MMC型多端柔性直流配电系统协同控制与故障电流抑制策略

针对基于直流母线以模块化多电平换流器(Modular Multilevel Converter, MMC)构成的多端柔性直流配电系统,参照实际直流工程,建立了连接低压直流设备的三端模块化多电平换流器等效网络数学模型,并基于下垂控制改进了协同控制控制策略。同时,针对配电系统换流站没有换流变压器的情况,设计了零序电流抑制环节。在PSCAD/EMTDC上搭建了多端柔直配电系统的仿真平台。验证了所设计协同控制策略可以使有功-无功功率的调节更加平稳,减少系统在异常情况下直流电压的波动;在发生交流侧单相接地瞬时故障时,零序电流抑制环节可以抑制过电流,保护设备,降低了换流站配置时的冗余度。

Coordinate control scheme for modular multilevel converter based multi-terminal DC distribution power systems and circuit suppression during faults

Aiming at the multi-terminal flexible DC power distribution system which is based on DC bus with Modularized Multilevel Converter (MMC), this paper establishes the mathematical model of the 3-terminal MMC system connected with low voltage device and improves the coordinate control scheme based on the droop control method, referred to practical project. To avoid the usage of converter transformer, this paper designs zero sequence current restrain control loop. The case study is carried out on a simulation system built in PSCAD/EMTDC. The time domain simulation results prove the validity of the proposed control scheme. The active and reactive power can be reallocated stably by the proposed coordinate control scheme and the DC voltage suffers less fluctuation when system exception happens; the zero sequence current can be eliminated by the proposed zero sequence current restrain control loop, which is good for reducing over current and protecting the converter. This work is supported by Sino-US international Science and Technology Cooperation Project (No. 2016YFE0105300).