A Modulation Compensation Scheme to Reduce Input Current Distortion in GaN-Based High Switching Frequency Three-Phase Three-Level Vienna-Type Rectifiers

Wide bandgap semiconductors are gradually being adopted in high power-density high efficiency applications, providing faster switching and lower loss, and at the same time imposing new challenges in control and hardware design. In this paper, a gallium nitride-based Vienna-type rectifier with SiC diodes is proposed to serve as the power factor correction stage in a high-density battery charger system targeting for aircraft applications with 800 Hz ac system and 600 V level dc link, where power quality is required according to DO160E standard. To meet the current harmonic requirement, PWM voltage distortion during the turn-off transient, is studied as the main harmonics contributor. The distortion mechanism caused by different junction capacitances of the switching devices is presented. A mitigation scheme considering the nonlinear voltage-dependent characteristics of these capacitances is proposed and then simplified from a pulse-based turn-off compensation method to a general modulation scheme. Simulation and experimental results with a 450 kHz Vienna-type rectifier demonstrate the performance of the proposed approach, showing a THD reduction from 10% to 3% with a relatively low-speed controller.

I. Introduction

The input current distortion caused by transistor turn-off delay can be very problematic for converters with switching frequencies in the hundreds of kHz, especially in the vicinity of the phase current zero-crossing. It has been reported in [1] that this distortion in the Vienna-type rectifier is mainly due to the nonlinear output capacitance of the super-junction mosfet, because the voltage rise time at turn-off can be quite long within a relatively short switching cycle. This leads to a significant voltage error at the converter ac terminal, as well as corresponding current harmonics through the input boost inductor.