Comparison of incremental encoder digital signal processing techniques for the induction motor flux-torque vector control systems

Abstract

The article presents the results of a study on the effectiveness of various techniques for synchronous reference frame angular position numerical calculation in flux-torque vector control system of induction motor. Investigation was caried out taking into account the discrete nature of the angular speed signal obtained using an incremental encoder. In this work for investigation by simulation used a direct torque vector control system, which, in the presence of an ideal rotor angular speed signal, ensures direct asymptotic field orientation, asymptotic tracking of torque-flux reference trajectories, as well as asymptotic decoupling torque and flux subsystems. The parameters of the induction motor and encoder used in the study correspond to those existing in traction electromechanical systems of city trolleybuses. It is shown that the discrete nature of the angular speed signal, which used in synchronous reference frame position equation of flux-torque vector control systems, introduces field orientation errors and leads to current and torque ripples, which in a real system increase acoustic noise and can cause mechanical vibrations and resonance phenomena. An analysis of possible ways to reduce the influence of the speed signal discreteness on flux-torque control is performed, and a method for practical implementation of the synchronous reference frame angular position numerical calculation is proposed. This method allows ensuring conditions for more precise field orientation and, by using an additional filter for the angular speed signal, reducing the level of current and torque ripples to negligibly small values without affecting the field orientation processes. The proposed solution can be used in the development of high dynamic flux-torque vector control systems for induction motors using incremental encoders, including for electric vehicles.