JP2018006239A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress cobalt elution in a positive electrode of a nickel hydrogen battery and negative electrode deterioration in a negative electrode while satisfying an output request to a power storage unit in a battery system coming with the nickel hydrogen battery.SOLUTION: When positive electrode potential of a cell contained in a first power storage device 10 becomes not more than first electric potential due to an output request, an ECU 100 suppresses discharge of the first power storage device 10 and controls discharge of a second power storage device 15 according to the output request. When negative electrode potential of the cell contained in the first power storage device 10 becomes not less than second electric potential due to the output request, the ECU 100 suppresses discharge of the first power storage device 10 and controls discharge of a second power control device 15 according to the output request. The first electric potential is electric potential causing cobalt elution in the positive electrode of the first power storage device 10. The second electric potential is electric potential causing negative electrode deterioration due to oxidation of the negative electrode of the first power storage device 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a battery system, and more particularly, to a battery system including first and second power storage devices.

  Japanese Patent Laying-Open No. 2006-81300 (Patent Document 1) discloses a hybrid vehicle including a power storage device, a motor driven by electric power stored in the power storage device, and an engine. In this hybrid vehicle, an upper limit voltage and a lower limit voltage are set for the input / output voltage of the power storage device. Thereby, the bad influence on the lifetime of an electrical storage apparatus can be reduced (refer patent document 1).

JP 2006-81300 A

  When a nickel metal hydride battery is used as the power storage device, if the positive electrode contains a cobalt compound, cobalt may be eluted from the positive electrode, which may cause deterioration of the positive electrode. In the negative electrode, the negative electrode may be deteriorated by oxidation of the negative electrode. The battery performance of the nickel metal hydride battery deteriorates regardless of which of cobalt elution at the positive electrode and deterioration of the negative electrode at the negative electrode.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a nickel-metal hydride battery in a battery system equipped with a nickel-metal hydride battery while satisfying an output request to a power storage unit. Cobalt elution in the positive electrode and negative electrode deterioration in the negative electrode are suppressed.

  A battery system according to an aspect of the present invention includes a power storage unit and a control device. The power storage unit includes first and second power storage devices. The control device controls charging / discharging of the power storage unit. The first power storage device is formed of a nickel metal hydride battery containing a cobalt compound in the positive electrode. When the positive potential of the first power storage device is equal to or lower than the first potential due to the output request to the power storage unit, the control device suppresses the discharge of the first power storage device and performs the second according to the output request to the power storage unit. When the negative potential of the first power storage device is equal to or higher than the second potential due to an output request to the power storage unit, the discharge of the first power storage device is suppressed and the discharge to the power storage unit is controlled. The discharge of the second power storage device is controlled according to the output request. The first potential is a potential at which cobalt elution occurs in the positive electrode of the first power storage device. The second potential is a potential at which negative electrode deterioration occurs due to oxidation of the negative electrode of the first power storage device.

  In this battery system, when the positive potential of the first power storage device is equal to or lower than the first potential (potential at which cobalt elution occurs in the positive electrode) due to an output request to the power storage unit, or due to an output request to the power storage unit When the negative electrode potential of the first power storage device is equal to or higher than the second potential (a potential at which negative electrode deterioration occurs due to oxidation of the negative electrode), discharge of the first power storage device is suppressed. By suppressing the discharge of the first power storage device, the decrease in the positive electrode potential and the increase in the negative electrode potential are suppressed. Therefore, according to this battery system, cobalt elution in the positive electrode and negative electrode deterioration in the negative electrode can be suppressed. Further, in this battery system, since the discharge of the second power storage device is promoted as the discharge of the first power storage device is suppressed, the output request to the power storage unit can be satisfied.

  According to the present invention, in a battery system equipped with a nickel metal hydride battery, it is possible to suppress cobalt elution at the positive electrode of the nickel metal hydride battery and deterioration of the negative electrode at the negative electrode while satisfying the output request to the power storage unit.

It is a figure which shows roughly the structure of the vehicle by which a battery system is mounted. It is a flowchart which shows the process sequence of charging / discharging control in a battery system. It is a figure for demonstrating control of the charge condition of a 2nd electrical storage apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals and description thereof will not be repeated.

(Battery system configuration)
FIG. 1 schematically shows a configuration of vehicle 1 in which battery system 2 according to the present embodiment is mounted. Below, although the case where the vehicle 1 is a hybrid vehicle is demonstrated, the battery system 2 by this Embodiment is not limited to what is mounted in a hybrid vehicle, The vehicle by which a nickel hydride battery is mounted generally, Furthermore, a vehicle It is applicable to other uses.

  Referring to FIG. 1, vehicle 1 includes a battery system 2, converters 25 and 27, an inverter 30, motor generators (MG) 41 and 42, an engine 50, a power split mechanism 60, and a drive. A shaft 70 and drive wheels 80 are provided. The battery system 2 includes a first power storage device 10, a second power storage device 15, monitoring units 20 and 35, and an electronic control unit (ECU) 100.

  The engine 50 generates a driving force for rotating the crankshaft by combustion energy generated when the air-fuel mixture is burned. The MGs 41 and 42 function as both a generator and an electric motor.

  The MG 41 is, for example, a three-phase AC rotating electric machine, and mainly operates as a generator that generates electric power using a part of the output of the engine 50 transmitted through the power split mechanism 60. The electric power generated by the MG 41 is used for charging the first power storage device 10 and the second power storage device 15 or driving the MG 42.

  MG42 is, for example, a three-phase AC rotating electric machine, and is driven by at least one of power from first power storage device 10, power from second power storage device 15, and power generated by MG41. The driving force of the MG 42 is transmitted to the driving shaft 70. Further, when the vehicle 1 is braked, the MG 42 operates as a generator by being driven by the rotational force of the drive wheels 80.

  First power storage device 10 stores electric power for driving MGs 41 and 42. The first power storage device 10 is composed of a battery pack including a plurality of nickel hydrogen single cells (single cells) connected in series. The positive electrode of each cell contains a cobalt compound as a conductive material, for example.

  The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects a voltage between terminals of each cell (hereinafter also referred to as “cell voltage VC”). Current sensor 22 detects a charge / discharge current (hereinafter also referred to as “current IC”) of first power storage device 10. The temperature sensor 23 detects the temperature of each cell (hereinafter also referred to as “cell temperature TC”). Each sensor outputs a signal indicating the detection result to ECU 100.

  Second power storage device 15 is formed of a power storage device including a power storage element other than a nickel metal hydride battery, for example. The second power storage device 15 includes, for example, an electric double layer capacitor, a lithium ion battery, and a fuel cell. As will be described later, there is a case where discharging of the first power storage device 10 is prohibited depending on the state of the first power storage device 10, and in this case, large power is discharged from the second power storage device 15. There is a possibility. Since the electric double layer capacitor is a device suitable for charging and discharging a large current, it is more preferable as the second power storage device 15.

  Similarly to the first power storage device 10, the second power storage device 15 stores power for driving the MGs 41 and 42. The monitoring unit 35 includes a voltage sensor 31, a current sensor 32, and a temperature sensor 33. Voltage sensor 31, current sensor 32, and temperature sensor 33 detect voltage VB, current IB, and temperature TB of second power storage device 15, respectively. Each sensor outputs a signal indicating the detection result to ECU 100.

  Converter 25 is provided between first power storage device 10 and inverter 30. Converter 25 is controlled by a control signal (PWC1) from ECU 100, and performs voltage conversion between first power storage device 10 and inverter 30.

  Converter 27 is provided between second power storage device 15 and inverter 30. Converter 27 is controlled by a control signal (PWC2) from ECU 100, and performs voltage conversion between second power storage device 15 and inverter 30. Converter 25 and converter 27 are connected in parallel to inverter 30.

  Inverter 30 is provided between converters 25 and 27 and MGs 41 and 42. Inverter 30 is configured to perform conversion between DC power and AC power between converters 25 and 27 and MGs 41 and 42 in accordance with a control signal from ECU 100. The inverter 30 is configured to be able to control the states of the MGs 41 and 42 separately. For example, the MG 42 can be in a power running state while the MG 41 is in a regenerative (power generation) state.

  ECU 100 includes a CPU (Central Processing Unit), an input / output interface, and a memory (none of which are shown). ECU 100 controls engine 50, converters 25 and 27, and inverter 30 based on signals from the sensors and information stored in the memory, thereby charging first power storage device 10 and second power storage device 15. Control the discharge.

(Both suppression of deterioration and drivability of the first power storage device)
As described above, the first power storage device 10 is composed of an assembled battery including a plurality of nickel metal hydride cells, and the positive electrode in each cell includes a cobalt compound. In such a positive electrode, cobalt elution occurs in the positive electrode when the positive electrode potential becomes a predetermined potential or lower during the discharge of the first power storage device 10.

  If cobalt elution occurs, then a re-precipitation of cobalt may occur locally, which may cause a fine short circuit or may deteriorate the battery. In addition, there is a concern that after the reprecipitation of cobalt, an active material that does not contribute to the battery capacity is generated due to the non-uniformity of the electron conductive network compared to the initial state. As a result, it may lead to deterioration of the battery such as a decrease in battery capacity and input / output performance.

  In battery system 2 according to the present embodiment, ECU 100 causes first power storage device 10 when the positive electrode potential of a cell included in first power storage device 10 is equal to or lower than a potential at which cobalt elution occurs in the positive electrode due to an output request. The discharge of the second power storage device 15 is controlled according to the output request. Therefore, according to this battery system 2, it is possible to suppress cobalt elution from the positive electrode.

  Further, if the negative electrode potential becomes equal to or higher than a predetermined potential during discharging of the first power storage device 10, negative electrode oxidation may occur. When negative electrode oxidation occurs, problems such as a decrease in battery capacity and an increase in resistance may occur.

  In battery system 2 according to the present embodiment, ECU 100 causes first power storage device when the negative electrode potential of a cell included in first power storage device 10 is equal to or higher than the potential at which negative electrode deterioration due to oxidation of the negative electrode occurs due to an output request. The discharge of second power storage device 15 is controlled according to the output request while suppressing the discharge of 10. Therefore, according to this battery system 2, it is possible to suppress negative electrode deterioration in the negative electrode.

  Further, in this battery system 2, since the discharge of the second power storage device 15 is promoted in accordance with the suppression of the discharge of the first power storage device 10, the output request to the battery is satisfied. The ability is not impaired.

(Processing procedure for charge / discharge control)
FIG. 2 is a flowchart showing a processing procedure of charge / discharge control in the battery system 2. Referring to FIG. 2, the process shown in this flowchart is repeatedly executed at a predetermined cycle during operation of the vehicle system, for example.

  ECU 100 obtains signals indicating voltage VC and temperature TC and current IC of each cell included in first power storage device 10 from voltage sensor 21, temperature sensor 23, and current sensor 22, respectively (step S100).

  ECU 100 calculates the positive electrode potential and the negative electrode potential of each cell by using voltage VC, temperature TC, and current IC (step S110). For example, data indicating the relationship between the cell voltage, temperature, and current, and the positive electrode potential and the negative electrode potential, obtained in advance by experiments, is stored in the memory in the ECU 100. The ECU 100 can calculate the positive electrode potential and the negative electrode potential by using the voltage VC, the temperature TC, and the current IC while referring to the data stored in the memory. Alternatively, the ECU 100 may estimate the potentials of the positive electrode and the negative electrode from the voltage VC, the temperature TC, and the current IC using a known electrochemical reaction model.

  Thereafter, ECU 100 determines whether or not there is an output request for the power storage unit including first power storage device 10 and second power storage device 15 (step S120). When it is determined that there is no output request (NO in step S120), when MGs 41 and 42 generate power, ECU 100 and inverters 30 and 30 are charged so as to charge first power storage device 10 and second power storage device 15. Converters 25 and 27 are controlled (step S130).

  On the other hand, when it is determined that there is an output request for the power storage unit (YES in step S120), ECU 100 determines whether the positive potential of each cell is equal to or lower than the first protection potential for first power storage device 10, or It is determined whether the negative electrode potential is equal to or higher than the second protection potential (step S140). Note that the first protective potential is a potential that is likely to cause cobalt elution in the positive electrode when the positive electrode potential is lower than that, and is determined in advance. The second protective potential is a potential that is likely to cause deterioration of the negative electrode due to negative electrode oxidation when the negative electrode potential is higher than that. Data indicating the first and second protection potentials is stored in a memory in the ECU 100, for example.

  If it is determined that the positive electrode potentials of all cells are higher than the first protection potential and the negative electrode potentials of all cells are lower than the second protection potential (NO in step S140), ECU 100 The inverter 30 and the converters 25 and 27 are controlled by the discharge of the first power storage device 10 and the second power storage device 15 so as to meet the output request to the power storage unit (step S160). In this case, the second power storage device 15 does not necessarily have to be discharged. For example, only the first power storage device 10 may respond to the output request.

  On the other hand, in first power storage device 10, if it is determined that the positive electrode potential is equal to or lower than the first protection potential or the negative electrode potential is equal to or higher than the second protection potential for at least some cells (YES in step S <b> 140). ), ECU 100 controls inverter 30 and converters 25 and 27 so as to respond to an output request to the power storage unit by inhibiting discharge of first power storage device 10 and discharging only second power storage device 15 (step S150). ).

  In this case, it is not always necessary to completely stop the discharge of the first power storage device 10. For example, the positive electrode potential exceeds the first protection potential and the negative electrode potential is lower than the second protection potential. In the range, the first power storage device 10 may be used. Moreover, the discharge only by the 2nd electrical storage apparatus 15 in step S150 is continued until the output request | requirement with respect to an electrical storage part falls below a predetermined level, for example. For example, even if the first power storage device 10 is discharged according to the output request, the predetermined level is such that the positive potential of the first power storage device 10 exceeds the first protection potential and the negative potential exceeds the second protection potential. Output request level below.

  As described above, in battery system 2 according to the present embodiment, ECU 100 suppresses the discharge of first power storage device 10 when the positive electrode potential is equal to or lower than the potential at which cobalt elution occurs in the positive electrode, and the first according to the output request. When the discharge of the second power storage device 15 is controlled and the negative electrode potential is equal to or higher than the potential at which the negative electrode deterioration occurs due to the oxidation of the negative electrode, the discharge of the first power storage device 10 is suppressed and the second power storage is performed according to the output request. The discharge of the device 15 is controlled.

  Therefore, according to this battery system 2, it is possible to suppress cobalt elution at the positive electrode and negative electrode deterioration at the negative electrode. Further, in this battery system 2, since the discharge of the second power storage device 15 is promoted in accordance with the suppression of the discharge of the first power storage device 10, the output request to the battery is satisfied. The ability is not impaired.

(Charge state control in second power storage device)
As described above, in the first power storage device 10, when the positive electrode potential becomes equal to or lower than the first protection potential, or when the negative electrode potential becomes equal to or higher than the second protection potential, the second power storage device 15. Only the output requirement to the battery is satisfied. In this case, with respect to the discharge power of the second power storage device 15, the second power storage device has a higher power than when the output request is satisfied by both the first power storage device 10 and the second power storage device 15. 15 to MG42.

  In the present embodiment, the state of charge of second power storage device 15 is controlled so as to be able to handle high-power discharge. For example, a target value of an SOC (State Of Charge) value indicating the state of charge of second power storage device 15 (a value representing the remaining capacity with respect to the full charge capacity in 0 to 100%) is, for example, the first power storage. The predetermined value (for example, 50% or more) higher than the target SOC value in the apparatus 10 is set. For example, the SOC value of second power storage device 15 is controlled so as to be slightly overcharged.

  FIG. 3 is a diagram for explaining the control of the state of charge of the second power storage device 15. Referring to FIG. 3, the upper diagram shows a change in SOC value of second power storage device 15, and the lower diagram shows a change in charge / discharge current of second power storage device 15. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates the SOC value of the second power storage device 15. In the lower diagram, the horizontal axis represents time, and the vertical axis represents the charge / discharge current of the second power storage device 15. For example, in this example, the target value of the SOC value is a predetermined value S2 (for example, 50% or more).

  At time t0, the SOC value is S1 smaller than the predetermined value S2. Therefore, ECU 100 controls converter 27 and inverter 30 such that current Id is charged in second power storage device 15. ECU 100 can estimate the SOC value of second power storage device 15 by an existing method using voltage VB or current IB, for example.

  It is assumed that at time t1, a power output request is generated, and in the first power storage device 10, the positive electrode potential becomes equal to or lower than the first protection potential, or the negative electrode potential becomes equal to or higher than the second protection potential. In this case, since the discharge of the first power storage device 10 is prohibited, the output request for the battery is satisfied only by the discharge of the second power storage device 15 as illustrated. For example, current Ic is output from second power storage device 15. Accordingly, the SOC value of second power storage device 15 rapidly decreases from time t1 to time t2. However, since the SOC value of second power storage device 15 is controlled in advance to a high value (for example, a value higher than S1), the SOC value of second power storage device 15 is the SOC even when discharging with high power is performed. The lower limit value (<S1) is not reached. Therefore, second power storage device 15 according to the present embodiment can cope with high-power discharge. Note that the same control as at times t0 to t2 is performed at times t2 to t4.

[Other embodiments]
As described above, the embodiment of the present invention has been described. However, the present invention is not necessarily limited to this embodiment. Here, an example of another embodiment will be described.

  In the above embodiment, the voltage (cell voltage) and temperature (cell temperature) are monitored for each cell. However, the voltage and temperature monitoring units are not limited to this. For example, a plurality of cells may be used as one monitoring unit.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention 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.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Battery system, 10 1st electrical storage apparatus, 15 2nd electrical storage apparatus, 20, 35 Monitoring unit, 21, 31 Voltage sensor, 22, 32 Current sensor, 23, 33 Temperature sensor, 25, 27 Converter, 30 inverter, 41, 42 MG, 50 engine, 60 power split mechanism, 70 drive shaft, 80 drive wheel, 100 ECU.

Claims (1)

A power storage unit including first and second power storage devices;
A control device for controlling the discharge of the power storage unit,
The first power storage device is composed of a nickel metal hydride battery containing a cobalt compound in the positive electrode,
The controller is
When the positive potential of the first power storage device is equal to or lower than the first potential due to the output request to the power storage unit, the second power storage device is suppressed according to the output request while suppressing the discharge of the first power storage device. Controlling the discharge of
When the negative potential of the first power storage device becomes equal to or higher than the second potential due to the output request, the discharge of the first power storage device is suppressed and the discharge of the second power storage device is controlled according to the output request. And
The first potential is a potential at which cobalt elution occurs in the positive electrode of the first power storage device,
The battery system, wherein the second potential is a potential at which negative electrode deterioration occurs due to oxidation of the negative electrode of the first power storage device.

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