Parallel interfacing converters under unbalanced voltage: Active power oscillation cancellation with peak current sharing

Unbalanced voltage has adverse effects on power electronic interfacing converters (IFCs) operation such as output power oscillations, DC link voltage oscillations and peak current increase. These adverse effects can be aggregated in parallel IFCs with common DC and AC link, which are commonly used to connect AC and DC subsystems in hybrid AC/DC microgrid or to interface high-power distributed generations/storage elements to AC subsystem. In this paper, two novel control strategies for parallel IFCs operation under unbalanced voltage are proposed, which are focusing on active power oscillation cancellation and sharing of collective peak current of parallel IFCs among IFCs considering their power ratings. In the first proposed control strategy, IFCs' power coefficient factors are controlled for cancellation of active power oscillation and collective peak current sharing of parallel IFCs. In the second proposed control strategy, IFCs' peak currents are controlled for controlling targets. In this paper, individual and parallel IFCs' peak currents are thoroughly studied, and their relationship with active power oscillation cancellation are analyzed. Based on analysis, it is proven that collective peak current of parallel IFCs is constant under zero active power oscillation in the fixed average active powers output. Both proposed control strategies ensure the peak currents of individual IFCs to be approximately in-phase with collective peak current of parallel IFCs, which provide minimum peak currents summation of IFCs.