Design and implementation of sensorless vector control of surface mounted PMSM using back-EMF estimation and PLL based technique

This paper presents a novel, reliable, simple and efficient sensor less vector control technique of a 8 pole, 750 rpm, 5 kW surface mounted permanent magnet synchronous motor(PMSM) without damper winding. Rotor position and speed are obtained from the estimated back-emf using a PLL which is synchronised with the back emf. A novel technique is used to estimate the back-emf. The reference voltages which are used for gate pulse generation have been used in a PLL to estimate the rotor position and speed simultaneously. Hence, no additional speed estimation algorithm is required. The starting in the sensorless operation of surafce mounted PMSM (as it has zero saliency) requires complex and computation extensive algorithms. Moreover, these techniques lacks accuracy. Here, simple V/f control technique is used to start the rotor. The machines enters into the vector control operation as it reaches a pre-specified threshold (here, 0.1 p.u. i.e. 75 rpm). Simulated and experimental results of speed and position estimation with the complete drive has been presented. These results establish the accuracy of the proposed sensorless vector control strategy and the precision of hardware implementation. The PMSM itself was designed and fabricated in the laboratory.