Synthesizing load impedance to frequency-tune an electro-mechanical vibration energy harvester

Energy harvesters based upon resonant mass-springdamper systems can only generate useful power over a narrow range of excitation frequencies. This is a significant limitation in applications where the vibration source frequency changes over time. In this paper an active electrical load is presented which can overcome the bandwidth limitations by parametrically tuning the overall harvester system. The electrical tuning technique synthesizes an optimum reactive load with high-efficiency switch-mode electronics, which also provides rectification, feeding power harvested into a DC store. The method is shown to be effective at increasing the power frequency bandwidth of resonant type harvesters, and offers the capability of autonomous operation. The theoretical basis for the technique is presented, and verified with experiment results. The paper illustrates the challenges of implementing the power electronic converter for a low quiescent power overhead and in choosing the control architecture and tuning algorithms.