TIME-VARYING FRACTIONAL-ORDER PID CONTROL FOR MITIGATION OF DERIVATIVE KICK

In this thesis work, a novel approach for the design of a fractional order proportional integral

derivative (FOPID) controller is proposed. This design introduces a new time-varying FOPID controller

to mitigate a voltage spike at the controller output whenever a sudden change to the setpoint occurs. The

voltage spike exists at the output of the proportional integral derivative (PID) and FOPID controllers when a

derivative control element is involved. Such a voltage spike may cause a serious damage to the plant if it is

left uncontrolled. The proposed new FOPID controller applies a time function to force the derivative gain to

take effect gradually, leading to a time-varying derivative FOPID (TVD-FOPID) controller, which maintains

a fast system response and signi?cantly reduces the voltage spike at the controller output. The time-varying

FOPID controller is optimally designed using the particle swarm optimization (PSO) or genetic algorithm

(GA) to ?nd the optimum constants and time-varying parameters. The improved control performance is

validated through controlling the closed-loop DC motor speed via comparisons between the TVD-FOPID

controller, traditional FOPID controller, and time-varying FOPID (TV-FOPID) controller which is created

for comparison with all three PID gain constants replaced by the optimized time functions. The simulation

results demonstrate that the proposed TVD-FOPID controller not only can achieve 80% reduction of voltage

spike at the controller output but also is also able to keep approximately the same characteristics of the system

response in comparison with the regular FOPID controller. The TVD-FOPID controller using a saturation

block between the controller output and the plant still performs best according to system overshoot, rise time,

and settling time.