基于能量分析的MMC-STATCOM电容电压三级平衡控制

Three-level Capacitor Voltage Balance Control of MMC-STATCOM Based on Energy Analysis

为实现模块化多电平变流器（MMC）作为电网静止同步补偿器（STATCOM）进行无功补偿的目的,同时满足各模块电容电压平衡的要求,可以采用三级能量平衡控制策略。首先对MMC中相与相之间、上桥臂与下桥臂之间、子模块与子模块之间能量变换和转移机理及特性进行了深入分析。详细探讨了影响MMC能量平衡的决定因素;又采用了基于准PR控制器的二倍频环流抑制策略抑制环流;在此基础上,借鉴了三级能量平衡控制策略,实现了电容电压的平衡控制。仿真结果表明：通过对MMC内部能量平衡控制,能够减缓系统遭受相间负载不平衡大扰动后的电容电压波动,从而避免由于三相不平衡所引起的STATCOM脱网运行事故。采用所提的电容电压平衡控制策略可以有效提高MMC-STATCOM的安全稳定运行能力。

To achieve the goal of reactive power compensation and capacitor voltage balance of modular multiple-level converters（MMC） used in static synchronous compensator（STATCOM）, the three-level energy balance control strategy is used. Firstly, we analyzed an energy transform and transfer for MMC in detail, which explains how the energy can be transmitted from one phase to another phase, between the upper and lower arms, and among the SMs. Then, we discussed the determinant of influencing energy balance of MMC is. Thirdly, we adopted the circulating current suppression strategy based on quasi-PR controller. Thereby, the three-level energy balance control strategy is used for reference to realize the balance control of capacitor voltage. The simulation results show that the capacitor voltage large fluctuations caused by load unbalance between phases can be smoothed by utilizing the three-level energy balance control of MMC. The occurrence of the STACOM＇s unstable operation which is caused by the load unbalance between phases can be avoided as well. Therefore, the proposed capacitor voltage balance control strategy can effectively enhance the security and stability of the MMC-STATCOM.