Stability Analysis and Optimal Control Design for Dual-Loop Voltage-Controlled Grid-Connected Inverters

This paper analyzes the stability of digitally dual-loop voltage-controlled inverters with consideration of grid impedance. It is revealed that both the digital delay and controller affect the system stability through adjusting the phase at the resonant frequency of the LCL filter. Then an optimal control for inner current loop is proposed to deal with different switching frequencies. Through tunning the feedback gain of inner current loop, the control scheme can cope with different switching frequencies or delays to keep system stable. Then the stable regions presented as the value range of current feedback gain are derived. Simulation and experiment validate the stability analysis and effectiveness of the proposed control.