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.
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.
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.
The U.S. Department of Energy (DOE) proposes to meet 20% of the nation's energy needs through wind power by
the year 2030. To accomplish this goal, the industry will need to produce larger (>100m diameter) turbines to
increase efficiency and maximize energy production. It will be imperative to instrument the large composite
structures with onboard sensing to provide structural health monitoring capabilities to understand the global
response and integrity of these systems as they age. A critical component in the deployment of such a system will be
a robust power source that can operate for the lifespan of the wind turbine. In this paper we consider the use of
discrete, localized power sources that derive energy from the ambient (solar, thermal) or operational (kinetic)
environment. This approach will rely on a multi-source configuration that scavenges energy from photovoltaic and
piezoelectric transducers. Each harvester is first characterized individually in the laboratory and then they are
combined through a multi-source power conditioner that is designed to combine the output of each harvester in
series to power a small wireless sensor node that has active-sensing capabilities. The advantages/disadvantages of
each approach are discussed, along with the proposed design for a field ready energy harvester that will be deployed
on a small-scale 19.8m diameter wind turbine.
Environmental concerns coupled with the depletion of fuel sources has led to research on ethanol, fuel cells,
and even generating electricity from vibrations. Much of the research in these areas is stalling due to expensive
or environmentally contaminating processes, however recent breakthroughs in materials and production has
created a surge in research on waste heat energy harvesting devices. The thermoelectric generators (TEGs) used
in waste heat energy harvesting are governed by the Thermoelectric, or Seebeck, effect, generating electricity
from a temperature gradient. Some research to date has featured platforms such as heavy duty diesel trucks,
model airplanes, and automobiles, attempting to either eliminate heavy batteries or the alternator. A motorcycle
is another platform that possesses some very promising characteristics for waste heat energy harvesting, mainly
because the exhaust pipes are exposed to significant amounts of air flow. A 1995 Kawasaki Ninja 250R was used
for these trials. The module used in these experiments, the Melcor HT3-12-30, produced an average of 0.4694 W
from an average temperature gradient of 48.73 °C. The mathematical model created from the Thermoelectric
effect equation and the mean Seebeck coefficient displayed by the module produced an average error from the
experimental data of 1.75%. Although the module proved insufficient to practically eliminate the alternator on a
standard motorcycle, the temperature data gathered as well as the examination of a simple, yet accurate, model
represent significant steps in the process of creating a TEG capable of doing so.