A Bidirectional Multilevel DC-DC Converter Applied to a Bipolar DC Grid: Analysis of Operation under Fault Conditions

Abstract

Recently, DC grids have been an important subject of research due to their attractive features comparing with AC grids. The characteristic advantages of DC grids are not only related with the integration of native DC technologies, as renewable energy sources (RES) and energy storage systems (ESS), but also with the reduced number of power converters. Relatively to the configurations of DC grids, in this paper, it is presented a bipolar DC grid, where an innovative bidirectional multilevel DC-DC converter is considered under a fault-tolerance analysis. This converter can be used to interface with several technologies, but, in the scope of this paper, it is considered the application of an electric vehicle (EV) battery charger. Taking into account that some failures can occur, namely in the DC-DC converter and in the bipolar DC grid, the operation of the DC-DC converter within the bipolar DC grid can be harmful. Therefore, this paper also presents a fault-tolerance analysis of the DC-DC converter when facing the occurrence of failures in itself and in the bipolar DC grid, namely for different scenarios of failure in the DC-link wires. Besides, the control strategy for the DC-DC converter is described in detail for distinct scenarios of operation, both in steady-state and transient-state.