JP2019215213A - Battery system - Google Patents

Abstract

To accurately grasp a current flowing in a battery cell in a battery system that has plural battery cells connected in parallel.SOLUTION: A battery system includes: plural cells connected in parallel; plural fuses serially connected to the plural cells, respectively; a voltage sensor for detecting a voltage on a fuse out of the plural fuses, the fuse being connected to a specific cell (a high-temperature cell); a temperature sensor for detecting a temperature of the high-temperature cell; and an ECU. The ECU calculates a temperature of the fuse connected to the high-temperature cell using the voltage of the fuse connected to the high-temperature cell and a model formula representing a heat balance of the fuse and calculates a current of the high-temperature cell using the calculated fuse temperature. Here, the model formula is a linear delay expression that specifies a relation among calorific power of the fuse due to a current on the high-temperature cell, calorific power of the fuse due to a difference between the temperature of the fuse and that of the high-temperature cell, and a temperature change amount of the fuse.SELECTED DRAWING: Figure 6

Description

  The present disclosure relates to a battery system configured by connecting a plurality of battery cells in parallel.

  Japanese Patent Laying-Open No. 2008-182779 (Patent Document 1) discloses a battery system including an assembled battery configured by connecting a plurality of battery cells in parallel. In this battery system, a current cutoff mechanism is built in each battery cell. Then, when the current cutoff mechanism of any one of the battery cells operates, the switching element provided between the assembled battery and the electric load is controlled to the off state, and the assembled battery is disconnected from the electric load. As a result, the charging and discharging of the battery pack is stopped, and the battery pack is protected.

JP 2008-182779 A

  As described above, in the battery system disclosed in Patent Literature 1, when the current cutoff mechanism of any one of the battery cells operates, the assembled battery is disconnected from the electric load to protect the assembled battery.

  However, in a battery system configured by connecting a plurality of battery cells in parallel, even if the current cutoff mechanism does not operate, the battery flows through each battery cell due to the variation in the temperature of each battery cell. Variations can occur between the currents. Therefore, in order to more appropriately protect the battery cells in the battery system, it is necessary to accurately grasp the current flowing through each cell in consideration of the influence of the current variation of the battery cells due to the temperature variation of the battery cells. desired.

  The present disclosure has been made to solve the above-described problem, and an object of the present disclosure is to accurately grasp a current flowing through a battery cell in a battery system including a plurality of battery cells connected in parallel. is there.

  A battery system according to the present disclosure includes a plurality of cells connected in parallel, a fuse connected in series to at least one of the plurality of cells, a voltage sensor that detects a voltage of the fuse, and a series connected to the fuse. A temperature sensor for detecting the temperature of the cell and a control device for calculating the current of the cell connected in series to the fuse are provided. The control device calculates the fuse temperature using the fuse voltage, the cell temperature, and the model formula representing the heat balance of the fuse, calculates the resistance of the fuse corresponding to the fuse temperature, and calculates the fuse voltage by using the fuse voltage. The value divided by the resistance is calculated as the cell current. The model equation is an equation that defines the relationship between the amount of heat generated by the fuse due to the cell current, the amount of heat dissipation of the fuse caused by the difference between the fuse temperature and the cell temperature, and the amount of change in the temperature of the fuse. .

  In the above system, the temperature of the fuse is calculated using a model equation representing the heat balance of the fuse. Here, the model formula defines the relationship between the amount of heat generated by the fuse due to the cell current, the amount of heat released from the fuse due to the difference between the fuse temperature and the cell temperature, and the amount of change in the temperature of the fuse. This is an equation (first-order lag equation). Therefore, even if a large current flows through a plurality of cells and the temperature of the fuse deviates from the temperature of the cell, the temperature of the fuse can be accurately calculated. Then, the resistance of the fuse corresponding to the temperature of the fuse accurately calculated using the model formula is calculated, and the value obtained by dividing the fuse voltage by the resistance of the fuse is calculated as the cell current. Therefore, in a battery system including a plurality of battery cells connected in parallel, it is possible to accurately grasp the current flowing through the battery cells.

  According to the present disclosure, it is possible. In a battery system including a plurality of battery cells connected in parallel, it is possible to accurately grasp the current flowing through the battery cells.

FIG. 2 is a diagram illustrating an example of an overall configuration of a battery system. It is a figure which shows typically an example of the dispersion | variation of the electric current which generate | occur | produces between several battery cells. FIG. 4 is a diagram illustrating an example of a correlation between a fuse temperature Tf and a fuse resistance Rf. FIG. 4 is a diagram illustrating an example of a change between a fuse temperature Tf and a cell temperature Tc. FIG. 9 is a diagram (comparative example) showing an example of a calculation error of a cell current Ic. It is a conceptual diagram at the time of modeling the heat balance of fuse F. 4 is a flowchart illustrating an example of a processing procedure of an ECU. FIG. 4 is a diagram (part 1) comparing a calculated value of a fuse temperature Tf with an actually measured value. FIG. 8 is a diagram (part 2) comparing a calculated value of the fuse temperature Tf with an actually measured value. FIG. 10 is a diagram (part 3) in which a calculated value of the fuse temperature Tf is compared with an actually measured value.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

<Overall configuration of battery system>
FIG. 1 is a diagram showing an example of the overall configuration of a battery system 1 according to the present embodiment. The battery system 1 is configured to be able to supply electric power to an electric load (not shown). For example, the battery system 1 is mounted on an electric vehicle (such as a hybrid vehicle or an electric vehicle) provided with a traveling motor, and transfers electric power to and from the traveling motor.

  The battery system 1 includes a plurality of battery cells B, a plurality of fuses F, a bus bar U1 for a positive electrode, a bus bar U2 for a negative electrode, a voltage sensor 12, a temperature sensor (thermistor) 14, a current sensor 20, An ECU (Electronic Control Unit) 100 is provided.

  The plurality of battery cells B are secondary batteries that store electric power to be supplied to an electric load (not shown). For example, as the secondary battery, a lithium ion battery, a nickel hydride battery, or the like can be used. The plurality of battery cells B are connected in parallel to each other with respect to the electric load. Specifically, the positive electrode of each battery cell B is connected to the bus bar U1 for the positive electrode, and the negative electrode of each battery cell B is connected to the bus bar U2 for the negative electrode. The bus bars U1 and U2 are connected to an electric load (not shown).

  The plurality of fuses F are connected in series to the plurality of battery cells B, respectively. In the example shown in FIG. 1, one end of each fuse F is connected to the bus bar U1, and the other end of each fuse F is connected to the positive terminal of the corresponding battery cell B. The material of each fuse F is a metal (for example, zinc or the like). Each fuse F is blown when a current exceeding an allowable value flows, and cuts off an energizing path between the corresponding battery cell B and bus bar U1. This suppresses an excessive current from flowing through each battery cell B, and protects each battery cell B.

  In the following description, among the plurality of battery cells B, the battery cell B arranged at a position where the temperature becomes relatively high when electric power is exchanged with an electric load is also referred to as a “high-temperature cell”. In general, the high-temperature cell can be specified in advance by the positional relationship between the plurality of battery cells B and the cooling device. For example, when a plurality of battery cells B are cooled by the cooling air, the battery cells B arranged at positions where the cooling air hardly hits (positions where the cooling efficiency is poor) are high-temperature cells. Further, when there is no cooling device, the battery cells B arranged near the center of the plurality of battery cells B are high-temperature cells. In the following, for convenience of explanation, it is assumed that the battery cell B disposed on the rightmost side in FIG. 1 is a high-temperature cell. The number of high-temperature cells is not necessarily one, but may be two or more.

  The voltage sensor 12 is connected to both ends of the fuse F, which is connected in series to the high-temperature cell (the battery cell B disposed on the rightmost side in FIG. 1) among the plurality of fuses F, via wirings L1 and L2, respectively. Voltage sensor 12 detects a voltage between both ends of fuse F connected in series to the high-temperature cell (hereinafter, also referred to as “fuse voltage Vf”), and outputs information indicating the detection result to ECU 100. Voltage sensor 12 may be provided exclusively for detecting fuse voltage Vf, or may be shared with a voltage sensor provided for detecting another voltage (for example, a voltage between bus bars U1 and U2). Good.

  The temperature sensor 14 is disposed near the high-temperature cell, detects the temperature of the high-temperature cell (hereinafter, also referred to as “cell temperature Tc”), and outputs information indicating the detection result to the ECU 100. The temperature sensor 14 may be provided exclusively for detecting the cell temperature Tc, or may be shared with a temperature sensor provided for detecting another temperature.

  Current sensor 20 detects current I flowing between the electric load and bus bar U1 (the sum of the currents flowing through a plurality of battery cells B), and outputs information indicating the detection result to ECU 100.

  The ECU 100 includes a CPU (Central Processing Unit) and a memory (not shown). The ECU 100 calculates a current flowing through the high-temperature cell (hereinafter, also referred to as “cell current Ic”) based on information from each sensor and information stored in the memory.

  Although FIG. 1 shows an example including a plurality of fuses F connected to a plurality of battery cells B, a battery system to which the present disclosure can be applied includes at least a fuse F connected to a high-temperature cell. Just do it.

<Calculation of Cell Current Ic>
In a configuration in which a plurality of battery cells B are connected in parallel as in the battery system 1 illustrated in FIG. 1, variation in current between the battery cells B may occur due to variation in temperature between the battery cells B. .

  FIG. 2 is a diagram schematically illustrating an example of a variation in current generated between a plurality of battery cells B. In the parallel circuit, the current I flows in a distributed manner to the plurality of battery cells B. At this time, the current distributed to each battery cell B may change depending on the resistance balance among the plurality of battery cells B. The resistance of each battery cell B tends to decrease as the temperature of each battery cell B increases. Therefore, in a high-temperature cell (the battery cell B disposed on the rightmost side in FIG. 2) whose temperature is higher than that of the other battery cells B during charging and discharging, the resistance is lower than that of the other battery cells B, and the current is concentrated I do. In other words, if the cell current Ic flowing through the high-temperature cell can be ascertained, the variation (maximum value) of the current flowing through each battery cell B can be ascertained.

  Therefore, ECU 100 according to the present embodiment regards fuse F connected to the high-temperature cell as a shunt resistor, and calculates the current flowing through fuse F as “cell current Ic”. Specifically, ECU 100 as a control device calculates cell current Ic using detection results (fuse voltage Vf, cell temperature Tc) of voltage sensor 12 and temperature sensor 14.

  As one of the calculation methods of the cell current Ic, the value obtained by dividing the fuse voltage Vf, which is the voltage between both ends of the fuse F connected in series to the high-temperature cell, by the resistance of the fuse F by using Ohm's law, A method of calculating as the current Ic is conceivable. The material of the fuse F connected in series to the high-temperature cell is metal, and is between the temperature of the fuse F (hereinafter also referred to as “fuse temperature Tf”) and the resistance of the fuse (hereinafter also referred to as “fuse resistance Rf”). Has a positive correlation.

  FIG. 3 is a diagram illustrating an example of a correlation between the fuse temperature Tf and the fuse resistance Rf. Since the fuse F is a metal resistor, as shown in FIG. 3, there is a linear relationship between the fuse temperature Tf and the fuse resistor Rf such that the fuse resistor Rf monotonically increases as the fuse temperature Tf increases. I do. Information indicating such a correlation between the fuse temperature Tf and the fuse resistance Rf is obtained in advance by an experiment or the like and stored in the memory of the ECU 100.

  If it is assumed that the fuse temperature Tf is substantially the same value as the cell temperature Tc, the cell temperature Tc is treated as the fuse temperature Tf, and the fuse resistance Rf (hereinafter referred to as the fuse resistance Rf) corresponding to the cell temperature Tc detected by the temperature sensor 14 is used. “Fuse resistance Rfc corresponding to cell temperature Tc” or simply “fuse resistance Rfc” can be calculated with reference to the correlation shown in FIG. Then, as shown in the following equation (1), a value obtained by dividing the fuse voltage Vf detected by the voltage sensor 12 by the fuse resistance Rfc can be calculated as the cell current Ic.

Cell current Ic = fuse voltage Vf / fuse resistance Rfc (1)
However, when the current I is large (for example, when the current exceeds several hundred amperes), the fuse temperature Tf becomes equal to the cell temperature Tc due to a difference in heat capacity (heat mass) between the fuse F and the battery cell B. However, there is a concern that the temperature may deviate from the cell temperature Tc.

  FIG. 4 is a diagram illustrating an example of a change between the fuse temperature Tf and the cell temperature Tc when the current I is large. As shown in FIG. 4, when the current I is large, the cell current Ic also increases, and the amount of heat generated by the high-temperature cell and the fuse F connected to the high-temperature cell also increases. Since the fuse temperature is smaller than the heat capacity, the fuse temperature Tf is considerably higher than the cell temperature Tc. Due to this effect, when the current I is large, it is assumed that the fuse temperature Tf is substantially the same value as the cell temperature Tc. (Difference) becomes large, and it is feared that the cell current Ic cannot be calculated with high accuracy.

  FIG. 5 is a diagram illustrating an example of a calculation error of the cell current Ic calculated by Expression (1). As shown in FIG. 5, when current I is relatively small predetermined value I1 (for example, about 10 amps) and predetermined value I2 (for example, about 100 amps), calculation of cell current Ic calculated by equation (1) is performed. The error is relatively small. However, when the current I is a large predetermined value I3 (for example, about 300 amperes), the calculation error of the cell current Ic calculated by the equation (1) becomes a considerably large value.

  In view of this point, in the present embodiment, the heat balance of the fuse F is modeled, and the relationship between the heat generation amount of the fuse F, the heat release amount of the fuse F, and the change amount of the fuse temperature Tf is defined by a first-order lag equation. I do. Then, the ECU 100 calculates the fuse temperature Tf by using the fuse voltage Vf, the cell temperature Tc, and the first-order lag equation that models the heat balance of the fuse F.

  FIG. 6 is a conceptual diagram when the heat balance of the fuse F is modeled. The heat balance of the fuse F is conceptually shown on the left side of FIG. On the right side of FIG. 6, a model of the heat balance of the fuse F is conceptually shown.

  As shown on the left side of FIG. 6, when the cell current Ic flows through the fuse F, the fuse F generates heat (Joule heat) according to the cell current Ic. The heat of the fuse F is radiated to the battery cell B and the bus bar U1 connected to the fuse F, and further to the surrounding atmosphere. In modeling such a heat balance of the fuse F, as shown on the right side of FIG. 6, the amount of heat released from the fuse F to the atmosphere is very small and can be ignored. Further, the heat radiation to the bus bar U1 can be included in the heat radiation to the battery cell B.

  Based on such a concept, the heat balance of the fuse F can be modeled by a first-order lag equation such as the following equation (2).

ΔTf = β · Rf · Ic ² + α · (Tf−Tc) (2)
“Β · Rf · Ic ² ” on the right side of the equation (2) is a heat generation term corresponding to the heat generation amount of the fuse F caused by the cell current Ic. “Α · (Tf−Tc)” on the right side of the equation (2) is a heat radiation term corresponding to a heat radiation amount of the fuse F caused by a difference between the fuse temperature Tf and the cell temperature Tc. “Α” is a negative coefficient that can be adapted in advance from the behavior of the fuse voltage Vf when the current is relaxed (when the current I is set to 0 amperes). “Β” is a positive coefficient (° C./J, the reciprocal of the heat capacity) determined from the physical properties of the fuse F.

  “ΔTf” on the left side of the equation (2) is a change amount of the fuse temperature Tf due to heat generation and heat radiation of the fuse F.

When calculating the fuse temperature Tf by a calculation using the equation (2), the variation ΔTf fuse temperature Tf from the fuse temperature Tf _n calculated in the current calculation cycle, the fuse temperature calculated in the previous calculation cycle It can be defined as a value obtained by subtracting Tf _n-1 (= Tf _n -Tf _n-1 ). In this case, equation (2) can be modified as equation (2A) below.

Tf _n = Tf _n−1 + β · Rf · Ic ² + α · (Tf _n−1 −Tc) (2A)
Since Ic = Vf / Rf according to Ohm's law, equation (2A) can be further transformed into equation (2B).

Tf _n = Tf _n−1 + β · Vf ² / Rf _n−1 + α · (Tf _n−1 −Tc) (2B)
In the equation (2B), “Tf _n−1 ” is the fuse temperature Tf calculated in the previous operation cycle, and is stored in the memory of the ECU 100. Note that the initial value of the fuse temperature Tf _n-1 can be the cell temperature Tc detected by the temperature sensor 14 since the current I has not yet flowed. “Rf _n−1 ” is a fuse resistance Rf corresponding to the previous fuse temperature Tf _n−1 and is stored in the memory of the ECU 100.

Therefore, the previous fuse temperature Tf _n−1 and fuse resistance Rf _n−1 stored in the memory, the fuse voltage Vf detected by the voltage sensor 12, and the fuse voltage Vf detected by the temperature sensor 14 are stored on the right side of the equation (2B). by substituting the cell temperature Tc, it is possible to calculate the current fuse temperature Tf _n. Thus, this fuse temperature Tf _n is calculated accurately by considering the heat balance of the fuse F.

Next, the ECU 100 calculates the resistance of the fuse F corresponding to the current fuse temperature Tf _n calculated accurately (hereinafter, also referred to as “current fuse resistance Rf _n ”) with reference to the correlation shown in FIG. calculate.

Then, as shown in the following equation (1A), the ECU 100 sets a value (= Vf / Rf _n ) obtained by dividing the fuse voltage Vf detected by the voltage sensor 12 by the current fuse resistance Rf _n as the cell current Ic. calculate.

Cell current Ic = fuse voltage Vf / fuse resistance Rf _n (1A)
FIG. 7 is a flowchart illustrating an example of a processing procedure executed when ECU 100 calculates cell current Ic. This flowchart is repeatedly executed at a predetermined cycle.

  The ECU 100 acquires the fuse voltage Vf from the voltage sensor 12 (Step S10). The ECU 100 acquires the cell temperature Tc from the temperature sensor 14 (Step S12).

Next, the ECU 100 uses the fuse voltage Vf, the cell temperature Tc, and the model equation representing the heat balance of the fuse F (see the above-described first-order lag equations (2) to (2B)) to determine the current fuse temperature Tf. _n is calculated (step S20). As described above, for example, ECU 100 substitutes fuse voltage Vf, cell temperature Tc, and previous fuse resistance Rf _n−1 and fuse resistance Rf _n−1 stored in the memory into equation (2B). by, to calculate the current fuse temperature Tf _n.

8 to 10 are both obtained by experiment or the like, and the calculated value of the fuse temperature Tf _n by the processing in step S20, a diagram comparing the measured value of the fuse temperature Tf. 8 shows a case where the current I is a predetermined value I4 (for example, about 150 amps), and FIG. 9 shows a case where the current I is a predetermined value I5 (for example, about 200 amps) larger than the predetermined value I4. Shows a case where the current I is a predetermined value I6 (for example, about 300 amperes) which is larger than the predetermined value I5. In any case of FIGS. 8 to 10, the calculated value of the fuse temperature Tf _n is approximately equal to the measured value of the fuse temperature Tf (error about several percent) has a calculation accuracy of the fuse temperature Tf _n It can be confirmed that is secured.

Referring back to FIG. 7, ECU 100 is a fuse resistor Rf _n corresponding to the fuse temperature Tf _n calculated in step S20, is calculated by referring to the correlation shown in aforementioned Figure 3 stored in the memory (step S22).

Then, ECU 100 is a fuse voltage Vf obtained in step S10, the value obtained by dividing the fuse resistor Rf _n calculated in step S22 the (= Vf / Rf _n), is calculated as the cell current Ic (step S24).

As described above, ECU 100 according to this embodiment calculates the fuse temperature Tf _n using a model expression representing the thermal budget of the fuse F a (the above equation (2) ~ (2B) refer). This model formula is based on the heat value of the fuse F (= β · Rf · Ic2) caused by the cell current Ic and the heat dissipation amount (= α · (Tf) of the fuse F caused by the difference between the fuse temperature Tf and the cell temperature Tc. −Tc)) and a first-order lag formula that defines the relationship between the variation ΔTf of the fuse temperature Tf due to heat generation and heat radiation of the fuse F. Therefore, for example, even if the current I is larger fuse temperature Tf and the cell temperature Tc deviates, it is possible to calculate better fuse temperature Tf _n accuracy.

The fuse resistor Rf _n corresponding to the fuse temperature Tf _n calculated accurately using a model formula is calculated with reference to the correlation shown in FIG. 3, the value obtained by dividing the fuse voltage Vf in fuse resistor Rf _n It is calculated as the cell current Ic. Therefore, the cell current Ic can be accurately grasped. By using the cell current Ic, it is possible to appropriately exchange power with the electric load without excessively limiting the current I.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 battery system, 12 voltage sensor, 14 temperature sensor, 20 current sensor, 100 ECU, B battery cell, F fuse, U1, U2 bus bar.

Claims (1)

Multiple cells connected in parallel;
A fuse connected in series to at least one of the plurality of cells;
A voltage sensor for detecting a voltage of the fuse;
A temperature sensor for detecting a temperature of a cell connected in series to the fuse;
A control device for calculating a current of a cell connected in series to the fuse,
The controller is
Calculating the temperature of the fuse using a voltage of the fuse, a temperature of the cell, and a model formula representing a heat balance of the fuse,
Calculating the resistance of the fuse corresponding to the temperature of the fuse;
A value obtained by dividing the voltage of the fuse by the resistance of the fuse is calculated as the current of the cell,
The model formula is a heat generation amount of the fuse caused by the current of the cell, a heat release amount of the fuse caused by a difference between the temperature of the fuse and the temperature of the cell, and a change amount of the temperature of the fuse. A battery system that is an expression that defines the relationship.

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