考虑频率耦合的并网逆变器不同域控制的稳定性比较

Stability comparison of grid-connected inverters controlled in different domains considering frequency coupling

高渗透率下并网逆变器(grid-connected inverter,GCI)与高电网阻抗的交互作用可能引发系统失稳问题。GCI的电流控制根据控制域的不同,可分为相域比例谐振(proportional resonance,PR)控制和dq域比例积分(proportional integral,PI)控制。首先,考虑频率耦合效应,基于谐波线性化方法分别建立了LCL型GCI采用相域PR控制和dq域PI控制的序导纳模型,并考虑电网电压前馈的影响,对这两种不同域控制的GCI的序导纳特性进行了对比分析。基于所建的序导纳模型和广义奈奎斯特判据(generalized Nyquist criterion,GNC),分析了电网电压前馈和电网强度对两种不同域控制的GCI并网系统稳定性的影响。稳定性分析结果表明:不考虑电网电压前馈时,相域PR控制的GCI系统稳定性强于dq域PI控制的GCI系统;而引入电网电压前馈后,二者系统稳定性基本相同。最后,通过仿真验证了理论分析的正确性。

Under high permeability,the interaction between a grid-connected inverter(GCI)and high grid impedance may lead to system instability.The current control of a GCI can be divided into proportional resonance(PR)control in the phase domain and proportional integral(PI)control in the dq domain according to different control domains.First,considering the frequency coupling effect,the sequence admittance models of the LCL GCIs with PR control in the phase domain and PI control in the dq domain are respectively established based on an harmonic linearization method.Then,the sequence admittance characteristics of the two GCIs are compared and analyzed considering the impact of the grid voltage feedforward.Based on the established sequence admittance models and generalized Nyquist criterion(GNC),the influence of the grid voltage feedforward and grid stiffness on the stability of the two GCI systems controlled in different domains is analyzed.The stability analysis results show that the stability of a PR-controlled GCI system in the phase domain is stronger than that of a PI-controlled GCI system in the dq domain without considering the grid voltage feedforward,while the stability of the two GCI systems is basically the same after introducing the grid voltage feedforward.Finally,simulations verify the correctness of the theoretical analysis.