Research On Multiphase Induction Motor Electronic Pole Changing System

The research of multiphase induction motor drives (the phase number n>3) has been deepened since half century ago. The multiphase induction motor drives have many advantages over the traditional three-phase motor drives, such as stable torque, easy to realize high-power transmission with the low-voltage devices and high reliability. Multiphase induction motor drives are suitable for high-power industrial fields such as electric ship propulsion, aircraft electric and traction. The vector control (VC) is based on dynamic model of AC motor according to a 3/2 coordinate transformation, utilizes coordinate rotation transformation to resolve the current vector of the stator into excitation component and torque component. The AC motor can control excitation component and torque component independently and obtain good dynamic performance as well as DC motor. VC makes the high-performance AC drives achieved and developed. The technique of electrical pole changing makes the motor have the ability of changing pole without poweroff. The motor would have wider operation range.The theory of multiphase induction motor and the control strategies of electronic pole-changing (EPC) are highlighted in this dissertation. This paper is organized as follows:First of all, the winding-function theory is introduced. Based on it, the mathematical model of a multiphase induction motor is established according to the analysis of the MMF. The magnetic field distribution is determined by both the winding structure and excitation, what is the physical nature of multiphase motor.The hardware realization of multiphase induction motor EPC system is introduced, including the main circuit and the control circuit. There are structure of main circuit, parallel type 12-pulse diode rectifiers system and multiphase inverter system in the main circuit. The circulated current between the rectifiers in the parallel type 12-pulse diode rectifiers system is analyzed, causing by the unequal voltages or leakage resistances unbalance of phase-shifting transformer secondary windings. The functions and roles of DSP TMS320F28335 and FPGA Cyclone EP1C6240C6 are introduced in the control circuit. The control program process plan of multiphase induction motor EPC system is given.Three kinds of SPWM (Space Pulse Width Modulation) control method are introduced briefly, the equations of multiphase SPWM are derivated. Rotor Filed Oriented Control (RFOC) based on harmonic current close loops is obtained according to analyzing the traditional RFOC of multiphase induction motor.The EPC technique of multiphase induction motor is proposed, which based on studying multiphase system transform theory and RFOC. The proposed technique was verified accrossing to these experiments. It is feasible to realize pole-changing without poweroff and the technique proposed has the ability to extend the constant-power operation range of multiphase motor. It is suitable for the applications of high power.