新型限流式统一潮流控制器限流分析与参数设计

Current Limiting Analysis and Parameter Design of A Novel UPFC With Fault Current Limiter

统一潮流控制器(unified power flow controller,UPFC)在电网系统发生短路故障时,极易受到大电流冲击而损毁。虽然具有短路限流功能的统一潮流控制器(限流式UPFC)在一定程度上限制了大电流冲击,但短路电流峰值仍然很大,限流时间较长。为此,提出一种采用RLC串联谐振电路的限流器二次侧拓扑结构,分析了其工作原理和限流动态过程,建立了发生故障时的数学模型。针对限流式UPFC直流侧电容电压在限流过程中不断上升,极易超出变换器IGBT耐压水平的缺陷,分析了故障模型中直流侧电容电压上升的原理,设计了用于改变短路电流流通路径的桥式电容限压器。仿真结果表明,改进方案能进一步减小短路电流峰值和上升率,使短路电流迅速衰减至零,同时限制直流侧电容电压的不断增大,确保限流式UPFC安全退出运行。

Unified power flow controller （UPFC） would be damaged due to large current when short-circuit fault occurs in power grid system, while UPFC with short-circuit current limiting function （UPFC-FCL） can limit impact of large current to a certain extent. However, peak value of short circuit current is still very large and current limiting time is still very long. In order to solve this problem, this paper proposed a secondary side topology of current limiter based on RLC series resonant circuit, and established mathematical fault model after analyzing working principle and dynamic limiting process of this method. In view of the defect that UPFC DC side capacitor voltage was rising in current limiting process, prone to exceed IGBT withstand level of converter, this paper analyzed mechanism of DC side capacitor voltage rise in the fault model and designed bridge capacitor voltage limiter to cut off short circuit current path. Simulation results show that the improved scheme can reduce peak value and rise rate of short-circuit current, making it rapidly decay to zero, while it can limit DC capacitor voltage increasing and ensure UPFC-FCL to withdraw from operation safely.