Fractional-order PI controller for Permanent Magnet Synchronous Motor: A design based comparative study

Permanent Magnet Synchronous Motor (PMSM) is a special type of brushless motor widely used for high-performance drives such as industrial robots and machine tools because of their advantages as high efficiency, high power density, high torque/inertia ratio and less maintenance. It has a highly nonlinear dynamics. Design of effective control strategy for a PMSM is a challenging task. Implementation of vector controlled speed drive of PMSM requires design of three proportional and integral (PI) controllers: two as current controllers for direct-axis (d-axis) and quadrature-axis (q-axis) current control and one for the speed control. All these three integer-order PI controllers can be replaced with fractional-order PI (popularly known as FOPI) controllers. As compared with conventional PI controller, FOPI controller provide more maneuverability and robustness due to an additional degree of freedom integration order. This chapter describes two different methods to design these FOPI controllers. First method, popularly known as intersection method, is based on Bode plot while, second method using robustness index, is based on Nyquist plot. Results of these methods are compared for various parameter indices such as rise time, percentage overshoot, settling time, control efforts