JP6648561B2 - Power system - Google Patents

Description

  The present invention relates to a power supply system for setting a maximum dischargeable power of a battery module.

  In recent years, hybrid vehicles that drive a vehicle with an engine and a motor have been widely used. The hybrid vehicle is equipped with a secondary battery that can supply drive power to the motor and store the generated power when the motor functions as a generator. In such a hybrid vehicle, a starter is not separately provided to start the engine, and the engine is started by a motor for driving the vehicle. When starting the engine, a large amount of power is discharged from the secondary battery, so the maximum dischargeable power from the secondary battery is temporarily increased to the power at which the voltage value of the secondary battery does not fall below the lower limit voltage value. A charge / discharge control device has been proposed (for example, see Patent Document 1).

  Further, in Patent Document 2, even when the engine is started after waiting for a while after estimating the maximum dischargeable power from the secondary battery, the voltage value of the secondary battery is lower than the lower limit voltage value when the engine is started. In order to prevent this, a power storage device output prediction device that sets the maximum dischargeable power of the secondary battery in consideration of discharge during standby has been proposed (for example, see Patent Document 2).

JP 2007-306771 A JP 2010-035332A

  Incidentally, nickel-metal hydride batteries and lithium-ion batteries are often used as secondary batteries for vehicles. As shown in FIG. 8A, in an initial state, a positive electrode active material layer 122b made of a positive electrode active material 122c and a conductive material 122d is formed on the surface of the current collector foil 122a of the positive electrode plate 122 of such a secondary battery. Is formed. The surface of the positive electrode active material 122c is covered with a conductive material 122d. When the positive electrode potential falls below the lower limit potential due to overdischarge, as shown in FIG. 8B, the conductive material 122d elutes into the electrolytic solution to generate an elute 122e. When the eluted substance 122e is generated, the amount of the conductive material 122d is reduced, and the conductivity of the positive electrode plate 122 is reduced, which may cause deterioration of the output performance of the secondary battery. Further, when the negative electrode potential rises to or above the upper limit potential due to overdischarge, the conductive material 121d of the negative electrode elutes into the electrolytic solution similarly to the positive electrode, the amount thereof decreases, and the conductivity of the negative electrode plate 121 decreases. This may cause deterioration of the secondary battery. Therefore, in order to prevent the secondary battery from being deteriorated due to overdischarge, it is desirable to determine the maximum dischargeable power based on the potentials of the positive electrode and the negative electrode of the secondary battery.

  However, the related arts described in Patent Documents 1 and 2 calculate the maximum dischargeable power based on the voltage value of the secondary battery, that is, the potential difference between the positive electrode and the negative electrode, not based on the potentials of the positive electrode and the negative electrode. Therefore, the calculation accuracy is low, and the dischargeable power of the secondary battery may not be sufficiently used, or deterioration due to overdischarge may be caused. Further, when the potentials of the positive electrode and the negative electrode are detected using the potential detection device and the dischargeable power is calculated based on the detected potential, there is a problem that the power supply system becomes complicated.

  Therefore, the present invention improves the calculation accuracy of the maximum dischargeable power of the secondary battery with a simple configuration, makes the dischargeable power of the secondary battery sufficiently usable, and suppresses the deterioration of the secondary battery due to overdischarge. The purpose is to:

A power supply system according to the present invention includes a battery module in which a plurality of battery cells are connected in series, a voltage sensor that detects a voltage value of the battery module, a current sensor that detects a current value of the battery module, A power supply system comprising: a temperature sensor that detects a temperature; and a control unit that adjusts a discharge power of the battery module, wherein the control unit includes: a current voltage value of the battery module detected by the voltage sensor; A current estimating unit that estimates a current positive electrode potential and a current negative electrode potential of the battery cell based on a current current value of the battery module detected by a current sensor and a current temperature of the battery module detected by the temperature sensor. the discharge lower limit voltage of the estimated current positive potential and the cathode battery cell Internal resistance based on the polarization resistance calculates a first maximum dischargeable electric power of the battery module when the current value of the positive electrode of the battery cell is increased from the current current value, estimated the current negative electrode potential and the negative electrode of the Power calculation for calculating the second maximum dischargeable power of the battery module when the current value of the negative electrode of the battery cell is lower than the current value based on the discharge upper limit potential of the battery cell and the internal resistance and polarization resistance of the battery cell. And a maximum discharge power setting unit configured to compare the first maximum dischargeable power and the second maximum dischargeable power and set a smaller one as the maximum dischargeable power of the battery module. I do.

  The present invention improves the calculation accuracy of the maximum dischargeable power of the secondary battery with a simple configuration, makes it possible to sufficiently use the dischargeable power of the secondary battery, and suppresses the deterioration of the secondary battery due to overdischarge. it can.

1 is a system diagram illustrating a configuration of a power supply system according to an embodiment. It is an outline view of a battery cell. FIG. 3 is an exploded perspective view of a belt-like power generation element in a battery cell. It is sectional drawing of the belt-shaped power generation element of a battery cell. It is a perspective view which shows the state which wound the belt-shaped electric power generation element shown in FIG. 3A, FIG. 3B. 5 is a flowchart illustrating an operation of the power supply system according to the embodiment. 5 is a map showing a current, temperature, SOC, and negative electrode potential _{V negative} relationship of a battery cell. 5 is a graph showing a temporal change of a positive potential V _positive , a positive current value I _positive , a negative current value I _negative , and a negative potential V _negative of a battery cell. FIG. 3 is an explanatory diagram showing an initial state and deterioration of a secondary battery.

  Hereinafter, the power supply system 100 of the present embodiment will be described with reference to the drawings. As shown in FIG. 1, the power supply system 100 of the present embodiment includes a battery module 10, a voltage sensor 17 for detecting a voltage value Vb of the battery module 10, and a current sensor 18 for detecting a current value Ib of the battery module 10. , A temperature sensor 19 for detecting the temperature Tb of the battery module 10, and a control unit 20 for adjusting the discharge power of the battery module 10. The battery module 10 is connected to a load 14 via a positive line 12 and a negative line 13. The load 14 operates by receiving the power output from the battery module 10. The load 14 can also generate electric power, and the electric power generated by the load 14 is supplied to the battery module 10. Thereby, the battery module 10 is charged.

  The power supply system 100 can use, for example, a motor generator as the load 14 that can be mounted on a vehicle. The motor generator receives power output from battery module 10 and generates motive power for running the vehicle. The power generated by the motor generator is transmitted to the wheels. The motor generator converts kinetic energy generated during braking of the vehicle into electric power, and supplies the electric power to the battery module 10.

  The voltage sensor 17, the current sensor 18, and the temperature sensor 19 are connected to the control unit 20, and the voltage value Vb, the current value Ib, and the temperature Tb detected by the sensors 17, 18, 19 are input to the control unit 20, respectively. . In the present embodiment, the current value Ib when discharging the battery module 10 is set to a positive value, and the current value Ib when charging the battery module 10 is set to a negative value.

  The control unit 20 controls charging and discharging of the battery module 10 based on the voltage value Vb, the current value Ib, and the temperature Tb. The control unit 20 is a computer having therein a CPU 21 for performing information processing and calculations and a memory 22 for storing control programs and control data. Further, control unit 20 includes a potential estimating unit 23, a power calculating unit 24, and a maximum discharge power setting unit 25, which will be described later.

  The battery module 10 has a plurality of battery cells 11 connected in series. The battery cell 11 is a chargeable / dischargeable secondary battery such as a nickel hydrogen battery or a lithium ion battery.

  Next, the structure of the battery cell 11 will be described with reference to FIG. In FIG. 2, the X axis and the Z axis are axes orthogonal to each other. In the present embodiment, the axis corresponding to the vertical direction is the Z axis. Note that an axis orthogonal to the X axis and the Z axis is defined as a Y axis.

  The battery cell 11 includes a battery case 110 and a power generation element 120 that performs charging and discharging. Battery case 110 houses power generation element 120. The battery case 110 is in a sealed state, and an electrolyte is injected into the battery case 110. A negative terminal 111 and a positive terminal 112 are fixed to the battery case 110. Negative electrode terminal 111 and positive electrode terminal 112 are electrically connected to power generation element 120.

  As shown in FIG. 3A, the power generation element 120 has a negative electrode plate 121, a positive electrode plate 122, and a separator 123. FIG. 3A is a diagram in which a part of the power generation element 120 is developed. In FIG. 3A, Y indicates the laminating direction of the negative electrode plate 121, the positive electrode plate 122, and the separator 123. The negative electrode plate 121 has a current collecting foil 121a and a negative electrode active material layer 121b formed on the surface of the current collecting foil 121a. Since the negative electrode active material layer 121b is formed on the lower surface of the current collector foil 121a in FIG. 3A, it is indicated by hatching with a broken line. As described with reference to FIG. 8A, the negative electrode active material layer 121b includes the negative electrode active material 121c, the conductive material 121d, the binder, and the like. The negative electrode active material layer 121b is formed in a partial area of the current collecting foil 121a, and the negative electrode active material layer 121b is not formed in the remaining area of the current collecting foil 121a.

  Similarly, the positive electrode plate 122 has a current collector foil 122a and a positive electrode active material layer 122b formed on the surface of the current collector foil 122a, and as described with reference to FIG. A positive electrode active material 122c, a conductive material 122d, a binder, and the like are included. Since the positive electrode active material layer 122b is formed on the upper surface of the current collector foil 122a in FIG. 3A, it is indicated by solid-line hatching. The positive electrode active material layer 122b is formed in a partial area of the current collecting foil 122a, and the positive electrode active material layer 122b is not formed in the remaining area of the current collecting foil 122a.

  As shown in FIG. 3B, the power generating element 120 is laminated with a separator 123 interposed between a negative electrode active material layer 121b of a negative electrode plate 121 and a positive electrode active material layer 122b of a positive electrode plate 122, and is arranged in a direction D shown in FIG. It is a strip-shaped thin plate extending long. Therefore, the current collecting foil 121a of the negative electrode plate 121 and the current collecting foil 122a of the positive electrode plate 122 are outer surfaces in the Y direction, which is the laminating direction of the power generation elements 120.

  In order to store the band-like power generation element 120 in the battery case 110 shown in FIG. 2, the band-like power generation element 120 shown in FIGS. 3A and 3B is moved around the X axis as shown in FIG. The winding is performed so that the direction D in which the power generating element 120 shown in FIG. As described above, since each of the current collecting foils 121a and 122a is an outer surface in the stacking direction of the band-shaped power generating element 120, the outer surfaces of the respective current collecting foils 121a and 122a do not contact each other when wound. When winding, the separator 124 shown in FIG. 3B is sandwiched between the current collecting foils 121a and 122a. Then, the power generating element 120 wound three-dimensionally is accommodated in the battery case 110. Although FIG. 4 shows the power generating element 120 wound in an elliptical cylindrical shape, the shape of the power generating element is not limited to this, and may be, for example, a rectangular shape.

  In the three-dimensional power generation element 120, only the current collector foil 121a of the negative electrode plate 121 is wound at one end of the power generation element 120 in the direction in which the X axis extends (referred to as the X direction). The portion where only the current collector foil 121a is wound is electrically connected to the negative electrode terminal 111 shown in FIG. At the other end of the power generation element 120 in the X direction, only the current collector foil 122a of the positive electrode plate 122 is wound. The part around which only the current collector foil 122a is wound is electrically connected to the positive electrode terminal 112 shown in FIG.

  After storing the three-dimensional power generating element 120 in the battery case 110, an electrolytic solution is put into the battery case 110, and the negative electrode active material layer 121b, the positive electrode active material layer 122b, and the separator 123 are impregnated with the electrolytic solution. In addition, an electrolytic solution as a surplus liquid exists outside the power generation element 120, that is, in a space formed between the power generation element 120 and the battery case 110.

  A region A illustrated in FIG. 4 is a region where the negative electrode active material layer 121b and the positive electrode active material layer 122b face each other with the separator 123 interposed therebetween. In the region A, a chemical reaction is performed according to the charging and discharging of the battery cells 11 (power generation elements 120).

  The battery module 10 illustrated in FIG. 1 is configured such that the battery cells 11 described with reference to FIGS. 2 to 4 are stacked in the Y direction such that the arrangement of the negative terminal 111 and the positive terminal 112 in the X direction is alternately opposite. A plurality of battery cells 11 are connected in series by sequentially connecting a negative electrode terminal 111 and a positive electrode terminal 112 of an adjacent battery cell 11.

Next, the operation of the power supply system 100 of the present embodiment will be described with reference to FIGS.
In the following description, as shown in FIG. 7, between time zero and time t0, a positive electrode current I _{+ 0} flows from the positive electrode and a negative current I _{+ 0} flows into the _negative electrode. _Positive voltage gradually decreases due to discharge, and negative electrode potential V _negative voltage gradually increases due to discharge. At time t0, the positive electrode voltage value becomes V _{positive 0 and the} negative electrode voltage value becomes V _{negative 0} . Further, the current values of the positive electrode and the negative electrode at time t0 are I _{positive 0} and I _{negative 0} , respectively. Note that time t0 is the current time. 7A shows a _positive change in the _positive electrode potential V, a line q in FIG. 7B shows a _positive change in the _positive electrode current value I, and a line r in FIG. The value I indicates a _positive change, and the line s in FIG. 7D indicates a negative potential V _negative change. Incidentally, the positive electrode current value I _positive, negative current value I _negative, positive, positive direction of the current flowing out from the negative electrode, a positive electrode, a negative direction of current flowing into the anode.

  As shown in step S101 of FIG. 5, the potential estimating unit 23 of the control unit 20 uses the voltage sensor 17, the current sensor 18, and the temperature sensor 19 shown in FIG. The value Ib0 and the current temperature Tb0 are detected.

Next, the potential estimating unit 23 of the control unit 20 performs a process of estimating the current negative electrode potential V _{negative 0} as in step S102 of FIG. The control unit 20 stores the current I (A) of the battery cell 11 on the X axis, the temperature (° C.) of the battery cell 11 on the Y axis, and the Z axis perpendicular to the XY plane as shown in FIG. A map plotting the negative electrode potential V _negative of the battery cell 11 is stored as the SOC 11.

The SOC of the battery module 10 at time t0 can be estimated from the current voltage value Vb0, the current value Ib0, and the current temperature Tb0. Further, since the battery cells 11 are connected in series, the current value Ib0 of the battery module 10 is the same as the current of the battery cell 11. The temperature of the battery module 10 is the same as the temperature of the battery cell 11. Therefore, the potential estimating unit 23 of the control unit 20 calculates the SOC of the battery module 10 based on the current voltage value Vb0, the current value Ib0, and the current temperature Tb0 of the battery module 10 detected at the time t0. From the battery cell 11 is calculated. Normally, the SOC of the battery cell 11 is the same as the SOC of the battery module 10, so the potential estimating unit 23 sets the SOC of the battery module 10 to the SOC of the battery cell 11. Therefore, the potential estimating unit 23 estimates the current negative electrode potential V _{negative 0} at time t0 from the map of FIG. 6 using the current value Ib0, the current temperature Tb0, and the SOC of the battery module 10.

で算出する。電位推定部２３は、電池セル１１の現在正極電位Ｖ_正０を以下の式を用いて推定する。

Next, the potential estimating unit 23 of the control unit 20 performs a process of estimating the current positive electrode potential V _{positive 0} at time t0, as shown in step S103 of FIG. Since the battery module 10 is configured by connecting a plurality of battery cells 11 in series, the voltage V0 at time t0 of the battery cells 11 is represented by n, where n is the number of battery cells 11.

Is calculated by The potential estimating unit 23 estimates the current positive electrode potential V _{positive 0} of the battery cell 11 using the following equation.

Next, the control unit 20 proceeds to step S104, and based on the current positive electrode potential V _{positive 0} at time t0 and the positive discharge lower limit potential V _{positive e at} time te, for example, one second later, at the power calculation unit 24, , The first cell maximum dischargeable power W _{positive e} is calculated. The discharge lower limit potential V _e of the _positive electrode varies depending on the type of the battery cell 11, but may be, for example, about 0.2 to 0.3 V.

As shown by a line q in FIG. 7B, assuming that the positive electrode current value increases from I _{positive 0} to I _{positive α} immediately after time t0, as shown by a line p in FIG. V _positive decreases by [(I _{positive α−} I _{positive 0} ) × R _positive ] from time t0 to time t1, where the internal resistance of the positive electrode is R _positive . The time from time t0 to time t1 is, for example, about 0.1 second. Assuming that the positive electrode potential at time t1 is V _{positive 1} , V _{positive 1} is expressed by the following equation.

（式４）をＩ_正αについて解くと、

となる。
そうすると、時刻ｔｅに正極の電位が放電下限電位Ｖ_正ｅとなる電池セル１１の第１セル最大放電可能電力Ｗ_正ｅは、以下の（式６）で算出される。

電力算出部２４は（式６）によって電池セル１１の第１セル最大放電可能電力Ｗ_正ｅを算出したら、それを電池セル１１の個数のｎをかけたものをバッテリモジュール１０の第１最大放電可能電力としてメモリ２２に格納する。

As shown in line p in FIG. 7 (a), the positive electrode potential V _positive by polarization of the battery cell 11 after time t1, [I _{positive alpha} × R _{positive dyn],} only slowly decreased, the time te The lower limit potential V of the _positive electrode becomes _{positive e} . V _{positive e} is expressed by the following (Equation 4), where the positive electrode polarization resistance is R _{positive dyn} . Here, the time from the time t0 to the time te is, for example, about one second.

Solving (Equation 4) for I _{positive α} ,

Becomes
Then, the first cell maximum dischargeable power W _{positive e} of the battery cell 11 in which the potential of the positive electrode becomes the lower discharge potential V _{positive e at} the time te is calculated by the following (Equation 6).

After calculating the first cell maximum dischargeable power W _{positive e} of the battery cell 11 by (Equation 6), the power calculation unit 24 multiplies the result by n of the number of the battery cells 11 to obtain the first maximum discharge power W of the battery module 10. It is stored in the memory 22 as possible power.

After calculating the first maximum dischargeable power, the power calculation unit 24 of the control unit 20 proceeds to step S105 in FIG. 5 and calculates the current negative electrode potential V _{negative 0 at} time t0 and the negative discharge upper limit potential V _{negative e at} time te. , The second maximum dischargeable power is calculated as described below. The discharge upper limit potential V _{negative e} of the negative electrode differs depending on the type of the battery cell 11, but may be, for example, about -0.6 to -0.7V.

Similarly to the positive electrode, as shown by the line r in FIG. 7C, if the negative electrode current value increases in the negative direction from I _{negative 0} to I _{negative α} immediately after time t0, the line s in FIG. as shown in, the anode potential V _negative, from time t0 to time t1, the internal resistance of the negative electrode as R _negative, [- (I _{negative alpha} -I _{negative 0)} × R _negative, only increases. The time from time t0 to time t1 is, for example, about 0.1 second. Assuming that the negative electrode potential at time t1 is V _{negative 1} , V _{negative 1} is represented by the following equation.

（式９）をＩ_負αについて解くと、

となる。
そうすると、時刻ｔｅに負極の電位が放電上限電位Ｖ_負ｅとなる電池セル１１の第２セル最大放電可能電力Ｗ_負ｅは、以下の（式１１）で算出される。

制御部２０の電力算出部２４は（式１１）によって電池セル１１の第２セル最大放電可能電力Ｗ_負ｅを算出したら、それに電池セル１１の個数ｎをかけたものをバッテリモジュール１０の第２最大放電可能電力としてメモリ２２に格納する。

As shown by the line s in FIG. 7D, after the time t1, the polarization of the battery cell 11 causes the negative electrode potential V _{negative to} slowly rise by [−I _{negative α} × R _{negative yn} ], and at the time te The discharge upper limit potential V of the negative electrode becomes _{negative e} . V _{negative e} is expressed by the following (Equation 9), where the polarization resistance of the negative electrode is R _{negative dyn} . Here, the time from the time t0 to the time te is, for example, about one second.

Solving (Equation 9) for I _{negative α} ,

Becomes
Then, the second cell maximum dischargeable power W _{negative e} of the battery cell 11 in which the _negative electrode potential becomes the discharge upper limit potential V _{negative e at} the time te is calculated by the following (Equation 11).

After calculating the second cell maximum dischargeable power W _{negative e} of the battery cell 11 by (Equation 11), the power calculation unit 24 of the control unit 20 multiplies the second cell maximum dischargeable power W by the number n of the battery cells 11 to obtain the second battery module 10 The maximum dischargeable power is stored in the memory 22.

  When the power calculating unit 24 calculates the first maximum dischargeable power and the second maximum dischargeable power using (Equation 7) and (Equation 12), the control unit 20 proceeds to step S106 in FIG. The maximum discharge power setting unit 25 of the control unit 20 reads the first maximum dischargeable power and the second maximum dischargeable power from the memory 22 and compares them. If the first maximum dischargeable power is less than the second maximum dischargeable power in step S106 of FIG. Set to power. If NO is determined in step S106 of FIG. 5, the second maximum dischargeable power is smaller than the first maximum dischargeable power, so the process proceeds to step S108, and the smaller second maximum dischargeable power is set. Is set to the maximum dischargeable power of the battery module 10.

As described above, the power supply system 100 of the present embodiment calculates the maximum discharge power of the battery module 10 based on the estimated positive electrode potential V _positive and negative electrode potential V _negative of the battery cell 11 without using the potential detection device. Since the calculation is performed, the calculation accuracy of the maximum dischargeable power is high with a simple configuration, and further, the first maximum discharge power and the negative electrode potential V calculated based on the positive electrode potential V _positive and the positive electrode discharge lower limit potential V _{positive e. Since the} smaller of the second maximum discharge power calculated based on the _negative and negative discharge upper limit potentials V _{negative e} is set as the maximum dischargeable power of the battery module 10, the discharge of the battery module 10 The available power can be sufficiently used, and the deterioration of the battery module 10 due to overdischarge can be suppressed.

  The maximum discharge power described above is larger than the maximum discharge power in the normal control of the battery module 10. For this reason, by setting the maximum discharge power of the battery module 10 as described above, the maximum discharge power of the battery module 10 is temporarily expanded to be larger than the maximum discharge power of the normal control at the time of starting the engine, and the like. The dischargeable power of the battery module 10 can be sufficiently used, and deterioration of the battery module 10 due to overdischarge can be suppressed.

  Reference Signs List 10 battery module, 11 battery cell, 12 positive electrode line, 13 negative electrode line, 14 load, 17 voltage sensor, 18 current sensor, 19 temperature sensor, 20 control unit, 21 CPU, 22 memory, 23 potential estimation unit, 24 power calculation unit , 25 maximum discharge power setting section, 100 power supply system, 110 battery case, 111 negative electrode terminal, 112 positive electrode terminal, 120 power generation element, 121 negative electrode plate, 121a, 122a current collector foil, 121b negative electrode active material layer, 121c negative electrode active material, 121d, 122d conductive material, 122 positive electrode plate, 122b positive electrode active material layer, 122c positive electrode active material, 122e eluate, 123, 124 separator.

Claims (1)

A battery module in which a plurality of battery cells are connected in series;
A voltage sensor for detecting a voltage value of the battery module;
A current sensor for detecting a current value of the battery module;
A temperature sensor for detecting a temperature of the battery module;
A control unit for adjusting the discharge power of the battery module,
The control unit includes:
The battery cell based on a current voltage value of the battery module detected by the voltage sensor, a current current value of the battery module detected by the current sensor, and a current temperature of the battery module detected by the temperature sensor. Potential estimating unit for estimating the current positive electrode potential and current negative electrode potential of
A first maximum value of the battery module when a current value of the positive electrode of the battery cell increases from a current value based on the estimated current positive electrode potential, a positive electrode discharge lower limit potential, an internal resistance of the battery cell, and a polarization resistance; dischargeable power is calculated, the case where the anode current value of the battery cells based on the internal resistance and polarization resistance of the discharge limit potential and the battery cells of the estimated current anode potential and the negative electrode becomes lower than the current the current value A power calculator for calculating a second maximum dischargeable power of the battery module;
A maximum discharge power setting unit that sets the smaller one of the first maximum dischargeable power and the second maximum dischargeable power as the maximum dischargeable power of the battery module;
A power supply system comprising:

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