Energy Harvesting Circuit for Road Energy Harvesting System from Multi-energy Source

Abstract

A piezo-solar hybrid road energy harvesting system was proposed to solve the independent power supply problem of countless smart sensors in smart road system. Previous piezoelectric road energy harvesting system has two problems. The one is that the output power of previous system is insufficient to supply the whole smart road system alone. The other one is low power generation efficiency which can generate power only by vehicle traffic. A proposed hybrid system combining piezo module and solar module can solve these two problems. Piezoelectric and solar have different types of output signal. A circuit design that can process different types of output signals is required. In this dissertation, a circuit capable of handling multi-energy source from piezo and solar was presented. The results of this study are expected to contribute to the development of the piezo-solar hybrid road energy harvesting technology. First, the output power of piezoelectric energy harvesting system (PEHS) was improved through research on piezoelectric part among the hybrid system. Piezoelectric energy harvesting module (PEHM) is the power generation unit of the harvesting system. A study was conducted to find optimized internal arrangement of the piezoelectric energy harvester (PEH) for harvesting the maximum output power in a limited volume of the PEHM. When the length and thickness of a single PEH were the same, arranging a small number of wide PEH could obtain higher output power than arranging a plurality of narrow PEH in the PEHM. As a result of one experiment, six 40 mm width PEHs was obtained 0.85 mW which was about 2.4 times higher than twelve 20 mm width PEHs. In the circuit part of piezoelectric energy harvesting system (PEHS), charging efficiency of harvesting circuit was improved by controlling rectification and smoothing part. The individual and parallel rectification method which individually connected rectifier elements to each PEHs showed the highest output power in multi-array system. In addition, by selecting an appropriate capacitance value of the smoothing part, the amount of energy accumulated in the smoothing capacitor was increased. At the same time, a stable high-efficiency circuit was designed that did not generate ripple in the output voltage. The finally designed road PEHM showed 4.15 mW/m2 output power in the road environment simulation performance test using a universal test machine (UTM). In order to test the proposed PEHS in a real road environment, the system was installed on the Yeo-ju test road located on the Jungbunaeryuk Expressway. Twenty four PEHMs were installed on concrete and asphalt roads. Twelve PEHMs were installed on the each road, and six PEHMs of each road installed the exposed and buried types. In both the exposed and buried types, the output power increased with the load and speed of vehicle. About buried type, the highest output power was shown in 1 cm depth buried type. More output power could be usually obtained in the exposed type than buried type. A single PEHM could generate about 24.6 Wmax output power per vehicle pass on asphalt road. Through this system, four delineators could be turned on for 14 seconds with the output power obtained from three times passage of minivan. A piezo-solar hybrid module was manufactured that combined the improved piezoelectric module and a solar module. The solar module was installed on the upper surface of the housing system for waterproof and dustproof of the road PEHM. A circuit was designed to simultaneously process the pulse voltage and DC voltage of piezo and solar. The problem of the Power ORing system which was previously used for commercial products was improved. The proposed circuit using the concept of voltage multiplier improved the problem of Power ORing in which the voltages of two energy sources could not be applied to the charging unit at the same time. As a result of the simulation, the proposed circuit was able to apply the sum of multi-energy sources to the charging unit even if the pulse voltage of piezo and the DC voltage of solar were simultaneously input. In the simulated environmental test, the charging efficiency of the proposed circuit was increased by 12.5% compared to the Power ORing system. Through this dissertation, the piezo-solar hybrid road energy harvesting system was confirmed to be one solution to supply the power of smart sensors for future smart road.