Study Of New Permanent Magnet Brushless Dc Motor Field Weakening Speed Expansion Method

Permanent Magnet Brushless Direct Current Motor (PMBLDCM) has been paid more attention in the past two decades by researchers in the motor and control system fields because of its excellent performance, such as simple structure, great power density, good performance of speed adjustment, high efficiency and so on.It's customary to use constant torque operation below base speed and constant power operation above base speed for electric vehicles. During the constant power operation, the motor back electromotive force increases with the rotor speed while the terminal voltage can't rise with the limitation of the fix rating of the inverter, which causes the current can't flow into the motor. Therefore, in order to get a wide speed range, field weakening control is necessary in constant power operation. However, the magnetic field for PM motor is hard to be weakened, which therefore arises many researchers' interests nowadays.In this dissertation, a novel inverter topology of BLDCM is introduced in order to get a wide speed range. The simulation model of the two control systems is built with Matlab/Simulink. From the simulation result, it's easy to find the advantage of this new method.Also BLDCM with new inverter topology is analyzed with the finite element method, the results show a better field weakening ability compared to conventional inverter topology.In addition, experiment based on the new control method is conducted. Both the simulation analysis and experiment show that this method is better than traditional method without any changing of the motor rotor.