Adaptive Notch filter based active damping for power converters using LCL filters

This paper proposes an active damping technique for grid-connected converters using inductor-capacitor-inductor (LCL) filters. The technique relies on a discrete-time adaptive notch filter (NF) which is able to adapt its resonance frequency and bandwidth in real-time. The tuning function of this filter can be used in the case when the resonance frequency of the LCL filter varies due to a change in the line inductance or the use of non-linear inductors employing magnetic materials, where the inductance is a function of the applied current. In particular, this paper addresses the difficulties of the discrete-time implementation of such filter due to the proximity to Nyquist-Shannon limit. A detailed analysis of the filter and the control system is also included. The experimental results validate the effectiveness of the proposed technique.