电网电压不平衡条件下模块化多电平换流器高压直流输电控制策略

在电网电压发生不平衡故障时,分析了模块化多电平换流器高压直流输电(MCHVDC)功率分量特性。为实现正负序电流统一控制,引入复合控制器(比例积分+准谐振控制器)作为电流内环控制,避免了同步旋转坐标系下电流序分量分解问题。研究了抑制负序电流、有功功率波动控制策略,并利用电压降落和不均衡度指标设计了对应的低压限流环节。为降低环流造成的额外损耗,在分析环流分量故障特性基础上,设计了桥臂环流抑制器。最后在PSCAD/EMTDC仿真环境中,搭建了仿真模型,对负序电流、有功波动抑制和环流抑制策略的有效性进行了仿真说明。

The Control Strategies of Modular Multilevel Converter- High Voltage Direct Current Transmission under Unbalanced Grid Voltage Conditions

Under unbalanced grid conditions, the power characteristics of high voltage direct current transmission based on modular multilevel converter (MMC-HVDC) are analyzed. In order to control the positive and negative sequence currents uniformly, a composite controller combing proportional integer with quasi resonant current controller is introduced as the synchronous rotational reference frame. Thus, the current sequences extraction can be avoided. The control strategies for eliminating the negative sequence current and active power ripples are studied, and the voltage dependent current order limiter (VDCOL) is also designed according to the voltage drop and imbalance indicator. Features of leg circulating current are analyzed, and accordingly the circulating current suppressor is designed to reduce the additional power loss. At last, the simulation model is built in PSCAD/EMTDC. The effectiveness and feasibility of these proposed control strategies are verified.