大规模光伏并网系统谐振机理及稳定性分析

在弱电网下或者装机容量增加时,大规模光伏并网系统易引发谐波谐振,危及光伏电站的正常稳定运行。针对上述问题,以大规模光伏并网系统为研究对象,分别从系统阻尼、闭环控制等角度揭示了大型光伏电站和电网之间的谐振机理。研究结果表明:LCL滤波器自身的有源阻尼策略并不会导致大规模光伏并网系统引发谐振,引发谐振的关键因素在于并网逆变器自身的稳定裕度。电网阻抗、装机容量、系统参数设计、控制策略等因素的综合效应可以使并网逆变器在某一特定条件下运行到临界稳定状态附近而引发谐振,谐振将导致入网电流在相应谐振频段产生大量谐波。如果稳定裕度进一步减小,系统将逐步由谐振状态过渡到振荡、发散等不稳定状态。仿真与实验结果验证了理论分析的正确性。

Resonance Mechanism and Stability Analysis of Large-scale Grid-connected Photovoltaic System

Under weak grid conditions or when the capacities of photovoltaic(PV) power plants increase, a large-scale grid-connected PV system will easily cause harmonic resonance, which endangers the normal and stable operation of PV power plants. In consideration of the above problems, the large scale grid-connected PV system is taken as the research object in this paper, and the resonance mechanism between the large scale PV power plant and grid is revealed from aspects including system damping and closed loop control. Theoretical analysis indicates that the active damping strategy for the LCC filter itself will not cause harmonic resonance to the system, and the key factor is the stability margin of the grid-connected inverter. The combined effect of factors, such as grid impedance, plant capacity, design of system parameters, and control strategy, can make the grid-connected inverter run in a critical stable state under a specific condition and further cause harmonic resonance, producing a large amount of harmonics in the corresponding resonance frequency band. With further shrinking of the stability margin, the system will gradually transit from the resonance state to the unstable states of oscillation and divergence. Simulation and experimental results validated the theoretical analysis.