[introduction]Charge batteries is being used increasingly at taller voltage and greater power, its application includes electric car (EV) and mixture motivation car (cleaning equipment of HEV) , dynamoelectric tool, lawn and UPS. Well-known, although a kind of any chemical goods need to be monitored carefully and manage, in order to ensure effective, reliable the operation with safety, but cascade of to satisfy the power requirement of these car or equipment need series connection a few batteries are unit, with respect to need design personnel gives more attention, especially below the condition that the battery unit amount of every batteries adds.

Charge batteries is being used increasingly at taller voltage and greater power, its application includes electric car (EV) and mixture motivation car (cleaning equipment of HEV) , dynamoelectric tool, lawn and UPS. Well-known, although a kind of any chemical goods need to be monitored carefully and manage, in order to ensure effective, reliable the operation with safety, but cascade of to satisfy the power requirement of these car or equipment need series connection a few batteries are unit, with respect to need design personnel gives more attention, especially below the condition that the battery unit amount of every batteries adds.

The small-sized batteries group that monitor and measure single battery unit or includes unit of a few battery only is a kind of measurable challenge only, the cell that photograph comparing is established ties by many battery unit and becomes is strung together for should get simply much. The architect of unit of splice much battery needs to consider a lot of issue, if undertake metrical below Gao Gongmo voltage, of unit of the influence that whether is retained in breakdown of unit of dangerous tension, single battery, many battery answer with, battery unit does not match and balance, and the difference in temperature of splice batteries, too numerous to mention one by one. These batteries need advanced batteries management integrated circuit already (BMIC) and batteries management system (BMS) will undertake parameter is measured with control, also need to design personnel to master knowledge of a few projects, so that use them correctly.

The article will discuss common, especially the administrative ABC of much uniter batteries reachs all sorts of challenges. Introduce next and explain how to use Analog Devices, Renesas Electronics Corp.  With the BMIC that Texas Instruments offers. These parts of an apparatus use the individual government problem that solves the cell that be established ties by many battery unit and becomes to string together technically.

Series connection batteries is strung together brought unique challenge

Common batteries monitors the electric current that includes to flow into and pour out of batteries (n) measure, terminal voltage is monitored, batteries capacity is evaluated, batteries temperature is monitored and charge / discharge cycle manages, optimize energy to store thereby function increases in ground of the utmost inside the service life of batteries fill discharge time. Use extensive BMIC or BMS to be able to be only by or two battery unit forms, the small-sized batteries group that voltage is a digit provides these functions. BMIC or BMS collect front as data, its data report manages controller to batteries (CMC) ; In more complex system, CMC and controller of administration of batteries be callinged (the join of advanced function parts of an apparatus of BMC) .

In the article, “Batteries is unit ” be alone store can unit, and ” batteries ” it is to show by many battery unit series connection is mixed / or the group of whole power source of shunt-wound composition. Although unit of a battery emerges tension of a few bend over only, but group of a batteries is OK by a few or more battery unit are comprised, be as high as the voltage of a few bend over in order to offer, and taller even voltage can be offerred after many batteries group is combined.

For active management, needing metrical crucial batteries parameter is terminal voltage, charge / discharge electric current and temperature. Contemporary batteries group measures function to comparative to what what need Yan Ke: Every batteries is unit must can be in a few millivolt (MV) and a few milliampere (in MA) and about 1 Celsius (℃ ) undertake metrical to its below the condition. The reason that has such Yan Ke monitor to battery unit includes:

• Of affirmatory batteries group charge condition (SOC) and health (SOH) , the odd size that calculates batteries group well and truly thereby (run time) with total life expectancy.

• Provide the data that implementation batteries requires evenly, although the interior of batteries is put in difference and different position, temperature and ageing circumstance, but already can charge evenly the voltage between battery unit. If do not undertake batteries is balanced, will bring about batteries group performance to reduce, damage even batteries is unit. Balance process can pass passive or active technology is finished; Latter effect is much better, but cost is higher, more complex also.

• The circumstance of the user safety problem such as the member that should prevent a lot of likelihoods to damage batteries causes such as car to reach its to multiply. These included a variety of adverse cases, be like:

• Be pressed too or charge in order to pass big electricity, the likelihood causes thermal breakdown.

• Under-voltage: Odd second cross discharge to won’t cause disastrous trouble, but the likelihood begins deliquescent and zincous conductor. Subsequently excessive discharge cycle can bring about reduplicative charge lithium appears to eletroplate in battery unit circumstance, appear again potential thermal breakdown.

• Temperature crosses tall meeting to affect the performance of batteries electrolyte material, bring about SOC to reduce; This also can increase solid electrolyte the photograph intermediate (the formation of SEI) , bring about resistor rate to increase thereby and inhomogenous, cause power loss.

• Temperature is too low also be a problem, because temperature crosses small possibility to cause lithium deposit, cause capacity loss then.

• Cross electric current and the interior that because in-house impedance is inhomogenous,bring about with ultimate hot out of control to give out heat; This meeting adds the SEI layer in batteries, increase resistor rate.

For example, below testboard or other and benign environment, accurate the voltage that measures unit of a certain battery is to comparative forthrightly practice, this is a difficult problem. Design personnel needs to join on the battery unit that wants to measure one drifts only (blame ground connection) or volmeter of batteries power supply number (DVM) (graph 1) .

Graph 1: The voltage of any single battery units that measure series connection batteries is told from the concept very simple, need volmeter of number of a float only can. (picture origin: Bill Schweber)

However, as a result of a lot of reasons, below the electric condition that waits in electric car or mixture motivation car and harsh environment, want self-confident and undertaking metrical surely is quite difficult. It is very clear to be in what in having case of representative group of electric car power source, behave at this o’clock. Group of this kind of power source includes unit of battery of 6720 lithium ion, control module government by 8 (graph 2) .

Graph 2: Actual batteries group is to point to what appear with module form, with array of unit of series connection and battery of shunt-wound means connective, stored in this kind of array much energy; These make namely batteries voltage measures the factor that becomes very complex. (picture origin: Analog Devices)

The capacity of every battery unit is 3.54 hours (Ah) , accordingly always nominal store can be 100 kilowatt hour (3.54 Ah X 4.2 V X 6720 batteries is unit) . Be in 96 in order to establish ties in group of unit of formal connective battery, every groups include 70 with unit of battery of shunt-wound means connective, batteries voltage is 403.2 V (4.2 V of 96 × ) , the capacity is 248 Ah (100 KWh/403.2 V or × of 3.54 A 70) .

Among them problem includes:

• Because be put in Gao Gongmo voltage (CMV) , when measuring the low voltage that has a digit only, must satisfy resolution and accuracy requirement, in order to obtain significant millivolt class accuracy. This is a kind of challenge, it may make gauge systematic overload or the effectiveness that affect reading. The CMV here is to show relative system is bit publiccer (also be called ” the ground ” , although this kind of view has by accident) , till be measured the voltage the sum of the batteries of all series connection of battery unit. Ask an attention, in electric car, can establish ties amount to 96 even 128 battery unit establishs ties, in order to achieve the CMV of hundreds bend over.
• As a result of tall CMV, for electric integrality and user / the system is safe, must have the other part of batteries and system report is kept apart, because should put an end to this both expose it is under complete CMV.
• Electric noise and report emerge to affect the reading that millivolt span expresses badly extremely easily.
• Must be inside a few millisecond and measure many battery unit at the same time almost, in order to determine the total position of accurate battery unit and batteries group. Otherwise, the measurement between battery unit time deviation can create misdirect sex conclusion and the measure that are based on misdirect sex conclusion.
• Some kind of multichannel answer needs to use position between the other part that unit means many batteries to collect subsystem in battery unit and data, interrelate otherwise the dimension of circuit, weight and cost can raise greatly.

Finally, still have a few with safe, redundant what concern with erroneous report is important and mandatory note, these must consider. The level of each industries is different; Industry and dynamoelectric tool and car are very different, the standard of concerned car is the strictest. In system of task key car, if run concerned system with batteries, its function is short of break must not bring about hazardous condition to happen. In interior of this kind of system the circumstance of occurrence breakdown falls, “Safe ” condition asks to close electronic plant, and must adopt appearance dial lamp or other indicator warn car driver.

However, to a few systems, malfunction or the function is short of break bring about dangerous incident likely, cannot shut its simply, because this is safe,the target may include to appoint ” related to safety ” usability requirement. Below this kind of circumstance, the likelihood needs the breakdown of certain type in patient system, in order to avoid dangerous incident.

To satisfy this kind of usability requirement related to safety, need is in specific time paragraph inside provide basic function or already defined ” exit ” method — the breakdown condition that although exist,already defined, and safe system must be in this time paragraph content bears breakdown happening. Depend on function of this kind of fault tolerance, the system can continue to move below acceptable safe level longer. ISO 26262 ” road car function is safe ” the guidance that crucial part developed personnel to offer the usability related to safety to ask for the system.

Integrated circuit company intensifies offerring a solution

The supplier had developed BMS integrated circuit, aim to solve read the issue that takes series connection battery accurately — although meeting faces tall CMV, abominable report,enrage an environment. These IC can offer basic reading not only, and still solved multichannel answer to use, the technical issue such as segregation and time deflection. This kind of IC accords with relevant safe level, can fall in suitable case, achieve the attestation requirement that ASIL-D car uses, this is car domain level of the highest, strictest attestation.

Grade of automobile safety integrality (ASIL) is the risk classification program that by security of function of car of ISO 26262 road the standard sets. This standard is adapted from the about auto industry safe integrality grade in IEC 61508 (SIL) regulation.

Although will tell the functional likeness of these BMS parts of an apparatus roughly, but they are in the function with the structure, battery speed of amount, scanning, resolution, individual unit that can handle and interrelate the difference with methodological respect constant presence:

• Framework of segregation type CAN is based on astral form configuration, have very strong stability, because keep apart the communication line in type CAN framework to rupture to be met only,destroy an IC, and the other part of batteries group is safe still. It is however in CAN framework, ask every IC has a microprocessor and CAN, make cost of this kind of method higher, and communication speed is relative however slower.

• Chrysanthemum catenary structure contrasts economic material benefit normally, because the chrysanthemum catenary of this kind of framework is based on general asynchronous,receive / emitter (UART) , can realize reliable, quick communication, and the complexity that does not have CAN. In this kind of framework, the most familiar segregation pattern is capacitance type segregation, but also can use transformer type segregation. But, the line appears to be able to bring about communication to interrupt in chrysanthemum catenary structure, because this has some of chrysanthemum catenary system to be able to be adopted ” flexible ” measure, can support a few operations during breaking a string.

Have representative BMS IC to have among them:

• MAX17843 Offer by Analog Deveice: MAX17843 is but the data of 12 passageways batteries that monitor collects process designing interface, have rich safe function (graph 3) . Group of the cell that after course of this parts of an apparatus is optimized, is used at car system, HEV batteries, electric car and any splice grow string of voltage highest the system of the 2 metals batteries that can amount to 48 V.
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Graph 3: The 12 passageways batteries of MAX17843 monitors data to collect interface compositive a variety of safe functions, make its special apply to car application and satisfy all sorts of regulations. (picture origin: Analog Devices)

MAX17843 is compositive difference of a high speed distributes UART bus line, use at powerful chrysanthemum catenary serial communication. Support of this bus line joins in catenary of a chrysanthemum amount to 32 IC (graph 4) . UART uses capacitance segregation, reduced stock detailed account not only (BOM) cost, still reduced seasonable breakdown (FIT) rate.

Graph 4: 12 passageways MAX17843 uses capacitance report segregation in configuration of UART of its chrysanthemum catenary, support of catenary of a chrysanthemum amounts to 32 parts of an apparatus. (picture origin: Analog Devices)

Imitate front measures data to collect system and input of group of switch of a high pressure to form by voltage of a 12 passageways. All measurement go up to undertake in order to differ minute of form in every battery unit. Full span measures limits to be 0 to 5.0 V, effective limits is 0.2 to 4.8 V. During measuring, successive of use high speed is approached (SAR) modulus converter (ADC) is opposite through exceeding sampling with 14 resolution battery unit voltage undertakes digitlization. Can complete all pair of 12 battery unit inside S of 142 μ measure.

MAX17843 uses double scanning to the method amasses battery unit measured value and undertake to its the error is amended, because this came true inside working temperature limits,measure precision outstandingly. Be in + below the condition of 25 ° C and 3.6 V, battery unit differs minute of metrical accuracy to set the 2 MV that it is ± . Enter this IC to facilitate the design guides, analog Devices offerred MAX17843EVKIT# to evaluate set. This kind is covered contain the graph that is based on PC to change user interface (GUI) , can use at setting, configuration to mix evaluate.

• By the ISL78714ANZ-T that Renesas offers: BMS IC of ISL78714 lithium ion but monitoring reachs unit of battery of 14 series connection, offer balance of accurate batteries voltage and temperature monitoring, batteries and rich system to diagnose a function. In typical configuration, advocate ISL78714 passes serial peripheral interface (SPI) port and advocate small controller corresponds, and still have amount to 29 ISL78714 parts of an apparatus to pass powerful only crewel chrysanthemum catenary is linked together (graph 5) . Height of system of this kind of communication is agile, can use capacitance segregation, transformer segregation or both combination, and speed is as high as 1 million bit / second (Mb/s) .

Graph 5: In the crewel chrysanthemum chain that ISL78714 uses SPI port to be in join of many parts of an apparatus to be able to use capacitance type or transformer type segregation. (picture origin: Renesas Electronics Corp. )

Initiative voltage measures precision to be ± 2 MV, come in 20 ° C + below 85 ° C and 1.65 it is 14 to the resolution inside 4.28 V limits; Inside the limits of battery unit input in ± 5.0 V, board the precision of parts of an apparatus after assembling is strict ± 2.5 MV (negative voltage limits is used at satisfying bus to discharge demand normally) .

This BMS includes 3 kinds of batteries to balance mode: Mode of hand dynamic balancing, time balance mode and self-poise mode. The charge amount that self-poise mode sets in lead plane moves from inside every battery unit after dividing, the end balances mode. If lose communication, the meeting in the function is diagnosed to a watchdog closes plant in the compositive type system of all crucial functions.

• BQ76PL455APFCR(andBQ79616PAPRQ1) all come from Texas Instruments: Bq76PL455A is a 16 unit batteries is monitored and protect parts of an apparatus, it is high reliability, tall voltage to industry applies and be designed only. Compositive high speed, poor cent, capacitance keeps apart interface support to amount to 16 Bq76PL455A parts of an apparatus, pass catenary of chrysanthemum of double skeining thread and lead plane communication in order to be as high as the speed of 1Mb/s through interface of high speed UART (graph 6) .

Graph 6: Bq76PL455A 16 unit batteries manages IC to be aimed at industrial application, use capacitance segregation will join amount to 16 parts of an apparatus, pass double skeining thread in order to be as high as the speed of 1 Mb/s to correspond through chrysanthemum catenary layout. (picture origin: Texas Instruments)

14 ADC use an interior fiducial, the changeover time that all battery unit exports all is 2.4 Ms. Bq76PL455A can be monitored and detect a few kinds of different breakdown conditions, had included to press, owe pressure, breakdown of too gentle communication. This parts of an apparatus supports the passive battery unit that uses exterior N-FET to balance, and the active balance that carries drive of grid of exterior switch matrix.

This kind of BMS can handle the batteries that does not exceed 16 battery unit at most easily to string together. The only limitation that such doing is must according to ascend use input, will all untapped inputs join one case to come to did not use highest VSENSE_ input. For example, in the design of 13 battery unit, input VSENSE14, VSENSE15 and VSENSE16 were not used (graph 7) .

Graph 7: Bq76PL455A can be used at little at 16 battery unit; Below this kind of circumstance, the input that did not use battery unit must be catenary in highest. (picture origin: Texas Instruments)

The other IC that waits like the Bq79616PAPRQ1 of Texas Instruments returns supportable annular configuration and two-way communication, the health that makes the system can monitor batteries group continuously and safe condition (graph 8) .

Graph 8: Bq79616PAPRQ1 supports two-way and annular develop to attack structure, so that be in,break a string or another link join way are offerred below the circumstance of node breakdown. (picture origin: Texas Instruments)

If be in this kind of configuration, two batteries monitor the situation that breakdown, open a way or short circuit appear between ASIC, control processor can deliver direction through the around of switch information, continue to monitor ASIC to have communication with all batteries. Accordingly, if normal communication encounters trouble, the system can use the fault tolerance ability of annular communication function to maintain usability, won’t lose the voltage that comes from batteries module and temperature information from time to tome together. Try the design personnel of Bq79616PAPRQ1 to the hope, texas Instruments offerred BQ79616EVM to evaluate board.

• LTC6813-1 comes from Analog Devices, inc. : LTC6813-1 is a group of much uniter batteries that accords with car standard monitor, contain through its but the ADC of 16 triangle integral of filter of process designing noise, measurable the batteries that amounts to 18 series connection is unit and always measure an error to be less than 2.2 MV (graph 9) . Ask an attention, photograph comparing is other the IC that can support battery unit directly will tell, the amount with this supportable parts of an apparatus is more. All 18 battery unit are OK finish inside S of 290 μ measure, and can choose inferior data gather speed in order to obtain taller fall effect of a confusion of voices.

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Graph 9: The most batteries with supportable LTC6813-1 is unit (18) , the precision that used 16 ADC to realize 2.2 MV and ability of scanning of unit of high speed battery. (picture origin: Analog Devices, inc. )

Can establish ties many LTC6813-1 parts of an apparatus, allow the battery unit that strings together to longer high-pressured batteries at the same time to undertake monitoring thereby. LTC6813-1 supports two kinds of serial port: Standard 4 lines SPI and interface of 2 lines segregation (IsoSPI) . Blame segregation 4 lines port is applied to relatively the link of stone’s throw and application of car of a few blame (graph 10) .

Graph 10: LTC6813-1 supports a level 4 lines SPI interrelates, use at relatively the link of stone’s throw and application of car of a few blame. (picture origin: Analog Devices, inc. )

1The segregation of Mbit/s is serial communication port uses Chan Genshuang skeining thread, the distance can amount to 100 M, have inferior electromagnetism to disturb (EMI) sensitivity and radiate, because this interface design aims to realize inferior data to include wrong rate, although get in cable,the influence of field of tall radio frequency also is such below the circumstance. Although appeared,method of such as communication breaks the breakdown such as the line, this kind of two-way ability of chrysanthemum catenary also can ensure the integrality of communication.

In its two lines configure mode to fall, segregation comes true through exterior transformer, standard SPI signal is to differ minute of pulse by encode. Transmission pulse intensity and level of receiver threshold value adopt RB1 of two exterior resistor and RB2 set (graph 11) . Resistance is chosen by design personnel, so that be in,power dissipation is mixed balance has between the intensity that fight a confusion of voices.

Graph 11: Port of serial communication of type of segregation of the 2 clues that LTC6813-1 still provided to pass odd root double skeining thread, 1 Mb/s, transformer, its distance can amount to 100 meters, and have low EMI sensitivity and low radiation at the same time. (picture origin: Analog Devices, inc. )

LTC6813-1 is OK and direct from the battery that gets its to monitor group or keep apart power source power supply alone from. The passive that this parts of an apparatus still includes to be used at every battery unit balances a function, and wide modulation of use arteries and veins (the odd exclusive air that PWM) has compares control function.

Summary

Accurate measure single battery unit or only the voltage of the small-sized batteries group that unit of a few battery forms, electric current and temperature, can bring a few challenges more or less. However, because a large number of batteries are unit, tall,noise of CMV, report, superintendency regulation is mixed other issue, accurate on the single battery unit that series connection batteries strings together measure these identical parameter to be in abominable car and industrial environment when undertaking metrical (the time deviation between battery unit is ignorred) , will be a challenge.

(author: Bill Schweber origin: Get nimble electron DigiKey)

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