AUTOTRONICS The main functions of the BMU are the electrical and thermal management, diagnosis functions, insulation monitoring, and the communication with other parts of the vehicle..pptx

The main functions of the BMU are the
electrical and thermal management, diagnosis functions, insulation monitoring, and the communication with other parts of the vehicle.
Electrical management includes charge balancing, charge determination, and the provision of status information, such as system voltage, system current, or power-time prediction (charging/ discharging) for vehicle control functions.
Thermal management functionality is used to monitor and evaluate the temperature in the battery system.
Disconnection monitoring, charge monitoring, and fault recording represent different diagnosis functions.
The insulation monitoring in the battery system is a coordinated function between the battery system and the vehicle.

1. Autotronics

2. Configuration of EV

3. Architecture of EV

4. Main components of EV

5. Description of Automotive Battery System Architecture 5 Fig: Battery system architecture—Illustration of the main parts of an automotive battery and their interrelations

6. Battery Management Unit (BMU): The main functions of the BMU are the electrical and thermal management, diagnosis functions, insulation monitoring, and the communication with other parts of the vehicle. Electrical management includes charge balancing, charge determination, and the provision of status information, such as system voltage, system current, or power-time prediction (charging/ discharging) for vehicle control functions. Thermal management functionality is used to monitor and evaluate the temperature in the battery system. Disconnection monitoring, charge monitoring, and fault recording represent different diagnosis functions . The insulation monitoring in the battery system is a coordinated function between the battery system and the vehicle.

7. HV Disconnection: Its main purpose is the disconnection of the battery system from the vehicle HV circuit, and it provides a galvanic separation of the battery and the vehicle in case of deactivation, accident or a safety-critical malfunction. The HV disconnection consists of special HV contactors for the plus and minus terminal. For the activation of the system, a specific pre-charge circuit for both terminals has to be included to realize a soft connection to the vehicle HV circuit. In case of an over-current, an emergency shut-off strategy has to be elaborated because the contactors can only guarantee a limited number of switching cycles under load over their expected lifetime. 7

8. HV Fuse: In the case of an over-current, the HV Fuse will disconnect the battery system from the vehicle’s HV circuit. Since an over-current causes the HV Fuse to be heated strongly, it must be thermally decoupled from other components (in particular the cells) to prevent a thermal breakdown. I-Sensor: The I-Sensor provides the current measurement of the whole vehicle HV circuit. The measured current value is used as an input for state-of-charge determination in the BMU and for the thermal management of the battery cells. Each battery has a specific current operation range for charge and discharge. The correct current is measured within this operating range of the battery system with a specified accuracy. If the current is lower or higher than the operating range, a special disconnection strategy has to be implemented with interaction of the HV Disconnection and the HV Fuse. 8

9. Electrical Interconnections: This includes all kinds of LV (low voltage wiring including the communication) and HV connections between the battery cell pack and the relevant E/E components of the battery system. Battery Cell Pack: The battery cell pack consists of serial and/or parallel connected battery cell modules and the battery cell module interconnection. – Battery Cell Modules consists of battery cells that are connected in series and/or parallel and a cell management unit (CMU). The CMU is responsible for cell charge balancing, measurement of cell voltage and temperature, and the communication between CMUs in different battery modules as well as between CMU and BMU. The cell modules contain a number of redundant temperature sensors to detect areas with critical temperatures. These sensors are connected with the thermal management in order to prevent critical temperature in the battery system. – Battery Cell Module Interconnection includes all electrical, mechanical, and thermal connections between battery modules. 9

10. Battery cells are the smallest unit in the battery. The three common types are the cylindrical, the prismatic and the pouch cell, as shown in Fig. Due to their sheet metal casing, cylindrical and prismatic cells have a higher structural integrity than pouch cells, but they are also heavier. Modularity and Battery Components

11. Modularity and Battery Components The casing is often made of quite strong aluminum sheets, in contrast to the polymer, coffee bag like, cover of the pouch cell. Modularity helps reduce the amount of different parts within a battery pack and allows packs to be designed using the same basic modules to handle different energy content, voltage and designs requirements. The battery pack contains all the cells and modules of the battery. It also usually contains the cooling part of an environmental system to keep the cells within their admissible temperature limits, a battery management system (BMS), and its associated hazardous voltage (HV) protection system.

12. The cell’s chemistry has a huge impact on the cost of the battery. Since the battery is the most expensive part in an electric vehicle, it’s an important consideration when it comes to minimizing production costs. Lithium Ion (Li-Ion): Lithium-ion cells are the most popular cell types because of their cost efficiency. They offer the best trade-off between energy storage capacity and cost efficiency. There are many types of li-ion cells. The Tesla Model 3, for example, used NCA cells (lithium nickel cobalt aluminium oxide) until 2021. In China, certain Tesla Model 3 cars are now using LFP cells (lithium iron phosphate). The Most Common Cell Chemistries Used in EVs

13. Nickel Manganese Cobalt (NMC): Nickel Manganese Cobalt cells offer a great balance between power and energy. They were the favorite chemistry for two generations of Chevy Volts. Nickel Metal Hydride (Ni-MH): The Nickel Metal Hydride chemistry was used in the very first hybrid cars such as the Prius because it was the most affordable technology at the time. Nowadays, they have mostly been outclassed by lithium batteries but are still used in some hybrid electric vehicles such as the 2020 Toyota Highlander. Lithium Sulphur (Li-S): Lithium Sulphur cells have a high-energy storage capacity, making them attractive for EV buses. However, they need to be heated up before they can be operated, making their use more complex and less attractive.

14. Lead-Acid: Lead-acid batteries have been used in the most popular EVs for decades: golf carts! Although their performance is low compared to other cell types, it’s enough to meet the needs of low-performance EVs like golf carts. Lead-acid batteries are low maintenance and easy to replace. Unlike other types of batteries, mechanics do not need to contact battery manufacturers for maintenance and replacement. But now, as li-ion batteries are becoming cheaper and easier to access, the popularity of lead-acid batteries is dropping, as some golf carts are starting to use lithium-ion batteries instead.

15. Introduction Lead-Acid Batteries Basic Chemistry Charging, discharging, and state of charge Key equations and models The Nernst equation: voltage vs. ion concentration Battery equivalent circuit model Battery capacity and Peukert s law Energy efficiency, battery life, and charge profiles Coulomb efficiency, voltage drops, and round-trip efficiency Battery life vs. depth of discharge Charging strategies and battery charge controllers

16. Lead-acid battery: cell chemistry The electrolyte contains aqueous ions (H+ and SO4 -2). The conduction mechanism within the electrolyte is via migration of ions via drift & diffusion.

17. Reaction at Negative (Pb) Electrode Charged sulfate ion approaches uncharged lead electrode surface, dipole attraction kicks in on close approach Lead atom becomes ionized and forms ionic bond with sulfate ion. Two electrons are released into lead electrode This reaction releases net energy under standard conditions (T = 298˚K, 1 molar concentration) Release of two conducting electrons gives lead electrode a net negative charge As electrons accumulate they create an electric field which attracts hydrogen ions and repels sulfate ions, leading to a double-layer near the surface. The hydrogen ions screen the charged electrode from the solution which limits further reactions unless charge is allowed to flow out of electrode.

18. Reaction at Positive (PbO2) Electrode Charged sulfate and hydrogen ions approach lead-dioxide molecule (net uncharged) on surface of electrode Lead atom changes ionization and forms ionic bond with sulfate ion. Two water molecules are released into solution This reaction releases net energy

19. As positive charge accumulates an electric field is created which will attract sulfate ions and repel hydrogen ions (charge screening) limiting further reaction unless charge is allowed to flow out of electrode. Note: Both half reactions cause the electrodes to become coated with lead sulfate (a poor conductor) and reduce the concentration of the acid electrolyte

20. Battery Voltage at Zero Current (equilibrium) As described in earlier slides, reactions at electrodes lead to opposite charge buildup on electrodes and hence a voltage difference Open-circuit voltage under standard conditions (T = 298˚K and 1 molar acid electrolyte) is “Sulfation” of electrodes and double-layers at surfaces limits further reactions Temperature plays an important role (see Nernst equation later)

21. External load allows electrons to flow and chemical reactions to proceed As battery is discharged, additional sulfation of electrodes occurs and acid electrolyte becomes weaker, lowering the terminal voltage Note that current must flow through electrolyte to complete the circuit (combination of drift & diffusion currents) The conductivity of electrolyte and the contact resistance of sulfated electrodes contribute to internal resistance of battery. Strong function of temperature and the state-of-charge of the system Discharging through External Load

22. Charging from External Source External source forces electrons to flow from positive to negative terminals The chemical reactions are driven in the reverse direction, converting electrical energy into stored chemical energy As the battery is charged, the lead sulfate coating on the electrodes is removed, and the acid electrolyte becomes stronger

23. Battery state of charge (SOC)

24. Lithium – Ion Battery

25. Lead-Acid Battery Electrolyte: Dilute sulfuric acid (H₂SO₄). Electrodes: Lead dioxide ( PbO ₂) as cathode, sponge lead (Pb) as anode. Energy density: Low (30–50 Wh /kg). Weight & Size: Heavy and bulky. Cost: Cheap. Cycle life: Short (300–500 cycles). Charging time: Slow (8–16 hours). Efficiency: 70–80%. Applications: Automobiles (car batteries), UPS, inverters, backup power.

26. Lithium-Ion (Li-ion) Battery Electrolyte: Lithium salt in organic solvent. Electrodes: Graphite (anode), lithium metal oxide (cathode, e.g. LiCoO ₂). Energy density: High (150–250 Wh /kg). Weight & Size: Light and compact. Cost: Expensive. Cycle life: Long (1000–3000 cycles). Charging time: Fast (1–3 hours). Efficiency: 90–95%. Applications: Mobile phones, laptops, EVs, renewable energy storage.

27. Feature Lead-Acid Battery Lithium-Ion Battery Weight Heavy Light Energy density Low High Life span Short Long Cost Cheap Expensive Charging Slow Fast Common use Cars, UPS Phones, EVs, laptops Lead-acid = cheap, heavy, short life, low energy → best for backup power & vehicles. Li-ion = costly, light, long life, high energy → best for portable devices & EVs.

28. Characteristics of Battery

29. Capacity, Energy and Power are usually expressed by unit of mass or volume for comparison purpose.

30. Battery Geometry Cells come in many shapes: round, rectangular, prismatic or hexagonal. They are normally packaged into rectangular blocks. Some batteries can be supplied with a fixed geometry only. Some can be supplied in a wide variation of heights, widths and lengths. This can give the designer considerable scope, especially when starting with a blank sheet of paper – or more likely today a blank CAD screen. The designer could, for example, spread the batteries over the whole floor area ensuring a low centre of gravity and very good handling characteristics

31. Battery Temperature, Heating and Cooling Needs While most batteries run at ambient temperature, some run at higher temperatures and need heating to start with and then cooling when in use. In others, battery performance drops off at low temperatures, which is undesirable, though this problem could be overcome by heating the battery. When choosing a battery the designer needs to be aware of battery temperature, heating and cooling needs and has to take these into consideration during the vehicle design process.

32. Battery Life and Number of Deep Cycles Most rechargeable batteries will only undergo a few hundred deep cycles to 20% of the battery charge. However, the exact number depends on the battery type, and also on the details of the battery design and on how the battery is used. This is a very important figure in a battery specification, as it reflects the lifetime of the battery, which in turn reflects the EV running costs. More specific information about this, and all the other battery parameters mentioned, are given in the sections that follow on particular battery types.

33. Special Characteristics of Lead Acid Batteries The lead and lead dioxide are not stable in sulfuric acid and decompose, albeit very slowly, with the reactions: At the positive electrode: 2 PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O + O2 (3.4) At the negative electrode: Pb + H2SO4 → PbSO4 + H2 (3.5) This results in the self-discharge of the battery. The rate at which these reactions occur depends on the temperature of the cell – faster if hotter. It also depends on other factors, such as the purity of the components (hence quality) and the precise alloys used to make up the electrode supports. These unwanted reactions, which also produce hydrogen and oxygen gas, also occur while the battery is discharging. In fact they occur faster if the battery is discharged faster, due to lower voltage, higher temperature and higher electrode activity. This results in the ‘lost charge’ effect that occurs when a battery is discharged more quickly

34. It is a further unfortunate fact that these discharge reactions will not occur at exactly the same rate in all the cells, and thus some cells will become more discharged than others. This has very important consequences for the way batteries are charged. But, in brief, it means that some cells will have to tolerate being ‘overcharged’ to make sure all the cells become charged. The reactions that occur in the lead acid battery when it is being ‘overcharged’ are GASSING. These ‘gassing’ reactions occur when there is no more lead sulfate on the electrodes to give up or accept the electrons. They thus occur when the battery is fully or nearly fully charged.

35. Battery Life and Maintenance We have seen that gassing reactions occur within the lead acid battery, leading to loss of electrolyte. Traditional acid batteries require topping up with distilled water from time to time, but modern vehicle lead acid batteries are sealed to prevent electrode loss. In addition the electrolyte is a gel, rather than liquid. This means that maintenance of the electrolyte is no longer needed. However, the sealing of the battery is not total: there is a valve which releases gas at a certain pressure, and if this happens the water loss will be permanent and irreplaceable. This feature is a safety requirement and leads to the name ‘valve-regulated sealed lead acid’ (VRLA) for this modern type of battery. Such buildup of gas will result due to the reactions, which occur on overcharge, proceed too fast. This will happen if the charging voltage is too high. Clearly this must not be allowed to happen, or the battery will be damaged. On the positive side, it means that such batteries are essentially ‘maintenance free’.

36. However, this does not mean that the batteries will last for ever. Even if there is no water loss, lead acid batteries are subject to many effects that shorten their life. One of the most well known is the process called ‘sulfation’. This occurs if the battery is left for a long period (i.e. 2 weeks or more) in a discharged state. The lead sulfate on the electrodes forms into larger crystals, which are harder to convert back into lead or lead dioxide, and which form an insulating layer over the surface of the electrodes. By slowly recharging the battery this can sometimes be partially reversed, but often it cannot.

37. Battery Charging Charging a lead acid battery is a complex procedure and, as with any battery, if carried out incorrectly it will quickly ruin the battery and decrease its life. As we have seen, the charging must not be carried out at too high a voltage, or water loss results. There are differing views on the best way of charging lead acid batteries and it is essential that, once a battery is chosen, the manufacturer’s advice is sought. The most commonly used technique for lead acid batteries is called multiple step charging. In this method the battery is charged until the cell voltage is raised to a predetermined level. The current is then switched off and the cell voltage is allowed to decay to another predetermined level, and then the current is switched on again. A problem is that the predetermined voltages vary depending on the battery type, but also on the temperature. However, the lead acid battery is used in so many applications that suitable good-quality chargers are available from a wide range of suppliers.

38. An important point that applies to all battery types relates to the process of ‘charge equalisation’ that must be done in all batteries at regular intervals if serious damage is not to result. It is especially important for lead acid batteries .

39. Battery Performance Characteristics Generally, the amount of electric charge that a battery can store is the battery’s capacity. The battery capacity size directly relates to the amount of electrolyte and electrode material inside the battery. Hence, greater capacity can be achieved if more electrolyte and electrode material are provided. The battery capacity is also a function of other battery parameters such as the magnitude of the current, the allowable terminal voltage of the battery, the temperature, and other factors. The measurement unit of a battery’s capacity is Ah (1Ahˆ at 3600C or coulomb). In vehicle applications, it is preferable to measure energy stored in the battery as watt-hour (Wh).

40. The energy capacity of a battery measured in Wh can be converted to Ah using Ohm’s rule that states battery power ˆ where and are the voltage and current of the battery. Thus: Therefore: Theoretically, the battery’s capacity can be calculated using Faraday’s law of electrolysis. where: Ms = is the mass of the substance altered at an electrode in kg Q = is the total electric charge passed through the substance Fb= ˆ96,485 C/mol is the Faraday constant Mm=is the molar mass of the substance in g/mol Zb = is the valency number of ions of the substance  

41. Note that the equivalent weight of the substance altered is Q, Fb, and zb are constants; thus, the larger equivalent weight results in the larger ms. Therefore, the theoretical capacity of a battery, C T,b , can be calculated as: where the dimension of capacity is in coulombs. Here, n b is the amount of substance (“number of moles”) altered: In the above equation, symbol C T,b is used for the battery capacity since typically symbol C is used for battery capacity. The theoretical capacity in Ah is :

42. In practice, a variable electrical current is the case. Thus, the usable capacity, C U,b , of a battery is the electric current i(t) integrated over time: where, t is the time when a battery is at a full charge and t cut is the time when a battery terminal voltage is at the voltage cut, v cut .

43. State of Charge/Discharge State of the charge (SoC) is a measure of residual capacity of a battery and is the equivalent of a fuel gauge for the battery pack in EVs/HEVs. In other words, it is the amount of capacity that remains after the discharge from the fully charged condition. The units of SoC are percentage points (0% ˆempty; 100% ˆ full). Direct determination of SoC is not usually possible. However, it can be theoretically calculated using battery voltage and current. The current is the rate of charge given by: where q is the per-unit charge (charged divided by the capacity) flowing thorough the circuit.

44. For a time interval, dt, the theoretical battery state of charge, S o C T,b is: If it represents the charging current and the state of the charge is zero at initial time, the formula for S o C T,b is

45. Depth of Discharge depth of discharge, DoD, is a measure of the amount of discharged energy capacity from the battery, typically expressed as a percentage of maximum capacity. The state of discharge can be given as:

46. Battery Energy Density and Specific Energy energy density is the amount of energy capacity per unit volume, while specific energy is the amount of usable energy capacity per unit mass in Wh /kg. The theoretical energy stored in a battery directly relates to the battery voltage and its theoretical capacity. Typically, the theoretical stored energy is: where Vb is the nominal no load terminal voltage (open circuit voltage) and CT;b is the theoretical battery capacity in coulombs. It is noted that 1 Ah is equivalent to 3600 coulombs(C). The available energy can be formulated

47. Accordingly, the battery specific energy is Battery Power Density and Specific Power. Power density refers to the energy rate (in Watts) that can be delivered per unit volume, while specific power is the energy rate (in Watts) available to deliver per unit mass. According to the definition of power, the instantaneous battery terminal power is: where Vbt (t) is the battery terminal voltage and i(t)… †is the battery discharge current. The maximum power where Mb is the total mass of battery.

48. During heavy load operating conditions such as rapid acceleration, the maximum power output is needed. In such situations, the electric motor draws a significant amount of current to provide the maximum power required for traction. The rated power specifications, based on the ability of the battery to dissipate heat, can assess the performance of the batteries in fulfilling heavy duty operating conditions, such as rapid acceleration and hill climbing. The definition of rated continuous power is the maximum power at which the battery can provide prolonged discharge intervals without damaging the battery, whereas the rated instantaneous power is the maximum power that the battery can deliver over very short discharge intervals without damaging the battery. The rated power specifications, along with the maximum continuous discharge current, the top sustainable speed and acceleration of the vehicle can be defined. According to the definition, the specific power of a battery is:

49. Battery Efficiency Similar to other systems, batteries are not 100% efficient. Some battery input power is lost due to internal resistance. This can be presented by: where, Pb;out and Pb;in are output and input battery powers, while Pb;L is the internal lost power. The internal power loss of a battery can be obtained as: As well, the battery discharging power is: By defining the load resistance as R l ˆ = Vbt / i and noting that the discharge efficiency is the ratio of output power to input power, the battery discharge efficiency is: Rl can be obtained by measuring the terminal voltage and current values.

50. During the charging phase, the direction of the current is reverse of that in the discharging phase, and the charging (terminal) voltage, Vc , is higher than the open circuit voltage. With the same procedure for calculating the efficiency of the battery during the discharging phase, the battery charging efficiency is: the internal resistance varies during charging and discharging phases and depends on the battery state-of-charge, temperature, etc.

51. An EV with a 55 kWh battery pack (400 V) starts at 75% SoC . The driver covers 90 km on flat terrain with an average consumption of 160 Wh /km , and then descends a slope, recovering 3.5 kWh of energy through regenerative braking at 80% efficiency . Find: The final SoC of the battery. Initial energy in pack: Energy consumed on drive: Net energy after drive (before regen): Energy actually recovered (regen efficiency): Final energy in battery: Final SoC:  

52. An EV has a nominal 64 kWh battery whose state-of-health (SOH) is 88% . The manufacturer exposes a usable SoC window of 8%–92% on the dash. The car’s dash currently shows 54% (displayed). You plan a 150 km trip at 155 Wh /km . Question: After the trip, will the car show more than 10% displayed SoC ? Actual pack capacity (accounting for SOH) Usable energy between 8% and 92% (usable window = 84%) Convert displayed 54% → absolute energy in battery Energy at the lower limit (8%): . Energy shown by displayed portion: . Total initial energy in pack:  

53. Energy required for the trip Energy remaining after trip Absolute SoC after trip (fraction of actual pack) Displayed SoC after trip (map absolute SoC back to 8–92% display) Displayed percent satisfies:  

54. An EV has a nominal 70 kWh battery whose state-of-health (SOH) is 90% . The manufacturer exposes a usable SoC window of 5%–95% on the dash (the dash percentage maps only to that usable window). The car currently shows 80% on the dash . During a trip the vehicle uses 24 kWh . Question: After the trip, what will the dash show as the displayed SoC? Actual pack capacity (accounting for SOH) Usable energy between 5% and 95% (usable window = 90%) Convert displayed 80% → absolute SoC (fraction) Displayed 80% corresponds to the usable-window fraction . The absolute SoC (fraction) is:  

55. Initial energy in the pack (absolute) Energy remaining after trip Absolute SoC after trip (fraction and percent) Convert absolute SoC back to displayed SoC (5%–95% mapping) Displayed percent satisfies: Round reasonably: Displayed SoC ≈ 37.67% (absolute SoC ≈ 38.90%, remaining energy ≈ 24.51 kWh).