Loss Minimization using Linear Soft-Switching with Wide Bandgap Devices in Efficient High-Frequency DC-DC Converters

Abstract

Switching power converters are used for voltage-level conversions in various applications. With progress in device technology, the wide bandgap devices offer smaller parasitic capacitances and lower switching energy values. Efforts are being made to use higher frequencies to realize more power-dense converters with smaller volume of the passive components. The maximum switching frequency is limited by the ability of the switching devices to dissipate their losses. This thesis presents a framework for the design and modeling of efficient high-frequency high-energy density DC/DC converters using soft-switching techniques with wide bandgap devices. Various online switching loss estimation methods are discussed demonstrating improved accuracies, enabling a better cooling system design. A comparison is made between various soft-switching methods and the use of turn-off snubbers to reduce the switching losses. A linear soft-switching method is proposed and validated for both SiC and GaN devices. A simpli fied analytical model is presented which predicts the actual turn-off losses very accurately. This method is found to enable buck converter operation at 1 MHz switching frequency and 1 kW output power with switch losses smaller by nearly five times from a hard-switched system using GaN devices. These losses are further reduced with the use of SiC schottky diodes, with future scope to achieve higher efficiency using custom inductors designed for high frequency and current ripple values.