A new variable structure controller for direct torque controlled interior permanent magnet synchronous motor drive

In order to reduce the torque and flux ripples of interior permanent magnet synchronous motor (IPMSM) drives, a variable structure speed controller with integral-operation switching surface for direct torque controlled IPMSM has been proposed. The variable structure control law is derived from the proposed integral-operation switching surface and the system equations of direct torque control (DTC) IPMSM. Furthermore, integral-operation switching surface can possess the exponential stability for variable structure control (VSC) by using its integral component. Moreover, the dynamic response of the variable structure speed controller is studied. Then, the chattering which is a very significant problem in variable structure control is investigated. In this paper, we proposed a proper continuous function to substitute the traditional discontinuous sign function to obtain a continuous control signal which can reduce the chattering of the system. Finally, the validity of the proposed scheme is demonstrated through computer simulations. The results show that, in comparison with conventional DTC, variable structure DTC (VS-DTC) obviously reduces the torque and flux ripples of IPMSM and with this integral-operation switching surface, the stability is guaranteed and insensitivity to uncertainties and disturbance is obtained as well.