Research On Torque Ripple Attenuation Techniques For PM Brushless DC Motors

This dissertation presents several novel control techniques for the torque ripple minimization of PM BLDCM. According to the different back-EMF waveforms of BLDCM, this dissertation gives a detailed analysis to the torque ripple due to trapezoidal EMF, pseudo-sinusoidal EMF, and general shape EMF respectively, and from each one proposes a kind of control technique for torque ripple minimization.In order to minimize the commutation torque ripple of traditional trapezoidal BLDCM using 120°cconduction mode, firstly, analytical formulae of commutation torque in the condition of perfect back-EMF waveforms are developed in this thesis, based on which the effects to the torque ripple by the PWM modes, overlapping commutation techniques and so on are analyzed, and the applicable speed ranges of the motors using the overlapping commutation techniques are derived. Secondly, the effects of the crest width of the back-EMF waveform to the torque ripple in the 120?conduction mode are analyzed, among which the effects of the advance commutation angle to the torque ripple are quantificationally analyzed for the BLDCM drives whose back-EMF waveform crest width is less than 120?, and a new technique for commutation torque ripple minimization based on overlapping commutation together with current compensation is proposed. The simulation results prove that this control technique can effectively minimize the torque ripple for the BLDCM drives whose back-EMF waveform crest width is less than 120 .This dissertation also discusses the effects of the methods for minimizing the cogging torque to the back-EMF waveforms. For the BLDCM which has a general crest width of the back-EMF waveform, two kinds of torque ripple conditions when drived by sine-wave current as well as by square-wave current are deduced based on the mathematical models. In addition, a comparison is carried out between these two conditions, which indicates that sinusoidal current driving is more favorable to minimizing the torque ripple when the crest width of the back-EMF waveform is less than a certain value. For the BLDCM which has a pseudo-sinusoidal back-EMF waveform, this dissertation presents a SVPWM control method using six discrete position signals for minimizing the torque ripple. The main aspects for theimplementation of this method are analyzed, including the initial orientation of the voltage vector, reasonable choice of the impedance angle and the advance commutation angle, and estimation of the successive rotor positions. Furthermore, this dissertation also gives a comprehensive analysis and comparison to the torque ripple factor, torque-current ratio and other aspects for pseudo-sinusoidal EMF BLDCM drived by 120° conduction mode, 180° conduction mode and self-synchronous SVPWM mode respectively. The simulation and the experimental results indicate that self-synchronous SVPWM method is more effective for minimizing the torque ripple without any expense of the torque-current ratio when the crest width of the back-EMF waveform is less than 107° electrical angles.For the BLDCM which has a neither sinusoidal nor trapezoidal back-EMF, that is, for a general shape back-EMF BLDCM, this dissertation proposes a novel id = 0 vector control method. By this method, the iq for a constant torque to produce is calculated through coordinate transformation, and the reference iq is tracked by vector control in the dq0 frame. To implement this method, the structures of both the hardware and the software are analyzed in detail. The simulation and the experimental results show that this control technique can effectively minimize the torque ripple caused by distortion of the back-EMF.