Optimization of Cantilever-type Piezoelectric Energy Harvesting System under Free Vibrational Behavior

Abstract

Piezoelectric energy harvesting technology is one of clean energy technologies which is drawing attention recently. Piezoelectric has been studied due to its some advantages like high mechanical to electrical energy conversion efficiencies, high power density and simple application. This paper presents a study on optimization of piezoelectric energy harvesting system under free vibrational behavior for much higher power performance from material, mechanical and electrical parts. In material part, this paper presented piezoelectric characteristics comparison for a piezoelectric energy harvester with different length and width proportion. The area of the piezoelectric ceramics fixed in this study was about 60 percent of the substrate area while the width of the ceramics are 19 mm, 28.5 mm, 38 mm and the length of the ceramics is maintained to be 38 mm. From the finite element analysis showed that the stress distribution on the three ceramic plates were the same. Under same load condition using a pushing tester, small number of wide piezoelectric beams together generated larger output power than large number of narrow piezoelectric beams. In mechanical part, this paper selected a contact magnetic force piezoelectric energy harvesting system for hitting system of this study. The stopper in this system made same displacement about 4 mm of each piezoelectric beams from different input conditions. This paper also presented a specially designed lab-scale energy harvester for uniform output. In design of electric circuit, all of piezoelectric beams in parallel are connected to the same number of DF04 rectifier for rectifying the output signal from each piezoelectric beam. The wider piezoelectric beam harvester presented the most highest impedance value about 105 kΩ for maximum output power under no load condition. For the impedance matching, this paper suggested Discontinuous Conduction Mode (DCM) Flyback Converter. At the point of Pmat of the 38 mm width harvester, the efficiency at the output power of this converter was 81%. This result was proved that DCM Flyback Converter has more high efficiency performance for cantilever-type piezoelectric energy harvester than Oscillator circuit, Start-up circuit, Buck converter which were presented about 63.72% average efficiency. For optimization of cantilever-type piezoelectric energy harvesting system, this paper presented material, mechanical and electrical parts designs and demonstrated through practical experiments. Although matching impedance increased depanding on increase in the width of piezoelectric beam, the wider piezoelectric energy harvester generated larger output power in the same load condition. Also, DCM Flyback Converter can support upper 80 % efficiency of converter curcuit part that it is helpful for applying to practical situation. Thus, this piezoelectric energy harvesting system design can be an useful guideline for commercialization of cantilever-type piezoelctric energy harvesting technology.