Stability Analysis of LCL-type Grid-Connected Inverters with Digital Delay based on Loop Gain Reconfiguration

Active damping is an effective method to suppress high frequency oscillation of LCL inverter. However, the digital control delay may introduce the right half plane poles into the control loop, which complicates the stability analysis and parameter design of the LCL inverter with active damping. Therefore, this paper proposed a loop gain reconfiguration method. With the proposed loop gain, the delay in the original loop gain denominator is cancelled to avoid the effect of right half plane poles on stability analysis. With the proposed loop gain, the analytic formula is derived to judge the stable range of the inverter. Based on the formula, the design method of the active damping gain and effect of delay and grid impedance on the stability are derived, which greatly simplifies the stability analysis and the parameter design of active damping.