Inverter dead-time effects have been investigated in detail in the past for three-phase drives supplied from a three-phase voltage source inverter (VSI). A similar study has never been conducted in conjunction with multi-phase (more than three phases) drives, supplied from multi-phase VSIs. Regardless of the type of ac machine and its number of phases, the power supply of the drive is typically a two-level VSI, which requires a method of PWM for its operation. If a multi-phase machine is with sinusoidal field distribution, the PWM technique must generate sinusoidal harmonic-free output voltages in order to avoid appearance of low-order stator current harmonics. Recently a great deal of research has concentrated on PWM methods suitable for multi-phase VSIs. All of these PWM methods theoretically produce sinusoidal output voltages with no low order harmonics. As a consequence, rotor flux oriented control of multi-phase ac machines with sinusoidal MMF distribution can be theoretically realised by using only two current controllers in the synchronous reference frame. The paper shows that despite using a PWM method that does not produce low-order harmonics, in practice they do appear in the output voltage, and consequently currents, of the multi-phase VSI. Simulation studies show that low-order harmonics are generated as a result of inverter dead-time and that the effect of such harmonics on a five-phase ac machine can be significant due to the low machine impedance presented to these harmonics. Experimental results collected from a five-phase induction motor drive laboratory prototype are presented which reinforce this hypothesis. The paper further suggests a modified current control scheme that is able to fully compensate inverter dead-time effect and thus provide practically perfect sinusoidal currents. The proposed current control scheme is validated via simulation and experimentally.
Drazen Dujic, Andrea Cervone, Tianyu Wei
Drazen Dujic, Andrea Cervone, Tianyu Wei
Drazen Dujic, Andrea Cervone, Tianyu Wei