Single Active Vector Pulse-width 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 pulse-width modulation (SVPWM) is often used in this situation, its harmonic performance can become unsatisfactory because of its low frequency carrier sidebands. Synchronous optimal pulse-width 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 paper, a new single active vector pulse-width modulation strategy (SAVPWM) 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 380V, 12000rpm high speed motor.