This paper presents the sensorless control of BLDC motor drive with 150 ο conducting mode for minimizing the torque ripple. The proposed method defines the energizing interval in phase voltage commutation every 30 electrical degrees. In each phase commutation, two or three switches conduct alternately in order to obtain the quasi sinusoidal phase voltage waveform. Compared with traditional control, the torque ripple of BLDC motor can be significantly reduced by using the proposed method. Both simulation and experimental results have been presented to validate the reduction of torque ripple by using the proposed method.
I. INSTRODUCTIONRecently, the brushless dc (BLDC) motor is widely used in industrial applications and home appliances due to its high efficiency, high power density and low maintenance. However, the BLDC motor drive requires a position sensor which reduces the reliability of overall system. Also, the BLDC motor drive produces the torque pulsation. Torque pulsation produced in the conventional BLDC motor drive system causes the oscillating speed and resonance in mechanical portions of the drive, leading to acoustic noises and observable vibration in machines. Since an ideal BLDC motor theoretically has a trapezoidal back-EMF waveform, the BLDC motor has to be fed by an ideal rectangular current waveform. In practice, the BLDC motor drive inherently produces the current ripple during commutations because the motor current naturally flows through the freewheeling diodes [1]. To improve the torque ripple, the methods in [2]- [3] proposed the novel PWM to eliminate the ripple current by using PWM_ON_PWM mode. However, the commutation interval time is determined by calculations which require the computation time and higher performance MCU's. In [4], the effective commutation torque ripple using different PWM modes was presented. The results showed that the PWM-ON pattern achieves the smallest torque ripple. Another method of torque ripple reduction in a sensorless BLDC motor drive was proposed in [5]. Their proposed method used the measured terminal phase voltages to determine the commutation intervals and then computed the optimal duty ratio applied during commutation intervals to minimize the torque ripple. However, it did not provide the good performance in high speed operation because of limitation of duty cycle compensation.Although the fed current could be typically controlled as rectangular waveform, the torque ripple is still produced due to the non-ideal back EMF. The ideal back EMF would be trapezoidal shape. There are many reasons of non-ideal back EMF in the BLDC motor such as non-uniformity of magnetic material, stator winding configuration, tooth winding with pole shoe, and etc. as shown in Fig.1 [6]. Fig.1 Comparative FEA back EMF's waveforms [6]In order to reduce the torque ripple in BLDC motor with non-ideal back EMF, In [7], the new current control method was adopted. The duty cycle was calculated in the current controller by measuring the angular position and the offline measured back ...