Isolated ESS Charger Including Voltage Balancing Capability for Bipolar LVDC Distribution System

Abstract

A bipolar low voltage DC (LVDC) distribution system used in residential and building applications requires AC-DC converters and voltage balancers that balance two DC bus voltage polarities. The bipolar DC bus voltage level only relies on the voltage balancer tied with the AC grid. An isolated DC-DC charger for ESS including voltage balancing capability is proposed to prevent the failure of the main grid-tied converters. The proposed ESS charger topology is an enhanced three-port dual-active-bridge (DAB) converter, which has bidirectional power transfer capability for the battery charging. It can balance the bipolar DC bus voltage level without complex control algorithm to prevent the grid-tied converter failure. The effectiveness of the proposed ESS charger is verified with a 3-kW laboratory-level prototype converter.