兼具开路故障诊断能力的MMC电容电压测量方法

模块化多电平换流器在高电压等级、大输送容量场合的应用中,各桥臂大量子模块的电压需要实时采集并维持在允许范围内,但电压传感器配置数量的增加影响了系统的经济性与可靠性。为解决以上问题,提出了一种基于电容电压预估和组电压测量的子模块电容电压测量方法。该方法对桥臂子模块进行了分组,每组仅配备一个电压传感器,从而使传感器数量得以减少。在该测量方法基础上提出了一种子模块开路故障诊断策略,通过比较电压实测值与预估值完成开路故障的快速诊断,并且对传感器设置了故障冗余,在传感器发生故障的情况下系统仍能保持稳定运行。基于PSCAD/EMTDC搭建了21电平基于模块化多电平换流器的高压直流仿真系统。仿真结果表明,所述方法具有与传统方法近似的测量精度,同时能在较短时间内诊断子模块开路故障与传感器故障。

Measuring Method of MMC Capacitor Voltage with Diagnostic Ability of Open-circuit Fault

In the high-voltage and high-power applications of modular multilevel converters(MMCs), large amounts of sub-module(SM)capacitor voltages need to be sampled and maintained in an acceptable range, but the increase in the number of voltage sensors compromises both economy and reliability of the overall system. To solve this problem, a new method of measuring SM capacitor voltages based on voltage estimation and group voltage measurement is proposed. The proposed method divides SMs in the same converter arm into groups, with each group equipped with only one voltage sensor to reduce the number of voltage sensors. On the basis of the new measuring method, a SM open-circuit diagnosis strategy is introduced, which can detect and locate faulty SM rapidly by comparing voltage measurement and estimation, and voltage sensor redundant technique is given to guarantee system normal operation in case voltage sensor fault should occur. A 21-level MMC based high voltage direct current simulation system is set up in PSCAD/EMTDC software environment. It is shown by simulation results that the new method has an approximate measuring accuracy as the traditional one. Meanwhile, SM open-circuit fault and voltage sensor fault can be diagnosed within a relatively short time.