Boosting the efficiency of a footstep piezoelectric-stack energy harvester using the synchronized switch technology

Abstract

In this article, the self-supported power conditioning circuits are studied for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on the synchronized switch harvesting on inductance (SSHI) technology, the power conditioning circuits are designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, for example, standard energy harvesting circuit, series-SSHI, and parallel-SSHI, are compared in terms of their output power to find the best candidate for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 74% more power than the standard energy harvesting counterpart, while the use of series-SSHI circuit demonstrates a similar performance in comparison to the standard energy harvesting interface. The reasons for such a huge efficiency improvement using the parallel-SSHI interface are detailed in this article.

Piezoelectric Energy Harvesting Solutions: A Review

“…Centuries later, human-based kinetic energy generators remain unexploited [ 5 ]. A healthy person takes around 10,000 steps a day [ 15 ], therefore, human walking can generate significant power if harvested [ 57 ]. Human steps have a frequency between 1.2 Hz to 2.2 Hz when considering 1.4 m/s as an average walking speed [ 58 ].…”

“…PZT was developed in the 1950s at the Tokyo Institute of Technology, and its versions PZT-5A and PZT-5H are the most widely implemented piezoelectric ceramic materials [ 93 ]. The popularity of PZT is due to the fact that it is one of the most efficient and cost-acceptable materials [ 15 ]. To improve conversion efficiency, two mechanisms of force amplification frames are offered: concave shape [ 94 ] and convex shape [ 95 ].…”

“…To rectify the AC power generated by the piezoelectric transducers, an AC-DC energy conditioning circuit is needed between the transducer and the energy storage [ 15 ]. There are several electrical schemes used to obtain the highest energy conversion efficiency, but the most popular circuit uses a bridge rectifier to convert the output voltage of both polarities to a single polarity.…”

“…There are several electrical schemes used to obtain the highest energy conversion efficiency, but the most popular circuit uses a bridge rectifier to convert the output voltage of both polarities to a single polarity. This circuit is used to charge a capacitor to a required voltage, after which a switch is closed, connecting the capacitor to the load , as presented in Figure 15 [ 15 , 160 ], where the piezoelectric element is modeled as an equivalent current source in parallel with a capacitor and the internal leakage resistance .…”

“…There are three typical ways to convert mechanical energy into electrical energy: electromagnetic, electrostatic/triboelectric, and piezoelectric [ 14 ]. If high efficiency in the mechanical-to-electrical energy transfer is required, electromagnetic systems are the most suitable because they usually involve coils and magnets, but this also means bulky and complicated mechanisms [ 15 ]. The choice between the three methods is highly dependent on the application but, of these, piezoelectricity is the most widely studied [ 15 ].…”