Research On Field-weakening Control For PM Brushless DC Motor Based On Novel Inverter

Brushless DC motors(BLDC) are increasingly utilized in many fields, including industrial controllers, mechanical equipment, robots, computer system, CNC machine tools etc, because of its excellent performance, such as simple structure, good performance of speed adjustment, easy to maintain, great power density, high effiency and so on.Field weakening control for brushless DC motor is a hot spot especially for electric vehicles. When brushless DC motor is used to drive electric vehicles, it’s customary to use constant torque operation below base speed and constant power operation above base speed. During constant power period, the back electromotive force(EMF) of BLDCM increases with the rotor speed. When exceeds the supply voltage, the back EMF feeds energy back to the DC power supply, which results in excessive current of stator winding. Therefore, in order to get a wide speed range, it’s necessary to conduct field weakening control. As the magnetic field of BLDCM produced by permanent magnet is non-adjustable, it’s hard to conduct field weakening control for BLDCM.This dissertation presents a novel inverter which can suppress the back EMF effectively and extend the speed range. The simulation model is built with Matlab/Simulink to analyze advantages of the novel inverter in field weakening control. In addtion it also built a hardware system with a core of dSPACE to certify the function of the novel inverter to extend the speed range of BLDCM compared with the traditional inverter.The simulation and experiment results show that the brushless DC motor can operate in a wide speed range with novel inverter.