Position sensorless control of high-speed brushless pm motor based on an improved sliding mode observer

With the advantages of simplicity and robustness, the position estimation method based on a sliding mode observer (SMO) has been widely used in brushless PM motor sensorless control such as turbo-molecular pump (TMP). Due to the chattering phenomenon of a typical sliding mode algorithm, a low-pass filter is necessary to suppress the estimated back electromagnetic force (back-EMF) harmonics, which results in phase lag. It would degrade the performance of sensorless control in the high-speed range. On the one hand, the phase lag increases position error as the motor accelerates. On the other hand, the harmonics induced by the nonlinearity of inverter are hardly to be suppressed by low-pass filters since the signal frequency varies with rotor speed. In order to solve this problem, an improved sensorless control method is proposed. Instead of low-pass filters, a Second-Order generalized integrator (SOGI) is used to get the fundamental component of the back-EMF with minimal phase lag. Besides, a tracking differentiator (TD) replaces the backward difference algorithm to estimate speed and filter position. At last, it is tested on a magnetically levitated TMP and the experimental results verify the validity and reliability of the proposed control method.