Optimizing PWM Control for Efficiency and Reduction of False Turn-On Events in Synchronous Buck GaN Converters

Nishant Kashyap,Jennifer Bauman

doi:10.1109/access.2021.3121633

Nishant Kashyap, Jennifer Bauman

Open Access

https://doi.org/10.1109/access.2021.3121633

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Abstract

Half-bridge GaN power converters are susceptible to false turn-on events, which can lead to shoot-through and potentially device-damaging currents. There are three main parameters that can be adjusted in PWM schemes to reduce the likelihood of false turn-on events: negative gate bias, gate resistance, and deadtime. However, these PWM parameters also affect converter efficiency in the inverse way, meaning less false turn-on events must be balanced with lowered efficiency. The novelty of this paper is to investigate the trade-off between reducing GaN false turn-on events (by reducing the transient peak of gate to source voltage) and maximizing the power converter efficiency, which has not been done in prior work. This paper investigates this trade-off using a synchronous buck converter over numerous operating points with variation of the three key PWM parameters. Six converter scenarios are considered with input voltage of 200/400V, switching frequency of 50/100kHz, and output power of 500W/1kW. For each scenario, negative gate bias is set to ™4.4V and −5V, gate on-resistance is set to $10\Omega $ and $12.5\Omega $ , and deadtime is varied at 60ns, 80ns, and 110ns. The results are organized into Pareto plots to find optimal points for efficiency and reduction of false turn-on events. The experimental results show that a further negative gate bias (−5V) most significantly reduces the false turn-on voltage peak and still achieves very high efficiency with appropriate selection of gate resistance and deadtime.

Highlights

Due to having low losses and the capability of attaining very high switching frequencies, gallium nitride (GaN) switching devices are excellent options for power converters requiring high efficiency and low volume
If it is most important to have a good balance between reliability and efficiency, the recommended PWM strategy is Vgs,off = −5 V, Rg,on = 10, and to completely remove the false turn-on Vgs,low peak for 400 V operation
WORK The novelty of this paper is that it investigates the tradeoffs between reducing GaN false turn-on events and achieving high power converter efficiency, which has not been covered in prior work

Summary

INTRODUCTION

Due to having low losses and the capability of attaining very high switching frequencies, gallium nitride (GaN) switching devices are excellent options for power converters requiring high efficiency and low volume. The novelty of this paper is that there is no earlier work which endorses an effective PWM strategy for halfbridge eGaN-HEMTs circuits, which can relate to both false turn-on issues and power converter efficiency with a variation in all the three critical PWM parameters: gate resistance, negative bias and deadtime. In this investigation, the trade-off between converter reliability (i.e., false turn-on from voltage oscillations) and efficiency is thoroughly analyzed in order to recommend ideal PWM strategies. This paper will quantify the benefits and drawbacks of using further negative gate biases of −4.4 V and −5 V on both false turn-on likelihood and converter efficiency

DEAD TIME

EXPERIMENTAL RESULTS AND DISCUSSION

CONCLUSION AND FUTURE WORK