figure 5, and replacing the output power calculation unit 23 of Figure 5 with an output power calculation unit 23A. A detailed explanation of a configuration similar to the DC voltage control unit 20 will not be repeated.

[0102] The output power calculation unit 23A calculates the unbalanced components P2uv, P2vw, P2wu and the common component Pall of the output power of arms 7uv, 7vw, 7wu based on the representative values ​​of the output currents (e.g., currents Icuv, Icvw, Icwu) and the representative values ​​of the output voltages (e.g., voltages Vcuv, Vcvw, Vcwu) of the cell groups included in arms 7uv, 7vw, 7wu.

[0103] Figure 16 is a block diagram showing an example configuration of the output power calculation unit 23A according to Embodiment 2. Referring to Figure 16, the output power calculation unit 23A has the same configuration as the output power calculation unit 23 in Figure 6, with the addition of an adder 235 and an arithmetic unit 236. A detailed explanation of a configuration similar to that of the output power calculation unit 23 will not be repeated.

[0104] The adder 235 calculates the sum of the output values ​​of the multiplier 231u (i.e., the output power of arm 7uv), the output value of the multiplier 231v (i.e., the output power of arm 7vw), and the output value of the multiplier 231w (i.e., the output power of arm 7wu). The arithmetic unit 236 calculates the common component Pall of the output power of each arm 7 by multiplying this sum by 1 / 3.

[0105] Referring again to Figure 15, the total control current command calculation unit 25 generates a first q-axis current command value I1q* based on the total phase active power command value Pall* and the common component Pall. In Embodiment 2, the total control power command calculation unit 24 and the total control current command calculation unit 25 function as a "first current command calculation unit" that calculates the first q-axis current command value I1q*.

[0106] Figure 17 is a block diagram showing an example configuration of the total control current command calculation unit 25 according to Embodiment 2. Referring to Figure 17, the total control current command calculation unit 25 includes a subtractor 251 and a controller 253.

[0107] The subtractor 251 outputs a value obtained by subtracting the common component Pall from the all-phase active power command value Pall* (i.e., the deviation between Pall* and Pall). The controller 253 performs a control calculation to make this deviation zero (i.e., so that the common component Pall follows the all-phase active power command value Pall*) and generates the first q-axis current command value I1q*.

[0108] <Advantages> Control calculations are performed to compensate for the deviation between the unbalanced component command values ​​P2uv*, P2vw*, P2wu* generated by the second voltage control by the phase control power command calculation unit 27 and the unbalanced components P2uv, P2vw, P2wu. The current command values ​​I2uv*, I2vw*, I2wu* generated by these control calculations are reflected in the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz*.

[0109] During voltage fluctuations in the three-phase AC power supply or when the three-phase AC voltage is unbalanced, active power (i.e., three-phase unbalanced power) common to each arm is output by the current output from the power converter 3 according to the second d-axis current command value I2d*, the second q-axis current command value I2q*, and the zero-sequence current command value Iz* generated based on the second voltage control, and the voltage of the three-phase unbalanced three-phase AC power supply 1. This active power can become a disturbance to the first voltage control by the total control power command calculation unit 24.

[0110] However, in Embodiment 2, the three-phase unbalanced power is calculated as a common component Pall by the output power calculation unit 23A, and the common component Pall is input to the total control current command calculation unit 25. Subsequently, the total control current command calculation unit 25 performs a control calculation to compensate for the deviation between the total-phase active power command value Pall* generated by the total control power command calculation unit 24 and the common component Pall, and generates a first q-axis current command value I1q*. Then, the power converter 3 outputs a current according to the first q-axis current command value I1q*.

[0111] With the above configuration, the three-phase unbalanced power that could become a disturbance to the total control power command calculation unit 24 is compensated for by the total control current command calculation unit 25. Therefore, when the three-phase AC power supply 1 is three-phase unbalanced, interference between the total control power command calculation unit 24 and the phase control power command calculation unit 27 can be prevented, and the operational continuity of the power converter 2 can be improved.

[0112] Embodiment 3. Embodiment 3 describes other configurations of the phase control current command calculation unit 28 of Embodiment 1, as explained in Figure 9. The configurations other than the phase control current command calculation unit 28 in Embodiment 3 are the same as those in Embodiment 1.

[0113] Figure 18 shows an example of the configuration of the phase control current command calculation unit 28A according to Embodiment 3. In the phase control current command calculation unit 28 shown in Figure 9, the controllers 283u, 283v, and 283w were described as generating current command values ​​I2uv*, I2vw*, and I2wu* respectively, but the method of generating each current command value I2uv*, I2vw*, and I2wu* was the same except for the input and output signals. This is also the case for the phase control current command calculation unit 28A.

[0114] Therefore, in Figure 18, only the generation method of the current command value I2uv* will be explained as a representative example. The phase control current command calculation unit 28A corresponds to the phase control current command calculation unit 28 in Figure 5 or Figure 15, but for convenience, it is denoted with the letter "A" to distinguish it from the phase control current command calculation unit 28 according to Embodiment 1. The same applies to Figure 19 below.

[0115] Referring to Figure 18, the phase control current command calculation unit 28A includes a subtractor 281u, a controller 283u, a gain circuit 284u, and an adder 285u as a configuration for calculating the current command value I2uv*.

[0116] The subtractor 281u calculates the deviation between the unbalanced component command value P2uv* and the unbalanced component P2uv. The controller 283u performs a control operation to make the deviation calculated by the subtractor 281u zero (i.e., so that the unbalanced component P2uv follows the unbalanced component command value P2uv*) and calculates the control command value.

[0117] The gain circuit 284u outputs a value obtained by multiplying the unbalanced component command value P2uv* by a constant (for example, by a gain of K). The adder 285u calculates the sum of the output value of the gain circuit 284u and the output value of the controller 283u (i.e., the control command value) as the current command value I2uv*. The current command values ​​I2vw* and I2wu* are calculated in the same manner.

[0118] With the above configuration, the phase control current command calculation unit 28A calculates a control command value for each of the three arms 7uv, 7vw, and 7wu such that the unbalanced component of the arm follows the unbalanced component command value of the arm, and calculates the sum of the control command value and the multiplied value obtained by multiplying the unbalanced component command value by the gain as the current command value for the phase corresponding to the arm.

[0119] Here, ignoring the output value of controller 283u, the gain circuit 284u is a calculation that converts the unbalanced component command value P2uv* to the current command value I2uv*. When the amplitude of voltage Vcuv is constant and sinusoidal, this conversion is possible by setting the gain K to the reciprocal of the amplitude of voltage Vcuv. By setting the gain K to the reciprocal of the amplitude of voltage Vcuv, the path including controller 283u only needs to operate when the amplitude of voltage Vcuv deviates from the ideal state of constant and sinusoidal. Therefore, the response of controller 283u to changes in voltage Vcuv is improved. Response of controller 283v to changes in voltage Vcvw, and voltage V c The response of controller 283w to changes in wu is similarly improved.

[0120] Figure 19 shows an example of the configuration of the phase control current command calculation unit 28B according to a modified example of Embodiment 3. Referring to Figure 19, the phase control current command calculation unit 28B includes a subtractor 281u, a filter 282u, a controller 283u, a gain circuit 284u, and an adder 285u. The phase control current command calculation unit 28B in Figure 19 differs from the phase control current command calculation unit 28A in Figure 18 in that the unbalanced component command value P2uv* is not input to the subtractor 281u, and a filter 282u is added.

[0121] The subtractor 281u subtracts the unbalanced component P2uv from 0 and outputs a value with the polarity of the unbalanced component P2uv reversed. The filter 282u outputs a value that has been filtered to remove low-frequency components from the output value of the subtractor 281u. The filter 282u is, for example, a high-pass filter.

[0122] Controller 283u performs a control calculation to set the output value of filter 282u to zero and outputs a control command value. Gain circuit 284u outputs a value obtained by a constant multiplier of the unbalanced component command value P2uv*. Adder 285u generates the current command value I2uv* by adding the output value of gain circuit 284u and the output value of controller 283u. Current command values ​​I2vw* and I2wu* are calculated in the same manner.

[0123] With the above configuration, the phase control current command calculation unit 28B calculates a control command value for each of the three arms 7uv, 7vw, and 7wu, to set to zero the value obtained by applying a high-pass filter to the value obtained by inverting the polarity of the unbalanced component of that arm, and calculates the sum of this control command value and the multiplied value obtained by multiplying the unbalanced component command value by the gain as the current command value for the phase corresponding to that arm.

[0124] Here, the unbalanced component command value P2uv* is calculated in the phase control power command calculation unit 27 using the voltage Vdccell as input. The voltage Vdccell is the voltage of the energy storage element 10, and since it is proportional to the integrated value of the active power input and output of cell 9 excluding losses, its fluctuations mainly consist of low-frequency components. The unbalanced component command value P2uv* calculated using the voltage Vdccell as input also mainly consists of low-frequency components. On the other hand, since the unbalanced component P2uv is an estimated value of a part of the active power output of cell 9, the frequency components of the fluctuations of the unbalanced component P2uv are distributed in a higher frequency range compared to the voltage Vdccell, which is proportional to the integrated value of the active power input and output of cell 9.

[0125] According to the configuration shown in Figure 19, by inputting the unbalanced component P2uv, from which the low-frequency components have been removed by the filter 282u, to the controller 283u, it is possible to easily raise the control frequency bandwidth of the controller 283u and enhance the effect of suppressing fluctuations in the unbalanced component P2uv. The same applies to the other unbalanced components P2vw and P2wu.

[0126] Other embodiments. The configurations illustrated above as embodiments are examples of the configurations of this disclosure, and can be combined with other known technologies, or modified, such as by omitting parts, without departing from the gist of this disclosure. Furthermore, in the embodiments described above, processes and configurations described in other embodiments may be appropriately adopted and implemented.

[0127] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0128] 1 Three-phase AC power supply, 2 Power converter, 3 Power converter, 4 Control device, 5a Transformer, 5s, 11 Voltage detector, 6uv, 6vw, 6wu Current detector, 7uv, 7vw, 7wu Arm, 8 Reactor, 9 Cell, 10 Energy storage element, 20, 20A DC voltage control unit, 23, 23A Output power calculation unit, 24 Full control power command calculation unit, 25 Full control current command calculation unit, 27 Phase control power command calculation unit, 28, 28A, 28B Phase control current command calculation unit, 29 Current command conversion unit, 30 Current command calculation unit, 35 Voltage command generation unit, 40 Current control unit, 50 phase Voltage command calculation unit, 60 DC voltage control unit for each cell, 61 Voltage command selection unit, 62, 241, 271 Representative value calculation unit, 63 Cell voltage extraction unit, 67 Arm current selection unit, 70 Gate signal generation unit, 600 Cell control unit.

Claims

1. A power converter connected to a three-phase AC power supply, A power converter including three delta-connected arms, The system includes a control device for controlling the power converter, Each of the three arms is configured by connecting multiple unit converters in series. Each of the plurality of unit converters includes a plurality of switching elements and an energy storage element connected to the plurality of switching elements, The control device is A first current command calculation unit calculates a first current command value for the power converter based on a representative voltage value and a DC voltage command value that represent the voltage values ​​of all the energy storage elements included in the power converter. For each of the three arms, a power calculation unit calculates the unbalanced component of the output power of the arm based on the representative output current and output voltage values ​​of the cell group including each of the unit converters contained in the arm, A first power command calculation unit calculates an unbalanced component command value for the output power of each of the three arms so that the voltage values ​​of the energy storage elements are balanced between the three arms, A phase current command calculation unit that generates current command values ​​for each phase based on the unbalanced component of the output power of each arm and the unbalanced component command value of the output power of each arm, A second current command calculation unit calculates a second current command value for the power converter based on the representative output voltage value of the cell group included in each arm and the current command value of each phase. A voltage command generation unit generates an output voltage command value for controlling the output voltage of each unit converter based on the output current of the power converter and a current command value calculated from the first current command value and the second current command value. A power converter comprising a gate signal generation unit that generates control signals for each of the switching elements included in the power converter based on the output voltage command value.

2. The power converter according to claim 1, wherein the first current command calculation unit calculates a first power command value for the power converter such that the representative voltage value follows the DC voltage command value, and outputs the first power command value as the first current command value.

3. The power calculation unit further calculates a common component of the output power of the three arms based on the representative output current value and the representative output voltage value of the cell group included in each of the three arms. The first current command calculation unit is: The first power command value of the power converter is calculated so that the aforementioned representative voltage value follows the aforementioned DC voltage command value. The power conversion device according to claim 1, wherein the first current command value is calculated such that the common component follows the first power command value.

4. The power conversion device according to any one of claims 1 to 3, wherein the phase current command calculation unit calculates a control command value for each of the three arms such that the unbalanced component of the arm follows the unbalanced component command value of the arm, and calculates the control command value as the current command value of the phase corresponding to the arm.

5. The power converter according to any one of claims 1 to 3, wherein the phase current command calculation unit calculates a control command value for each of the three arms such that the unbalanced component of the arm follows the unbalanced component command value of the arm, and calculates the sum of the control command value and the multiplied value obtained by multiplying the unbalanced component command value of the arm by a gain as the current command value of the phase corresponding to the arm.

6. The control command value is calculated by feedback control to make the deviation between the unbalanced component and the unbalanced component command value zero. The power conversion device according to claim 4, wherein the feedback control is P control or PI control.

7. The power converter according to any one of claims 1 to 3, wherein the phase current command calculation unit calculates a control command value for each of the three arms to set to zero the value obtained by applying a high-pass filter to the value obtained by inverting the polarity of the unbalanced component of the arm, and calculates the sum of the control command value and the multiplied value obtained by multiplying the unbalanced component command value of the arm by a gain as the current command value of the phase corresponding to the arm.

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