Fuzzy logic-based solar charge controller for microbatteries

A severe limitation on the functional capability of remote, autonomous, microelectromechanical (MEMS)-based sensors is the lack of a suitable micropower supply to power these devices. Such sensors often have low power requirements that may be provided by the combination of an energy scavenger (e.g., a solar cell) and a microbattery (“μbattery”) made rechargeable using integrated circuit fabrication methods. While rechargeable μbatteries and solar cells have been previously demonstrated, the development of a microcharge/discharge controller has not. In this paper we present a novel, fuzzy logic-based solar charge controller that allows control of the charge/discharge of μbatteries. A breadboard implementation of the controller and its integration with a solar cell and μattery is presented. The circuit topology of the μbattery controller is based on a buck converter design. During charging, the solar cell´s operating point is adjusted by modulating the duty cycle of the buck converter´s switching MOSFET using a fuzzy logic control algorithm to optimally charge the μbattery. Discharge data on the μbatteries and current-voltage characteristics of the solar cell are presented and the fuzzy logic model development for the charge control are also presented