Abstract:

To solve the difficulty of acquiring back electromotive force (back-EMF) and the chattering problem existing in the conventional sliding mode control, a direct torque control (DTC) based on the second-order sliding mode observer (SOSMO) is proposed for brushless DC motor (BLDCM). According to the mathematical model of BLDCM, traditional linear sliding mode surface and its first-order derivative are selected to constitute the second-order sliding mode surface. Simultaneously, the control law was deduced by using an improved reaching law. Then, the SOSMO was designed, and it could make the sliding mode chattering be focused on the higher order differential of phase error and integrate the higher order differential term. So, the weaker chattering and faster convergence was guaranteed. Moreover, the back-EMF could be accurately estimated by SOSMO without an additional low-pass filter. The SOSMO was applied to DTC of sensorless BLDCM, and the torque ripple and system performance could be improved effectively. The simulation results show that the proposed method is superior.

Key words: Brushless DC motor, second-order sliding mode observer, torque ripple, direct torque control

摘要： 针对无刷直流电机直接转矩控制中反电动势获取困难和常规滑模控制存在系统抖振的问题，提出了一种基于二阶滑模观测器的直接转矩控制策略。根据无刷直流电机的数学模型，选择传统线性滑模面及其一阶导数构成二阶滑模面，采用改进型趋近律推导控制律，设计了一种二阶滑模观测器，该观测器将滑模抖振集中在相电流误差的高阶微分上，并通过积分作用，削弱抖振的同时加快了收敛速度。二阶滑模观测器无需低通滤波器即可准确估计反电动势，将其应用于无刷直流电机无位置传感器直接转矩控制中，可有效减小转矩脉动，改善系统的性能，仿真结果表明了所提方法的优越性。

关键词: 无刷直流电机, 二阶滑模观测器, 转矩脉动, 直接转矩控制