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.