N of batteries of high accuracy 60V monitors a system to be made so!

N of batteries of high accuracy 60V monitors a system to be made so!

[introduction] monitor around batteries n, the article introduces ADI LTC2944 to follow coulomb meter plan high to 60V essence for everybody by the engineer Boris Wang of science and technology of dragon of ADI agential fine horse, aid force to make high-powered batteries monitor a system, the popularizes gender, accurate n to monitor value that covers batteries equipment and n measure the principle of the quantity, and principle of the internal composition to LTC2944, job and specific coulomb meter plan have development analytic.

Of battery device popularize application

From mobile phone computer, dynamoelectric bicycle, dynamoelectric tool, arrive again equipment of instrument of car of new energy resources, medical treatment, industry, batteries has become the mark of increasing electron product to distribute a part. Especially the birth of portable lithium ion batteries, let all equipment broke away from power supply cord to become a possibility. These equipment can show current odd n or run time, this is a product one of the mainest user experiences in using.

As the elapse of time, we can be experienced apparently, batteries is to meet from beginning to end more and more not durable. Occasionally, this meeting forms a kind ” add boat angst ” , for example, although equipment shows the rest ” 10% ” n, however it is issueing one second to close immediately machine. In the equipment of much cell of a lot of high power, if the user does not have enough and seasonable discovery batteries n is extinct, may appear very critical or serious consequence, for example of instrument of clinical medical treatment cut off the power suddenly the abrupt delay opportunity that can endanger instrument of patient life, factory is caused produce a line urgent close stop.

Following graphs (graph 1) place is shown, for the relation of the cycling life of batteries of ion of some model lithium and discharge deepness, can see apparently, fill discharge to make an appointment with deepness, batteries spendable life is briefer. In daily products plan, we go to those who restrain a client very hard filling discharge habit, because this battery life often cannot be cast ahead of schedule, must effective through going electric measure a method.

1684828217593523.jpg

Graph the cycling life of 1 lithium battery and discharge deepness concern

How essence of life measures batteries the rest definitely n, forecast batteries ability of true add boat, it is the technical issue that electronic engineering group is dedicated to solving all the time. Because batteries is a kind of not stable electrochemistry system, collect to its accurate report parameter crucial, the implementation n function that monitor needs nicety apparently and plan of appropriative imitate circuit.

Tall compositive change n to monitor

Besides charge, outside protection and batteries balance circuit, batteries n is measured also is one of common functions in system of intelligent much batteries. No matter be equipment of what kind of batteries power supply, the circuit system that involves batteries is facing a series of unique design challenges, because the electric property of batteries always is,changing. For example, of batteries most high capacity (also call health or SOH) and always reduce as the elapse of time from discharge rate, and charge to also be met with discharge rate as the change of temperature change. The batteries system of elaborate design need not break quake condition to handle these parameter to change, the person that so that be,use is offerred consistent and accurate batteries function changes show parameter. Correspondence arrives in practical experience, we are OK and accurate output a few index, let a product be provided more ” advanced feeling ” , include:

● Current the rest charges time

● Time of boat of current system add

● Anticipate battery life (or the rest charges frequency)

From at present the mainstream technology of electronic industry looks, accurate batteries n measures a function, the batteries coulomb meter that needs an essence to allow IC and relevant batteries die for special purpose, final system is to need to form a crucial parameter — state of report of carry on one’s shoulder (SOC) . SOC is show batteries uses period of time or lay aside for a long time need not hind, odd capacity is as brand-new as its and charge completely the ratio of the capacity when condition, its extraction is worth in 0 to 1 between. We understand OK and simply for, SOC is current batteries capacity is occupied most the per cent of high capacity. Although there are a few coulombmeters on market IC is compositive batteries model and algorithm, export the worth of SOC directly even, but anatomize can discover, these IC often can be cost with sacrificial accuracy, in order to simplify the estimation of SOC is algorithmic.

Pursue as follows (the coulomb meter that graph 2) place shows the LTC2944 of a model that is ADI, it can support the batteries voltage of highest 60V, what it offers is plan of the most radical accurate coulomb meter of essence of life, the batteries model that uses actually by user basis again undertakes n estimates operation, realize coulombmeter function. This is a kind of rigorous technology offers way, not will certain factor opens an user, use parts of an apparatus with freer land, compatible and more pinpoint accuracy applies, later development will undertake be discussinged further.

25.png

Plan of coulomb meter of graph 2 LTC2944 60V

N measures the principle of the quantity

Current research makes clear, exact coulomb count, voltage, electric current and temperature are the precondition of accurate estimation SOC, up to now, the SOC estimation error that industry internal energy accomplishs quite is the smallest for 5% . Following graphs (the model that graph 3) place is shown is all sorts of batteries fills discharge curve, reckon in traditional voltage n the method is medium, the most difficult part fills the n estimation of discharge interval in evenness, because at this moment the change of batteries n can bring change of very little tension only, then meeting occurrence system reports inside very long period of time the SOC of 75% , drop suddenly however next the SOC of 15% .

Library human relations is enumerated means, can decide current batteries is in a curve accurately which position, especially the position of even area. Specific means is:

● When batteries fills report, the user is coulomb tally initialization foregone batteries capacity.

● Degressive when releasing coulomb computation or charging increase by degrees when coulomb computation (the circumstance) that can suit to fill one portion report only.

The dominant position with this kind of the largest program depends on, this kind of coulombmeter calculates means not to need to know the chemical part of batteries. Because ADI LTC2944 is compositive coulomb tally, because this IC is used easily at a variety of battery device, have nothing to do with the chemistry of batteries.

1684828192313273.jpg

Graph the model of all sorts of 3 type batteries fills discharge curve

Data of computation of library human relations gets in circuit system later, on software algorithm, want to undertake mathematical conversion according to batteries model, in order to determine the value of SOC, pursue as follows (what graph 4) place shows is a kind of classical batteries model, involve the many parameter of series connection paralell connection, actually, here still compares main temperature parameter effect without the consideration. The method of model analysis and conversion is professional domain knowledge, do not undertake give uncecessary details here, but OK and affirmatory is, the ginseng count that what this model should learn the most basically is voltage, electric current and coulomb meter number is occupied.

27.jpg

Graph 4 classical batteries models

The coulomb meter plan with standard essence

Mentioned in above paragraphs accurate the premise that undertakes SOC is analysed, it is accurate get voltage, electric current, temperature, coulomb meter counts parameter. LTC2944 is such can the platform program that odd chip gets all parameter. Its periphery circuit is very simple also, design development easily, the demand safeguard high accuracy is compositive in chip interior.

LTC2944 internal composition and working principle

Following graphs (graph 5) place shows the working principle that is LTC2944. From physical meaning for, charge (coulomb) it is electric current the integral in time level. LTC2944 passes the tension that two end produce resistor of the sampling that monitor to measure charge, this voltage limits is ± 50mV, chip is as high as 99% to his precision. Differ minute of voltage to be brought to bear on to divide imitate integrator to the difference of automatic zero among them with conversion charge.

When integrator output brae supreme and referenced n is mixed low referenced n (when REFHI and REFLO) , switch will switch in order to invert voltage change direction. The state that controls circuit to will observe switch and voltage change direction in order to decide polarity. Next, but process designing beforehand scale down implement allow an user to increase integral time 1 to 4096 times. As beforehand scale down implement next spilling over or go up every time spill over, accumulate charge register (ACR) increases by degrees finally or decrease successively an unit of enumeration.

1684828166697396.jpg

The working principle of graph 5 LTC2944

Notable is, the imitate integrator that uses in LTC2944 coulomb tally introduced tension of the least the deflection that need branch, because this utmost ground reduced the effect to total charge error. A lot of coulomb meter IC measure resistor to feeling the voltage of two end undertakes modulus is changed, accumulate changeover to decide charge in order to push as a result. In such plan, voltage of the deflection that need branch may be the main source of the error, read in small signal especially during taking.

For example, suppose in plan of a coulombmeter, it is the coulomb tally that is based on ADC principle, what have 20uV is the biggest specify level of deflection of the voltage that need branch, criterion after this voltage deflection undertakes digital integral to the input signal of 1mV, deflection brings about charge the error is 2% . Under photograph comparing, the imitate integrator of use LTC2944, charge error is only 0.04% , 50 times smaller.

Extremely tall precision is behaved

When the interval that fills discharge curve in evenness when coulomb meter job, electric current and temperature are the crucial parameter that the system needs to get. The challenge of this kind of design depends on, the terminal voltage of batteries (belt when carrying) can get the distinct effect of batteries electric current and temperature. Accordingly, must have corrective compensation to voltage reading, compensating factor is with voltage of batteries electric current, open a way (when carrying for nothing) , temperature proportionate. In unit process of cargo bandling to measure open circuit voltage, disconnect with respect to need batteries and laden join, this is highbrow, because this is a basis in real operation,electric current and temperature curve adjust terminal voltage reading.

Because obtain tall SOC precision,be the system designs an object finally, LTC2944 uses 14 to be used at measuring voltage, electric current and temperature without ADC of defer Δ Σ , precision is as high as respectively 1.3% with ± 3 ℃ . In fact, the function of LTC2944 is behaved actually even better. Pursue as follows (how follow temperature and tension and the certain precision value that graph 6) indicated LTC2944 is medium changes, basically reflected the following 3 rules characteristic.

● When measuring voltage, ADC did not adjust an error always to be less than ± 0.5% , and in feeling measure voltage range inside more constant

● When measuring electric current, ADC gain error is less than ± below working temperature normally 0.5%

● To any given feeling measure voltage, temperature error makes an appointment with ± along with temperature change only 1 Celsius

All these precision index add in, with respect to the precision of SOC of can distinct effect, this is why of voltage, electric current and temperature it is very important to batteries coulombmeter application to monitor.

1684828151789008.jpg

All sorts of precision of graph 6 LTC2944 behave a graph

When LTC2944 is measuring voltage, electric current and temperature, offer 4 kinds of ADC to operate mode. Below automatic mode, chip carries out ADC changeover continuously with the cycle of a few millisecond, and scanning mode is changeover of every 10 seconds, enter Morpheus state next. Below type of hand movable mould, chip carries out changeover to the command, enter Morpheus state next. Every time when chip is in Morpheus mode, static electric current can fall to 80uA. The whole imitate part of LTC2944 also can be shut completely, with reducing static electric current 15uA further. This makes LTC2944 additional in the system the existence feeling of bad news report is reduced further.

Why don’t have batteries model?

The user can use digital I2C interface to be read from LTC2944 take batteries n, voltage, electric current and temperature. The user still can configure a few through I2C 16 register, read take condition, control to leave / close, set the high threshold value that can call the police and low threshold value for every parameter. Warming system eliminated the need of successive software poll, release I2C bus line and lead plane to carry out other job. In addition, ALCC brings a foot to be able to use as already SMBus alarm output, also configure to be full of report or the clew signal that put empty report. Had all these digital functions, somebody still can ask possibly, “Why is LTC2944 done not have inside buy batteries model or SOC appraise numeration? ” the answer is very simple, to seek the accuracy of acme.

Although have inside file of buy batteries configuration and algorithmic coulombmeter chip can simplify design, but they often are do according to actual batteries inadequate or irrelvant model, sacrificed in this process the accuracy of SOC. For example, the user may be forced to use fill discharge curve by what generate inside sealed origin or sealed temperature limits; The likelihood does not support accurate batteries chemistry, this meeting causes bigger effect to SOC precision.

The key is, accurate batteries builds a model to consider a lot of variable normally, and enough and complex, because this user can be in software,undertake building a model to oneself batteries, in order to obtain the SOC precision of top level, is not to rely on inaccurate general inside buy model. Model of the buy inside these also makes coulombmeter function becomes not agile, in repeating a design to go to other applying hard. In debugging development actually, change in what SOC algorithm undertakes in software should get more easily than be in hardware much.

In addition, tall voltage limits also is the product of other and similar function is truly different place on LTC2944 and current market. LTC2944 is OK by low the batteries to 3.6V is direct power supply, OK also by the power supply of group of full report batteries that is as high as 60V, solved from low power comsumption portable electron product arrives high pressure is dynamoelectric any application of the car. The periphery circuit of LTC2944 is very compact also, this can reduce the total power comsumption of LTC2944 circuit to raise precision further.

Summary

Batteries n is monitored is an intricate circuit design work, because have,a lot of interdependent parameter can affect SOC. What approbate generally is inside the industry, accurate coulomb meter is counted, add electrify pressing, electric current and temperature reading, it is the most accurate method that estimates SOC. LTC2944 coulomb meter offers all measurement of these parameter function, and intended avoid in-house batteries builds modular function, allow an user to realize his relevant configuration file and algorithm in specific application software. In addition, measure and configure register to be able to pass I2C interface to come true easily, support the batteries system of highest 60V, and can be used at the batteries of any chemical composition, the most important is, its accuracy is an industry inside unapproachable.

Avoid duty statement: The article is reprint an article, reprint this article purpose to depend on passing more information, the person that copyright puts in original work ‘s charge is all. If involve work copyright issue,article place uses video, picture, written language, contact please small make up undertake handling.

Leave a Reply

Your email address will not be published. Required fields are marked *