Multifrequency Output Voltage Generation for Asymmetrical Dual Three-Phase Drives

Research on multiphase drives has been intense during the last years. The first topologies considered the use of a number of phases multiple of three, being the most studied the asymmetrical double three-phase machine with independent neutral points supplied by a VSI (Voltage Source Inverter). Due to the discrete quantity of VSI outputs, Pulse Width Modulation (PWM) techniques are used to generate variable output voltage in amplitude and frequency. Several modulation methods have been proposed for this topology. However, when a motor is being controlled sometimes it is necessary to generate voltages that are not necessarily sinusoidal, due to asymmetries in the motor's winding, asymmetries in the converter, or due deadtimes effects. For these cases, the space vector modulation techniques proposed until now are not useful because they were developed to generate, on average, a zero voltage in the x-y space. So, typical solutions use carrier-based techniques, rather than SVPWM (Space Vector PWM). This paper present a SVPWM technique that is capable to reach a composite voltage reference in the two control planes. A theoretical explanation for the implementation is given and results are supported by simulation results.