Stability Analysis of Grid-Connected Inverter With LCL Filter Adopting a Digital Single-Loop Controller With Inherent Damping Characteristic

The stability problem of the grid-connected inverter with LCL filter adopting a digital single-loop controller without extra damping resistance is analyzed. The digital single-loop control based on the grid-side current feedback can attenuate the resonance introduced by LCL filters due to the inherent damping characteristic embedded in the control loop. The stability analysis is performed by means of a Nyquist diagram in the discrete domain and to provide a general design direction for filter and controller. The quantitative relationship of ratios of LCL resonance angular frequency to control frequency and controller parameters on the system stability is investigated. It is derived that the system would obtain preferable stability margin when the ratio is located at a certain range. The theoretical analyses are validated by experimental tests based on a 5-kW single-phase inverter laboratory prototype.