适用于半桥型MMC附加限流控制的直流线路纵联保护方案

半桥型模块化多电平换流器的附加限流控制能有效降低对线路保护速动性的要求、增强实体限流装置的限流效果，降低了故障暂态电流的上升梯度及其幅值，因此，基于故障暂态电流信息的直流线路保护会受到限流控制器影响。提出了计及附加限流控制器影响的直流线路自适应纵联保护方案：利用极线电压及其零模电压变化率构成或逻辑来启动限流控制器；推导了限流控制器作用下的直流侧故障电流解析关系，并根据限流控制器对故障电流抑制程度和换流阀两侧的故障电流信息，建立了一种基于换流阀两侧差流的纵联保护方案。该方案仅用到各站端的本地量，通过与其对端换流站交换判别结果，其不受线路分布电容影响、无需多端数据同步，具有自适应性。大量仿真实验验证了利用限流控策略的有效性和保护方案的可靠性。

DC line pilot protection scheme suitable for half bridge MMC additional current limiting control

The additional current limiting control of half bridge modular multilevel converter(MMC) can effectively reduce the requirements for the rapidity of line protection, enhance the current limiting effect of physical current limiting device, and reduce the rising gradient and amplitude of fault transient current. Therefore, DC line protection based on fault transient current information will be affected by current limiting controller. An adaptive pilot protection scheme for DC line considering the influence of additional current limiting controller is proposed. The current limiting controller is started by using pole line voltage and its zero-mode voltage change rate to form the OR logic. The analytical relationship of fault current at DC side under the action of current limiting controller is deduced. According to the suppression degree of fault current by current limiting controller and the fault current information at both sides of converter valve, a pilot protection scheme based on differential current at both sides of converter valve is established. The scheme only uses the local quantity of each station. By exchanging the discrimination results with its opposite converter station, the scheme is not affected by the line distributed capacitance, does not need multi-terminal data synchronization, and has adaptability. A large number of simulation experiments verify the effectiveness of the current limiting control strategy and the reliability of the protection scheme.