Optimizing Battery Accuracy for EVs and HEVs.zip_bms_battery accuracy

<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8"> <meta name="generator" content="pdf2htmlEX"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <link rel="stylesheet" href="https://static.pudn.com/base/css/base.min.css"> <link rel="stylesheet" href="https://static.pudn.com/base/css/fancy.min.css"> <link rel="stylesheet" href="https://static.pudn.com/prod/directory_preview_static/624f522d74bc5c0105332fcf/raw.css"> <script src="https://static.pudn.com/base/js/compatibility.min.js"></script> <script src="https://static.pudn.com/base/js/pdf2htmlEX.min.js"></script> <script> try{ pdf2htmlEX.defaultViewer = new pdf2htmlEX.Viewer({}); }catch(e){} </script> <title></title> </head> <body> <div id="sidebar" style="display: none"> <div id="outline"> </div> </div> <div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/624f522d74bc5c0105332fcf/bg1.jpg"><div class="c x1 y1 w2 h2"><div class="t m0 x2 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">1 </div></div><div class="c x3 y1 w3 h2"><div class="t m0 x4 h3 y2 ff2 fs0 fc0 sc0 ls0 ws0">Renesas Electronics </div></div><div class="c x5 y1 w4 h2"><div class="t m0 x4 h4 y3 ff2 fs1 fc0 sc0 ls0 ws0"> </div></div><div class="t m0 x1 h4 y4 ff2 fs1 fc0 sc0 ls0 ws0"> </div><div class="t m0 x6 h5 y5 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x7 h5 y6 ff3 fs2 fc0 sc0 ls0 ws0">Optimizing Battery Accuracy for EVs and HEVs<span class="_ _0"></span> </div><div class="t m0 x1 h4 y7 ff2 fs1 fc0 sc0 ls0 ws0"> </div><div class="t m0 x1 h6 y8 ff4 fs3 fc0 sc1 ls0 ws0">Introduction </div><div class="t m0 x1 h4 y9 ff2 fs1 fc0 sc0 ls0 ws0">Automotive battery m<span class="_ _1"></span>anagement system <span class="_ _1"></span>(BMS) technology<span class="_ _1"></span> has advanced <span class="_ _1"></span>considerably over the<span class="_ _1"></span> last decade. </div><div class="t m0 x1 h4 ya ff2 fs1 fc0 sc0 ls0 ws0">Today, several m<span class="_ _1"></span>ulti-cell balancing (<span class="_ _1"></span>MCB) IC features play <span class="_ _1"></span>a key role in meetin<span class="_ _1"></span>g the stringent sa<span class="_ _1"></span>fety, reliability </div><div class="t m0 x1 h4 yb ff2 fs1 fc0 sc0 ls0 ws0">and performan<span class="_ _1"></span>ce requirements of batter<span class="_ _1"></span>y systems in electric vehi<span class="_ _1"></span>cles (EVs), p<span class="_ _1"></span>lug-in hybrid electric vehicl<span class="_ _1"></span>es </div><div class="t m0 x1 h4 yc ff2 fs1 fc0 sc0 ls0 ws0">(PHEVs), and hybr<span class="_ _1"></span>id electric vehicle<span class="_ _1"></span>s (HEVs). IC man<span class="_ _1"></span>ufacturers are now <span class="_ _1"></span>focusing their efforts <span class="_ _1"></span>on further </div><div class="t m0 x1 h4 yd ff2 fs1 fc0 sc0 ls0 ws0">functional optimiz<span class="_ _1"></span>ation by integrat<span class="_ _1"></span>ing key features such <span class="_ _1"></span>as internal cell bala<span class="_ _1"></span>ncing a<span class="_ _0"></span>nd curre<span class="_ _1"></span>nt measurement. </div><div class="t m0 x1 h4 ye ff2 fs1 fc0 sc0 ls0 ws0">One of the crit<span class="_ _1"></span>ical functions of a <span class="_ _1"></span>BMS IC is the accur<span class="_ _1"></span>ate measurement <span class="_ _1"></span>of individual cell v<span class="_ _1"></span>oltages<span class="_ _0"></span>, which has <span class="_ _1"></span>a </div><div class="t m0 x1 h4 yf ff2 fs1 fc0 sc0 ls0 ws0">direct influence on b<span class="_ _1"></span>attery life and <span class="ff5">range over<span class="_ _1"></span> the vehicle’s service li<span class="_ _1"></span>fe<span class="ff2">. Accuracy is particularly<span class="_ _1"></span> important for </span></span></div><div class="t m0 x1 h4 y10 ff2 fs1 fc0 sc0 ls0 ws0">battery cell types t<span class="_ _1"></span>hat have a flat di<span class="_ _1"></span>scharge curve, like lit<span class="_ _1"></span>hium<span class="_ _0"></span>-iron phosphate <span class="_ _1"></span>cells, which benefits s<span class="_ _1"></span>maller </div><div class="t m0 x1 h4 y11 ff2 fs1 fc0 sc0 ls0 ws0">packs due to their lo<span class="_ _1"></span>w internal impedance. <span class="_ _1"></span>These cell t<span class="_ _1"></span>ypes make it necessary <span class="_ _1"></span>for system engineer<span class="_ _1"></span>s to </div><div class="t m0 x1 h4 y12 ff2 fs1 fc0 sc0 ls0 ws0">detect small ch<span class="_ _1"></span>anges in cell voltage as t<span class="_ _1"></span>he <span class="_ _0"></span>batter<span class="_ _1"></span>y discharges. Meas<span class="_ _1"></span>uring small cell voltage c<span class="_ _1"></span>hanges </div><div class="t m0 x1 h4 y13 ff2 fs1 fc0 sc0 ls0 ws0">requires a sop<span class="_ _1"></span>histicated combinatio<span class="_ _1"></span>n of accurate an<span class="_ _1"></span>d stable voltage refer<span class="_ _1"></span>ence, an analog fro<span class="_ _1"></span>nt end (AFE), </div><div class="t m0 x1 h4 y14 ff2 fs1 fc0 sc0 ls0 ws0">and a precision ADC, w<span class="_ _1"></span>hich is a consi<span class="_ _1"></span>derable design<span class="_ _1"></span> challenge for MCB IC <span class="_ _1"></span>designers. Adding to the system </div><div class="t m0 x1 h4 y15 ff2 fs1 fc0 sc0 ls0 ws0">design challeng<span class="_ _1"></span>e is the fact that d<span class="_ _1"></span>etecting these change<span class="_ _1"></span>s has become critical<span class="_ _1"></span> for accurate state <span class="_ _1"></span>of charge </div><div class="t m0 x1 h4 y16 ff2 fs1 fc0 sc0 ls0 ws0">(SOC) and state of <span class="_ _1"></span>health (SOH) calculation<span class="_ _1"></span>s. </div><div class="t m0 x1 h4 y17 ff2 fs1 fc0 sc0 ls0 ws0">This white paper <span class="_ _1"></span>discusses the <span class="_ _1"></span>decisions a system d<span class="_ _1"></span>esigner must make w<span class="_ _1"></span>hen selecting a <span class="_ _1"></span>BMS <span class="_ _0"></span>IC that can </div><div class="t m0 x1 h4 y18 ff2 fs1 fc0 sc0 ls0 ws0">provide accurate<span class="_ _1"></span> cell measurement acro<span class="_ _1"></span>ss the entire operating<span class="_ _1"></span> environment a<span class="_ _1"></span>nd life of the vehicle. <span class="_ _1"></span>For </div><div class="t m0 x1 h4 y19 ff2 fs1 fc0 sc0 ls0 ws0">automobile manu<span class="_ _1"></span>facturers, success<span class="_ _1"></span>ful BMS implementation req<span class="_ _1"></span>uires careful s<span class="_ _1"></span>election of the MCB IC <span class="_ _1"></span>at the </div><div class="t m0 x1 h4 y1a ff2 fs1 fc0 sc0 ls0 ws0">outset of system <span class="_ _1"></span>design, and that requires un<span class="_ _1"></span>derstanding the diff<span class="_ _1"></span>erences in measurement <span class="_ _1"></span>accuracy an<span class="_ _1"></span>d </div><div class="t m0 x1 h4 y1b ff2 fs1 fc0 sc0 ls0 ws0">stability between th<span class="_ _1"></span>e various IC vendor o<span class="_ _1"></span>fferings. Achieving the high<span class="_ _1"></span>est levels of automotiv<span class="_ _1"></span>e safety integrit<span class="_ _1"></span>y </div><div class="t m0 x1 h4 y1c ff2 fs1 fc0 sc0 ls0 ws0">level (ASIL)-<span class="ls1">D </span><span class="ff5">c<span class="_ _1"></span>ompliance is an<span class="_ _1"></span>other important consi<span class="_ _1"></span>deration, and we’ll sh<span class="_ _1"></span>ow how <span class="ff2">a redundant back-up </span></span></div><div class="t m0 x1 h4 y1d ff2 fs1 fc0 sc0 ls0 ws0">battery manageme<span class="_ _1"></span>nt device enables <span class="_ _1"></span>an ASIL-D compliant sy<span class="_ _1"></span>stem. </div><div class="t m0 x1 h6 y1e ff4 fs3 fc0 sc1 ls0 ws0">Key Elements in a Multi-Cell Balancing IC </div><div class="t m0 x1 h4 y1f ff2 fs1 fc0 sc0 ls0 ws0">At the core of any MC<span class="_ _1"></span>B IC is a precisio<span class="_ _1"></span>n reference. The ty<span class="_ _1"></span>pes of reference topol<span class="_ _1"></span>ogies employed can vary, </div><div class="t m0 x1 h4 y20 ff2 fs1 fc0 sc0 ls0 ws0">although bandg<span class="_ _1"></span>aps tend to be the most c<span class="_ _1"></span>ommonly used due to t<span class="_ _1"></span>heir optimal trade-off in a<span class="_ _1"></span>ccuracy versus die </div><div class="t m0 x1 h4 y21 ff2 fs1 fc0 sc0 ls0 ws0">area. For example, t<span class="_ _1"></span>he ISL78600 multi-cell Li<span class="_ _1"></span>-ion battery manager<span class="_ _1"></span> uses a precision bandg<span class="_ _1"></span>ap reference </div><div class="t m0 x1 h4 y22 ff2 fs1 fc0 sc0 ls0 ws0">design that ha<span class="_ _1"></span>s a solid track recor<span class="_ _1"></span>d, and is well suited f<span class="_ _1"></span>or demanding automotive applicatio<span class="_ _1"></span>ns. The </div><div class="t m0 x1 h4 y23 ff2 fs1 fc0 sc0 ls0 ws0">technology is stab<span class="_ _1"></span>le, mature, well ch<span class="_ _1"></span>aracterized, and<span class="_ _1"></span> has been optimized over <span class="_ _1"></span>many years of use, </div><div class="t m0 x1 h4 y24 ff2 fs1 fc0 sc0 ls0 ws0">underpinned by a <span class="_ _1"></span>substantial amount o<span class="_ _1"></span>f real-world performance <span class="_ _1"></span>data. Its excellent<span class="_ _1"></span> performance </div><div class="t m0 x1 h4 y25 ff2 fs1 fc0 sc0 ls0 ws0">characteristics m<span class="_ _1"></span>ake the precision<span class="_ _1"></span> bandga<span class="ff5">p reference very stable <span class="_ _1"></span>and linear ov<span class="_ _1"></span>er an MCB IC’s deploye<span class="_ _1"></span>d </span></div><div class="t m0 x1 h4 y26 ff2 fs1 fc0 sc0 ls0 ws0">lifetime. This is <span class="_ _1"></span>a key consideratio<span class="_ _1"></span>n when designers <span class="_ _1"></span>make vehicle batt<span class="_ _1"></span>ery<span class="_ _0"></span>-life calculations, <span class="_ _1"></span>and it directly </div><div class="t m0 x1 h4 y27 ff5 fs1 fc0 sc0 ls0 ws0">influences an auto<span class="_ _1"></span>maker’s warranty <span class="_ _1"></span>and cost of ow<span class="_ _1"></span>nership metrics.<span class="ff2"> </span></div><div class="t m0 x1 h4 y28 ff2 fs1 fc0 sc0 ls0 ws0">Along with a precisi<span class="_ _1"></span>on reference, the A<span class="_ _1"></span>DC is another key fun<span class="_ _1"></span>ctional block for m<span class="_ _1"></span>easuring accuracy. IC </div><div class="t m0 x1 h4 y29 ff2 fs1 fc0 sc0 ls0 ws0">designers must n<span class="_ _1"></span>ow decide which t<span class="_ _1"></span>ype of ADC to use as t<span class="_ _1"></span>he main cell-voltage-measurement b<span class="_ _1"></span>lock. Two of </div><div class="t m0 x1 h4 y2a ff2 fs1 fc0 sc0 ls0 ws0">the most popul<span class="_ _1"></span>ar and commonly use<span class="_ _1"></span>d types of ADCs <span class="_ _1"></span>are successive approxim<span class="_ _1"></span>ation register (SAR) and del<span class="_ _1"></span>ta-</div><div class="t m0 x1 h4 y2b ff2 fs1 fc0 sc0 ls0 ws0">sigma. Having the f<span class="_ _1"></span>astest sampli<span class="_ _1"></span>ng rate of the two t<span class="_ _1"></span>echnologies, the SAR<span class="_ _1"></span> offers high-speed voltage </div><div class="t m0 x1 h4 y2c ff2 fs1 fc0 sc0 ls0 ws0">conversion and <span class="_ _1"></span>excellent noise immunity, b<span class="_ _1"></span>ut tends to requir<span class="_ _1"></span>e a larger die are<span class="_ _1"></span>a. SAR ADCs also offer the<span class="_ _1"></span> best </div><div class="t m0 x1 h4 y2d ff2 fs1 fc0 sc0 ls0 ws0">combination of <span class="_ _1"></span>data acquisition speed, accura<span class="_ _1"></span>cy, robustness a<span class="_ _1"></span>nd immunity to<span class="_ _1"></span> the effects of EMI. </div><div class="t m0 x1 h4 y2e ff2 fs1 fc0 sc0 ls0 ws0">On the other han<span class="_ _1"></span>d, IC designers like delta-sigm<span class="_ _1"></span>a ADCs because they t<span class="_ _1"></span>ypically require les<span class="_ _1"></span>s die area, and are </div><div class="t m0 x1 h4 y2f ff2 fs1 fc0 sc0 ls0 ws0">relatively easy to imple<span class="_ _1"></span>ment. However, t<span class="_ _1"></span>hey tend to <span class="_ _1"></span>be slower because they use a decim<span class="_ _1"></span>ation filter, whic<span class="_ _1"></span>h </div><a class="l" rel='nofollow' onclick='return false;'><div class="d m1"></div></a></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div> </body> </html>

<div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/624f522d74bc5c0105332fcf/bg2.jpg"><div class="c x1 y1 w2 h2"><div class="t m0 x2 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">2 </div></div><div class="c x3 y1 w3 h2"><div class="t m0 x4 h3 y2 ff2 fs0 fc0 sc0 ls0 ws0">Renesas Electronics </div></div><div class="c x5 y1 w4 h2"><div class="t m0 x4 h4 y3 ff2 fs1 fc0 sc0 ls0 ws0"> </div></div><div class="t m0 x1 h4 y4 ff2 fs1 fc0 sc0 ls0 ws0"> </div><div class="t m0 x1 h4 y30 ff2 fs1 fc0 sc0 ls0 ws0">reduces the s<span class="_ _1"></span>ample rate and data <span class="_ _1"></span>acquisition speed.<span class="_ _1"></span> To overcome this i<span class="_ _1"></span>ssue, designers will use tw<span class="_ _1"></span>o or more </div><div class="t m0 x1 h4 y31 ff2 fs1 fc0 sc0 ls0 ws0">delta-sigma ADCs in a<span class="_ _1"></span>n interleaved con<span class="_ _1"></span>figuration. Another co<span class="_ _1"></span>nsideration when <span class="_ _1"></span>implementing delta-sigma </div><div class="t m0 x1 h4 y32 ff2 fs1 fc0 sc0 ls0 ws0">ADCs is their tenden<span class="_ _1"></span>cy to saturate whe<span class="_ _1"></span>n subjected to EMI, w<span class="_ _1"></span>hich causes the <span class="_ _1"></span>misreporting of cell v<span class="_ _1"></span>oltages. </div><div class="t m0 x1 h4 y33 ff5 fs1 fc0 sc0 ls0 ws0">The individual <span class="_ _1"></span>cells’ interface is m<span class="_ _1"></span>anaged by the AF<span class="_ _1"></span>E, which integrates input <span class="_ _1"></span>buffers, level shifter<span class="_ _1"></span>s and fault </div><div class="t m0 x1 h4 y34 ff2 fs1 fc0 sc0 ls0 ws0">detection circuitry. T<span class="_ _1"></span>he AFE is key to h<span class="_ _1"></span>andling hot plug tr<span class="_ _1"></span>ansients when the cel<span class="_ _1"></span>ls are initially connecte<span class="_ _1"></span>d to the </div><div class="t m0 x1 h4 y35 ff2 fs1 fc0 sc0 ls0 ws0">BMS. The ISL78<span class="_ _1"></span>600 is designe<span class="_ _1"></span>d with a fully differe<span class="_ _1"></span>ntial AFE that enables<span class="_ _1"></span> negativ<span class="_ _1"></span>e input voltages to be </div><div class="t m0 x1 h4 y36 ff2 fs1 fc0 sc0 ls0 ws0">measured witho<span class="_ _1"></span>ut affecting the a<span class="_ _1"></span>djacent cell measur<span class="_ _1"></span>ements. This is a<span class="_ _1"></span>dvantageous in systems where bus bar </div><div class="t m0 x1 h4 y37 ff2 fs1 fc0 sc0 ls0 ws0">interconnection i<span class="_ _1"></span>s required. To improve robu<span class="_ _1"></span>stness under tr<span class="_ _1"></span>ansient conditions<span class="_ _1"></span>, an external low-pass filter is </div><div class="t m0 x1 h4 y38 ff2 fs1 fc0 sc0 ls0 ws0">added to the cell v<span class="_ _1"></span>oltage inputs. The i<span class="_ _1"></span>nput filtering requirement<span class="_ _1"></span>s have been o<span class="_ _1"></span>ptimized for maximum E<span class="_ _1"></span>MI and </div><div class="t m0 x1 h4 y39 ff2 fs1 fc0 sc0 ls0 ws0">hot plug immunity, wit<span class="_ _1"></span>hout compromising <span class="_ _1"></span>speed or accuracy. <span class="_ _1"></span>By contrast, ICs <span class="_ _1"></span>that use a bipolar A<span class="_ _1"></span>FE rather </div><div class="t m0 x1 h4 y3a ff2 fs1 fc0 sc0 ls0 ws0">than a charge c<span class="_ _1"></span>oupled AFE can have th<span class="_ _1"></span>eir accuracy detriment<span class="_ _1"></span>ally affected by t<span class="_ _1"></span>he component valu<span class="_ _1"></span>es selected </div><div class="t m0 x1 h4 y3b ff2 fs1 fc0 sc0 ls0 ws0">for the input filter. <span class="_ _1"></span>Figure 1 shows a si<span class="_ _1"></span>mplified diagr<span class="_ _1"></span>am of the<span class="_ _0"></span> <span class="ff5">ISL78600’s t<span class="_ _1"></span>hree function<span class="_ _1"></span>al blocks and their<span class="_ _1"></span> </span></div><div class="t m0 x1 h4 y3c ff2 fs1 fc0 sc0 ls0 ws0">interconnection. </div><div class="t m0 x8 h4 y3d ff2 fs1 fc0 sc0 ls0 ws0"> </div><div class="t m0 x7 h4 y3e ff2 fs1 fc0 sc1 ls0 ws0">Figure 1. Simplified block diagram of the ISL7860<span class="_ _1"></span>0 multi-cell Li-ion battery manager </div><div class="t m0 x1 h4 y3f ff2 fs1 fc0 sc0 ls0 ws0">The combination <span class="_ _1"></span>of a stable and line<span class="_ _1"></span>ar bandgap refer<span class="_ _1"></span>ence, SAR ADC and fully <span class="_ _1"></span>differential AFE gives <span class="_ _1"></span>a multi<span class="_ _0"></span>-</div><div class="t m0 x1 h4 y40 ff2 fs1 fc0 sc0 ls0 ws0">cell Li-ion battery man<span class="_ _1"></span>ager fast dat<span class="_ _1"></span>a acquisition capab<span class="_ _1"></span>ility combined with robu<span class="_ _1"></span>stness and preci<span class="_ _1"></span>sion accuracy. </div><div class="t m0 x1 h4 y41 ff2 fs1 fc0 sc0 ls0 ws0">Rather than relying <span class="_ _1"></span>simply on the me<span class="_ _1"></span>asu<span class="ff5">red accuracy values <span class="_ _1"></span>as it leaves the fa<span class="_ _1"></span>ctory, the ISL78600’<span class="_ _1"></span>s high </span></div><div class="t m0 x1 h4 y42 ff2 fs1 fc0 sc0 ls0 ws0">accuracy is indepen<span class="_ _1"></span>dently verified after<span class="_ _1"></span> mounting on a PCB. </div><div class="t m0 x1 h4 y43 ff2 fs1 fc0 sc0 ls0 ws0"> </div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>