Alexander Schlichting

Passive multi-source energy harvesting schemes

Mobile electronics have continually decreased in size; however, mobile power sources have not had comparable increases in energy density or specific energy. Researchers are considering energy harvesting technologies to reduce dependence on batteries, providing alternate sources of power. Combining multiple energy harvesters onto a single platform is a logical and practical method to increase energy output and system robustness. This study explored the dynamics of two passive, multi-source energy harvesting schemes: disparate sources of piezoelectric and photovoltaic, as well as an array of piezoelectrics. A series and a parallel topology were explored for each scheme. For both the schemes, the series topology lends itself to high-level, low-duty cycle load characteristics as it is able to achieve greater amounts of energy on a storage capacitor. The parallel topology lends itself to low-level, high-duty cycle load characteristics due to increased maximum power levels. Both the parallel and the series topologies of the array of piezoelectrics effectively combine the power from the two harvesters in the absence of differences between the two signals. The series topology is insensitive to amplitude differences, and the parallel topology is insensitive to a phase angle or a frequency difference.

Toward efficient aeroelastic energy harvesting: device performance comparisons and improvements through synchronized switching

This paper presents experimental energy harvesting efficiency analysis of a piezoelectric device driven to limit cycle oscillations by an aeroelastic flutter instability. Wind tunnel testing of the flutter energy harvester was used to measure the power extracted through a matched resistive load as well as the variation in the device swept area over a range of wind speeds. The efficiency of this energy harvester was shown to be maximized at a wind speed of about 2.4 m/s, which corresponds to a limit cycle oscillation (LCO) frequency that matches the first natural frequency of the piezoelectric structure. At this wind speed, the overall system efficiency was 2.6%, which exceeds the peak efficiency of other comparably sized oscillator-based wind energy harvesters using either piezoelectric or electromagnetic transduction. Active synchronized switching techniques are proposed as a method to further increase the overall efficiency of this device by both boosting the electrical output and also reducing the swept area by introducing additional electrical energy dissipation. Real-time peak detection and switch control is the major technical challenge to implementing such active power electronics schemes in a practical system where the wind speed and the corresponding LCO frequency are not generally known or constant. A promising microcontroller (MCU) based peak detector is implemented and tested over a range of operating wind speeds.

ENERGY HARVESTING TO POWER SENSING HARDWARE ONBOARD WIND TURBINE BLADE

Wind turbines are becoming a larger source of renewable energy in the United States. However, most of the designs are geared toward the weather conditions seen in Europe. Also, in the United States, manufacturers have been increasing the length of the turbine blades, often made of composite materials, to maximize power output. As a result of the more severe loading conditions in the United States and the material level flaws in composite structures, blade failure has been a more common occurrence in the U.S. than in Europe. Therefore, it is imperative that a structural health monitoring system be incorporated into the design of the wind turbines in order to monitor flaws before they lead to a catastrophic failure. Due to the rotation of the turbine and issues related to lightning strikes, the best way to implement a structural health monitoring system would be to use a network of wireless sensor nodes. In order to provide power to these sensor nodes, piezoelectric, thermoelectric and photovoltaic energy harvesting techniques are examined on a cross section of a CX-100 wind turbine blade in order to determine the feasibility of powering individual nodes that would compose the sensor network.

A low-loss hybrid rectification technique for piezoelectric energy harvesting

Embedded systems have decreased in size and increased in capability; however, small-scale energy storage technologies still significantly limit these advances. Energy neutral operation using small-scale energy harvesting technologies would allow for longer device operation times and smaller energy storage masses. Vibration energy harvesting is an attractive method due to the prevalence of energy sources in many environments. Losses in efficiency due to AC?DC rectification and conditioning circuits limit its application. This work presents a low-loss hybrid rectification technique for piezoelectric vibration energy harvesting using magnetically actuated reed switches and a passive semiconductor full-bridge rectifier. This method shows the capability to have higher efficiency levels and the rectification of low-voltage harvesters without the need for active electrical components. A theoretical model shows that the hybrid rectification technique performance is highly dependent on the proximity delay and the hysteresis behavior of the reed switches. Experimental results validate the model and support the hypothesis of increased performance using the hybrid rectification technique.

Practical implementation of piezoelectric energy harvesting synchronized switching schemes

Many closed-loop control methods for increasing the power output from piezoelectric energy harvesters have been investigated over the past decade. Initial work started with the application of Maximum Power Point Tracking techniques (MPPT) developed for solar power. More recent schemes have focused on taking advantage of the capacitive nature of piezoelectric harvesters to manipulate the transfer of energy from the piezoelectric to the storage element. There have been a couple of main techniques investigated in the literature: Synchronous Charge Extraction (SCE), Synchronized Switching and Discharging to a Capacitor through an Inductor (SSDCI), Synchronized Switch Harvesting on an Inductor (SSHI), and Piezoelectric Pre-Biasing (PPB). While significant increases in harvested power are seen both theoretically and experimentally using powerful external control systems, the applicability of these methods depends highly on the performance and efficiency of the system which implements the synchronized switching. Many piezoelectric energy harvesting systems are used to power devices controlled by a microcontroller (MCU), making them readily available for switching control methods. This work focuses on the practical questions which dictate the applicability of synchronized switching techniques using MCU-based switching control.

Multi-Source Energy Harvesting Schemes With Piezoelectrics and Photovoltaics on an Avian Bio-Logger Draft

Solar energy harvesting possesses relatively high energy and power densities when compared to other energy harvesting methods. However, solar energy harvesting applications are severely limited by diurnal cycles and weather patterns. For biological applications, such as avian bio-loggers, the subject’s activity levels and location introduce further variability into the availability of solar energy. This work focuses on the challenges associated with developing a multi-source energy harvesting solution and overall power management system for an avian bio-logger. It uses an ATmega128RFA1 microcontroller along with lithium batteries and both a solar and piezoelectric energy harvester. The power management system and microcontroller operation were tested using a solar harvester.Copyright

Insight and Applications in Energy Harvesting from Bullets to Birds

Power requirements for microelectronics continue a downward trend and power production from vibrational power harvesting is ever increasing. The result is a convergence of technology that will allow for previously unattainable systems, such as infinite life wireless sensor nodes, health monitoring systems, and environmental monitoring tags, among others. The Laboratory of Intelligent Machine Systems at Cornell University has made many significant contributions to this field, pioneering new applications of piezoelectric energy harvesting, as well as contributing to harvesting circuitry and mechanical design theory. In this work, we present a variety of new applications for energy harvesting technology, including infinite life avian based bio-loggers, flutter induced vibrational wind power, and in-flight energy harvesting in munitions. We also present theoretical contributions to the field including an energy harvester beam design guide and multisource energy harvesting circuitry.

Multi-source energy harvester power management

Much of the work on improving energy harvesting systems currently focuses on tasks beyond geometric optimization and has shifted to using complex feedback control circuitry. While the specific technique and effectiveness of the circuits have varied, an important goal is still out of reach for many desired applications: to produce sufficient and sustained power. This is due in part to the power requirements of the control circuits themselves. One method for increasing the robustness and versatility of energy harvesting systems which has started to receive some attention would be to utilize multiple energy sources simultaneously. If some or all of the present energy sources were harvested, the amount of constant power which could be provided to the system electronics would increase dramatically. This work examines two passive circuit topologies, parallel and series, for combining multiple piezoelectric energy harvesters onto a single storage capacitor using an LTspice simulation. The issue of the relative phase between the two piezoelectric signals is explored to show that the advantages of both configurations are significantly affected by increased relative phase values.

Passive Multi-Source Energy Harvesting Schemes: Multiplicity of Piezoelectrics

Energy harvesting technologies present a solution to decreasing battery size and to the in-situ recharging of batteries in mobile devices or wireless sensor nodes. Combining multiple energy harvesters to power one system can increase the viability of potential designs as solutions for many applications. This work uses LTspice circuit simulations to examine passive circuit topologies for a multiplicity of piezoelectrics as a multisource energy harvesting solution. The simulation results show increases in the maximum instantaneous power seen on the storage capacitor for both a series and parallel circuit topology. There is also an increase in the available voltage level for the series topology. However, these increases in output power and voltage are sensitive to differences in the harvester outputs. Therefore, passive multi-source topologies present a viable solution for combining the energy from a multiplicity of piezoelectric harvesters.Copyright

Combined AC and DC Energy Harvesting Methods

Much of the work on ambient energy harvesting currently focuses on maximizing the efficiency of the power extraction method or increasing the power output. However, an important goal is still out of reach: to produce sufficient and sustained power for wireless sensor nodes and their associated components. Achieving this goal will significantly impact the fields of structural health monitoring, secure location surveillance and a multitude of other pertinent applications. While many energy harvesters can power these electronics with a constant energy source, most ambient sources for desired wireless sensor networks only provide intermittent energy. One method for increasing the robustness and versatility of energy harvesting systems would utilize multiple energy sources simultaneously. In order to achieve this, the problem of effectively combining multiple energy harvesting sources, specifically an AC and a DC source, is thoroughly explored with the experimental analysis of proposed circuit configurations. Also, a multi-source energy harvesting circuit configuration is proposed.Copyright