STUDY ON INFLUENCE OF BRAKING CIRCUIT AND STATOR-ROTOR STRUCTURE ON THE DAMPING CHARACTERISTICS OF PERMANENT MAGNET MOTOR

Permanent magnet motor is used as the power source to provide driving force for the lowering, lifting and holding action of the control rod in high-temperature gas-cooled reactor. When reactor scram and the rods falling by gravity, the permanent magnet motor also can act as a damping system to convert the gravitational potential energy of the control rods into the thermal energy consumed in the braking resistor, that enables a damping function of limiting the speed along the long dropping stroke and effectively buffering the impact of the control rods on the reactor internals. In order to further investigate the damping capability of the motor, a finite element model was established for the permanent magnet motor, as well as its external circuit. The braking and damping performance of the motor under different rod drop speeds was analyzed by simulation methods. An important performance parameter for evaluating the damping capability of motor is the damping torque, which is mainly affected by the braking resistance in the external circuit model and the stator-rotor structure of the motor. First, a full-size motor with external circuit model was established based on Ansys Maxwell software, and reasonable meshing and irrelevance verification of the motor body model was carried out to improve the solution accuracy and modeling efficiency of finite element simulation. Then the influence of the motor structural parameters (such as air gap, stator-rotor tooth shape, permanent magnet structure, and braking resistance setting of the external circuit) on the damping torque was studied through parameter-sensitive simulation and analysis, especially through the reasonable setting of the external circuit the adjustment of the damping torque was realized. The effect of motor structural parameters on damping performance was also obtained. According to the required falling speed of the control rod, the appropriate resistance value could be selected to regulate the falling rod speed, which provided a strong support for the realization of the falling rod buffer of the control rod drive mechanism with the permanent magnet motor serving as the second damping system. At present, the research work had been carried out based on the finite element model of the permanent magnet motor, which would provide a validation basis for the subsequent experimental research.