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To improve performance of the field-oriented controlled position sensorless interior permanent magnet synchronous motors (IPMSM) drive, a model-based high-order sliding-mode observer with a software quadrature phase-locked loop (PLL) is proposed. A simplified method of designing the feedback gain matrix of the sliding-mode observer is introduced for easy application. The PLL coefficients are analyzed by considering the expected position estimation error and the operating condition. Compared with the conventional arc-tangent calculation method, the proposed quadrature PLL estimation method can be immune to the influence of the noise and distortion. To achieve the robust high-efficiency operation of the sensorless IPMSM, an enhanced online maximum torque per ampere (MTPA) control strategy without motor parameters dependent is adopted for the vector control drive. The optimal MTPA operation is achieved by searching the optimal current angle online to make the current amplitude be the minimum. The effectiveness of the proposed method is verified with a 2.2-kW IPMSM sensorless drive.