Continuous PWM Techniques for Sinusoidal Voltage Generation with Seven-Phase Voltage Source Inverters

Multi-phase motor drives are typically supplied from two-level voltage source inverters (VSIs). It is thus necessary to develop pulse width modulation (PWM) schemes for inverter control in order to utilise the benefits offered by multiphase motor drives. This paper deals with seven-phase VSI and develops continuous PWM schemes that enable generation of sinusoidal voltages at the output. Carrier-based sinusoidal PWM, sinusoidal PWM with the 7th harmonic injection, and sinusoidal PWM with the triangular zero-sequence injection, as well as the space vector PWM are elaborated. Presented PWM schemes are analysed in terms of DC bus utilisation and direct correlation between carrier-based and space vector approach is established. All schemes are implemented in a digital signal processor and are compared through experimentation on a seven-phase custom designed VSI supplying a seven-phase star-connected static load.