Optimum Design of Fractional Order PIᵅ Speed Controller for Predictive Direct Torque Control of a Sensorless Five-Phase Permanent Magnet Synchronous Machine (PMSM) Noureddine Bounasla * , Said Barkat Laboratoire de Génie Electrique, Faculté de Technologie, Université de M'sila, M'sila 28000, Algeria Corresponding Author Email: noureddine.bounasla@univ-msila.dz https://doi.org/10.18280/jesa.530401 ABSTRACT Received: 10 June 2020 Accepted: 1 August 2020 In both direct torque control (DTC) and predictive direct torque control (PDTC) strategies, just single voltage vector is applied. The question arose, is this applied vector the optimumin terms of minimizing torque and stator flux ripples? In DTC, it may not be the optimum one. However, in case of PDTC, there is a possibility to evaluate the performance of different voltage vectors, where a cost function is proposed to determine the appropriate voltage vector that brings the lowest torque and stator flux ripple within one cycle. On the other hand, PI controller provides a good performance but if the parameters change, the system may lose its performance. With the aim of enhancing the robustness of the PDTC scheme, a fractional order PI controller is proposed that can be considered as a generalization of the classical PI controller, and to set its parameters, a Grey Wolf Optimization algorithm is employed. Furthermore, omitting the sensor increases reliability and decrease the size and cost of the drive system. For these reasons, an extended Kalman filter observer is adopted, where the rotor speed and rotor position as well as the load torque are estimated. In this work, a fractional order PI controller tuned by GWO for PDTC of a five-phase permanent magnet synchronous machine (PMSM) based on EKF observer is presented. Analysis of simulation results exhibit clearly the efficiency and robustness of the suggested control compared to conventional DTC based on classical PI controller. Keywords: five-phase PMSM, DTC, PDTC, fractional order PI controller, grey wolf optimization algorithm, extended Kalman filter 1. INTRODUCTION Compared to three-phase machines, the usage of multiphase machines allows to obtain less torque ripples, can produce higher torque per phase current, and guarantee a reliable drive that keep working with a failure in one or more phases. Due to these merits, this has motivated researchers to increase interest in the use of multiphase machine for critical applications such as electrical propulsion systems for ships, offshore wind farms, and electric aircraft. Among the multiphase machines, five- phase and six phase induction or synchronous machines are the most considered in the literature [1-4]. In the present study a special focus will be given to the five-phase permanent magnet synchronous motor drive (PMSM). In order to ensure an effective control of five-phase PMSM, various control methods have been suggested in the literature. Although these control methods have a different principle, but it leads to achieve the same main goal consisting of decoupled control between flux and torque, similar to a DC machine with separate excitation. One of these strategies is the direct torque control [5-9]. It has a simple control structure, because it does not require the use of inner current control loops, pulse width modulation block and less parameters dependence; this leads to give a good dynamic performance compared to vector control. However, the use of hysteresis controllers generates a variable switching frequency that leads to the emergence of high ripples in the torque and stator flux. This latter drawback is the major disadvantage of the conventional DTC. This shortcoming can be effectively overcome by using a space vector modulation (SVM)algorithm. Indeed, instead of a switching table and hysteresis controllers, an SVM with linear PI controllers are used. The combination of conventional DTC and SVM forms the direct torque control space vector modulation (DTC-SVM) [10-13]. However, in spite of the mentioned advantage, the DTC-SVM dynamic still depends on the quality of the applied PI controller design algorithm. Other structure of the DTC based on predictive approach known as Model Predictive Control (MPC) has been lately published in the domain of electrical drives [14-20]. This control strategy manages to minimize torque and stator flux ripples. It can be divided into two main classes, namely, continuous and finite-state model predictive control. The continuous MPC (C-MPC), it can give good performance. However, the use of modulator block increases the complexity of control design. On the contrary, finite-state MPC (FS-MPC) does not need to use a modulation block, it integrates the converters model in the control design. In the literature, the main FS-MPC strategies used to control electrical drives can be divided into two distinct categories:(i) predictive current control (PCC) and (ii) predictive torque control (PTC), which will be the focus of our attention in this paper. it relies on to apply an only single control vector during a sampling period. From this point, it is similar to DTC using a switching table that may not be the optimum one in terms of minimizing torque and stator flux ripples. In the contrary of the DTC, the PDTC examines the impact of each one and selects one that reduces the value of cost function, which defines the behavior of the system. The PDTC strategy for five-phase PMSM adopts on classical PI controller can achieve a good performance, but it Journal Européen des Systèmes Automatisés Vol. 53, No. 4, August, 2020, pp. 437-449 Journal homepage: http://iieta.org/journals/jesa 437