Loss analysis of GaN devices in an isolated bidirectional DC-DC converter

GaN devices have emerged as a possible replacement for silicon devices in various power conversion applications and as an enabler of new applications not previously possible. This paper presents a 600V Gallium-Nitride (GaN) device based isolated bidirectional DC-DC converter applied in battery energy storage systems. Apart from the features of low turn-off loss, low output capacitance and low drain-source on-state resistance, the most salient one in our bidirectional DC-DC converter application is the ultra-fast freewheeling "body diode" that GaN devices have when compared with Si devices. To distinguish the above mentioned performances of GaN from those of the comparable Si devices, a figure of merit for power devices operating in synchronous rectifying mode is proposed. The converter´s operating principle is analyzed in steady state. Switching losses of high voltage and low voltage side switches are simulated based on detailed PSpice models. The converter´s safe operation area is extended by using GaN device is explained by calculating the loss in hard switching mode. A thermal simulation is conducted to predict its temperature. Experimental results are presented for a 1 kW, 380-to-12 V prototype DC-DC converter, which demonstrate the validity of the analysis and simulation.