TWI651911B - Cascaded power converter apparatus - Google Patents

Abstract

The series-connected power conversion device includes a plurality of grid voltage generators, a plurality of autonomous voltage adjustment controllers, and a total current adjustment controller. The grid voltage generators respectively provide a plurality of grid voltages, and each grid voltage generator comprises a plurality of power converters connected in series, the power converter being divided into a plurality of pre-stage power converters and at least one post-stage power converter. Each autonomous voltage adjustment controller controls the voltage conversion action of each of the preceding stage power converters according to the corresponding front stage DC voltage and the grid voltage. The total current adjustment controller controls the voltage conversion action of the subsequent stage power converter according to the plurality of grid currents and the plurality of subsequent stage DC voltages received by the subsequent stage power converter.

Description

Series power conversion device

The present invention relates to a series-connected power conversion device, and more particularly to a series-connected power conversion device having a distributed control mechanism.

The multi-level tandem power conversion device is a series of bridge converters and can be applied to a higher voltage level network. Wherein, each bridge converter performs a voltage conversion action on the received DC voltage and generates a plurality of supply powers of different phases. In the conventional technical field, the multi-level serial-connected power conversion device realizes the signal transmission back and forth through a central controller and performs the switching control signals required for transmitting the bridge converters. As a result, a large and complex communication connection wire arrangement is required between the central controller and the bridge converter. Moreover, since the central controller needs to process a large number of feedback signals, the central controller has to bear a large amount of computation. In addition, when a single bridge converter fails, since the overall system signal connection is connected, it is easy to cause the shutdown of the entire series of series-type power conversion devices. As the number of serially connected converters increases, the above factors will increase the difficulty in hardware implementation.

The invention provides a series-connected electric energy conversion device with a distributed control mechanism, which can effectively improve the fault tolerance, reduce the number of wirings in the series-connected electric energy conversion device, and reduce the complexity of the system design.

The series-connected power conversion device of the present invention includes a plurality of grid voltage generators, a plurality of autonomous voltage adjustment controllers, and a total current adjustment controller. The grid voltage generators respectively provide a plurality of grid voltages, and each grid voltage generator comprises a plurality of power converters connected in series, the power converter being divided into a plurality of pre-stage power converters and at least one post-stage power converter. The autonomous voltage adjustment controllers are respectively coupled to the pre-stage power converters in the grid voltage generator, and the respective main voltage adjustment controllers control the voltage conversion actions of the respective pre-stage power converters according to the corresponding pre-stage DC voltages and the grid voltage. The total current adjustment controller is coupled to the level electric energy converters in the grid voltage generator, and controls the post-level electric energy according to the plurality of grid currents on the grid voltage generator and the plurality of post-stage DC voltages received by the post-stage power converter. The voltage conversion action of the converter.

Based on the above, the present invention provides a plurality of autonomous voltage adjustment controllers for controlling voltage conversion actions of a plurality of preceding stage power converters in respective grid voltage generators in a series-connected power conversion apparatus. Moreover, the present invention further provides a total current adjustment controller for controlling voltage conversion actions of a plurality of subsequent stage power converters in the series-connected power conversion apparatus. With the decentralized control mechanism, the number of transmission wires in the series-type power conversion device can be reduced, and the length of the wires can be reduced, the difficulty in layout of the hardware is reduced, and the area required for the hardware is reduced. Effectively reduce the cost of production, And increase the competitiveness of the product. In addition, the series-connected power conversion device of the present invention can improve fault tolerance, wherein the normal operation of the system can be maintained even when a part of the power conversion device fails.

The above described features and advantages of the invention will be apparent from the following description.

100‧‧‧Series power conversion device

110, 120, 130‧‧‧ grid voltage generator

AVR11-AVR1J, AVR21-AVR2J, AVR31-AVR3J‧‧‧ independent voltage adjustment controller

TCR1‧‧‧ total current adjustment controller

V _a0 , V _b0 , V _c0 ‧‧‧ grid voltage

111-11N, 121-12N, 131-13N‧‧‧ power converter

PWM, PWM _a1 , PWM _a2 , PWM _b1 , PWM _b2 , PWM _c1 , PWM _c2 , PWM _aN , PWM _bN , PWM _cN ‧‧‧ control signal

i _a , i _b , i _c ‧‧‧ grid current

V _dcaN , V _dcbN , V _{dccN ‧‧ ‧} DC voltage

200‧‧‧Series power conversion device

210-230‧‧‧ Grid voltage generator

211-21N‧‧‧Power Converter

V _dca1 -V _dcaN ‧‧‧(pre-stage) DC voltage

i _dca1 -i _dcaN ‧‧‧ DC current

V _a1 , V _a2 , V _a3 , V _aM ‧‧‧ voltage

O‧‧‧ origin

M‧‧‧ connection point

300‧‧‧Autonomous voltage adjustment controller

310, 330‧‧‧ arithmetic

320‧‧‧ adjuster

340‧‧‧Transformer

V _dc *‧‧‧ DC voltage command

V _a1 *‧‧‧ command voltage value

331‧‧‧Multiplier

332‧‧‧Adder

V _mag ‧‧‧ voltage

400‧‧‧Total current adjustment controller

410‧‧‧Total power controller

420‧‧‧ Cluster voltage controller

430‧‧‧ Current controller

440‧‧‧Transformer

413‧‧‧ adjuster

460‧‧‧Independent voltage balance controller

4122, 470‧‧‧ arithmetic

411‧‧‧Part 1

412‧‧‧Part II

4123‧‧‧Subtractor

4124‧‧‧Adder

V _dcaJ+1 ~V _dcaN , V _dcbJ+1 ~V _dcbN , V _dccJ+1 ~V _dccN ‧‧‧ After DC voltage

F11~F1M, F21~F2M, F31~F3M‧‧‧ filter

4111a~4111c, 4112a~4112c, 4121, 4122‧‧‧ arithmetic

V' _dcaJ+1 ~V' _dcaN , V' _dcbJ+1 ~V' _dcbN , V' _dccJ+1~ V' _{dccN ‧‧‧Filtered} DC voltage

V _dcaT , V _dcbT , V _{dccT ‧ ‧} average

I _q ^P* ‧‧‧Power Current Command

I _ff *‧‧‧ Offset current command

421-423‧‧‧Subtractor

424-426‧‧‧ adjuster

427‧‧‧ Zero Sequence Voltage Command Calculator

P _Ca *, P _Cb *, P _Cc *‧‧‧ Cluster Power Command

V _o * _TCR ‧‧‧ demand voltage command

V _qd ^pn ‧‧‧injection voltage

I _qd ^pn ‧‧‧Inject current and voltage

AD1-AD6‧‧‧Adder

I _d ^P* , I _d ^n* , I _q ^n* ‧‧‧Inject current command

V _a3 *, V _b3 *, V _c3 *‧‧‧ voltage control commands

1 is a schematic diagram of a series-connected power conversion device according to an embodiment of the invention.

2 is a schematic diagram showing the hardware architecture of a grid voltage generator of a series-connected power conversion device according to an embodiment of the present invention.

3 is a schematic diagram of an embodiment of an autonomous voltage adjustment controller according to an embodiment of the present invention.

4 is a schematic diagram of an embodiment of a total current adjustment controller in accordance with an embodiment of the present invention.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a series-connected power conversion device according to an embodiment of the present invention. The series-connected power conversion device 100 includes grid voltage generators 110, 120, and 130, autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, AVR31~AVR3J, and a total current adjustment controller TCR1. The grid voltage generators 110, 120, and 130 provide grid voltages V _a0 , V _{b0 ,} and V _{c0 , respectively} . The grid voltage generator 110 includes power converters 111-11N; the grid voltage generator 120 includes power converters 121-12N; and the grid voltage generator 130 includes power converters 131-13N. In the grid voltage generator 110, the power converters 111~11J may be pre-stage power converters, and the power converters 11J+1~11N may be post-stage power converters; in the grid voltage generator 120, the power converters 121~12J can be a pre-stage power converter, and the power converter 12J+1~12N can be a post-stage power converter; in the grid voltage generator 130, the power converters 131~13J can be a pre-stage power converter, The power converter 13J+1~13N can be a post-stage power converter.

The autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, and AVR31~AVR3J are respectively coupled to the power converters 111, 112, 121, 122, 131, and 132 as the front stage power converters. Each of the autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, AVR31~AVR3J controls each of the preceding stage power converters according to the corresponding front stage DC voltage and the grid voltage (ie, the power converters 111, 112, 121, 122, 131 and 132) Voltage conversion action. Taking the autonomous voltage adjustment controller AVR11 as an example, the autonomous voltage adjustment controller AVR11 is coupled to the power converter 111 and receives the front-end DC voltage V _dca1 received by the power converter 111. In addition, the autonomous voltage adjustment controller AVR11 senses the corresponding grid voltage V _a0 and generates a control signal PWM _a1 according to the pre-stage DC voltage V _dca1 and the grid voltage V _a0 . The control signal PWM _a1 is transmitted to the power converter 111 and used to control the voltage conversion action of the power converter 111.

It can be seen that in the embodiment of the present invention, the autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, and AVR31~AVR3J are respectively according to the corresponding front-level DC voltages V _dca1 ~V _dcaJ , V _dcb1 ~V _dcbJ , V _Dcc1 ~ V _dccJ , and respectively generate control signals PWM _a1 ~ PWM _aJ , PWM _b1 ~ PWM _bJ , PWM _c1 ~ PWM _cJ according to the corresponding grid voltages V _a0 , V _b0 and V _c0 . The control signals PWM _a1 ~PWM _aJ , PWM _b1 ~PWM _bJ , PWM _c1 ~PWM _cJ are respectively transmitted to the power converters 111~11J, 121~12J and 131~13J as the pre-stage power converter, and respectively control the electric energy conversion Voltage conversion operations performed by the respective switches 111 to 11J, 121 to 12J, and 131 to 13J.

The total current adjustment controller TCR1 is coupled to the subsequent stage power converters (the power converters 11J+1~11N, 12J+1~12N, and 13J+1~13N) of the grid voltage generators 110, 120, and 130. The total current adjustment controller TCR1 receives the grid currents i _a , i _b and i _{c of} different phases on the grid, and receives the subsequent stage DCs corresponding to the power converters 11J+1~11N, 12J+1~12N and 13J+1~13N. The voltages V _dcaJ+1 ~V _dcaN , V _dcbJ+1 ~V _dcbN and V _dccJ+1 ~V _dccN are respectively based on the grid currents i _a , i _b and i _c and the subsequent DC voltage V _dcaJ+1 ~V _dcaN V _dcbJ+1 ~V _dcbN and V _dccJ+1 ~V _dccN to generate control signals PWM _aJ+1 ~PWM _aN , PWM _bJ+1 ~PWM _bN and PWM _cJ+1 ~PWM _cN . The control signals PWM _aJ+1 ~PWM _aN , PWM _bJ+1 ~PWM _bN and PWM _cJ+1 ~PWM _cN are respectively transmitted to the power converters 11J+1~11N, 12J+1-12N as the power converters of the latter stage. And 13J+1-13N, and used to control the voltage conversion action of the power converters 11N-13N.

As can be seen from the above description, for the pre-stage power converters (electric energy converters 111~11J, 121~12J, 131~13J) in the grid voltage generators 110-130, The embodiments of the present invention provide one-to-one autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, and AVR31~AVR3J to control the voltage conversion actions of the power converters 111~11J, 121~12J, 131~13J, respectively. For the subsequent stage power converters (power converters 11J+1~11N, 12J+1~12N, and 13J+1~13N), the voltage conversion operation is controlled by the total current adjustment controller TCR1. In this way, the total current adjustment controller TCR1 does not need to communicate with all the power converters 111~13N, thereby effectively reducing the number of transmission wires required. Moreover, the autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, AVR31~AVR3J and the corresponding power converters 111~11J, 121~12J, 131~13J can also be arranged in close positions to make the total current adjustment control. The TCR1 and the after-stage power converters 11J+1~11N, 12J+1~12N and 13J+1~13N are arranged in close positions to reduce the length of the signal transmission path, in addition to improving the signal quality, the system can also be reduced. The complexity of the design reduces production costs. Moreover, the series-connected power conversion device 100 of the embodiment of the present invention can improve the fault tolerance, wherein the series-connected power conversion device 100 can maintain the normal operation of the system when a part of the power conversion device fails.

Incidentally, the pre-stage power converter mentioned in this embodiment is the power of the transmission line of the grid voltage generators 110-130 which is located closer to the transmission line voltages V _a0 , V _b0 , V _c0 . converter. In contrast, the so-called after-stage power converter is a power that is disposed at a position closer to the common coupling point M of the grid voltage generators 110-130 (a transmission line that is farther away from the grid voltages V _a0 , V _b0 , V _c0 ). converter. Moreover, corresponding to the grid voltage of a single phase, the number of power converters in the latter stage may be one or more, and there is no fixed limit.

In this embodiment, the grid voltages V _a0 , V _b0 , V _c0 may be three voltage signals having different phases, wherein the grid voltages V _a0 , V _b0 , V _c0 may have a phase difference of 120 ⁰ . .

Referring to FIG. 2, FIG. 2 is a schematic diagram of a hardware architecture of a grid voltage generator of a series-connected power conversion device according to an embodiment of the present invention. The series-connected power conversion device 200 includes grid voltage generators 210-230. The grid voltage generators 210-230 may have the same hardware architecture with each other. Taking the grid voltage generator 210 as an example, the grid voltage generator 210 may include a plurality of power converters 211 to 21N, and the power converters 211 to 21N may have the same hardware architecture with each other. As shown by the power converter 211, each of the power converters 211 to 21N may be composed of four transistor switches. The power converters 211 to 21N receive the DC voltages V _dca1 VV _dcaN and the corresponding DC currents i _dca1 to i _dcaN , _respectively , and respectively switch the four transistors according to the received control signals to generate voltages V _a1 and V respectively. _A2 and V _a3 . The grid voltage generator 210 generates a voltage V _aM through the series connected voltages V _a1 , V _{a2 ,} and V _a3 , thereby generating a grid voltage V _a0 .

Additionally, grid voltage generators 210-230 can provide grid currents i _a , i _{b ,} and i _{c , respectively} . In the present embodiment, the grid voltage generators 210-230 can be coupled to the origin O to form a Y-shaped connection configuration.

Please refer to FIG. 3 . FIG. 3 is a schematic diagram of an embodiment of an autonomous voltage adjustment controller according to an embodiment of the present invention. The autonomous voltage adjustment controller 300 includes an arithmetic unit 310, an adjuster 320, an arithmetic unit 330, and a modulator 340. The operator 310 receives the pre-stage DC voltage V _dca1 and the DC voltage command V _dc * received by the corresponding pre-stage power converter, and calculates a difference between the DC voltage command V _dc * and the pre-stage DC voltage V _dca1 . In the present embodiment, the arithmetic unit 310 is a subtractor.

The adjuster 320 is coupled to the operator 310 and receives the difference calculated by the operator 310. The adjuster 320 adjusts for the received difference and produces an adjusted difference. In this embodiment, the adjuster 320 can be a proportional integral adjuster (PI regulator), and the transfer function can be K _pti +K _iti /S, wherein the constants K _pti , K _iti can be set by the designer. There is no fixed limit on its value.

The operator 330 is coupled to the adjuster 320 and receives the adjusted difference, and performs an arithmetic operation on the adjusted difference according to the corresponding grid voltage V _a0 to generate a command voltage value V _a1 *. In the present embodiment, the arithmetic unit 330 includes a multiplier 331 and an adder 332. Wherein, the grid voltage V _ao can be first divided by the voltage V _mag to generate a normalized grid voltage (V _a0 /V _mag ). Wherein, the voltage V _mag may be the maximum possible voltage value of the grid voltage V _ao . The multiplier 331 multiplies the adjusted difference by the normalized grid voltage (V _a0 /V _mag ). Further, the adder 332 adds the multiplication result generated by the multiplier 331 to the quotient obtained by dividing the grid voltage V _a0 by N (as a feedforward signal), and thereby generates the command voltage value V _a1 *. Where N can be equal to the number of phases of the series-connected power conversion device.

The modulator 340 receives the command voltage value V _a1 * and performs a modulation operation according to the command voltage value V _a1 *, and thereby generates a control signal PWM _a1 . The control signal PWM _a1 can be a wide modulation signal and is used to control the switching action of the transistor switch of the corresponding power converter.

Please refer to FIG. 4, which is a schematic diagram of an embodiment of a total current adjustment controller according to an embodiment of the present invention. The total current adjustment controller 400 includes a total power controller 410, a cluster voltage controller 420, a current controller 430, a modulator 440, an independent voltage balance controller 460, and an operator 470. The total power controller 410 includes a first portion 411 and a second portion 412 and is used to perform overall voltage control of the series-connected power conversion device. The first portion 411 is an average voltage calculator, and the average _{values of the} subsequent DC voltages V _dcaJ+1 ~V _dcaN , V _dcbJ+1 ~V _{dcbN ,} and V _dccJ+1 ~V _dccN are calculated. The cluster voltage controller 420 is used to perform voltage control of a cluster formed by a power converter corresponding to a grid voltage of the same phase in a series-connected power conversion device, wherein a grid voltage of three phases is taken as an example, and the series connection The power conversion device has three power converter clusters.

The total power controller 410 includes a plurality of filters F11 to F1M, F21 to F2M, and F31 to F3M, operators 4111a to 4111c, 4112a to 4112c, 4121 and 4122, a subtractor 4123, an adjuster 413, and an adder 4124. Filters F11~F1M, F21~F2M, and F31~F3M are filtered for the subsequent DC voltages V _dcaJ+1 ~V _dcaN , V _dcbJ+1 ~V _{dcbN ,} and V _dccJ+1 ~V _{dccN ,} respectively. The arithmetic units 4111a to 4111c calculate the sum of the filtered subsequent-stage DC voltages V' _dcaJ+1 to V' _dcaN , V' _dcbJ+1 ~V' _dcbN , and V' _{dccJ+1 to} V' _dccN . The operators 4112a to 4112c respectively calculate the average V _dcaT and V _{dcbT of the} filtered subsequent DC voltages V' _dcaJ+1 ~V' _dcaN , V' _dcbJ+1 ~V' _dcbN , V' _dccJ+1~ V' _dccN . And V _dccT , and calculate the _average of the filtered DC voltages V' _dcaJ+1 ~V' _dcaN , V' _dcbJ+1 ~V' _dcbN , V' _dccJ+1~ V' _dccN through the arithmetic unit 4121 The sum V _dcT . The arithmetic unit 4122 divides the total V _dcT by 3 and calculates an _average value of the subsequent DC voltages V _dcaJ+1 to V _dcaN , V _dcbJ+1 to V _{dcbN ,} and V _dccJ+1 to V _dccN . The subtractor 4123 subtracts the above average value from the DC voltage command V _dc * to produce a subtraction result. The adjuster 413 adjusts the subtraction result to produce an adjusted subtraction result. The adjuster 413 can be a proportional integral adjuster, and the transfer function can be K _pto +K _ito /S, wherein the constants K _pto , _Kito can be set by the designer, and the value thereof has no fixed limit.

The adder 4124 adds the above-described adjusted subtraction result to the offset current command I _ff *, and thereby generates a power current command I _q ^P* (on the q-axis).

In another aspect, cluster voltage controller 420 includes a plurality of subtractors 421-423, a plurality of adjusters 424-426, and a zero sequence voltage command calculator 427. The subtracters 421-423 subtract the outputs of the operators 4112a-4112c from the outputs of the operators 4122, respectively, and generate a plurality of subtraction results. The adjusters 424-426 receive the subtraction results produced by the subtractors 421-423, respectively, and adjust the subtraction results produced by the subtractors 421-423 to generate a plurality of cluster power commands P _Ca *, P _Cb *, and P _{Cc , respectively.} *. The adjusters 424-426 may be proportional integral adjusters having the same transfer function, and the transfer function may be K _ptc +K _itc /S, wherein the constants K _ptc , K _itc can be set by the designer, and the values are not fixed. limit.

The zero sequence voltage command calculator 427 receives the cluster power commands P _Ca *, P _Cb *, and P _Cc *, and performs zero sequence voltage command calculations according to the cluster power commands P _Ca *, P _Cb *, and P _Cc * to generate the required voltage. Command V _o * _TCR .

In the present embodiment, the zero sequence voltage command calculator 427 may be a processor having computing power. The zero sequence voltage command calculator 427 can read the presence memory The calculation of the zero sequence voltage command calculation in (or any other storage medium) is performed. Here, the algorithm for calculating the zero sequence voltage command can apply various algorithms well known to those skilled in the art without particular limitation.

The current controller 430 receives the power current command I _q ^P* and the positive and negative injection voltages V _qd ^pn and the injection current voltage I _qd ^pn on the dq axis for calculation and generates a voltage demand for the three phases. In the present embodiment, the current controller 430 additionally receives the positive injection current command I _d ^{P* of the} d-axis and sets the negative injection current command I _d ^n* , I _q ^n* of the dq axis to be equal to zero. The current controller 430 additionally applies the adders AD1-AD3 to add the required voltage command V _o * _TCR to the calculated three-phase voltage demand, and respectively generates a voltage control command through the arithmetic unit 470 and the adders AD4 to AD6. V _a3 *, V _b3 *, V _c3 *. The adders AD4~AD6 further receive the balanced signals corresponding to the respective phases generated by the independent voltage balance controller 460 to achieve the three-phase voltage balance.

The modulator 440 receives the voltage control commands V _a3 *, V _b3 *, V _c3 * and generates a control signal PWM according to the voltage control commands V _a3 *, V _b3 *, V _c3 * , respectively. Wherein, the control signal PWM controls the voltage conversion action of the subsequent stage power converter corresponding to the grid voltages of three different phases.

It can be seen from the above description that the present invention provides a decentralized control mechanism for individually controlling the voltage conversion actions of each of the preceding stage power converters through the autonomous voltage adjustment controller, and controlling the overall and each through the total current adjustment controller. The voltage conversion action of the cluster power converter. With a decentralized control architecture, the number of communication channels between the controller (autonomous voltage regulation controller and total current regulation controller) and the power converter can be reduced to a limited extent, greatly reducing the complexity of the system design. Have Improve the performance of the series-connected power conversion device.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

Claims (9)

A series-connected power conversion device includes: a plurality of grid voltage generators respectively providing a plurality of grid voltages, each grid voltage generator comprising a plurality of power converters connected in series, the power converters being divided into a plurality of front a stage power converter and at least one post-stage power converter; a plurality of autonomous voltage adjustment controllers respectively coupled to the pre-stage power converters in the grid voltage generators, each of the autonomous voltage adjustment controllers according to a corresponding a front-end DC voltage and a grid voltage to control voltage conversion actions of each of the pre-stage power converters; and a total current adjustment controller coupled to the post-stage power converters in the grid voltage generators, according to the a plurality of grid currents on the grid voltage generator and a plurality of post-stage DC voltages received by the post-stage power converters to control voltage conversion actions of the post-stage power converters, wherein each of the autonomous voltage adjustment controllers comprises: a first operator calculates a difference between the corresponding front-level DC voltage and the DC voltage command; a first regulator coupled to the first The controller adjusts the difference to obtain an adjusted difference; a second operator is coupled to the first regulator to perform an arithmetic operation on the adjusted difference according to the corresponding grid voltage to generate a command a voltage value; and a first modulator that receives the command voltage value and generates a control signal according to the command voltage value, The control signal is used to control the voltage conversion action of the corresponding front stage power converter. The tandem power conversion device of claim 1, wherein the first operator is a subtractor, and the subtractor receives a corresponding front-end DC voltage and the DC voltage command, and causes the DC voltage command The corresponding front stage DC voltage is subtracted to produce the difference. The tandem power conversion device of claim 1, wherein the first regulator is a proportional integral regulator. The serial power conversion device of claim 1, wherein the second operator comprises: a multiplier, multiplying the adjusted difference value according to the corresponding grid voltage to obtain a multiplication result; An adder multiplies the corresponding grid voltage according to the multiplication result to obtain the command voltage value. The series-connected power conversion device of claim 1, wherein the total current adjustment controller comprises: a total power controller, generating a power current command according to an average value of the second-level DC voltages; And a cluster voltage controller, respectively generating a plurality of cluster power commands according to the plurality of differences between the subsequent DC voltages and the average value, and performing zero sequence voltage command calculations on the cluster power commands to generate a demand voltage command ; a current controller that generates a plurality of voltage control commands according to the current command, the injection voltage, the injection current, and the demand voltage command; and a second modulator that generates a plurality of control signals to control according to the voltage control commands The voltage conversion actions of the latter power converters. The tandem power conversion device of claim 5, wherein the total power controller comprises: an average voltage calculator that calculates the average value of the DC voltages of the latter stages; and a subtractor to make the average The value is subtracted from the DC voltage command to generate a subtraction result; a second regulator adjusts the subtraction result to produce an adjusted subtraction result; and an adder that adds the adjusted subtraction result to an offset current command This power current command is generated. The tandem power conversion device of claim 6, wherein the second regulator is a proportional integral regulator. The series-connected power conversion device of claim 5, wherein the cluster voltage controller comprises: a plurality of subtractors respectively subtracting the latter DC voltage from the average value and generating a plurality of subtractions a result; a plurality of second adjusters respectively adjusting the subtraction results to generate the cluster power commands respectively; A zero sequence voltage command calculator performs zero sequence voltage command calculations based on the cluster power commands to generate the demand voltage command. The series-connected power conversion device of claim 8, wherein the second regulators are proportional integral regulators.