CN-121984363-A - Mixing regulation and control method and device based on four-bridge arm type mixing solid-state transformer

CN121984363ACN 121984363 ACN121984363 ACN 121984363ACN-121984363-A

Abstract

The invention discloses a mixing regulation and control method and device based on a four-leg type mixing solid-state transformer, wherein the method comprises the steps of respectively calculating modulation signals of four sub-legs in the solid-state transformer; the method comprises the steps of utilizing the nearest level to approach modulation, respectively carrying out quantization processing on modulation signals of four sub-bridge arms to generate a step wave, determining the number of basic sub-modules which are put into use in each sub-bridge arm according to the voltage amplitude of the step wave, controlling the corresponding sub-bridge arm if the step wave changes in a control period, and putting N sub-modules in the sub-bridge arm into use if the voltage imbalance value is larger than a corresponding threshold value in the control period, wherein N is the number of the basic sub-modules. By adopting the technical scheme, the sub-module switching operation frequency is obviously reduced by controlling the sub-module switching only when the step wave changes, the switching frequency is reduced, and the sub-bridge arm sub-module switching is controlled in a forced sequence only when the voltage imbalance value is too high, so that the switching frequency is reduced, and the switching loss is reduced.

Inventors

SUN YICHAO
Pan Moyun
Yan Yinyu
CHEN WENZHE
Qian Xuancheng
ZHANG YUZHUO

Assignees

南京师范大学

Dates

Publication Date: 20260505
Application Date: 20260409

Claims (10)

1. A mixing regulation and control method based on a four-bridge arm type mixing solid-state transformer is characterized by comprising the following steps: The method comprises the steps of respectively calculating modulation signals of four sub-bridge arms in a solid-state transformer, wherein a rectifying bridge arm comprises an upper bridge arm and a lower bridge arm which are connected in series, a plurality of sub-modules which are connected in series are arranged on the bridge arm, the sub-bridge arm of the upper bridge arm comprises a first sub-upper bridge arm and a second sub-upper bridge arm which are connected in series, the sub-bridge arm of the lower bridge arm comprises a first sub-lower bridge arm and a second sub-lower bridge arm which are connected in series, connecting wires led out from connecting points of the first sub-upper bridge arm and the second sub-upper bridge arm and connecting points of the first sub-lower bridge arm and the second sub-lower bridge arm are connected in series, the primary side of the transformer is connected, the secondary side of the transformer is connected with an input port of a rectifying circuit, the output ports of the rectifying circuit are connected with a three-phase inverter, the ports on two sides of the rectifying bridge arm are medium-voltage direct current ports, the connecting points of the upper bridge arm and the lower bridge arm are medium-voltage alternating current ports, and the output ports of the three-phase inverter are low-voltage alternating current ports; the method comprises the steps of respectively carrying out quantization processing on modulation signals of four sub-bridge arms by utilizing the latest level approximation modulation, generating corresponding ladder waves, and determining the number of basic sub-modules put into use in each sub-bridge arm at each time of an operation period according to the voltage amplitude of the ladder waves; In the control period, if the capacitance voltage of the submodule in the subleg deviates from the stable range of the voltage of the medium-voltage direct-current port, executing optimized sequencing voltage-sharing control on the corresponding subleg, otherwise executing frequency-reducing sequencing voltage-sharing control; The optimized sorting voltage equalizing control comprises that in a control period, if a voltage unbalance value is larger than a corresponding threshold value, N sub-modules in a sub-bridge arm are put into use, wherein N is the number of the basic sub-modules; The frequency-reducing sequencing equalizing control comprises the steps of determining the number of submodules which are put into use at the last moment and the number of submodules which are required to be put into use at the current moment, determining the number of optimized submodules which are required to be supplemented into or cut off from a current bridge arm at the current moment, and putting M submodules with the highest or lowest submodule capacitor voltage into use in the submodules which are not put into use according to the positive and negative currents of the bridge arm, or cutting off the M submodules with the highest or lowest submodule capacitor voltage in the submodules which are put into use, wherein M is the number of the optimized submodules.
2. The mixing regulation method based on the four-leg mixing solid-state transformer according to claim 1, wherein the calculating the modulation signals of the four sub-legs in the solid-state transformer respectively includes: calculating a basic modulation signal of each sub-bridge arm based on the fundamental frequency port voltage component, the intermediate frequency port voltage component and the direct current voltage component of the solid-state transformer; based on the circulating current suppression, the overall energy control and the capacitor voltage balance control of the solid-state transformer, corresponding circulating current suppression components, circulating voltage components and capacitor voltage balance control components are calculated respectively and are superposed on basic modulation signals of each sub-bridge arm, and four sub-bridge arm modulation signals are obtained.
3. The mixing regulation method based on the four-leg mixing solid-state transformer according to claim 2, wherein the modulation signals of the sub-legs are calculated by adopting the following formula: u p1 * =1/4U dc - 1/2u 1 * - 1/2u m * + u cir * + u spr * +Δu x * , u p2 * =1/4U dc - 1/2u 1 * + 1/2u m * + u cir * + u spr * +Δu x * , u n1 * =1/4U dc + 1/2u 1 * + 1/2u m * + u cir * + u spr * +Δu x * , u n2 * =1/4U dc + 1/2u 1 * - 1/2u m * + u cir * + u spr * +Δu x * , Wherein U p1 * 、u p2 * 、u n1 * and U n2 * represent voltage modulation signals of the first sub-upper arm, the second sub-upper arm, the first sub-lower arm and the second sub-lower arm, respectively, U dc represents a medium voltage direct current port voltage, U 1 * represents a fundamental frequency port voltage component, U m * represents an intermediate frequency port voltage component, U cir * represents a ring voltage component, U spr * represents a loop current suppression component, and Δu x represents a capacitance voltage balance control component.
4. The mixing regulation method based on the four-leg type mixing solid-state transformer according to claim 1, wherein the determining the number of the basic sub-modules put into use in each sub-leg at each time of the operation period according to the voltage amplitude of the step wave includes: And determining the number of the basic submodules put into use in the bridge arms according to the multiple relation between the amplitude of the step wave voltage and the capacitance voltage of the submodules at each time of the operation period.
5. The mixing regulation method based on the four-leg mixing solid-state transformer according to claim 1, wherein the calculating to obtain the corresponding voltage imbalance value comprises: Dividing the difference between the maximum submodule capacitance voltage and the minimum submodule capacitance voltage in the bridge arm by the average submodule capacitance voltage to obtain a voltage imbalance value corresponding to the bridge arm.
6. The mixing regulation method based on the four-leg mixing solid-state transformer according to claim 1, wherein the putting into use N sub-modules in the sub-leg comprises: And putting N sub-modules with the lowest sub-module capacitance voltages in the sub-bridge arms into use.
7. The mixing regulation method based on the four-leg type mixing solid-state transformer according to claim 6, wherein the N sub-modules with the lowest sub-module capacitance voltages in the sub-leg are put into use, and the method comprises the following steps: and determining the number of basic sub-modules at corresponding moments according to the step wave of the sub-bridge arm when the voltage unbalance value is larger than the corresponding threshold value.
8. The mixing regulation method based on the four-leg type mixing solid-state transformer according to claim 1, wherein the stabilizing range of the medium-voltage direct-current port voltage is 0.95U dc to 1.05U dc ,U dc , which represents the medium-voltage direct-current port voltage.
9. The mixing regulation and control method based on the four-leg type mixing solid-state transformer according to claim 1, wherein the frequency-reducing ordering voltage-sharing control comprises: When the sub-module needs to be added at the current moment, if the current of the sub-arm is positive, M sub-modules with the lowest capacitance voltage of the sub-modules are added into use in the sub-modules which are not added into use; when the submodules are required to be cut off on the bridge arm at the current moment, if the current of the bridge arm is positive, M submodules with the highest capacitance voltage of the submodules are cut off in the used submodules, and if the current of the bridge arm is negative, M submodules with the lowest capacitance voltage of the submodules are cut off in the used submodules.
10. A mixing regulation and control device based on a four-bridge arm type mixing solid-state transformer is characterized by comprising a modulation signal calculation unit, a first control unit and a second control unit, wherein: The modulating signal computing unit is used for respectively computing modulating signals of four sub-bridge arms in the solid-state transformer, wherein the phase rectifying bridge arm comprises an upper bridge arm and a lower bridge arm which are connected in series, a plurality of sub-modules which are connected in series are arranged on the bridge arm, the sub-bridge arm of the upper bridge arm comprises a first sub-upper bridge arm and a second sub-upper bridge arm which are connected in series, the sub-bridge arm of the lower bridge arm comprises a first sub-lower bridge arm and a second sub-lower bridge arm which are connected in series, connecting wires which are led out from connecting points of the first sub-upper bridge arm and the second sub-upper bridge arm and connecting points of the first sub-lower bridge arm and the second sub-lower bridge arm are connected with the primary side of the transformer, the secondary side of the transformer is connected with an input port of a rectifying circuit, an output port of the rectifying circuit is connected with a three-phase inverter, two-side ports of the phase rectifying bridge arm are medium-voltage direct-current ports, connecting points of the upper bridge arm and the lower bridge arm are medium-voltage alternating-current ports, and output ports of the rectifying circuit are low-voltage direct-current ports; The first control unit is used for carrying out quantization processing on the modulation signals of the four sub-bridge arms respectively by utilizing the latest level approximation modulation, generating four corresponding ladder waves, and determining the number of basic sub-modules put into use in each sub-bridge arm at each time of an operation period according to the voltage amplitude of the ladder waves; The second control unit is configured to execute optimized sequencing voltage-sharing control on a corresponding sub-bridge arm if the capacitance voltage of the sub-module in the sub-bridge arm deviates from a stable range of the voltage of the medium-voltage direct-current port in a control period, and execute down-sequencing voltage-sharing control otherwise, where the optimized sequencing voltage-sharing control includes that in the control period, if the voltage imbalance value is greater than a corresponding threshold value, N sub-modules in the sub-bridge arm are put into use, N is the number of basic sub-modules, the voltage imbalance value is calculated based on the degree of difference between the capacitance voltages of the sub-modules in the sub-bridge arm, the down-sequencing voltage-sharing control includes determining the number of sub-modules put into use at the last moment and the number of sub-modules that should be put into use at the current moment, determining the number of optimized sub-modules that need to be supplemented or cut off on the sub-bridge arm at the current moment, and according to the positive and negative sub-bridge arm current, in the sub-modules that the capacitance voltage of the sub-modules that is the sub-module is the highest or the sub-module is the lowest, or M sub-modules that have the capacitance voltage that is the highest or the sub-module is put into use.

Description

Mixing regulation and control method and device based on four-bridge arm type mixing solid-state transformer Technical Field The invention relates to the technical field of power electronics, in particular to a mixing regulation and control method and device based on a four-bridge arm type mixing solid-state transformer. Background The renewable energy industry is beginning to develop in an overall scale today, and high-permeability renewable energy grid connection presents a serious challenge to traditional ac grid architecture. The AC/DC hybrid power distribution network has the advantages of both an AC power grid and a DC power grid, has the capability of multi-voltage class and multi-voltage form access, can transmit and convert electric energy between AC/DC ports and high/low voltage ports, meets the requirements of new energy acceptance and high-efficiency load access, and is an important form of a future power distribution system. The solid-state transformer (solid state transformer, SST) is core equipment for constructing an efficient, reliable and intelligent alternating-current and direct-current hybrid power distribution network by virtue of the power electronic conversion and high-frequency magnetic isolation capability of the solid-state transformer. The modular multilevel converter type solid-state transformer (MMC-SST) (Modular Multilevel Converter, MMC) is provided with an MVDC port, can be applied to middle and high voltage power transmission and distribution occasions, and has wide application prospect. The structure of this type of MMC-SST can be mainly divided into an Input-Series Output-Parallel (ISOP-DAB) type and a Parallel-serial hybrid (MMC+parallel DAB group) type according to the connection mode of the intermediate-stage dual-active bridge DAB (Dual Active Bridge, DAB). The DAB type MMC-SST topology has the advantages of flexible control, easiness in realizing redundancy fault tolerance and the like, but a large number of switching devices are needed. The ISOP type MMC-SST has the problems that switching devices are reduced and the number of conversion grades is excessive, so that the power density of the SST is low, and the application of the MMC-SST is severely restricted. Aiming at the mixed solid-state transformer, the existing mixed modulation method superimposes high-frequency modulation wave components on the basis of traditional MMC fundamental frequency modulation waves, and the generated mixed modulation signals generate switching pulses through carrier phase shifting. Although the method can realize the basic function of mixing SST, the carrier frequency is required to be very high, and the switching loss is increased. Disclosure of Invention The invention aims to provide a mixing regulation and control method and device based on a four-bridge arm type mixing solid-state transformer, which aim to solve the problems that in the prior art, the power density of MMC-SST topology is low and the switching loss is caused by high switching frequency. The invention provides a mixing regulation and control method based on a four-leg mixing solid-state transformer, which comprises the steps of respectively calculating modulation signals of four sub-legs in the solid-state transformer; in the solid-state transformer, a rectifying bridge arm comprises an upper bridge arm and a lower bridge arm which are connected in series, wherein a plurality of submodules which are connected in series are arranged on the bridge arm, the submodule of the upper bridge arm comprises a first submodule upper bridge arm and a second submodule upper bridge arm which are connected in series, and the submodule of the lower bridge arm comprises a first submodule lower bridge arm and a second submodule lower bridge arm which are connected in series; the method comprises the steps of connecting a connecting point of a first sub upper bridge arm and a second sub upper bridge arm, connecting wires led out from the connecting point of the first sub lower bridge arm and the second sub lower bridge arm, connecting a primary side of a transformer, connecting a secondary side of the transformer with an input port of a rectifying circuit, connecting an output port of the rectifying circuit with a three-phase inverter, connecting two side ports of the rectifying circuit with a medium-voltage direct-current port, connecting the upper bridge arm and the lower bridge arm with a medium-voltage alternating-current port, connecting the output port of the rectifying circuit with a low-voltage direct-current port, performing quantization processing on modulation signals of the four sub bridge arms respectively by utilizing the nearest level approximation modulation, generating corresponding ladder waves, determining the number of basic sub modules put into use in each sub bridge arm at each moment of an operation period according to the voltage amplitude of the ladder waves, controlling the corresponding sub bridge arm if the