Torque Ripple Suppression Technique In Permanent Magnetic Brushless DC Motors

The permanent magnetic brushless dc motor (BLDCM), which actually belongs to the permanent magnetic synchronous motor, has trapezoidal EMF (Electromotive Force) waveform and rectangle current waveform. BLDCM system is of low cost, easy control, short development period and high reliability. Nowedays, BLDCM is widely used in industry. However, the problems such as rotor position estimation or the torque ripples have become the obstacles for the BLDCM to be used in high precision fields. In the paper, torque ripple suppression techniques have been studied in detail and some novel effective measures have been proposed.First of all, the effects on the torque ripples induced by the PWM methods are studied. The torque ripples, according to the different operation periods of the motor, are composed of the commutation torque ripples and the non-commutation torque ripples. As far as the commutation torque ripples are concerned, an important conclusion is gained. That is, the commutation torque ripples in those PWM methods, in which the upcoming phase is modulated, are lower than that in those PWM methods, in which the non-commutation phase is modulated. As for the non-commutation torque ripples, a novel torque ripple suppression scheme, PWMONPWM, is proposed. In the proposed PWM method, the diode freewheeling currents in the inactive phase are eliminated completely so that the torque ripples caused by the conventional PWM methods in the non-commutation interval are reduced or eliminated.Sequentially, the commutation torque ripples are mainly investigated in the paper. Through the detailed analysis of the commutation torque ripples and the relationship between the DC current and phase current in the commutation interval, two effective methods are proposed to reduce the commutation torque ripples. The two methods are the negative DC current elimination method and the commutation current prediction control method, respectively. A large amount of experiments are implemented to verify the validations of the proposed methods. The analytical and experimental results convince us that more satisfied results of the commutation torque ripple suppression can be acquired while the two proposed methods are combined with together to be used in the BLDCM system. As a result, a smooth commutation is realized.The proposed methods show the good adaptability in the BLDCM application system.The compensation extents of the commutation current are well and automatically implemented by the algorithms of the proposed methods. The current in the non-commutation phase is well controlled constantly in the commutation interval. The proposed algorithms can be imbedded in almost any control systems easily. In addition, the proposed method is not sensitive to the disturbances or the variations of the motor parameters.Finally, a DSP (Digital Signal Processor) based control system is designed for experimental use. Furthermore, a BLDCM drive system used in industrial sewing machine is studied. Some special technical problems are investigated and the corresponding resolved measures are presented.The validities of the proposed methods are strongly supported by the strict theoretical analysis and the large amounts of the experimental results.