Topology Design and Analysis of Bidirectional Battery DC-DC Converter for DC Grid Voltage Control

This paper presents the design and analysis of Dual Active Bridge (DAB), CLLLC resonant circuit, and CLLC resonant circuit topologies applied as bidirectional battery DC/DC converters for the DC bus voltage control in the low-voltage and low-power DC microgrid application. The circuit design process starts with the high-frequency transformer design (HFT) for the DAB and CLLLC converters. All DC/DC converter designs are optimized to maximize the phase shift control variable resolution in the rated power range through the circuit parameter iterative adjustment based on the converter circuit simulation results. The CLLC converter parameters are derived from optimized CLLLC parameters with its HFT redesigned to meet the turns ratio and the modified magnetization inductance requirement. The secondary side compensation capacitor ratio of the CLLC resonant circuit is adjusted iteratively based on circuit simulation results to maximize the phase shift control variable resolution in the rated power range. The PLECS circuit simulation is constructed to compare and evaluate the voltage and current waveforms of the converters and transformers, the power loss, and the efficiency of different circuit topologies. The proposed method is applied to identify the best battery DC/DC converter topology for a 4 kW 100 V DC microgrid with a 4 kW PMAC generator connected as an AC power source. The circuit simulation results validate that the CLLLC resonant converter has the best efficiency over a wide power range in the full battery voltage range.