The Research of Zero-sequence Circulating Currents Between Parallel Three-phase Inverters

It is well known that zero-sequence circulating currents could exist in parallel three-phase converters. However, these conclusions are normally drawn out without considering the magnetic couples caused by the three-pole transformers and three-pole reactors. In fact, for the cost and size, the three-phase reactors and transformers used in three-phase inverters normally have only three poles. In parallel three-phase inverter systems, the magnetic couples between three phases in each three-phase inverter make the zero-sequence circulating currents behave differently from those of three-phase inverters with only three single-phase reactors and three single-phase transformers. In this paper, the instantaneous model of zero-sequence circulating current between parallel three-phase inverters with three-pole reactors and three-pole transformers is established. The analysis based on this model indicates that magnetic couples caused by three-pole reactors and transformers have great influence on the zero-sequence circulating currents. Simulations and experiments validated the above conclusion.