CN-121984360-A - Carrier phase shift modulation method and system suitable for mixed MMC overmodulation working condition

CN121984360ACN 121984360 ACN121984360 ACN 121984360ACN-121984360-A

Abstract

The application provides a carrier phase shift modulation method suitable for a mixed MMC overmodulation working condition, which comprises the steps of generating initial modulation wave signals of a half-bridge submodule and a Quan Qiaozi module of any phase bridge arm in the mixed MMC, correcting the initial modulation wave signals of the same bridge arm, superposing a second harmonic voltage on a modulation wave of the half-bridge submodule, simultaneously subtracting the same second harmonic voltage from the modulation wave of a full-bridge submodule, and respectively carrying out carrier phase shift pulse width modulation on the half-bridge submodule and the full-bridge submodule based on the corrected modulation wave. According to the application, the negative value of the half-bridge submodule modulation wave is eliminated by injecting opposite second harmonic voltages into the half-bridge submodule and the full-bridge submodule modulation wave in the same bridge arm, and meanwhile, the low harmonic characteristic of the bridge arm output voltage is maintained.

Inventors

ZHOU JIANQIAO
ZHANG JIANWEN
TONG YU
SHI GANG
YANG RENXIN
CAI XU
WANG HAN

Assignees

上海交通大学

Dates

Publication Date: 20260505
Application Date: 20260130

Claims (10)

1. The carrier phase shift modulation method suitable for the mixed MMC overmodulation working condition is characterized by comprising the following steps of: Generating initial modulation wave signals of a half-bridge sub-module and Quan Qiaozi modules of any phase bridge arm in the mixed MMC; Correcting the initial modulated wave signal of the same bridge arm, namely superposing a second harmonic voltage on the modulated wave of the half-bridge submodule and simultaneously subtracting the same second harmonic voltage from the modulated wave of the full-bridge submodule; and carrying out carrier phase-shifting pulse width modulation on the half-bridge submodule and the full-bridge submodule respectively based on the corrected modulated wave.
2. The carrier phase shift modulation method suitable for mixed MMC overmodulation conditions according to claim 1, wherein the modulation degree is the ratio of the amplitude of the phase voltage to half of the voltage of the direct current bus; The overmodulation working condition is a working condition that the modulation degree is larger than a preset value, and when the overmodulation degree working condition is adopted, the bridge arm output voltage has a negative value interval, and at the moment, the half-bridge submodule cannot output negative voltage, so that alternating current output voltage distortion can be caused.
3. The carrier phase shift modulation method suitable for the overmodulation condition of a hybrid MMC according to claim 1, wherein the correcting the initial modulated wave signal of the same bridge arm includes: when the second harmonic voltage is not injected, the initial modulation waves of the half-bridge sub-module and the Quan Qiaozi module of any phase bridge arm are obtained; determining the phase angle and amplitude of the injected second harmonic voltage according to the initial modulation waves of the half-bridge sub-module and the Quan Qiaozi module and the set principle; and adding one second harmonic voltage to the modulated wave of the half-bridge submodule, reducing one second harmonic voltage in the modulated wave of the half-bridge submodule, and generating new modulated waves of the half-bridge submodule and the full-bridge submodule after the second harmonic voltage is injected.
4. The carrier phase shift modulation method suitable for mixed MMC overmodulation conditions according to claim 3, wherein the setting principle is that when the phase angle of the second harmonic voltage is determined, the modulation wave of a bridge arm reaches a minimum value and the second harmonic voltage is at a maximum value when the second harmonic voltage is not injected.
5. The carrier phase shift modulation method for mixed MMC overmodulation of claim 4, wherein when the phase angle of the second harmonic voltage is δ 2nd , the phase angle of the second harmonic voltage needs to satisfy: ; Taking an upper bridge arm of a phase as an example, wherein delta is the phase angle of an a-phase voltage initial modulation wave of the MMC; The phase angle of the b-phase voltage initial modulation wave of the MMC lags 120 degrees with the phase angle of the a-phase voltage initial modulation wave of the MMC, and the phase angle of the c-phase voltage initial modulation wave of the MMC lags 240 degrees with the phase angle of the a-phase voltage initial modulation wave of the MMC.
6. The carrier phase shift modulation method for mixed MMC overmodulation according to claim 5, wherein a mixing ratio is defined when determining the phase angle and amplitude of the injected second harmonic voltage, and the amplitude of the injected second harmonic voltage and the phase angle of the second harmonic voltage are determined by the mixing ratio; The defined mixing ratio is the ratio of the number of half-bridge submodules to the total submodules; After the optimal phase angle of the second harmonic voltage is determined, the modulated wave expression of the half-bridge submodule after the second harmonic voltage is injected is as follows: ; Taking an a-phase upper bridge arm plate bridge sub-module as an example, wherein ap is an a-phase upper bridge arm; For a mixing ratio; U 2nd is the amplitude of the second harmonic voltage; is the voltage of a direct current bus; Is the amplitude of the phase voltage; is angular frequency; Time is; Is a modulation degree; wherein the second harmonic voltage is at a maximum value, minimizing the amplitude of the injected second harmonic voltage.
7. The carrier phase shift modulation method for mixed MMC overmodulation of claim 6, wherein the optimal amplitude of the second harmonic voltage is determined by the minimum value of the modulation wave of the half-bridge sub-module; And the minimum value of the modulation wave of the half-bridge submodule is larger than 0.
8. The carrier phase shift modulation method for mixed MMC overmodulation of claim 7 wherein said half-bridge submodule has a minimum value of the modulated wave to As a variable which is to be taken as a result, obtaining an extremum of a quadratic function; minimum value of modulation wave of the half-bridge submodule : ; In the formula, Is a modulation degree; For a mixing ratio; the amplitude of the phase voltage, and U 2nd is the amplitude of the second harmonic voltage.
9. The carrier phase shift modulation method suitable for mixed MMC overmodulation conditions of claim 8, wherein the second harmonic voltage has an amplitude expressed as: ; In the formula, For a mixing ratio; Is the magnitude of the phase voltage.
10. Carrier phase shift modulation system suitable for mixed MMC overmodulation condition, characterized by comprising: The initial modulation wave generation module is used for generating initial modulation wave signals of a half-bridge sub-module and Quan Qiaozi modules of any phase bridge arm in the mixed MMC; The harmonic injection module is used for correcting the initial modulation wave signals of the same bridge arm, namely superposing a second harmonic voltage on the modulation wave of the half-bridge submodule and simultaneously subtracting the same second harmonic voltage from the modulation wave of the full-bridge submodule; And the control module is used for respectively carrying out carrier phase-shifting pulse width modulation on the half-bridge submodule and the full-bridge submodule based on the corrected modulated wave.

Description

Carrier phase shift modulation method and system suitable for mixed MMC overmodulation working condition Technical Field The application relates to the technical fields of power electronics and electrochemical energy storage in a power system, in particular to a carrier phase shift modulation method and system suitable for a mixed MMC overmodulation working condition. Background In recent years, the installed capacity of renewable energy sources such as wind energy, solar energy and the like is continuously increasing. In order to cope with the volatility and intermittence of renewable energy sources, more and more energy storage technologies are applied in the renewable energy power generation field. The battery energy storage system has a very wide application range due to the diversity of the carriers. The power conversion system (power conversion system, PCS) is used as an interface between the battery system and the alternating current power grid and is a core component for the grid connection of the BESS, so that the charge and discharge efficiency and the system reliability of the BESS are determined. The high-voltage linear battery pack is intensively deployed on the direct-current bus of the modularized multi-level converter (modular multilevel converter, MMC) to separate the battery system from the PCS, so that a power frequency transformer can be omitted to reduce the volume and improve the efficiency, and the heat management problem and the maintenance difficulty problem caused by the integration of the battery module into the PCS unit can be avoided. In the prior art, publication number CN114204586A discloses a second harmonic injection method for restraining MMC capacitor voltage fluctuation, which is suitable for multiple working conditions and comprises the following steps of 1, obtaining a three-phase bridge arm instantaneous power expression after double frequency circulation injection, establishing an optimized objective function based on fundamental frequency and double frequency fluctuation components of the three-phase bridge arm instantaneous power, 2, determining the double frequency circulation and injection amplitude and phase according to an optimized calculation result, and 3, generating reference signals required by a controller according to the calculated amplitude and phase. However, when the high-voltage direct-connected battery pack discharges, the dc bus voltage of the MMC may decrease, and an overmodulation problem may occur. In view of modulation degree and economy, the PCS may employ a hybrid MMC, i.e., the bridge arm submodule includes a half-bridge submodule and Quan Qiaozi modules. When the mixed MMC works under the overmodulation working condition, the half-bridge submodule cannot output negative voltage, and the traditional carrier phase-shifting modulation strategy can cause the output voltage distortion of the half-bridge submodule, so that the harmonic content of the output voltage is increased. The MMC sub-modules in the medium voltage occasion have fewer numbers, and the low harmonic content requirements of alternating voltage and current are hardly met by adopting the nearest level approximation modulation. Disclosure of Invention Aiming at one of the defects in the prior art, the application aims to provide a carrier phase shift modulation method and a carrier phase shift modulation system suitable for a mixed MMC overmodulation working condition. In a first aspect of the present application, a carrier phase shift modulation method suitable for a mixed MMC overmodulation condition is provided, including: Generating initial modulation wave signals of a half-bridge sub-module and Quan Qiaozi modules of any phase bridge arm in the mixed MMC; Correcting the initial modulated wave signal of the same bridge arm, namely superposing a second harmonic voltage on the modulated wave of the half-bridge submodule and simultaneously subtracting the same second harmonic voltage from the modulated wave of the full-bridge submodule; and carrying out carrier phase-shifting pulse width modulation on the half-bridge submodule and the full-bridge submodule respectively based on the corrected modulated wave. Optionally, the modulation degree is the ratio of the amplitude of the phase voltage to half of the voltage of the direct current bus; The overmodulation working condition is a working condition that the modulation degree is larger than a preset value, and when the overmodulation degree working condition is adopted, the bridge arm output voltage has a negative value interval, and at the moment, the half-bridge submodule cannot output negative voltage, so that alternating current output voltage distortion can be caused. Optionally, the correcting the initial modulated wave signal of the same bridge arm includes: when the second harmonic voltage is not injected, the initial modulation waves of the half-bridge submodule and the Quan Qiaozi module of any phase bridge arm are obtai