CN-121984362-A - Parallel port type hexagonal mixing solid-state transformer and regulation and control method and device thereof

CN121984362ACN 121984362 ACN121984362 ACN 121984362ACN-121984362-A

Abstract

The invention discloses a parallel port type hexagonal mixing solid-state transformer and a regulating method and a regulating device thereof, wherein the method comprises the steps of calculating a stable relation between a fundamental frequency alternating current port current distribution coefficient and an intermediate frequency alternating current port current distribution coefficient in each sub-bridge arm under the condition that direct current active power and alternating current active power of the solid-state transformer are equal and instantaneous active power absorbed by each sub-bridge arm is 0; and calculating the bridge arm circulation current through the stable relation, so as to obtain a bridge arm circulation voltage reference value, calculating a sub-module capacitance voltage reference value of each sub-bridge arm, superposing each sub-module capacitance voltage correction component of each sub-bridge arm, obtaining a corresponding optimized sub-module capacitance voltage, and generating a corresponding modulation signal. By adopting the technical scheme, the method is suitable for the multi-scene access requirement of the AC/DC hybrid power distribution network, and can realize the inherent decoupling of the DC, fundamental frequency and intermediate frequency components without additional frequency selection network under the corresponding control method.

Inventors

SUN YICHAO
LU TIANYI
Yan Yinyu
CHEN WENZHE

Assignees

南京师范大学

Dates

Publication Date: 20260505
Application Date: 20260409

Claims (10)

1. The parallel port type hexagonal mixing solid-state transformer is characterized by comprising a left main bridge arm, a right main bridge arm, an intermediate frequency alternating current port, a fundamental frequency alternating current port, a medium voltage direct current port and a low voltage direct current port, wherein: The left main bridge arm and the right main bridge arm are connected in parallel, the parallel connection point is a first parallel point and a second parallel point, the left main bridge arm and the right main bridge arm both comprise sub-bridge arms, and a plurality of cascaded sub-modules are arranged on the sub-bridge arms; the left main bridge arm comprises a first left sub-bridge arm, a second left sub-bridge arm and a third left sub-bridge arm which are connected in series, and the serial connection points of the sub-bridge arms are a first left serial connection point and a second left serial connection point in sequence; The right main bridge arm comprises a first right sub-bridge arm, a second right sub-bridge arm and a third right sub-bridge arm which are connected in series, and the serial connection points of the sub-bridge arms are a first right serial connection point and a second right serial connection point in sequence; The first left series point and the first right series point are paired to form a first alternating current port, and the second left series point and the second right series point are paired to form a second alternating current port; the first parallel point and the second parallel point are paired to form a medium-voltage direct current port; the medium-frequency alternating current port is connected with the primary side of the transformer, the secondary side of the transformer is connected with the input end of the rectifying circuit, and the output end of the rectifying circuit is used as a low-voltage direct current port.
2. The parallel port type hexagonal-shaped mixed solid state transformer of claim 1, comprising a full-bridge structure of the submodule on a bridge arm of which the voltage does not contain a direct-current voltage component, and a half-bridge structure of the submodule on a bridge arm of which the voltage contains a direct-current voltage component.
3. The parallel port type hexagonal-shaped mixed solid-state transformer of claim 2, comprising the number of upper half-bridge sub-modules of a sub-bridge arm, which is calculated based on a medium-voltage direct-current port voltage and a rated sub-module capacitance voltage, the number of full-bridge sub-modules of the sub-bridge arm, which is calculated based on a fundamental frequency alternating-current port voltage amplitude, a medium frequency alternating-current port voltage amplitude and a rated sub-module capacitance voltage, and the method is calculated by adopting the following formula: N=ceil(U dc /2U C ), M=ceil((U 1m +U 2m )/2U C ), The function ceil represents an upward rounding, N represents the number of half-bridge sub-modules on a sub-bridge arm, M represents the number of full-bridge sub-modules on the sub-bridge arm, U dc represents a medium-voltage direct-current port voltage, U C represents a rated sub-module capacitance voltage, U 1m represents a fundamental frequency alternating-current port voltage amplitude, and U 2m represents an intermediate frequency alternating-current port voltage amplitude.
4. A method for controlling a parallel port type hexagonal-shaped hybrid solid state transformer, which is applied to the parallel port type hexagonal-shaped hybrid solid state transformer as claimed in any one of claims 1 to 3, comprising: Under the condition that the direct current active power and the alternating current active power of the solid-state transformer are equal and the instantaneous active power absorbed by each sub-bridge arm is 0, calculating the stable relation between the fundamental frequency alternating current port current distribution coefficient and the intermediate frequency alternating current port current distribution coefficient in each sub-bridge arm; And calculating the bridge arm circulation current through the stable relation, so as to obtain a bridge arm circulation voltage reference value, further calculating to obtain a sub-module capacitance voltage reference value of each sub-bridge arm, superposing each sub-module capacitance voltage correction component of each sub-bridge arm, calculating to obtain a corresponding optimized sub-module capacitance voltage, and generating a corresponding modulation signal to control.
5. The method for controlling a parallel port type hexagonal-shaped mixed solid state transformer according to claim 4, wherein the stable relationship is represented by the following formula: λk=(1+k)/2, β=(λ-1)k, where λ represents a fundamental frequency ac port current distribution coefficient, β represents an intermediate frequency ac port current distribution coefficient, and k represents a ratio of fundamental frequency port power to intermediate frequency port power.
6. The method for regulating and controlling the parallel port hexagonal-shaped mixed solid state transformer according to claim 5, wherein the calculating the bridge arm circulating current through the stable relationship, thereby calculating the bridge arm circulating voltage reference value, comprises: Calculating to obtain each sub-bridge arm current through the fundamental frequency alternating current port current distribution coefficient and the intermediate frequency alternating current port current distribution coefficient, the fundamental frequency alternating current port current, the intermediate frequency alternating current port current and the medium voltage direct current port current under the stable relation, so as to obtain the actual value of the bridge arm circulating current; The current of each sub-bridge arm is calculated by adopting the following formula: i Pu =1/2I dc + λi o1 + βi o2 ,i Pm =1/2I dc + (λ - 1)i o1 + βi o2 ,i Pl =1/2I dc + (λ - 1)i o1 + (β - 1)i o2 , i Qu =1/2I dc - λi o1 - βi o2 ,i Qm =1/2I dc + (1 - λ)i o1 - βi o2 ,i Ql =1/2I dc + (1 - λ)i o1 + (1 - β)i o2 , Wherein I Pu 、i Pm and I Pl respectively represent a first left sub-arm current, a second left sub-arm current and a third left sub-arm current, I Qu 、i Qm and I Ql respectively represent a first right sub-arm current, a second right sub-arm current and a third right sub-arm current, I dc respectively represents a medium voltage direct current port current, and I o1 and I o2 respectively represent a fundamental frequency alternating current port current and a medium frequency alternating current port current; the bridge arm circulating current actual value and the bridge arm circulating current reference value are subjected to difference and are input into the QPR controller, and the bridge arm circulating current reference value is obtained through output.
7. The method for adjusting and controlling the parallel port type hexagonal mixed solid state transformer according to claim 4, wherein the further calculating to obtain the sub-module capacitance voltage reference value of each sub-bridge arm comprises: Superposing a fundamental frequency alternating current port voltage reference value or an intermediate frequency alternating current port voltage reference value on the basis of a bridge arm circulating current voltage reference value, a bridge arm circulating current restraining voltage and a medium voltage direct current port direct current common mode voltage to obtain each sub-bridge arm voltage reference value; the voltage reference value of each sub-bridge arm is calculated by adopting the following formula: U Pu_ref =1/2U dc - 1/2u o1_ref + U dc_com + u cir_ref + u spr , U Pm_ref =1/2u o1_ref - 1/2u o2_ref + U dc_com + u cir_ref + u spr , U Pl_ref =1/2U dc + 1/2u o2_ref + U dc_com + u cir_ref + u spr , U Qu_ref =1/2U dc + 1/2u o1_ref + U dc_com - u cir_ref + u spr , U Pm_ref =- 1/2u o1_ref + 1/2u o2_ref + U dc_com - u cir_ref + u spr , U Pl_ref =1/2U dc - 1/2u o2_ref + U dc_com - u cir_ref + u spr , Wherein U Pu_ref 、U Pm_ref and U Pl_ref respectively represent a first left sub-arm voltage reference value, a second left sub-arm voltage reference value, and a third left sub-arm voltage reference value, U Qu_ref 、U Qm_ref and U Ql_ref respectively represent a first right sub-arm voltage reference value, a second right sub-arm voltage reference value, and a third right sub-arm voltage reference value, U dc represents a medium voltage dc port voltage, U o1_ref and U o2_ref respectively represent a fundamental frequency ac port voltage reference value and a medium frequency ac port voltage reference value, and U dc_com 、u cir_ref and U spr respectively represent a medium voltage dc port dc common mode voltage, a bridge arm circulation voltage reference value, and a bridge arm circulation suppression voltage.
8. The method for adjusting and controlling the parallel port type hexagonal mixed solid state transformer according to claim 7, wherein the further calculating to obtain the sub-module capacitance voltage reference value of each sub-bridge arm comprises: Dividing the voltage reference value of each sub-bridge arm by the number of sub-modules on the corresponding sub-bridge arm to obtain the capacitance voltage reference value of the sub-module of each sub-bridge arm.
9. The method for controlling a parallel port type hexagonal mixed solid state transformer according to claim 4, wherein the capacitance-voltage correction component of each sub-module is calculated based on the capacitance-voltage balance control of the sub-module in the sub-bridge arm.
10. A regulation and control device of a parallel port type hexagonal mixed solid state transformer is characterized by comprising a stable relation calculation unit and an execution unit, wherein the regulation and control device is applied to the parallel port type hexagonal mixed solid state transformer as claimed in any one of claims 1 to 3, and the regulation and control device comprises the following components: The stable relation calculating unit is used for calculating the stable relation between the current distribution coefficient of the fundamental frequency alternating current port and the current distribution coefficient of the intermediate frequency alternating current port in each sub-bridge arm under the condition that the direct current active power and the alternating current active power of the solid-state transformer are equal and the instantaneous active power absorbed by each sub-bridge arm is 0; The execution unit is used for calculating the bridge arm circulation current through the stable relation, so as to calculate a bridge arm circulation voltage reference value, further calculate a sub-module capacitance voltage reference value of each sub-bridge arm, superimpose each sub-module capacitance voltage correction component of each sub-bridge arm, calculate a corresponding optimized sub-module capacitance voltage, and generate a corresponding modulation signal to control.

Description

Parallel port type hexagonal mixing solid-state transformer and regulation and control method and device thereof Technical Field The invention relates to the technical field of solid-state transformers, in particular to a parallel port type hexagonal mixing solid-state transformer and a regulating method and device thereof. Background With rapid development and application of new energy power generation, energy storage equipment and various direct current loads, an alternating current-direct current hybrid power distribution network becomes one of important directions of future power grid development. The solid-state transformer (Solid State Transformer, SST), also called a power electronic transformer (Power Electronics Transformer, PET), has the advantages of high efficiency, high reliability, permission of multi-voltage-class access, flexible control and the like, and is a key device of an alternating current-direct current hybrid power distribution network. However, the existing SST still has the problems of multiple power conversion stages, multiple modules and the like, so that the improvement of the power density of the SST system is limited to a great extent. In this regard, many research teams at home and abroad have attempted to improve these problems from the viewpoints of reducing the number of power conversion stages and reducing the number of module units, wherein the most representative is the mixing SST constructed based on the idea of multiplexing switching elements. However, the existing mixing SST almost introduces additional inductance and capacitance elements as frequency-selecting networks to realize frequency decoupling between ports, and the frequency-selecting networks increase the cost and the volume of the device to a certain extent, thus the idea of mixing is violated. In addition, the existing mixing SST is an improvement based on modular multilevel converter MMC topology and is limited by the factors of large number of MMC topology modules, bridge arm symmetry and the like, and the power density improvement and port expansion are limited. Disclosure of Invention The invention aims to provide a parallel port type hexagonal mixing solid-state transformer and a regulating method and device thereof, and aims to solve the problem that in the prior art, the mixing MMC-SST topology depends on an additional frequency-selecting network, so that the cost and the volume are increased. The technical scheme includes that the parallel port type hexagonal mixing solid-state transformer comprises a left main bridge arm, a right main bridge arm, an intermediate frequency alternating current port, a fundamental frequency alternating current port, a medium voltage direct current port and a low voltage direct current port, wherein the left main bridge arm and the right main bridge arm are connected in parallel, parallel connection points are a first parallel point and a second parallel point, the left main bridge arm and the right main bridge arm respectively comprise a sub bridge arm, a plurality of cascaded sub modules are arranged on the sub bridge arms, the left main bridge arm comprises a first left sub bridge arm, a second left sub bridge arm and a third left sub bridge arm which are connected in series, the serial connection points of the sub bridge arms are a first left serial point and a second left serial point in sequence, the serial connection points of the right main bridge arm comprise a first right sub bridge arm, a second right sub bridge arm and a third right sub bridge arm which are connected in series, the serial connection points of the sub bridge arms are a first right serial point and a second parallel point, the first left serial point is matched with the first right serial point and the first parallel point, the second left serial point is matched with the second serial connection point is formed into a first alternating current port, the second left sub bridge arm and the intermediate frequency alternating current port is matched with the intermediate frequency alternating current port, the serial connection points of the second direct current port is connected with the intermediate frequency rectifying circuit, and the intermediate frequency port is formed into an alternating current port, and the direct current port is connected with an alternating current port in parallel connection port. Specifically, on the sub-bridge arm of which the voltage does not contain a direct-current voltage component, the structure of the sub-module is a full-bridge structure, and on the sub-bridge arm of which the voltage contains a direct-current voltage component, the structure of the sub-module is a half-bridge structure. The number of the full-bridge sub-modules on the sub-bridge arm is calculated based on the amplitude of the fundamental frequency alternating current port voltage, the amplitude of the intermediate frequency alternating current port voltage and the capacitance voltage o