Analysis of the Bipolar Voltage Bus Balancing of a DC Microgrid with Bidirectional Converters

This paper presents an analysis of the voltage balancing of a dc bipolar bus of a dc microgrid. The bipolar dc bus derives from the dc side of a three-phase four-wire PWM rectifier which interfaces the main ac grid. While the PWM rectifier regulates the total dc bus voltage and the ac input currents, a voltage balancer consisting of a buck-boost circuit topology regulates the differential voltage of the dc bus. Analysis of the differential voltage balancing control is carried out for dc-dc bidirectional converters yielding unbalanced and reverse power flow in the dc bipolar bus.