TW201919298A - Cascaded power converter apparatus - Google Patents

Abstract

A cascaded power converter apparatus includes a plurality of grid voltage generators, a plurality of autonomous voltage regulators (AVRs) and a total current regulator (TCR). The grid voltage generators respectively provide a plurality of grid voltages, each of the grid voltage generators includes a plurality of power converters, and the power converters are divided into a plurality of prior stage power converters and at least one rear stage power converter. Each of the AVRs controls a voltage converting operation of corresponding prior stage power converter according to corresponding prior direct current (DC) voltage and grid voltage. The TCR controls voltage converting operations of the rear stage power converters according to a plurality of grid currents and rear stage DC voltages of the rear stage power converters.

Description

<invention-title lang="zh">Serial-type power conversion device</invention-title><invention-title lang="en">CASCADED POWER CONVERTER APPARATUS</invention-title><technical-field><p> 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. </p></technical-field><background-art><p>Multi-level tandem power conversion devices are cascaded from a number of bridge converters and can be applied to higher voltage level grids. 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. </p></background-art><disclosure><p>The present invention provides a series-connected power conversion device with a distributed control mechanism, which can effectively improve fault tolerance and reduce the series-connected power conversion device The amount of wiring in the system reduces the complexity of the system design. The series-connected power conversion apparatus 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 performing voltage conversion actions of a plurality of pre-stage power converters in respective grid voltage generators in a series-connected power conversion device. control. 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 products. 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 present invention will be more apparent from the following description. </p></disclosure><mode-for-invention><p> Referring 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. Wherein, the grid voltage generators 110, 120 and 130 respectively provide the grid voltage V_a0 , V_b0 And V_c0 . 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. </p><p> 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 pre-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 according to the front stage DC voltage V_dca1 And the grid voltage V_a0 To generate the control signal PWM_a1 . Wherein, the control signal PWM_a1 It is transmitted to the power converter 111 and used to control the voltage conversion action of the power converter 111. </p><p> 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 based on the corresponding front-end DC voltage V<sub>dca1< /sub> ~V_dcaJ , V_dcb1 ~V_dcbJ , V_dcc1 ~V_dccJ And according to the corresponding grid voltage V_a0 , V_b0 And V_c0 To generate the control signal PWM_a1 respectively ~PWM_aJ ,PWM_b1 ~PWM_bJ ,PWM_c1 ~PWM_cJ . Control signal PWM_a1 ~PWM_aJ ,PWM_b1 ~PWM_bJ ,PWM_c1 ~PWM_cJ The power converters 111~11J, 121~12J and 131~13J are respectively transmitted to the power converters of the preceding stage, and respectively control the voltage conversion actions of the power converters 111~11J, 121~12J and 131~13J respectively. . </p><p>The total current adjustment controller TCR1 is coupled to the post-stage power converters in the grid voltage generators 110, 120, and 130 (the power converters 11J+1~11N, 12J+1~12N, and 13J+) 1~13N). The total current regulation controller TCR1 receives the grid current i_a at different phases on the grid , i_b And i_c And receiving the power converters 11J+1~11N, 12J+1~12N, and 13J+1~13N corresponding to the subsequent DC voltage V_dcaJ+1 ~V_dcaN , V_dcbJ+1 ~V_dcbN And V_dccJ+1 ~V_dccN And according to the grid current i_a , i_b And i_c And the subsequent stage DC voltage V_dcaJ+1 ~V_dcaN , V_dcbJ+1 ~V_dcbN And V_dccJ+1 ~V_dccN To generate the control signal PWM_aJ+1 ~PWM_aN ,PWM_bJ+1 ~PWM_bN And PWM_cJ+1 ~PWM_cN . Control signal PWM_aJ+1 ~PWM_aN ,PWM_bJ+1 ~PWM_bN And PWM_cJ+1 ~PWM_cN Transfer to the power converters 11J+1~11N, 12J+1-12N<u style="single"> and </u><u style="single">13J+1< as the power converters of the latter stage /u> -13N and used to control the voltage conversion action of the power converters 11N-13N. </p><p> As can be seen from the above description, the present invention is implemented for the pre-stage power converters (electric energy converters 111~11J, 121~12J, 131~13J) in the grid voltage generators 110-130. For example, one-to-one autonomous voltage adjustment controllers AVR11~AVR1J, AVR21~AVR2J, and AVR31~AVR3J are provided 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. </p><p> Incidentally, the pre-stage power converter mentioned in this embodiment is in each of the grid voltage generators 110-130, and the configuration position is closer to the grid voltage V<sub>a0< /sub> , V_b0 , V_c0 The power converter for the transmission line. In contrast, the so-called post-stage power converter is a common coupling point M whose configuration position is closer to the grid voltage generators 110~130 (relatively far from the grid voltage V_a0) , V_b0 , V_c0 Power transmission). 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. </p><p>In this embodiment, the grid voltage V_a0 , V_b0 , V_c0 It can be three voltage signals with different phases, wherein the grid voltage V_a0 , V_b0 , V_c0 Can have 120⁰ The phase difference. </p><p> Please refer to FIG. 2 below. FIG. 2 is a schematic diagram showing the hardware architecture of the grid voltage generator of the series-connected power conversion device according to the 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 211~21N respectively receive the DC voltage V_dca1 ~V_dcaN And the corresponding DC current i_dca1 ~i_dcaN And respectively, according to the received control signal, the four transistors respectively perform a switching action to respectively generate a voltage V_a1 , V_a2 And V_a3 . Through the series voltage V_a1 , V_a2 And V_a3 The grid voltage generator 210 can be caused to generate a voltage V_aM And generate grid voltage V_a0 . </p><p>In addition, the grid voltage generators 210-230 can respectively provide grid current i_a , i_b And i_c . In the present embodiment, the grid voltage generators 210-230 can be coupled to the origin O to form a Y-shaped connection configuration. </p><p> Please refer to FIG. 3 below. 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 received by the corresponding pre-stage power converter. And DC voltage command V_dc *, and calculate the DC voltage command V_dc * with the front stage DC voltage V_dca1 The difference. In the present embodiment, the arithmetic unit 310 is a subtractor. </p><p> 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, where constant K_pti , K_iti It can be set by the designer, and its value has no fixed limit. </p><p> The arithmetic unit 330 is coupled to the adjuster 320 and receives the adjusted difference according to the corresponding grid voltage V_a0 To perform an arithmetic operation on the adjusted difference to generate a command voltage value V_a1 *. In the present embodiment, the arithmetic unit 330 includes a multiplier 331 and an adder 332. Among them, the grid voltage V_ao Can pass through the voltage V_mag Divide by to generate a normalized grid voltage (V_a0 /V_mag ). Where the voltage V_mag Can be the grid voltage V_ao The maximum possible voltage value. The multiplier 331 can make the adjusted difference and the normalized grid voltage (V_a0 /V_mag ) Multiply. In addition, the adder 332 causes the multiplication result generated by the multiplier 331 to be related to the grid voltage V_a0 Divide by the quotient obtained by N (as a feedforward signal) and generate a command voltage value V_a1 *. Where N can be equal to the number of phases of the series-connected power conversion device. </p><p> modulator 340 receives command voltage value V_a1 *, and according to the command voltage value V_a1 * Perform a modulation action and thereby generate a control signal PWM_a1 . Control signal PWM_a1 It can be a wide-tune signal and is used to control the switching action of the transistor switch of the corresponding power converter. </p><p> Please refer to FIG. 4 below. FIG. 4 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 part 411 is an average voltage calculator, and the DC voltage of the latter stage is calculated as V_dcaJ+1 ~V_dcaN , V_dcbJ+1 ~V_dcbN And V_dccJ+1 ~V_dccN average of. 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. </p><p>The total power controller 410 includes a plurality of filters F11~F1M, F21~F2M<u style="single"> and </u><u style="single">F31~F3M</ u><u style="single">, computing unit</u><u style="single">4111a~4111c</u><u style="single">,</u><u style=" Single">4112a~4112c</u><u style="single">,</u><u style="single">4121</u><u style="single">and</u>< u style="single">4122</u> The subtractor 4123, the adjuster 413, and the adder 4124. Filters F11~F1M, F21~F2M<u style="single"> and </u><u style="single">F31~F3M</u><u style="single">for </u > After-stage DC voltage V_dcaJ+1 ~V_dcaN , V_dcbJ+1 ~V_dcbN And V_dccJ+1 ~V_dccN Filtering is performed. The arithmetic unit 4111a~4111c calculates the filtered subsequent stage DC voltage V'_dcaJ+1 ~V’_dcaN , V’_dcbJ+1 ~V’_dcbN , V’_dccJ+1~ V’_dccN And. The arithmetic units 4112a to 4112c respectively calculate the filtered subsequent stage DC voltage V'_dcaJ+1 ~ V’_dcaN , V’_dcbJ+1 ~V’_dcbN , V’_dccJ+1~ V’_dccN Average V_dcaT , V_dcbT , V_dccT And calculating the filtered after-stage DC voltage V'_dcaJ+1 through the arithmetic unit 4121 ~ V’_dcaN , V’_dcbJ+1 ~V’_dcbN , V’_dccJ+1~ V’_dccN The average sum of V_dcT . The operator 4122 makes the sum V_dcT Divide by 3 and calculate the DC voltage of the latter stage V_dcaJ+1 ~V_dcaN , V_dcbJ+1 ~V_dcbN And V_dccJ+1 ~V_dccN average of. Subtractor 4123 causes DC voltage command V_dc * Subtract the above average 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, where constant K_pto , K_ito It can be set by the designer, and its value has no fixed limit. </p><p>Adder 4124 causes the above-mentioned adjusted subtraction result and offset current command I_ff *Add and generate (on the q-axis) power current command I_q^P* . </p><p> In another aspect, the 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, respectively. *, P_Cb *and P_Cc *. 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, where constant K_ptc , K_itc It can be set by the designer, and its value has no fixed limit. </p><p>The zero sequence voltage command calculator 427 receives the cluster power command P_Ca *, P_Cb *and P_Cc *, and according to the cluster power command P_Ca *, P_Cb *and P_Cc * Perform zero sequence voltage command calculation to generate demand voltage command V_o *_TCR . </p><p> 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 algorithm for the calculation of the zero sequence voltage command in the memory (or any other storage medium) for calculation. 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. </p><p>The current controller 430 receives the power current command I_q^P* And positive and negative injection voltages on the d-q axis V_qd^pn Injection current voltage I_qd^pn To calculate and generate three-phase voltage requirements. In the present embodiment, the current controller 430 additionally receives the positive injection current command of the d-axis I_d^P* And set the negative injection current command of the d-q axis I_d^n* , I_q^n* Equal to 0. The current controller 430 additionally applies the adders AD1-AD3 to make the demand voltage command V_o *_TCR Adding to the calculated three-phase voltage demand, and generating a voltage control command V_a3 through the arithmetic unit 470 and the adders AD4~AD6, respectively. *, 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. </p><p>The modulator 440 receives the voltage control command V_a3 *, V_b3 *, V_c3 * and according to the voltage control command V_a3 *, V_b3 *, V_c3 * To generate the control signal PWM. 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. </p><p> It can be known from the above description that the present invention provides a decentralized control mechanism for individually controlling the voltage conversion action of each pre-stage power converter through an autonomous voltage adjustment controller, and through the total current adjustment control. The controller controls the voltage conversion actions of the overall and each 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. Effectively improve the performance of the series-connected power conversion device. The present invention has been disclosed in the above embodiments, and is not intended to limit the scope of the present invention. There are a few changes and modifications, and the scope of protection of the present invention is defined by the scope of the appended claims. </p></mode-for-invention><description-of-drawings><description-of-element><p>100‧‧‧ tandem power conversion device</p><p>110, 120, 130‧‧‧ Grid voltage generator</p><p>AVR11-AVR1J, AVR21-AVR2J, AVR31-AVR3J‧‧‧Autonomous voltage adjustment controller</p><p>TCR1‧‧‧Total current adjustment controller </p><p>V_a0, V_b0, V<sub>c0</us> ‧‧‧ grid voltage</p><p>111- 11N, 121-12N, 131-13N‧‧‧Power Converter</p><p>PWM, PWM_a1, PWM_a2, PWM<sub>b1< /sub>, PWM_b2, PWM_c1, PWM_c2, PWM_aN, PWM<sub>bN< /sub>,PWM_cN‧‧‧Control Signal</p><p>i_a, i_b, i_c‧‧‧ Grid current</p><p>V_dcaN, V_dcbN, V_dccN DC voltage</p><p>200‧‧‧Serial type power conversion device</p><p>210-230‧‧‧Grid voltage generator</p><p>211-21N‧‧‧electric energy Converter</p><p>V_dca1-V_dcaN‧‧‧(previous) DC voltage</p><p>i _dca1-i_dcaN‧‧‧ DC current</p><p>V_a1, V_a2, V_a3, V_aM‧‧‧voltage</p><p>O‧‧‧ origin</p><p>M‧‧‧ connection point< /p><p>300‧‧‧Autonomous Voltage Adjustment Controller</p><p>310, 330‧‧‧Operator</p><p>320‧‧‧ Adjuster</p><p> 340‧‧‧Transformer</p><p>V_dc*‧‧‧DC Voltage Command</p><p>V_a1*‧‧ Command voltage value</p><p>331‧‧‧Multiplier</p><p>332‧‧‧Adder</p><p>V_mag‧‧‧ Voltage< /p><p>400‧‧‧Total Current Regulation Controller</p><p>410‧‧‧Total Power Controller</p><p>420‧‧‧ Cluster Voltage Controller</p>< p>430‧‧‧ Current controller</p><p>440‧‧‧ 调器</p><p>413‧‧‧ adjuster</p><p>460‧‧‧ Independent voltage balance Controller</p><p>4122,470‧‧‧Operator</p><p>411‧‧‧Part 1</p><p>412‧‧‧Part II</p><p >4123‧‧‧Subtractor</p><p>4124‧‧Adder</p><p>V_dcaJ+1~V_dcaN, V _dcbJ+1~V<sub>dcbN</ Sub>, V_dccJ+1~V_dccN‧‧‧ After DC voltage</p><p>F11~F1M, F21~F2M<u style=" Single">,</u><u style="single">F31~F3M</u>‧‧‧Filter</p><p><u style="single">4111a~4111c</u> <u style="single">,</u><u style="single">4112a~4112c</u><u style="single">,</u><u style="single">4121 </u><u style="single">,</u><u style="single">4122</u>‧‧‧<u style="single">Operator</p><p> </u>V'_dcaJ+1~ V'_dcaN, V'_dcbJ+1~V'_dcbN >,V'_dccJ+1~V'_dccN‧‧‧Filtered post-level DC voltage</p><p>V<sub>dcaT</sub >, V_dcbT, V_dccT‧‧‧ average</p><p>I_q^P* ‧‧‧Power Current Command</p><p>I_ff*‧‧‧Offset Current Command</p><p>421-423‧‧‧Subtractor</p>< p>424-426‧‧‧ adjuster</p><p>427‧‧‧ Zero-order voltage command calculator</p><p>P_Ca*, P_Cb*, P_Cc*‧‧‧Cluster Power Command</p><p>V_o*_TCR‧ ‧Required voltage command</p><p>V_qd^pn‧‧‧Injection voltage</p><p>I_qd< Sup>pn</sup>‧‧‧Inject current and voltage</p><p>AD1-AD6‧‧‧Adder</p><p>I_d<sup>P*< /sup>, I_d^n*, I_q^n*‧‧‧Inject current command</p ><p>V_a3*, V_b3*, V_c3*‧‧‧Voltage Control Command</p></description- FIG. 1 is a schematic diagram of a series-connected power conversion device according to an embodiment of the present 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. </p></description-of-drawings><bio-deposit></bio-deposit><sequence-list-text></sequence-list-text>

Claims (10)

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 of 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 subsequent stage DC voltages received by the after-stage power converters control voltage conversion actions of the subsequent stage power converters. The serial power conversion device of claim 1, wherein each of the autonomous voltage adjustment controllers comprises: a first operator that calculates a difference between the corresponding front-level DC voltage and the DC voltage command; a regulator coupled to the first operator to adjust the difference to obtain an adjusted difference; a second operator coupled to the regulator to perform the adjusted difference according to the corresponding grid voltage An arithmetic operation to generate a command voltage value; and a modulator that receives the command voltage value and generates a control signal according to the command voltage value, wherein the control signal is used to control a voltage of the corresponding front stage power converter Conversion action. The tandem power conversion device of claim 2, 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 series-connected power conversion device of claim 2, wherein the regulator is a proportional integral regulator. The tandem power conversion device of claim 2, 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 modulator that generates a plurality of control signals according to the voltage control commands to control the The voltage conversion action of some of the latter power converters. The tandem power conversion device of claim 6, 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; an adjuster adjusts the subtraction result to produce an adjusted subtraction result; and an adder that adds the adjusted subtraction result to an offset current command to generate the subtraction result Power current command. The series-connected power conversion device of claim 7, wherein the regulator is a proportional-integral regulator. The series-connected power conversion device of claim 6, wherein the cluster voltage controller comprises: a plurality of subtractors respectively subtracting the latter DC voltages from the average value and generating a plurality of subtractions As a result, a plurality of adjusters respectively adjust the subtraction results to generate the cluster power commands respectively; and a zero sequence voltage command calculator to perform a zero sequence voltage command calculation according to the cluster power commands to generate the demand voltage command. The series-connected power conversion device of claim 9, wherein the adjusters are proportional integral adjusters.