Ultra-high Efficiency DC-DC Converter using GaN Devices

The demands for high efficiency dc-dc power converters are increasing day by day in various
applications such as telecommunication, data-centers, electric vehicles and various renewable
energy systems. Silicon (Si) has been used as the semiconductor material in majority of the
power devices for many decades. However, the rate of improvement slowed as the silicon power
materials asymptotically approached its theoretical bounds. Compared to Si, wideband gap
materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are promising
semiconductors for power devices due to their superior material properties such as high
temperature operation, high breakdown voltage and high frequency operation. Among wide
band-gap devices, GaN has an enhanced mobility of electrons, compared to SiC, which helps
in achieving smaller size for a given on-resistance and breakdown voltage. These superior
properties of GaN devices can be utilized in power converters to make them more compact and
highly efficient.
This thesis entitled “Ultra-high Efficiency DC-DC Converter using GaN devices” focuses on
achieving ultra-high conversion efficiency in an isolated dc-dc converter by the optimal
utilization of GaN devices. Simple replacement of Si or SiC devices with GaN devices in the
converter will not give an expected increase in efficiency or any improvement in the
performance of the converter. The use of GaN devices has defined another dimension in the
design of power converters, which mainly deals with the PCB layout and the magnetics.
This thesis mainly covers the design and implementation of various high efficiency isolated dcdc
converters in the range of 1 to 2.5 kW of output power. Both hard-switched and soft-switched
topologies in isolated dc-dc converters has been studied and realized in this thesis. Efficiency
measurements from the hardware prototype of both the topologies are also presented in this
thesis. Finally, the bidirectional operation of an optimized isolated dc-dc converter is presented.
The optimized converter has achieved an ultra-high efficiency of 98.8% in both directions of
power flow.