Revisit of synchronized electric charge extraction (SECE) in piezoelectric energy harvesting by using impedance modeling

Piezoelectric energy harvesting (PEH) systems convert ambient vibration energy into useful electricity. An interface circuit intervenes the electromechanical energy conversion; it has a significant effect on the electromechanical joint dynamics and harvested power. Among the existing interface circuits, the synchronized electric charge extraction (SECE) solution was known for its unique feature of load independence. However, the actual harvested power was usually shown to be lower than the previous theoretical predictions. The reason is that the energy dissipation in power conditioning, e.g. the diode dissipation in the rectifier and the switching dissipation in each energy extraction, have not received sufficient consideration. This paper revisits the joint dynamics and harvested power of PEH systems with a SECE interface circuit by using the energy flow analysis and impedance modeling. By qualitatively scrutinizing the energy cycle of SECE, the electrically induced dynamic characteristics are broken down into three components: the equivalent capacitance, dissipative resistance, and harvesting resistance, which have the same effects but different values, like those in other PEH interface circuits. The three components are equivalent to an additional stiffness, a dissipative damper, and a regenerative damper in the mechanical domain. The theoretical harvested power, which is estimated based on the impedance modeling, shows good agreement with the experimental results under different loading conditions and operating frequencies. Owing to its modular way of thinking, the impedance modeling technique once again shows its effectiveness and efficiency towards the analyses of joint dynamics and harvested power in PEH systems using different power conditioning interface circuits. (paper)