考虑Chopper动作的双馈风电机组三相短路电流分析

直流母线并接直流卸荷电路(Chopper)以保护转子侧变频器(RSC)是一种较常用的双馈风电机组低电压穿越改造方案。目前对称故障下双馈风电机组短路电流特性研究以故障后投入撬棒(Crowbar)电阻为主,Chopper动作下双馈风电机组短路电流特性研究几乎没有,故而难以分析其作用下双馈风电机组短路电流特性对系统中保护动作可靠性和设备安全的影响。类比双馈风电机组故障后投入Crowbar电阻的分析思路——转子回路串入电阻,通过分析对称故障后Chopper动作下的转子电流回路,将被闭锁的RSC和Chopper等效为可变电阻,分析了该等效电阻阻值随电压跌落程度和故障前转差率的变化规律。根据故障后双馈感应发电机的磁链、电压关系,通过数学解析得到Chopper动作下对称短路电流解析表达式。在MATLAB/Simulink中搭建配置Chopper的双馈风电机组模型,仿真验证了该表达式的有效性。

Analysis on Three-phase Short-circuit Current of DFIG-based Wind Turbines Considering Chopper Protection

Utilizing the direct current (DC) dump circuit (Chopper) on DC-link to protect the rotor side converter (RSC) is commonly done for improving the low-voltage ride through (LVRT) capability of doubly-fed induction generator (DFIG)-based wind turbines. The insertion of Chopper protection will have a greater impact on the short-circuit current characteristics of DFIG-based wind turbines, however present research on DFIG-based wind turbines fault current features under symmetrical short-circuit is primarily conducted on the assumption that the Crowbar acts after fault inception, whereas, the short-circuit current characteristics of DFIG-based wind turbines under Chopper action is rarely studied, making it difficult to analyze the reliability of protection action and equipment safety under its impact in power systems. According to the analysis on the short circuit current of DFIG-based wind turbines unit after Crowbar operates, i.e. the rotor circuit is in series with a resistor, the rotor current loop after fault under Chopper action is analyzed, the blocked RSC and Chopper are equivalent to a variable resistance, the variation of the equivalent resistor along with the voltage drop and running slip is also analyzed. According to the relationship between the DFIG flux and voltage after symmetrical fault, a current analytical expression is obtained for DFIG-based wind turbines under Chopper action by mathematical analysis methods. Finally a simulation model for DFIG-based wind turbines with Chopper protection in MATLAB/Simulink is built to verify the validity of the proposed method.