International Journal of Computer Applications (0975 – 8887) Volume 28– No.2, August 2011 25 A Novel Current Controlled Space Vector Modulation based Control Scheme for Reducing Torque Ripple in Brushless DC Drives V.Viswanathan Research Scholar, Department of EEE JNTU, Hyderabad, India Dr.S.Jeevananthan Professor, Department of EEE, Pondicherry University, India ABSTRACT A novel Current Controlled Space Vector Pulse Width Modulation (CCSVPWM) technique for Brushless Direct Current (BLDC) motor drives, with a view to reduce torque ripple is proposed. The current ripple, created due to the stator winding inductance, leads to generation of ripple in the torque and prevents the usage of BLDC motor in a precise servo drive system. The paper includes MATLAB/SIMULINK results of conventional, unipolar, bipolar current control algorithms (CCAs), varying input voltage method (VIVM) and a new CCSVPWM approach. The comparison of simulation results reveal that the CCSVPWM technique is effective in reducing the ripple. This control method improves the system performance with low torque ripple thus making it suitable for immense applications employing electromechanical actuators. Keywords Brushless DC motor, current controlled SVPWM technique, torque ripple reduction. 1. INTRODUCTION Brushless Direct Current (BLDC) motors are one of the motor types rapidly gaining popularity. BLDC motors have some advantages over conventional brushed DC motors and induction motors. Some of these are; better speed versus torque characteristics, high dynamic response, high efficiency, long operating life, noiseless operation and higher speed ranges. In addition, BLDC motors are reliable, easy to control, and inexpensive. Due to their favorable electrical and mechanical properties, BLDC motors increasingly are being used in computer, automotive, aerospace, industrial and household products because of its high power density, compactness, low maintenance and ease of control. In spite of their advantages, they show some drawbacks: stator current commutation torque ripples which occur due to the loss of ideal phase current commutation. An idealized brushless dc motor has a trapezoidal back electromotive force (EMF) waveform. For this back EMF waveform it can be shown that zero torque ripple is produced when the motor is fed by a rectangular current waveform [1].However, in a practical BLDC drive, since machines has both inductance and resistance, the stator currents are different from the ideal case and the currents reach to their final values with delay. In other words, circuit has a time constant. Therefore, the current ripple is produced by influence of the inductance and the torque ripple is affected by current ripple directly [2]. The torque ripple generated in commutation period is the main drawback of BLDC motor which deteriorates the precision of BLDC motor [3], [4].Therefore, the torque ripple minimization or elimination is a considerable issue in BLDC motor drives. Several theoretical approaches for analysis of the commutation torque ripple have been reported in literature [5], [6]. A direct torque control (DTC) by employing a hybrid 2- phase and 3-phase switching mode during the commutation periods was presented in [7]. Commutation torque ripple reduction was reported in [8] which based on a fact that current slopes of the incoming and outgoing phases during the commutation interval can be equalized by a proper duty-ratio control. Adaptive torque ripple control for current shaping during commutation was proposed in [9]. A current control method has been presented in [10] to reduce torque ripple. However, torque ripple caused by commutation is not fully considered in [11]. In [12], the commutation torque is reduced by changing the DC-link voltage which requires additional DC- link voltage control circuit and capacitors, and thereby increasing the cost. A method for commutation torque ripple minimization in direct torque controlled BLDC drives is presented in [13]. A hardware polynomial based profile generator was used for minimizing the torque. Novel resonant pole inverter for Brushless DC motor drive system is presented in [14]. A PWM control algorithm for eliminating torque ripple caused by stator magnetic field jump of brushless DC motors is proposed by [15]. Reference [16] proposed a PWM chopping method to improve the torque ripple for brushless DC miniature motors. Reference [17] discussed the influences of PWM mode on the current generated by back-EMF of switch off phase in BLDC motor. Three-phase PWM techniques are presented to reduce the commutation torque ripple in[18-20]. Several PWM techniques [21-22] have been proposed to eliminate reversal DC-link current or circulating current of BLDC motor drives. In this paper, a current controlled Space Vector PWM technique for torque ripple reduction is proposed.