Power evaluation of dynamic behavior of advanced energy-harvester using graphical analysis

In this paper, we present the benefits of bond-graph analysis for mechanical-electrical systems, which are energy-harvesters based on structural vibrations and electric loads. The bond-graph is an energy-based approach to describing physical-dynamic systems. It shows power flow graphically, which helps us understand the behavior of complicated systems in simple terms. Energy-harvesting involves conversion of power in mechanical form to the electrical one and the bond-graph is a good tool to analyze this flow. The bond-graph method can be used to calculate the dynamics of the combining mechanical and electrical systems simultaneously. The biggest advantage of the bond-graph technique is that it can be used with the systems that are subject to component swaps. The bond-graph method involves solving simultaneous algebraic equations, instead of differential equations. On the other hand, in common simulation methods, such as solving differential equations, it is difficult to change the number of components because the differential equations will have to be reconstructed. To use the bond-graph methodology for analyzing an energy-harvester composed of piezoelectric transducers, it is necessary to create a piezoelectric model suited for bond-graph analysis. Few describing piezoelectric models have been proposed so far, but most of them are not suitable for bond-graph analysis. In this paper, we first present a piezoelectric model and assess its validity. We also propose a diode-bridge model and a control circuit model that are suitable for bond-graph analysis. We analyze the advanced energy-harvester that is composed of a SDOF structure and complex circuits that include a rectifier and control circuits.