Design of a 14V nominal dual battery system Audi AG, Gehrmann, Johannes
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
Overview of electrification level of powertrain electrification * generating electrical energy internal (in the vehicle) charging electrical energy external (out of the vehicle) * ICE = internal combustion engine
Increasing demand for CO2-reduction How to achieve further CO2-reduction by supporting the ICE in most-recent mass-market applications? Developing conditions: Easy to integrate Efficient (reduced additional weight) Economically (costs)
Increasing demand for electric energy and power How to reduce weight but also provide greater convenience? Example: electricity balance of 12V Pb battery while using auxiliary heating Current situation: [Ah] 0-1 electricity balance of 12V Pb battery [Ah] outside/battery temperature < -15 C auxiliary heating driving cycle Strong negative electricity balance leads to low availability or large size of 12V Pb battery -2-3 -4 time 0 30min 45min
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
Mildhybrid functions engine start speed-up coasting recuperation start stop ignition-off vehicle speed [km/h] no alternator load boost engine off deactivate fuel injection max. 6kW engine off longer stopps auxiliary heating * 100 80 60 light weight no-brake more powerful restart active el.steering 40 20 brake 10 30 50 70 90 110 time [s] * better perfomance of power supply
Important feature about recuperation periods [km/h] * 140 120 100 80 total duration of recuperation periods [s] total duration of brake recuperation periods [s] duration [s] ** no brake 60 40 20 0 0 300 time [s] 600 900 1200 1500 1800 brake More than half of recuperation periods are without braking Frequent, short periods (avergage 3s, max. 30s, share ~13%) * WLTC = worldwide harmonized light vehicle test cycle ** based on vehicle measurements
Voltage-controlled network speed-up coasting recuperation start stop vehicle speed [km/h] U [V] no alternator load boost engine off deactivate fuel injection engine off 100 15,5V 80 60 40 20 12,2V 10 30 50 70 90 time [s] U [V] = configurable generator voltage
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
Possible architecture of a 14V dual battery system Hard parallel connection - combining advantages Pb cheap, high discharge power at low temperatures Li excellent charge acceptance, high cycle stability Enables start stop on the move add-on to 12V power supply * Li Pb * high-power generator
Voltage compatibility of add-on battery OCV * [V] 15,5V Pb-Battery Example I 14V Li Example II 14V Li 12,8V 100% 12,2V 50% >= 34Ah > 6Ah > 6Ah usable amount of energy while driving [Ah] * open circuit voltage [V]
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
U gen [V] U Li-Ion [V] Low resistance, minimal weight High recuperation power needs minimizing total system resistance between generator (source) and battery (drain) Minimal weight impacts fuel consumption in acceleration periods Key implications: Minimal pack resistance of battery is absolutely essential I recu [A] R IC Optimizing of 12V wiring is necessary Li Pb
Right OCV - characteristic example battery cell type 1 example battery cell type 2 OCV * [V] 15,5V Li OVC [V] 15 6,5[Ah] 5,5[Ah] 14 12,8V 13 12,2V 12 10V 0V 11 10 0 1 operating range battery capacity [Ah] 2 3 4 5 6 7 8 9 10 11 Right OCV-characteristic within specific operating range at same internal pack resistance * open circuit voltage [V]
High cycle stability Discharge lithium battery to support the ICE Consumed energy needs to be recharged Targets: Balanced charge High cycle stability is necessary using the complete potential of available energy Requirements of cycle stability need to be fulfilled till EOL* [km/h] 140 120 100 80 60 40 vehicle speed [km/h] electricity balance Li-Ion-Battery [Ah] [Ah] 1,5 1 0,5 0-0,5 20-1,5 0-2 0 80 160 240 320 400 480 560 640 time [s] -1 * EOL = end of life
High recuperation capability Charge lithium ion battery to recuperate energy during deceleration periods Limitations by charging currents reduce the possible recuperation energy during deceleration periods [km/h] 140 120 100 80 60 40 20 0 [A] 400 350 300 250 200 150 100 50 0-50 battery-voltage of Li-Ion Add-on-Battery [V] current of Li-Ion Add-on-Battery [A] vehicle speed [km/h] max. 350A@1s >150A@25s time [s] 0 10 20 30 40 50 60 70 80 [V] 15 14,5 14 13,5 13 12,5 12 11,5 acceleration deceleration start stop
Cold-cranking support Battery temperature = -28 C Using Li-Ion Battery to support cold engine start of ICE Targets: Fulfill current characteristic under consideration of safety & lifetime requirements Pb-Battery [A] Li-Ion Add-on-Battery [V] and [A] [V] 12,5 11,25 10 8,75 7,5 6,25 5 [A] 0-200 -400-600 -800-1000 -1200 Conventional engine starter [V] and [A] cold engine start 10V min. 8,4V time [s] 1 2 3 4 5 6 7 8 9 10 11 12 200A max. 580A time [s] 0 1 2 3 4 5 6 7 8 9 10 11 12
Support power supply of auxiliary heating voltage of Li-Ion Battery [V] current of Li-Ion Battery [A] current of Pb-Battery [A] Battery temperature <= -15 C Add-on battery supports power supply of auxilary heating period Capability of recharging consumed energy leads to more availability by smaller sizes of Pb- Battery Fulfill current characteristic under consideration of safety & lifetime requirements [A] 120 100 80 60 40 20 0-20 auxiliary heating max. 116A@3s driving cycle > 80A @ 60s 15 30 time [min] 45 [V] 15 13 11 9 7 5
High temperature stability Air cooling Example: temperature development of 14V Li-Ion battery while driving when positioned close to engine Asymptotic characteristic depends on ambient temperature and operating strategy trip time [h] Battery temperature while driving [ C] temperature distribution over lifetime [%] * 10 20 30 40 50 60 70 80 * temperature distribution at close to engine position in hot-climate regions operating temperature [ C]
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
14V Lithium-Ion Battery Cell Topology Energy content Power Audi 14V Battery 11Ah prismatic 1p4s 150 Wh (BOL) + 5kW (25 C,2s,35%,BOL) Current Voltage +/- 500A (25 C,1s,>=20%) 10V 17V Operating temperature -30 C to 75 C Weight Dimension (LxWxH mm³) Cooling < 5kg 175 x 110 x 190 mm³ air
86,5 mm High power cell for 14V Lithium-Ion Battery Cell data Cell type Cell capacity Nominal voltage Width Height Thickness Operating temperature Weight cathode material prismatic, hard case 11 Ah 3,4 V 174,0 mm 86,5 mm 22,2 mm -30 C to 75 C 600 g NMC 22,2 mm anode material Carbon
Agenda Introduction and background Functions Design and architecture of a 14V dual battery system Challenges and key requirements for a dual battery system 14V Lithium Ion Battery Summary and outlook
Summary and Outlook Main drivers for a new 14V dual battery system are additional functions Main use case: the average energy demand of the 12V electrical system can be supplied by recuperated energy Key requirement: low cell- and pack resistance to assure high ability of recuperation Ongoing challenges: high cycle and temperature stability Additional charge and discharge power at low temperatures open opportunity to reduce size of 12V Pb battery Next steps: More available energy within specific voltage range? Developing a 2p-System to comparable system costs?
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Author and Source References Audi AG, 2017 Author: Johannes Gehrmann, Audi AG Co-Author: Daniel Renner, Audi Electronics Venture Ltd.