| The bearingless motor is a new type of motor which hybridizes the motors and the magnetic bearings. Different from the traditional suspension principle of magnetic suspension motor, the bearingless motor winds the levitation windings together with conventional motor windings to produce radial forces by taking advantages of the similarity between the structure of magnetic bearing and that of the AC motor. The rotor shaft can be successfully suspended by the electromagnetic forces. As the bearingless motor is constructed with contact-free bearings, it works free of wear, frictionless, free of abrasion and without lubrication. With these advantages and other features, the bearingless motor demonstrates the potential applications in space technology, machine tools, high vacuum technology, ultra high-speed drives and so on. This paper first expounds the basic principle of bearingless induction motor, then analyzes some characteristics of flux orientation control contraposing the mathematical model of bearingless induction motor. For the levitation winding, the method of air-gap flux traced PWM is proposed to eliminate coupling of levitation control caused by neglecting rotor current of the levitation winding. The independent control of levitation subsystem is realized based on magnetic flux detecting with search coils or with the method of voltage-model. The affect of harmonics and rotor eccentricity is analyzed when measuring the air-gap flux density, and the possibility of measuring the shaft displacement with search coils is also studied. A digital control system for real-time control is designed with single DSP (TMS320F2812). Experimental results validate the performance efficiency of the proposed controller in steady state, as well as transient state. Acknowledge the grants of National Nature Science Foundation of China (50377012), National Defense Foundational Science Research of China (K1600060603), and Delta Electric & Electronics Science & Education Development Foundation.
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