An active damping technique for a current source inverter employing a virtual negative inductance

A grid connected CSI requires a CL filter stage. In this work, the isolation transformer leakage inductance constitutes this filter inductance. This CL filter is lightly damped for efficiency constraints. Hence, it is subject to resonance if excited by inverter current harmonics, pre-existing grid voltage harmonics, or due to step changes in power. Previous work on active damping employed a virtual resistance at high frequencies, including the resonance frequency. However, this method shows limited gain and phase stability margins. In this paper an active damping technique employing a virtual negative inductance for the CSI is proposed. The introduction of a virtual negative inductance around the resonance frequency causes active frequency shifting. The advantages of the proposed system are better time response and increased stability margins. Simulation results for a grid connected CSI have been presented to substantiate the proposed technique.