Antônio Augusto Torres Maia

Superheating control using an adaptive PID controller

Electronic expansion valves have been used to replace conventional expansion devices in many refrigeration systems. Electronically controlled valves respond more rapidly to changes in operating conditions and improve the steady-state superheating. These valves are usually used with an automatic controller that regulates the superheating at the evaporator outlet. The controller gains (Kp, Ti, and Td) must be properly tuned for efficient operation. However, these controllers can result in poor performance because they have been poorly tuned or put into operation using factory tuning. For refrigeration systems that are subject to large changes in operating conditions, the controller gains should be adjusted for each change to improve the system performance. Within this context, we developed an adaptive Proportional-Integral-Derivative controller (PID controller) in this study to regulate the degree of superheating. A dynamic model obtained from experimental tests was used in the controller design. The controller effectiveness was evaluated using computer simulations and experimental tests. In comparison to a nonadaptive PID controller, the adaptive controller provided better disturbance rejection and set-point tracking and was able to control the superheating more efficiently, demanding less servomotor effort.

Thermal Performance of Commercial Vehicle Braking Process during the Vehicle Descending Speed Control on Roads with Long Length Steep Inclination - A Case Study

Study about the performance of the service brakes and the retardation systems of commercial vehicles during the descending speed control on roads with long length steep inclination in Brazil. Mathematical models, based in the equations of the energy balance during the vehicle braking process are used. The thermal performance of the service braking system, of the engine cooling system, and of retarders, are verified for the established maximum safety speeds for a vehicle traveling downhill. The simulations are performed with programs elaborated in the Matlab-Simulink platform and with the vehicles as per the European norm ECE R13 requirements (test type II A) and the Brazilian norm requirement (NBR 10967) for the downhill functional test (test type III). The obtained results show that it is possible to have a forecast of the dissipated power in the engine and the retarder, of the capacity of dissipated heat of the radiator, and other parameters to guarantee the effective speed control of the vehicle, as per the requirements of the norms, even before the road test are performed.