The objective of this thesis is to design, analyze, and fabricate an innovative backpack energy harvester for human walking. To model human walking with backpack energy harvester, a simple dual-mass model has been developed and studied first. Dual-mass model for three types of distinct harvesters were investigated, pure damping, traditional rack pinion energy harvester and our MMR based energy harvester. A comparison in the output power and human comfort between the three types of harvesters is discussed. However, the dual-mass model could not effectively represent human walking in real situation with sinusoidal input, like M shaped Ground Reaction Force (GRF), vertical Center of Mass (COM) motion, etc. Thus, a bipedal walking model has been proposed to simulate human walking with backpack harvester. Experiments were conducted to compare power output and efficiency of MMR based backpack energy harvester with traditional rack pinion backpack energy harvester, and verify conclusions from the bipedal walking model that the proposed backpack energy harvester using mechanical motion rectifier (MMR) mechanism has larger power output than traditional backpack energy harvester at different walking speed. In human treadmill test, subjects were asked to wear the backpack frame which embedded with harvesters walking on a treadmill. Two walking speed, 3mph and 3.5mph, and four resistor values has been tested. The test results showed that the MMR based backpack energy harvester generated more power regardless of resistor values and walking speed. Up to 4.84W average power and instant power of 12.8W could be obtained while the subject walking on the treadmill at 3.5mph speed with MMR based backpack energy harvester. / Master of Science

Wave energy has great potential in energy harvesting, but due to its high system cost per electricity production, it is still in the pre-commercialization stage for grid connection. A wave energy converter (WEC) system that harvests energy through wave motion consists of a wave energy converter and a power take-off (PTO). A wave energy converter, usually a floating buoy, absorbs the hydrodynamic motion from wave and generates a mechanical oscillation. A power take-off (PTO) with mechanical transmission, which harvests the electrical energy through the mechanical energy, usually includes a transmission that converts linear motions from the buoy to rotational motions, an electromagnetic generator that produces electricity from a rotational shaft, and a power electronics converter that converts the ac electric power from the generator and charges the output dc battery or the ac grid. The models of the WEC system are usually oversimplified in a multi-physics study. A PTO model as an ideal actuator with 100 % efficiency will show a different frequency response than the real tested results and can make the controller design invalid. A conventional regular-wave circuit model shows discrepancies in power and force prediction in time-domain under irregular wave conditions. A model that can bring the multiple fields together, and provides an accurate prediction from irregular wave dynamics and non-ideal PTO mechanism is needed. A methodology that converts mechanical transmission equations into a circuit model is created. The equivalent circuits of mechanical components such as one-way clutches, gears, a ball screw, mechanical couplings, and generator are derived respectively to describe the dry frictions, viscous damping, and mechanical compliances in these components. The non-ideal efficiency and force of the PTO are predicted in electrical simulations by integrating these sub-circuit models. The circuit model is simplified, and its parameters are categorized as dc and ac unknowns. Using PTO with a mechanical-motion-rectifier (MMR) gearbox as an example, the dc and ac tests on the PTO are performed sequentially to extract two sets of parameters through linear regression or nonlinear curve fitting. The simulated efficiencies of 30 – 80% match well with experimental results. The model is validated through its prediction capability over 25 test conditions on input forces, output voltages, and efficiencies, with correlation coefficients R2 value of 0.9, 0.98, and 0.981, respectively. An equivalent circuit model of fluid-body dynamics for irregular waves, applicable to real ocean conditions with frequency-dependent radiation damping, is developed. Different from PTO modeling, the time-invariant circuit is created from a fourth-order RLC equivalent circuit through transfer function approximation in the frequency domain and Brune network. The circuit-based wave energy converter (WEC) model is verified by comparing the results with the predictions of a detailed model under irregular wave conditions in the time and frequency domains based on a point absorber type of WEC with a power take-off (PTO). The results show that the developed model gives an accurate dynamic prediction for a WEC under both regular and irregular conditions. Along with the PTO model, the circuit-based W2W model is completed for control and design optimization of the WEC system. Wave energy converter systems have faced various challenges such as reciprocal wave motion, high peak-to-average power ratio, and potential wave height from hundred-year storm conditions. These could lead to an overdesigned power take-off (PTO) of the system and significantly reduce the lifetime of the power electronics converter. The power ratio between the peak and the average power of the wave power converter is around 10 – 20 times. Power optimization is necessary to reduce the over design ratio of the power electronics converter. The design guideline that optimizes the power ratings for the power converter and the generator is introduced. The methodology is developed from the W2W circuit model taking the losses of the power converter and the generator into consideration. By optimizing the power limiting and field-weakening controls, the ratio from the average output power to the rated power of the power converter is reduced to 2.4 in the maximum wave condition, and 15 in the annual wave profile. A maximum energy control algorithm on the power electronics in wave energy application is developed to increase the total energy produced from the power converter in a wave energy converter (WEC) system. A 4-D damping and power leveling maps for maximum energy are built for the algorithm. The maps are based on the irregular W2W circuit model and reliability analysis on the IGBT module. From the yearly wave mission profile, the strategy is proved to increase energy by 16 times or increase the lifetime from 3 to 18 years in exchange for 6 % of average output power than the conventional maximum power algorithm. In conclusion, this work provides a new circuit-based perspective for co-designing the multi-disciplinary WEC system. The methodologies of circuit modeling can benefit the co-design process of other mechatronic power systems, such as electric vehicle or renewable energy system. The newly invented mechanical device – the mechanical motion rectifier, is understood thouroughly via the non-ideal electrical model. The commercialization of wave energy converter is driven forward through the reduction of the levelized cost of electricity (LCoE) which is made possible by increasing the energy production and optimizing the cost per output power of the generation and power conditioning stages. / Doctor of Philosophy / Wave energy, if all been harvested along the U.S. coastline, can power around 65% of the energy consumption in U.S.. Comparing to other renewable energy sources like solar or wind, ocean wave can provide up to 90% of steady uptime. With the high energy density (2-3 kW/m2), it can produce more energy with the same amount of installation area comparing to the energy density of wind turbine (0.6 kW/m2) and solar panel(0.2 kW/m2). The predictability of wave provides advantages like planning installation, power dispatching, and maintenance activities. Although with all these advantages, wave energy converter system is still in the research stage due to its high system cost per electricity production. One of the challenges that need to be solved is the irregularity from the wave motion that leads to high instantaneous peak power into the wave energy converter, which usually reaches up to 10 - 20 times of the average power. The high peak power will not only bring high mechanical/electrical stress but also result in an overrating design of the components in the system. Another obstacle that prevents the wave energy system from moving forward is the high testing cost from the validations in wave-energy-test sites or tank-test sites. A high-fidelity multi-disciplinary system model, including hydrodynamics, mechanical dynamics, electromagnetics, and power electronics, is needed to predict the behavior of the system and reduce the cost of design validation. This work provides a unified circuit-based perspective for co-designing the multi-disciplinary wave energy system. The efficiencies and mechanical dynamics of the system are accurately predicted via the non-ideal electrical model. These methodologies of circuit modeling can also benefit the co-design process of other mechatronic power systems, such as electric vehicles or renewable energy systems. The peak of the irregular power is controlled by the power-leveling and field-weakening control, and as a result, the overdesign ratio of the power converter reduces from 11.1 to 2.4. Through proper design of the converter's control algorithm, the total produce electric energy is increased by 15 times, as well as the lifetime of the power electronics extended from 3 years to 18 years. Therefore, the commercialization of wave energy converter is driven forward through the reduction of the levelized cost of electricity (LCoE), which is made possible by optimizing the component lifetime and the output energy utilizing the developed circuit-based wave-to-wire model.

Point absorber style marine energy harvesters have been investigated based on their structure, energy harvesting efficiency, and reliability along with costs. However, due to the continuously varying ocean conditions and climates, the system usually suffers low power output and reliability from low input and high Peak to Average Ratio (PAR). Therefore, a Mechanical Motion Rectifier (MMR) based point absorber is introduced in this thesis to promote the harvesting efficiency and reduce the PAR by unifying the input rotation, and allow disengagement inside the gearbox during low power output phase. A 1:20 scale full system was then designed, prototyped, and tested based on the MMR. The bench test results show that the proposed MMR based point absorber could improve the energy conversion efficiency by 10 percent, which brings feasibility to the implementation. Traditional Wave Energy Converter(WEC) can only harvest ocean waves while ocean current is also one of the significant energy sources widely existing in ocean. In order to further increase the energy harvesting efficiency, one individual energy input source shows its limits. A vast majority of places around the world tends to co-exist both marine waves and current, and extracting energy from both sources could potentially increase the electric power output. Therefore, the Hybrid Wave and Current Energy Harvester (HWCEC) is introduced along with the hybrid gearbox. It is capable of harvesting energy from both ocean waves and current simultaneously so that the electric power output is significantly higher from a combined system. Tank test data shows 38-79 percent of electric power output promotion of an HWCEC compared to a regular WEC, and 70 percent reduced PAR in irregular wave condition. After that, system electric damping has been thoroughly investigated on both electrical side and mechanical side. The best power output corresponding electrical resistance is identical to the generator internal resistance while the best gear ratio of 3.5 is determined via both simulation and tank test. Furthermore, the system's PAR has been investigated by analyzing the trend of the peak occurrence. Tank test data shows the HWCEC's output power peak occurrence is at roughly 20 percent located at its PAR average. Therefore, the HWCEC system can promote energy harvesting efficiency to the combined system design, and improve its reliability from a significantly reduced peak to average ratio. It also gives HWCEC a large variety of deployable locations compared to a regular WEC under more marine environment. Furthermore, a new design of the Hybrid model, Hybrid LITE, is then developed, which not only features the HWCEC features, but also a lightweight, immersive and inflatable design for fast deployment and transportation. Since the system is built with an open water chassis, the overall system robustness is significantly improved since no water sealing is required on the powertrain compared to the HWCEC. / Master of Science / Ocean contains enormous amount of Marine Hydrokinetic (MHK) energy including ocean waves, tidal streams, and ocean current. Marine energy was investigated due to its continuous, massive and high-density hydrokinetic power output. In order to better serve the needs for ocean surface applications and take advantage of high energy density compared to other renewable energy sources, Wave Energy Converters (WEC) has been investigated, which harvests energy from the ocean wave. In the past years of study, it came to our attention that places such as the west coast of the U.S., northern Europe, and the Mediterranean area tend to have both abundant marine wave and current energy. Therefore, a new design of the Hybrid Wave and Current Energy Converter (HWCEC) is investigated for higher power output. In order to combine the energy sources from waves and current, a Hybrid Gearbox was selected to joint the power and unifies the motion from the wave for a higher efficiency. Simulations and 1:10 ratio co-existing wave and current basin test have been conducted for the HWCEC. By using the same system, single wave or current input are used as the baselines and the dual input HWCEC has demonstrated great benefit and potential. The electric damping and the gearbox ratio of the HWCEC are studied for the best power output in both simulation and tank test. The result shows that the HWCEC could promote up to 38-71 percent of electricity output in a regular wave condition, and 79 percent in irregular wave condition. The Peak to Average Ratio (PAR) is a key factor for system's mechanical reliability. The testing shows that the HWCEC can reduce 70 percent of the peak motion and contribute to the average, which is an indirect indicator of the system's better reliability. Furthermore, to align the needs of the design for real-life applications, The Hybrid LITE Converter idea was then developed for special deployment requirements for the future application of the Hybrid system. It has a novel open-system design with the implementation of a newly designed hybrid gearbox. This converter has the potential of promoting the reliability, deployability and weight reduction for easy transportation from its open system design compared to HWCEC. The system modeling could be done as future work varies from the changing deployment locations for higher electric power output.

Instead of dissipating vibration energy into heat waste via viscous damping elements, this dissertation proposes an innovative vibration control method which can simultaneously mitigate vibration and harvest the associated vibration energy using electromagnetic energy harvesters. This dissertation shows that the electromagnetic energy harvester can work as a controllable damper as well as an energy harvester. The semi-active control of a linear electromagnetic energy harvester, for improvement of suspension performance, has been experimentally implemented in a scaled-down quarter-car suspension system. While improving performance, power produced by the harvester can be harvested through energy harvesting circuits. This dissertation also proposes a mechanical-motion-rectifier(MMR)-based electromagnetic energy harvester using a ball-screw mechanism and two one-way clutches for the application of replacing the viscous damper in vehicle suspensions. Compared to commercial linear harvesters, the proposed design is able to provide large damping forces and increase power-dissipation density, making it suitable to vehicle suspensions. In addition, the proposed MMR-based harvester can convert reciprocating vibration into unidirectional rotation of the generator. This feature significantly increases energy-harvesting efficiency by enabling the generator to rotate at a relatively steady speed during irregular vibrations and improves the system reliability by reducing impact forces among transmission gears. Extensive theoretical and experimental analysis have been conducted to characterize the proposed MMR-based energy harvester. The coupled dynamics of the suspension system with the MMR-based energy harvester are also explored and optimized. Furthermore, a new control algorithm is proposed to control the MMR-based energy harvester considering its unique dynamics induced by the one-way clutches. The results show that the controlled proposed electromagnetic energy harvester can possibly improve ride comfort of vehicles over conventional oil dampers and simultaneously harvest the associated vibration energy. / Ph. D.

Sufficient power supply to run GPS machinery and transmit data on a long-term basis remains to be the key challenge for wildlife tracking technology. Traditional ways of replacing battery periodically is not only time and money consuming but also dangerous to live-trapping wild animals. In this paper, an innovative wildlife tracking collar with multi-source energy harvester with advantage of high efficiency and reliability is proposed. This multi-source energy harvester entails a solar energy harvester and an innovative rotational electromagnetic energy harvester is mounted on the "wildlife tracking collar" which will extend the duration of wild life tracking by 20% time as was estimated. A feedforward and feedback control of DC-DC converter circuit is adopted to passively realize the Maximum Power Point Tracking (MPPT) logic for the solar energy harvester. A novel electromagnetic pendulum energy harvester with motion regulator is proposed which can mechanically rectify the irregular bidirectional swing motion of the pendulum into unidirectional rotational motion of the motor. No electrical rectifier is needed and voltage drops from diodes can be avoided, the EM pendulum energy harvester can provide 200~300 mW under the 0.4g base excitation of 4.5 Hz. The nonlinearity of the disengage mechanism in the pendulum energy harvester will lead to a broad bandwidth frequency response. Simulation results shows the broadband advantage of the proposed energy harvester and experiment results verified that at some frequencies over the natural frequency the efficiency is increased. / Master of Science