Design and statistical robustness analysis of FOPID, IOPID and SIMC PID controllers applied to a motor-generator system

This paper presents the design, implementation and robustness analysis for a family of PID controllers used for the speed control of a motor-generator system. The comparison includes the integer-order PID controller, the fractional-order PID controller and SIMC PID controller. The control systems are implemented employing the STATEFLOW toolbox from MATLAB and the acquisition card NI 6008. The robustness analysis uses a factorial experiment design 2^3. The factors of the experiments design are the presence of random noise in the feedback loop, the existence of an external disturbance to the input of the process and the uncertainty in the load. The output variables of the experiment measure the performance of each controller through the step response of the system and the control action. The robustness statistical analysis shows that for all the PID controllers, the step response is further affected by the external-disturbance factor and the control action is mainly altered by the uncertainty in the load factor. The results present quantitatively that the fractional-order PID controller has a better robust performance and stability against the cited factors.