Vibration Energy Harvesing with PZT Cantilevers and Mxximum Power Point Tracking

1. Vibration Energy Harvesing with PZT Cantilevers and Mxximum Power Point Tracking • Na Kong (MS or Ph.D.) and Dong S. Ha • ECE Dept, Virginia Tech, Virginia PZT • Motivation: • Vibration energy is abundant in nature. • Example Sources and Applications • Automobiles, bridges, industry machines, and human body. • Wireless sensor nodes, Portable devices • PZT cantilevers offer high density and scale well. ZL • Low Power Controller Design: • Adopt constant on-time control for a lower clock frequency. • Duty cycle for the MPPT algorithm • Execute the MPPT algorithm for 20 ms at 8-MHz clock, and go to the sleep mode for 2 sec at 1-MHz clock. 50 MHz Constant Frequency Control 10 MHz 1 MHz Constant On-time Control Mechanical Model • Impedance Matching: • The maximum power is transferred under the complex conjugate matching. However, the required inductance is impractical. • Resistive matching is adopted. MPPT 2.6 mA for 20 ms Sleep 110 uA for 2 sec • Maximum Power Point Tracking: • It sets the input resistance of the DC/DC converter to the optimal value dynamically under varying operation condition. • A sophisticated algorithm can harvest more energy, but higher power dissipation.The goal is to maximize the net harvested energy. • A “Perturb and Observation” algorithm is simple and effective. • Experiment Set Up: • 4 PZT Cantilevers Converter and Controller Decrease load resistance. Increase load resistance. • Efficiency: • 62 – 73 % under 0.5g base acceleration • Breakdown of losses Did power to battery increase? Did power to battery increase? Yes Yes No No • Proposed System: • A microcontroller unit (MCU) implements the MPPT – flexible. • Flyback Converter PZT Cantilever MCU • Conclusion: • The MCU-based approach is flexible and achieves reasonably high efficiency. • Future improvements, use • a synchronous rectifier. • an ASIC for the controller. Average power Equivalent Input Resistance