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LPRDS – CMS – 2011 Per Cell Management Design

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LPRDS – CMS – 2011 . Per Cell Management Design. Presentation Outline. Introduction Project Goals One Board Per Pack ESS Controller Board System Communication Mechanical Design ATP / Requirements Analysis Budget Schedule. Presentation Outline. Introduction Project Goals - PowerPoint PPT Presentation

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LPRDS CMS 2011

LPRDS CMS 2011 Per Cell Management Design1Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule2Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule3

3-year Senior Design Project

2009 Legacy Work2010 Legacy Work2011 Projected WorkLafayette Photovoltaic Research and Development System (LPRDS)

LCD DisplaySCADA Interface Box (SIB)Fit PCSystem Status Display Filter Inverter Box (FIB)Switch Controller / Energy Management Unit(SC / EMU)Energy Storage System (ESS)TransformerEnergy Storage System (ESS)LPRDS-CMS-2011Finish a per-cell balancing scheme for the 64-cell LiFePO4 battery pack.

Complete design so that energy storage system is capable of being utilized by the LPRDS system.

Plan of WorkDevelop a Slave Board (OBPP PCB) which will balance during charge/discharge a pack of 4 cellsDevelop a Master Board (ESSCB PCB) which will control the functioning of the OBPPs to charge/discharge/bypass a particular cell.Develop a Stand-alone mode for the OBPP in which a pack and OBPP together do not need the master to make decisions for bypassing during charge/discharge.

Aggregate Battery Stack with OBPP PCBsEnergy Storage System Master Controller Board (ESSCB PCB)10

Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule12Project GoalsDevelop a One Board Per Pack PCB which can handle the balancing of a 4-cell battery pack.

Modify previous ESS Controller Board which can control individual OBPP packs for total pack charging/discharging.

Develop method of visually demonstrating operation of ESS.13Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule14One Board Per Pack (OBPP)

15One Board Per Pack :: Key FeaturesIndividual cell balancing capabilitiesTwo Modes of Operation (Slave & Stand-alone)Boots in Stand-alone ModeLEDs indicating operational state of packLEDs indicating operation of bypassScalabilityTemperature Fail-Safe System

16One Board Per Pack :: Design

One Board Per Pack :: DesignResistive burn-off bypass solutionIndependent redundant temperature safety system (RTSS)Individually addressable packs for master-slave configurationStand-alone operation with charge state controlled open collector outputImplements I2C communication in master-slave configuration*Current sensing capability18Cell Balancing DesignBreakdown of design trade-offsActive vs. Passive BalancingLevel of IntegrationDelegation between Controller and OBPP boardsScalabilityLayout SpaceCostManufacturabilityAvailability19Active Vs. Passive BalancingActive: Using capacitive or inductive loads to shuttle charge from higher charged cells to lower charged cells.Is more efficient from a power perspectiveHas scalability issuesOBPP boards are larger and handle more workManufacturability issuesActive Vs. Passive BalancingPassive: Bypasses cells and burns off the excess charge from the cell.

Better large-stack scaling

Burn off can be significant

Controller board handles decision-making

Bypass DesignGrounding the floating reference

Choosing a resistor value

Choosing a suitable transistor

Bypass Design Resistor Choice

Bypass DesignBypass Design Transistor Simulation

These numbers give a maximum power dissipation of 2.122 * 1.5 = 6.74W, which is about 35 degree temp rise using the thermal resistance of the resistor alone.Bypass Final ThoughtsOnly the most recent simulationsSeveral different iterations of components and control schemesFinal design can reasonably bypass 1/5 C at full chargeLimitations of the bypass circuit heavily influenced the balancing algorithmCritical MonitoringBattery VoltagesTemperatureOn board and RTSSCurrentDirection and AmplitudeOpen-Drain OutputOptional Automatic ControlFuseCritical Monitoring - Voltage

Critical Monitoring - VoltageDifference Amp to buffer and isolate battery voltages

Monitors for voltage thresholds that indicate a full or empty state

Balancing algorithm requires themCritical Monitoring - TemperatureRTSS discussed later

Voltage output temperature sensors for non-critical temperature monitoring Critical Monitoring - CurrentA relatively new addition

Gives a way to independently judge whether the pack is charging or discharging

Required for the balancing algorithmCritical Monitoring Output PinBased entirely on OBPP calculations

Allows the user to have a charging circuit that is autonomous

An open drain output from the microcontrollerCritical Monitoring - FuseAnother new addition

Will protect the CMS from currents above 25ADigital I/OMaster/OBPP communications will be over I2C

OBPP will have a 4 bit switch addressing

OBPP will transfer from Standalone to Slave when I2C becomes active Master commands override OBPP automated tasksRedundant Temperature Safety System (RTSS)Independent functionality to shut down system when temperature exceeds 65C

Connection to each OBPP using AD22105 Low Voltage, Resistor Programmable Thermostatic Switch Integrated Circuit(Setpoint accuracy = 2C)

When any board exceeds the temperature limit, the switch within the safety loop is activated and the system shuts down.35Overall RTSS

Does not work as stand-alone pack

Must be connected to ESSCB Safety LoopRTSS parts on OBPP

To other OBPPs37OBPP Connection to Safety Loop

to OBPPs

OBPP Thermal Analysis (Charging/Discharging)AluminumCopperFR4 (Circuit board)Lithium Iron Phosphate (Aluminum)Acrylic Plastic

OBPP Thermal Analysis (Bypass Scenario)AluminumCopperFR4 (Circuit board)Lithium Iron Phosphate (Aluminum)Acrylic PlasticStationary Analysis (1 cell heating)

Stationary Analysis (4 cells heating)

Stationary Analysis (Conductive slabs)

Stationary Analysis (Bypass scenario)

Time Dependent (1 cell)

Time dependent (Bypass Scenario)

OBPP Operational VerificationBypass LEDs to indicate resistive bypassing

LEDs to indicate charge/discharge and mode of operationSolid ChargedBlink ChargingSolid DischargedBlink DischargingSolid SlaveBlink Stand-aloneSolid Bypassing47OBPP Additional NotesMultiple levels of electrical isolation

Microcontroller/bypass loop

I2C on OBPP and Master board

RTSS isolated as wellOBPP FirmwareStand-alone Mode

Slave Mode

Cell Balancing Algorithm49OBPP Firmware - StandaloneBegins after a reset or losing the I2C clock signal

Watches for voltage thresholds

Cell balancing is enabled

Waits for I2C connection

First firmware development milestoneOBPP Firmware SlaveMany of the same responsibilities

If no explicit instructions from the master, very similar to Standalone

Master commands are executed first and prioritizedOBPP FirmwareStand-alone ModeDis-chargingSlave ModeChargingCheck StatusBypassBypassSleepDis-chargingChargingCheck StatusBypassBypassSleepType- Lithium Iron Phosphate (LiFePO4) Nominal Voltage - 3.2 V Capacity 10 A-h

Cell SpecificationsCell Behavioral Simulation

54Cell Behavioral Simulation

Cell Behavioral Simulation

Average Slope (V/min)0.00208 ChargingIf the voltage of any cell in a pack of 4 is greater than any of the other 3 cells by more than 40mV, then that cell will go into bypass for 20 minutes. During charge, a green LED on the OBPP will blinkIf the voltage of any cell exceeds 3.8V, then the pack will be considered fully charged, and the CMS will notify the user to discontinue charging (this must happen regardless of whether the cell is in bypass or not)If the temperature of any cell exceeds 40 above ambient, then the CMS will notify the user to discontinue charging (this must happen regardless of whether the cell is in bypass or not)Cell Balancing Algorithm (1 Cell)DischargingIf the voltage of any cell in a pack of 4 is less than any of the other 3 cells by more than 40mV, then all other cells will go into bypass for 20 minutes.During discharge, a Red LED on the OBPP will blinkIf the voltage of any cell drops below 2.8V, then the pack will be considered fully discharged, and the CMS will notify the user to discontinue discharging (this must happen regardless of whether the cell is in bypass or not)If the temperature of any cell exceeds 40 above ambient, then the CMS will notify the user to discontinue discharging (this must happen regardless of whether the cell is in bypass or not)Cell Balancing Algorithm (1 Cell)OFFIf the CMS is in the OFF state, either a Solid Red LED will indicate that the pack is fully discharged, or a Solid Green LED will indicate that the pack is fully chargedIf the CMS is in the OFF state, no cells will be in bypassIf the CMS is in the OFF state, all time differentials will be set to zeroCell Balancing Algorithm (1 Cell)BypassIf a cell is in bypass, a Solid Red LED in parallel with the Bypass resistor will be lit Cell Balancing Algorithm (1 Cell)Cell Balancing Algorithm (1 Cell)

61Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing Simulations

Cell Balancing SimulationsPower dissipation across power resistor

TimePower Dissipation (W)Cell Balancing Algorithm ProsCell Balancing within 10 charge/discharge cyclesAbility to be done in Standalone ModeRelative SimplicityStrict conditions to keep cell within safe rangesBypass current does not scale at same rate as charge current Cell Balancing Algorithm ConsCell Characteristic DifferencesState of Health of CellHigh State Of Charge MismatchPower Losses to Bypass Resistor (especially during discharge cycle)Losing balancing time by limiting maximum temperature (limit to bypass resistance) Minimum charge and discharge currentsPresentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule73ESS Controller Board

ESS Controller Board redesigned

NCNCPIC 18F4525HV Lines12/5 V SuppliesSafetyRS-485I2CTemp Safety LoopNC

To ABS(Aggregate Battery Stack)ESS Controller Board :: Key FeaturesFuel Gauge Algorithm (FGA)I2C Interface Communication with OBPPI2C Interface LCD Screen4 LEDs indicating state of CMSCurrent SensingRS-485 Communication with SCADARedundant Temperature Safety System (RTSS)76ESS Control Board

PRELIMINARY DESIGNESS Control BoardPrimary Functions:Transmit CMS information (Voltage, Temperature, Current) to SCADA systemMonitor currentFuel Gauge AlgorithmHigh Voltage IndicatorCMS Display (LEDs and/or LCD)Safety LoopOverride OBPPs if necessaryESSCB ContinuedRe-use PIC18F4525Re-use code from last yearRe-use power sources, sensors, terminals, LEDs, etc from last yearRe-use safety loopCommunicationRS-485 Interface with SCADA system (SPI)I2C Interface with OBPPs and LCDFor the PIC I2C and SPI share the same lineTI I2C I/O ExpanderESSCB ContinuedFuel Gauge AlgorithmCoulomb countingUse current sensor to measure charge in and out of cellsReset to full capacity at full voltage threshold

ESSCB ContinuedDisplaySeveral LEDs: Charging, Discharging, Fault, 30V IndicatorLCD DisplayI2C interfaceSystem ResetSystem Power

ESS Bill of MaterialsPart numberDescriptionPriceQuantitySubtotalCFA533-YYH-KCLCD Panel/ Keypad$54.841$54.84LCD Cable$5.001$5.00PIC18F4525Microntroller$5.601$5.60ADUM2250Opto$6.003$18.00LM2901Comparator$1.201$1.20HLMP-1790-A0002LED-Green$0.626$3.72HXS 20-NPCurrent Sensor$14.001$14.00M57184N-715BVoltage Regulator$7.811$7.81LM2936Voltage Regulator$1.931$1.93555-1058-NDVoltage Regulator$12.101$12.10PCB$66.001$66.006N135Optoisolator$0.731$0.73SN75240PEDS Protection$1.151$1.15BS170Mosfet$0.231$0.23tca9554aI/O Expander$2.841`$2.84Caps, Resistors, Connectors$15.001$15.00TOTAL:$210.15

LPRDS Software Architecture 2010SCADA CommunicationSCADA CommunicationAdd additional parameters for query

Increase polling times/ polling delay

Poll ESS ESS Poll OBPP OBPP Respond ESS Respond to OBPPSystem CommunicationRPIEMUESSSIBFitPC11623456781514131211109RS-485 SCADA Communication (half-duplex & daisy-chained)I2C Communication (half-duplex)Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule86Mechanical Design

87

88Pack Indicators & Heatsink Possibilities

HeatsinkCELL 1 BYPASSCELL 2 BYPASSCELL 3 BYPASSCELL 4 BYPASSCHARGEDISCHARGEMODE

Negative TerminalPositive TerminalNylon Standoff2-Position Terminal BlockFemale Wire ConnectorMale Wire ConnectorFemale Plug

Wire harness 1 (packs 1-8)Wire harness 2 (packs 9-16)

Physical Dimensions

117 mm107 mm53 mm15 mm160 mm

21 mm8 mmEnergy StorageManual Battery DisconnectStatus of ESSDANGER

96Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule97Acceptance Test Plan (ATP)Modified the requirements of the systemAgreed upon by Professor NadovichTesting at the highest level: full CMSAll requirements not verified at top level:Low-level Testing (QA Audit)Analysis (Technical Memos)Requirements are checked off on the Acceptance Test Report (ATR) as they are metATR is based on the ATP

Expected TestsATP Test 001Demonstrates per cell battery managementCharge every cell to maximum capacityStand alone operation Operate for at least 24 hours autonomouslyQA Test 001Prevent over-charge or over-dischargeQA Test 002Verifies operation of SCADA systemQA Test 00330V Indicator LEDEnhanced Requirement AnalysisBreakdown of the ATPMatches each of the requirements with its respective top-level or low-level testATP T001QA Audit R002-4QA Audit R002-6QA Audit R002b-10R002-2XR002-3XR002-4XR002-5XR002-6XR002b-2XR002b-10XR002b-13XGPR006-4XBrief Maintainability AnalysisRecommended Spare Parts: fuses, connectors, wires, full boardsTroubleshooting scenarios in Users Manual using parts in Maintenance ManualHow to replace a blown fuseReset buttons on system boardsReprogram OBPP/ESS microcontrollersBrief Manufacturability AnalysisAll components listed on Bill of Materials can be purchased from at least two independent suppliers.Critical components are identified and tolerances of these components are considered.RTSS resistor to set activation temperatureVoltage threshold for cell balancing algorithmResistors to manage the bypass loopComponents for fuel gauge algorithm -> NOT critical (only used for general measurements)Reliability AnalysisAccomplishments Simplified schematic of OBPP board to be used for analysis MTBF of each isolated component

Upcoming tasksMTBF for Temperature Sensor Determine failure criteriaCalculate overall MTBF

FusePower OP-AmpsVoltage RegulatorTemp. SensorprocessorOptoisolatorBypass mechanisms (resistor + BJT)Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule104Budget$1915.85$418.86$257.70$208.60$198.99Budget With 14 Added OBPPs$2061.60$418.86$111.95$198.99$208.60Presentation OutlineIntroductionProject GoalsOne Board Per PackESS Controller BoardSystem CommunicationMechanical DesignATP / Requirements AnalysisBudgetSchedule

107ScheduleWe made several complete design changes which caused us to stray from the initial schedule.Initial schedule was incredibly vigorous and less reasonable.Current schedule is more reasonable, but we have still fallen behind due to redesigns of the OBPP and fine-tuning our stand-alone operation.108

Most of schedule slip occurred because design took longer than expected.Questions?Thank you for your attention.112Company Name

Check Status

ChargingBlink Green LED

Bypass CellBypass LEDBlink Green LED

OFFSolid Red/Green

V < (V of any Cell 40mV)

DischargingBlink Red LED

Bypass CellsNot in This StateBlink Green LED

isCharging

ELSE

V > (40mV + V of any Cell) || V > 3.5V

ELSE

isDischarging

Time < 20 min

Always

Time < 20 min

Temp > 60C || V < 2.8V

Reset || Change in Status

Temp > 60C || V > 3.8V

Any Other Cell is in OFF State

Cell Balancing Algorithm

State DiagramJustin Bunnell

LPRDS-CMS-2011

Temp > 60C || V > 3.8V

Temp > 60C || V < 2.8V