电网对称故障下双馈风力发电机的虚拟同步控制策略

将虚拟同步控制策略运用于双馈感应发电机(DFIG)变频器控制,可使DFIG为电网提供有惯量的频率与电压支撑。但现有虚拟同步控制策略主要关注DFIG对同步发电机机电动态特性的模拟,未考虑DFIG的电磁暂态过程。分析了基于虚拟同步控制的DFIG在电网对称故障下的电磁暂态特性,指出了现有虚拟同步控制策略存在的两大缺陷:无法完全模拟同步电机故障暂态下的电磁关系,且无法抑制转子过电流。提出了一种适用于电网对称故障的DFIG暂态电压补偿虚拟同步控制策略,即通过补偿转子控制电压的暂态分量来抵消或削弱转子暂态反电势对转子过电流的影响。通过仿真对比了现有虚拟同步控制策略与所提策略对DFIG的控制效果,证明了所提虚拟同步控制策略不仅具备更好的惯性支撑能力,同时可显著抑制DFIG转子过电流与电磁转矩暂态冲击,并对系统进行无功支撑,有效提高了DFIG不间断运行能力与电网故障恢复能力。

Virtual Synchronous Control Strategy for Doubly-fed Induction Generator Wind Turbines Under Symmetrical Grid Faults

The virtual synchronous control strategy for the doubly-fed induction generator(DFIG)is a promising control technique to provide inertial frequency and voltage support when DFIG is integrated to the power grid. However, the existing virtual synchronous control strategy for DFIG mainly focuses on mimicking the electromechanical dynamic behavior of the synchronous generator, while neglecting the electromagnetic transient responses of DFIG. Firstly, the electromagnetic transient characteristics of virtual synchronous control-based DFIG during symmetrical grid faults are analyzed. Two severe flaws of existing virtual synchronous control strategy are revealed, that is, the incapability of fully imitating the transient characteristics of synchronous generators, or limiting the overcurrent in DFIG rotor. Then, a transient voltage compensation virtual synchronous control strategy for DFIG is proposed. The main principle is compensating for the transient component of the control voltage of rotor side converter to weaken the influence of transient electromotive force in rotor windings to suppress the overcurrent in DFIG rotor. Finally, a simulation analysis is made to compare the performances of existing and proposed virtual synchronous control strategies to show that the proposed virtual synchronous control strategy can not only enhance the advantage of providing inertial support, but also effectively limit the overcurrent in DFIG rotor and the oscillations of electromagnetic torque, with the capability to offer reactive power support to power grid. All of these improve the possibility for DFIG to implement fault ride through and the ability of power system to recover from grid faults.