A Low Torque Ripple Hybrid Vector Drive System For BLDCM Applied To Electric Vehicles

Brushless DC Motor (BLDCM) is being widely used in the field of variable speed drives because of its simple structure, low cost, high power density, and other characteristics. Used in electric vehicles, BLDCM is generally driven in a traditional120°square-wave current drive control. In this square-wave current drive mode, a large torque ripple will be generated during the commutation for inductive effect of the motor winding current. This torque ripple will cause great motor noise, which can block BLDCM applied to the field of electric vehicles. Therefore, the torque ripple suppression becomes the main focus of the permanent magnet brushless motor scholars study. In this paper, the problem of torque ripple BLDCM will be researched, and an effective and easy to implement suppression strategy will be proposed.Firstly, this paper analyzes the composition of the structure and working principle of BLDCM, and compares with sinusoidal permanent magnet synchronous motor (PMSM) in structure. The BLDCM mathematical model is analyzed for providing a theoretical basis of torque ripple. In the square wave drive status, the cause of torque ripple is analyzed which is changed at different speeds and other parameters. And variation of the ideal square wave drive torque ripple is closely linked with the actual width of the back EMF variation. However, torque ripple will be changed as the width of the back EMF varying in this scheme.Then, due to non-ideal width of the back EMF on torque ripple, a sine wave vector control is proposed for BLDCM. And this strategy is verified to be a good commutation torque ripple suppression scheme through theoretical and simulation analysis. After Fourier transform analysis, this paper finds that the third harmonic back EMF has no effect on the torque, so a new current drive scheme without triple harmonics is proposed. In this drive, the torque ripple of BLDCM approaches zero in theoretical.Finally, through analysis and comparison of these types of drive control method, a new hybrid vector control scheme is proposed based on low-cost hall switch position sensor. Experimental results verify that this method implemented in electric vehicle not only reduces the torque ripple but also run at high-performance vector control. It works reliably in complex working conditions with low speed start-up performance as well.