For many low-powered portable and wireless electronic applications the finite energy density of chemical batteries places limits on their functional lifetime. Through the use of energy harvesting techniques, ambient vibration energy can be captured and converted into usable electricity in order to create self-powering systems which are not limited by finite battery energy. Typical energy harvesting systems are composed of two components, a transducer that converts the mechanical vibrations into electrical energy and a power converter that efficiently delivers the harvested energy to the electronic load. The practical design of energy harvesting systems must include both components and consider how coupling between the two affects overall system performance. In order to effectively design an energy harvesting system for a specific application, a model is needed that accurately characterizes the energy harvesting process.

This work focuses on the development and experimental characterization of a system-level model for a vibration energy harvesting system. The system considered in this work is comprised of a piezoelectric composite beam transducer and a pulsed resonant converter (PRC). In addition to capturing the general electromechanical behavior, the system modeling developed in this work also considers the effects of non-ideal operation of the transducer and power converter. Specifically, this work examines the effects of non-resonant frequency operation, conduction losses in the PRC, and non-ideal switch timing. Unlike previous research, which typically focuses on only the electrical domain behavior, the effects of harvesting energy on the mechanics of the transducer are also considered.

In this work, lumped element modeling techniques are used to model the behavior of the piezoelectric transducer. Two system-level models are presented, one using a full lumped element model (LEM) of the transducer and the other using a simplified resonant transducer model. The finite losses in the PRC are included in both models. An experimental test bed is developed, which includes several piezoelectric transducers and a discrete PRC implementation. Through experimental characterization of the energy harvesting system, it is shown that the full LEM accurately captures the behavior of the system over a range of vibration frequencies, while the simplified resonant model is only valid at a single operating frequency. The effects of modeling losses in the power converter are also demonstrated. For the specific systems implemented in this work, is it shown that an ideal model with zero losses overpredicts the power delivered to the load by 30–50%.