改进的多端柔性直流系统多点直流电压无差协调控制策略

针对换流站采用传统下垂控制消纳不平衡功率时引起的直流电压偏差问题，提出一种改进的多点直流电压优化协调控制策略。将不平衡功率作为前馈补偿量注入传统下垂控制中，通过平移下垂曲线来实现直流电压的准无差调节；根据换流站功率裕度，来合理设定各换流站的前馈补偿量；为避免不平衡功率过大而导致下垂控制换流站满载运行，将偏差控制引入定有功功率换流站，协同下垂控制换流站消纳余下的不平衡功率。最后，基于PSCAD/EMTDC建立五端基于电压源换流器的多端柔性直流输电系统(voltage source converter based multi-terminal high voltage direct current, VSC-MTDC)系统模型进行仿真，仿真结果表明，所提控制策略可以实现直流电压的准无差调节，优化了系统的潮流分布，提升了系统的运行稳定性。

An Improved Multi-point Direct Current Voltage Non-differential Coordination Control Strategy for Multi-terminal Direct Current System

Aiming at the direct-current (DC) voltage deviation caused by the conventional droop control of unbalanced power consumption in converter station, an improved multi-point DC voltage optimal coordination control strategy is proposed. The strategy involves injecting unbalanced power into the conventional droop control as a feedforward compensation and achieving non-differential regulation of the DC voltage by translating the droop curve. The feedforward compensation amount of each converter station is set according to its power margin. In order to avoid the full load operation of the droop control converter station caused by the excessive unbalanced power, the deviation control is introduced into the constant active power converter station, and the droop control converter station is coordinated to consume the remaining unbalanced power. Finally, a five-terminal (voltage source converter based multi-terminal high voltage direct current, VSC-MTDC) system model is established based on PSCAD / EMTDC for simulation. The simulation results show that the proposed control strategy can achieve non-differential regulation of DC voltage, optimize the power flow distribution of the system, and improve the operation stability of the system.