A back-EMF based sensorless speed control of permanent magnet synchronous machine

This paper proposes a sensor less speed control technique for permanent magnet synchronous machine (PMSM), using field oriented control technique, by sensing the back-emf developed across the stator windings. Conventionally, t o control the speed of a PMSM, speed encoders like optical encoders, proximity sensors, precision encoders etc are used to sense the speed. These encoders are very expensive and are also prone to external noises as they are mounted on the motor shaft. So a sensor less speed detection algorithm is developed by sensing the back-emf and the speed is calculated. A field-oriented control (FOC) technique is used in which the rotor flux is oriented along the d-axis of the rotating frame, at rotor speed (synchronous speed). The q-axis current component represents the armature current. Thus both field and armature current can be independently controlled. A surface mounted permanent magnet synchronous machine (SPMSM) is selected for study. The entire system was simulated in MATLAB/Simulink and the performance was analyzed for various speed and torque references.