并网型双馈异步发电机奇异诱导分岔型电压崩溃机理

Study on Voltage Collapse Caused by Singularity-induced Bifurcation of Grid-connected Doubly-fed Induction Generators

双馈异步发电机(doubly-fed induction generator,DFIG)中含有各种时间尺度的机械量、电气量与控制量,暂态过程复杂,目前对其暂态电压崩溃研究尚未深入。该文针对DFIG的暂态稳定性问题提出规范化的微分–代数方程(differentialalgebraic equations,DAE)模型,并依据DAE的奇异面理论研究风机发生暂态电压崩溃的内部机理。仿真分析表明DFIG不仅会由于状态量移出吸引域而出现典型的动力学失稳,还时常伴随出现2种瞬时的电压崩溃现象,即短路电流激增导致系统状态量接触到网络方程约束产生的奇异面,从而在局部失去代数方程解的唯一性;或由于直流母线电压的快速下降而致使系统无法顺利穿越电压零点。不同于以往同步发电系统中恒功率电源引入造成的系统奇异,DFIG发生失稳的机理主要同其与电网的连接强度密切相关。并通过基于规范化模型的数值仿真验证上述理论分析的正确性。

Mechanical, electric and control variables of different time-scales are included in the wind turbine of doubly-fed induction generator （DFIG）, hence its dynamic behaviors rather complex. A standardized prototype model in differential-algebraic equations （DAE） form was proposed for system-level transient stability of wind-power-integration system. Then internal mechanisms of transient voltage collapse were analyzed using the singularity-induced bifurcation theory. The results show that, besides instability appearing when variables move out of the attraction zone, the state variable trajectory would come across the singular surface, and the DC bus voltage might also collapse in critical faults. The mechanisms differ with varying levels of connection strength, which is distinct from the similar bifurcation caused by constant-power source in conventional grids. Simulation results verify the correctness of theoretical analysis.