Compared with L-and LC-filter, the LCL-filter attracts more and more research interests for its excellent harmonic suppression ability. However, the resonance peak of the LCL-filter may introduce potentially unstable dynamics that need to be carefully damped. Considering the PWM discrete nature and practical implementation in discrete form, to analysis the overall system stability is complex especially when considering the controller and the LCL-filter active damping as a whole system. Moreover different sampling frequency and different delay time that are specific in discrete domain influence the system stability scenario, which increase the analysis complexity. Different from the low order filter, LCL-filter offers two kinds of possible current feedback, which presents totally different impact on overall system stability. In this paper, the stability of the overall system in discrete domain with two kinds of possible current feedback is investigated in detail. Three typical sampling frequency: high sampling frequency, medium sampling frequency and low sampling frequency are considered. And three typical delay time of active damping control: 0, Ts∕2, Ts are introduced into stability analysis process. Experimental results get from a 3 kW laboratory prototype based on the TMS320F2808 are provided to validate the theoretical analysis presented in this paper.
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