P11401: Portable High Power-Density Energy System
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Select Product Concept(s)

Table of Contents

This page shows the steps taken in the concept selection process.

1. ENERGY HARVESTING CONCEPT SELECTION

Many ideas for energy capture methods were brainstormed. The most feasible potential solutions for MSD are listed below.

These solutions were evaluated in a concept selection matrix in order to narrow down the concepts that best satisfy our customer needs. Customer needs were listed as selection criteria, and each concept was evaluated on a scale indicated in the legend. The concept selection matrix for energy harvesting methods is shown below. Click on the image for a larger view.

ENERGY HARVESTING CONCEPT SELECTION MATRIX

ENERGY HARVESTING CONCEPT SELECTION MATRIX

Based on the selection matrix, the concepts that most satisfy the customer needs are hand crank, foot crank, piezo electric, wind energy, and solar energy. These concepts were then evaluated in a screening matrix to determine the best option based on a weighted ranking system. In the screening matrix shown below, the customer needs were each assigned a weight value on the scale of 1,3,9 based on the needs ranking established early on in the customer needs page. Each concept was then ranked on this 1,3,9 scale according to how strongly the concept satisfies that need. A product of the need weight and the concept weighting was obtained for each concept, and the sum was totaled at the bottom. Click on the image for a larger view.

ENERGY HARVESTING SCREENING MATRIX

ENERGY HARVESTING SCREENING MATRIX

Detailed Analysis of Performance Capability

Based on the screening matrix, the concepts that most satisfy the customer needs are hand crank and wind energy. Solar energy has a very close ranking with wind energy. Because of this, extra steps were taken to evaluate the potential advantages of one over the other.

The performance of wind energy and solar energy were analyzed using historical data of weather pattern trends for Rochester, NY. Based on calculations shown in the Excel and Word document file links below, it was determined that wind energy will provide us with a more readily available energy source when it comes time to do proof of concept for our design project. Matlab was used to create Simulink diagrams that run calculations for expected power (Watt hours) for each month of the year. The chart trends and Simulink diagrams can be viewed in the WIND VS SOLAR ANALYSIS.

The WINDPOWER ANALYSIS is an Excel file that shows the expected distribution of windspeed at varying heights in Rochester, NY (historical wind data provided by the New York State Energy Research and Development Authority). The analysis examines the probability of wind speeds at varying height levels, as well as the power in the wind and power that can be captured from this wind energy. The file shows that a windspeed of 4.5 m/s at a height of 3 meters will yield about 20 Watts of instantaneous power, assuming a power capture efficiency of 20% and a blade diameter of 1.5 meters. This wind speed will allow for more than enough power to reach the target value of 5 Watts needed for the WOCCS transceiver modules. According to our analysis of a small off the shelf wind turbine generator, typical moderate wind speeds can be used to generate electrical power values in the range of 50 Watts to 500+ Watts. Click link to view this GENERATOR ANALYSIS. This capability makes the idea of a wind powered generator a very feasible option not only for this project in powering the WOCCS modules, but also for the project roadmap with greater power requirements in sight.

The SOLAR ANALYSIS is an Excel file that reads information from the government issued TMY3 solar data. This data can be accessed at http://rredc.nrel.gov. In the analysis, a good sunny day in February is selected and analyzed to determine the total solar radiation available. The end of February is chosen because this is the time when our project proof of concept will be made. The analysis shows that on a sunny day in February, the total solar insolation reaches about 950 Watts/m^2. This total is a summation of direct beam radiation, diffuse radiation, and reflected radiation. Assuming an efficiency of 15% for solar photovoltaics, the edge length of a solar panel would need to be about 40 cm (or 1.3 feet) in order to achieve an instantaneous power level of 20 Watts. The value of 20 Watts in this case was chosen as a means of comparison with wind energy at 4.5 m/s. To achieve power levels of 50 Watts, the size of the solar panel length would need to be about 60 cm, or about .36 square meters. This size is pushing the threshold of portability.

Concepts Selected

The top two concepts, wind turbine and hand crank, can be combined in the sense that the hand crank can be used in place of the wind turbine during times of low/no wind. This would provide for a more versatile energy generation system applicable to multiple environments and circumstances.

Energy Harvest Concepts:

2. Energy Conversion

Energy Conversion Block Diagram

Energy for this project will need to be converted if a PM Synchronous Generator is used.

Problems:

1) The generation device will be providing mechanical power to a PM synchronous generator. The output of the generator will be in the form of 3-phase AC power. This must be converted to DC in order to charge the lithium ion batteries.

2) The design of the power electronics is dependent on whether the windmill will be operating as a fixed-speed or variable-speed device.

Solutions:

1) Use a Controllable rectifier circuit configuration. In this configuration the rectifier will be triggered on when a specific voltage is detected at the gates of various different SCR's (Silicon Controlled Resistors).

3 Phase Controlled Rectifier

3 Phase Controlled Rectifier

2) Use a normal 3-phase rectifier, and then send the output to a DC-DC converter. This could be a buck, buck-boost, boost, or flyback converter. This portion of the circuit would act as the voltage regulator or controller.
3 Phase Rectifier with DC/DC Converter

3 Phase Rectifier with DC/DC Converter

3) Use a PWM Controlled rectifier. This design is built with semiconductors with gate-turn off capability. This allows full control of the converter because valves can be switched on and off whenever required. This allows switching cycles to be much faster than in standard 3 phase controllable rectifiers. The advantage is the current or voltage can be modulated and the power factor can be controlled.

PWM controlled rectifier

PWM controlled rectifier

4)Use an uncontrolled 3 phase rectifier and utilize a capacitor to keep the voltage steady. The use of an external DC/DC converter may be unnecessary.

PWM controlled rectifier

PWM controlled rectifier

A second problem is changing the voltage the AC-DC converter puts out to a usable voltage

Solutions:

  1. Using a Boost or Buck Converter
    1. Advantages
      1. Easiest to understand
      2. Requires the least amount of parts
      3. Most Efficient
    2. Disadvantage
      1. Have to make sure that voltage is always higher or lower then the desired output
  2. Using a Buck-Boost Converter
    1. Advantages
      1. The input voltage can be higher or lower then the output voltage
    2. Disadvantage
      1. The positive input creates a negative output
      2. Less Efficient
  3. Using SEPIC
    1. Advantages
      1. The input voltage can be higher or lower then the output voltage
      2. A positive inputs creates a positive output
    2. Disadvantages
      1. Less Efficient

A third problem is what happens when the wind dies?

The wind could stop for a period of time.

A supercapacitor could be put in place so that it could store energy in the event that the wind stops. It sounded good until the battery would need approximately 40W Hours. Meaning a total of 144000 joules of energy. For a capacitor E = .5CV^2. Typical super capacitors are on the order of 5V and 1F is a big capacitor! So it is almost impossible to do it with a super capacitor.

3. Energy Storage

The converted DC voltage will be used to charge a battery. The battery used to store the generated energy will be a lithium ion battery. This is a given non negotiable criteria for this project.

There are different options available for choosing a lithium ion battery type.

These battery type concepts were evaluated using the concept selection matrix shown below. A positive, neutral, negative rating scale was used to narrow down the concepts that are most feasible for our project in providing power to our primary customer, the WOCCS family. Click image to view larger.

BATTERY CONCEPT SELECTION MATRIX

BATTERY CONCEPT SELECTION MATRIX

Based on the selection matrix above, we narrowed the concepts down to a generic battery pack, a military grade battery, and lithium ion battery cells with battery protection design. These concepts were evaluated based on a weighted ranking scale similar to the energy harvesting screening matrix. The battery selection screening matrix is shown below. Click image to view larger.

BATTERY SCREENING MATRIX

BATTERY SCREENING MATRIX

The concept selected for battery type is a generic battery pack that can be purchased off the shelf.


A Power Pack From a Laptop Company (Gateway)

A Military Grade Battery

A Li-Ion Battery Cell and Make Our Own Pack

4. ENERGY DELIVERY

Another set of concept options that was evaluated for this project was power conversion location. The energy that we harvest needs to be converted into a form of power that can be used by the WOCCS wireless system. The power electronics need to be placed in a location that best meets the WOCCS family needs. The concepts evaluated were the following:

POWER ELECTRONIC PLACEMENT CONCEPT SELECTION

POWER ELECTRONIC PLACEMENT CONCEPT SELECTION

Based on the selection matrix above, all options except option A were continued for further evaluation in a ranking matrix. This ranking matrix is shown below.

POWER ELECTRONIC PLACEMENT CONCEPT SELECTION

POWER ELECTRONIC PLACEMENT CONCEPT SELECTION

The screening matrix was weighted based on a 1,3,9 rating scale. Heaviest weight was assigned to the selection criteria that are most critical. Each concept was evaluated on this same rating scale based on how well that concept meets the criteria. The concept that most meets the needs of this project is to place the power electronics in their own compartment inside the module created by the WOCCS packaging group.


Where do we put the Power Electronics?

  1. On the Board of another Group
    1. Advantage
      1. Save on Efficiency of the transfer of wire.
        1. If we used a 24 gauge wire: The resistance of a foot is .02. If we were going 3 inches the resistance would be .005. The efficiency lost would be .5%.
      2. Save on Board Space
      3. Allow each RF group to have different voltage requirements
    2. Disadvantage
      1. A switching power supply very close to the RF receiver which will most likely jam it.
  2. On its own Board
    1. Advantage
      1. Would be able to isolate the Board from the RF Board
      2. Allow the Power Group to handle the Board where it would have been a efficient between all the groups
    2. Disadvantage
      1. Not as cost efficient
      2. Will have to be a universal Board

Due to the large possibility of the Power Electronics jamming the RF groups it is better for the Power electronics to have its own board.

Where do we put the Board?

  1. In its own compartment in the Package (having a shield around it)
    1. Advantages
      1. Only need one package (Except for the Battery Pack)
      2. Will not be needing to replace the power electronics so putting in its own compartment is fine
    2. Disadvantages
      1. Will have to build a shield within the box.
  2. In its own Package
    1. Advantages
      1. Allows the possibility to replace the power electronics
      2. Can fully isolate the Board from the RF circuitry
    2. Disadvantages
      1. Extra Package
  3. In the Battery pack's package
    1. Advantages
      1. Having all the Power electronics in one box so the groups are not as dependent on each other
    2. Disadvantages
      1. Would need a set of power electronics for every battery that you have

Decided to go with a small shield box within the overall package. That way it is more secure and we don't have to have more boxes hanging of each other.

A display is desired so the user can tell if the battery is going low. A display is desired vs. LCDS because you can show the battery's various stages of dissipation. There are two options:

Monitoring Battery Levels Using a Chip

Monitoring Battery Levels Using a Chip


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