This paper presents a new control scheme for sensorless starting and running of a permanent magnet brushless DC motor (PMBLDCM) while using single current sensor for control of motor torque. The starting is carried out using pulsed starting technique and control is shifted to back EMF sensing method under running condition. The proposed control scheme uses aligning the rotor of PMBLDCM at a known position and then starting the motor by energizing the three phase stator winding through the three phase voltage source inverter (VSI) in a pre defined pulse width modulated (PWM) switching sequence so that the starting current is also controlled within the desired range. After certain speed where the back-EMF is traceable, the control is shifted to back-EMF based sensorless operation. The proposed scheme is designed, modeled and simulated for smooth starting from any unknown position without using any sensor and provides smooth transition. The hardware prototype of PMBLDCMD is controlled using the digital signal processor TI2812 and obtained results are presented to demonstrate successful implementation of the position sensorless operation.
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