Flux Weakening Technology Study On Permanent Magnet Brushless D.C.Motor

With the city traffic and environment pollution being more and more serious, subways, city-trains and electric vehicles have been in boom in the past decades. Hence the electric drive technology for vehicles has been getting more and more attention. In which, permanent magnet motors have been very attractive for its high power density and no mechanical brushes. But at the other hand, as the permanent magnetic field can't be regulated after the permanent magnet material was magnetized, the application of this type motor in electric drive technology for vehicles has been limited, which requires constant power operation and wide speed region. At the same time, it also gets researchers' more and more attention. In the past decades, the research on flux weakening of Permanent Magnet Synchronous Motor has been in a great progress, but the research on flux weakening of Permanent Magnet Brushless D.C. Motor, which processes higher power density, is still under development, needing to get more deep research. This paper's work is just under this background, trying to get some more valuable discovery.This paper's research is on the constant power flux weakening of Permanent Magnet Brushless D.C. Motor, which covers from simulation to experiment, from theory to practice. At the same time, the sufficient theory analysis on traditional Surface Permanent Mounted Brushless D.C. Motor and Hybrid Rotor Structure Permanent Magnet Brushless D.C. Motor has been made, and a set of relative theory on the Hybrid Rotor Structure Permanent Magnet Brushless D.C. Motor has been developed.This paper is beginning from the conduction rules and the winding structure of Permanent Magnet Brushless D.C. Motors. The physical process of the speed regulation on traditional Surface Permanent Magnet Brushless D.C. Motor has been simulated, and the analytical expression under constant torque mode and constant power mode was developed. Hence the flux weakening mechanism of Permanent Magnet Brushless D.C. Motor has get reflection. At the same time, the key parameters on constant power speed region are put forward.Referencing the successful application of hybrid rotor structure on Permanent Magnet Synchronous Motor for constant power flux weakening, apply this type rotor structure on Permanent Magnet Brushless D.C. Motor. And two prototype motors with different reluctance rotor structure and rated power, voltage were build. Aimed at the limitation of the past d, q coordinate method, a state-space model based on the combination approach of electric-circuit and electromagnetic field was set up, which can simulate the real way of Permanent Magnet Brushless D.C. Motor conduction. Based on it, the difference of the flux weakening rules between the two methods was compared, and some new rules were pointed out, hence developing the relative theory on the flux weakening of the Permanent Magnet Brushless D.C. Motor.Based on the combination approach of electric-circuit and electromagnetic field, the true cause of the reluctance portion enhancing the constant power speed region was pointed out. And a new thought on applying a space angle between the d axis of permanent magnet portion and of reluctance portion was set up to get widen speed region, which has been verified in practice. And therefore a new regulation means was offered for the performance optimization of this hybrid rotor structure type permanent motor.