Field Sustainment Power ConditioningField Sustainment Power Conditioning #TA3-04-5#TA3-04-5 (Solar Battery Chargers) (Solar Battery Chargers)

Brad Lehman, Northeastern UniversityBrad Lehman, Northeastern UniversityKhalil Shujaee, Clark Atlanta UniversityKhalil Shujaee, Clark Atlanta UniversityWes Tipton, Army Research LaboratoryWes Tipton, Army Research Laboratory

George Frazier, SAIC (Year 5 - helping with technology transfer)George Frazier, SAIC (Year 5 - helping with technology transfer)

Presentors: Khalil Shujaee (CAU) and Florent Boico (NU)

Presented at CTA Conference:

June 2, 2005

Motivation/BackgroundMotivation/Background

• Background– Dept. Army recently mandated that all training exercises must use

rechargeable batteries;– Estimated to save $70M annually (versus non-rechargeable);– About 75% of Army rechargeable batteries are BB390 NiMH (4lbs). (BB390 has

2 x 12V legs and can be used as either 24V or 12V battery.)

• Motivation for Solar Chargers

– Soldiers carry four BB390 batteries (= 16 lbs) for portable electronic equipment;

– Forward field observers, scouts, special ops, are constrained to stay within 10 miles of TOC (Tactical Operation Center where there is a charging facility shelter);

– Portable solar arrays carried by soldier (~1lb) reduce number of batteries carried and eliminate the need to stay near TOC.

TOC

Operation area

10 mi.

Spare batteries, generator ,Chargers, shelter, etc.

Soldiers using batteries

Solar Charging BB390Solar Charging BB390

– Companies have attempted to work with CERDEC to build NiMH solar chargers: • Chargers failed: They falsely terminate charging before completion;• CERDEC refused to use any of these chargers. BUT batteries become damaged or

have reported reduced life-cycle when connecting directly to the solar array.– Known charging algorithms are applicable to constant power source:

• Termination for “dumb” NiMH batteries (BB390) occurs based on battery V, dV/dt, time, and sometimes temperature T or dT/dt.

– Solar arrays produce varying current sources depending on clouds (fools known chargers)• Fast charge Slow charge Fast charge …

– How to correctly predict charge termination for DUMBDUMB batteries like BB390 (basic research)?

I VV1I1I2 V211:00am 11:00am

11:15am11:15am

Summary: Research OutcomesSummary: Research Outcomes

Major Accomplishments: Explained that performance degradation of

batteries when charging with solar array is due to high temperature overcharging;

Designed, built and tested Phase I solar array NiMH battery charger control algorithms;Over 50 experiments: 0% failure rate!! Preliminary patent disclosure

Maximum Power Point Tracker (Phase II) - charger forces solar array to produce more power;

2005 IEEE PESC paper to appear in June.

Prototype Charger

Must Be Sure Algorithm:• Immune to changing illumination or temperature conditions• Permits a little overcharging to « make sure » battery is full SOC

Hardware: Monitors voltage, current and temperature for each leg (thermistors inside BB390) Differential temperature measurements between battery legs determine when charge is complete.

PIC µC

ADCBatterythermistors

voltage leg 1&2

leg1

leg2

BB390leg1 leg2

Prototype

charging current

Phase II: Maximum Power Point Tracking (MPPT)

We have built preliminary Phase II chargers that include MPPT:

• Adjusting the duty ratio of the Up-Down converter forces the solar array to operate at its maximum producing power point; • MPPT adaptively optimize charging to different NiMH batteries (12V, 24V, 9.6V, etc.)• Bypass switch improves power efficiency when MPPT not needed.

µ controller

Up-Down converter

ADCd

CurrentSensingresistor

DPWM

Iout

filter

PV array

Bypassswitch

µ controller

Up-Down converter

ADCd

CurrentSensingresistor

DPWM

Iout

filter

PV array

Bypassswitch

Battery Voltage

Current when solar array is directly connected to the battery

Current when the proposed charger with MPPT is used.

4.8V 660 mA 720 mA

12V 310 mA 310 mA

24V 0 mA 160 mA

Higher Charging Current is Achieved with MPPT

Relevance to Army’s VisionRelevance to Army’s Vision• Army Future Force Warrior (FFW)

– Power Vision: “72-hour continuous autonomous team operations, high density, low weight/volume, self-generating/re-generating, reliable, safe power source/system.” (from FFW home web page)

• Roadmap/Relevance of Research to FFW1. Our proposed solar battery chargers are lightweight, use renewable

energy, are reliable quiet: Directly impact FFW power requirements.

2. We are attempting to transition technology developed: – Negotiating with vendors to implement the algorithms on their existing chargers;– Discussing with CERDEC on “convincing” their vendors to use new algorithms;– Two recent meetings with US Army Natick Research Center (they seem to deal with

larger (kW) power systems, but have been open to discuss new projects)

3. Year 6 – 8 outcomes hope to provide great flexibility to the soldier:i. Develop charger that can utilize various input power sources (from solar to wind)

ii. Ability to recharge any battery chemistry type, such as Li-ion, NiMH, NiCd.

4. Potential commercial, dual-use, technology transfer to portable solar battery chargers for campers, RV’s, etc.

US Army Natick Research Center vision of what a FFW in 2020 (left) and 2010

(right) will look like

Source 1:AC Mains90V~240V

Microcontroller

IntermediatePower Bus(10V~28V)

SW1

Bus

-Enab

le

Source 2:Primary DC

Source

Source 3:Rechargeable

Battery(hot-swappable)

Battery-Enable

SW2

10V~48V

AC

-good

prim

-goo

d

V/I c

ontrol

CC

V/I

Bat

-V

Bat

-Tem

p

SM

B D

ata

Bus-

V/I

DC-DCConverter 1

Load 1

DC-DCConverter n

Load nB

at V

/I

SW3Charger /Converter

Up-Down

AC/DC

Isolated Push-Pull

Cha

rgin

g-E

nabl

e

SM

BC

lock

Proposed Research Activity For Year 6-8Proposed Research Activity For Year 6-8

VISION: Design and build a smart Future Force Warrior power system architecture capable of:

• Sensing and adapting charge algorithms according to battery chemistry• Running from primary source, rechargeable battery or from combination thereof• Ability to recharge battery with virtually any primary source (AC, DC, solar wind, etc.) • Programmable output voltage. • Handling input voltage range of up to 5:1

A vision of a Future Force Warrior power system architecture

AppendixAppendix

• Supporting slides for presentation that will not be shown in the limited 10 minute presentation

YEAR 4 Achievements:• Designed a robust solar NiMH battery charge control algorithm.• Built charge controller that clamps onto BB390 with embedded algorithm.

YEAR 5 Expectations/Objectives:• Transfer charger algorithms to existing CERDEC vendors to implement within their

BB390 chargers: target timeframe to achieve this is by the end of GFY 2005.• Conduct field testing of the prototypes.• Technology Transition:

- Extend algorithm to other NiMH batteries, e.g., commercial AA cells- STO program: Help optimize layout of solar cells in for applications at US Army Natick

Soldier Center.

New NiMH

Algorithm

Lab Prototypeof BB390 Charger

Field TestablePrototypes

Field Testing

(CERDEC)

Generalization to AA& Other Battery Types

STO/RDECOMSolar Panel

Layout Optimization

YEAR 4(Beginning of the Project)

YEAR 5

Technology Transfer

Roadmap YEAR 4-5Roadmap YEAR 4-5