负载不平衡条件下MMC-STATCOM补偿策略研究

文中介绍了静止同步补偿器(STATCOM)在电网中的无功补偿原理及电压补偿原理,针对传统STATCOM拓扑电平数提升困难问题,采用了模块化多电平换流器(MMC)拓扑的STATCOM补偿负载不平衡条件下的电压。针对传统平衡条件下的控制策略在负载不平衡时控制效果较差的问题,在正负序模型下对此无功补偿器进行分析并提出了采用将电压和电流分成正序和负序分别控制的分序控制策略,用解耦双同步参考坐标系的锁相环技术锁住公共连接点处电压,同时对MMC子模块电容电压平衡采用分布式控制,最后在电磁暂态仿真软件PSCAD/EMTDC中搭建五电平静止无功补偿器,通过仿真验证了分序控制策略和子模块电容电压分布式控制策略的有效性。

The compensation method of MMC-STATCOM under unbalanced load condition

In this paper, the reactive power and voltage compensation principles of static synchronous compensator (STATCOM) are introduced. In order to easily increase the output voltage levels, a STATCOM based on modular multilevel converter (MMC) is proposed as well. Since the conventional control strategy is mostly focused on the system performance with balanced load and its control performance is usually unsatisfying under unbalanced conditions. In this paper, the STATCOM is analyzed using positive-, negative- sequence model and based on that, the sequence control method is applied and elaborated. The voltages at point of common coupling (PCC) are locked by applying the decoupled double synchronous reference frame-Phase locked loop (DDSRF-PLL). The sub-module (SM) capacitor voltages of MMC are balanced by a distributed control strategy which avoids large amount of information exchange between central controller and local controllers. The simulation model of a five-level MMC based STATCOM is built in PSCAD/EMTDC. Simulation results validate the correctness of the proposed controllers.