Research on Control Mechanism of Active Damping for LCL Filters

A technology named active damping is commonly adopted to eliminate the resonance peak of LCL filters.Many active damping strategies have been proposed in the literatures before.However,the control mechanism of active damping has not been involved yet,also the theoretical basis for the proposed strategies.In this paper,a thorough research on active damping has demonstrated that the essence of active damping is the feedback control at the frequencies where the resonance peak lies.Moreover,a better damping effect is obtained when the control is negative feedback,and the deeper the feedback the better the inhibition of the resonance peak.Based on this,the essence of the existing control strategies based on inverter-side inductor current,filter capacitor current and voltage was analyzed;the principles for the design of active damping control through filter capacitance,inverter-side inductance or even grid-side inductance were proposed,as well as the feasible active damping control strategies in systems with LCL filters.Experimental tests validate the analysis.