Comparative analysis of modulation schemes for multilevel half-bridge bidirectional DC–DC converter in microgrid applications

This paper analyses the performance of multilevel half-bridge bidirectional DC–DC converter (MHBDC) under wide change in voltage transformation ratio. The advantage of MHBDC topology over conventional isolated bi-directional dc–dc converter (CIBDC) includes reduced voltage stress across the semiconductor switches and the transformer windings, which is suitable for high voltage applications in DC microgrids. Microgrids is inclined to voltage variations at both input and output side, which direct towards increased current stress in MHBDC. The rise in current stress can be minimized by employing various phase shift modulation techniques. The paper presents steady state time domain analysis of MHBDC under conventional phase shift modulation (CPSM), extended phase shift modulation (EPSM) and dual phase shift modulation (DPSM). A computational procedure is developed and demonstrated to obtain the phase shift angles at minimum value of current stress and varying voltage transformation ratio in the converter. Current stress analysis, soft switching region of operation and reverse power flow analysis in MHBDC are examined under different modulation schemes. A 1.5 kW hardware prototype of MHBDC is built, evaluated and presented the results. Power loss analysis and efficiency plots for the converter is determined and quantitatively evaluated with different modulation techniques considering high, medium and low power ranges.