Research On Vector Control Of Nine-phase Induction Motor

Multi-phase (in excess of three) motor drives possess many advantages over the traditional three-phase motor drives such as reducing the voltage ratings of power electronic devices while handling the same power capacity, reducing the amplitude and increasing the frequency of torque pulsation, offering a greater number of degrees of control freedom, exhibiting better fault tolerance capability and having higher reliability, which make them especially suitable for applications such as electric vehicles, aerospace applications, ship propulsion and high power applications. Multi-phase motor drives have attracted a considerable amount of interest from researchers and engineers.The vector control of nine-phase induction motor drives under non-sinusoid currents (the combination of the fundamental, the third, fifth and seventh harmonic currents) and multi-phase PWM generation scheme are highlighted in this thesis. The organization of the thesis is as follows:Based on the winding-function theory, an exhaustive analysis of the magneto-motive force (MMF) distribution of the multi-phase motor is presented. The differences of harmonic effects between three-phase induction motors and nine-phase induction motors are compared. According to the comparison, the third, fifth and seventh harmonic currents play an important role in improving the air-gap flux waveform, increasing iron utilization and electromagnetic torque.The dynamic model of the nine-phase induction motor supplied by non-sinusoid currents under an arbitrary rotating reference frame is deduced. Therefore, the nine-phase induction motor under non-sinusoid currents can be equivalent to four independent nine-phase sinusoidal induction motors. The flux and torque can be controlled independently on each harmonic plane, which serves as the theoretical basis for vector control of the nine-phase induction motor.The vector control algorithm is extended to the nine-phase induction motor drives to perform direct control of flux and torque independently. The corresponding algorithm with non-sinusoid currents are divided into three groups and discussed separately through simulations. The vector control of nine-phase induction motors with only the third harmonic current injected obtains a considerable (10%) enhancement of torque, while the torque has no significant increase with the third, fifth and seventh harmonic currents.The number of the required PWM signals increases with the increase of the number of motor phases. Therefore, a multi-phase PWM generation scheme utilizing a FPGA (Field Programmable Gate Array) base on the reusable IP (Intellectual Property) soft core is proposed and verified by simulations and experiments in the thesis. The synchronization and phase-shifting of PWM signals can be easily realized by the proposed method. Moreover, the method can be extended to any other channels of PWM signals.