JP2018106916A - Power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage system which enables the increase in inputtable/outputtable amount of power while protecting a battery in such a range that the temperature of the battery is under a freezing temperature of an electrolyte solution.SOLUTION: A power storage system comprises: a battery 12 capable of being charged/discharged, which includes an electrolyte solution; a temperature sensor 20 operable to detect a battery temperature Tb of the battery 12; a voltage sensor 22 operable to detect a battery voltage Vb of the battery 12; and a controller 30 operable to control the charge/discharge of the battery 12. When the battery temperature Tb detected by the temperature sensor 24 is equal to or lower than a freezing temperature Tf of the electrolyte solution, the controller 30 acquires a voltage correction value Vc depending on an increase of DC resistance Ra of the battery 12 resulting from the freezing of the electrolyte solution based on an open-circuit voltage Vo of the battery 12, which can be obtained from the battery voltage Vb, and the battery temperature Tb, and performs the collection to lower a lower limit voltage Vmin and to raise an upper limit voltage Vmax according to the voltage correction value Vc thus acquired.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power storage system including a battery that can be charged and discharged including an electrolytic solution, and a control device that controls charging and discharging of the battery.

  As one of driving sources for running a vehicle, an electric vehicle (for example, a hybrid vehicle or an electric vehicle) equipped with a motor has been widely known. In such an electric vehicle, a chargeable / dischargeable secondary battery is mounted as an in-vehicle battery that supplies electric power to the traveling motor and receives regenerative power generated by the traveling motor.

  In a power storage system including such a secondary battery, charging / discharging of the secondary battery is controlled so as not to cause overdischarge and overcharge. More specifically, the input / output power of the secondary battery is limited, and the battery voltage is controlled so as not to exceed a predetermined allowable voltage range. Here, as the secondary battery is placed in a lower temperature environment, the allowable voltage range of the secondary battery for preventing overdischarge and overcharge is more severely limited.

  Patent Document 1 describes an input / output control device for a secondary battery that receives a battery temperature and a battery voltage of the secondary battery and sets a limit value of power input / output to / from the secondary battery. . In this input / output limiting device, the rate of change of the limit value relative to the battery voltage is changed according to the battery temperature. More specifically, as the battery temperature decreases, the secondary voltage target voltage and the battery The control gain used for the control calculation based on the deviation from the voltage is reduced.

  Patent Document 2 includes a battery and a control device that controls charging / discharging of the battery. When the temperature of the battery is lower than a predetermined temperature, it is determined that the electrolyte is frozen and charging / discharging of the battery is performed. There is described a power storage system that restricts and then determines that the freezing of the electrolytic solution has been resolved when the amount of decrease in internal resistance is greater than a predetermined threshold value, and releases the charge / discharge restriction.

JP 2008-125161 A JP 2016-129103 A

  However, in the conventional power storage system, the allowable range of input / output power and battery voltage is limited in the extremely low temperature range where the battery temperature of the secondary battery is lower than the freezing temperature of the electrolyte. On the other hand, fuel consumption and power performance are reduced. In particular, when a part of the electrolyte contained in the secondary battery is frozen, the conduction path is limited and the internal resistance of the secondary battery increases rapidly. For this reason, for example, even if an attempt is made to start a motor using a secondary battery in which a part of the electrolyte is frozen, the battery voltage exceeds the allowable range, and the secondary battery requires power required for starting the motor. May not be output.

  Therefore, an object of the present application is to provide a power storage system capable of increasing the amount of power that can be input and output while protecting the battery in a range where the battery temperature of the battery is equal to or lower than the freezing temperature of the electrolyte. .

  The power storage system according to the present invention includes a battery that includes an electrolyte and that can be charged and discharged, a temperature detection unit that detects a battery temperature of the battery, a voltage detection unit that detects a battery voltage of the battery, and the voltage detection A control device that controls charging / discharging of the battery so that the battery voltage detected by the unit does not fall below a predetermined lower limit voltage and does not exceed a predetermined upper limit voltage. When the battery temperature detected by the temperature detection unit is equal to or lower than the freezing temperature of the electrolytic solution, a voltage correction value corresponding to an increase in the direct current resistance of the battery due to the freezing of the electrolytic solution is obtained from the battery voltage. Obtained based on the open-circuit voltage of the battery and the battery temperature, and the correction for decreasing the lower limit voltage and increasing the upper limit voltage is performed by the acquired voltage correction value. That.

  According to the power storage system of the present invention, since the allowable range of the battery voltage of the battery is expanded according to the increase in the electrical resistance due to the freezing of the electrolyte, the amount of electric power that can be input and output while protecting the battery is increased. A power storage system that can be increased can be provided.

It is a figure showing the schematic structure of the electrical storage system concerning this embodiment. It is a graph which shows the relationship between the battery temperature of a battery, and battery resistance. It is a graph which shows the relationship between the battery temperature and battery voltage of a battery, and the lower limit voltage used for the discharge control of the conventional battery. It is a graph which shows the relationship between the battery temperature and battery voltage of a battery, and the lower limit voltage used for the discharge control of the battery which concerns on this embodiment. It is a flowchart which shows the flow of a process of the electrical storage system which concerns on this embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a power storage system 10 according to the present embodiment. The power storage system 10 is mounted on an electric vehicle such as an electric vehicle or a hybrid vehicle that obtains a vehicle driving force by the rotating electrical machine 16.

  The battery 12 is configured by connecting a plurality of single cells in series or in parallel (in the illustrated example, in series). The number of single cells constituting one battery 12 can be appropriately set based on the required output of the battery 12 or the like. The single battery is a chargeable / dischargeable secondary battery, for example, a lithium ion secondary battery, a nickel hydride secondary battery, or the like.

  The battery 12 is connected to the inverter 14 via a system main relay (hereinafter referred to as “SMR”) 18. The SMR 18 electrically connects or disconnects the battery 12 and the inverter 14. When the SMR 18 is turned on, charging / discharging of the battery 12 is allowed. When the user activates the vehicle, the start switch mounted on the vehicle is turned on. The SMR 18 is switched on / off in conjunction with the start switch.

  The inverter 14 converts DC power (discharge power) from the battery 12 into AC power and supplies the AC power to a rotating electrical machine 16 described later. Thereby, the rotary electric machine 16 functions as a motor and outputs driving power. Further, the inverter 14 converts AC power from the rotating electrical machine 16 into DC power and supplies it to the battery 12. The battery 12 is charged with electric power (charging power) supplied from the rotating electrical machine 16 via the inverter 14.

  The rotating electrical machine 16 functions as a drive source that outputs the traveling power of the vehicle by the electric power supplied from the battery 12 via the inverter 14. The rotating electrical machine 16 also functions as a generator and supplies power to the battery 12 via the inverter 14.

  In the vicinity of the battery 12, a temperature sensor 20 is provided as a temperature detection unit. The temperature sensor 20 detects the temperature of the battery 12. The detected temperature value of the temperature sensor 20 is sent to the control device 30 as the battery temperature Tb. There may be one or more temperature sensors 20. When a plurality of temperature sensors 20 are provided, a statistical value calculated from a plurality of detected values, for example, an average value, a minimum value, a maximum value, etc. may be used as the battery temperature Tb, and the minimum value is used as the battery temperature Tb. It is preferable to use from the viewpoint of detecting freezing of the electrolyte solution of the battery 12.

  The battery 12 is provided with a voltage sensor 22 as a voltage detection unit that detects a voltage between the positive terminal and the negative terminal of the battery 12. The detection voltage value of the voltage sensor 22 is sent to the control device 30 as the battery voltage Vb. The battery voltage Vb is an index indicating the remaining power amount of the battery 12.

  The battery 12 is provided with a current sensor 24 as a current detection unit that detects a current flowing through the battery 12 during charging and discharging. The detected current value of the current sensor 24 is sent to the control device 30 as the battery current Ib. The battery current Ib has a positive value during discharging and a negative value during charging.

  The detection of various parameters by the temperature sensor 20, the voltage sensor 22, and the current sensor 24 described above is repeatedly performed at a predetermined sampling period (for example, several tens of milliseconds to several hundreds of milliseconds) during the startup period of the battery 12.

  The charging / discharging of the battery 12 is managed and controlled by the control device 30. The control device 30 includes, for example, a CPU that performs various calculations and a storage unit that stores various programs and parameters. In FIG. 1, the control device 30 is a single unit, but the control device 30 may be configured by combining a plurality of control units each having a CPU and a storage unit. Therefore, the control device 30 may be configured to have a plurality of CPUs and storage units. In addition, some functions of the control device 30 may be realized by an outside vehicle control unit that is provided outside the vehicle and can communicate with the onboard control unit.

  The control device 30 generates a control command for controlling the driving state of the rotating electrical machine 16. At this time, the control device 30 acquires the allowable range of the battery voltage Vb at the time of charging / discharging of the battery 12, and the rotating electrical machine so that the battery voltage Vb of the battery 12 detected by the voltage sensor 22 does not exceed the allowable range. 16 drive states are controlled. The allowable range of the battery voltage Vb is defined by the upper limit voltage Vmax and the lower limit voltage Vmin, and each of the upper limit voltage Vmax and the lower limit voltage Vmin may be a predetermined value, as will be described later. The value may be different depending on the battery temperature Tb and / or the open circuit voltage Vo of the battery 12.

  When the battery 12 is discharged, the battery voltage Vb decreases as the output power amount increases. If the battery voltage Vb falls below the lower limit voltage Vmin and becomes overdischarged, for example, the metal constituting the positive electrode may be eluted, and the eluted metal may precipitate during charging, causing an internal short circuit, etc. In the negative electrode, there may be a problem that the function as the secondary battery is impaired, such as irreversibly decomposing the film covering the negative electrode active material. Therefore, the control device 30 generates a control command for limiting the power used by the rotating electrical machine 16 so that the battery voltage Vb does not fall below the lower limit voltage Vmin, and performs control to increase the battery voltage Vb.

  On the other hand, when the battery 12 is charged, the battery voltage Vb increases as the input power amount increases. If the battery voltage Vb exceeds the upper limit voltage Vmax and becomes overcharged, for example, lithium may be deposited on the negative electrode surface to cause an internal short circuit, which may also impair the function as a secondary battery. There is sex. Therefore, the control device 30 generates a control command that suppresses the generation of regenerative power by the rotating electrical machine 16 so that the battery voltage Vb does not exceed the upper limit voltage Vmax, and performs control to reduce the battery voltage Vb.

  Hereinafter, regarding the charge / discharge control of the battery 12 and the charge / discharge control performed by the power storage system 10 according to the present embodiment, the battery voltage Vb does not fall below the allowable lower limit voltage Vmin when the battery 12 is discharged. A case where the control is performed will be described as an example.

The battery voltage Vb of the battery 12 is a value obtained by subtracting the product of the battery current Ib of the battery 12 and the battery resistance (internal resistance) Rb of the battery 12 from the open circuit voltage (OCV) Vo of the battery 12. )
Vb = Vo−Ib × Rb (1)
Represented by The product (Ib × Rb) of the battery current Ib and the battery resistance Rb of the battery 12 represents the amount of voltage drop from the open circuit voltage Vo due to the battery resistance Rb of the battery 12. Since this voltage drop amount is also the sum of the drop voltage Vr due to the DC resistance Ra of the battery 12 and the polarization voltage (reaction overvoltage) Vp due to the polarization phenomenon at the positive and negative electrodes, the battery voltage Vb is expressed by the following formula (2).
Vb = Vo− (Vr + Vp) (2)
Also represented by

  By the way, the malfunction that may occur due to the overdischarge of the battery 12 is caused by the fact that the polarization voltage Vp due to the polarization phenomenon at the positive electrode and the negative electrode becomes higher than the threshold value Vp0. The threshold value Vp0 varies depending on the composition and crystal structure of the positive electrode and the negative electrode, the composition of the electrolytic solution, and the like. Further, as the battery temperature Tb of the battery 12 decreases, the threshold value Vp0 of the polarization voltage Vp also decreases. The lower limit voltage Vmin of the battery 12 is set based on the threshold value Vp0 of the polarization voltage Vp so as not to overdischarge when the battery 12 is discharged. Since the battery voltage Vb increases as the polarization voltage Vp decreases from the above equation (2), it is necessary to increase the lower limit voltage Vmin as the threshold value Vp0 decreases. Therefore, for example, the lower limit voltage Vmin is set such that the lower limit voltage Vmin is higher as the battery temperature Tb of the battery 12 is lower. Further, the lower limit voltage Vmin may be invariable with respect to the change in the battery temperature Tb. In this case, the lower limit voltage Vmin is set based on the threshold value Vp0 at the lower limit value (minimum temperature) of the assumed temperature range of use of the battery 12. Is done. As will be described later, the lower limit voltage Vmin may be different according to the open circuit voltage Vo of the battery 12.

  On the other hand, in the actual battery 12, it is known that the battery resistance Rb of the battery 12 increases as the battery temperature Tb of the battery 12 decreases. That is, from the above equation (1), the battery voltage Vb of the battery 12 decreases as the battery temperature Tb of the battery 12 decreases. Therefore, in the conventional charge / discharge control of the battery 12, as the battery temperature Tb of the battery 12 decreases, the difference between the battery voltage Vb and the lower limit voltage Vmin decreases, and the range of the amount of power that the battery 12 can output is limited. End up.

  The limitation on the amount of electric power that can be output due to the temperature drop of the battery 12 is more remarkable in the range where the battery temperature Tb of the battery 12 is equal to or lower than the freezing temperature Tf of the electrolyte (hereinafter also referred to as “very low temperature region”). appear. This is because, in a very low temperature range (for example, −30 ° C. or lower), when a part of the electrolyte contained in the battery 12 is frozen, the battery resistance Rb of the battery 12 rapidly increases, and the battery voltage Vb of the battery 12 is accordingly increased. This is because it drops rapidly. The electrolytic solution freezing temperature Tf is a temperature at which at least a part of components contained in the electrolytic solution is solidified.

  FIG. 2 is a graph showing an example of the relationship between the battery temperature Tb and the battery resistance Rb in a temperature range including a very low temperature range. In FIG. 2, the horizontal axis represents the reciprocal of temperature, and the vertical axis represents resistance. The broken line indicates the freezing temperature Tf of the electrolytic solution. The battery resistance Rb is expressed as the sum of the DC resistance Ra and the polarization resistance Rp due to the polarization phenomenon in the positive and negative electrodes. As shown in FIG. 2, in the range where the battery temperature Tb is higher than the freezing temperature Tf of the electrolytic solution, both the DC resistance Ra and the polarization resistance Rp increase as the battery temperature Tb decreases, and the DC resistance Ra and the polarization are increased. The ratio with the resistance Rp is approximately the same. However, in the range where the battery temperature Tb is equal to or lower than the freezing temperature Tf (extremely low temperature range), the DC resistance Ra increases rapidly as compared with the polarization resistance Rp as the battery temperature Tb decreases.

  The increase in the DC resistance Ra in the cryogenic region can be explained as follows. Where the direct current resistance Ra includes the resistance of the electrolytic solution, the solidified electrolytic solution is segregated locally below the freezing temperature Tf. As a result, the conductive path is limited, and the resistance due to the electrolytic solution increases. Therefore, it is considered that the DC resistance Ra increases rapidly as the battery temperature Tb decreases. Here, the value of the direct current resistance Ra when it is assumed that the electrolyte solution is not frozen in a cryogenic temperature region is defined as a resistance component Ra ′. As indicated by the alternate long and short dash line in FIG. 2, the resistance component Ra 'is considered to increase gradually as the battery temperature Tb decreases. The increase in the DC resistance Ra of the battery 12 due to the freezing of the electrolytic solution is represented by a resistance component ΔRa that is a difference between the DC resistance Ra and the resistance component Ra ′. As shown in FIG. 2, in the extremely low temperature range, the resistance component ΔRa increases rapidly as the battery temperature Tb decreases, and as a result, the DC resistance Ra also increases rapidly.

  FIG. 3 is a graph showing the relationship between the battery temperature Tb of the battery 12 and the battery voltage Vb. The relationship between the battery temperature Tb and the battery voltage Vb of the battery 12 shown in FIG. 3 is based on FIG. 2 and the above equation (1). FIG. 3 also shows a lower limit voltage Vmin set in the conventional charge / discharge control. In FIG. 3, the horizontal axis represents the reciprocal of the temperature, and the vertical axis represents the voltage. In FIG. 3, the drop voltage Vr based on the DC resistance Ra and the polarization voltage Vp based on the polarization resistance Rp are shown. As shown in the above equation (2), the sum of the drop voltage Vr and the polarization voltage Vp is the battery 12. Is the difference obtained by subtracting the battery voltage Vb from the open circuit voltage Vo. In the extremely low temperature range, the drop voltage Vr is expressed as the sum of the voltage component Vr ′ due to the resistance component Ra ′ and the voltage component ΔVr due to the resistance component ΔRa. That is, it has a relational expression of Vr = Vr ′ + ΔVr. In FIG. 3, the lower limit voltage Vmin of the battery 12 shows a constant value with respect to the battery temperature Tb of the battery 12.

  As shown in FIG. 3, in the extremely low temperature range, the battery voltage Vb rapidly decreases as the battery temperature Tb decreases, and eventually reaches the lower limit voltage Vmin. As described above, the rapid decrease in the battery voltage Vb is caused by a part of the electrolytic solution being frozen and the resistance component ΔRa of the DC resistance Ra increasing rapidly, and the amount of decrease in the battery voltage Vb due to the drop voltage Vr increasing rapidly. It depends on. Therefore, in the conventional power storage system, the battery voltage Vb of the battery 12 tends to be closer to the lower limit voltage Vmin in the extremely low temperature range where the battery temperature Tb is equal to or lower than the freezing temperature Tf. The amount is more strictly limited. Therefore, for example, even if it is attempted to start the rotating electrical machine 16 in a situation where the battery 12 is placed in an extremely low temperature region, a situation may occur in which electric power necessary for starting the rotating electrical machine 16 cannot be output.

  In the conventional charge / discharge control of the battery 12, as the battery voltage Vb to be compared with the lower limit voltage Vmin, the total amount of the polarization voltage Vp and the drop voltage Vr is calculated from the open circuit voltage Vo as shown in the above equation (2) and FIG. The subtracted value is used. However, as described above, the malfunction that may occur due to overdischarge of the battery 12 is caused by the polarization voltage Vp exceeding the threshold value Vp0, and is not caused by the drop voltage Vr due to the DC resistance Ra. Therefore, when charge / discharge control of the battery 12 is performed, the lower limit voltage Vmin can be reduced according to the amount of decrease due to the drop voltage Vr from the open circuit voltage Vo. In particular, regarding the lowering of the lower limit voltage Vmin based on a rapid increase in the DC resistance Ra (resistance component ΔRa) caused by the electrolyte freezing in a very low temperature range where the battery temperature Tb is equal to or lower than the freezing temperature Tf of the electrolyte. Until now, was not considered.

  In the charge / discharge control of the battery 12 in the power storage system 10 according to the present embodiment, the lower limit in the cryogenic temperature range is determined by the voltage correction value Vc corresponding to the increase in the DC resistance Ra (resistance component ΔRa) of the battery 12 due to the freezing of the electrolyte. The correction is performed to reduce the voltage Vmin. The voltage correction value Vc is acquired based on the battery temperature Tb detected by the temperature sensor 20 and the open circuit voltage Vo of the battery 12 obtained from the battery voltage Vb detected by the voltage sensor 22.

  FIG. 4 is a graph showing the relationship between the battery temperature Tb of the battery 12 and the battery voltage Vb, as in FIG. FIG. 4 also shows the lower limit voltage Vmin after correction by the voltage correction value Vc corresponding to the resistance component ΔRa that increases due to freezing of the electrolytic solution in the cryogenic temperature region. As shown in FIG. 4, in the power storage system 10 according to the present embodiment, when the battery 12 is discharged, the lower limit voltage Vmin is set by the voltage correction value Vc in the extremely low temperature range where the battery temperature Tb is equal to or lower than the freezing temperature Tf of the electrolyte. Make corrections to reduce. As shown in FIG. 4, when the lower limit voltage Vmin is reduced by the voltage correction value Vc, the allowable range of the battery voltage Vb of the battery 12 is expanded. Thereby, since the electric energy which can be output of the battery 12 increases, the startability of the rotary electric machine 16 can be improved, for example. Further, the correction by the voltage correction value Vc is set to a value at which the amount of decrease due to the polarization voltage Vp does not exceed the threshold value Vp0. Therefore, the control device 30 controls the discharge of the battery 12 so that the battery voltage Vb does not fall below the corrected lower limit voltage Vmin, whereby the battery 12 can be protected from overdischarge.

  Acquisition of the lower limit voltage Vmin corrected by the voltage correction value Vc will be described. The lower limit voltage Vmin is stored in the control device 30 and is referred to when charge / discharge control of the battery 12 is performed. As described above, the lower limit voltage Vmin may be set such that the lower limit voltage Vmin is higher as the battery temperature Tb of the battery 12 is lower, and the lower limit voltage Vmin may be invariant to changes in the battery temperature Tb. Further, considering that the battery voltage Vb detected by the voltage sensor 22 is a value obtained by subtracting the polarization voltage Vp and the drop voltage Vr from the open circuit voltage Vo, the drop voltage Vr with respect to the polarization voltage Vp (in the extremely low temperature range, the electrolyte solution) The lower limit voltage Vmin may be corrected in advance based on the ratio of the voltage component Vr ′) by the direct current resistance Ra (resistance component Ra ′) when it is assumed that no freezing has occurred. As described above, since the ratio of the drop voltage Vr (voltage component Vr ′) to the polarization voltage Vp decreases as the open circuit voltage Vo decreases, the lower limit voltage Vmin is set to decrease as the open circuit voltage Vo of the battery 12 decreases. It may be.

  The control device 30 stores a map indicating a correspondence relationship between parameters such as the battery temperature Tb and the open circuit voltage Vo and the lower limit voltage Vmin, and the control device 30 applies the actually detected parameter values to the map. To obtain the lower limit voltage Vmin.

The voltage correction value Vc used for correcting the lower limit voltage Vmin is appropriately set according to the resistance component ΔRa at each battery temperature Tb. For example, when the lower limit voltage Vmin is corrected based only on the resistance component ΔRa, which is an increase in the DC resistance Ra due to freezing of the electrolytic solution, the difference between the open circuit voltage Vo and the lower limit voltage Vmin is calculated based on the graph shown in FIG. The following formula (3) multiplied by ΔVr / (Vp + Vr ′)}
Vc = (Vo−Vmin) × ΔVr / (Vp + Vr ′) (3)
Thus, the voltage correction value Vc can be calculated, and the calculated voltage correction value Vc can be subtracted from the lower limit voltage Vmin to obtain the corrected lower limit voltage Vmin.

Further, the voltage correction for correcting the lower limit voltage Vmin when the lower limit voltage Vmin before correction is not corrected based on the ratio of the drop voltage Vr (voltage component Vr ′ in the extremely low temperature range) to the polarization voltage Vp described above. The value Vc may be corrected based on the total amount of the DC resistance Ra as well as the resistance component ΔRa, which is an increase in the DC resistance Ra due to freezing of the electrolytic solution. That is, based on the graph shown in FIG. 4, the difference between the open circuit voltage Vo and the lower limit voltage Vmin is multiplied by {Vr / Vp} (4)
Vc = (Vo−Vmin) × Vr / Vp (4)
Thus, the voltage correction value Vc can be calculated, and the calculated voltage correction value Vc can be subtracted from the lower limit voltage Vmin to obtain the corrected lower limit voltage Vmin.

  As shown in FIG. 2, in the cryogenic temperature range, the ratio of the resistance component ΔRa to the resistance component Ra ′ and the polarization resistance Rp increases as the battery temperature Tb decreases. Similarly, as shown in FIG. 4, in the extremely low temperature range, the ratio of the voltage component ΔVr to the voltage component Vr ′ and the polarization voltage Vp increases as the battery temperature Tb decreases. Thus, the voltage correction value Vc varies depending on the battery temperature Tb of the battery 12, and the voltage correction value Vc of the lower limit voltage Vmin increases as the battery temperature Tb decreases.

  Further, the voltage correction value Vc varies depending on the open circuit voltage Vo of the battery 12. In the battery 12, the ratio Vr / Vp of the drop voltage Vr to the polarization voltage Vp decreases as the open circuit voltage Vo decreases. Therefore, the voltage correction value Vc decreases as the open circuit voltage Vo of the battery 12 decreases.

  The control device 30 stores a map indicating a correspondence relationship between the battery temperature Tb, the open circuit voltage Vo, and the voltage correction value Vc. The control device 30 applies the actually detected parameter values to the map, The voltage correction value Vc is acquired. The ratio of the resistance component ΔRa that increases due to freezing of the electrolytic solution to the DC resistance Ra for creating a map showing the correspondence between the battery temperature Tb and the voltage correction value Vc is calculated as follows.

  In a temperature range exceeding the freezing temperature Tf, the direct current resistance Ra of the battery 12 is measured by a known method. Since the reciprocal of the battery temperature Tb and the logarithm of the DC resistance Ra are in a proportional relationship, a regression line can be obtained from these measured values, for example, by applying the least square method. By applying the regression line obtained in this way even in a very low temperature range, that is, when the battery temperature Tb detected by the temperature sensor 20 is equal to or lower than the freezing temperature Tf, The resistance component Ra ′ can be calculated. By subtracting the calculated resistance component Ra 'from the DC resistance Ra in the extremely low temperature region measured in parallel, the resistance component ΔRa that increases due to freezing of the electrolyte in the extremely low temperature region can be calculated. As a known method for measuring the direct current resistance Ra of the battery 12, for example, based on the fact that the direct current resistance Ra has a fast time response to the polarization resistance Rp, a short time from the start of charging / discharging of the battery 12 can be used. (For example, within 0.1 second) The method of measuring resistance after progress, the method of calculating | requiring DC resistance Ra from the frequency response result in the alternating current impedance measurement of the battery 12, etc. are mentioned.

  The open circuit voltage Vo of the battery 12 is obtained from the battery voltage Vb detected by the voltage sensor 22. When the battery 12 is not charged / discharged, the battery current Ib = 0 in the above formula (1), so the open circuit voltage Vo of the battery 12 is the battery voltage Vb detected by the voltage sensor 22. When the battery 12 is being charged / discharged, a map indicating the correspondence between the battery temperature Tb and the battery resistance Rb is stored in the control device 30 in advance, and the battery temperature Tb detected by the temperature sensor 20 is applied to the map for calculation. The battery resistance Rb, the battery voltage Vb detected by the voltage sensor 22, and the battery current Ib detected by the current sensor 24 are applied to the above equation (1) to calculate the open circuit voltage Vo of the battery 12. Further, when the battery 12 is being charged / discharged, the detected value of the voltage sensor 22 during the period when the battery 12 immediately before that is not charged / discharged may be used as the open voltage Vo of the battery 12.

  The control device 30 may repeatedly perform a series of processes for correcting the lower limit voltage Vmin in a predetermined cycle (for example, several tens of milliseconds to several hundreds of milliseconds) after the output of the battery 12 is started. Usually, when the output of the battery 12 is performed, the temperature of the electrolytic solution rises and the frozen electrolytic solution component melts, so that the resistance component ΔRa, which is an increase in the DC resistance Ra due to the freezing of the electrolytic solution, decreases. It is done. Therefore, since the voltage correction value Vc greatly fluctuates when the battery 12 is discharged, the lower limit voltage Vmin is periodically corrected and the lower limit voltage Vmin compared with the battery voltage Vb is updated, whereby a more appropriate battery 12 It is preferable to perform discharge control.

  The above-described discharge control and allowable voltage range correction performed by the power storage system 10 according to this embodiment can be applied even when the battery 12 is charged. That is, in the power storage system 10 according to the present embodiment, when the battery 12 is charged, correction is performed to increase the upper limit voltage Vmax by the voltage correction value Vc in an extremely low temperature range where the battery temperature Tb is equal to or lower than the freezing temperature Tf of the electrolyte. Thereby, the input electric energy of the battery 12 can be increased while protecting the battery 12 from overcharging.

  Hereinafter, according to the flowchart shown in FIG. 5, a flow of a series of processes related to the correction of the lower limit voltage Vmin and the discharge control by the power storage system 10 shown in FIG. 1 will be described. This series of processing is executed every predetermined period or every time a predetermined condition is satisfied.

  Referring to FIGS. 1 and 5, when the process is started, temperature sensor 20 detects battery temperature Tb of battery 12 in step S102. Next, in step S <b> 104, the voltage sensor 22 detects the battery voltage Vb of the battery 12.

  In step S106, control device 30 determines whether or not battery temperature Tb is equal to or lower than freezing temperature Tf of the electrolyte solution of battery 12. The freezing temperature Tf of the electrolytic solution is, for example, −30 ° C. If it is determined in step S106 that battery temperature Tb exceeds freezing temperature Tf (NO in step S106), the process proceeds to step S118. If it is determined in step S106 that the battery temperature Tb is equal to or lower than the freezing temperature Tf (YES in step S106), the process proceeds to step S108. In step S106, the control device 30 uses a known method for determining the solidification state of the electrolyte solution of the battery 12 instead of determining whether or not the battery temperature Tb is equal to or lower than the freezing temperature Tf of the electrolyte solution of the battery 12. May be. For example, the solidification state of the electrolyte solution of the battery 12 may be determined according to the method for determining the solidification state of the electrolyte solution of the lithium ion secondary battery described in JP-A-2006-117413.

  In step S108, the control device 30 determines whether or not the battery 12 is charging / discharging. If it is determined in step S108 that the battery 12 is not charging / discharging (NO in step S108), the process proceeds to step S110, and the control device 30 acquires the battery voltage Vb of the battery 12 as the open voltage Vo.

  If it is determined in step S108 that the battery 12 is charging / discharging (YES in step S108), the process proceeds to step S112. In step S112, the control device 30 acquires the open circuit voltage Vo by another known method. For example, the parameters detected by the temperature sensor 20, the voltage sensor 22, and the current sensor 24, the map showing the correspondence between the battery temperature Tb and the battery resistance Rb stored in the control device 30, and the relational expression of the above equation (1). Is used to calculate the open circuit voltage Vo. Alternatively, the detection value of the voltage sensor 22 during the period when the previous charging / discharging is not performed is acquired as the open circuit voltage Vo.

  In step S114, the control device 30 acquires the voltage correction value Vc based on the battery temperature Tb detected by the temperature sensor 20 and the open circuit voltage Vo acquired in step S110 or step S112. Next, in step S116, the control device 30 performs correction for reducing the lower limit voltage Vmin by the acquired voltage correction value Vc.

  In step S118, control device 30 determines whether or not battery voltage Vb is lower than lower limit voltage Vmin. If it is determined in step S118 that battery voltage Vb is not lower than lower limit voltage Vmin (NO in step S118), the process proceeds to step S122. In step S122, the current usage status of the battery 12 is maintained.

  If it is determined in step S118 that battery voltage Vb is lower than lower limit voltage Vmin (YES in step S118), the process proceeds to step S120. In step S120, for example, the control device 30 generates a control command for limiting the power used by the rotating electrical machine 16, and performs control to increase the battery voltage Vb.

  As is apparent from the above description, in the power storage system 10 of the present embodiment, the battery temperature Tb and the open circuit voltage Vo of the battery 12 obtained from the battery voltage Vb are within the range where the battery temperature Tb is equal to or lower than the freezing temperature of the electrolyte. Based on this, the voltage correction value Vc corresponding to the increase in the DC resistance Ra of the battery 12 due to the freezing of the electrolyte is acquired, the lower limit voltage Vmin is reduced by the acquired voltage correction value Vc, and the upper limit voltage Vmax is set to Perform correction to increase. Thereby, since the allowable range of the battery voltage Vb of the battery 12 is expanded, it is possible to increase the amount of power that can be input / output while protecting the battery 12.

DESCRIPTION OF SYMBOLS 10 Power storage system, 12 Battery, 14 Inverter, 16 Rotating electric machine, 18 System main relay, 20 Temperature sensor, 22 Voltage sensor, 24 Current sensor, 30 Control apparatus.

Claims (1)

A battery that can be charged and discharged, including an electrolyte;
A temperature detector for detecting a battery temperature of the battery;
A voltage detector for detecting a battery voltage of the battery;
A control device that controls charging and discharging of the battery so that the battery voltage detected by the voltage detection unit does not fall below a predetermined lower limit voltage and does not exceed a predetermined upper limit voltage;
When the battery temperature detected by the temperature detection unit is equal to or lower than the freezing temperature of the electrolytic solution, the control device sets a voltage correction value corresponding to an increase in the direct current resistance of the battery due to freezing of the electrolytic solution, Obtaining based on the open circuit voltage of the battery obtained from the battery voltage and the battery temperature, performing the correction to lower the lower limit voltage and raise the upper limit voltage by the acquired voltage correction value,
A power storage system characterized by that.

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