Active Piezoelectric Energy Harvesting: General Principle and Experimental Demonstration

In piezoelectric energy harvesting systems, the energy harvesting circuit is the interface between a piezoelectric device and an electrical load. A conventional view of this interface is based on impedance matching concepts. In fact, an energy harvesting circuit can also apply electrical boundary conditions, such as voltage and charge, to the piezoelectric device for each energy conversion cycle. An optimized electrical boundary condition can therefore increase the mechanical energy flow into the device and the energy conversion efficiency of the device. We present a study of active energy harvesting, a type of energy harvesting approach which uses switch-mode power electronics to control the voltage and/or charge on a piezoelectric device relative to the mechanical input for optimized energy conversion. Under quasi-static assumptions, a model based on the electromechanical boundary conditions is established. Some practical limiting factors of active energy harvesting, due to device limitations and the efficiency of the power electronic circuitry, are discussed. In the experimental part of the article, active energy harvesting is demonstrated with a multilayer PVDF polymer device. In these experiments, the active energy harvesting approach increased the harvested energy by a factor of five for the same mechanical displacement compared to an optimized diode rectifier-based circuit.