Analysis and comparison of three energy harvesting circuits for impact-type piezoelectric energy harvester

The impacted-type piezoelectric energy harvesters (IPEHs) are widely used to harvest the energy of low-frequency impact forces from raindrops, human motion, machines, and other environmental sources. Owing to the typically low impact frequency, the output voltage between the two excitations undergoes damping. The attenuation coefficient λ, which reflects the damping rate, directly affects the performance of the energy harvesting circuit. This study analyzes and compares the variations of three energy harvesting circuits: full-bridge rectifier (FBR), parallel synchronized switch harvesting on inductor (P-SSHI), and synchronous electrical charge extraction (SECE) circuits under varying λ. First, the ideal energies of the three energy harvesting circuits during one impact event are summarized according to their maximum output power per half-cycle related to λ. Derivations of the IPEH with self-powered FBR, P-SSHI, and SECE circuits are provided, including the energy consumption and start-up voltage. Furthermore, these self-powered circuits connected with an IPEH are simulated. The optimal load resistance and capacitance of these circuits are analyzed relative to the variation of λ. The optimal load resistance of the SECE circuit varies significantly as λ increases, whereas the optimal loads of other circuits remain relatively constant. The output energies of the three self-powered circuits are analyzed as the force intensity and λ vary. The P-SSHI circuit yields the highest energy when appropriate components are selected. Under large λ or weak external forces, the output energy of the FBR circuit surpasses that of the SECE circuit. Finally, the three self-powered circuits are implemented in the IPEH. The experimental results show that the self-powered P-SSHI circuit generates the highest energy, with the figure of merit gradually increasing with the external force, which is consistent with the theoretical analysis. The guidance provided in this study is a reference for designing IPEH circuits.