向无源网络供电的MMC-HVDC系统控制与保护策略

Control and Protection Strategies for MMC-HVDC Supplying Passive Networks

向无源网络供电的模块化多电平换流器型高压直流输电(modular multilevel converter based HVDC,MMC-HVDC)系统是柔性直流输电技术的一个重要应用领域,因此有必要对其控制与保护策略进行研究。基于MMC电磁暂态数学模型,建立了d-q同步旋转坐标系下MMC欧拉?拉格朗日(Euler-Lagrange,EL)数学模型,推导了适于MMC控制的无源控制规律,设计了内环电流无源控制器及向无源网络供电的MMC-HVDC系统定交流电压控制器。针对电网电压不平衡或交流系统不对称故障引起的负序电流,提出了基于EL模型的正负序电流无源控制器。为保证故障时系统能满足安全运行的条件,提出了故障时的控制保护策略。最后在PSCAD/EMTDC中对MMC-HVDC系统各种运行工况进行了仿真验证,并对正负序无源控制器和矢量控制器的控制性能做了仿真对比,仿真结果表明,所提出的控制器和控制保护策略具有良好的动稳态控制性能,便于工程实际应用。

This paper investigates the control and protection strategies for modular multilevel converter based HVDC （MMC-HVDC） supplying passive network. Based on the electromagnetic mathematical model of MMC, the Euler-Lagrange （EL） mathematical model in d-q synchronous reference frame is developed. The passive control law of MMC is deduced, then the corresponding inner-loop current passive controller and constant AC voltage controller for MMC-HVDC is designed. To suppress negative sequence current caused by unbalanced grid faults, the decoupled positive-negative sequence passive controller based on EL mathematical model is proposed. Moreover the control and protection strategies under fault conditions are proposed to ensure the MMV-HVDC meet the requirement of its safety operation. Finally the MMC-HVDC systems under different operating conditions are simulated in PSCAD/EMTDC, the control performances of the positive-negative sequence passive controller are compared to that of the vector controller. The results show that the proposed controller and protection strategies have good dynamic performance and can be valuable to the practical system.