弱电网下LCL型并网逆变器输出阻抗复合重塑策略

A Study on the Complex Remodeling Strategy of Output Impedance of LCL-Type Grid-Connected Inverters under Weak Grids

针对电网电压比例前馈和锁相环(PLL)影响下,电网阻抗宽范围变化时易导致并网逆变器失稳的问题,首先建立了考虑电网电压比例前馈和PLL影响的并网逆变器输出阻抗模型,借助阻抗稳定判据对系统稳定性进行了分析;然后提出一种基于电网电压前馈的复合阻抗重塑策略,通过在电网电压比例前馈环节串联低通滤波器以及加入消除PLL影响的电网电压前馈支路,重塑并网逆变器输出阻抗;最后通过仿真和实验验证所提阻抗重塑策略能够有效提升并网逆变器在电网阻抗宽范围变化情况下的稳定性,改善并网电流质量。

Under the influence of the grid voltage proportional feed-forward and phase-locked loop(PLL),changes of grid impedance wide-range can easily lead to instability of the grid-connected inverter.For this reason,this paper firstly establishes an output impedance model of the grid-connected inverter with the influence of the grid voltage proportional feed-forward and PLL considered,and analyzes the system stability with the help of impedance stability criterion.Furthermore,the paper proposes a composite impedance remodeling strategy based on the grid voltage feed-forward.In addition,the output impedance of the grid-connected inverter is reshaped to improve the stability of the grid-connected inverter by connecting a low-pass filter in series in the grid-voltage proportional feed-forward link as well as adding a grid-voltage feed-forward branch to eliminate the influence of PLL.Finally,the results of simulation and experimental verification show that the proposed impedance reshaping strategy can effectively improve the stability of grid connected inverters under wide range impedance changes,and improve the quality of the grid connected current.