Single Active Vector Pulsewidth Modulation With Improved Harmonic and Dynamic Performance for Low-Carrier Ratio Applications

High-power converters and high-speed motor drives typically operate at low carrier ratios to minimize power device switching losses. While space vector pulsewidth modulation (SVPWM) is often used in this situation, its harmonic performance can become unsatisfactory because of its low frequency carrier sidebands. Synchronous optimal pulsewidth modulation (SOPWM) has a theoretically optimal harmonic performance, but its poor dynamic performance limits its wider application and its switching frequency varies significantly as the fundamental frequency varies. In this article, a new single active vector pulsewidth modulation (SAVPWM) strategy is proposed to overcome these limitations that uses only one active vector per switching period. The strategy is based on the switching characteristics of SOPWM, the modulation principles of SVPWM and a modulation index determined using a hexagonal “virtual flux linkage” trajectory. SAVPWM achieves a harmonic performance that almost equals SOPWM at low carrier ratios, while still providing a high dynamic performance capability since the duty cycle can be varied in real-time at a fixed carrier frequency. The fixed carrier frequency also facilitates fully utilizing the available switching frequency of the power devices. The SAVPWM approach has been verified by simulation, and experiment results with a 380 V, 12 000 rpm high speed motor.