Synchronised PWM strategies based on space vector approach. II. Performance assessment and application to V/f drives

The harmonic distortion due to the four space-vector-based synchronised PWM strategies discussed in Part I of this paper is studied in the whole linear modulation range. Different strategies give the best performance for different ranges of fundamental voltage V1. A hybrid PWM using the different strategies at appropriate voltages is proposed. Theoretical and experimental results show that this hybrid PWM results in a significant reduction in harmonic currents in V/f drives with a base frequency of 50 Hz and different maximum switching frequencies fsw(max) of the inverter. Experimental results show that the current transients during change of pulse number are also reduced. Compared to the other real-time, open-loop, synchronised PWM techniques with a uniform sampling rate, the proposed hybrid PWM shows superior performance in the medium-voltage range. In the high-voltage range, its performance is inferior only to that of the more complicated high-voltage suboptimal (HVSO) strategy. With fsw(max)=450 Hz, the harmonic distortion in the whole speed range of the drive is brought down to less than that of a six-step operation, which is regarded as an acceptable level for such low switching frequencies. This has not been possible with other comparable strategies