考虑锁相环多单相光伏逆变器并联稳定性分析

Stability Analysis of Multi-paralleled Grid-connected Single-phase Inverters Considering Phase-locked Loop Influence

诺顿等效阻抗方法是多逆变器并联系统控制稳定性分析重要方法,但其建模过程忽略锁相环,无法分析锁相环对控制稳定性影响。对现有诺顿等效阻抗方法进行改进,建立含二阶广义积分锁相环的单相并网逆变器等效导纳模型。基于该模型,分析锁相环环节对多台单相逆变器并联系统控制稳定性影响。分析结果表明,并网逆变器等效导纳的低频段特性主要由锁相环等效导纳决定,高频段特性主要由诺顿等效导纳决定。相比于现有诺顿阻抗方法,所提方法能更准确分析系统低频段控制稳定性。随着锁相环带宽和参考电流的增加,多逆变器并网系统控制稳定裕度降低,允许接入逆变器台数减少,失稳后低频振荡频率降低。基于RTLAB平台,建立多逆变器并网实时仿真系统,结果验证了分析结论的正确性。

The Norton equivalent impedance method is the common method for the stability analysis of multiinverter grid-connected systems,but it ignores the phase-locked loop and cannot analyze the influence of the phaselocked loop on control stability.TheNorton equivalent impedancemethodwas improved,and the equivalent admittance of single-phase grid-connected inverter with second-order generalized integral phase-locked loop was established.Based on the equivalent modeling,the influence of phase-locked loop on the control stability of multi-inverter gridconnected systems was analyzed.The analysis results show that the low-frequency characteristics of the inverter admittance is determined by the equivalent admittance of the phase-locked loop,and the high-frequency characteristics is consistent as the Norton equivalent admittance.Compared with the existing Norton impedance method,the method proposed considering phase-locked loop can more accurately analyze the stability in the low-frequency region.As the phase-locked loop bandwidth and reference current increase,the stability margin of multiple inverters gird connected system is decreased,connected number of inverters is allowed to be reduced,and the frequency of lowfrequency oscillation after destabilization is reduced.Based on the RT-LAB platform,a multi-inverter gridconnected real-time simulation system was built.The simulation results verify the correctness of the analysis.