JP4071207B2 - Battery current measuring device - Google Patents

Description

  The present invention relates to a current measuring device that measures a charging current and a discharging current of a battery.

  A battery (battery) mounted on a vehicle supplies (discharges) electric power to a vehicle driving motor and the like, and is charged by a generator that operates with engine power. In order to accurately detect the state of charge of a battery, a technique for correcting a measurement error of a current sensor that measures the charge current and discharge current of the battery is known.

  In Patent Document 1, a current flows only through a specific system when an ignition switch of a vehicle is switched to a starter start position, and an offset error of a current sensor is detected from a known current consumption of the system. Technology is shown. Patent Document 2 discloses a technique for offset-correcting a detected current using an integrated value of detected currents of a current sensor in a period from a full charge to a subsequent full charge.

JP 2002-238181 A JP 2001-78365 A

  In the technique described in Patent Document 1, it is necessary to shut off the other system when detecting the offset error, so that the system configuration is significantly limited, or when the detection of the offset error is switched to the starter start position and the starter Offset error when it is necessary to perform in a very short period of time before driving, when it is necessary to accurately measure the current consumption of a specific system in advance, or when the current flowing through a specific system fluctuates during starter startup There is a concern that the detection accuracy will be deteriorated, and that the accuracy of error detection will deteriorate if a current flows into another shut-off system.

  On the other hand, the technique described in Patent Document 2 uses a fully charged state and is not suitable for a battery (such as a battery for a drive motor of a hybrid vehicle) in which a fully charged state does not occur frequently. There is a concern that the detection accuracy of the offset error deteriorates when the full charge state is not accurately determined due to the hysteresis characteristics when charging / discharging the battery.

  The present invention has been made in view of the above problems, and an object thereof is to improve the accuracy of current detection by accurately calculating a measurement error of a current sensor.

  In order to achieve the above object, a battery current measurement device according to a preferred embodiment of the present invention includes a current sensor that measures a charging current and a discharge current of a battery, a correction unit that corrects a measurement error of the current sensor, And the correction unit calculates an offset error of the current sensor based on a capacity difference between the battery capacity obtained from the integrated value of the current measured by the current sensor and the battery capacity obtained from the open circuit voltage of the battery. It is characterized by calculating.

  Preferably, the correction unit calculates an offset error from a change per unit time of the capacity difference. Desirably, the said correction | amendment part utilizes the sum of the integrated value of a charging current and the integrated value of the discharge current by the electric current value of the magnitude | size substantially the same as the charging current as an integrated value of the current measured with a current sensor. It is characterized by that. Preferably, the correction unit is configured such that a difference between a corrected battery capacity obtained by correcting an integrated value associated with the offset error from an integrated value of current measured by a current sensor and a battery capacity obtained from an open circuit voltage of the battery. The gain error of the current sensor is calculated on the basis of the corrected capacitance difference. Preferably, the correction unit calculates a gain error based on a change amount per unit time of the correction capacity difference.

  In order to achieve the above object, an error correction method for a current sensor, which is a preferred embodiment of the present invention, is an error correction method for a current sensor that measures a charging current and a discharging current of a battery, wherein the correction means is a current sensor. An offset error of the current sensor is calculated based on a capacity difference between the battery capacity obtained from the integrated value of the measured current and the battery capacity obtained from the open circuit voltage of the battery.

  Desirably, the correction means calculates a difference between a corrected battery capacity obtained by correcting the integrated value associated with the offset error from an integrated current value measured by a current sensor, and a battery capacity obtained from an open circuit voltage of the battery. The gain error of the current sensor is calculated on the basis of the corrected capacitance difference.

  According to the present invention, the measurement error of the current sensor can be accurately calculated, and the current detection accuracy can be improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a preferred embodiment of a battery current measuring apparatus according to the present invention.

  The battery pack 11 has a configuration in which a plurality of battery modules 12 are connected in series. The battery pack 11 is, for example, a lithium ion battery, and is used in a system mounted on a vehicle. The generator 20 charges the battery module 12 in the battery pack 11, and is driven by, for example, engine power. On the other hand, the load 21 is a vehicle driving motor or the like, and operates with power supplied from the battery module 12. That is, the battery pack 11 is charged by the generator 20 and discharged to the load 21. Then, the current sensor 13 measures the discharge current and the charge current of the battery pack 11.

  A temperature sensor 15 is attached to each battery module 12, and the measured value is output to the temperature detector 16. Furthermore, a voltage detection unit 14 for detecting a voltage between the positive and negative electrodes of each battery module 12 is provided to detect a voltage between both terminals of each battery module 12 or a voltage between both electrodes of the battery pack 11. Is done. The current measurement value of the current sensor 13, the voltage detection result of the voltage detection unit 14, and the temperature detection result of the temperature detection unit 16 are output to the CPU 17.

  The CPU 17 functions as a current measuring device together with the current sensor 13. In the current measurement, the CPU 17 functions as a correction unit that performs error correction of the current sensor 13 using the voltage detection result of the voltage detection unit 14. Note that the CPU 17 may implement a function of monitoring the overall charge state of the battery pack 11 using not only the current measurement but also the detection result of the temperature detection unit 16 or the like.

  The RAM 19 is a memory for storing and reading out arithmetic processing results in the CPU 17, and the display unit 18 displays arithmetic processing results in the CPU 17. For example, the capacity of the battery pack 11, the charging current, the discharging current, the temperature of each battery module 12, etc. are displayed on the display unit 18.

  In the present embodiment, the CPU 17 calculates the offset error and gain error of the current sensor 13, and corrects the measured values of the current sensor 13 based on the calculation results to measure the correct charging current and discharging current. Therefore, the offset error and gain error of the current sensor 13 will be described.

  FIG. 5 is a diagram for explaining the offset error and the gain error, and shows a graph in which the horizontal axis indicates the true value of the current and the vertical axis indicates the measured value of the current sensor. The true value of the current is an actually measured current value, that is, an ideal measured value when there is no measurement error. If there is no error in the current sensor, the true value of the current coincides with the measured value of the current sensor, so that the measurement result of the ideal straight line 52 is obtained. However, if there is an offset error in the current sensor, the measured current value is shifted from the true value by, for example, a constant value in the positive direction, and the measurement result of the offset error straight line 54 is obtained. Further, if there is a gain error in the current sensor, the measured current value is deviated from the true value by a value proportional to the current value, and the measurement result shown in the current sensor output straight line 50 is obtained.

The current sensor output straight line 50 includes an offset error and a gain error. For example, when the true value of the current is A ₁ , the offset error influence A _off and the gain error influence A _1g are measured. The result will be off. Further, when the true value of the current is A ₂ , the measurement result is shifted by the offset error effect A _off and the gain error effect A _2g . In this embodiment, the offset error and the gain error are corrected.

  FIG. 2 is a diagram for explaining offset error and gain error correction processing in the present embodiment. Hereinafter, the correction processing executed by the CPU 17 will be described with reference to FIG.

  When charging / discharging of the battery pack 11 is started by the generator 20 or the load 21, the counter value n, the elapsed time t, the current integrated value ah, and the flag Flag are all reset to zero in the initialization step. In S200, measurement of the detected current value I of the current sensor 13, the detected voltage value V of the voltage detecting unit 14, the detected temperature T of the temperature detecting unit 16, and the elapsed time t from the start of charging / discharging is started. In S201, An open circuit voltage v of the battery pack 11 is detected. The open circuit voltage v is a detected voltage value between the positive and negative terminals of the battery pack 11 when the input / output current of the battery pack 11 is zero. When the open circuit voltage v is detected, the SOC of the battery pack 11 is obtained from the correspondence between the open circuit voltage and the SOC (State Of Charge) in S202.

  FIG. 6 shows a graph (open circuit voltage-SOC characteristic) showing the correspondence between the open circuit voltage and the SOC. In the battery pack 11 (for example, a lithium ion battery), the SOC is uniquely determined from the open circuit voltage. Therefore, the SOC is uniquely determined from the open circuit voltage by using the open circuit voltage-SOC characteristic shown in FIG. 6 where the horizontal axis indicates SOC (percent) and the vertical axis indicates open circuit voltage (volt). The

  Returning to FIG. 2, when the SOC is obtained, the counter value n is incremented by 1 in S203, and further, the time Tm (n) when the open circuit voltage is detected, the open circuit voltage V (n), and the SOC: S (N), the current integrated value Ah (n) is recorded in the RAM 19. The integrated current value is an integrated value of the current value detected by the current sensor 13 from the start of charging / discharging to the present time, and corresponds to the integrated capacity flowing into and out of the battery pack 11. In S204, it is confirmed whether or not the counter value is {n> 1}. After the start of charging / discharging, the process proceeds to S205 because {n = 1} at the first detection time, and {n> 1} at the second and subsequent detection times (counted up at S203). Proceed to

  In S205, various parameters at the time of {n = 1} are set as initial values. That is, the values recorded in the RAM 19 in S203 are registered as the initial time value Tmst, the initial value Vst of the open circuit voltage, the initial value Sst of the SOC, and the initial value Ahst of the current integrated value. When the initial value of each value is set, the steps from S200 to S203 are executed again. Then, at the second and subsequent detection time points {n> 1}, the process proceeds to S206 via the branch of S204.

  In S206, it is confirmed whether or not {Flag = 0}. The flag is set to an initial value of 0 in the initialization step, and is appropriately rewritten in S209 and S210 described later. When S206 is executed for the first time, since {Flag = 0}, the process proceeds to S207.

  In S207, it is determined whether or not {S (n)> S (n-1) + Sc} is satisfied. Here, S (n) is the current SOC, and S (n−1) is the SOC at the previous time. Sc is a determination value of the change amount. That is, it is determined whether or not the SOC tends to increase and the increase amount is larger than the determination value Sc. If the amount of change is too small, a calculation error of a current offset and a current gain, which will be described later, becomes large. In this step, it is confirmed that the amount of change is a certain amount or more. Incidentally, although the accuracy of calculation increases as the determination value Sc increases, on the other hand, it does not fit into a system in which the change in SOC is slow. For this reason, the determination value Sc is determined based on, for example, experimental results according to the system in which the battery pack 11 is employed.

  When the increase amount of the SOC is larger than the determination value, the process proceeds to S209, and the flag Flag is set to “1”. If it is determined in S207 that {S (n)> S (n-1) + Sc} is not satisfied, it is determined in S208 whether {S (n) <S (n-1) -Sc} is satisfied. The That is, it is determined whether or not the SOC is decreasing and the amount of decrease is larger than the determination value Sc. If the amount of decrease is larger than the determination value, the process proceeds to S210 and the flag Flag is set to “2”. Is done. On the other hand, if it is determined in S208 that {S (n) <S (n-1) -Sc} is not satisfied, the steps after S200 are executed again.

  In S211, the flag is determined again. If {Flag = 1}, the process proceeds to S212. If {Flag = 1}, the process proceeds to S213. In S212, it is confirmed whether or not the SOC continues to increase. In S207, it is confirmed that the SOC has increased. In S209, the flag is set to {Flag = 1}. After returning to S200 through the subsequent processing and reaching S206, {Flag = 1} is maintained and S212 is passed through S212. To reach. In other words, after confirming that the SOC tends to increase in S207, at S212, {S (n)> S (n-1)} at the next time point (after one count value n is added). It is determined that the number continues to increase if {S (n)> S (n-1)}.

  On the other hand, in S213, it is confirmed whether or not the SOC continues to decrease. In S208, it is confirmed that the SOC is decreasing and is set to {Flag = 2} in S210. After returning to S200 through the subsequent processing and reaching S206, {Flag = 2} is maintained and S213 is passed through S211. To reach. That is, after confirming that the SOC tends to decrease in S208, whether or not {S (n) <S (n-1)} is performed in S213 at the next time point, and {S (n ) <S (n−1)}, it is determined that the number continues to decrease.

  If it is determined in S212 that the value does not continue to increase, or if it is determined that the value does not continue to decrease in S213, various parameters at the present time are set as initial values in S215. That is, each value (recorded in S203) currently recorded in the RAM 19 is registered as an initial value Tmst of time, an initial value Vst of open circuit voltage, an initial value Sst of SOC, and an initial value Ahst of current integrated value. Further, after the flag is set to {Flag = 0}, the processes after S200 are executed again.

なお、カウンタ値ｃは、初期値を０として、Ｓ２１４の処理が実行されるたびに一つカウントアップされる。つまり、Ｓ２１４の処理が実行されるたびに、ｄｓ（ｃ）、ｄｔ（ｃ）、ｄａｈ（ｃ）およびｄｓｄｔ（ｃ）がＲＡＭ１９に記録されていく。 If it is determined in S212 that it continues to increase, or if it is determined that it continues to decrease in S213, values necessary for calculating the current offset and current gain are recorded in the RAM 19 in S214. The values necessary for the calculation include the SOC change amount ds (c), the time change amount dt (c), the current integrated value change amount dah (c), and the SOC change amount per unit time, which are calculated as follows: dsdt (c) is recorded.

The counter value c is incremented by one each time the process of S214 is executed with the initial value set to 0. That is, ds (c), dt (c), dah (c), and dsdt (c) are recorded in the RAM 19 each time the process of S214 is executed.

  In S216, it is confirmed whether charging / discharging of the battery pack 11 is completed. When the current value of the inflow / outflow current of the battery pack 11 is 0 for a predetermined period, or when the operation of the system using the battery pack 11 is completed, it is determined that charging / discharging has been completed. If it is determined that charging / discharging has been completed, calculation of a current offset error (see FIG. 3) is executed in S217 based on the value recorded in S214, and further calculation of a current gain error (see FIG. 3). 4) is executed, each calculated error is corrected, and this flow ends.

  FIG. 3 is a flowchart for explaining the current offset error calculation process, and shows the process executed in S217 of FIG.

ここで、Ｃｄｓｄｔは絶対値の差の判定値であり、電池パック１１を利用するシステムに応じて設定される。 First, in S300, a combination (c = j, k) related to the counter value c used in S301 is selected. Then, in S301, for the SOC change amount dsdt (c) per unit time recorded in the RAM 19 in S214 of FIG. Specifically, a combination satisfying the following expression is extracted with the combination relating to the counter value c being c = j, k.

Here, Cdsdt is a determination value of the difference between the absolute values, and is set according to the system using the battery pack 11.

  In S301, the meaning of extracting a set of absolute values dsdt (k) and dsdt (j) that are substantially equal with opposite signs is to remove the influence of the current gain error. In other words, the effect of the current gain error is offset by using the sum of the integrated capacities when charging and discharging are performed with substantially the same charging current and discharging current. The process of S301 is executed for each set of j and k selected in S300. That is, in S300, all combinations (j, k) that satisfy j ≦ c, k ≦ c, and j <k are generated, and the processing of S301 is executed for each combination.

さらに、上記で求めた各値からオフセット誤差Ａｏｆｆ（ｃｆ）が次式のとおり算出される。

つまり、オフセット誤差は、電流センサによる積算容量とＳＯＣ変化から算出される容量との差を経過時間で割った値となる。なお、カウンタ値ｃｆは、初期値を０として、Ｓ３０２の処理が実行されるたびに一つカウントアップされる。そして、Ｓ３０２の処理が実行されるたびに、Ａｏｆｆ（ｃｆ）、Ｄａｈ（ｃｆ）、Ｄｓ（ｃｆ）およびＤｔ（ｃｆ）の値がＲＡＭ１９に記録されていく。 In S302, for each set of dsdt (k) and dsdt (j) extracted in S301, the sum Dah of the accumulated capacity, the sum Ds of the absolute values of the SOC change, and the sum Dt of the time change are as follows: Desired.

Further, the offset error Aoff (cf) is calculated from the values obtained above as follows:

That is, the offset error is a value obtained by dividing the difference between the accumulated capacity by the current sensor and the capacity calculated from the SOC change by the elapsed time. The counter value cf is incremented by one each time the process of S302 is executed with the initial value set to 0. Each time the process of S302 is executed, the values of Aoff (cf), Dah (cf), Ds (cf), and Dt (cf) are recorded in the RAM 19.

  In S300 to S302, when the processing for all the combinations (j, k) is completed, the process proceeds to S303, and the average value of all the Aoff (cf) values calculated in S302 is calculated as the current offset error Aoff.

  FIG. 4 is a flowchart for explaining the calculation process of the current gain error, and shows the process executed in S218 of FIG.

さらに、Ｄｓａ（ｍ）を時間変化Ｄｔ（ｍ）で割った値が、ゲイン誤差に伴う電流値のずれの時間平均値ａｇとして算出され、また、時間変化Ｄｔ（ｍ）間の平均電流、つまりオフセット誤差とゲイン誤差の両方を含んだ値ａｖが次式のように算出される。

そして、｛電流の真の値＝電流センサの値ａｖ−Ａｏｆｆ−ａｇ｝の関係から、ゲイン誤差Ａｇ（ｃｇ）を次式のように算出する。

なお、カウンタ値ｃｇは、初期値を０として、Ｓ４０１の処理が実行されるたびに一つカウントアップされる。そして、Ｓ４０１の処理が実行されるたびに、算出された電流ゲイン誤差Ａｇ（ｃｇ）の値がＲＡＭ１９に記録されていく。 In S400, the counter value m used in S401 is set. In S401, the current gain error Ag (cg) is calculated based on Dah (cf), Ds (cf), Dt (cf) recorded in the RAM 19 in S302 of FIG. 3 and the average value Aoff calculated in S303 of FIG. ) Is calculated. Specifically, Dsa (m) obtained by subtracting the offset error capacity and the capacity calculated from the SOC change from the integrated capacity of the current sensor is calculated as follows.

Further, the value obtained by dividing Dsa (m) by the time change Dt (m) is calculated as the time average value ag of the deviation of the current value due to the gain error, and the average current during the time change Dt (m), that is, A value av including both an offset error and a gain error is calculated as follows.

Then, the gain error Ag (cg) is calculated from the relationship {true value of current = value of current sensor av−Aoff−ag} as follows.

Note that the counter value cg is incremented by one each time the process of S401 is executed with the initial value set to 0. Each time the process of S401 is executed, the value of the calculated current gain error Ag (cg) is recorded in the RAM 19.

  In S400 and S401, when the processing for all the counter values m is completed, the process proceeds to S402, and the average value of all Ag (cg) values calculated in S401 is calculated as the current gain error Ag.

  The offset error and gain error of the current sensor are calculated by the calculation process described with reference to FIGS. 3 and 4, and the offset error and gain error are corrected based on the calculated values. In FIG. 3, in S301, the method of extracting an offset error by extracting a set satisfying the condition of a pair dsdt (k) and dsdt (j) having substantially the same value with opposite signs is described. Even if is not satisfied, the offset error can be calculated as follows.

  FIG. 7 is a diagram for explaining the change in capacity of the battery pack when the charging current and the discharging current are different. The accumulated capacity 70 and the true capacity 72 of the current sensor are shown with the elapsed time on the horizontal axis and the capacity on the vertical axis. It is shown. Since the accumulated capacity 70 of the current sensor includes an error due to an offset error and a gain error, an error occurs with the true capacity 72. The true capacity 72 is a value calculated using the SOC determined from the open circuit voltage.

During the elapsed time Δt ₁ , the true capacity 72 increases by ΔQ _A1 . During this period, the average current A ₁ continues to increase. The integrated capacity 70 of the current sensor is increased by ΔQ _B1 . Further, during the elapsed time Δt ₂ , the true capacity 72 decreases by ΔQ _A2 . In the meantime, the average current A ₂ continues to decrease. The integrated capacity 70 of the current sensor is reduced by ΔQ _B2 .

また、ゲイン誤差が一定であると考えると次式が成立する。

上記（ａ）式、（ｂ）式および（ｃ）式から、オフセット誤差Ａｏｆｆが次式のように算出できる。

このように、開回路電圧から計算される真の容量７２と電流センサの積算容量７０から電流センサのオフセット誤差Ａｏｆｆを算出することができる。 Here, let us consider a case where the correspondence shown in FIG. 5 exists between the measured value of the current sensor and the true value of the current. That is, a measure of the current sensors corresponding to the true value A ₁ of the current _{(A 1 + A 1g + Aoff} ), measurements of the current sensors corresponding to the true value A ₂ of the current (A ₂ + A _2g + Aoff ), The following equation holds.

If the gain error is considered to be constant, the following equation is established.

From the equations (a), (b), and (c), the offset error Aoff can be calculated as the following equation.

Thus, the offset error Aoff of the current sensor can be calculated from the true capacitance 72 calculated from the open circuit voltage and the integrated capacitance 70 of the current sensor.

また、｛ΔＱ_A1＝−ΔＱ_A2｝の場合、｛Ａ_1g×Δｔ₁｝と｛−Ａ_2g×Δｔ₂｝がほぼ等しくなるため、

となる。したがって、（ｅ）式から、オフセット誤差Ａｏｆｆが次式のように算出できる。

このように、オフセット誤差の算出を簡略化することもできる。 In FIG. 7, when the condition {ΔQ _A1 = −ΔQ _A2 } is further satisfied, the following equation is derived from the equations (a) and (b).

In the case of {ΔQ _A1 = −ΔQ _A2 }, {A _1g × Δt ₁ } and {−A _2g × Δt ₂ } are substantially equal.

It becomes. Therefore, the offset error Aoff can be calculated from the equation (e) as follows:

Thus, the calculation of the offset error can be simplified.

  As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention.

It is a figure for demonstrating suitable embodiment of the current measuring device which concerns on this invention. It is a figure for demonstrating the correction process of the offset error and gain error in this embodiment. It is a flowchart for demonstrating the calculation process of an electric current offset error. It is a flowchart for demonstrating the calculation process of an electric current gain error. It is a figure for demonstrating an offset error and a gain error. It is a graph which shows the correspondence of an open circuit voltage and SOC. It is a figure for demonstrating the capacity | capacitance change in case charging current and discharge current differ.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Battery pack, 12 Battery module, 13 Current sensor, 14 Voltage detection part, 17 CPU.

Claims (7)

A current sensor for measuring the charging current and discharging current of the battery;
A correction unit for correcting a measurement error of the current sensor;
Have
The correction unit calculates an offset error of the current sensor based on a capacity difference between the battery capacity obtained from the integrated value of the current measured by the current sensor and the battery capacity obtained from the open circuit voltage of the battery.
A battery current measuring device. In the battery current measuring device according to claim 1,
The correction unit calculates an offset error from a change per unit time of the capacity difference.
A battery current measuring device. In the battery current measuring device according to claim 1,
The correction unit uses, as an integrated value of the current measured by the current sensor, a sum of an integrated value of the charging current and an integrated value of the discharging current based on a current value substantially the same as the charging current,
A battery current measuring device. In the battery current measuring device according to claim 1,
The correction unit is a correction that is a difference between a corrected battery capacity that is obtained by correcting an integrated value associated with the offset error from an integrated value of current measured by a current sensor, and a battery capacity that is obtained from an open circuit voltage of the battery. Calculate the gain error of the current sensor based on the capacitance difference.
A battery current measuring device. The battery current measuring device according to claim 4,
The correction unit calculates a gain error based on a change amount per unit time of the correction capacity difference.
A battery current measuring device. In the current sensor error correction method for measuring the charging current and discharging current of the battery,
Correction means
Calculate the offset error of the current sensor based on the capacity difference between the battery capacity obtained from the integrated value of the current measured by the current sensor and the battery capacity obtained from the open circuit voltage of the battery.
An error correction method for a current sensor. In the current sensor error correction method according to claim 6,
The correction means is
Based on a corrected capacity difference, which is a difference between a corrected battery capacity obtained by correcting an integrated amount associated with the offset error from an integrated value of current measured by a current sensor, and a battery capacity obtained from an open circuit voltage of the battery. Calculate the gain error of the current sensor,
An error correction method for a current sensor.

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