Fuzzy logic-based microbattery controller for MEMS applications

Microelectromechanical (MEMS) sensors often have low power requirements that may be provided by the combination of an energy scavenger (e.g., a solar cell) and a rechargeable microbattery ("battery") made using integrated circuit fabrication methods. While rechargeable microbatteries 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 controller that allows control of the charge/discharge of microbatteries. A breadboard implementation of the controller and its integration with a solar cell and microbattery is presented. The circuit topology of the microbattery 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 microbattery. Charge/discharge data on the microbatteries and current-voltage characteristics of the solar cell are presented and the fuzzy logic model development for the charge control is also presented.