Energy consumption optimization for rotation control of a parametric pendulum with variable length

FRANCO EZEQUIEL DOTTI; FLORENCIA REGUERA

Foz do Iguaçu

Congreso; EngOpt 2016: 5th International Conference on Engineering Optimization; 2016

Coppe ? Instituto Alberto Luiz Coimbra de Pós-Graduação e Pesquisa de Engenharia, da Universidade Federal do Rio de Janeiro

In recent years, there has been a growing interest in energy harvesting from the parametrically excited pendulum, based on the high energy of its rotational motion. Two sources are mainly considered: vibrating machines and the motion of the sea waves. In both cases, rotations can be achieved only for some forcing conditions and initial conditions. Since stable rotations are required to extract energy, the pendulum needs to be controlled. One of the possible control actions corresponds to a telescopic adjustment of the pendulum length, which can be performed by a hydraulic or pneumatic actuator. The control consists in giving the pendulum and aid to reach (and maintain) rotations, accelerating the motion by modifying conveniently the position of the bob. Since the pendulum harvester is supposed to be autonomous, the control system must take power from the generation. Consequently, the energy required for the control action must be the least possible in order to make the technology viable.We address in this article the minimization of the energy spent by the rotation control system. This implies that the work done by the actuator during the control action must be minimal, being of course mandatory the reaching of a rotational motion. Three parameters are considered in the optimization analysis. One is the threshold angular velocity of the pendulum, above which the pendulum is supposed to be rotating and thus no control action is needed. Hence, a low threshold velocity is desired in order to reduce the control action. But an excessively low threshold velocity may not be enough to reach rotations. The other two parameters are steepness factors involved in the transition of the telescopic adjustment. This transition must be steep in order to adequately reach rotations. But high steepness requires high velocities and accelerations of the actuator, which lead to an increased energy consumption.The control parameters which minimize the energy consumption are obtained for different forcing scenarios. Then a technique for the selection of these parameters is proposed and discussed with a view of energy harvesting from pendulum systems.