一种基于子模块投入优先级的模块化多电平换流器电容电压均衡控制策略

A Capacitor Voltage Balancing Control Method for Modular Multilevel Converter Based on Insertion Priority of the Sub-modules

针对传统排序均压策略应用于高电平数模块化多电平换流器时存在计算量大、功率器件开关频率高等问题,提出一种基于子模块投入优先级的新型均压策略。该策略引入"电压容许分布带"来约束电容电压的波动范围,无需对子模块电压排序。分别将上一控制周期投入和切除的子模块电压值与分布带上下限比较,以确定各子模块在当前控制周期的投入优先级,并按优先级由高到低的顺序重新排列形成优先投入子模块序号向量,再根据投入子模块数指令值选取该向量最前面相应数量的子模块投入。接着分析各投入优先级间的子模块数量约束关系,给出电压离散度阈值上下限的确定依据,并讨论所提均压策略对混合型MMC的适应性。基于MATLAB/Simulink的仿真结果表明,所提均压策略不论在稳态还是暂态过程,都能保证较高的电容电压一致性并显著降低功率器件的开关频率,具有较好的稳态和动态性能。

Aiming at the computation complexity and high switching frequency existing in conventional voltage balancing method of high-level modular multilevel converter, a novel voltage balancing method based on insertion priority of sub-modules(SMs) was proposed. Instead of sorting the voltage values of SMs, the allowable voltage distribution band(AVDB) was applied to constrain the voltage distribution of SMs. The insertion priorities of each SM in current control cycle were determined by comparing the voltage values of SMs switched IN or OUT in last control cycle with the upper and lower limits of AVDB respectively. Then the serial number vector of SMs was rearranged according to the high-to-low priority rule, and the corresponding number of SMs at the forefront of the vector was selected to insert. Furthermore, the quantity relationship of SMs among each priority was analyzed, and the basis for determining the upper and lower limits of the voltage dispersion threshold was given. The simulation results based on MATLAB/Simulink show that the proposed method can reduce the switching frequency of power devices significantly when maintaining high capacitor voltage consistency, whether in steady or transient process.