1. M OBILE P OWER S TATION IRP Presentation December 10 th 2010 Team: Brad Jensen William Klema Nathan Schares Advisor: Dr. Ayman Fayed Client: PowerFilm, Inc.

2. P LANNING P ROBLEM S TATEMENT & S OLUTION Photovoltaic (PV) solar arrays can be used to power mobile devices; however, solar array output power is non-constant and most mobile device chargers require a constant voltage and current source. Team dec1013 purposed building a MPS that would supply a constant voltage and current to mobile devices, while tracking the maximum power point of a PV solar array.

3. P LANNING C ONCEPT S KETCH Major Concepts MPPT DC-DC Charging Li-Ion Battery Charging Variable Source Batteries, 100W Charging circuitry MPPT Power Distribution Solar Panel Source 12V DC 120V AC Source (with AC/DC Adapter)

4. P LANNING M ARKET & U SERS MPS idea developed from market research by PowerFilm, Inc. MPS focused mainly on military market Designed to carry in backpack Simple user interface Connect source Foldable solar array AC/DC Adapter Connect load AC inverter 12VDC Device Light weight Efficient MPS also valid in consumer market

5. P LANNING R EQUIREMENTS FR-01Solar panel input – 1.2A @ 5.4V (20W) Amorphous Silicon Panel FR-02100W minimum Lithium-Ion battery capacity FR-0315V DC input (with AC-DC Adapter) FR-0412V DC output FR-05Operation in temperature range of -20°C and 60°C FR-06State of charge indicator FR-07Charge Balancing Circuitry to keep Li-Ion Batteries balanced FR-08 Achieve 80% or greater efficiency NFR-01 MPS should have a weight of less than 5 pounds NFR-02 MPS should be manufactured for a cost of under $500 per unit NFR-03 MPS should easily fit inside a military backpack D ELIVERABLES MPS prototype PCB with Li-ion batteries MPS poster MPS Final Report

6. P LANNING S CHEDULE

7. P LANNING R ESOURCES AND R ISKS Adequate lab space provided for development TI Analog Design Contest Free analog evaluation modules PCB fabrication and parts ECpE Parts Shop PowerFilm, Inc. Knowledge resources Dr. Fayed PowerFilm Brad Scandrett Frank Jeffrey Risks Short circuit Li-ion overcharge Unavailable parts

8. D ESIGN S YSTEM D ECOMPOSITION Li-ion Batteries (3 series cells x 8Ah) Buck Converter Microprocessor (MSP430) Solar Panel Source 5VDC (USB) 12VDC 120VAC Serial Communication (UART) to PC Voltage and Current Sense PWM Control Signal Charge Control (BQ20Z70) Feedback Voltage/Current Sense Possible Loads

9. D ESIGN S YNCHRONOUS B UCK C ONVERTER Synchronous rectification improves efficiency Eliminates voltage drop across safety diode D1 Controlled by FET driver IR2104

10. D ESIGN P SPICE S IMULATION Functionality Testing Parasitic inductance

11. D ESIGN MPPT & L I -I ON C HARGING Solar I-V CurveLi-Ion Charge Cycle

12. D ESIGN MSP430 M ICROPROCESSOR

13. D ESIGN H IGH S IDE C URRENT S ENSE,

14. D ESIGN L OW S IDE C URRENT S ENSE,

15. D ESIGN V OLTAGE S ENSE,

16. D ESIGN GUI & MPS C OMMUNICATION UART Comm. (via USB) Live reporting & plotting Processing (Java) All measured values Voltages Currents Duty cycle Charging state Debugging tool Demonstration tool

17. D ESIGN L I -I ON B ATTERY B ALANCING T EXAS I NSTRUMENTS - BQ20Z70 I MPEDANCE T RACK BALANCING ALGORITHM BQ E VALUATION SOFTWARE INCLUDED

18. I MPLEMENTATION & T ESTING B READBOARD Test functionality of buck converter Used signal generator for PWM (100 kHz) Successfully bucks DC voltage Varying duty cycle Connected buck converter and MSP430 MSP430 controls duty cycle Reset problem Breadboard adapters used for ICs

19. I MPLEMENTATION & T ESTING B READBOARD T ESTING Voltage transients Parasitic Inductance MOSFET Switching Snubber RC filter GROUNDING! Transients caused inaccurate voltage/current readings Fought issues for three weeks Solution? Design and fabricate PCB with large grounding plane

20. I MPLEMENTATION & T ESTING PCB R EV. 1 Designed with EagleCAD No solder mask for mods. Transient voltage problem fixed with ground plane! Accurate voltage and current readings Used low-ESR components Surface-mounting components eliminates noise Problem with differential amplifier used for measuring high-side current Insufficient common-mode voltage input range Solution? Differential amplifier with rail-to-rail common-mode voltage input. PCB Rev. 2

21. I MPLEMENTATION & T ESTING PCB R EV. 2 PCB Changes: Updated high-side current sense differential amplifier. Zener diode protection Solder mask One connector for both programming and UART Resume calibration and testing e

22. I MPLEMENTATION & T ESTING C ALIBRATION Sweep duty cycle range and record serial data for: Solar input voltage and current Battery voltage and current Load current (30Ω load resistor) Import data to excel and run macro to take linear regression and convert serial data to actual voltage and current readings. e

23. I MPLEMENTATION & T ESTING T ESTING Start with power supply: Constant V & I Variable V & I Monitor output V & I Measure efficiency Practice charging algorithm on lead-acid battery (more forgiving) Trickle charge if pack voltage is less than 9V Constant current mode (≤ 500mA) & MPPT Constant voltage mode (12.6V) Shut down if: Battery pack current (≤ 100mA) AND Load current (≤ 100mA) e

24. I MPLEMENTATION & T ESTING T ESTING ( CONT ’ D ) Connect PowerFilm Solar array Power solar array and tested on few sunny days Fine tuned MPPT algorithm Verified all charging states Connect Li-ion battery Charged pack using MPS Monitor cell balancing with TI software and MPS GUI Power external load Warmed resistors LED lamp Laptop through inverter e

25. F INAL R EMARKS C ONCLUSION Many lessons learned Technical Breadboards are terrible for certain circuits. Use only to test functionality. PCBs, surface mount components, and large ground plane help transient and noise problems. Never assume parts will work as planned. GUIs and Macros are tools that make life easier. Management Utilize talents. Stick to schedule. Establish ambitious goals. Take lots of picture and screen shots. Documentation is just as important as the product.

26. M OBILE P OWER S TATION Thank You: Dr. Ayman Fayed Brad Scandrett Frank Jeffrey Dr. Daji Qiao CSG PowerFilm Inc. ECpE Faculty & Staff Texas Instruments C2 Development