A Discrete-Time Fractional Order PI Controller for a Three Phase Synchronous Motor Using an Optimal Loop Shaping Approach

Abstract

The paper presents an implementation of a discrete-time fractional order PI controller based on an optimal loop shape approach. This approach consists of a linearisation of the system using a geometric state feedback and after that a loop shaping problem is formulated in terms of an optimisation problem with constraints. The load sensitivity is minimised with some classical loop shape constraints using a random (genetic) algorithm. The system which is considered is using a synchronous motor with permanent magnets (PMSM). Such kind of motors are commonly used in electric or hybrid road vehicles. For railway vehicles, the PMSM as drive motors have not been widely used yet. The control strategy consists of a combination of a state feedback linearisation together with a PI and a PMW techniques. A fractional PI controller is used to obtain robustness and to guarantee the specification of such kind of strategy. The advantage of using a fractional order PI controller is emphasized using a loop shaping design technique. A feedforward Euler discretisation is used to realise the discrete form of the controller. Simulation analysis is carried out to validate the effectiveness of the proposed application.