Superheating control, PID controller, Artificial bee colony algorithm
Electronic Expansion Valves (EEV) have been used in refrigeration systems to replace conventional expansion devices. Their quick response to changes in the operating conditions improves the steady-state superheating, what contributes to increase the system efficiency. EEV are usually used with automatic controllers in order to keep the superheating close to its optimal value. Among the controllers employed in these devices, the Proportional, Integral and Derivative (PID) controller is the most common. In general, this controller allows for adjustments in the proportional, integral, and differential gains. If these gains are not properly adjusted, the system can display a slow, oscillatory, or unstable closed-loop response, poor disturbance rejection ability and low robustness. In the last decades, several tuning methods for PID controllers were proposed. Among them, the methods based on bio-inspired optimization techniques, in special the Artificial Bee Colony (ABC), are relatively new in PID controller tuning. The ABC algorithm is based in the food search behavior of bee colonies. In this algorithm, the position of a food source represents a possible controller gain. Each food source has a quality that is defined based on the system response, when using this potential controller gain. This work presents an adaptive PID controller to regulate the opening of an EEV. The controller gains were determined using ABC algorithm for each operating point. A dynamic model obtained from experimental tests was used in the controller design. The controller effectiveness was evaluated through computer simulations and by means of experimental tests. Preliminary results indicated that the proposed controller provides good disturbance rejection and set point tracking, and was able to control the superheating efficiently.