适用于电网不对称故障的双馈风力发电机虚拟同步控制策略

双馈感应发电机(DFIG)虚拟同步控制策略可使DFIG为电网提供频率与电压支撑,改善其并网特性。现有虚拟同步控制策略的主要目标是模拟同步发电机机电动态特性,未深入探讨电磁暂态过程中如何对DFIG进行控制。分析了电网发生不对称故障时,基于虚拟同步控制的DFIG的故障特性;得出了现有虚拟同步控制策略难以抑制DFIG故障电流与电磁转矩振荡的结论。在此基础上,提出了一种适用于电网不对称故障的DFIG电压补偿虚拟同步控制策略,该策略通过补偿转子电压的故障分量来改善DFIG转子电压的响应速度,抵消或削弱转子反电势故障分量的影响。仿真对比了现有虚拟同步控制策略与所提出策略的控制效果,验证了所提策略能够显著降低DFIG转子故障电流,抑制电磁转矩的暂态冲击与持续振荡,有效提高DFIG不对称故障穿越能力。

Virtual Synchronous Control Strategy for Doubly-fed Induction Generator Under Asymmetrical Grid Faults

Virtual synchronous control for doubly-fed induction generator(DFIG)is a promising control technique to provide frequency and voltage support when DFIG is integrated to power grid. Existing virtual synchronous control strategy for DFIG mainly focuses on mimicking the electromechanical dynamic behavior of synchronous generator, while paying little attention to the control strategy during electromagnetic transient process. This paper firstly analyzes the fault characteristics of virtual synchronous control based DFIG during asymmetrical grid faults, and reveals the major flaws of existing virtual synchronous control strategy, that is, incapability of limiting the fault current and oscillations of electromagnetic torque of DFIG. Then, a voltage compensation virtual synchronous control strategy for DFIG is proposed. The main principle is compensating the fault components of the control voltage of rotor side converter to weaken the influence of the fault components of electromotive force in rotor windings, and therefore suppressing the overcurrent in DFIG rotor. Finally, simulation analysis is given to compare the performances of existing and proposed virtual synchronous control strategies, which validates that the proposed virtual synchronous control strategy can not only maintain the advantage of providing inertial support, but also effectively limit the overcurrent in DFIG rotor and the oscillations of electromagnetic torque. Therefore, the possibility for DFIG can be improved to implement fault ride-through during asymmetrical grid faults.