Simple multilevel inverter-based induction motor drive scheme using sigma-delta converter with space-vector quantiser

In this study, sigma-delta (Sigma Delta) modulation-based random pulse width modulations (PWM) scheme with vector quantisation for three-level inverter is proposed. In the proposed scheme, the instantaneous reference space vector is mapped to an equivalent two-level inverter and the proposed space-vector-based Sigma Delta modulation is applied on this mapped reference space vector. The scheme uses the principle of vector quantisation for quantising the mapped reference space vector in the Sigma Delta modulator. The switching signals are generated directly from the amplitude of the three-phase reference signal without using lookup table and complex arithmetic calculations. The resultant vectors of the two-level inverter can be easily translated to the actual switching vectors, and this proposed method of working on the mapped reference space vector makes the proposed scheme suitable for any general n-level inverter. The switching vectors of the inverter are naturally selected ensuring optimum switching sequence under all conditions including the over-modulation region. The proposed scheme is implemented for three-level inverter driving a two-horse power (HP) three-phase induction motor. The performance of the proposed scheme is compared with space-vector PWM scheme and random PWM schemes with different modulation indices and experimental results are presented.