考虑MMC主动限流控制的直流短路电流计算方法

为了保证模块化多电平换流器(MMC)不闭锁退出运行,需要限制直流短路电流的上升速度。MMC的主动限流控制能够通过减少电容放电时间实现短路电流的限制,并且不产生额外成本,是一种新型限流方案。目前的直流短路电流计算方法无法体现MMC主动限流控制带来的故障电路结构和参数变化。文中提出一种考虑MMC主动限流控制的直流短路电流计算方法。通过引入电容放电状态占空比参数来体现主动限流控制对直流短路电流的影响,基于状态空间平均法建立直流短路电流的状态方程,给出直流短路电流的时域解析表达式。基于PSCAD/EMTDC仿真平台验证了所提计算方法的有效性。

Calculation Method of DC Short-circuit Current Considering Active Current-limiting Control of Modular Multilevel Converter

In order to prevent the trip of modular multilevel converter (MMC) due to block, the rising speed of DC short-circuit current should be limited. The active current-limiting control of MMC is a new current-limiting method, which can limit the DC short-circuit current by reducing the discharging time of capacitor without extra cost. The existing calculation method of DC short-circuit current cannot reflect the change of circuit structures and parameters caused by active current-limiting control. This paper proposes a calculation method of DC short-circuit current considering active current-limiting control of MMC. A duty circle index for discharging state of capacitor is introduced to represent the effect of active current-limiting control on DC short-circuit current. The state equation of DC short-circuit current is built based on state space averaging method, and the time-domain analytical expression of DC short-circuit current is given. The effectiveness of the proposed calculation method is validated by the simulation results based on PSCAD/EMTDC.