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A position sensorless control scheme of surface-mounted permanent magnet synchronous machine (SPMSM) using a novel sliding mode observer (SMO) is proposed, suitable for applications where low speed and standstill operations are not required. Compared with traditional SMO, the sign function is replaced by a saturation function, to increase the precision of the rotor position estimation at low speed and the stability of the system at high speed, the estimated back electromotive force (back-EMF) is feed back to current observer. To achieve better filtering effect and simplify the hardware structure, a variable cut-off frequency low-pass filter is designed. Details of the implementation of the algorithm are fully explored. Experimental results on an PMSM drive system used in electric bicycle are provided to demonstrate the effectiveness and robustness of the proposed control strategy.