考虑光伏动态特性的功角电压交互失稳机理分析

在大容量直流和高比例新能源集中接入电网的背景下,研究了考虑光伏动态特性影响的直流大功率扰动引发功角电压交互失稳问题。首先,从理论上推导了两机等值系统发电机转子运动方程和电动机负荷运动方程;然后,分析了直流大功率扰动引发功角和电压交互作用导致系统失稳的物理机理;最后,进一步分析了光伏低电压穿越期间不同有功/无功特性对系统稳定性的影响规律,通过吉泉直流实际系统算例进行了仿真验证。研究结果表明,两侧发电机功角拉开和负荷母线电压跌落(电动机电阻减小)形成恶性循环最终导致系统失稳,不同的光伏低电压穿越有功/无功特性对系统稳定性的影响需要通过理论结合仿真综合分析。

Analysis on Instability Mechanism of Power Angle and Voltage Interaction Considering Dynamic Characteristics of Photovoltaic Generator

Under the background of centralized access of large-capacity DC systems and high-penetration renewable energy, this paper studies the problem of power angle and voltage interaction instability resulted by the large power disturbance of DC system considering the impact of dynamic characteristics of photovoltaic generator. Firstly, the motion equations of generator rotor and motor load of the two-machine equivalent system are derived in theory. Then, the physical mechanisms of the system instability caused by power angle and voltage interaction after large power disturbance of DC system are analyzed. Finally, the impacts of different active/reactive power characteristics of photovoltaic generator during low voltage ride-through (LVRT) process on the system stability are studied. The results are verified through the simulation of Changji-Guquan high voltage direct current (HVDC) system in China. The study results show that the system instability is eventually resulted by the vicious circle between the relative power angle increase of generators and the load-bus voltage drop (i.e. the decrease of motor resistance). And the impact of different active/reactive power characteristics of photovoltaic generator during LVRT process on the system stability should be comprehensively analyzed by theory combined with simulation.