A Peak 1.2MHz, >99.5% Efficiency, and >10kW/L Power Density Soft-Switched Inverter for EV Fast Charging Applications

A >99.5% efficient grid-tied inverter with peak values of 30kW power, 13.7kW/L volumetric power density, 10.17kW/kg gravimetric power density, and 1.2MHz switching frequency is proposed in this paper. This union of high efficiency and high power density is achieved through a unique combination of technologies and is maximally leveraged through an ηρ optimization. The first is a variable frequency critical soft-switching (VFCSS) scheme that allows the converter to maintain soft-switching over all permissible load conditions. This enables a simultaneous increase of the switching frequency and a decrease of the inductance without penalizing efficiency. The second technology is an additional capacitance placed across the drain-source terminals of each FET. This can allow for over a 40% reduction in turn-off losses at the expense of an increase in the required dead time. The last technology is a simple open-loop duty cycle compensation scheme that effectively mitigates the distortion caused by the combination of high switching frequencies and large dead times. An ηρ optimization process with its associated volume and loss estimations are provided. A brief discussion on the control of the converter is shown followed by a description of the constructed physical prototype. Lastly, experimental results showing efficiency, rated power operation, total harmonic distortion, and transient load steps are provided for a grouping of different grid voltages.