Modeling and Analysis of PZT Micropower Generator
Type of DegreeDissertation
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The goal of this research is to theoretically and experimentally investigate behaviors of a power harvesting system that was constructed with a bimorph cantilever made of Lead Zirconate Titanate (Pb[ZrxTi1-x]O3) and a tungsten proof mass. The device should be capable of generating power in an environment where vibration frequency is around 100Hz, and the vibration amplitude is greater than 9.8m/s2, and within the temperature range from -200C to 800C. The basic materials selected for the device was soft Lead Zirconium Titanate (PZT-5H) because of the accessible large strain, acceptable mechanical strength and high piezoelectric constant. The main factors considered in the research were the resonant frequency, the output power density, power conversion circuitry and the effects of temperature. Consistent with the goal, mathematical models were developed for the device and experimentally compared with the power outputs. Primarily, development of the models aimed at prediction of the power output from the bimorph PZT cantilever structure. The device used for validation of the models were designed and fabricated by a research group in the Materials Engineering directed by Dr. Dong-Joo Kim. Three different mathematical models were developed with a focus on power output and efficiency. The first model for the device was approached with lumped electrical components that result in an electrical equivalent circuit. The second model used the energy conservation principal in conjunction with the PZT constitutive equations to estimate the power output. The third model was derived from the principle of couple field analysis that separately models the mechanical and electrical components of the generator and then coupled together with electro-mechanical coupling based on PZT constitutive equations. Based on the comparison of the simulation and experimental data, it was found that the coupled field model better predicts the power output and efficiency of the device as compared with the other two models. For this reason, the coupled field model was used for further analysis of effect of temperature on the power generation and efficiency of the device. Power generation experiments were then conducted to assess the accuracy of the model for prediction of the effect of temperature on power output from the device. The mathematical models developed were implemented in Matlab/Simulink and compared with experimental data to assess performance of the model. Analysis also included AC/DC power conversion using a bridge rectifier circuit, DC/DC converter and a load tester. The voltage and power results show that the results are reasonably close to the experimental data when the natural frequencies match, which is expected. The experimental results and analysis also reveals that the increase or decrease in temperature has an effect on both the resonant frequency and the power output. The resonant frequency of the bimorph PZT cantilever and power output decreases with an increase in temperature which matches quite well with the simulation results from the coupled field model.