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Automatic Offset Calibration of Quadrature Encoder Pulse Sensor for Vector Controlled Drive of Permanent Magnet Synchronous Motors

Quadrature encoder pulse (QEP) sensor has been widely used to detect the rotor position of permanent magnet synchronous motors (PMSMs) in the vector controlled drive systems. However, the information regarding to the angular difference between the index signal and the back emfs of motor (so called the index offset) is sometimes lacked in the manufacturers' datasheets. As a result, by using the incorrect offset, the back emfs are not in phase with the stator currents. Then, the produced electromagnetic torque is not optimal in the vector controlled drive system of PMSM using QEP sensor. This paper presents a practical and simple technique to automatically calibrate this offset. The experimental results will also demonstrate the effects of incorrect offset to the torque production. The overall drive system is implemented on a 32-bit fixed-point digital signal processor based controller (TMS320F2808eZdsp board).