双馈风电机组虚拟惯量控制对电力系统机电振荡的影响分析

虚拟惯量控制能使双馈风电机组为电网提供类似同步发电机的调频特性而得到广泛关注,但同时这种有功—频率外特性将不可避免地使双馈风电机组参与到同步发电机的机电振荡模式中,导致系统动态变得更为复杂。为了揭示双馈风电机组中虚拟惯量控制对电力系统机电振荡模式的影响规律,文中建立了基于虚拟惯量控制的双馈风电机组并网系统小信号模型,采用模态分析法分析了虚拟惯量控制相关控制回路(即虚拟惯量模拟环、锁相环和有功控制环)对同步发电机间机电振荡模式的影响规律。基于改进四机两区域系统的研究表明,增大下垂系数和适当增大滤波时间常数能改善系统阻尼,锁相环带宽和功率外环带宽过小将使双馈风电机组有功控制延迟,从而无法提供正向的阻尼转矩,导致系统阻尼减小。

Analysis on Impact of Virtual Inertial Control of DFIG-based Wind Turbine on Electromechanical Oscillation of Power System

The virtual inertia control(VIC)has got widely attention because it can make doubly-fed induction generators(DFIGs)to provide frequency support like synchronous generators(SGs). However, at the same time, this kind of power and frequency external characteristics will inevitably make DFIGs participate in the electromechanical oscillation modes of SGs, resulting in the more complicated system dynamics. To illustrate the impact rule of VIC of DFIGs on the electromechanical oscillation modes of power system, a small signal model for power system with DFIGs integrated is established and the modal analysis is then conducted to study the impact of parameters of VIC loop on the electromechanical oscillation modes of SGs, including the time constant of the frequency measurement in inertial control, the bandwidth range of the phase lock loop(PLL)and the power outer loop. A modified four-machine and two-area system is adopted for case study and the results show that it can improve the power system damping characteristics by increasing the droop coefficient and filter time constant appropriately, as well as the PLL bandwidth and power outer loop bandwidth are set to be too small to cause the active power control delay of DFIGs, thus failing to provide the positive damping torque and leading to the reduction of the damping ratio of power system.