Research On The Torque Ripple Of Sensorless Brushless DC Motor

With the development of power electronics technology and ceaseless advance of permanent magnet material, Brushless DC Motor(BLDCM) is appealing candidates for many high performance motion control applications. Their popularity is justified by several advantages over commonly used motors in these applications, such as highly efficient, high power density and rapid dynamic response. Beside these, the absence of the external rotor excitation slip rings on the rotor and brushes obsolete, eliminates the commutation spark, makes the BLDCM more suitable for these applications with very strict conditions, but BLDCM have biggish torque ripple, so in these strict occasions, the smoothness of torque is requested. So in BLDCM control system, the minimization of torque ripple must be considered.In order to minimize the commutation torque ripple of traditional trapezoidal BLDCM using 120o condition mode. Firstly, analytical formulae of commutation torque in the condition of perfect BEMF 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. The conclusion is reached: When motor is been ascertained, the commutation torque ripple varies with the rotor speed. Secondly, the applicable speed ranges of the motors using the overlapping commutation techniques are derived.After the analysis and comparison of various detection technologies of the sensorless position, this dissertation chooses BEMF-zero-crossing detecting and chooses syllogism jump-start motor. This dissertation designs control systems that is based on dsPIC30F6010 chip, and makes detailed introduce about the hardware and software of control system. This dissertation expresses the detection principles and algorithms of BEMF-zero-crossing detecting and how to make the algorithms to come true. At last the dissertation makes detailed discussion about the software development for how to realize open-loop jump-start strategy and designing start-programming and zero-detecting procedures.Motor body model is built in Matlab according to Brushless DC Motor principles and mathematical mode. The simulation models are constructed based on Matlab/Simulink and respectively, and simulated the Motor models. Finally, the results of starting operating are analyzed in this dissertation.The experiments prove the realization that control system of the Brushless DC Motor can minimize the commutation torque ripple varies by different PWM methods and the experiments also prove this control system are safety, stability, practicality and reliability.