弱电网下并网逆变器的相位裕度补偿方法

Phase margin compensation method for grid-connected inverter under weak grid

光伏并网逆变器与弱电网连接时,较高的电网阻抗使逆变器稳定裕度下降,易引发并网电流谐波谐振,影响逆变器的安全运行。本文建立了三相LCL型并网逆变器模型,利用阻抗稳定判据分析了电网阻抗对系统稳定性的影响。为增强逆变器在电网阻抗变化过程中的鲁棒性,提出一种基于超前校正的相位裕度补偿方法,采用串联方式补偿逆变器相位,使超前校正的最大补偿相角处频率始终等于阻抗交截频率,保证逆变器具有足够的相位裕度。给出了超前环节的设计过程和电网阻抗增大时灵活设定补偿环节参数的方法,提升了系统稳定性与鲁棒性。仿真结果验证了控制策略的有效性。

When the PV grid-connected inverter is connected with the weak grid, the high grid impedance reduces the stability margin of the inverter, which will easily lead to harmonic resonance of the grid-connected current and affect the safe operation of the inverter. In this paper, a model of a three-phase LCL grid-connected inverter is established. The influence of the grid impedance on the system stability is analyzed by impedance stability criterion. In order to enhance the robustness of the inverter when the grid impedance changes, a method of phase margin compensation based on phase lead correction is proposed. The phase compensation is adopted in series so that the frequency at the maximum compensation phase angle of the lead correction is always equal to the impedance intercept frequency, which ensures that the inverter has sufficient phase margin. The design process of the lead correction and the method of how to set the compensation parameters flexibly when the grid impedance increases are given, which improves the stability and robustness of the system. Simulation results verify the effectiveness of the control strategy.