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Multilevel inverter supplied multiphase variable-speed drive systems have in recent times started attracting more attention, due to various advantages that they offer when compared to the standard three-phase two-level drives. For proper functioning of such systems good pulsewidth modulation (PWM) strategy is of crucial importance. Control complexity of multiphase multilevel inverters increases rapidly with an increase in the number of phases and the number of levels. This paper deals with a three-level neutral point clamped (NPC) inverter supplied five-phase induction motor drive and analyses five PWM strategies: three are carrier-based (CBPWM) and two are space vector based (SVPWM). The aim is to provide a detailed comparison and thus conclude on pros and cons of each solution, providing a guideline for the selection of the most appropriate PWM technique. Experimental results are provided for all analysed PWM methods. The comparison of the PWM techniques is given in terms of the voltage and current waveforms and spectra, as well as the total harmonic distortion (THD) in a whole linear modulation index range, which is used as the global figure of merit. Properties of the common mode voltage (CMV) are also investigated. Complexity of the algorithms, in terms of the computational time requirements and memory consumption, is addressed as well. It is shown that the performance of the PWM techniques is very similar and that one CBPWM and one SVPWM technique are characterised with identical performance. However, using the algorithm complexity as the main criterion, space vector techniques are more involved.
Date of Publication: May 2013