Research On The Control Strategy Of Multi-Phase Induction Motor Under Open Phases Operation

In AC variable frequency drive system, the research of theory and practice is three-phase speed control system mostly. However, with the development of industry, people has higher requirement on the performance of speed control system. Therefore, the speed control system of three-phase induction motor cannot satisfy all of the occasions. And the multi-phase motor control system has been coming into view gradually.Due to its special structure, multi-phase motor AC drive system can reduce the electromagnetic torque ripple and the harmonic loss, and realize high power output of motor using low voltage devices. However, the most unique characteristic of multiphase motor is that the system doesn’t have to stop running when a fault occurs, and it can continue to operate stably by reducing load. And this characteristic is what the traditional three-phase AC variable frequency speed regulation system doesn’t achieve. The advantages of multi-phase AC variable frequency speed control system are more prominent, especially in occasions requiring high reliability.Firstly, the research of multiphase motor is based on seven-phase induction motor. According to space decoupling coordinate transformation theory, seven-phase induction motor space decoupling mathematical model is deduced by analyzing its winding structure. In addition, the space-time harmonic magnetmotive force (MMF) expression of seven-phase induction motor is derived.Secondly, to solve the problem of open-phase running, the open-phase mathematical model of multi-phase motor is established. A comparison of space vector between normal operation and open-phase situation is analyzed, and the mathematical expression of electromagnetic torque is also provided. Modeling and simulation verification of multi-phase motor in normal operation and open -phase operation are studied using MATLAB/Simulink, and the simulation results verified the performance parameters alternation.Thirdly, according to the MMF constant principle, its compensation control methods based on current amplitude minimum and stator copper loss minimum are introduced. These control methods with current hysteresis regulators are simulated. In addition, rotor flux field-oriented vector control method, which is based on effective time carrier wave SVPWM, is provided in phase-open condition. This method can ensure the rotor flux is a circle before and after open-phase, and reduce the harmonics of stator current. Theoretical analysis and simulation results show that these two proposed methods are both effective and the vector control method has a better performance.Finally, the experiment platform of seven-phase induction motor speed control system is designed, which is consisted of the main circuit, the main control board and the drive circuit. The system programs are compiled by Language C in CCS3.3 platform, and the results are analyzed in detail. The simulation and experimental results prove the validity and effectiveness of the control algorithm in this paper.