Comparative Evaluation of Y-Inverter against Three-Phase Two-Stage Buck-Boost DC-AC Converter Systems

Modern motor drives feature output filtering capability in order to protect the motor from high converter output voltage du/dt rates and provide a sinusoidal current to the machine in order to minimize the rotor losses. The incorporation of such motor drive into a fuel-cell (FC) application is challenging since the power electronics converter has to cope with the power dependent variation of the FC voltage. In this paper three candidate converter concepts are comparatively evaluated i.e. a voltage source inverter with front-end DC-DC boost converter (boost VSI), a current source inverter with front-end DC-DC buck converter (buck CSI), and the recently proposed buck-boost Y-inverter topology. In a first step, the three implementations are assessed based on fundamental scaling laws, i.e. the semiconductor losses and/or the required chip area and the inductive components volume, which constitute a major part of the total system losses and volume, are analytically derived. In a second step, the exact performance of the different motor drive solutions in terms of efficiency η and power density ρ is quantified by means of a comprehensive multi-objective optimization. The optimization results reasonably mach the scaling-laws approach and hence further verify the practical value of the analytic calculations. Both the scaling-laws based analysis and the accurate optimization indicate a clear power density advantage in favor of the Y-inverter.