Increasing Current Loop Performance Using Variable Accuracy Feedback for GaN Inverters

With the appearance of wide-bandgap power electronic devices such as SiC and GaN, the pulse-width modulation frequency is growing. In modern servodrives based on GaN devices it can reach 100 kHz and more. However, the performance of the drive is now limited by the delay in the current feedback rather than the modulation frequency. When using shunt current sensing with delta-sigma modulation, the delay in feedback can be adjusted with simultaneous change of the measurement accuracy. This paper proposes to use inaccurate but fast feedback when error between reference of the motor current and its actual value is big, and to use accurate but slow feedback in case of small error. This requires simultaneous change of the current controller parameters. The performance of the system was examined using model of the servodrive and showed twice higher cutoff frequency of the current loop.