Sliding mode based zero-sequence current mitigation of parallel-connected power converters

When multiple three-phase voltage source converters sharing the same DC bus are operated in parallel to supply an AC voltage bus or a load, a zero-sequence path exists. With this path, a zero-sequence circulating current is introduced into the three-phase system, which may be caused by the circuit asymmetry. The zero-sequence circulating currents introduce further asymmetry of electrical variables and are suggestive of abnormal conditions of the circuit. This paper presents a method to mitigate zero-sequence circulating currents based on sliding mode control. The design procedure is discussed. Time-domain simulation studies are performed to validate the performance of the sliding mode controller, compared with a PI controller, and the effects of parameter variations in the sliding mode controller on the zero-sequence currents.