JP2004271342A

JP2004271342A - Charging and discharging control system

Info

Publication number: JP2004271342A
Application number: JP2003062613A
Authority: JP
Inventors: Akihiko Kudo; 彰彦工藤; Masaki Nagaoka; 正樹長岡; Noriyoshi Sasazawa; 憲佳笹澤; Shigeyuki Yoshihara; 重之吉原
Original assignee: Hitachi Ltd; Shin Kobe Electric Machinery Co Ltd; Hitachi Car Engineering Co Ltd
Current assignee: Hitachi Ltd; Hitachi Automotive Systems Engineering Co Ltd; Resonac Corp
Priority date: 2003-03-10
Filing date: 2003-03-10
Publication date: 2004-09-30
Anticipated expiration: 2023-03-10
Also published as: JP4415074B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging and discharging control system which will not make wrong decision in the degradation of a secondary battery. <P>SOLUTION: The charging and discharging current I a secondary battery and the charging and discharging voltage V of the same are measured at regular intervals (S112), and the measured values are stored in a nonvolatile RAM. The internal resistance R of the battery is calculated (S122) by the regression analysis of the constant amount of the stored measurement data. The accumulated electric charge quantity or the accumulated electric discharge quantity of the battery is calculated from the integrated value of the charging and discharging current; and the degradation state of the battery is decided, based on the calculated values of the internal resistance R and the accumulated electrically charged and discharged quantity (S128). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は充放電制御システムに係り、特に、二次電池の充放電電流と充放電電圧とを一定時間毎に測定し、該測定値から充電状態を推定して電池の充放電を制御する充放電制御システムに関する。
【０００２】
【従来の技術】
従来、二次電池の簡易充放電制御システムでは、充電終了後状態を検出したときを満充電状態として電池の充電を終了させ、放電終止電圧を検出したときを完全放電状態として放電を終了させる方式が用いられてきた。一方、高精度充放電制御システムでは、二次電池の充放電電気量を測定して制御する方式も用いられている。この方式では、充放電電気量を測定しているので、電池の残存容量を把握できるという利点がある。また、満充電状態から放電末期状態まで放電した場合には満充電容量を実測しているので、この放電容量から電池の劣化状態を把握することができる。
【０００３】
しかしながら、例えば、二次電池とモータジェネレータ及びエンジンとを用いたハイブリッド車等の、完全な充放電を繰り返さない用途では、二次電池は短時間の充放電を頻繁に繰り返して使用される。ハイブリッド車では、二次電池として鉛電池、ニッケル水素電池、リチウムイオン電池等が用いられており、最近では高エネルギー密度のリチウムイオン電池が使用されるようになってきている。この場合、電池の入出力特性を最大限に引き出し、かつ寿命を長くするためには、充放電させる残存容量乃至充電状態の値（ＳＯＣ：満充電が１００％、完全放電が０％）が重要であり、ＳＯＣの管理を行わないと充分な入出力特性が得られないだけでなく、寿命が短くなってしまう。
【０００４】
また、ハイブリッド車用等の短時間の充放電を行うシステムでは、電池の満充電容量よりも最大入出力電力が重要であり、この最大入出力電力を決定する電池の内部抵抗が電池の状態を示すパラメータとして劣化判断に用いられている。このような劣化判断方法として、一定時間毎に電池の入出力電圧と電流とを測定し、その測定値の一定数量のデータを回帰分析して内部抵抗を算出する技術が知られている（例えば、特許文献１参照）。
【０００５】
【特許文献１】
特開平１０−１０６６３５公報
【０００６】
【発明が解決しようとする課題】
ところが、従来の方式では、回帰分析して得られた内部抵抗の値にバラツキが生ずるため、二次電池の劣化判断を誤る可能性を持っている。
【０００７】
この例を図面を参照して説明する。図３は定格３．６Ａｈ、ＳＯＣ５０％で内部抵抗約４ｍΩのリチウムイオン電池に短時間の充放電を繰り返した場合の電流推移を示し、図４はそのときの電圧推移を示している。なお、これらの電流、電圧推移は１ｓｅｃ毎に測定したものである。また、図５は６０秒間の電流と電圧の測定値を回帰分析して内部抵抗を算出した結果を、図６は３０秒間の回帰分析結果の内部抵抗値をそれぞれ示している。
【０００８】
図５に示すように、内部抵抗の算出値は０から６ｍΩまで変化しており、バラツキが大きい。この例は回帰分析を６０秒間行ったものであるが、図６に示す３０秒間回帰分析を行った結果では更にバラツキが大きくなり、内部抵抗の計算値は−１から１０ｍΩまで変化している。このリチウムイオン電池では内部抵抗が約８ｍΩまで上昇した場合に所定の入出力特性が得られないため寿命と判定されるが、この結果のみから劣化を判断すると充放電電流によっては寿命との判定がなされ、劣化判定を誤る可能性があることになる。
【０００９】
本発明は上記事案に鑑み、二次電池の劣化判定を誤ることのない充放電制御システムを提供することを課題とする。
【００１０】
【課題を解決するための手段】
上記課題を解決するために、本発明は、二次電池の充放電電流と充放電電圧とを一定時間毎に測定し、該測定値から充電状態（ＳＯＣ）を推定して前記電池の充放電を制御する充放電制御システムにおいて、前記充放電電流及び充放電電圧測定値の一定数量のデータから回帰分析を行って前記電池の内部抵抗を算出すると共に、前記充放電電流の積算値から前記電池の累積充電電気量又は累積放電電気量を算出し、前記内部抵抗及び前記累積充放電電気量の算出値に基づいて前記電池の劣化状態を判定することを特徴とする。
【００１１】
本発明によれば、回帰分析で求めた内部抵抗の算出値だけでなく、累積の充放電電気量を含めて二次電池の劣化判断を行うので、バラツキの大きい回帰分析から求めた内部抵抗の算出値からの劣化判定ミスを無くすことができる。なお、二次電池にリチウムイオン電池を用いる場合には、充電効率がほぼ１００％のため、充電電気量及び放電電気量のいずれを用いてもよい。
【００１２】
この場合に、電池の内部抵抗が所定値以上、かつ、電池の累積充電電気量又は累積放電電気量が所定値以上となったときに、電池が劣化したと判定することが好ましい。また、電池が充放電されているときの電池温度を測定し、この測定値と充放電電流又は充放電電圧から算出した充電状態とを、電池温度と充電状態とをパラメータとするマップに当てはめて内部抵抗の算出値の補正を行い、補正後の値を内部抵抗の算出値として電池の劣化状態を判定すれば、回帰分析で求めた内部抵抗の算出値を温度とＳＯＣとで補正しているので、真の値に近い内部抵抗値で劣化判断が可能なため、更に正確に二次電池の劣化判定を行うことができる。このとき、内部抵抗の算出値の補正は、予め定められた標準温度及び標準充電状態における内部抵抗値に補正することが望ましい。
【００１３】
また、何らかの原因で真に内部抵抗が大きくなった場合には、回帰分析で求めたバラツキを含む内部抵抗の算出値も大きくなる可能性が大きいので、電池が充放電されているときの電池温度を測定し、この測定値と充放電電流又は充放電電圧から算出した充電状態とを、電池温度と充電状態とをパラメータとするマップに当てはめて内部抵抗の算出値の補正を行うことで得られた内部抵抗値が所定値以上となったときに電池が劣化したと判定してもよく、又は、電池の劣化は電池の充放電電気量に概ね比例するので、電池の累積充電電気量若しくは累積放電電気量が所定値以上となったときに電池が劣化したと判定してもよい。
【００１４】
【発明の実施の形態】
以下、本発明が適用可能な充放電制御システムの実施の形態について説明する。
【００１５】
（構成）
図１に示すように、本実施形態の充放電制御システムは、ホール素子等の電流センサを有しリチウムイオン電池が９６直列に接続されたリチウムイオン電池群１に流れる充放電電流を測定する充放電電流測定回路２、リチウムイオン電池群１の総電圧を測定する総電圧測定回路３、サーミスタ等の温度センサを有しリチウムイオン電池群１のうち略中央部に配置された特定のリチウムイオン電池の電池温度を測定する温度測定回路４、及び、中央演算処理装置として機能するＣＰＵ、充放電制御システムの基本制御プログラム及び後述するテーブルデータ等を記憶したＲＯＭ、ＣＰＵのワークエリアとして機能するＲＡＭ、並びにＡ／Ｄコンバータ等を有するデータ処理用のマイクロコンピュータ部５を備えている。マイクロコンピュータ部５には測定したデータを記憶する不揮発性ＲＡＭ７が接続されている。従って、充放電制御システムは、電源の供給が停止しても、不揮発性ＲＡＭ７に記憶されたデータは保存される構成を有している。
【００１６】
リチウムイオン電池群１は、例えば、直列接続された２つの電池モジュール（不図示）で構成されており、各電池モジュールには４８個のリチウムイオン電池が直列に接続されている。各電池モジュールは図示しないマイクロコンピュータ部を内蔵しており、このマイクロコンピュータ部の制御により、リチウムイオン電池群１の充放電中に、電池モジュールを構成する各リチウムイオン電池がほぼ同一の容量を維持するように容量調整が実行される。
【００１７】
実際のリチウムイオン電池群１の充放電は、上位の充放電電流制御部により制御される。充放電システムは、後述するように、リチウムイオン電池群１の充電状態（ＳＯＣ）やリチウムイオン電池群１の劣化判定結果等の情報を報知するために、マイクロコンピュータ部５に接続された通信インターフエイス部６を介して上位の充放電電流制御部に接続されている。
【００１８】
（動作）
次に、フローチャートを参照して充放電制御システムの動作について、マイクロコンピュータ部５のＣＰＵを主体として説明する。なお、マイクロコンピュータ部５に電源が投入されると、リチウムイオン電池群１を構成するリチウムイオン電池の劣化を判定する劣化判定ルーチンが実行される。
【００１９】
図２に示すように、劣化判定ルーチンでは、まずステップ１１２で、総電圧測定回路３及び電流測定回路２からのアナログデータをＡ／Ｄコンバータでデジタルデータに変換してリチウムイオン電池群１の総電圧Ｖ及びリチウムイオン電池群１に流れる充放電電流Ｉを取り込み（測定し）、ＲＡＭ７に格納する。次にステップ１１４で、リチウムイオン電池群１に流れる充放電電流Ｉの積算値Ｑ（Ｑ＝∫Ｉｄｔ）を不揮発性ＲＡＭ７に格納する。このような処理は、例えば、ＲＡＭ７に前回格納した積算値Ｑを読み出して、前回の積算値Ｑに、今回測定した放電電流Ｉと前回からの今回までの時間Δｔとを掛けた値、を加算してＲＡＭ７に格納すればよい。
【００２０】
次にステップ１１６において、電池温度Ｔを測定するタイミングか否かを判断する。このような測定タイミングを判断するために、例えば、カウンタを用いることができる。肯定判断のときは、ステップ１１８で温度測定回路４からのアナログデータをＡ／Ｄコンバータでデジタルデータに変換して電池温度Ｔを取り込み（測定し）、否定判断のときは、次のステップ１２０へ進む。すなわち、電池温度Ｔは、総電圧Ｖ及び充放電電流Ｉの測定周期より長い周期で測定される。なお、ステップ１１２〜ステップ１１８で測定されるデータは、総電圧Ｖ、充放電電流Ｉ、電池温度Ｔの３種類であり、従来の充放電制御システムと何ら変わるところはない。
【００２１】
次いでステップ１２０では、ステップ１１２で測定された総電圧Ｖの値と充放電電流Ｉの値とから電池の充電状態（以下、ＳＯＣという。）を演算し、次のステップ１２２において、ＲＡＭ７に格納した総電圧Ｖ及び充放電電流Ｉの値の時系列的な変化データのうち直近の一定数量（例えば、各１００個）のデータから、最小二乗法等の回帰分析により電池の内部抵抗Ｒを演算する。
【００２２】
次にステップ１２４では、ステップ１１８で測定された電池温度Ｔとステップ１２０で演算したＳＯＣとをパラメータとするマップにより係数αを求め、この係数αをステップ１２２で演算した内部抵抗Ｒの値に乗じることで、標準ＳＯＣ、標準温度での内部抵抗の値に変換（補正）する。なお、本例では、下表１に示すように、マップにＳＯＣが５０％、電池温度Ｔが２５°Ｃに変換可能なテーブルを使用した。表１は離散値のテーブルであるが、ステップ１２０では補完によって正確な値に変換可能である。
【００２３】
【表１】

【００２４】
ステップ１２６ではＳＯＣ及び補正後の内部抵抗Ｒを上位の充放電電流制御部へ報知し、次のステップ１２８において、電池が劣化したか否かを判定する。電池の劣化判定は下表２に示す劣化判定テーブルに基づいて行われる。表２は補正後の内部抵抗と累積充放電電気量をパラメータとするテーブルであり、内部抵抗値がある設定値以上、かつ、累積充放電電気量がある設定値以上の場合に劣化したと判定するテーブルである。
【００２５】
【表２】

【００２６】
ステップ１２８で肯定判定のときは、次のステップ１３０で上位の充放電電流制御部へ電池の劣化を報知し、否定判定のときは、ステップ１１２へ戻る。電池の劣化の報知を受けた上位の充放電電流制御部は、インストールメンタルパネル（インパネ）を制御する表示制御部（不図示）又はその上位の制御部（不図示）へインパネに電池の劣化を表示すべき旨を報知する。これにより、インパネに電池の劣化が表示され、ドライバは電池が劣化したことを知ることができる。
【００２７】
（作用等）
本実施形態の充放電制御システムでは、表２に示したように、内部抵抗Ｒと累積充放電電気量との両者で電池の劣化判定を行うので（ステップ１２６）、回帰分析から求めた内部抵抗のバラツキが大きくても、誤ることなく電池の劣化判定を行うことができる。図７に本例での累積充放電電気量と内部抵抗との関係を示す。図７に示すように、充放電を行って累積充放電電気量が増えると内部抵抗は間違いなく増加するので、累積充放電電気量が設定値以上となった場合に、電池が劣化している可能性は大きく、劣化判定ミスを行う可能性は少ない。
【００２８】
また、本実施形態の充放電制御システムでは、表１に示したように、回帰分析で求めた内部抵抗を電池温度とＳＯＣとで補正するので（ステップ１２４）、真の値に近い内部抵抗値で正確に電池の劣化判定を行うことが可能である（ステップ１２６）。図８に本例での内部抵抗の温度依存性を、図９に内部抵抗のＳＯＣ依存性をそれぞれ示す。このように、内部抵抗は温度とＳＯＣとによって変化するので、基準の温度と基準のＳＯＣとを決定しておけば、より正確な内部抵抗値で劣化判定を行うことが可能である。
【００２９】
更に、本実施形態の充放電制御システムは累積充放電電気量を測定できればよく、従来の充放電制御システムに不揮発性ＲＡＭ７等の記憶装置を付加するだけの構成で、劣化判定を正確に行うことが可能である。
【００３０】
なお、本実施形態では、内部抵抗Ｒ及び累積充放電電気量で電池の劣化判定を行う例を示したが、補正後の内部抵抗は真の内部抵抗値に近く、また、図７に示したように累積充放電電気量と内部抵抗とには相関関係が存在するので、補正後の内部抵抗及び累積充放電電気量の一方で電池の劣化判定を行うようにしてもよい。
【００３１】
また、本実施形態では、表１に「正常」と「劣化」の２状態の区別を行うだけのテーブルを例示したが、本発明はこれに限定されず、要求特性に応じて「要注意」等の３段階以上の判断を行うテーブルとしてもよい。更に、本実施形態では、マップにテーブルを例示したが、数式等を用いるようにしてもよい。
【００３２】
そして、本実施形態では、説明を簡単にするために、温度センサを１個とした例を示したが、電池モジュール毎に１個又は複数個でリチウムイオン電池の温度を測定し、測定した温度の平均値や体操平均値等を用いるようにしてもよい。
【００３３】
【発明の効果】
以上説明したように、本発明によれば、回帰分析で求めた内部抵抗の算出値だけでなく、累積の充放電電気量を含めて二次電池の劣化判断を行うので、バラツキの大きい回帰分析から求めた内部抵抗の算出値からの劣化判定ミスを無くすことができる、という効果を得ることができる。
【図面の簡単な説明】
【図１】本発明が適用可能な実施形態の充放電制御システムの概略構成を示すブロック回路図である。
【図２】実施形態の充放電制御システムの劣化判定ルーチンのフローチャートである。
【図３】充放電時の充放電電流の推移を示す特性線図である。
【図４】充放電時の充放電電圧の推移を示す特性線図である。
【図５】６０秒間の電圧と電流の回帰分析値から算出した内部抵抗の推移を示す特性線図である。
【図６】３０秒間の電圧と電流の回帰分析値から算出した内部抵抗の推移を示す特性線図である。
【図７】累積充放電電気量と内部抵抗の関係を示す特性線図である。
【図８】内部抵抗の温度依存性を示す特性線図である。
【図９】内部抵抗のＳＯＣ依存性を示す特性線図である。
【符号の説明】
１リチウムイオン電池群
２充放電電流測定回路
３総電圧測定回路
４温度測定回路
５マイクロコンピュータ部
６通信インターフエイス部
７不揮発性ＲＡＭ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charge / discharge control system, and in particular, measures a charge / discharge current and a charge / discharge voltage of a secondary battery at regular intervals, estimates a state of charge from the measured values, and controls the charge / discharge of the battery. It relates to a discharge control system.
[0002]
[Prior art]
Conventionally, in a simple charge / discharge control system for a secondary battery, a method of terminating charging of a battery when a state after the end of charge is detected is set to a fully charged state and terminating discharge when a discharge end voltage is detected is set to a complete discharge state. Has been used. On the other hand, in a high-precision charge / discharge control system, a method of measuring and controlling the amount of charge / discharge of a secondary battery is also used. In this method, since the amount of charge / discharge electricity is measured, there is an advantage that the remaining capacity of the battery can be grasped. Further, when the battery is discharged from the fully charged state to the end of discharge state, the fully charged capacity is actually measured, so that the state of deterioration of the battery can be grasped from the discharged capacity.
[0003]
However, in applications in which complete charge / discharge is not repeated, such as a hybrid vehicle using a secondary battery, a motor generator, and an engine, the secondary battery is frequently used by repeatedly charging and discharging for a short time. In a hybrid vehicle, a lead battery, a nickel-metal hydride battery, a lithium ion battery, or the like is used as a secondary battery, and a lithium ion battery having a high energy density has recently been used. In this case, in order to maximize the input / output characteristics of the battery and extend the life, the value of the remaining capacity to be charged / discharged or the state of charge (SOC: 100% full charge, 0% complete discharge) is important. However, if the SOC is not managed, not only the sufficient input / output characteristics cannot be obtained, but also the life is shortened.
[0004]
In a system that charges and discharges in a short time, such as for a hybrid vehicle, the maximum input / output power is more important than the full charge capacity of the battery, and the internal resistance of the battery that determines the maximum input / output power determines the state of the battery. These parameters are used for determining deterioration. As such a deterioration determination method, a technique is known in which the input / output voltage and current of a battery are measured at regular intervals, and the internal resistance is calculated by performing regression analysis on a fixed quantity of data of the measured values (eg, for example). And Patent Document 1).
[0005]
[Patent Document 1]
JP-A-10-106635
[Problems to be solved by the invention]
However, in the conventional method, since the value of the internal resistance obtained by the regression analysis varies, there is a possibility that the deterioration judgment of the secondary battery is erroneously made.
[0007]
This example will be described with reference to the drawings. FIG. 3 shows a current transition when a short-time charge / discharge operation is repeatedly performed on a lithium ion battery having a rating of 3.6 Ah and an SOC of 50% and an internal resistance of about 4 mΩ, and FIG. 4 shows a voltage transition at that time. Note that these current and voltage transitions are measured every 1 sec. FIG. 5 shows the result of regression analysis of the measured values of current and voltage for 60 seconds to calculate the internal resistance, and FIG. 6 shows the internal resistance value of the result of regression analysis for 30 seconds.
[0008]
As shown in FIG. 5, the calculated value of the internal resistance changes from 0 to 6 mΩ, and the variation is large. In this example, the regression analysis was performed for 60 seconds. However, the result of the regression analysis performed for 30 seconds shown in FIG. 6 shows that the variation was further increased, and the calculated value of the internal resistance changed from -1 to 10 mΩ. In this lithium ion battery, when the internal resistance rises to about 8 mΩ, a predetermined input / output characteristic cannot be obtained, so that the life is judged. However, when the deterioration is judged only from this result, the life is judged depending on the charging / discharging current. That is, there is a possibility that the deterioration determination is erroneously made.
[0009]
The present invention has been made in view of the above circumstances, and has as its object to provide a charge / discharge control system that does not erroneously judge deterioration of a secondary battery.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention measures the charging / discharging current and charging / discharging voltage of a secondary battery at regular intervals, estimates a state of charge (SOC) from the measured values, and charges / discharges the battery. In the charge / discharge control system that controls the battery, a regression analysis is performed from a fixed number of data of the charge / discharge current and the charge / discharge voltage measurement value to calculate the internal resistance of the battery, and the battery is calculated from the integrated value of the charge / discharge current. And calculating the accumulated state of charge of the battery based on the internal resistance and the calculated value of the accumulated state of charge and discharge.
[0011]
According to the present invention, not only the calculated value of the internal resistance obtained by the regression analysis, but also the deterioration judgment of the secondary battery including the cumulative amount of charge and discharge electricity, so that the internal resistance of the internal resistance obtained from the regression analysis with large variation It is possible to eliminate a deterioration determination error from the calculated value. In the case where a lithium ion battery is used as the secondary battery, the charging efficiency is almost 100%. Therefore, any of the charged electricity amount and the discharged electricity amount may be used.
[0012]
In this case, it is preferable to determine that the battery has deteriorated when the internal resistance of the battery is equal to or more than a predetermined value and the accumulated charge amount or the accumulated discharge amount of the battery is equal to or more than a predetermined value. Also, the battery temperature when the battery is charged and discharged is measured, and the measured value and the charge state calculated from the charge / discharge current or the charge / discharge voltage are applied to a map using the battery temperature and the charge state as parameters. If the calculated value of the internal resistance is corrected, and the corrected value is used as the calculated value of the internal resistance to determine the state of deterioration of the battery, the calculated value of the internal resistance obtained by the regression analysis is corrected by the temperature and the SOC. Therefore, the deterioration can be determined by the internal resistance value close to the true value, so that the deterioration of the secondary battery can be more accurately determined. At this time, it is desirable that the calculated value of the internal resistance is corrected to the internal resistance value at a predetermined standard temperature and standard charging state.
[0013]
Also, if the internal resistance really increases for some reason, the calculated value of the internal resistance including the variation obtained by regression analysis is likely to increase, so the battery temperature when the battery is charged and discharged Is obtained by correcting the calculated value of the internal resistance by applying the measured value and the charge state calculated from the charge / discharge current or the charge / discharge voltage to a map using the battery temperature and the charge state as parameters. It may be determined that the battery has deteriorated when the internal resistance value is equal to or greater than a predetermined value, or since the deterioration of the battery is substantially proportional to the charge / discharge electricity amount of the battery, the accumulated charge electricity amount or the accumulated charge amount of the battery may be determined. The battery may be determined to have deteriorated when the amount of discharged electricity is equal to or greater than a predetermined value.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a charge / discharge control system to which the present invention can be applied will be described.
[0015]
(Constitution)
As shown in FIG. 1, the charge / discharge control system of the present embodiment measures a charge / discharge current flowing through a lithium ion battery group 1 having a current sensor such as a Hall element and having 96 lithium ion batteries connected in series. A specific lithium-ion battery having a discharge current measurement circuit 2, a total voltage measurement circuit 3 for measuring the total voltage of the lithium-ion battery group 1, and a temperature sensor such as a thermistor, which is disposed substantially in the center of the lithium-ion battery group 1 A temperature measuring circuit 4 for measuring the battery temperature, a CPU functioning as a central processing unit, a ROM storing a basic control program of a charge / discharge control system and table data described later, a RAM functioning as a work area of the CPU, And a data processing microcomputer unit 5 having an A / D converter and the like. The microcomputer unit 5 is connected to a nonvolatile RAM 7 for storing measured data. Therefore, the charge / discharge control system has a configuration in which the data stored in the nonvolatile RAM 7 is saved even when the power supply is stopped.
[0016]
The lithium-ion battery group 1 is composed of, for example, two battery modules (not shown) connected in series, and 48 lithium-ion batteries are connected in series to each battery module. Each battery module has a built-in microcomputer unit (not shown). Under the control of the microcomputer unit, during charging and discharging of the lithium ion battery group 1, each lithium ion battery constituting the battery module maintains substantially the same capacity. Capacity adjustment is performed.
[0017]
The actual charge / discharge of the lithium ion battery group 1 is controlled by a higher-order charge / discharge current controller. As will be described later, the charge / discharge system communicates with the microcomputer unit 5 to notify information such as the state of charge (SOC) of the lithium ion battery group 1 and the result of the deterioration determination of the lithium ion battery group 1. It is connected to a higher-order charge / discharge current control unit via a face unit 6.
[0018]
(motion)
Next, the operation of the charge / discharge control system will be described mainly with the CPU of the microcomputer unit 5 with reference to a flowchart. When the microcomputer unit 5 is turned on, a deterioration determination routine for determining the deterioration of the lithium ion batteries constituting the lithium ion battery group 1 is executed.
[0019]
As shown in FIG. 2, in the deterioration determination routine, first, in step 112, the analog data from the total voltage measurement circuit 3 and the current measurement circuit 2 are converted into digital data by an A / D converter, and the total The voltage V and the charging / discharging current I flowing through the lithium ion battery group 1 are taken (measured) and stored in the RAM 7. Next, at step 114, the integrated value Q (Q = ∫Idt) of the charge / discharge current I flowing through the lithium ion battery group 1 is stored in the nonvolatile RAM 7. In such processing, for example, the integrated value Q previously stored in the RAM 7 is read, and a value obtained by multiplying the previous integrated value Q by the discharge current I measured this time and the time Δt from the previous time to the present time is added. And store it in the RAM 7.
[0020]
Next, in step 116, it is determined whether or not it is time to measure the battery temperature T. In order to determine such a measurement timing, for example, a counter can be used. If the determination is affirmative, the analog data from the temperature measurement circuit 4 is converted into digital data by the A / D converter to take in (measure) the battery temperature T in step 118, and to the next step 120 if the determination is negative. move on. That is, the battery temperature T is measured in a cycle longer than the measurement cycle of the total voltage V and the charging / discharging current I. It should be noted that the data measured in steps 112 to 118 are three types of the total voltage V, the charge / discharge current I, and the battery temperature T, and there is no difference from the conventional charge / discharge control system.
[0021]
Next, at step 120, the state of charge (hereinafter referred to as SOC) of the battery is calculated from the value of the total voltage V and the value of the charge / discharge current I measured at step 112, and stored in the RAM 7 at the next step 122. The internal resistance R of the battery is calculated by regression analysis such as the least squares method from the latest fixed quantity (for example, 100 pieces) of the data of the time series change data of the total voltage V and the charge / discharge current I. .
[0022]
Next, in step 124, a coefficient α is obtained from a map using the battery temperature T measured in step 118 and the SOC calculated in step 120 as parameters, and the coefficient α is multiplied by the value of the internal resistance R calculated in step 122. Thus, the value is converted (corrected) into the value of the internal resistance at the standard SOC and the standard temperature. In this example, as shown in Table 1 below, a table that can convert the SOC to 50% and the battery temperature T to 25 ° C. was used for the map. Table 1 is a table of discrete values, but in step 120, it can be converted to an accurate value by interpolation.
[0023]
[Table 1]

[0024]
In step 126, the SOC and the corrected internal resistance R are notified to the upper-level charge / discharge current controller, and in the next step 128, it is determined whether or not the battery has deteriorated. The battery deterioration determination is performed based on the deterioration determination table shown in Table 2 below. Table 2 is a table in which the internal resistance after correction and the accumulated charge / discharge electricity amount are used as parameters. When the internal resistance value is equal to or greater than a certain set value and the accumulated charge / discharge electricity amount is equal to or greater than a certain set value, it is determined that the battery is deteriorated It is a table to do.
[0025]
[Table 2]

[0026]
If the determination in step 128 is affirmative, the next step 130 is to notify the higher-order charge / discharge current control unit of the deterioration of the battery, and if the determination is negative, the process returns to step 112. The upper-level charge / discharge current control unit that has received the notification of the battery deterioration notifies the display control unit (not shown) or the upper-level control unit (not shown) that controls the installation mental panel (instrument panel) of the battery deterioration to the instrument panel. Notify that it should be displayed. Thereby, the deterioration of the battery is displayed on the instrument panel, and the driver can know that the battery has deteriorated.
[0027]
(Action, etc.)
In the charge / discharge control system of the present embodiment, as shown in Table 2, the deterioration of the battery is determined based on both the internal resistance R and the accumulated charge / discharge electricity amount (step 126). Even if the variation of the battery is large, the battery deterioration can be determined without error. FIG. 7 shows the relationship between the accumulated charge / discharge electricity amount and the internal resistance in this example. As shown in FIG. 7, the internal resistance definitely increases when charging / discharging is performed to increase the accumulated charge / discharge electricity amount. Therefore, when the accumulated charge / discharge electricity amount exceeds a set value, the battery is deteriorated. The possibility is large, and the possibility of making a deterioration determination error is small.
[0028]
Further, in the charge / discharge control system of this embodiment, as shown in Table 1, the internal resistance obtained by the regression analysis is corrected by the battery temperature and the SOC (step 124), so that the internal resistance value close to the true value is obtained. Thus, it is possible to accurately determine the deterioration of the battery (step 126). FIG. 8 shows the temperature dependence of the internal resistance in this example, and FIG. 9 shows the SOC dependence of the internal resistance. As described above, since the internal resistance changes depending on the temperature and the SOC, if the reference temperature and the reference SOC are determined, it is possible to determine the deterioration with a more accurate internal resistance value.
[0029]
Furthermore, the charge / discharge control system of the present embodiment only needs to be able to measure the accumulated charge / discharge electricity amount, and is configured to simply add a storage device such as the non-volatile RAM 7 to the conventional charge / discharge control system. Is possible.
[0030]
In the present embodiment, an example in which the deterioration of the battery is determined based on the internal resistance R and the accumulated charge / discharge amount of electricity has been described. However, the internal resistance after correction is close to the true internal resistance value, and is shown in FIG. As described above, since there is a correlation between the accumulated charge / discharge electricity amount and the internal resistance, the deterioration of the battery may be determined based on the corrected internal resistance and the accumulated charge / discharge electricity amount.
[0031]
Further, in the present embodiment, Table 1 merely exemplifies a table for distinguishing between two states of “normal” and “deteriorated”, but the present invention is not limited to this, and “need attention” according to required characteristics. The table may be a table that makes a determination of three or more steps such as. Further, in the present embodiment, a table is exemplified in the map, but a mathematical expression or the like may be used.
[0032]
In the present embodiment, for simplicity of description, an example in which one temperature sensor is used has been described. However, the temperature of the lithium ion battery is measured with one or more battery modules for each battery module, and the measured temperature is measured. May be used.
[0033]
【The invention's effect】
As described above, according to the present invention, not only the calculated value of the internal resistance obtained by the regression analysis but also the deterioration judgment of the secondary battery including the accumulated charge / discharge electricity amount is performed. Thus, it is possible to obtain an effect that it is possible to eliminate a deterioration judgment error from the calculated value of the internal resistance obtained from the above.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram illustrating a schematic configuration of a charge / discharge control system according to an embodiment to which the present invention can be applied.
FIG. 2 is a flowchart of a deterioration determination routine of the charge / discharge control system of the embodiment.
FIG. 3 is a characteristic diagram showing a transition of a charge / discharge current during charge / discharge.
FIG. 4 is a characteristic diagram showing transition of a charge / discharge voltage during charge / discharge.
FIG. 5 is a characteristic diagram showing changes in internal resistance calculated from regression analysis values of voltage and current for 60 seconds.
FIG. 6 is a characteristic diagram showing changes in internal resistance calculated from regression analysis values of voltage and current for 30 seconds.
FIG. 7 is a characteristic diagram showing the relationship between the accumulated charge / discharge electricity amount and the internal resistance.
FIG. 8 is a characteristic diagram showing the temperature dependence of the internal resistance.
FIG. 9 is a characteristic diagram showing SOC dependence of internal resistance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lithium ion battery group 2 Charge / discharge current measuring circuit 3 Total voltage measuring circuit 4 Temperature measuring circuit 5 Microcomputer part 6 Communication interface part 7 Nonvolatile RAM

Claims

A charge / discharge control system that measures a charge / discharge current and a charge / discharge voltage of a secondary battery at predetermined time intervals, estimates a state of charge from the measured values, and controls the charge / discharge of the battery. Performing a regression analysis from a certain number of data of the discharge voltage measurement value to calculate the internal resistance of the battery, and calculating the cumulative charge amount or the cumulative discharge amount of the battery from the integrated value of the charge / discharge current, A charge / discharge control system, wherein a deterioration state of the battery is determined based on an internal resistance and a calculated value of the accumulated charge / discharge electricity amount.

2. The battery according to claim 1, wherein the battery is determined to have deteriorated when an internal resistance of the battery is equal to or more than a predetermined value and an accumulated charge amount or an accumulated discharge amount is equal to or more than a predetermined value. 3. The charge / discharge control system according to item 1.

The battery temperature when the battery is being charged and discharged is measured, and the measured value and the charge state calculated from the charge / discharge current or charge / discharge voltage are applied to a map in which the battery temperature and the charge state are used as parameters. The charge / discharge control system according to claim 1, wherein the calculated value of the internal resistance is corrected, and a deterioration state of the battery is determined using the corrected value as the calculated value of the internal resistance. 4. .

The charge / discharge control system according to claim 3, wherein the correction of the calculated value of the internal resistance is corrected to an internal resistance value at a predetermined standard temperature and standard charge state.

The battery temperature when the battery is being charged and discharged is measured, and the measured value and the charge state calculated from the charge / discharge current or charge / discharge voltage are applied to a map in which the battery temperature and the charge state are used as parameters. When the internal resistance value obtained by performing the correction of the calculated value of the internal resistance is equal to or more than a predetermined value, or when the accumulated charge amount or the accumulated discharge amount of the battery is equal to or more than a predetermined value. The charge / discharge control system according to claim 1, wherein it is determined that the battery has deteriorated.