The purpose of the following worksheet is to document the EE/CPE Design project, design team, and faculty mentor, prior to beginning the course.

1. High-level project description (problem solved by design and functionality).

There are many situations where power sources are limited (remote locations, construction areas) in size and capability. This leads, first off, to small power sources being incapable of handling peak demands or incapable of maintaining voltage regulation during quick load changes. Secondly, unnecessarily heavy, bulky, and expensive portable power sources are often used to handle larger loads.
This project seeks to eliminate both problems by allowing a user to combine the power output of multiple power sources to drive a single load. This would be useful, for example, to combine the output capability of two or more small, easily portable generators to drive a single large load. The power sources could be AC or DC, different voltages, and different frequencies. Additionally, the electronic voltage regulation should react to changing load conditions faster than a mechanical generator, maintaining better regulation during quick load changes.
For this project, the output inverter will not necessarily be implemented. This component is readily available off-the-shelf, but is cost-prohibitive for college students. If one is available, however, we will use it for demonstration purposes. If an inverter is not available the output will be a regulated DC bus tested with a resistive DC load (hair dryer heater wire).
For practical use, this device would operate in the kW range. However, for proof-of-concept, this prototype device will operate in the sub-kW range. The technology should easily scale with more resources.



2. A brief discussion of relevant technical background material on which the project is based (identify at least 3 published references).

Website with good overview of dc-dc converter topologies
http://www.hills2.u-net.com/electron/smps.htm

TI App note slup126 - DC-DC converter transformer design
http://focus.ti.com/lit/ml/slup126/slup126.pdf

TI App note slup127 - DC-DC converter inductor design
http://focus.ti.com/lit/ml/slup127/slup127.pdf

TI App note slup232 - Digital control of DC-DC converters
http://focus.ti.com/lit/ml/slup232/slup232.pdf

Fairchild Semiconductor App Note AN-4134 - Forward converter design
http://www.fairchildsemi.com/an/AN/AN-4134.pdf

A procedure for designing EMI filters for AC line applications
Fu-Yuan Shih Chen, D.Y. Yan-Pei Wu Yie-Tone Chen
Dept. of Electr. Eng., Nat. Taiwan Univ., Taipei ;
This paper appears in: Power Electronics, IEEE Transactions on
Publication Date: Jan 1996
Volume: 11, Issue: 1
On page(s): 170-181



3. Projects are evaluated, in part, on the inclusion of a number of the following "real-world" concerns. Provide preliminary comments on how these issues relate to your design.

Economic:

This project's primary focus is economic. This design would allow multiple small, cheap power sources to replace one large one. This improves reliability (through redundancy), reduces equipment cost, and reduces transportation cost.


Environmental:

If combined with alternative energy, this project could allow a normally inadequate system to participate in providing power thus allowing alternative energy sources to be used where they normally could not be considered.


Sustainability:

This device will be overrated for the task and include safety cutoff features for long equipment life.


Manufacturability:

This device should be at least as manufacturable as a COTS inverter.


Ethical:

(none)


Health and Safety:

Safety is a major concern for a project designed to handle mains power. UL guidelines concerning insulation, power rating, and conductor separation will be respected. The input sources will be galvanically isolated from the output DC bus as well as the other input sources.


Social:

(none)


Political:

(none)


4. More detailed description of hardware and software design components (both hardware and software design are required for CPE students and both are strongly encouraged for EE students).


  • Hardware:

    • Input power filters

      • Reduce ripple and non-linear current harmonics seen by generator

    • 2x DC-DC converters for input power regulation to the DC Bus

      • Isolated topology, 300W each, for a maximum combined output of 600W

        • Voltage will be regulated by software

        • Maximum current will be limited to 12.5A, yielding 300W each for 24VDC output, or 450W each for 36VDC output

      • Must be capable of 90-300VAC 50-200Hz input

        • 120VAC 60Hz will be tested, other combinations will be guaranteed by design

      • DC Input option will be investigated

    • AC Inverter

      • Optional component (due to cost)

      • COTS inverter, ideally 1 kW +


  • Software:

    • Microcontroller-based DC-DC converter control

      • Maintain constant DC Bus voltage

      • Voltage will be 24-36 VDC dependent upon inverter chosen

      • regulated within 10% nominal value

      • maintain 10% or less ripple

      • Monitor current contribution of each power source

        • Programmable UVLO, Power Limit

      • Balance current contribution of the sources according to a profile

        • Percentage Load Sharing, Backup



5. Vision for participation in project by team members.

Members mentioned below are in charge of a particular section. Although these members will likely be the primary contributor to his section, all members will participate in all aspects of this project both for the learning experience and to ensure adequate safety considerations are made.

Power Filters: Tyler
DC-DC Design: Chris
DC-DC Layout: Chris
DC-DC Performance Evaluation: Tyler
Board Integration: Chris
Mechanical Enclosure: Chris
Physical User Interface: Tyler
Software - control loop: Daniel
Software - load balancing: Daniel
Software - User Interface: Daniel



6. Preliminary schedule of what you are planning to do and discussion of feasibility.

Hardware

* August 31st, 2008: Choose converter topology, have simple spice simulations showing feasibility
* September 15th, 2008: Complete hardware design, complete spice simulations including filtering showing adequate feasibility, failsafe, and margins
* October 6th, 2008: Demonstrate basic system functionality in the lab with one controller, start work on board design
* October 15th, 2008: Finalize board design, order boards and parts for three units (need 2)
* November 17th, 2008: Must have two boards functional
* December 1st, 2008: Both boards working as a pair


Software

* August 31st, 2008: Complete software flow diagram for system functionality, including voltage regulation, control, and balancing for both converters
* October 6th, 2008: Complete software functionality for one controller, demonstrate basic functionality in the lab
* November 17th, 2008: Finalize software, functionality for two controllers including load balancing


Second semester

* January-April 2009: Enclose the system, tweak and complete software functionality, complete business plan