Using Battery Modeling as a Sizing Tool - PowerPoint Presentation

Using Battery Modeling as a Sizing Tool IEEE ESSB Summer Meeting Chicago – June 12, 2016

IEEE battery sizing Sizing standardsIEEE Std 485-2010 for vented and valve-regulated lead-acidIEEE Std 1115-2014 for nickel-cadmiumBoth use modified Hoxie methodHoxie, E. A., “Some discharge characteristics of lead-acid batteries,” AIEE Transactions (Applications and Industry), vol. 73, no. 1, pp. 17–22, Mar. 1954.Divide duty cycle into successive periods with constant loadSize by section with progressively more periodsSection 1 with first period onlySection 2 with first two periods Etc. Using Battery Modeling as a Sizing Tool 2

IEEE cell sizing worksheet (IEEE 1115) Using Battery Modeling as a Sizing Tool 3

Limitations for the IEEE method Cumbersome for numerous load steps No consideration for temperature changes during operation Ambient changes during prolonged duty cycles I2R heating effectsNo consideration for ramping loadsNo consideration (yet) for new technologiesUsing Battery Modeling as a Sizing Tool4

Battery modeling – an alternative approach Various platforms depending on need. Examples:COMSOL Multiphysics ‘Micro’ modeling e.g. electronic & ionic charge transfer Useful for cell design Matlab-Simulink‘Macro’ modeling of electrical and thermal characteristicsScalable to battery level for interactions with dc systemModels for advanced technologies may include battery-management algorithmsUsing Battery Modeling as a Sizing Tool5

Saft Li-ion Matlab-Simulink models Models run same algorithms as battery management systems Exactly mimic real battery behavior, including contactor management Include aging inputs and outputs 6Using Battery Modeling as a Sizing Tool

Example 1 – from IEEE 485 Model requires random load to be in correct location Assume ambient temperature of 10 °C Using Battery Modeling as a Sizing Tool 7

Example 1 – model results BOL 100% SOH E OL 80% SOH Using Battery Modeling as a Sizing Tool 8

Example 2 – PJM regulation PJM Interconnection runs the grid in 13 statesBiggest Independent System Operator in the USA PJM power market includes fast regulation service (RegD) typically supplied by battery energy storage systems Approx. 300 MW in service or being built RegD signal is energy neutral and changes every 2 sec.Sample day:Using Battery Modeling as a Sizing Tool 9

Example 2 – model results Using Battery Modeling as a Sizing Tool 10

So is modeling the future of battery sizing? For Saft, the answer is ‘yes’But not every battery manufacturer has a model Most are less sophisticated Tabular discharge data does not exist for Saft Li-ion cellsThe model is the source of all performance characteristicsUsing Battery Modeling as a Sizing Tool11

Where do we go with sizing standards? The IEEE sizing standards have their origins in the time before computer-driven modeling Needed to avoid use of different sizing methods for the same project Continue to be vital for the nuclear industry Why do we need sizing standards if models exist?Is validation an issue?How is ‘trust the model’ different from ‘trust the tabular discharge data’?Food for thought…Using Battery Modeling as a Sizing Tool12

Questions? Thoughts? 13 Using Battery Modeling as a Sizing Tool jim.mcdowall@saftbatteries.com

‘Bonus’ material – cycle counting QuestionHow many cycles? …of what depth? Answers are important for folks who want to compare cycle count with published cycle-life curves The following slides show the Saft methodOthers may follow a slightly different approachUsing Battery Modeling as a Sizing Tool 14

Cycle counting technique Cycle must be ‘closed’ SOC must return to starting point Example with 2 closed cycles From 80% SOC to 20% SOC and back again (60% DOD)From 55% SOC to 50% SOC and back again (5% DOD)Using Battery Modeling as a Sizing Tool15

Modified example Still 2 closed cycles From 65% SOC to 20% SOC and back again (45% DOD) From 55% SOC to 50% SOC and back again (5% DOD) Cycle starting from 80% still waiting to be closedIf charging continued (after pause) up to 80% SOC... 45% cycle would become 60% DOD cycleUsing Battery Modeling as a Sizing Tool16

Another modification Now 3 closed cycles From 65% SOC to 20% SOC and back again (45% DOD) From 55% SOC to 50% SOC and back again (5% DOD)From 80% SOC to 30% SOC and back again (50% DOD)With Li-ion we count only delta-DOD cyclesCycle between 20% and 10% SOC counts same as one between 90% and 80% SOCHence no 60% DOD cycle above Using Battery Modeling as a Sizing Tool 17