Synchronised PWM strategies based on space vector approach. Part 2: Performance assessment and application to V/f drives

The harmonic distortion due to the four space-vector-based synchronised PWM strategies discussed in Part 1 is studied in the whole linear modulation r ange. Different strategies give the best performance for different ranges o f fundamental voltage V-1. A hybrid PWM using the different strategies at a ppropriate voltages is proposed. Theoretical and experimental results show that this hybrid PWM results in a significant reduction in harmonic current s in Vlf drives with a base frequency of 50Hz and different maximum switchi ng frequencies f(sw(max)) of the inverter. Experimental results show that t he current transients during change of pulse number are also reduced. Compa red to the other real-time, open-loop, synchronized PWM techniques with a u niform sampling rate, the proposed hybrid PWM shows superior performance in the medium-voltage range. In the high-voltage range, its performance is in ferior only to that of the more complicated high-voltage suboptimal (HVSO) strategy. With f(sw(max)) = 450Hz, the harmonic distortion in the whole spe ed range of the drive is brought down to less than that of a six-step opera tion, which is regarded as an acceptable level for such low switching frequ encies. This has not been possible with other comparable strategies.