Solar-Powered Mobile Power Station (MPS)

1. Solar-PoweredMobile Power Station (MPS) • Team: • Brad Jensen • Will Klema • Nate Schares • Client: • PowerFilm, Inc. • Advisor: • Dr. Ayman Fayed

2. Problem Statement • Create a portable device that allows users to store solar energy to operate and charge their devices in remote locations. The device must also be capable of charging from an external source (AC).

3. Conceptual Sketch

4. Use-Case Scenario • Military: • Individual Soldier Power Source • Charge Laptop, GPS, etc. • Commercial: • Camping/Remote Destination • Personal electronics charging

5. Functional Requirements • Optimized for standard Solar Panel input – 4A @ 15V (60W) Amorphous Silicon Panel • 100W minimum Lithium-Ion battery capacity • 12V DC input (with AC-DC Adapter) • Outputs: • 5V USB output (USB 2.0 output) • 12V DC output • 120V AC output with switch • Circuitry must be able to function in a temperature range of -25° C and 60°C • Charging LED Indicators/state of charge indicators • Charge Balancing Circuitry to keep Li-Ion Batteries balanced to prevent over or under charging • Temperature sensor for batteries with alarm LED • Achieve 80% or greater efficiency on all outputs • MPPT Charge controller with rating of up to 200W (12A @ 15V – PowerFilm Solar Quad) (optional)

6. Non-Functional Requirements • The MPS shall be designed mainly for military soldier use • The MPS should also be designed with options for commercial use • The unit should have a weight of less than 5 pounds • Unit should be manufactured for a cost of under $500 per unit • The unit should easily fit inside a military backpack

7. Potential Risks and Mitigation • Overheating • AC Inverter • Climate Conditions • Battery Charging • Electrical Shock • AC Voltage • Overcharging Li-Ion Batteries • Hydrogen gas build up • Explosions • Li-ion very sensitive to overcharge • Mitigation • AC Circuit Breaker • Monitor Battery Temp. • Charge Balancer

8. Deliverables • Upon completion of the project, the team will provide: • Project Plan • Design Document • MPS prototype and PCB – Populated and tested for functional requirements • Schematic diagram • Operational manual • Final report

9. Work breakdown • Communication Liason: Brad Jensen • Worked with PowerFilm Engineers • Buck Converter Design • Research MPPT & Buck Converter • Schematic Design • Team Leader: Nathan Schares • Organized meetings, Weekly Updates • Ordered Parts • Buck Converter Design • Research MPPT & Buck Converter • Webmaster: Will Klema • Designed & Updated Website • MSP430 setup • UART Communication • PWM • MPPT Algorithm

10. Cost Estimate

11. Costs to Date

12. Schedule

13. System Decomposition Solar Panel Source Buck Converter • Fart External Power Sources (5VDC, and 12VDC) Voltage and Current Sense PWM Control Signal Feedback Voltage Sense Microprocessor (MSP430) Charge Control (BQ78PL114) Power Distribution Circuitry 5VDC (USB) 12VDC Li-ion Batteries 120VAC

14. Maximum Power Point Tracking • Optimized for standard Solar Panel input – 4A @ 15V (60W) Amorphous Silicon Panel

15. Buck Converter • Convert panel voltage (14-17) volts to approx. 12.5 volts for charging 3 cell Li-Ion batteries • Impedance matching for maximum power • Capable of delivering up to 4 Amps from solar arrays (8A output) • 100 KHz switching frequency • Microprocessor controlled (MSP 430 , Texas Instruments)

16. Buck Converter Schematic

17. Buck Converter Calculations Voltage and Current ripple calculations:

18. MSP 430 • 16 bit ADC (3 channels) • PWM generation with Timer A • UART communication • MPPT algorithm development

19. MSP 430 Voltage Sense: Current Sense:

20. Charging Circuitry • BQ78PL114 Li-Ion charging chip , Texas Instruments • Originally built for charging electric car batteries • Capable of charging and delivering high currents

21. Schematic

22. Test Plan • An open circuit will be created on both the input and the output of the buck converter to enable measuring Input and Output current  Power efficiency can be deduced  Target is 90% • An oscilloscope and LabView software will be used to measure both the output current and voltage ripple  to ensure operation is within the specified limits • Two full discharge/charge cycles will be run on the batteries to assure that the Li-Ion charging chip meets safety standards  load is provided by Powerfilm as well as a purely resistive load. • Using the oscilloscope and LabView software we will measure the PWM output of the MSP430  to test the control loop stability and input/load regulation.

23. Project Milestones • May 7, 2010 – Test buck converter using microprocessor and Li-Ion charging evaluation board (Testing functionality) • Summer Break – Work on improving MPPT Algorithm, Finalize schematic layout and begin PCB layout • September 10, 2010 – Test the design using phase one testing procedure • October 29, 2010 – Finalize design, create deliverables • November 19, 2010 – Submit Final Report

24. Current Status • Evaluation module phase • Built Buck Converter • Tested Buck Converter with varying duty cycles • Microprocessor Coding • PWM generation with Timer A • USART Setup • Began MPPT Algorithm • Li-Ion Charging • Program and test Li-Ion charging chip during Finals week

25. Plan for next semester • Charging Chip • Program Battery Parameters • Integrate into buck-converter • MSP430 • Implement MPPT algorithm • Ensure buck-converter stability • Determine MPPT sweep frequency • MPS Inputs/Outputs • Select DC/DC output converters • Select 12V DC to 120V AC inverter • Integrate input charging priority system