JP5051661B2 - Method and apparatus for estimating SOC value of secondary battery, and degradation determination method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for estimating the SOC value of various secondary batteries typified by lithium ion secondary batteries, and a method and apparatus for determining the deterioration of such secondary batteries.

  2. Description of the Related Art In recent years, secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries have come to be used as power sources, for example, as power sources for driving motors in hybrid vehicles. In applications such as hybrid vehicles, SOC (State of Charge), which is the ratio of the amount of charge currently stored in the secondary battery and the capacity of the secondary battery, that is, the battery capacity, is calculated from time to time. Based on the SOC value, control of the drive motor in the vehicle and control of charge / discharge of the secondary battery are performed. Specifically, for example, when the SOC becomes 20% or less, control is performed such that the engine is started, the power is generated by the generator, and the secondary battery is charged by the electric power. For example, the SOC is 80% or more. In such a case, control is performed so that the secondary battery is not charged any more.

The SOC indicates the amount of available energy charged in the secondary battery as a percentage. If the initial SOC value SOC _init is known, the charge / discharge current I of the secondary battery is monitored. Then, by performing current integration, the SOC can be obtained as shown in Expression (1). As the initial value of the SOC, for example, a value indicating that the state of charge is 0% or 100% is used.

ここでＱは、二次電池の容量であり、一般的には［Ａｈ］を単位として表わされる。駆動モータの制御や充放電の制御には、通常、マイクロプロセッサなどが使用されるので、実際には、微小な時間間隔Δｔ［秒］ごとに充放電電流Ｉ［Ａ］を計測することとして、式（１）の代わりに、デジタル演算により適した式（１Ａ）に基づいて、ＳＯＣ値が算出される。車両用途の場合、Δｔは、例えば、数十ミリ秒から数秒の範囲内で設定される。

Here, Q is the capacity of the secondary battery, and is generally expressed in units of [Ah]. In general, a microprocessor or the like is used for driving motor control or charge / discharge control. Actually, the charge / discharge current I [A] is measured at a minute time interval Δt [seconds]. Instead of the equation (1), the SOC value is calculated based on the equation (1A) more suitable for digital calculation. In the case of a vehicle application, Δt is set within a range of several tens of milliseconds to several seconds, for example.

式（１）を用いるにせよ、式（１Ａ）を用いるにせよ、電流積算によるＳＯＣ値の算出には、初期のＳＯＣの値ＳＯＣ_ｉｎｉｔが分かっている必要があり、そのため、一般の二次電池の場合には、ＳＯＣが１００％である満充電状態から、あるいはＳＯＣが０％であるゼロ充電状態から出発した電流積算を行った場合にのみ、現時点でのＳＯＣ値を求めることができる。

Whether the equation (1) is used or the equation (1A) is used, the calculation of the SOC value by the current integration needs to know the initial SOC value SOC _init. In this case, the current SOC value can be obtained only when the current integration starting from the fully charged state where the SOC is 100% or from the zero charged state where the SOC is 0% is performed.

In certain types of secondary batteries represented by lithium ion secondary batteries, it is known that the battery terminal voltage changes according to the state of charge, that is, the SOC value, and a characteristic curve representing the relationship of the battery terminal voltage to the SOC value Can be obtained in advance. The battery terminal voltage here is an open voltage of the battery. Therefore, in this type of secondary battery, before the start of use of the battery, the open circuit voltage between the battery terminals is sufficiently balanced, and the open circuit voltage is obtained from the obtained value according to the above characteristic curve. Can be estimated, and the SOC value can be used as the initial value SOC _init in the equation (1) or the equation (1A). If the secondary battery is a lithium ion secondary battery or the like, the SOC value can be calculated by current integration even from a state other than the zero charge state or the full charge state. FIG. 1 illustrates the relationship between the open circuit voltage and SOC in a lithium ion secondary battery. In the figure, V _0% represents the open circuit voltage in the zero charge state, and V _100% represents the open circuit voltage in the fully charged state.

In some cases, control may be performed using a DOD (Depth of Discharge) value that is a ratio of the discharge capacity to the battery capacity. Ignoring the so-called irreversible capacity,
DOD [%] = 100-SOC [%] (2)
Therefore, the DOD value can be calculated in the same manner as described above.

  By the way, when obtaining the SOC value from moment to moment by current integration, errors during integration accumulate, so it is difficult to continue to obtain the SOC value over a long period of time. On the other hand, in the method of estimating the SOC value based on the open circuit voltage of the battery, in principle, the terminal voltage (that is, the open circuit voltage) when the charge / discharge current is zero should be used. The SOC value cannot be estimated during the period in which the discharge is performed.

JP Patent Publication No. 2001-303627 (Patent Document 1) discloses that the measured terminal voltage is such that the SOC value can be estimated from the terminal voltage of the battery even when the charge / discharge current is flowing. a polarization voltage V _P of the battery, corrects the voltage drop represented the internal resistance R of the battery at the I × R by the flow discharge current I, and estimates the SOC value based on the corrected terminal voltage It is disclosed. However, since the internal resistance value R of the battery greatly varies depending on the battery temperature and the degree of deterioration of the battery, the method described in Japanese Patent Laid-Open No. 2001-303627 must accurately know the temperature and the degree of deterioration. Thus, the SOC cannot be estimated with high accuracy. FIG. 2 is a graph schematically showing the relationship between the internal resistance value and the temperature in the lithium ion secondary battery. Here, the discharge resistance is used as the internal resistance value. FIG. 2 shows that the internal resistance increases as a whole due to deterioration.

In addition, the assignee of the present invention pays attention to the fact that, in applications such as hybrid vehicles, charging and discharging of the secondary battery are frequently switched, and the charging / discharging current becomes zero at the switching timing. The initial voltage used to calculate the SOC value by integrating the current using the estimated SOC value based on the measurement result of the terminal voltage of the secondary battery measured at the timing of switching between charging and discharging. It is proposed to update the value SOC _init (Japanese Patent Publication: JP-A-2004-245673 (Patent Document 2)). According to this method, since the initial value SOC _init is updated at every timing when charging and discharging are switched, the accumulated error of current integration is cleared at that time, and as a result, an accurate SOC value can always be obtained. It becomes possible.

By the way, as is clear from the formula (1) or the formula (1A), the SOC value depends on the battery capacity Q. The battery capacity Q depends on the battery temperature, the degree of deterioration of the battery, the charge / discharge current, and the like. It also changes depending on the rate. Therefore, in order to accurately estimate the SOC value by current integration, the initial value SOC _init used for current integration must be accurate, and changes in the battery capacity Q must be taken into consideration. If the battery capacity Q can be obtained, the change amount of the battery capacity due to the deterioration can be obtained by removing the contribution of the battery temperature and the charge / discharge current rate in the battery capacity change, and the degree of deterioration of the battery itself Can also be estimated.

  Battery capacity reduction due to deterioration is performed by charging / discharging the battery to be evaluated under preset conditions for temperature, charge / discharge current, charge / discharge time, and charge / discharge voltage, that is, in so-called capacity measurement mode It was evaluated by performing charging and discharging. However, in an environment where a secondary battery is mounted on a vehicle and charging / discharging is repeated randomly, it is difficult to charge / discharge the secondary battery in the capacity measurement mode. It was difficult to measure the battery capacity of the secondary battery.

  When using a lithium ion secondary battery or the like, these secondary battery cells are rarely used alone, and a plurality of single cells are connected in series and / or in parallel so as to obtain a desired discharge voltage and discharge current. Generally, it is configured as a connected battery pack. In addition to the secondary battery cell, the battery pack is often provided with a safety circuit such as an overcharge prevention circuit, a circuit that measures the SOC (remaining capacity), and outputs the measured value.

  As related to the present invention, Japanese Patent Publication: JP-A-8-29505 (Patent Document 3) is charged from the voltage change of the secondary battery during a certain period when the current of the secondary battery is below a predetermined value. The secondary battery capacity in the fully charged state is estimated from the difference between the charge rate measured last time and the charge rate measured this time and the time integral value of the secondary battery current between them. The estimation of the SOC of the secondary battery from the capacity of the secondary battery in the fully charged state and the charge rate measured this time is disclosed. JP Patent Publication No. 2003-207552 (Patent Document 4) calculates the state of charge of a secondary battery based on the current-voltage characteristics obtained from the relationship between the discharge current of the secondary battery and the terminal voltage. Is disclosed. JP Patent Publication No. 2003-294817 (Patent Document 5) estimates an open circuit voltage of a secondary battery based on a two-dimensional relationship between an integrated value of a discharge current and an integrated value of a charging current. The SOC is estimated based on the released open circuit voltage. JP Patent Publication No. 2003-307557 (Patent Document 6) uses current and voltage over time when a secondary battery is charged by a constant-current constant-voltage power supply, and uses a constant-current constant-voltage power supply. It discloses that a secondary battery is connected, current is passed, a current or voltage value after a predetermined time is measured, and the SOC of the secondary battery is estimated based on these measured values.

JP Patent Publication No. 2002-247773 (Patent Document 7) obtains the actual battery capacity at that time from the amount of discharged electricity when discharged from a fully charged state to a predetermined discharge stopped state, The determination is disclosed. JP Patent Publication No. 2002-243913 (Patent Document 8) is based on the open circuit voltage at the start of discharge current integration, the open circuit voltage at the end of discharge current integration, and the correlation between the open circuit voltage and SOC. The amount of change in SOC ΔSOC from the start of discharge current integration to the end of discharge current integration is calculated, the capacity of the battery is calculated from this ΔSOC and the actual amount of discharge electricity, and further corrected by temperature, etc. Is estimated. JP Patent Publication No. 2003-338315 (Patent Document 9) discloses a battery estimated from an open circuit voltage by obtaining a difference ΔSOC between an SOC value obtained by an open circuit voltage of a secondary battery and an SOC value obtained by current integration. The difference ΔIR between the internal resistance value and the internal resistance value calculated from the voltage change when the discharge current is changed is determined, and the deterioration of the battery is determined from ΔSOC and ΔIR. Japanese Patent Publication: Japanese Patent Application Laid-Open No. 2001-343437 (Patent Document 10) describes a battery based on a difference between an SOC calculated from an actual amount of charge / discharge electricity and an SOC estimated from an open circuit voltage (or battery voltage). Is disclosed.
JP 2003-303627 A JP 2004-245673 A JP-A-8-29505 JP 2003-207552 A JP 2003-294817 A JP 2003-307557 A JP 2002-247773 A Japanese Patent Laid-Open No. 2002-243813 JP 2003-338325 A JP 2001-343437 A

  In the above-described method for obtaining the SOC value of a secondary battery such as a lithium ion secondary battery by current integration, an accurate error occurs due to an integration error or a change in battery capacity itself due to a temperature drop or deterioration at that time. There is a problem that the SOC value cannot be obtained. In addition, when estimating the SOC value from the open circuit voltage, in order to obtain a more accurate estimated value, the secondary battery is left in an open state for a long time, and the open circuit voltage when the battery reaches a sufficient equilibrium However, there is a problem that it is difficult to use an open-circuit voltage when equilibrium is reached in an actual battery usage situation. Although several methods for estimating the SOC value from the terminal voltage of the secondary battery under actual usage conditions have been proposed as described above, they do not necessarily give an accurate SOC value.

  Accordingly, an object of the present invention is to provide a method capable of accurately estimating the latest SOC value without being affected by a change in capacity of the battery itself due to a temperature drop or deterioration.

  Another object of the present invention is to provide a method capable of accurately estimating the capacity of the battery itself and determining the deterioration of the battery.

  Still another object of the present invention is to provide an apparatus capable of accurately estimating the latest SOC value without being affected by a change in capacity of the battery itself due to a temperature drop or deterioration.

  Still another object of the present invention is to provide an apparatus capable of accurately estimating the capacity of the battery itself and determining the deterioration of the battery.

  According to the uniform aspect of the present invention, the SOC estimation method for estimating the SOC value of the secondary battery monitors the charge / discharge current of the secondary battery and continuously accumulates to obtain the first accumulated value. By adding the result obtained by dividing the integrated value by the capacity value of the secondary battery to the SOC initial value, the first SOC value is continuously calculated, and the timing at which charging and discharging in the secondary battery are switched. At this timing, the terminal voltage of the secondary battery at this timing is obtained, the correction value for converting the terminal voltage to the open circuit voltage in the equilibrium state of the secondary battery, and the terminal voltage is corrected. The second SOC value is obtained based on the result of adding the values, and every time the second SOC value is obtained, the SOC initial value is updated with the second SOC value, and the first accumulated value is integrated. To restart and in the past Obtaining the current capacity value of the secondary battery from the difference between the calculated second SOC value and the second SOC value obtained this time and the integrated value of the charge / discharge current at the time interval corresponding to the difference; Updating the capacity value used for calculating the first SOC value with the current capacity value.

  According to another aspect of the present invention, an SOC estimation device for estimating the SOC value of a secondary battery includes current detection means for detecting a charge / discharge current in the secondary battery, and voltage measurement for detecting a terminal voltage of the secondary battery. A result of dividing the first integrated value by the capacity value of the secondary battery; and a means for calculating the first integrated value by continuously integrating the charge / discharge current based on the detected charge / discharge current. Is added to the SOC initial value, and the SOC value calculating means for continuously calculating the first SOC value and the timing for detecting the timing at which charging and discharging of the secondary battery are switched based on the output of the current detection means Detection means, correction value acquisition means for acquiring a correction value for converting the terminal voltage of the secondary battery into an open circuit voltage in an equilibrium state of the secondary battery, and a result of adding the correction value to the terminal voltage at the detected timing SOC value estimating means for obtaining the second SOC value based on the difference between the second SOC value obtained in the past and the second SOC value obtained this time, and the charge / discharge current in the time interval corresponding to the difference Capacity calculation means for obtaining the current capacity value of the secondary battery from the integrated value, the capacity value used for calculating the first SOC value is updated with the current capacity value, and the second SOC Each time a value is obtained, the SOC initial value is updated with the second SOC value, and the integration calculation of the first integration value is restarted.

  The present invention has an advantage that, for example, the battery capacity Q at each time point can be accurately determined without introducing a capacity measurement mode. Further, according to the present invention, since the SOC value can be continuously calculated by current integration based on the accurate battery capacity Q, for example, the SOC value at an arbitrary timing can be obtained without being affected by the accumulated error accompanying current integration. The effect that it becomes possible to acquire correctly is acquired.

  When the battery capacity Q is obtained as described above when the temperature, the charge / discharge rate, etc. satisfy the requirements specified in advance, according to the present invention, for example, the battery capacity Q and the original of the secondary battery It is possible to determine the degree of deterioration of the secondary battery by comparing the battery capacity.

FIG. 1 is a graph showing an example of the relationship between the open circuit voltage of the battery and the SOC (remaining capacity). FIG. 2 is a graph showing an example of the relationship between temperature and battery internal resistance. FIG. 3 is a block diagram showing an example of the configuration of the SOC estimation device based on the first embodiment. FIGS. 4 (a) and 4 (b) is a waveform diagram illustrating the correction value _{V c.} FIG. 5 is a waveform diagram for explaining the principle of remaining capacity estimation. FIG. 6A is a flowchart for explaining the operation of SOC estimation, and FIG. 6B is a flowchart for explaining the operation of capacity estimation. FIG. 7 is a block diagram showing an example of the configuration of the SOC estimation apparatus based on the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,40 SOC estimation apparatus 11 Secondary battery 12 Battery pack 21 Current detector 22 Voltage measurement part 23 A / D converter 24 Polarity detection part 25 Edge detection part 26 SOC value estimation part 27 SOC value calculation part 28 Accumulation calculation part 29 Ring buffer 31 Correction value acquisition unit 32 Capacity calculation unit 33 Temperature sensor 41 Degradation determination unit

The SOC (remaining capacity) estimation method based on the first embodiment of the present invention estimates the SOC values of various secondary batteries represented by lithium ion secondary batteries. This SOC estimation method is used in a hybrid vehicle or the like, and in a secondary battery such as a lithium ion secondary battery, discharging and charging are frequently switched, and the direction of the current flowing in the secondary battery is switched. The focus is on the fact that the charge / discharge current is zero. In the method of this embodiment, the continuously performed SOC value calculated by the current integration, the current measures the terminal voltage V _t of the secondary battery in the zero timing. In practice, the measured terminal voltage V _t is generally different from the terminal voltage after the zero current state has reached the equilibrium, that is, the open circuit voltage in the equilibrium state. A correction value V _c for converting to an open circuit voltage at V is determined, V _SOC = V _t + V _c , V _SOC is applied to the relationship obtained in advance between the open circuit voltage and the SOC value, and the _SOC at that time The value is estimated, and the initial value SOC _init at the time of calculating the SOC value by current integration is updated.

The correction value V _c can be determined based on, for example, the average current value of the charge / discharge current in a certain period immediately before the terminal voltage V _t is captured, and in addition to the average current value immediately before, You may make it determine using temperature. Instead of the average current value, the current integrated value during the certain period may be used as it is. When using the average current value or the current integration value in a predetermined period, divides the predetermined period into a plurality of sections, the weighting for each section as better towards the section close to the timing for taking a terminal voltage V _t is important The integrated current value may be obtained by performing.

Further, in the method of the first embodiment, the SOC value of the temporary determined based on the terminal voltage V _t, when SOC value of the temporary is smaller correction value is small, the correction value If SOC values of the provisional is greater as larger, it may be determined a correction value V _c.

  In the method of the first embodiment, the SOC value is estimated twice or more based on the terminal voltage, and the error of the SOC value calculation by the current integration at the time interval between the two estimations is small. When it is considered that there is, the charge / discharge electricity quantity q within the time interval is calculated by current integration. Further, since the SOC value is estimated based on the terminal voltage at both the start point and the end point of the time interval, the difference ΔSOC between the two estimated SOC values is calculated, and Q = q / ΔSOC is calculated. Therefore, the battery capacity Q at that time is obtained. When the battery capacity Q is determined in this way, the battery capacity Q is used for calculation of the SOC value by current integration.

  Note that, in the SOC estimation method of the first embodiment, even when the battery capacity changes due to a temperature drop or deterioration of the battery itself, the battery capacity at that time is calculated, and the calculated battery capacity depends on the calculated battery capacity. An SOC value is calculated. Since the battery capacity at each time point is calculated, if the change in the battery capacity due to the change in the battery temperature or the different charge / discharge current rate can be removed, the change in the battery capacity accompanying the deterioration of the battery itself can be obtained. Therefore, the battery manufacturer has determined the capacity calculation conditions for detecting deterioration in advance, and the battery capacity was determined as described above when the capacity calculation conditions were satisfied. In this case, it is possible to estimate the degree of deterioration of the secondary battery by comparing the obtained battery capacity with the nominal capacity (reference value) of the secondary battery. As the capacity calculation condition, for example, temperature or charge / discharge current rate is used. Alternatively, each time the battery capacity is calculated as described above, the battery temperature and the charge / discharge current rate at that time are stored, and the secondary battery capacity is compared with the battery capacity calculated under the same conditions in the past. It is possible to determine battery capacity deterioration.

  FIG. 3 shows an example of the configuration of the SOC estimation apparatus that operates based on the method of the first embodiment described above. Here, as an example, it is assumed that the SOC estimation device 10 is incorporated in the battery pack 12, and a lithium ion secondary battery is used as the secondary battery 11, for example.

SOC estimating unit 10 includes a current detector 21 for detecting the charging current and discharging current of the secondary battery 11, a voltage measuring unit 22 and outputs the measured terminal voltage V _t of the secondary battery 11, the current detector 21 A / D converter 23 that samples and outputs analog / digital signals at a constant sampling rate, a polarity detector 24 that shapes the output waveform of current detector 21 and detects the polarity of charge / discharge current, and polarity detection An edge detection unit 25 that detects an edge in the output of the unit 24 and outputs a trigger signal; an SOC value estimation unit 26 that estimates an SOC value based on a terminal voltage of the secondary battery 11; and an SOC value based on current integration. An SOC value calculation unit 27 that constantly calculates and outputs the current SOC value, and an integration calculation unit 2 that calculates current integration based on the current sample value output from the A / D converter 23 8, the ring buffer 29 for storing the current sample value from the A / D converter 23, and the current value for a certain period in the ring buffer 23 based on the trigger signal from the edge detection unit 25, and the SOC value The correction value acquisition unit 31 that acquires the correction value _Vc used when the SOC value is estimated by the estimation unit 26, the capacity calculation unit 32 that estimates the current capacity of the secondary battery 11, and the temperature of the secondary battery 11 And a temperature sensor 33 for measuring. Here, the polarity of the charging / discharging current is different from charging or discharging.

  The secondary battery 11 may be an assembled battery in which a plurality of unit cells are connected in series. The voltage measuring unit 22 measures the voltage between the positive electrode terminal and the negative electrode terminal of the secondary battery as a terminal voltage. If the assembled battery is used as the secondary battery 11, the voltage measuring unit 22 The voltage between the positive terminal and the negative terminal is measured as the terminal voltage.

  As the current detector 21, an open loop type using a Hall sensor or a type having a shunt resistor and measuring a voltage at both ends thereof can be used. The current detector 21 is proportional to the magnitude of the charge / discharge current and generates a voltage that is negative for charge and positive for discharge, for example. The difference between the charging current and the discharging current is distinguished by the direction of the current with respect to the secondary battery 11. For example, the polarity detection unit 24 identifies whether the output is positive or negative depending on whether the output of the current detector 21 is positive or negative, and outputs “1” at a logical level during the discharge period, and during the charge period. Is configured to output “0”. As such a polarity detection unit 24, a comparator in which a waveform from the current detector 21 is input to a non-inverting terminal and 0 V is supplied as a reference potential to the inverting terminal can be used. The edge detection unit 25 outputs a trigger signal at the rising edge and the falling edge of the output of the polarity detection unit 24. The rising edge is an edge that transitions from “0” to “1”, and the falling edge is an edge that transitions from “1” to “0”.

When the relationship between the open circuit voltage (open circuit voltage) of the secondary battery 11 and the SOC value is known, the SOC value estimation unit 26 attempts to estimate the SOC value from the measured open circuit voltage using this relationship. To do. As described above, the open-circuit voltage used for estimating the SOC value should be the open-circuit voltage after a sufficient time has elapsed since the charge / discharge current becomes zero, that is, the open-circuit voltage in an equilibrium state. It is difficult to obtain an open circuit voltage in an equilibrium state for a secondary battery that is actually in use. Therefore, in the SOC estimation device 10, a _{V SOC} by adding a correction value _{V c} with respect to the actually measured terminal voltage _{V t,} as the _{V SOC} is in an open voltage at equilibrium, so as to estimate the SOC value I have to. For obtaining the correction value V _c, the ring buffer 29, the correction value acquisition unit 31 and the temperature sensor 33 is provided. Will be described later acquires the correction value V _c.

The SOC value estimation unit 26, the terminal voltage V _t that is represented by a digital value measured by the voltage measuring unit 22, and a trigger signal generated by the edge detector 25 are inputted. The SOC value estimation unit 26 takes in the correction value _{V c} obtained by the terminal voltage _{V t} and the timing of the secondary battery 11 at the timing when the trigger signal is _input, calculates a _V SOC ₌ V t + V _c , The SOC value corresponding to V _SOC is output. Actually, the SOC value estimation unit 26 includes a look-up table showing the relationship between the open circuit voltage (in the equilibrium state) of the lithium ion secondary battery and the SOC, and this _SOC is used as the open circuit voltage in the equilibrium state. The SOC value is output with reference to the lookup table. When the secondary battery which is the target of SOC estimation is a secondary battery other than the lithium ion secondary battery, a lookup table corresponding to the characteristics of the secondary battery is provided.

The following describes the acquisition of the correction value V _c.

  The ring buffer 29 sequentially stores the current sample values from the A / D converter 23. When the number of current sample values to be stored exceeds the memory capacity of the ring buffer 29, the oldest sample is stored. The value is rewritten to the latest sample value, and thereby, each current sample value that goes back from the latest time point to the past is stored in the ring buffer 29 by the capacity of the ring buffer 29. Become.

The correction value acquisition unit 31 searches the ring buffer 29 when the trigger signal is input from the edge detection unit 25, that is, at the timing when charging and discharging of the secondary battery 11 are switched, and from that time toward the past. The current sample value in a certain period is read, the read current sample value is integrated, and the integrated value (charge amount) of the current in the certain period is calculated. Here, since the integration period is constant, the integration value is equivalent to the average current value within that period. The correction value acquisition unit 31 outputs the correction value V _c according to the accumulated current value obtained. Actually, the correction value acquisition unit 31 includes a lookup table showing the relationship between the current integrated value and the correction value V _c , refers to this lookup table by the current integrated value, and outputs the correction value V _c . . Needless to say, the contents of the look-up table differ depending on the type and standard of the secondary battery that is the target of SOC estimation. Therefore, a lookup table may be created in accordance with a test to be performed in advance.

In addition, since the difference between the terminal voltage at the timing when the charge / discharge current becomes zero and the open circuit voltage in the equilibrium state also depends on the temperature, in the first embodiment, the temperature measured by the temperature sensor 33 is also included. It is preferable to calculate the correction value V _c by using it. When the correction value V _c is obtained also using the temperature, the correction value acquisition unit 31 sets a plurality of lookup tables representing the relationship between the current integrated value and the correction value V _c for each battery temperature. of storing a look-up table to select a lookup table based on the temperature measured by the temperature sensor 33, it is sufficient to obtain a correction value V _c based on the selected lookup table.

FIGS. 4 (a) and 4 (b) are each a diagram for explaining a correction value _{V c.} FIG. 4A shows changes in the terminal voltage V and SOC when the secondary battery shifts from the discharged state to the state where the current I is zero at time t _{I = 0} . During discharge, the terminal voltage V and SOC gradually decrease, and when the discharge stops, the voltage drop due to the internal resistance disappears, so-called IR drop, and the terminal voltage V increases accordingly. Thereafter, the SOC remains constant, but the terminal voltage V gradually increases and eventually converges to a constant value that is an open circuit voltage in an equilibrium state. Therefore, the correction value V _c is set so as to be the difference between the terminal voltage when t _{I = 0} and the convergence value of the terminal voltage. Since the correction value V _c depends on the average discharge current value and temperature in the period immediately before the discharge stops, the correction value V _c is determined by the look-up table corresponding to the integrated current value and temperature as described above. .

Similarly, FIG. 4B shows changes in the terminal voltage V and the SOC when the secondary battery shifts from the charged state to the state where the current I is zero at time tI _{= 0} . During charging, the terminal voltage V and the SOC gradually increase, and when the charging is stopped, the voltage drop due to the internal resistance disappears, so the terminal voltage V drops accordingly. Thereafter, the SOC remains constant, but the terminal voltage V gradually decreases and finally converges to a constant value that is an open circuit voltage in an equilibrium state. Therefore, the correction value V _c is set so as to be the difference between the terminal voltage when t _{I = 0} and the convergence value of the terminal voltage. Since the correction value V _c depends on the average discharge current value and temperature in the period immediately before the stop of charging, as described above, the correction value V _c is determined by the look-up table corresponding to the integrated current value and temperature. .

Incidentally, in addition to those described above also, how to determine the correction value V _c is those various. For example, when the correction value is determined based on the current integrated value within a certain period from the timing when the trigger signal is input to the past, the certain period is divided into a plurality of sections and is close to the timing when the trigger signal is input. The current integrated value may be obtained by weighting each section so that the one section is more important. In general, it is known that the correction value V _c increases when the SOC is large, and the correction value V _c decreases when the SOC is small. Therefore, the SOC value of the temporary determined based on the terminal voltage V _t, when SOC value of the temporary is smaller correction value is small, if the SOC value of the provisional large correction value as the greater, the correction value V _c You may make it decide.

Such correction value V _c determined by the, as described above, is sent from the correction value acquisition unit 31 to the SOC value estimating unit 26, is used from the terminal voltage V _t when estimating the SOC value.

  The integration calculation unit 28 integrates the output of the A / D converter 23 for each sampling of the A / D converter 23, that is, the equation (1).

あるいは式（１Ａ）のΣＩΔｔを計算し、その計算結果をＡ／Ｄ変換器２３のサンプリングごとにＳＯＣ値演算部２７に出力する。積算演算部２８には、トリガ信号が供給されており、トリガ信号が入力するごとに、すなわち、充電と放電とが切り替わるごとに、積算値がゼロにリセットされるようになっている。

Alternatively, ΣIΔt of equation (1A) is calculated, and the calculation result is output to the SOC value calculation unit 27 for each sampling of the A / D converter 23. The integration calculation unit 28 is supplied with a trigger signal, and the integration value is reset to zero each time the trigger signal is input, that is, every time charging and discharging are switched.

The capacity calculation unit 32 calculates the current capacity of the secondary battery 11 by the method of the first embodiment. Assume that the SOC value estimation unit 26 estimates the SOC value based on the terminal voltage V _t at time t _n−1 and time t _n , and these SOC estimated values are SOC _n−1 and SOC _n , respectively. The capacity calculation unit 32 receives the trigger signal to know the timing at which the SOC value is estimated, receives SOC _n−1 and SOC _n from the SOC value estimation unit 26, and from the integration calculation unit 28. receives a current integrated value _{q n} between times _{t n-1} and the time _{t n.} In this case, since a trigger signal is generated at time t _{n and} the integrated value of the integration calculating unit 28 is reset, the integrated value immediately before the reset may be set to q _n .

In the battery capacity is Q, if there is out of only q _n as the accumulated current value represented as the charge amount, SOC values before and after should vary by q _{n /} Q. On the other hand, it is known from the estimation from the terminal voltage that the SOC value changes by SOC _n −SOC _n−1 before and after the increase / decrease of the charge amount q _n . As a result, _if the capacitance at time t _n is Q _n ,

が成立する。ＳＯＣの単位を［％］、電池容量Ｑ_ｎの単位を［Ａｈ］、電流積算値ｑ_ｎの単位を［Ｃ］（＝［Ａｓ］）とすると、

Is established. The unit of SOC [%], the unit of battery capacity _{Q n} [Ah], When the unit of current accumulated value _{q n [C] (= [} As]),

となる。

It becomes.

Capacity calculation unit 32 in this manner, calculates the battery capacity at time t _n. The calculated battery capacity value Q _n is sent to the SOC value calculation unit 27. FIG. 5 is a waveform diagram showing the relationship between the charge / discharge current, the time when the SOC is estimated, the estimated SOC, and the time interval used for calculating the capacity.

The SOC value calculation unit 27 calculates the SOC value every moment based on the formula (1) or the formula (1A), and outputs the current SOC value to the outside in real time. The latest estimated SOC value to be output is set as SOC _init in the equation (1A), and the latest capacity value output from the capacity calculating unit 32 is set as Q in the equation (1A). Assuming that the current integrated value is ΣIΔt in equation (1A), equation (1A) is calculated, and the current SOC value is output. To describe the example shown in FIG. 5, the time _{t n} in the period between the time point _{t n + 1,} using the SOC value SOC _n estimated at time _{t n} as _{SOC init,} time _{t n-1} and the time t _Using the capacity Q _n calculated from the period between _n as the capacity Q, the current SOC value is calculated every moment.

  As described above, the SOC estimation apparatus 10 according to the first embodiment continuously calculates the SOC of the secondary battery 11 by the charge / discharge current integration calculation, and performs the integration calculation at the timing at which charging and discharging are switched. Update the SOC initial value and battery capacity value used with their correct values. As a result, various error factors in calculating the SOC by current integration are eliminated, and an accurate SOC value at that time can be known at any time.

The SOC estimation apparatus 10 of the first embodiment is generally implemented using a microcomputer. In that case, each function of the edge detection unit 25, the SOC value estimation unit 26, the SOC value calculation unit 27, the integration calculation unit 28, the ring buffer 29, the correction value acquisition unit 31, and the capacity calculation unit 32 is realized by a microcomputer. . Specifically, the microcomputer continuously performs the integration calculation using the charge / discharge current, and the output signal from the waveform shaping unit such as the comparator is input to the input capture terminal of the microcomputer. A rising edge and a falling edge in the output signal are detected. Then, when detecting the edge interrupt task is generated in the microcomputer, obtains the correction value V _c, calculation of V _SOC, see the lookup table of the SOC value by V _SOC, such calculation of the capacity Q is performed By doing so, it is possible to realize the function of the SOC estimation device described above.

  FIG. 6 is a flowchart showing an example of the operation of such a microcomputer. FIG. 6A shows a process for estimating the SOC value from the terminal voltage, and FIG. 6B shows a process for estimating the capacity of the secondary battery 11. Although not shown here, the microcomputer constantly calculates the SOC value by current integration based on the above-described equation (1) or equation (1A), and always outputs the SOC value by current integration.

In the estimation of the SOC value based on the terminal voltage, as shown in FIG. 6A, first, in step 101, a condition capable of estimating the SOC value, such as the timing at which the charge / discharge current becomes zero, is detected. Then, it is determined whether or not such a condition is satisfied. If not satisfied, the process returns to Step 101 for waiting. If the condition is satisfied, in Step 103, the terminal voltage V of the secondary battery 11 is determined. _t is detected. Further, in step 104, the ring buffer is searched, and the average current value is calculated by integrating the current values for a certain period immediately before the condition is satisfied. Here, since the period of integration is constant, using the average current value and using the integrated value itself are equivalent to each other. Then, the correction value V _c is calculated using the calculated average current value. In calculating the correction value _Vc , the battery temperature may be further used as necessary. In step 105, V _SOC = V _t + V _c is calculated. In step 106, the SOC value corresponding to V _SOC is estimated, and the process returns to step 101. The initial value SOC _init used in the calculation of the SOC value by the current integration based on the formula (1) or the formula (1A) is updated by the SOC value thus estimated. Note that the integrated value of the current integration is also reset to zero at the timing when the SOC _init is updated.

In the estimation of the capacity Q, as shown in FIG. 6B, first, in step 111, the time tn _{-1 at} which the previous SOC value was estimated by the terminal voltage and the current SOC value were estimated. A condition capable of estimating the capacity is detected, for example, whether the time interval from the time t _n is within a predetermined range. In step 112, it is determined whether or not such a condition is satisfied. If not satisfied, the process returns to step 101 for waiting. If the condition is satisfied, in step 103, the time t _{n is determined. The} integrated current value q _n in the period between ₋₁ and time t _n is calculated as follows.

実際には、端子電圧によってＳＯＣ値を推定するたびに積算演算部２８での電流積算がリセットされているので、リセットされる寸前の電流積算値をｑ_ｎとすればよい。次に、ステップ１１４において、前回推定されたＳＯＣ値をＳＯＣ_ｎ−１とし、今回推定されたＳＯＣ値をＳＯＣ_ｎとして、下式に基づき、時刻ｔ_ｎにおける二次電池１１の電池容量Ｑ_ｎを算出する。

In fact, since the current integration in the integration operation section 28 each time the estimated SOC value by the terminal voltage has been reset, the accumulated current value immediately before being reset or if q _n. Next, in step 114, the previously estimated SOC value is SOC _n−1 , and the currently estimated SOC value is SOC _n. Based on the following equation, the battery capacity Q _n of the secondary battery 11 at time t _n is calculated based on the following equation. calculate.

その後、ステップ１１５において、算出された容量Ｑ_ｎに基づいて、ＳＯＣの補正を行う。具体的には、式（１）あるいは式（１Ａ）に基づいて電流積算によってＳＯＣ値を演算する際に、式（１）あるいは式（１Ａ）中のＱをＱ_ｎで更新する。

Thereafter, in step 115, based on the calculated capacity _{Q n,} correct the SOC. More specifically, when calculating the SOC value by current integration based on formula (1) or formula (1A), and updates the Q in the formula (1) or formula (1A) in _{Q n.}

  By causing the microcomputer to execute the above processing, the SOC estimation apparatus of the first embodiment can be configured by software.

  By the way, in the SOC estimation apparatus of the first embodiment, even when the battery capacity changes due to a temperature drop or deterioration of the battery itself, the battery capacity at that time is calculated, and the calculated battery capacity depends on the calculated battery capacity. An SOC value is calculated. Since the battery capacity at each time point is calculated, if the change in the battery capacity due to the change in the battery temperature or the different charge / discharge current rate can be removed, the change in the battery capacity accompanying the deterioration of the battery itself can be obtained. Therefore, this SOC estimation device can also be used as a deterioration determination device that determines the deterioration of the secondary battery. FIG. 7 shows an SOC estimation apparatus having a function of determining the deterioration of the secondary battery in this way, based on the second embodiment.

  When determining the deterioration of the secondary battery 11, a battery manufacturer or the like predetermines capacity calculation conditions for detecting deterioration. As the capacity calculation condition, for example, temperature or charge / discharge current rate is used. Then, when the battery capacity is obtained as described above when the capacity calculation condition is satisfied, the obtained battery capacity is compared with the nominal capacity (reference value) of the secondary battery. Thus, the degree of deterioration of the secondary battery may be estimated. The SOC estimation device 40 shown in FIG. 7 is the same as the SOC estimation device shown in FIG. 3, but differs from that shown in FIG. 3 in that a deterioration determination unit 41 is provided in the SOC estimation device.

In SOC estimation device, upon operation of the capacitance at the capacity calculation unit 32, a current integrated value _{q n} from time _{t n-1} described above until time _{t n,} and time interval from time _{t n-1} to time _{t n} Therefore, the average charge / discharge current rate when the capacity Q _n is calculated is known. Further, the temperature is measured by the temperature sensor 33. Therefore degradation determining unit 41 obtains the average discharge current rate and the capacity value Q _n from the capacity calculation unit 32 obtains the measured value of the battery temperature from the temperature sensor 33, determines meets the capacity calculation condition , if you meet the capacity calculation condition is compared with the nominal capacitance value stored in advance and Q _n, perform the deterioration determination, and outputs the determination result.

  Alternatively, each time the capacity calculation unit 32 calculates the capacity value, the deterioration determination unit 41 captures and stores the capacity value, the battery temperature at that time, and the average charge / discharge current rate, and calculates under the same conditions in the past. By comparing with the obtained battery capacity, the capacity deterioration of the secondary battery may be determined.

  Similarly to the SOC estimation apparatus 10 of the first embodiment, the SOC estimation apparatus 40 of the second embodiment can also be implemented using a microcomputer. In that case, the functions of the edge detection unit 25, the SOC value estimation unit 26, the SOC value calculation unit 27, the integration calculation unit 28, the ring buffer 29, the correction value acquisition unit 31, the capacity calculation unit 32, and the deterioration determination unit 41 are Realized by computer.

  The present invention has been described above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application claims the priority on the basis of Japanese patent application: Japanese Patent Application No. 2006-232160 for which it applied on August 29, 2006, and takes in those the indications of all here.

Claims (15)

An SOC estimation method for estimating an SOC value of a secondary battery,
The charging / discharging current of the secondary battery is monitored and continuously integrated to obtain a first integrated value, and the result obtained by dividing the first integrated value by the capacity value of the secondary battery is added to the initial SOC value. Continuously calculating the first SOC value;
Detecting the timing of switching between charging and discharging in the secondary battery, and obtaining the terminal voltage of the secondary battery at the timing at the timing;
Obtaining a correction value for converting the terminal voltage into an open circuit voltage in an equilibrium state of the secondary battery;
Obtaining a second SOC value based on a result of adding the correction value to the terminal voltage;
Each time the second SOC value is determined, updating the SOC initial value with the second SOC value and restarting the integration calculation of the first integration value;
From the difference between the second SOC value obtained in the past and the second SOC value obtained this time, and the integrated value of the charge / discharge current in the time interval corresponding to the difference, the current capacity value of the secondary battery Asking for
Updating the capacity value used to calculate the first SOC value with the current capacity value;
An SOC estimation method comprising:   2. The second integrated value obtained by integrating charge / discharge currents in a certain period immediately before the timing is calculated, and the correction value is determined from the second integrated value and the temperature of the secondary battery. SOC estimation method.   3. The second integrated value is calculated according to claim 2, wherein the fixed period is divided into a plurality of sections, and the second integrated value is calculated by weighting each section so that the section closer to the timing is more important. SOC estimation method.   A third SOC value is determined based on the terminal voltage, and the correction value is decreased when the third SOC value is relatively small, and is increased when the third SOC value is relatively large. The SOC estimation method according to claim 1, wherein:   The SOC estimation method according to any one of claims 1 to 4, further comprising a step of determining deterioration of the secondary battery based on the current capacity value.   The SOC estimation method according to any one of claims 1 to 5, wherein the secondary battery is a lithium ion secondary battery. A deterioration determination method for estimating deterioration of secondary battery capacity,
Detecting the timing of switching between charging and discharging in the secondary battery, and obtaining the terminal voltage of the secondary battery at the timing at the timing;
Obtaining a correction value for converting the terminal voltage into an open circuit voltage in an equilibrium state of the secondary battery;
Obtaining an SOC value based on a result of adding the correction value to the terminal voltage;
The current capacity value of the secondary battery is obtained from the difference between the SOC value obtained in the past and the SOC value obtained this time and the integrated value of the charge / discharge current for the secondary battery in the time interval corresponding to the difference. And
Determining whether the temperature and charge / discharge current rate of the secondary battery when the current capacity value is obtained satisfy a predetermined condition;
Determining the deterioration of the secondary battery by comparing the current capacity value when the predetermined condition is satisfied with a reference value;
A method for determining deterioration. A deterioration determination method for estimating deterioration of secondary battery capacity,
Detecting the timing of switching between charging and discharging in the secondary battery, and obtaining the terminal voltage of the secondary battery at the timing at the timing;
Obtaining a correction value for converting the terminal voltage into an open circuit voltage in an equilibrium state of the secondary battery;
Obtaining an SOC value based on a result of adding the correction value to the terminal voltage;
Obtaining the capacity value of the secondary battery from the difference between the SOC value obtained in the past and the SOC value obtained this time, and the integrated value of the charge / discharge current for the secondary battery in the time interval corresponding to the difference; ,
Every time the capacity value is determined, the capacity value, and the temperature and charge / discharge current rate of the secondary battery when the capacity value is determined;
Determining the deterioration of the secondary battery by comparing the current capacity value with a capacity value obtained in the past under the condition that the secondary battery temperature and charge / discharge current rate are equivalent;
A method for determining deterioration.   The deterioration determination method according to claim 7 or 8, wherein the secondary battery is a lithium ion secondary battery. An SOC estimation device for estimating the SOC value of a secondary battery,
Current detection means for detecting a charge / discharge current in the secondary battery;
Voltage measuring means for detecting a terminal voltage of the secondary battery;
Based on the detected charging / discharging current, integration calculation means for continuously integrating the charging / discharging current to obtain a first integrated value;
SOC value calculation means for continuously calculating the first SOC value by adding the result obtained by dividing the first integrated value by the capacity value of the secondary battery to the SOC initial value;
Timing detection means for detecting timing at which charging and discharging in the secondary battery are switched based on the output of the current detection means;
Correction value acquisition means for acquiring a correction value for converting the terminal voltage of the secondary battery into an open circuit voltage in an equilibrium state of the secondary battery;
SOC value estimating means for obtaining a second SOC value based on a result of adding the correction value to the terminal voltage at the detected timing;
From the difference between the second SOC value obtained in the past and the second SOC value obtained this time, and the integrated value of the charge / discharge current in the time interval corresponding to the difference, the current capacity value of the secondary battery Capacity calculating means for obtaining
Have
The capacity value used for the calculation of the first SOC value is updated with the current capacity value, and the SOC initial value is updated with the second SOC value each time the second SOC value is obtained. The SOC estimation apparatus in which the integration calculation of the first integration value is restarted.   The correction value acquisition unit has a ring buffer that sequentially stores sample values obtained by sampling the charge / discharge current, and integrates the charge / discharge current in a certain period immediately before the timing with reference to the ring buffer. The SOC estimation apparatus according to claim 10, wherein a second integrated value is calculated, and the correction value is determined from the second integrated value. A temperature measuring means for measuring the temperature of the secondary battery;
The SOC estimation apparatus according to claim 11, wherein the correction value acquisition means calculates the correction value using the temperature in addition to the second integrated value.   The SOC estimation apparatus according to any one of claims 10 to 12, further comprising means for determining deterioration of the secondary battery based on the current capacity value. The SOC estimation apparatus according to any one of claims 10 to 13,
A secondary battery whose SOC value is estimated by the SOC estimation device;
Having a battery pack. A deterioration determination device for determining deterioration of a secondary battery,
Current detection means for detecting a charge / discharge current in the secondary battery;
Voltage measuring means for detecting a terminal voltage of the secondary battery;
Timing detection means for detecting timing at which charging and discharging in the secondary battery are switched based on the output of the current detection means;
Correction value acquisition means for acquiring a correction value for converting the terminal voltage of the secondary battery into an open circuit voltage in an equilibrium state of the secondary battery;
SOC value estimating means for obtaining an SOC value based on a result of adding the correction value to the terminal voltage at the detected timing;
Capacity calculation means for determining the capacity value of the secondary battery from the difference between the SOC value determined in the past and the SOC value determined this time, and the integrated value of the charge / discharge current in the time interval corresponding to the difference;
A deterioration determination means for determining deterioration of the secondary battery by comparing the capacity value obtained this time with a reference value or a capacity value obtained in the past;
A deterioration determination device having

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