Complete Charging for Piezoelectric Energy Harvesting System

Under an in-phase assumption, the complete charging for an energy harvesting system is studied, whichconsists of a piezoelectric energy harvester （PEH）, a bridge rectifier, a filter capacitor, a switch, a controller and arechargeable battery. For the transient charging, the results indicate that the voltage across the filter capacitor increasesas the charging proceeds, which is consistent with that reported in the literature. However, a new finding shows thatthe charging rate and energy harvesting efficiency decrease over time after their respective peak values are acquired.For the steady-state charging, the results reveal that the energy harvesting efficiency can be adjusted by altering thecritical charging voltage that controls the transition of the system. The optimal energy harvesting efficiency is limitedby the optimal efficiency of the transient charging. Finally, the relationship between the critical charging voltage andthe equivalent resistance of the controller and rechargeable battery is established explicitly.