MOBILE POWER STATION

IRP PresentationDecember 10th 2010

Team:Brad Jensen

William KlemaNathan Schares

Advisor:Dr. Ayman Fayed

Client:PowerFilm, Inc.

PLANNING

PROBLEM STATEMENT & SOLUTION 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.

PLANNING

CONCEPT SKETCH • 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)

PLANNING

MARKET & USERS• 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

PLANNING

REQUIREMENTSFR-01 Solar panel input – 1.2A @ 5.4V (20W) Amorphous Silicon PanelFR-02 100W minimum Lithium-Ion battery capacityFR-03 15V DC input (with AC-DC Adapter)FR-04 12V DC outputFR-05 Operation in temperature range of -20°C and 60°CFR-06 State of charge indicatorFR-07 Charge Balancing Circuitry to keep Li-Ion Batteries balancedFR-08 Achieve 80% or greater efficiencyNFR-01 MPS should have a weight of less than 5 poundsNFR-02 MPS should be manufactured for a cost of under $500 per unitNFR-03 MPS should easily fit inside a military backpack

DELIVERABLES• MPS prototype PCB with Li-ion batteries• MPS poster• MPS Final Report

PLANNING

SCHEDULE

PLANNING

RESOURCES AND RISKS• 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

DESIGN

SYSTEM DECOMPOSITION

Li-ion Batteries(3 series cells

x 8Ah)Buck Converter

Microprocessor (MSP430)

Solar Panel

Source

5VDC (USB)

12VDC120VAC

Serial Communication (UART) to PC

Voltage and Current Sense

PWM Control Signal

Charge Control(BQ20Z70)

Feedback Voltage/Current

Sense

Possible Loads

DESIGN

SYNCHRONOUS BUCK CONVERTER• Synchronous rectification improves efficiency

• Eliminates voltage drop across safety diode D1• Controlled by FET driver IR2104

DESIGN

PSPICE SIMULATION• Functionality• Testing• Parasitic inductance

DESIGN

MPPT & LI-ION CHARGING

Solar I-V Curve Li-Ion Charge Cycle

DESIGN

MSP430 MICROPROCESSOR

DESIGN

HIGH SIDE CURRENT SENSE

,

DESIGN

LOW SIDE CURRENT SENSE

,

DESIGN

VOLTAGE SENSE

,

DESIGN

GUI & MPS COMMUNICATION• UART Comm. (via USB)

• Live reporting & plotting• Processing (Java)

• All measured values• Voltages• Currents• Duty cycle• Charging state

• Debugging tool

• Demonstration tool

DESIGN

LI-ION BATTERY BALANCING•TEXAS INSTRUMENTS - BQ20Z70

•IMPEDANCE TRACK BALANCING ALGORITHM

•BQ EVALUATION SOFTWARE INCLUDED

IMPLEMENTATION & TESTING

BREADBOARD• 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

IMPLEMENTATION & TESTING

BREADBOARD TESTING• 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

IMPLEMENTATION & TESTING

PCB REV. 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

IMPLEMENTATION & TESTING

PCB REV. 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

IMPLEMENTATION & TESTING

CALIBRATION• 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

IMPLEMENTATION & TESTING

TESTING• 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

IMPLEMENTATION & TESTING

TESTING (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

FINAL REMARKS

CONCLUSION• 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.

MOBILE POWER STATION Thank You:

• Dr. Ayman Fayed• Brad Scandrett• Frank Jeffrey• Dr. Daji Qiao

• CSG• PowerFilm Inc.

• ECpE Faculty & Staff• Texas Instruments• C2 Development