Experimental Evaluation of Medium-Voltage Cascode Gallium Nitride (GaN) Devices for Bidirectional DC–DC Converters

Abstract

As renewable energy sources, such as photovoltaic (PV) cells and wind turbines, are rapidly implemented in DC microgrids, energy storage systems play an increasingly significant role in ensuring uninterrupted power supply and in supporting the reliability and stability of microgrid operations. Power electronics, especially bidirectional DC–DC converters, are essential parts in distributed energy storage and alternative energy systems because of their grid synchronization, DC power management, and bidirectional power flow capabilities. While there is increasing demand for more efficient, compact, and reliable power converters in numerous applications, most existing power converters are hindered by traditional silicon (Si) based semiconductors, which are reaching their theoretical and material limits as there is an insignificant possibility for further improvements. Wide bandgap (WBG) semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), exhibit superior physical properties and demonstrate great potential for replacing conventional Si semiconductors with WBG technology, pushing the boundaries of power devices to handle higher switching frequencies, output power levels, blocking voltages, and operating temperatures. However, tradeoffs in switching performance and converter efficiency when substituting GaN devices for Si and SiC counterparts are not well defined, especially in a cascode configuration. Additional research with further detailed investigation and analysis is necessitated for medium-voltage GaN devices in power converter applications. Therefore, the objective of this research is to experimentally investigate the impact of emerging 650/900 V cascode GaN switching devices on bidirectional DC–DC converters that are suitable for energy storage and distributed renewable energy systems. Dynamic characteristics of Si, SiC, and cascode GaN power devices are examined through the double-pulse test (DPT) at different gate resistance values, device currents, and DC-bus voltages. Furthermore, the switching behavior and energy loss as well as the rate of voltage and current changes over the time are studied and analyzed at different operating conditions. A 500 W experimental converter prototype is designed and implemented to validate the benefits of cascode GaN devices on the converter operation and performance. Comprehensive analysis of the power losses and efficiency improvements for Si- based, SiC-based, and GaN-based converters are performed and evaluated as the switching frequency, working temperature, and output power level are increased. The experimental results reveal a significant improvement in switching performance and energy efficiency from cascode GaN power devices used in the bidirectional converters.