基于分裂电容法的LCL并网逆变器控制策略分析与改进

Analysis and Improvement of the Control Strategy of LCL Grid-Connected Inverter Based on Split-Capacitor

在目前已有的LCL并网逆变器电流控制方法中,分裂电容法作为一种单电流反馈控制方法,通过降阶实现了较小的稳态误差和电流谐波失真,然而传统的分裂电容法未能解决LCL滤波器固有的谐振问题。经分析发现分裂电容法降阶过程中对消掉的极点为临界稳定极点,使得电流反馈中不包含谐振频率处的分量,闭环系统不完全能控。采用加入无源阻尼的方法并合理配置阻尼电阻的比例关系,既实现了降阶特性也改善了滤波器的谐振特性。在此基础上,为了更好地抑制电网扰动,推导了适用于分裂电容法的电网电压前馈策略。经过仿真与实验,验证了理论分析的正确性和改进方法的有效性。

Among the existing current control methods of LCL grid-connected inverter, the split-capacitor method is a single current feedback control approach, which can achieve low steady error and THD of grid current. However, the resonant problem of LCL filter still exists in the traditional splitting capacitor method. Through analysis of the deflation progress of the splitting capacitor method, the cancelled poles are proven to be critical steady poles. The characteristic make the close-loop system incompletely controllable because the signal component at resonant frequency is not included in the current feedback signal. By introducing the equal-ratio passive resistors in series with capacitor branch, deflation is satisfied while the resonant problem of the LCL filter is solved. For better attenuation of the grid voltage disturbances, the voltage feed-forward strategy is derived. The result of simulation and experiment verifies the theoretical analysis and effectiveness of the proposed method.