Power processing circuits for vibration-based energy harvesters

In this paper the behavior of a piezo-electric vibration-driven energy harvester is assessed with different power processing circuits. Firstly, a general model for vibration-driven harvesters is described. Using this model, an optimal linear resistive load for the harvester can be analytically calculated. As the vibration-based harvester provides varying AC power, while electronic loads need a stable DC power supply, it is useful to analyze the harvester behavior when connected to a non-linear AC-DC rectifier. Using the same general model, an optimal DC voltage load can be calculated for every frequency. The difference between the optimal output power flow from the harvester to both load circuits depends on the coupling coefficient of the harvester device. To validate previous conclusions, two power processing circuits are designed and built, the first emulating a resistive input impedance and the second with a constant input voltage. A piezo-electric bimorph is taken as energy harvesting device. A buck-boost DC-DC converter without input filter capacitor, operating in discontinuous conduction mode, is shown to have a resistive input impedance. A buck converter with input filter capacitor is used to evaluate the rectifier load-case. Simulations and experimental validation show that the efficiency of the overall system, harvester device with power processing circuit, increases if the power processing circuit has a fixed DC-voltage as input.