Eigenvalue Analysis and Behavioural Common-Mode Equivalent Circuit for an Asymmetric Active Phase Converter

Abstract

A common-mode (CM) filter for a reduced switch active phase converter (APC) is proposed in this article for mitigation of switching frequency, and higher order CM current (CMC) injected into the grid. Due to asymmetry of the APC topology, a mixed-mode analysis of the differential-mode (DM) and CM components becomes essential. The presented state-space approach for the converter analysis captures the mixed-mode behavior of the APC. The eigenvalue analysis of the system shows that the inclusion of the proposed CM filter does not affect the existing DM APC system poles. Hence, the CM filter does not affect the APC control structure. This work also introduces an equivalent behavioral circuit which simplifies the CM filter component selection. This article provides a design methodology for the selection of the CM filter components by identifying the range of CM resonance frequencies. This design method results in active damping of the CM resonance without any additional control loop. The simulation results validate the behavioral CM equivalent circuit. The experimental validation is carried out on a laboratory APC prototype feeding a three-phase 3 hp induction motor from a single-phase grid. The measured CM voltages and currents validate the efficacy of the proposed CM filter for the APC.