CN-121984361-A - MMC loss balance control method and system based on upper and lower limits of switching factors

CN121984361ACN 121984361 ACN121984361 ACN 121984361ACN-121984361-A

Abstract

The invention discloses an MMC loss balance control method and system based on upper and lower limits of switching factors, which specifically comprises the steps of adjusting actually sampled submodule capacitor voltage based on submodule switching states, defining the actually sampled submodule capacitor voltage as first submodule correction capacitor voltage, calculating the switching factors of all submodules, calculating second correction capacitor voltage based on the switching factors of the submodules and the upper and lower limits of the switching factors, calculating third submodule correction capacitor voltage based on the upper and lower limits of the submodule capacitor voltage, and selecting corresponding submodules for switching and cutting based on the third correction capacitor voltage and an MMC modulation strategy. The invention can effectively balance the switching frequency and the switching loss distribution among the submodules of the modularized multi-level converter under the low switching frequency, thereby effectively improving the running reliability of the converter, simultaneously, the invention does not need to additionally increase a sensor, does not need to change the hardware structure of an MMC system, has simple control and easy implementation, and has stronger economy and practicability.

Inventors

DENG FUJIN
LI ZHOU
MEI JUN
Cheng Chenwen
LI HUAILONG
DAI SHANGJIAN
LI HUI
YAO RAN
LAI WEI
ZHU JING
LEI JIAXING
ZOU ZHIXIANG

Assignees

东南大学
重庆大学

Dates

Publication Date: 20260505
Application Date: 20260408

Claims (10)

1. The MMC loss balance control method based on the upper limit and the lower limit of the switching factor is characterized by comprising the following steps: based on the submodule switching state of the last control period, the actual sampled submodule capacitor voltage is adjusted, and the actual sampled submodule capacitor voltage is defined as a first submodule correction capacitor voltage; collecting bridge arm current and a switching signal of each sub-module, and calculating switching factors of the sub-modules; Based on the switching factor of the sub-module and the upper limit and the lower limit of the switching factor, the correction capacitance voltage of the first sub-module is adjusted to obtain the correction capacitance voltage of the second sub-module; Based on the upper limit and the lower limit of the capacitance voltage of the submodule, the correction capacitance voltage of the second submodule is adjusted to obtain the correction capacitance voltage of the third submodule; And based on the capacitance voltage corrected by the third submodule and the modulation strategy of the MMC, selecting a corresponding submodule to carry out investment and excision.
2. The method of claim 1, wherein the first submodule corrects the capacitor voltage to: , Wherein the method comprises the steps of Representing the corrected capacitor voltage of the first sub-module, Representing the actual sampled sub-module capacitance voltage, The submodule switching state of the last control period is represented, =1 Indicates that the ith sub-module is in the on state in the last control period, =0 Means that the submodule was in the cut-off state in the last control cycle; Is bridge arm current; The voltage is adjusted for the first submodule capacitance.
3. The method according to claim 2, wherein the switching factor calculation method of the sub-module is: , Wherein the method comprises the steps of Representing the switching factors of the sub-modules, Switching loss of the power device of the ith sub-module in the bridge arm; is the average switching loss of all sub-modules in the bridge arm.
4. A method according to claim 3, wherein the second submodule modified capacitor voltage calculation method is as follows: ① When (when) At the time, there are ; ② When (when) In the time-course of which the first and second contact surfaces, Satisfies the following conditions , ③ When (when) In the time-course of which the first and second contact surfaces, Satisfies the following conditions , Wherein the method comprises the steps of 、 Respectively representing an upper switching factor limit and a lower switching factor limit, Representing the voltage of the second modified capacitor, The voltage is adjusted for the second submodule capacitance.
5. The method of claim 1, wherein the third submodule corrects the capacitor voltage to: , Wherein, the Indicating that the third sub-module corrects the capacitor voltage, 、 Respectively represent the upper limit and the lower limit of the capacitance voltage of the submodule, The voltage is adjusted for the third submodule capacitance.
6. The method according to claim 1, characterized in that the submodule investment and excision principle is as follows: if the bridge arm current Input into The third submodule corrects the submodule with the lowest capacitance voltage and cuts off The third submodule corrects the submodule with the highest capacitance voltage; if the bridge arm current Input into The third submodule corrects the submodule with the highest capacitance voltage and cuts off The third submodule corrects the submodule with the lowest capacitance voltage; Wherein the method comprises the steps of The method is obtained by a modular multilevel converter modulation mode, and N represents the number of sub-modules.
7. MMC wear-leveling control system based on switching factor upper and lower limit, characterized by comprising: the first capacitance voltage correction module is used for adjusting the actually sampled capacitance voltage of the submodule based on the switching state of the submodule in the last control period to obtain the corrected capacitance voltage of the first submodule; The second capacitance voltage correction module is used for collecting bridge arm current and a switching signal of each sub-module and calculating a switching factor of each sub-module, and based on the switching factor of the sub-module and the upper limit and the lower limit of the switching factor, the first sub-module correction capacitance voltage is adjusted to obtain a second sub-module correction capacitance voltage; The third capacitance voltage correction module is used for adjusting the capacitance voltage corrected by the second submodule based on the upper limit and the lower limit of the capacitance voltage of the submodule to obtain the capacitance voltage corrected by the third submodule; and the control module is used for correcting the capacitor voltage and the modulation strategy of the MMC based on the third submodule, and selecting the corresponding submodule to carry out investment and excision.
8. A computer program product comprising computer programs/instructions which, when executed by a processor, implement the steps of the method of any of claims 1-6.
9. An electronic system comprising at least one processor and a memory communicatively coupled to the at least one processor, wherein the memory stores instructions executable by the at least one processor, wherein the instructions are executable by the at least one processor to enable the at least one processor to perform the method steps recited in any one of claims 1-6.
10. A computer readable storage medium storing computer instructions for causing the computer to perform the method steps of any one of claims 1-6.

Description

MMC loss balance control method and system based on upper and lower limits of switching factors Technical Field The invention belongs to the field of multi-level power electronic converters, and particularly relates to an MMC loss balance control method. Background MMC (Modular Multilevel Converter), modularized multi-level converter, by virtue of the advantages of high modularization, high power quality, high control flexibility and the like, is widely applied to the fields of high-voltage flexible direct current transmission and the like. In order to improve the operation efficiency of the modularized multi-level converter, the switching frequency of the modularized multi-level converter in the flexible direct current transmission system is generally low, and the switching frequency is only about 80 Hz-120 Hz. At present, most researches focus on realizing the capacitance and voltage balance control of the submodule under the low switching frequency, but neglecting the influence of the low switching frequency on the loss distribution of the submodule. In practice, the lower switching frequency will cause serious imbalance in switching frequency and switching loss distribution among the sub-modules in the bridge arm of the modular multilevel converter, and further cause imbalance in operation life distribution among the sub-modules, which affects reliable operation of the modular multilevel converter and even the whole high-voltage flexible direct current transmission system. Disclosure of Invention The invention aims to solve the technical problems that the switching frequency and the switching loss distribution among all sub-modules in an inner bridge arm of an existing modularized multi-level converter are seriously unbalanced, and the reliable operation of the modularized multi-level converter is affected. In order to solve the technical problems, the invention adopts the following technical scheme: Firstly, the invention discloses an MMC loss balance control method based on upper and lower limits of a switching factor, which specifically comprises the following steps: Step 1, submodule switching state based on the previous control period Adjusting the capacitance voltage of the sub-module obtained by actual samplingDefined as the first submodule corrects the capacitor voltage; Step 2, collecting bridge arm current and switching signals of each sub-module, and calculating switching factors of each sub-module; Step 3, switching factor based on sub-moduleUpper limit of switching factorAnd a lower limit of the switching factorAdjusting the first submodule correction capacitor voltage generated in the step 1Obtaining a second corrected capacitor voltage; Step 4, based on the upper limit of the capacitance voltage of the submoduleAnd submodule capacitor voltage lower limitAdjusting the second submodule correction capacitor voltage generated in the step 3Obtaining the corrected capacitance voltage of the third submodule; Step 5, correcting the capacitance voltage based on the third submodule generated in the step4And the modulation strategy of the MMC, and selecting corresponding submodules to carry out investment and excision. Further, the first submodule in the step 1 corrects the capacitor voltageThe method comprises the following steps: , Wherein the method comprises the steps of =1 Indicates that the ith sub-module is in the on state in the last control period,=0 Means that the submodule was in the cut-off state in the last control cycle; Is bridge arm current; The voltage is adjusted for the first capacitance, typically, Can be selected as the rated capacitor voltage of the submodule. Further, the sub-module switching factor in the step 2Is that , Wherein the method comprises the steps ofSwitching loss of the power device of the ith sub-module in the bridge arm; is the average switching loss of all sub-modules in the bridge arm. AndThe calculation method of (2) is as follows: , wherein N is the number of sub-modules in the bridge arm; Switching loss for the jth IGBT device; Switching losses for the j-th diode device; An opening energy function of the IGBT device; the turn-off energy function of the IGBT device; reverse recovery energy function for the diode device; the total switching times of the submodule in a power frequency period are; the current flowing in the kth switching operation of the jth IGBT; a current flowing through the jth diode device during the kth switching operation; The capacitance voltage of the sub-module in the kth switching operation. Further, the upper limit of the switching factor in the step3And a lower limit of the switching factorTypical values can be selected to be 10% and-10%, respectively, and the second sub-module corrects the capacitor voltage in step 3The calculation method comprises the following steps: ① When (when) At the time, there are; ② When (when)In the time-course of which the first and second contact surfaces,Satisfies the following formula: , Wh