Investigations on dependence of duration of active vectors on modulation index for inverters

Fixed switching frequency Random Pulse Width Modulation (RPWM) schemes have been implemented based on random placement of active vectors. The effectiveness of this technique depends on duration of active vectors compared to switching period. In this paper, dependence of duration of active vectors with modulation index is investigated to find the range of modulation index in which this RPWM scheme is effective. For multilevel inverters, a mapping technique is used for calculating the duration of switching vectors by translating the reference space vector into a vector lying in 2-level inverter. This paper also presents the effect of mapping on reference signal. The effectiveness of random placement of active vectors is experimentally verified for 2, 3 and 4-level inverters in a 2 hp induction motor based drive using TMS320LF2407 DSP platform and the results are presented.