Power conditioning for energy harvesting

Abstract

Vibration powered electrical generators produce a raw AC electrical output that often needs to be converted into DC for use by the load systems. There are many possible ways to achieve this conversion (rectification) however the specific application of vibration energy harvesting requires a solution that is a delicate balance between efficiency, converter quiescent loss and impact upon the resonant generator operation. In this paper we investigate how vibration powered generators interact with typical rectification schemes and assess the overall system performance, comparing it to the theoretical maximum power that could be generated. Further to this we present practical circuits that address the inherent problems of passive rectification techniques including a unity power factor power converter, realised at ultra low powers, suitable for energy harvesting applications. Numerical models are validated with measured results.

Review of Power Conditioning for Kinetic Energy Harvesting Systems

“…One possible solution is to use active components that can be powered directly from the generator's output, as demonstrated in [22] and [28]. Alternatively, active circuit designs that can also operate passively can be used.…”

“…In an ideal sinusoidal excitation scenario, both the output voltage and current of a linear generator are sinusoidal with a unity power factor. However, components such as diodes or capacitors result in a nonsinusoidal harvester current and therefore a reduced power factor, which in turn increases the conduction losses within the power conditioning circuits due to the added current associated with the reactive power transfer [28]. Even classic switching converters, for example, a boost converter, draw nonsinusoidal current from the harvester as the envelope of the average inductor current does not follow a pure sinusoidal waveform when operated at a fixed duty cycle and switching frequency [109], as shown in Fig.…”

“…Active or synchronous rectifier designs [28] can be used to further increase the efficiency by reducing the conduction losses. However, the control circuitry of active topologies presents additional power consumption and may require conditioned supply.…”

PENDEXE: A novel energy harvesting concept for low frequency human waistline

“…Data was taken from reference [23] where motion of rigid backpack frame was measured with the wearer engaged in two types of locomotion, namely walking and jogging. The result shows that the displacement frequencies relevant to the present study (i.e.…”

Open-loop power conditioning for vibration energy harvesters

“…The power conditioning also determines the mechanical operating conditions by setting the equivalent load impedance seen by the harvester. Rectification can be implemented using a full bridge of Schottky diodes, or for lower losses a synchronous scheme can be adopted [3]. It is tempting to follow the rectifier stage by a high efficiency switched-mode converter with closed-loop output voltage regulation, of which many low-power commercial examples are available; however, such converters are designed for applications where the source impedance is much lower than the load impedance (i.e.…”