Analysis And Research On Self-starting PMSM With Pole Width Modulation

Surface mounted PMSM have many advantages, but it cannot line-start and need variable-frequency drives for starting. The rotor structure of surfaced-mounted cannot produce perfect sinusoidal air-gap magnetic flux density waveform. There are a great deal of harmonious wave in it, which increase the loss of machines and reduce the energy index, so can not reflect the advantage of energy saving. Meanwhile, the non- sinusoidal magnetic flux density waveform bring pulsate electromagnetism torque and make rotate velocity surged, influence the stability and reliability, directly limit the using and popularization of PMSM.For solving the problem, an approach of placing distributed magnetic pole on the surface of the rotor iron core of PMSM is proposed. It is called pole width modulation method. By designing the thickness, width and the arrange method of the magnet reasonably, the air-gap magnetic field is closer to sinusoidal waveform so that the loss is reduced and the energy index is raised. With placing start stripes between different magnets, machines with pole width modulation rotor structure could line start.The theory of the modulation structure is given at first for introducing pole width modulation method. Then, the influence of different modulation scheme of pole width modulation to air-gap magnetic flux density waveform is analyzed using analytic method and finite element method. According to different thickness of magnet, different air-gap length and different shaft material, the air-gap magnetic flux density waveform is contrasted. Then, the starting process is simulated by Ansoft and the dynamic torque and speed curve with different modulation method are got as the theory foundation for designing the starting coil. Finally, the scheme for traditional rotor structure and five magnet arrays pole width modulation rotor structure are designed, and prototypes with different rotor structure are developed. The experiment system is built, the reactance parameter of the new prototype has been measured by parameter measure experiment; the improving of air-gap magnetic flux density waveform has been validated indirectly by placing detecting coil; the operating character curve of the prototype is obtained by no-load and load experiment using loss separating method, the energy index improves obviously.The feasibility and the practical engineering value of this method are proved by theory analysis, simulation and a series of experiments on the prototype.