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

A
${>}99.5\%$
efficient grid-tied inverter with peak values of 30-kW power, 13.7-kW/L volumetric power density, 10.17-kW/kg gravimetric power density, and 1.2-MHz switching frequency is proposed in this article. This union of high efficiency and high power density is achieved through a unique combination of technologies and is maximally leveraged through an
$\eta \rho $
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
$\eta \rho $
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. Finally, experimental results showing efficiency, rated power operation, total harmonic distortion, and transient load steps are provided for a grouping of different grid voltages.