Research On Wound-rotor Line-start Permanent Magnet Synchronous Motor

Considering the problem of frequent overloading starting and variable load operation in lifting, metallurgy, mining and other machinery and equipment, WRLS-PMM (Wound-rotor line-start permanent magnet motor) is proposed and studied in this dissertation based on the project of Natural Science Foundation of China. It combines the characteristics of controllable starting in wound rotor asynchronous motor and high efficiency at underloading of permanent magnet motor. According to the special problems brought by this new structure, this article focuses on the design method of rotor winding and magnetic circuit structure of WRLS-PMM, as well as the selection basis of rotor chopper control circuit device. Influence of grid circuit impedance characteristics and the weak magnetic winding on the brake torque are studied. The chopper starting control method based on real-time output biggest asynchronous torque is proposed and studied. Field-circuit coupled movement simulation analysis and experimental research are carried on about starting performance of WRLS-PMM. The main research results of the dissertation are as follows:First of all, rotor winding and magnetic circuit structure design methods are summed up. In order to improve the pull in torque, the effective conductor cross-sectional area of each rotor slot should be improved. So the equivalent resistance of rotor winding can be reduced. It is found that the method of increasing the number of turns of the rotor winding can effectively reduce the rotor current under the condition of constant rotor equivalent resistance. The calculation method of electrical parameters in locked-rotor state is put forward based on the saturation coefficient and voltage iteration for the selection of rotor chopper control device. Considering that the back emf has important influence on the motor efficiency, power factor, rated current, pull in torque and brake torque, the design basis of per unit value of the back emf is summarized. In addition, the other design patterns include the design method of relative location of permanent magnet and rotor slots, as well as the internal relations between permanent magnetic torque, reluctance torque, overload ratio and magnetic circuit structure.Secondly, influence law of external power supply circuit impedance characteristics on the brake torque is studied. It is found that the equivalent resistance of power supply circuit will only change the maximum brake torque moment without its maximum value. The equivalent inductance of power supply circuit can affect the maximum brake torque and its moment. And the equivalent inductance is inversely proportional to the maximum brake torque. The finite element simulation calculation program of Field-circuit coupling movement is established and programmed with the consideration of the rotor chopper adjustable resistance process. The impact of open rotor winding and rotor resistance variation on locked-rotor characteristic is summed up. Induced voltage of rotor winding increases significantly under locked-rotor and winding open, so it is necessary to check the voltage grade of control device. The method of increasing the weak magnetic winding (WMW) is proposed and studied. By connecting all the WMW of each pole in series, the magnetic field of permanent magnet will be weakened by the WMW. So the brake torque can be inhibited in the startup phase. The simulation results indicate that weak magnetic winding can effectively weaken air-gap magnetic field in the initial starting moment and restrain the brake torque.Thirdly, the strategy of rotor chopper adjustable resistance starting control is proposed and studied based on real-time asynchronous torque output maximum for giving full play to the starting performance of WRLS-PMM. Combined rotor chopper control demand, the dynamic mathematical model of rotor circuit of IGBT chopper adjustable resistance is established based on two kinds of buffer circuit. Influence law of rotor loop inductance, capacitance, resistance, speed and frequency of chopper on calculation model of rotor equivalent resistance is analyzed. The calculation method of conduction duty cycle based on the chopper circuit with the RCD buffer circuit is deduced. Equivalent series resistance computation model has low parameter sensitivity when chopper frequency exceeds1k. And there is very simple linear relationship between equivalent series resistance and chopping duty ratio. The effect of temperature on chopping control strategy is researched. Research shows that temperature influence for chopping control strategy is limited when the stator winding temperature is higher than the rotor winding and the temperature difference is bigger. Moreover, the chopper starting controller of WRLS-PMM is set, and the control program is compiled.Finally, design and manufacture three kinds of motor with the same rated parameters which are WRLS-PMM, winding asynchronous motor and LS-PMSM. The experimental results show that WRLS-PMM can achieve high efficiency and high power factor as well as PMSM. Compared with LS-PMSM, the maximum starting torque of WRLS-PMM can increase by more than80%and starting current can be reduced by20%with reasonable chopper control method. The influence law of power supply on starting performance of WRLS-PMM is summarized.