Optimized piezoelectric energy harvesting circuit using step-downconverter in discontinuous conduction mode

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Ottman, G.K.; Hofmann, H.F.; Lesieutre, G.A.
Power Electronics Specialists Conference, 2002. pesc 02. 2002 IEEE 33rd Annual
Volume 4, Issue , 2002 Page(s): 1988 - 1994
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Summary:An optimized method of harvesting vibrational energy with a piezoelectric element using a step-down DC-DC converter is presented. In this configuration, the converter regulates the power flow from the piezoelectric element to the desired electronic load. Analysis of the converter in discontinuous current conduction mode results in an _expression_ for the duty cycle-power relationship. Using parameters of the mechanical system, the piezoelectric element, and the converter an optimal duty cycle can be determined where the harvested power is maximized for a given frequency of mechanical excitation. It is shown that, as the magnitude of the excitation increases, the optimal duty cycle becomes essentially constant, greatly simplifying the control of the step-down converter. The _expression_ is validated with experimental data showing that the optimal duty cycle can be accurately determined and maximum energy harvesting attained. A circuit is proposed which implements this relationship, and experimental results show that the converter increases the harvested power by approximately 325%