Mitigation Zero-crossing Distortion of Active Neutral-Point-Clamped Rectifier with Improved Hybrid PWM Technique

This paper presents a modified hybrid PWM technique for a 3-level active neutral-point clamped (ANPC) rectifier to mitigate current distortion during zero-crossing. In the structure of the converter both Silicon (Si) power MOSFETs and Gallium-Nitride (GaN) FETs are utilized. By utilizing the GaN devices the switching frequency of the converter is increased to 140 kHz. Increasing switching frequency reduces the size of the passive components of output filters. A hybrid modulation technique is employed in which four out of six switches (Si) are switching at fundamental frequency. Since the characteristics of switches are different, a proper switching commands should be applied to the converter to prevent the current distortion during zero-crossing. In the suggested PWM method during zero-crossing, the switching commands of all switches are applied at different times. To implement the modified hybrid PWM, an FPGA is utilized to control the switches. The experimental results show the ability of modified switching commands to reduce the voltage and current variation during zero-crossing.