PROJECT TITLE :

Optimized Controller Design for $LCL$-Type Grid-Connected Inverter to Achieve High Robustness Against Grid-Impedance Variation

ABSTRACT:

Capacitor-current-feedback active damping is a good methodology to suppress the LCL-filter resonance in grid-connected inverters. However, due to the variation of grid impedance, the LCL-filter resonance frequency can vary in a very big selection, which challenges the planning of the capacitor-current-feedback coefficient. Moreover, if the resonance frequency is equal to one-sixth of the sampling frequency (fs/6), the digitally controlled LCL-sort grid-connected inverter can be hardly stable no matter how abundant the capacitor-current-feedback coefficient is. In this paper, the optimal design of the capacitor-current-feedback coefficient is presented to house the wide-range variation of grid impedance. 1st, the gain margin necessities for system stability are derived below varied resonance frequencies. By evaluating the result of grid impedance on gain margins, an optimal capacitor-current-feedback coefficient is obtained. With this feedback coefficient, stable operations will be retained for all resonance frequencies except (fs/half-dozen). Second, so as to boost system stability for a resonance frequency of (fs/six), a phase-lag compensation for the loop gain is proposed. Finally, a vi-kW prototype is tested to verify the proposed style procedure.