Power Factor Correction of Direct Torque Controlled Brushless DC Motor Drive

In this paper, an algorithm for power factor correction (PFC) of direct torque control (DTC) brushless dc motor drive in the constant torque region is presented. The proposed DTC approach introduces a two-phase conduction mode as opposed to the conventional three-phase DTC drives. Unlike conventional six-step PWM current control, by properly selecting the inverter voltage space vectors of the two-phase conduction mode from a simple look-up table at a predefined sampling time, the desired quasi-square wave current is obtained. Therefore, a much faster torque response is achieved compared to conventional current control. Furthermore, to eliminate the low-frequency torque oscillations caused by the non-ideal trapezoidal shape of the actual back-EMF waveform of the BLDC motor, a pre-stored back-EMF versus position look-up table is designed. The duty cycle of the boost converter is determined by a control algorithm. This control algorithm is based on the input voltage, output voltage which is the dc-link of the BLDC motor drive, and the inductor current using the average current control method with input voltage feed-forward compensation during each sampling period of the drive system. A theoretical concept is developed and the validity and effectiveness of the proposed DTC of BLDC motor drive scheme with PFC are verified through the experimental results. The test results verify that the proposed PFC for DTC of BLDC motor drive improves the power factor from 0.77 to about 0.9997 irrespective of the load.