Control Technology For Square-wave Voltage Driven Multi-phase Induction Motors

Multi-phase machines can take the advantage of harmonic waves to enhance the electromagnetic torque. It is also noted that by employing multi-phase motor drive systems the required rating of power electronic components for given output powers can be reduced. Besides, multi-phase motor drive systems have a greater fault tolerance and higher reliability. All above leads up to an upsurge of interest in multi-phase motor drive systems.This paper focuses on the control strategy of nine-phase induction motor drive system which is supplied by square-wave voltage. The nine-phase induction machine, which has concentrated stator windings and squirrel cage rotator, is employed as the controlled plant. And the paper is organized as follows:General theory of electric machines provides mathematical representation of a multi-phase induction motor. By applying multi-phase Park transform, the general representation is mapped into different harmonic planes. Based on space decoupling method, the mathematical model of the nine-phase induction motor is derived.The theory of multi-phase motor drive system with square-wave power supply is highlighted in this section. Firstly distribution of time harmonic and space harmonic in the air-gap field is studied in detail. In order to research the flux density of the air-gap field, different stator voltage is then supplied separately into nine-phase induction motor and the relative flux density waveform is studied.Emulation of the nine-phase induction motor drive system is accomplished in MATLAB Simulink environment. Corresponding experimental hardware platform and program flow is designed and realized as well. Emulation results and experimental results are presented at the final, which prove the correctness and accuracy of the theory.