An Exponential Sliding-Mode Observer with a Continuous Boundary Layer for Position-Sensorless IPMSM Drives

This study presents an exponential sliding-mode observer with a continuous boundary layer for position-sensorless interior permanent magnet synchronous motor drives. The observer combines linear and fractional-power error feedback with a smooth switching function. The exponential reaching law provides finite-time convergence, while the continuous observer analysis establishes ultimate boundedness and finite-time entry into the prescribed boundary layer under bounded forcing. Compared with a super-twisting sliding-mode observer, the proposed method achieves smaller speed-estimation error, lower current distortion, and reduced calculated torque fluctuations in the reported tests. The speed-reversal experiments further demonstrate accurate rotor-position tracking at commanded speeds of ±500 and ±1000 r/min. Component-ablation results confirm the combined contribution of the linear reaching term and continuous smoothing mechanism to the estimation performance.