Design and experimental application of an improved cascade controller optimized via genetic algorithm for cascade systems

A single-loop conventional controller will not initiate corrective action for disturbances unless the output variable moves away from the set point. In this case, the cascade control strategy can be benefitted to obtain better control system performance, especially in the existence of strong disturbances. ProportionalIntegral-Derivative (PID) type controllers are usually preferred in both loops of a classical cascade control structure. However, if the outer loop transfer function of cascade control has an unstable pole or an integrator, then its performance may not be as good as desired due to the limitations of PID controllers. In this study, a new improvement in the outer loop of the cascade control structure incorporating a PI-PD controller is been proposed. To obtain, optimal parameters of controllers in the proposed improved cascade control scheme have been simultaneously used Genetic Algorithm (GA). The superiority of the proposed improved cascade control structure over some cascade control schemes suggested in the literature has been shown by simulation examples. Also, a real-time DC PM motor speed control application on the DIGIAC 1750 process control set has been performed to illustrate the validity of the proposed improved cascade control structure.