Tuning the Resonant Frequency and Damping of an Electromagnetic Energy Harvester Using Power Electronics
In order to maximize power density, the resonant frequency of an energy harvester should be equal to the source excitation frequency and the electrical damping set equal to the parasitic damping. These parameters should be adjustable during device operation because the excitation characteristics can change. This brief presents, for the first time, a power electronic interface that is capable of continual adjustment of the damping and the resonant frequency of an energy harvester by controlling real and reactive power exchange between the electrical and mechanical domains while storing the harvested energy in a battery. The advantages of this technique over previously proposed methods are the precise control over the tuning parameters of the electrical system and integrated rectification within the tuning interface. Experimental results verify the operation, and the prototype system presented can change the resonant frequency of the electromechanical system by ±10% and increase the damping by 45%. As the input excitation frequency was swept away from the unmodified resonant frequency of the harvester, the use of the tuning mechanism was shown to increase real power generation by up to 25%. The prototype harvester is capable of generating 100 mW at an excitation frequency of 1.25 Hz.
Available from: Marcelo Savi
- "The general idea of energy harvesting is the objective of several research efforts   . Theoretical and experimental studies investigate the design and performance optimization of vibration-based energy harvesters   . "
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ABSTRACT: Vibration-based energy harvesting with piezoelectric elements has an increasing importance nowadays being related to numerous potential applications. A wide range of nonlinear effects is observed in energy harvesting devices and the analysis of the power generated suggests that they have considerable influence on the results. Linear constitutive models for piezoelectric materials can provide inconsistencies on the prediction of the power output of the energy harvester, mainly close to resonant conditions. This paper investigates the effect of the nonlinear behavior of the piezoelectric coupling. A one-degree of freedom mechanical system is coupled to an electrical circuit by a piezoelectric element and different coupling models are investigated. Experimental tests available in the literature are employed as a reference establishing the best matches of the models. Subsequently, numerical simulations are carried out showing different responses of the system indicating that nonlinear piezoelectric couplings can strongly modify the system dynamics.
Available from: ieeexplore.ieee.org
- "However, in most applications, including automotive ones, this is not realistic. Several techniques have been proposed to broaden bandwidth, including using reactive loads synthesized by a power converter , and by mechanical means by modifying the spring. Recently, a new low-power method of changing the resonant frequency has been demonstrated  where a magnetic potential well is used to add a spring-like effect in parallel with the physical harvester spring and this has been shown to decrease the necessary power consumption for tuning by around 30% with appropriately shaped pole pieces. "
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ABSTRACT: Energy harvesting has become a very popular research topic over the last 12 years, but has only made an industrial impact in a few areas, noticeably in process plant monitoring, including the water and petrochemical processing industries. Like most technologies, greater adoption needs to be realized if performance is to increase and cost to decrease. Batteries cost only tens of pence per Wh, and whilst harvesters can in theory generate very large amount of energy over a long enough period of operation, a typical harvester can require a capital expenditure of tens to hundreds of pounds, making them unattractive in many applications. The automotive sector is a potential area in which harvesters could provide useful functionality and gain from economies of scale, if they can be made reliable enough with a high enough power density and work well in a wide enough variety of scenarios. Recent work on increasing the power density of energy harvesters has focused on improving the power electronic interface, tuning the resonant frequency of motion-driven harvesters and reducing the power consumption of the load electronics.
Available from: Sebastien Boisseau
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