Secondary battery system

Abstract

To provide a secondary battery system for improving efficiency of power supply to a low voltage power system.SOLUTION: A secondary battery system 1 of the present invention comprises: a first cell group 11 comprising a plurality of battery cells BC connected in series, one end of which is connected with a negative electrode line 20 and the other end of which is connected with a low voltage side positive electrode line 21; a second cell group 12 comprising the plurality of battery cells connected in series, one end of which is connected with the low voltage side positive electrode line 21 and the other end of which is connected with a high voltage side positive electrode line 22; and a plurality of Zener diodes ZD1, ZD2 connected in parallel with each of the battery cells included in the second cell group 12. In the Zener diodes ZD1, ZD2, anodes are connected with negative electrode terminals of the battery cells in parallel and cathodes are connected with positive electrode terminals of the battery cells connected in parallel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a secondary battery system using a non-aqueous electrolyte secondary battery, such as a lithium ion secondary battery. [Background technology]

[0002] For example, electric vehicles and hybrid vehicles are equipped with both a high-voltage power system that supplies high-voltage power to drive loads and a low-voltage power system that supplies low-voltage power to control loads such as an ECU (Electronic Control Unit) and auxiliary devices. In addition, separate batteries have often been installed for the power source of the high-voltage power system and the power source of the low-voltage power system. However, in order to reduce the weight of the vehicle, it has been considered to not install the power source of the low-voltage power system and to supply power from the power source of the high-voltage power system to the low-voltage power system. Therefore, technologies for supplying power from the power source of the high-voltage power system to the low-voltage power system are disclosed in Patent Documents 1 and 2.

[0003] The vehicle power supply device described in Patent Document 1 drives a first system with power supplied from a storage battery, and drives a second system with a lower voltage than the first system via a step-down circuit that reduces the voltage of the power supplied from the storage battery. The vehicle power supply device includes a switch means that disables the supply of power from the storage battery to the first system and the step-down circuit, and a conduction means that has a capacitor that is charged by the power source stepped down by the step-down circuit when power is supplied from the storage battery to the step-down circuit, and uses the power charged in the capacitor to turn the switch means on.

[0004] The in-vehicle electrical system described in Patent Document 2 comprises a battery having a plurality of battery cells, a first electrical device driven based on the output voltage of the battery, a second electrical device driven at a lower voltage than the first electrical device, a step-down unit that steps down the output voltage of the battery and supplies it to the second electrical device, and a supply unit that is connected in parallel with the step-down unit to the second electrical device and is capable of supplying power to the second electrical device using some of the battery cells that are a part of the battery as a power source, wherein the supply unit has a first inhibition unit that inhibits current flow from the step-down unit to the some of the cells, and the step-down unit supplies a stepped-down voltage that is higher than the rated output voltage of the some of the cells to the second electrical device. Vehicle electrical system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-287242 A [Patent Document 2] JP 2019-30108 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the examples described in Patent Documents 1 and 2, a low voltage generated by stepping down a high voltage using a step-down circuit is supplied to a low-voltage power system. At this time, power loss occurs in the step-down circuit, so in the examples described in Patent Documents 1 and 2, the power efficiency is low when supplying power to a load in the low-voltage power system, and the battery capacity is effectively reduced.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to improve the efficiency of power supply to a low-voltage power system. [Means for solving the problem]

[0008] One aspect of the secondary battery system of the present invention has a first cell group including a plurality of battery cells connected in series, one end of which is connected to a negative electrode line and the other end of which is connected to a low-voltage side positive electrode line; a second cell group including a plurality of battery cells connected in series, one end of which is connected to the low-voltage side positive electrode line and the other end of which is connected to a high-voltage side positive electrode line; and a plurality of Zener diodes connected in parallel to each of the battery cells included in the second cell group, the anodes of the Zener diodes being connected to the negative electrode terminals of the battery cells connected in parallel and the cathodes being connected to the positive electrode terminals of the battery cells connected in parallel. Effect of the Invention

[0009] According to the secondary battery system of the present invention, the efficiency of power supply to a low-voltage power system can be improved. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a secondary battery system according to a first embodiment. [Diagram 2] FIG. 4 is a diagram for explaining a discharging operation of the secondary battery system according to the first embodiment. [Diagram 3] FIG. 4 is a diagram for explaining a charging operation of the secondary battery system according to the first embodiment. [Figure 4] 4 is a flowchart illustrating a charging operation of the charging system according to the first embodiment. [Diagram 5] 4 is a timing chart illustrating a charging and discharging operation of the charging system according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In order to clarify the description, the following description and drawings are omitted and simplified as appropriate. In addition, each element shown in the drawings as a functional block performing various processes can be configured in hardware with a CPU (Central Processing Unit), memory, and other circuits, and in software, can be realized by a program loaded into memory. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware alone, software alone, or a combination thereof, and are not limited to any one of them. In addition, the same elements are given the same symbols in each drawing, and duplicated explanations are omitted as necessary.

[0012] Moreover, the above-mentioned program includes a set of instructions (or software code) for making the computer perform one or more functions described in the embodiment when the program is read into the computer. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or the tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, the transitory computer-readable medium or the communication medium includes electrical, optical, acoustic, or other forms of propagating signals.

[0013] In the secondary battery system according to the first embodiment described below, the temperature estimation process of the Zener diode is performed by a program executed on a computer (for example, a processor in a battery management device).

[0014] First embodiment Fig. 1 shows a schematic diagram of a secondary battery system 1 according to the first embodiment. As shown in Fig. 1, the secondary battery system 1 according to the first embodiment includes a battery pack 10, an ammeter 13, a voltmeter 14, a battery management device 15, a negative electrode line 20, a low-voltage side positive electrode line 21, a high-voltage side positive electrode line 22, and a plurality of Zener diodes (two Zener diodes ZD1 and ZD2 are shown in Fig. 1 as examples). The battery pack 10 also has a configuration in which a first cell group 11 and a second cell group 12 are connected in series.

[0015] The first cell group 11 includes a plurality of battery cells BC connected in series, one end of which is connected to the negative electrode line 20 and the other end of which is connected to the low-voltage side positive electrode line 21. The second cell group 12 includes a plurality of battery cells BC connected in series, one end of which is connected to the low-voltage side positive electrode line 21 and the other end of which is connected to the high-voltage side positive electrode line 22. The number of battery cells BC included in the second cell group 12 may be greater or less than that of the first cell group 11. The number of battery cells BC to be set in each of the first cell group 11 and the second cell group 12 is determined by the voltage applied to the low-voltage side positive electrode line 21 and the voltage applied to the high-voltage side positive electrode line 22.

[0016] The multiple Zener diodes are connected in parallel to each of the battery cells BC included in the second cell group 12. In the example shown in FIG. 1, two battery cells BC are shown in the second cell group 12. A Zener diode ZD1 is connected in parallel to one of the battery cells BC, and a Zener diode ZD2 is connected in parallel to the other battery cell BC. The anodes of the Zener diodes are connected to the negative terminals of the battery cells BC connected in parallel, and the cathodes are connected to the positive terminals of the battery cells BC connected in parallel.

[0017] Ammeter 13 measures the current flowing through the negative electrode line and outputs the current measurement value. Voltmeter 14 measures the output voltage of battery pack 10, that is, the voltage difference between the voltage of high-voltage side positive electrode line 22 and the voltage of negative electrode line 20, and measures the measured voltage as the output voltage of battery pack 10.

[0018] The battery management unit 15 at least controls the state of charge of the battery cells BC included in the first cell group 11 and the second cell group 12. More specifically, in a period after the rate of change per unit time of the current measurement value exceeds a preset current threshold, the battery management unit 15 performs a temperature estimation process of calculating a Zener diode temperature estimation value, which is an estimate of the temperature of the Zener diode, by applying the current measurement value to a preset estimation formula, and a charge stop process of notifying a charging device of a charge stop instruction to stop charging the battery cells included in the first cell group 11 and the second cell group 12 when the Zener diode temperature estimation value exceeds a preset charge control threshold.

[0019] Here, although the charging device is not shown in Fig. 1, the charging device may be a device detachably provided in the secondary battery system 1, and may be, for example, a device that uses regenerative power from a drive motor arranged in a high-voltage power system of an electric vehicle or the like. The battery management unit 15 notifies a device that supplies charging power to the battery pack 10 of a charge stop instruction directly or via a higher-level system (not shown) that further manages the battery management unit 15. The route through which the charge stop operation in response to the charge stop instruction is performed is appropriately selected depending on the configuration of the charging device and the specifications of the entire system including the secondary battery system according to the first embodiment.

[0020] The battery management unit 15 also has a function of measuring the output voltage of each battery cell BC included in the assembled battery 10. In Fig. 1, wiring and measuring devices used to measure the voltage of each battery cell BC are omitted in order to simplify the drawing, but these are necessary functions for battery control when the battery management unit 15 controls the assembled battery 10. The battery management unit 15 also has a function of measuring the temperature of the battery cells BC included in the assembled battery 10, but devices and wiring related to temperature measurement are omitted in Fig. 1 in order to simplify the drawing.

[0021] Next, a description will be given of the operation of the secondary battery system 1 according to the embodiment 1. First, a description will be given of the discharging operation of the secondary battery system 1 according to the embodiment 1. FIG. 2 shows a diagram for explaining the discharging operation of the battery system according to the embodiment 1.

[0022] 2 shows a low-voltage load circuit 30 and a high-voltage load circuit 31 as destinations of power supply from the secondary battery system 1. The low-voltage load circuit 30 is a circuit connected between the negative electrode line 20 and the low-voltage positive electrode line 21. The low-voltage load circuit 30 is, for example, a control system load circuit of an ECU (Electronic Control Unit) or auxiliary devices. The high-voltage load circuit 31 is a circuit connected between the negative electrode line 20 and the high-voltage positive electrode line 22. The high-voltage load circuit 31 is, for example, a circuit including a drive motor for an electric vehicle or the like.

[0023] As shown in FIG. 2, in the secondary battery system 1 according to the first embodiment, power is supplied from the first cell group 11 to the low-voltage load circuit 30. Moreover, power is supplied to the high-voltage load circuit 31 using the first cell group 11 and the second cell group 12. That is, in the secondary battery system 1 according to the first embodiment, power is supplied to the low-voltage load circuit 30 and the high-voltage load circuit 31 without using a circuit that generates loss, such as a step-down circuit. As a result, in the secondary battery system 1 according to the first embodiment, power efficiency when supplying power to the load circuit is improved, and it is possible to efficiently use the power stored in the assembled battery 10. Moreover, the improvement in power efficiency in the secondary battery system 1 according to the first embodiment can be regarded as a substantial increase in the battery capacity of the assembled battery 10.

[0024] On the other hand, in the secondary battery system 1 according to the first embodiment, the battery cells BC included in the first cell group 11 tend to consume more power than the battery cells BC included in the second cell group 12. Therefore, it becomes necessary to charge the first cell group 11 more than the second cell group 12. Therefore, in the secondary battery system 1 according to the first embodiment, a Zener diode is connected in parallel to each of the battery cells BC included in the second cell group 12, and a charging current after the battery cells BC included in the second cell group 12 are fully charged is passed to the first cell group 11 side via the Zener diode, thereby putting the second cell group 12 in a non-charging state and putting the first cell group 11 in a charging state.

[0025] 2 shows a diagram for explaining the charging operation of the secondary battery system 1 according to the first embodiment, and the charging operation of the secondary battery system 1 according to the first embodiment will be described in detail. In the example shown in FIG. 2, a charging device 32 is connected between the negative electrode line 20 and the high voltage side positive electrode line 22. In addition, in the example shown in FIG. 2, a path for notifying the charging device 32 of a charging stop instruction issued by the battery management unit 15 is shown. The charging device 32 charges the battery pack 10, and when a charging stop instruction is notified from the battery management unit 15, stops charging the battery pack 10.

[0026] 2, in the secondary battery system 1 according to the first embodiment, a current path is switched between a first charging period in which the output voltage of the battery cell BC included in the second cell group 12 is equal to or lower than the voltage at which the battery cell BC included in the second cell group 12 is determined to be fully charged, and a second charging period in which the output voltage of the battery cell BC included in the second cell group 12 is higher than the voltage at which the battery cell BC is determined to be fully charged. Specifically, in the first charging period, the secondary battery system 1 according to the first embodiment passes a charging current through the first cell group 11 via the second cell group 12. On the other hand, in the second charging period, the secondary battery system 1 passes a charging current through the first cell group 11 via a Zener diode (e.g., Zener diodes ZD1 and ZD2) without passing through the second cell group 12. The reason why such switching of the charging current is necessary is that the first cell group 11 is used to supply power to both the low-voltage side load circuit 30 and the high-voltage side load circuit 31, while the second cell group 12 is used to supply power to the high-voltage side load circuit 31, resulting in a difference in power consumed between the first cell group 11 and the second cell group 12.

[0027] In the secondary battery system 1 according to the first embodiment, by selecting a Zener diode whose Zener breakdown voltage is equal to the output voltage of the battery cell BC when fully charged, the battery management unit 15 realizes path switching as shown in Fig. 2 without switching paths individually. In addition, since the Zener diode generates heat in response to a reverse current, when the amount of heat generated by the Zener diode exceeds a certain value, the secondary battery system 1 notifies the charging device 32 of a charge stop instruction to stop charging. By performing such charge stop processing, the secondary battery system 1 can prevent damage to the Zener diode.

[0028] Furthermore, in the secondary battery system 1 according to the first embodiment, the battery management device 15 calculates an estimated temperature value of the Zener diode by applying a current measurement value obtained from the ammeter 13, which is required for various reasons in controlling the battery cell BC, to a preset prediction formula. As a result, in the secondary battery system 1 according to the first embodiment, it is possible to prevent heat damage of the Zener diode and improve the safety of the secondary battery system 1 without adding a new temperature detection element or wiring for measuring the temperature of the Zener diode.

[0029] Therefore, the charging operation of the secondary battery system 1 according to the first embodiment will be described with reference to a flowchart of Fig. 4 which explains the charging operation of the charging system according to the first embodiment. In the example shown in Fig. 4, the processes of steps S1 to S3 are performed in the charging operation during the first charging period, and the processes of steps S4 to S6 are performed in the charging operation during the second charging period.

[0030] As shown in Fig. 4, when charging is started in the secondary battery system 1 according to the first embodiment, first, charging of the assembled battery 10 including the first cell group 11 and the second cell group 12 is continued until the cell voltage of the battery cells in the second cell group becomes equal to or higher than the Zener breakdown voltage (steps S1, S3). Here, in the secondary battery system 1, even if the cell voltage of the battery cells in the second cell group is lower than the Zener breakdown voltage, if the output voltage of the assembled battery 10 becomes equal to or higher than the charging setting voltage set for determining that the assembled battery 10 is fully charged, a charging stop instruction is notified to the charging device 32 and charging is terminated (steps S3, S7). By performing the processes of steps S3 and S7 in this manner, overcharging of the assembled battery 10 can be prevented.

[0031] In the secondary battery system 1 according to the first embodiment, when the cell voltage of the battery cell BC in the second cell group 12 becomes equal to or higher than the Zener breakdown voltage of the Zener diode, the current path of the charging current flowing from the charging device 32 to the battery pack 10 is switched from the path via the second cell group 12 to the path via the Zener diodes ZD1 and ZD2. When such a path switching occurs, in the secondary battery system 1, the resistance value of the path through which the charging current flows drops suddenly, and the current measurement value measured by the ammeter 13 changes suddenly. Therefore, in the secondary battery system 1, the battery management device 15 detects the switching of the current path using as an index the rate of change per unit time of the current measurement value exceeding a preset current threshold value (step S2).

[0032] In the secondary battery system 1 according to the first embodiment, the battery management unit 15 performs a temperature estimation process in response to the charging current path being switched to via the Zener diode (step S4). This temperature estimation process is performed in a period after the rate of change of the current measurement value (i.e., the rate of change of the current measurement value per unit time) acquired by the battery management unit 15 from the ammeter 13 at a predetermined time period exceeds a preset current threshold. In the temperature estimation process, the current measurement value is applied to a preset estimation formula to calculate a Zener diode temperature estimation value, which is an estimate of the temperature of the Zener diode. Various estimation formulas can be obtained, but as an example, an estimation formula obtained by discretizing a first-order linear nonhomogeneous differential equation can be used. This estimation formula is expressed, for example, by formula (1).

number

[0033] In equation (1), the first term on the right side is the previous value, the second term on the right side is a generation term that estimates the amount of heat generated using a current measurement value, and the third term on the right side is a decay term that calculates a decay value due to time of the Zener diode temperature estimate calculated in the previous cycle. In equation (1), the current Zener diode temperature estimate is calculated by subtracting the value of the decay term from the sum of the previous value and the value of the generation term.

[0034] In the secondary battery system 1 according to the first embodiment, in the second charging period in which the temperature estimation process of step S4 is performed, charging is continued until the output voltage of the battery pack 10 exceeds the charging set voltage or the Zener diode temperature estimated value exceeds a preset charging control threshold (steps S5 and S6). In the secondary battery system 1 according to the first embodiment, when it is determined in steps S3 and S5 that the output voltage of the battery pack 10 has become equal to or higher than the charging set voltage, or when the Zener diode temperature estimated value in step S6 has become equal to or higher than the charging control threshold, the battery management unit 15 notifies the charging device 32 of a charging stop instruction to stop charging the battery cells included in the first cell group 11 and the second cell group 12 (step S7).

[0035] Next, the charging and discharging operation of the secondary battery system 1 according to the first embodiment will be described using a timing chart. Fig. 5 shows a timing chart for explaining the charging and discharging operation of the charging system according to the first embodiment. The example shown in Fig. 5 shows the time change in cell voltage of one of the battery cells belonging to the first cell group 11 and one of the battery cells belonging to the second cell group 12 when discharging and charging operations are performed.

[0036] 5, in the secondary battery system 1 according to the first embodiment, during the discharging period in which the discharging operation is performed, the discharge rate of the first cell group 11 is faster than the discharge rate of the second cell group 12. This is because the first cell group 11 supplies power to both the low-voltage power system and the high-voltage power system, whereas the second cell group 12 supplies power only to the high-voltage power system.

[0037] Next, in the secondary battery system 1 according to the first embodiment, when the charging period starts, the cell voltage of the battery cells belonging to the second cell group 12 is lower than the Zener breakdown voltage having a value corresponding to the cell full charge set voltage, so the Zener diode is in a cut-off state. Therefore, in the secondary battery system 1 according to the first embodiment, at the start of the charging period, a first charging period is performed in which a charging current is supplied to the first cell group 11 via the second cell group 12. Thereafter, as the charging of the battery cells belonging to the first cell group 11 and the battery cells belonging to the second cell group 12 progresses, the cell voltages of the battery cells rise. Then, when the cell voltage of the battery cells belonging to the second cell group 12 reaches the cell full charge set voltage, the Zener diode is in a conductive state, so that the system transitions to a second charging period in which a charging current is supplied to the first cell group 11 via the Zener diodes ZD1 and ZD2.

[0038] At the timing of the transition from the first charging period to the second charging period, the current measurement value detected by the ammeter 13 increases sharply, and the battery management unit 15 detects this current change and recognizes the transition to the second charging period. Then, during the second charging period, the battery management unit 15 continues charging until the output voltage of the assembled battery 10 reaches the charging set voltage while calculating the estimated temperature value of the Zener diode, unless the estimated temperature value of the Zener diode exceeds the charging control threshold. Note that in the example shown in FIG. 5, the upper limit of the cell voltage is set to the cell full charge set voltage, but the output voltage of the assembled battery 10 when the cell voltage of the battery cells of the first cell group 11 reaches the cell full charge set voltage is approximately the charging set voltage.

[0039] As described above, in the secondary battery system 1 according to the first embodiment, power is supplied to the low voltage power system and the high voltage power system without passing through a step-down circuit, etc. As a result, in the secondary battery system 1 according to the first embodiment, it becomes possible to operate the secondary battery system with reduced power loss, and it becomes possible to improve the power efficiency of the system.

[0040] Moreover, in the secondary battery system 1 according to the first embodiment, a Zener diode is connected in parallel to each of the battery cells belonging to the second cell group 12 related only to the power supply to the high-voltage power system. As a result, after the cell voltage of the battery cells of the second cell group 12 reaches the breakdown voltage of the Zener diode, a path can be configured to supply a charging current to the first cell group 11 side via the Zener diode. As a result, in the secondary battery system 1 according to the first embodiment, it is possible to avoid undercharging of the first cell group 11 while preventing overcharging of the second cell group 12.

[0041] Furthermore, in the secondary battery system 1 according to the first embodiment, the characteristics of the Zener diode are used to prevent overcharging of the battery cells of the second cell group 12, so there is no need to use special detection circuits or arithmetic circuits, which makes it possible to simplify the system configuration.

[0042] In addition, the Zener diode generates heat due to the charging current, but in the secondary battery system 1 according to the first embodiment, the amount of heat generated by the Zener diode is estimated using the measured value of the charging current measured by the ammeter 13, and charging is stopped when the estimated temperature value of the Zener diode exceeds the charging control threshold. As a result, in the secondary battery system 1 according to the first embodiment, it is not necessary to use elements and wiring required for measuring the temperature of the Zener diode to manage the temperature of the Zener diode. In other words, in the secondary battery system 1 according to the first embodiment, it is possible to prevent malfunctions caused by heat generation by the Zener diode and improve the reliability of the system without complicating the elements and wiring of the system.

[0043] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0044] 1. Secondary battery system 10 Battery pack 11 First Cell Group 12 Second Cell Group 13 Ammeter 14 Voltmeter 15 Battery Management Device 20 Negative Wire 21 Low voltage side positive wire 22 High voltage positive wire 30 Low-voltage load circuit 31 High voltage load circuit 32 Charging device

Claims

1. a first cell group including a plurality of battery cells connected in series, one end of which is connected to a negative electrode line and the other end of which is connected to a low-voltage positive electrode line; a second cell group including a plurality of battery cells connected in series, one end of which is connected to the low-voltage side positive electrode line and the other end of which is connected to the high-voltage side positive electrode line; a plurality of Zener diodes connected in parallel to each of the battery cells included in the second cell group; The Zener diode has an anode connected to the negative terminal of the battery cell connected in parallel and a cathode connected to the positive terminal of the battery cell connected in parallel.

2. an ammeter that measures a current flowing through the negative electrode line and outputs a current measurement value; a battery management unit that at least controls a state of charge of the battery cells included in the first cell group and the second cell group, The battery management device includes: a temperature estimation process for calculating a Zener diode temperature estimation value that is an estimate of a temperature of the Zener diode by applying the current measurement value to a predetermined estimation formula during a period after a rate of change per unit time of the current measurement value has exceeded a predetermined current threshold value; the charging device is configured to stop charging the battery cells included in the first cell group and the second cell group when the Zener diode temperature estimated value exceeds a predetermined charging control threshold value, and a charging stop process is performed to notify the charging device of a charging stop instruction to stop charging the battery cells included in the first cell group and the second cell group.

3. the charging device is detachably provided to the secondary battery system, The secondary battery system according to claim 2 , wherein the battery management unit issues the charge stop instruction to the charging device in a state where the charging device is connected to the secondary battery system.

4. 3. The secondary battery system according to claim 2, wherein the estimation formula includes the Zener diode temperature estimated value calculated in a previous cycle, a generation term that estimates a heat generation amount using the current measurement value, and a decay term that calculates a decay value due to time of the Zener diode temperature estimated value calculated in the previous cycle, and calculates a current Zener diode temperature estimated value by subtracting a value of the decay term from a sum of the Zener diode temperature estimated value calculated in the previous cycle and a value of the generation term.

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