Improved weighted average current control of LCL grid‐connected inverter and analysis of its order reduction characteristics

Abstract

LCL grid-connected inverter is good at suppressing the high frequency current, but the inherent resonance frequency of the filter will lead to the resonance peak. Therefore, the active damping is commonly used to suppress the resonance effect. Since the weighted average current control can provide better bandwidth for the system with high frequency and has the characteristics of system reduction, it is often used to replace the traditional dual-loop current control in the application of LCL grid-connected inverter. However, the reduction of current resonance peak at the grid side by the weighted average current control is limited, so it is necessary to combine the grid voltage and capacitor current feedback loop to achieve the ideal results. In weak grid, the newly added feedback path would easily lead to the loss of system reduction, which results in the existence of transient variables in the transfer function affecting the stability of the control strategy. To solve this technical problem, this paper addresses a new control method of LCL grid-connected inverter based on weighted average current control. By adding a capacitor current feedback path, pole-zero cancellation of the control system is realised as to reduce the systematic order and improve the robustness of the controller under the time-varying weak grid.