Common mode elimination in GaN three-phase four-leg inverters and the performance comparisons with traditional Si inverters using multiple modulation strategies.

This dissertation presents a novel wide bandgap four-leg inverter with common mode (CM) voltage elimination implemented using a Typhoon HIL 402 as the system-level controller. The four-leg inverter is built using GaN devices to minimize the switching losses and is controlled through pulse density modulation (PDM), and the comparison between PDM and pulse width modulation (PWM) are discussed. The comprehensive overview for current state-of-the-art CM elimination techniques and novel EMI filter designs for GaN four-leg inverters are included. The CM elimination method implemented in the GaN four-leg inverter satisfies the MIL-STD-1399 requirements including maintaining balanced voltages during unbalanced load conditions. The MIL-STD-461G conducted emission (CE) limits for current and voltage (CE101 and CE102 respectively) are also met without the use of a CM choke. Both simulation and experimental results are presented to demonstrate the efficacy of the novel control method. Different modulation strategies are detailed and compared to understand switching losses and dc-bus utilization between GaN inverters and Si inverters in motor drive applications. In addition, the comprehensive experimental results are provided for motor drive applications at 230V under varying load conditions including the effects of deadtime on the proposed CM elimination approach and in meeting the standard requirements, as well as the approaches to increase dc-bus utilization without interfering with the CM elimination method.