A sensorless detecting strategy of rotor position and speed on permanent magnet synchronous motor.

Abstract

A inverter-fed permanent magnet synchronous motor with a rotor position sensor and a speed sensor is used in many industrial applications as a DC-brushless motor. In this paper, a strategy which determines the rotor position and the speed of the permanent magnet synchronous motor by using the instantaneous values of phase voltage and phase current sensing is explained.In a permanent magnet synchronous motor, the permeance of the stater magnetic circuit is altered by rotating the rotor position; the inductance of a phase winding changes according to rotor positions. Hence, the phase voltages and currents of the motor have close relations with the rotor positions. Measured values of phase voltages and currents and the values of the equivalent circuit parameters are substituted to the voltage equation of the synchronous motor. Then, we can calculate the value of the rotor position angle by that voltage equation. The rotating speed of the rotor can be calculated from the voltage equation by substituting the rotor position angle. In these calculations, we used a 16-bit micro-computer and a DSP, and for sensing phase voltages and currents, 12-bit high quality A/D converters are used.Experimental results obtained by using the prototype system were congruous values of the rotor position angles and the rotating speed.