Bootstrap Gate Driver for GaN-Based Solar Inverter: Design Challenges and Solutions

This paper focuses on gate driver design for Gallium-Nitride (GaN)-based H6 solar inverter topology. Wide bandgap devices such as GaN offer lower on-state resistance and faster switching, leading to improved performance of the converters, such as high efficiency and power density. Bootstrap-based gate drivers are preferred over isolated supply and gate drivers due to their low cost and size. Nevertheless, bootstrap-based solutions present numerous issues that are examined and addressed in this paper. Firstly, the H6 inverter requires multiple cascaded bootstrap circuits in contrast to a full bridge inverter due to the presence of six switches. This increases the complexity of charging the bootstrap circuit during startup of the inverter. The bootstrap capacitors must be pre-charged to a sufficient voltage to ensure the proper functioning of the gate driver. In addition to that, the bootstrap capacitor voltage at the far end of the bootstrap ladder decreases below the desired value in a cascaded structure. Additionally, the voltage of the bootstrap capacitor fluctuates with changes in the duty cycle of the switches. Finally, the reverse conduction properties of the GaN switch might overcharge the bootstrap capacitor, potentially resulting in device failure due to gate over-voltage. The paper highlights the pre-charging of bootstrap gate driver circuits for the inverter operation. It also addresses the challenges related to bootstrap-based gate drivers for GaN devices and presents solutions to mitigate them. The simulation and experimental prototype is developed to validate the bootstrap-based gate driver and its solution for the associated challenges.