Comparison of Six and Four Switch Inverter Based Position Sensor Less Control of PMBLDC Motor Using the Third Harmonic Back EMF Integration Method

Permanent Magnet Brushless DC (PMBLDC) motors are one of the electrical drives that are rapidly gaining popularity, due to their high efficiency, good dynamic response, high mechanical power density, simplicity, cost effectiveness and low maintenance. The position of the rotor is estimated by using third harmonic back emf method. The third harmonic voltage component between the networking resistor of the stator phase voltage and the motor neutral point is applied for the sensorless PM BLDC Motor drives. The third harmonic back emf is obtained by adding the terminal voltages of the motor with respect to neutral and then it is integrated to find the third harmonic rotor flux. The resulting third harmonic signal keeps constant phase relationship with the rotor flux under any motor speed and load condition, and is practically free of noise that can be introduced by the inverter switching, making the sensing method. The zero crossing instants of the third harmonic rotor flux give the commutation instants of the inverter. In this paper the BLDC motor is driven with four switch inverter and six switch inverter. Also the performance of the two inverter configurations is compared and the effectiveness is clarified from the simulation results.