A Fuzzy Logic Speed Controller for Separately Excited Dc Motor and Its Comparison with PID Speed Controller

Abstract

DC motors are widely used in industrial and household applications as they provide benefits of high performance response, high efficiency, high torque and lower volume. This paper proposes the idea of implementing fuzzy logic controller to control the speed of separately excited DC motor. It provides an overview of performance with PID controller and fuzzy logic controller. Though PID controller improves both transients and steady state response characteristics with reduced rise time and steady state error, yet it has limitations of tuning its parameters and unsatisfactory control characteristics. Fuzzy logic can be described simply as computing words and can be designed without knowing the exact mathematical model of the process. Initially these controllers are designed and then tuned to analyze the performance of DC motor. Then the speed response of fuzzy logic is compared with the response achieved by PID controller. The experimental results prove that the control characteristic with fuzzy logic is better than that with the conventional PID controller. The modeling of separately excited DC motor and implementation of the two controllers is performed on software MATLAB/SIMULINK. An error detector compares a feedback signal which is the function of the output response, with the reference input. The variation between these two signals gives an error which is then sent to controller. The controller alters the conditions in the plant to reduce the original error. PID-controllers are extensively used in industrial applications due to reduced number of tuned parameters. In the PID controller, an appropriate proportional gain (Kp), integral gain (Ki), and differential gain (Kd) are adjusted to achieve the optimal control performance. The speed control with PID controller algorithm is simple, stable, easy adjustment and high reliable. However, most industrial processes include different degrees of nonlinear, parameter variability and uncertainty of mathematical model of the system. Thus tuning of parameters of PID controller is very difficult and lacks robustness. It is difficult to achieve the optimal state under field conditions in the actual production. Fuzzy Logic is a logical system having multiple logic values. However it is almost synonymous with the theory of fuzzy sets. The theory of fuzzy sets deal with the classes of objects with blunt boundaries in which membership is a matter of degree. Fuzzy Logic is the expedient way to map input space to an output space.