AC/DC Converter Architecture for Vibration Energy Harvesting

Description

Recent advances in semiconductor technology and material sciences have reduced the power consumption of modern microelectronic circuits and systems, such as Internet-of-Things and machine-to-machine devices, and have also advanced the efficiency of energy harvesting generators (EHGs), such as solar cells, thermoelectric, piezoelectric, electromagnetic, and electrostatic generators, in converting ambient energy into electricity. The goal of energy harvesting is to replace batteries or extend the recharge intervals of batteries. Among various ambient energy sources, vibration energy harvesting owns the merits of being stable, clean, high power density, and its compatibility with microfabrication.Typical vibration energy harvesting system consists of three main components. They are EHG, AC/DC converter, and energy storage element. The AC/DC converter converts the AC power harvested by the EHG into DC power for the energy storage element and load. Ideally, it operates the EHG at the true maximum power point (TMPP) to transfer energy from the EHG to the load under different loading conditions, and vibration amplitudes and frequencies. Mathematically, the input impedance of the converter should be equal to the complex conjugate of the output impedance of the EHG. The output current of the EHG should be of the same phase and wave shape as the open-circuit voltage of the EHG. However, less emphasis is placed on eliminating the effect of the output reactance of the EHG for maximizing power delivery. Thus, the EHG is not always operated at the TMPP. Such issue becomes more apparent if the EHG has large output reactance and is subject to a wide variation in the vibration frequency.This project aims to investigate an architecture for the AC/DC converter that can keep operating the EHG at the TMPP. Such architecture also allows to convert energy from an array of EHGs and have each EHG operated at its TMPP. The power processing unit (PPU) consists of a hybrid structure that can handle a wide range of harvested power. To minimize power losses, no lossy diode bridge is needed. Sophisticated control algorithms that can control the PPU to counteract the effect of the output reactance of the EHG and match with the output resistance of the EHG to achieve maximum power transfer will be formulated. Finally, the conditions and requirements that allow the load operating in a series of consumption modes for energy neutral operation, where the average power in a time interval harvested and consumed are the same, will be formulated.