基于导纳重构的大型光伏电站谐波谐振抑制策略

摘要

推导出一种基于系统导纳的大型光伏电站稳定性判据,当光伏电站内各逆变器稳定且电网自身稳定时,大型光伏并网系统的稳定性取决于其稳定性环路增益是否满足奈奎斯特稳定性判据.分析表明:电网阻抗的增加降低了系统稳定性,甚至引发谐波谐振,使光伏电站进入不稳定运行状态.通过对并网逆变器等效输出导纳特性的分析,提出对其进行改善的准则,即输出导纳幅值在基频处尽量小,在谐波频率处尽量大,相位在全频范围内不与90°线相交,且具有一定裕度.根据该准则提出一种导纳重构策略,将并网点电压经适当环节反馈至电流控制器输出端,提高系统对电网阻抗变化的适应能力,实现对谐波谐振的抑制.仿真及实验结果验证了理论分析的正确性.%A stability criterion based on system admittance is derived for the LSPV(Large-Scale PhotoVoltaic plant).When the inverters of LSPV and the grid are stable,the stability of grid-connected LSPV depends on the relation between its stability loop gain and Nyquist stability criterion.Analysis shows that,the increase of grid impedance may decrease the stability of LSPV,even trigger the harmonic resonance,resulting in unstable system operation.The equivalent output admittance of gird-connected inverter is analyzed and a guide line is proposed to enhance it,i.e,the magnitude of output admittance should be as low as possible at the fundamental frequency while as high as possible at the harmonic frequency;and its phase,with a certain margin,must not intersect with the 90° line in whole frequency range.According to the proposed guide line,an admittance reshaping strategy is proposed,which feeds the voltage at the point of common coupling back to the output terminal of the current regulator via a proper link for improving the system adaptability to the variation of grid impedance to suppress the harmonic resonance.Simulative and experimental results verify the correctness of theoretical analysis.