Study On Wide Speed Range Flux Weakening Control Of Interior Permanent Magnet Synchronous Motor

In order to obtain a wider speed range of interior permanent magnet synchronous motor(IPMSM), the flux weakening control system is studied in the thesis. In recent years,permanent magnet synchronous motor and its drive control technology have been further studied by experts and scholars, and also have been widely used in equipment manufacturing.The first reasons is the development of permanent magnetic materials technology, making NdFeB permanent magnet material with high-density and high-coercivity widely used in motors. High-performance permanent magnet materials make permanent magnet synchronous motor withstand greater armature reaction demagnetization effect, which means that demagnetization current can be greater. The second reason is the rapid development of microelectronics and power electronics technology, especially the advances in the high-frequency power electronics technology, which could reduce the size, weight and cost of electrical equipment and provides the technical basis for AC motor driving.When the permanent magnet motor is manufactured, the rotor magnetic field generated by the permanent magnet is fixed, so the excitation magnet motive force could not be adjusted.By increasing the direct axis demagnetization current, utilizing the demagnetization effects of direct axis armature reaction, the composite air gap magnetic field is weakened. The way to achieve higher speed is called flux weakening. The d-axis inductance and q-axis inductance of IPMSM are not equal, so the reluctance torque could be used to improve motor’s efficiency and speed adjusting performance. Adjusting the torque angle to obtain larger electromagnetic torque and better load performance at the same speed by the best use of the reluctance torque.A control method is presented in the thesis to achieve wide flux weakening speed range for such motor. Firstly, determine flux weakening area and use different methods to give currents in different regions. The flux weakening area could be separated into three sections by the speed: the low-speed region, region I and region II. The cut-off points are rated speed and the intersection of maximum power output trajectory and current limit circle. At low speed region, using the maximum torque per ampere control method could reduce the motor’s copper loss and improve efficiency of the system. When the speed surpass the rated speed and enters region I, the method of compensation of stator current phase angle could be used. When speedrises and enter region II, the of maximum torque per voltage control method is used to ensure that the motor obtains maximum output power. Therefore, the thesis presented a current correction method based on gradient descent, making the stator current vector change by the MTPV curve. In this method, the motor could obtain the maximum output torque at the same speed, achieve the best control of current and expand the flux weakening speed range. At the same time, the method to calculate motor’s inductance was described and Matlab/Simulink model was established to analysis the properties of flux weakening algorithm. At last, some experiments about the motor and the control system had been done, and the experiments and the datas verified the feasibility and practicality of the flux weakening control algorithm.