Mechanical Engineering
Steve Haldezos
Electrical Engineering
Charles Conway
Patrick Kalagher Patrick Vicente
Faculty Advisors:
Dr. Bryan Weber Dr. Peng Zhang
Dr. Shengli Zhou

Introduction / Background :
The UCONN School of engineering Power and Energy Systems Lab is developing a network of Autonomous Underwater Vehicles (AUV) to maintain and recharge underwater communications equipment. The AUV’s will need periodic recharging; an ocean going Wave Energy Converter (WEC) buoy design is needed to provide a ready supply of electricity for the fleet of AUV’s.
Oceans cover 75% of the e arth’s surface; its energy is continuously replenished by the sun and tides, which creates ocean currents, wind and waves. Research indicates that 0.1% of the ocean contains more than 5 times the worlds energy demand. Oceanic energy provides high power density, high availability and energy conversion of both kinetic and potential energy in an ocean wave.
There are different types of wave generators including direct drive linear generators, air or water breathing turbines, hydraulic cylinder pumps as well as many other non-conventional systems currently being developed.
During the summer of 2014 an undergraduate research project developed a functioning WEC. The generator used direct drive linear generator technology to reduce the number of moving parts, reduce cost and simplify construction. The initial prototype worked, however the power output was around 2W, which is inadequate for charging the needed batteries to maintain the AUV fleet.
Preliminary requirements:
The team is tasked with scaling the device up to produce 10 to 12W and build a power electronic converter system that is able to regulate the input power and charge or discharge a battery. Additionally, external power harnessing devices such as solar panels will be added to the linear drive system. The design process will require a detailed survey and materials from the current WEC technologies.
The team will need to collect data from current oceanic buoys to properly analyze the physical environment that the WEC will operate in. Analysis of the data will dictate additional design parameters. A list of additional design parameters is as follows.
Necessary Project Requirements:
1.
Harness wave energy and convert into electricity
2.
Designing a power conversion system
3.
Store power received into a battery
4.
Protect delicate internal electronics from harsh marine environment
5.
Device must be easy to maintain and install
6.
Device must be able to transmit data collected wirelessly to a computer for analysis
7.
Design and construct a test rig for WEC

Based on the above list of design parameters, a list of constraints was also developed. Many of the constraints are recognized, but not completely understood at this point.
Design Constraints:
1.
Limited Budget – at this point the EE department has committed $2000 to the project, the team awaits the financial contribution of the ME department.
2.
The Marine Environment – the device must be able to withstand submersion on corrosive salt water, keep the delicate internal components protected from the elements. Weather also plays a major role in the difficult environment, large waves, high winds, sub zero temperature
3.
Wave Irregularity - the randomness of the ocean environment may create problems in simulating the operations of the device with mathematical models.
4.
Device Scale - The device is projected to be approximately 10 feet in height and the construction of this device will require a workbench of appropriate size. Transport for testing, as well as finding an appropriate testing location could be an issue.
5.
Maritime laws could cause limit the use and testing of the device. Research would be required in such laws.
Solution
The linear wave power generator will output an AC waveform. We will most likely be using a 12 battery to store energy. So we want to design the generator so that the average AC peak voltage value based on normal wave conditions is a little above 12 volts. This will produce a dc voltage value of approximately 12 volts after rectification and losses associated with that. For full bridge rectification the signal will need to pass through 2 diodes that each use up 0.7 volts. The waveform will thus lose at least 1.4 volts. After the rectification the waveform will also need to undergo low pass filtration and undergo additional loses. The total loses are thus going to be approximated to be 2 volts. So we will design a system that produces an average AC peak value of 14 volts based on average wave conditions. Doing this means that the power electronics will be able to do the least amount of work possible.
Based on this information and average wave period in the area where we will be deploying our buoy (2.5 seconds for a frequency of 2.513 radians per second) the following graph was made for the voltage signal coming from the generator.

Graph 1. Output AC voltage signal directly from the coils of the wave power generator
This signal will then pass into a full bridge rectifier depicted by the following schematic.
Schematic 1. Full bridge rectifier
Here it will lose about 1.4 volts and the signal output will look like the following.

Graph 2. Voltage output from rectifier.
Notice after the rectifier it is a DC waveform but it is oscillating quite a bit. We want to smooth out this waveform by low pass filtering it. What will happen after low pass filtering is the voltage signal will look much more like a smooth line but will have what is called (ripple current) due to the series inductor slightly over compensating for each up and down of the waveform. The following shows the low pass filter circuit and a depiction of the output waveform after the LPF.

Schematic 2. Low pass filter circuit.
Graph 3. Depiction of ripple current.
After the LPF the waveform will be approximately a line at the 12 volts value with a slight ripple.
After this stage the power will be sent to a DC-to-DC buck boost converter that will make sure the voltage felt across the terminals of the battery is constantly at 12 volts.

Schematic 3. Simple depiction of a DC-to-DC buck boost converter
A buck boost converter is a simple device that employs the use of semiconductor switching devices, inductors, and capacitors, to either increase or reduce the current flow to maintain voltage at the output. Another important aspect of these converters is the power in equals the power out.
The complicated part is the controller for the buck boost converter. This controller will be a device that adjusts the frequency inputted to the switching devices to control how quickly they turn on or off.
We are using an MPPT controller, which stands for Maximum power point controller. This kind of a controller is perfect for this system because they are designed to adjust the voltage to deliver the maximum power possible when charging a batter.