Novel Technique of Controlling Synchronous Motors without the Use of Current Sensors

Abstract

This paper proposes a novel control method for synchronous motors without the use of current sensors. The proposed method is based on optimal placement of pole of the closed loop system that includes the motor controller. The voltage commands necessary are directly calculated based on the velocity error without any inner current loop. The main compensator consists of a notch filter and a PI regulator. The notch filter is designed such that its zeros cancel the poles of the plant, the transfer function of which, is the ratio of the output rotational velocity to the input q-axis voltage command. The poles of the notch filter and the parameters of the PI regulator are selected such that the resulting poles of the entire plant are located in the stable region. Based on the model of the synchronous motor, the currents of d and q axes are estimated using the reference voltage commands of d and q axes. The decoupled compensating voltages and the dead-time compensating voltages are calculated using the estimated currents in the d and q-axes, which in turn are used to generate the reference voltage commands. The proposed control technique was implemented on a practical system. Experimental results are given to show the effectiveness of the proposed technique for velocity and position control in a permanent magnet synchronous motor.