Thermal and electrical co-design of a modular high-density single-phase inverter using wide-bandgap devices

Abstract

This paper explores the multi-disciplinary design challenges in building a 240 VAC, 2 kVA modular single-phase inverter with high power-density using wide-bandgap transistors. The compromise between the electrical and mechanical design is extremely important in any high-density power converter. In this work the electrical and mechanical systems were iteratively co-designed using detailed 3D thermal and air-flow simulations. Custom copper heat-sinks and heat-pipes were developed for optimal thermal management. The inverter uses three soft-switching sub-inverters in parallel, which are controlled using a novel digital Hysteretic Current Mode Control (HCMC) scheme. To achieve a flat high efficiency curve with low THD over a wide load range, two operating modes are used: 1) Boundary Conduction Mode (BCM) with a slight negative inductor valley current for soft-switching, and 2) Continuous Conduction Mode (CCM) to limit the required saturation current in the inductors. The design of an active power decoupling scheme to minimize input capacitance is also discussed. The designed single-phase inverter has a volume of 33.1 in3 and resulting theoretical power-density of 60.3 W/in3 at 2 kW load. A measured efficiency of 97.7% is achieved for a single sub-inverter with 4.5% THD at 632.7 W.