Zero-Position Offset Calibration of PMSM Based on I/F Control Strategy and Slide Mode Observer for Electric Power Steering System

In this paper, I/f control strategy combined with slide mode observer (SMO) are applied to calibrate the zero-position offset between permanent magnet synchronous motor (PMSM) and its rotor position sensor (RPS) for electric power steering (EPS) system. The I/f control strategy can ensure the motor operates in a medium speed smoothly with full torque capacity; while the SMO offers a reliable estimation of the rotor position of the motor itself. As a result, the offset between motor and its RPS can be acquired. In addition, the time delay caused by process time and sampling period of the digital controller has also been analyzed. According to experiment result, it can be figured out that the proposed method can accurately align the zero-position offset angle whether the motor operates on-load or off-load, which is critical for EPS production line.