基于阻抗分析的LCL型并网逆变器多谐振控制

Multi-resonance Control of LCL Grid-connected Inverter Based on Impedance Analysis

弱电网条件下,由于电网阻抗与逆变器阻抗失配,并网电流容易发生谐波振荡,破坏了系统的稳定性。基于阻抗分析法,建立了考虑锁相环(PLL)和控制延时的单相LCL并网逆变器的小信号模型,通过阻抗稳定判据分析了弱电网在常规控制策略下的失稳机理,提出了一种基于多谐振控制器的电压前馈控制来独立控制公共耦合点(PCC)电压基频分量和谐波分量,增强系统稳定性的同时显著提升并网电能质量。该方法从阻抗角度分析PLL及电压前馈对逆变系统稳定性的影响,为抑制低频次谐波设计了多谐振控制器,并基于阻抗稳定准则详细推导实现方法和参数设计过程,最后仿真结果验证了所提控制方法的有效性和可行性。

Under weak grid conditions,due to the mismatch between grid impedance and inverter impedance,the grid-connected current is prone to harmonic oscillation,which destroys the stability of the system.Based on the impedance analysis method,a small-signal model of single-phase LCL grid-connected inverter with phase-locked loop(PLL) and control delay is established.The instability mechanism of weak grid under conventional control strategy is analyzed by impedance stability criterion.The voltage feedforward control of the multi-resonant controller independently controls the fundamental frequency component and harmonic components of the point of common coupling(PCC) voltage,enhances the stability of the system and significantly improves the grid-connected quality.The method analyzes the influence of PLL and voltage feedforward on the stability of the inverter system from the impedance angle,designs a multi-resonant controller for suppressing low-frequency subharmonics,and deduces the implementation method and parameter design process based on the impedance stability criterion.Finally,the simulation results verify the effectiveness and feasibility of the proposed control method.