This article proposes new methods for enhancing the active harvest of piezoelectric energy using the synchronized switch harvesting on inductor (SSHI) technique. It was experimentally confirmed that the energy harvested by the original synchronized switch harvesting on inductor technique was decreased by the suppression of the vibration amplitude, and this critical problem was solved by developing new control strategies, namely, switch harvesting considering vibration suppression (SCVS) and adaptive SCVS (ASCVS). The SCVS technique was designed to intentionally skip some of the switching actions of the original synchronized switch harvesting on inductor technique, while the ASCVS technique enables more flexible variation of the number of skipped switching actions. The skipping of the switching actions facilitates the recovery of the vibration amplitude produced by the excitation force, and the developed strategies thus maintain the vibration amplitude at the highest possible level, resulting in increased energy harvest. The results of the experimental implementation of the proposed strategies showed that they enabled the harvesting of as much as 10.5 times the energy harvested by the original synchronized switch harvesting on inductor technique. The ASCVS technique particularly enables flexible enhancement of the harvested energy under various vibration conditions.
In this paper, we propose a self-powered analog controller circuit to increase the efficiency of electrical energy harvesting from vibrational energy using piezoelectric materials. Although the existing synchronized switch harvesting on inductor (SSHI) method is designed to produce efficient harvesting, its switching operation generates a vibration-suppression effect that reduces the harvested levels of electrical energy. To solve this problem, the authors proposed—in a previous paper—a switching method that takes this vibration-suppression effect into account. This method temporarily pauses the switching operation, allowing the recovery of the mechanical displacement and, therefore, of the piezoelectric voltage. In this paper, we propose a self-powered analog circuit to implement this switching control method. Self-powered vibration harvesting is achieved in this study by attaching a newly designed circuit to an existing analog controller for SSHI. This circuit aims to effectively implement the aforementioned new switching control strategy, where switching is paused in some vibration peaks, in order to allow motion recovery and a consequent increase in the harvested energy. Harvesting experiments performed using the proposed circuit reveal that the proposed method can increase the energy stored in the storage capacitor by a factor of 8.5 relative to the conventional SSHI circuit. This proposed technique is useful to increase the harvested energy especially for piezoelectric systems having large coupling factor.
Vibration energy harvesting extracts electrical energy from vibrating structures. The past studies of vibration energy harvesting suggest that the efficiency can be improved by switch regulation in the harvesting circuit. The switch-regulation is carried out depending on the motion of the target structure with the use of vibration sensors such as displacement sensor or accelerometer. This paper proposes a new vibration self-sensing method for switching energy harvesters that do not use those vibration sensors. In this method, the voltage of the piezoelectric transducer is measured, and the structural vibrational status is estimated from the measured voltage. The transducer voltage is not smooth and does not maintain the sinusoidal wave even when the structure vibrates in a sinusoidal wave because the switch energy harvesting method inverses the transducer voltage at every period. Thus, we establish a state observer based on a Kalman filter to estimate three state values of the target harvesting system: modal displacement, modal velocity, and electric charge in the transducer. This paper describes the construction processes for the observer. The observed value is the transducer voltage. We also show an electric circuit for measuring the transducer voltage. Finally, we confirm the efficiency of the proposed state observer for switch harvesting with numerical simulations.
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