Mitigation of Voltage Unbalancing in the Series-Connected GaN Switches Using Gate Current Injection Method

Due to their lower voltage-blocking capacity, gallium nitride (GaN) devices have not been able to gain much popularity in higher voltage applications. Two devices can be connected in a series fashion to make a single device of higher voltage rating effectively. However, there is an issue of voltage unbalance in series-connected devices due to gate circuit and device parameters mismatch. In this article, first, the voltage unbalancing issue for the series-connected switches is explained by a simulation model using LTspice, incorporating commercially available GaN devices EPC2304 for a 300 V dc link. Then, a gate current injection technique is proposed to achieve voltage balancing of series-connected GaN switches during the turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> period while also reducing the voltage overshoot experienced by the switches during the turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> period. The technique uses an external control capacitance to sense the rate of transition of the drain voltage of the switches and inject additional gate currents to control their slew rate. The proposed technique was experimentally verified using the GaN switch EPC2304 and GS61008, and the worst case voltage unbalance was reduced under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 10\%$</tex-math></inline-formula> of dc links with minimal voltage overshoot.