JP2017050981A - Battery control device - Google Patents

Abstract

In an electric vehicle that is used for a long period of time, the degree of reduction in fuel consumption is reduced and deterioration of a secondary battery is suppressed. A battery control apparatus for controlling charging / discharging of a battery that supplies electric power to a vehicle driving motor, wherein a deterioration evaluation value due to a deviation in salt concentration in the electrolyte of the battery is based on charging / discharging current of the battery. ΣD is calculated, and the deterioration evaluation value ΣD approaches the deterioration restriction threshold ΣD1 before the deterioration evaluation value ΣD reaches the deterioration restriction threshold ΣD1 that limits the allowable charging power (Win) in order to suppress an increase in battery resistance. The allowable charging power (Win) to the battery is limited according to the above. [Selection] Figure 4

Description

  The present invention relates to a structure of a battery control device.

  In recent years, electric vehicles using a motor as a drive source and electric vehicles such as hybrid vehicles using an engine and a motor as drive sources are often used. Such an electric vehicle is equipped with a secondary battery such as a chargeable / dischargeable lithium ion battery that supplies electric power to the motor by discharging and charges regenerative power generated by the motor.

  It is known that secondary batteries such as lithium ion batteries deteriorate due to repeated charging and discharging, and the battery capacity gradually decreases and the internal resistance increases. In particular, it is known that deterioration progresses by repeated use at a large charge / discharge current (high rate), and is sometimes referred to as “high rate deterioration”. High-rate deterioration is a phenomenon in which when a large discharge current or a large charge current flows, the salt concentration in the electrolyte solution in the secondary battery is biased, thereby increasing the internal resistance.

  Therefore, based on the current flowing through the secondary battery, etc., the amount of damage of the secondary battery at a certain point in time is calculated, the amount of damage is integrated, and the threshold value set from the viewpoint of suppressing the increase in resistance is the damage integrated value. There has been proposed a method of limiting the charge / discharge current of the secondary battery when exceeding (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 2015-76958 JP2013-125607A

  In the prior art described in Patent Documents 1 and 2, since the charge / discharge current of the secondary battery is not limited until the damage integrated value reaches a predetermined threshold value, the fuel consumption is not greatly reduced until that time. However, if the damage integrated value exceeds a predetermined threshold value, the charge / discharge current is largely limited to protect the battery and suppress the deterioration of the battery.

  On the other hand, in recent years, even when charging / discharging current (high rate) is not large, if charging / discharging is repeatedly performed over a long period of time, salt concentration unevenness gradually occurs and deterioration progresses, and the integrated damage value increases in the negative direction. I understand that. For this reason, in an electric vehicle that is used for a long period of time, the damage integrated value of the secondary battery may reach a predetermined threshold during the period of use, and there may be a problem that the fuel consumption suddenly decreases.

  Accordingly, an object of the present invention is to alleviate the degree of reduction in fuel consumption and suppress deterioration of a secondary battery in an electric vehicle that is used for a long period of time.

  A battery control device that controls charging / discharging of a battery that supplies electric power to a vehicle drive motor, and calculates a deterioration evaluation value due to a deviation in salt concentration in the electrolyte of the battery based on charging / discharging current of the battery. Before the deterioration evaluation value reaches a predetermined threshold value that limits the allowable charge / discharge power in order to suppress an increase in resistance of the battery, the deterioration evaluation value is applied to the battery according to a change approaching the predetermined threshold value. The allowable charge / discharge power is limited.

  INDUSTRIAL APPLICABILITY According to the present invention, in an electric vehicle that is used for a long period of time, the degree of reduction in fuel consumption can be reduced and the deterioration of the secondary battery can be suppressed.

It is a systematic diagram which shows the system configuration | structure of the battery control apparatus in embodiment of this invention. 5 is a graph showing changes in battery output power and deterioration evaluation values in the battery control device according to the embodiment of the present invention. It is a flowchart which shows operation | movement of the battery control apparatus in embodiment of this invention. It is the map which prescribed | regulated the allowable charge electric power (Win) with respect to deterioration evaluation value (SIGMA) D in embodiment of this invention. It is the map which prescribed | regulated the allowable discharge electric power (Wout) with respect to deterioration evaluation value (SIGMA) D in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the battery device 100 in which the battery control device 40 of the present invention is used will be described. The battery device 100 includes a battery 10 connected to a motor generator 20 that is a vehicle driving motor via a positive line PL and a negative line NL, a voltage sensor 31 that detects a voltage Vb of the battery 10, and charging / discharging of the battery 10. A current sensor 32 for detecting the current Ib; a temperature sensor 33 for detecting the temperature Tb of the battery 10; and a battery control device 40 to which the detection signals of the voltage sensor 31, the current sensor 32, and the temperature sensor 33 are input. Yes.

  The battery 10 is a rechargeable secondary battery such as a lithium ion battery. Motor generator 20 receives the electric power output from battery 10 to drive the vehicle, converts the kinetic energy generated during braking of the vehicle into electric power, and charges battery 10. Therefore, the battery 10 is repeatedly charged and discharged while the vehicle is running. The current Ib from the battery 10 is positive (+) for the discharge current and negative (-) for the charge current.

  The battery control device 40 is a computer that includes a CPU 41 that performs internal information and a memory 42 that stores control programs, control data, and the like. As will be described later, the battery control device 40 calculates the deterioration evaluation value ΣD of the battery 10 based on the input temperature sensor 33 and the detection signals of the voltage sensor 31, the current sensor 32, and the temperature sensor 33. The allowable charge / discharge power (Win or Wout) of the battery 10 is limited according to the value of the deterioration evaluation value ΣD.

  Next, the operation of the battery control device 40 of the present embodiment will be described with reference to FIGS. First. A method of calculating the deterioration evaluation value ΣD of the battery 10 shown in step S101 of FIG. 3 will be described.

The damage rate D for high-rate deterioration is performed by calculating every predetermined period Δt using the following equation (1).

D [t + Δt]
= D [t]-[alpha] * [Delta] t * D [t] + [beta] * Ib * [Delta] t / c0 ---- (1)

In the above formula (1), t indicates time, D [t + Δt] is the amount of damage calculated this time, and D [t] in the first term on the right side indicates the amount of damage calculated last time. α is a forgetting factor, β is a current factor, Ib is a charging / discharging current of the battery 10 (+ at discharging, − at charging), and c0 is a limit threshold. As shown in the above equation (1), the current damage amount D [t + Δt] is calculated based on the previous damage amount D [t]. The damage amount D [0] as the initial value can be set to “0”, for example.

  Since the uneven concentration of the salt in the electrolytic solution is alleviated in accordance with the diffusion of ions with the passage of time, the damage amount D decreases with the passage of time. The second term on the right side of the above equation (1) is a term that takes into account the reduction in the amount of damage D during the predetermined period Δt. The forgetting factor α is a factor corresponding to the diffusion rate of ions in the electrolyte solution of the battery 10, and the forgetting factor α increases as the diffusion rate increases. The value of “α × Δt” is set within a range of 0 to 1. The absolute value of the second term on the right side increases as the value of “α × Δt” approaches “1”. Further, as the value of the forgetting factor α increases or the period Δt increases, the value of “α × Δt” approaches “1”.

  Since the forgetting factor α depends on the SOC and the temperature Tb of the battery 10, the forgetting factor α can be set according to the SOC and the temperature Tb. Specifically, the correspondence relationship between the forgetting factor α and at least one of the SOC and the temperature Tb is obtained in advance by experiments or the like, stored in the memory 42 as a map or function, and detected by the voltage sensor 31. Based on the map or function stored in the memory 42 using the SOC and the temperature Tb of the battery 10 detected by the temperature sensor 33, the SOC is obtained based on the voltage Vb and the current Ib of the battery 10 detected by the current sensor 32. The forgetting factor α may be set.

  The deviation of the salt concentration in the electrolyte increases as the absolute value of the current value increases. Moreover, the direction of the bias of the salt concentration is reversed between discharging and charging. For this reason, during the discharge in which the current Ib becomes positive (+), the third term on the right side of the equation (1) becomes a positive value to increase the damage amount D, and the current Ib becomes negative (−). During charging, the third term on the right side of Equation (1) becomes a negative value, and the damage amount D is reduced. Therefore, the damage amount D becomes positive (+) when a high-rate discharge current flows, and the damage amount D becomes negative (-) when a high-rate charging current flows.

  The current coefficient β and the limit threshold value c0 in the third term on the right side of Equation (1) depend on the SOC of the battery 10 and the temperature Tb. For this reason, as with the forgetting factor α, a correspondence relationship with at least one of the SOC and the temperature Tb is obtained in advance by experiments or the like, stored in the memory 42 as a map or a function, and the voltage of the battery 10 detected by the voltage sensor 31. The SOC is obtained based on Vb and the current Ib of the battery 10 detected by the current sensor 32, and the current based on the map or function stored in the memory 42 using this SOC and the temperature Tb of the battery 10 detected by the temperature sensor 33. The coefficient β and the limit threshold value c0 may be set.

The progress of the high rate deterioration uses ΣD obtained by integrating the damage amount D described above as an evaluation value. The deterioration evaluation value ΣD is calculated every predetermined period Δt as follows. Here, D [t] is the damage amount D calculated by the above equation (1).

ΣD [t + Δt] = γ × ΣD [t] + η × D [t] −−−− (2)

In the above equation (2), γ is an attenuation coefficient that is smaller than 1, and is a value that is set by predicting the degree to which the bias in salt concentration is alleviated by the diffusion of ions over time. 42 is a value stored in 42. Further, η is a correction coefficient, and is a value stored in the memory 42 as in the case of γ.

  As described above, the damage amount D becomes positive (+) when a high-rate discharge current flows, and the damage amount D becomes negative (−) when a high-rate charge current flows. It increases when a discharge current flows, and decreases when a high-rate charging current flows. However, when the deterioration evaluation value ΣD is negative, the absolute value decreases when a high-rate discharge current flows, and the absolute value increases when a high-rate charge current flows. That is, when the deterioration evaluation value ΣD is integrated on the positive (+) excessive discharge side, the charging decreases the deterioration evaluation value ΣD, brings the deterioration evaluation value ΣD close to zero, and the deterioration evaluation value ΣD When integration is performed on the negative (−) excessive charge side, the discharge increases the deterioration evaluation value ΣD to bring the deterioration evaluation value ΣD close to zero.

  Depending on the type of the battery 10, the deterioration evaluation value ΣD has a characteristic that the deterioration evaluation value ΣD easily accumulates on the positive (+) excessive discharge side by repeating charging / discharging, and the deterioration evaluation value ΣD has a negative (− ) Have characteristics that are easy to integrate on the overcharge side. FIG. 2A shows a change in the deterioration evaluation value ΣD when the battery 10 having the characteristic that the deterioration evaluation value ΣD is easily accumulated on the overcharge side where the deterioration evaluation value ΣD is negative (−) by repeating charge / discharge. It is a graph to show.

  As shown in FIG. 2A, the deterioration evaluation value ΣD at time zero is zero. Since the output power of the battery 10 is not large even if the battery 10 is discharged for a short time from time zero in FIG. 2B, the damage amount D of the high-rate deterioration is small, and the deterioration evaluation is performed as shown in FIG. The value ΣD remains almost zero. After that, if there is a high-rate charge with a large input power to the battery 10 from time t1 in FIG. 2B, a large negative damage amount D is generated. Therefore, as shown in FIG. ΣD greatly decreases from the vicinity at time t1. Next, when there is a high-rate discharge with a large output power from the battery 10 until time t2 in FIG. 2B, a positive damage amount D is generated, and the deterioration evaluation value ΣD increases near time t2, and becomes zero. Approaching. This is because the deterioration evaluation value ΣD approaches zero because the salt concentration generated by the high-rate charging is relaxed by the high-rate discharge. However, since FIG. 2A is a graph when charging and discharging the battery 10 having a characteristic that the deterioration evaluation value ΣD is easily accumulated on the overcharge side where the deterioration evaluation value ΣD is negative (−) by repeating charging and discharging, The increase in deterioration evaluation value ΣD near t2 is smaller than the decrease in deterioration evaluation value ΣD near time t1, and the deterioration evaluation value ΣD remains negative.

  Thereafter, when there is a high rate charge with a large input power to the battery 10 at time t3 in FIG. 2B, a large negative damage amount D occurs again, and deterioration evaluation is performed as shown in FIG. The value ΣD greatly decreases from time t2 to time t3. Thereafter, the discharge from the battery 10 continues, but since the output power of the battery 10 is small, the damage amount D due to the high rate is almost zero. From time t3 to time t4 shown in FIG. Almost no change. Then, at time t4 shown in FIG. 2B, if there is a high rate charge with a large input power to the battery 10, a large negative damage amount D is generated, and the deterioration evaluation value ΣD is greatly reduced in the vicinity of time t4. To do.

  As described above, when the battery 10 having the characteristic that the deterioration evaluation value ΣD is easily accumulated on the excessive charge side where the deterioration evaluation value ΣD is repeatedly charged and discharged is repeatedly charged and discharged as shown in FIG. As shown in (a), the deterioration evaluation value ΣD is integrated and decreased on the negative side with time. Furthermore, since the battery 10 has a characteristic that the deterioration evaluation value ΣD easily accumulates on the negative (−) excessive charge side by repeating charge and discharge, the battery 10 is long after the time t4 shown in FIG. When charging / discharging is repeated over a period, the deterioration evaluation value ΣD is further accumulated on the negative (−) side with time and further decreased. For this reason, the allowable charge power (Win) is limited in the battery 10 having the characteristic that the deterioration evaluation value ΣD easily accumulates on the excessive charge side where the deterioration evaluation value ΣD is repeatedly charged and discharged.

  As shown in step S101 of FIG. 3, the battery control device 40 according to the present embodiment calculates the damage amount D by the equation (1), and calculates the deterioration evaluation value ΣD by the equation (2). Next, as shown in step S102 of FIG. 3, with reference to the map of the allowable charging power (Win) of the battery 10 with respect to the deterioration evaluation value ΣD shown in FIG. 4 stored in the memory 42 shown in FIG. An allowable charging power (Win) is acquired. And as shown to step S103 of FIG. 3, the allowable charging power (Win) of the battery 10 is restrict | limited to the value acquired from the map of FIG. The battery control device 40 of the present embodiment performs an operation of repeating the above steps S101 to S103 every predetermined period Δt. The horizontal axis of the map shown in FIG. 4 indicates the minus side of the deterioration evaluation value ΣD. When the map of FIG. 4 is used, as the deterioration evaluation value ΣD decreases, the battery 10 acquired from the map is shown. The allowable charging power (Win) decreases.

  Therefore, as shown in FIG. 2A, when the deterioration evaluation value ΣD decreases with time, the allowable charging power (Win) of the battery 10 of the battery 10 decreases according to the degree of decrease. Come. When the deterioration evaluation value ΣD decreases to a deterioration limit threshold ΣD1 that is a predetermined threshold for limiting the allowable charging power (Win) in order to suppress an increase in the resistance of the battery 10 due to long-term use, the map shown in FIG. Thus, the allowable charging power (Win) of the battery 10 is rapidly reduced toward zero, and when the deterioration evaluation value ΣD decreases to the lower limit value ΣD2, the allowable charging power (Win) of the battery 10 approaches zero. That is, when the deterioration evaluation value ΣD reaches the deterioration limit threshold ΣD1, the amount of decrease is set to be larger than the amount of decrease in the allowable charging power Win so far.

  The battery control device 40 of the present embodiment deteriorates before the deterioration evaluation value ΣD decreases to the deterioration limit threshold ΣD1 that is a predetermined threshold for limiting the allowable charging power (Win) in order to suppress the resistance increase of the battery 10. Since the allowable charging power (Win) of the battery 10 is reduced in accordance with the decrease in the evaluation value ΣD or the change in the deterioration evaluation value ΣD approaching the deterioration limit threshold ΣD1, the deterioration evaluation value ΣD decreases. Then, it is possible to suppress the occurrence of a large negative damage amount D due to charging. For this reason, the rate of decrease in the degradation evaluation value ΣD due to charging / discharging can be slowed down, and even when the electric vehicle is used for a long time, the degradation evaluation value ΣD is prevented from decreasing to the degradation limit threshold ΣD1 during the usage period. can do. That is, deterioration of the battery 10 can be suppressed. Further, since it is possible to suppress the deterioration evaluation value ΣD from decreasing to the deterioration limit threshold ΣD1 during the use period, the allowable charging power (Win) of the battery 10 is rapidly reduced during the use period, and the fuel consumption is rapidly increased. It can suppress that it falls.

  In the case of the battery 10 having the characteristic that the deterioration evaluation value ΣD is likely to be integrated on the negatively charged excessive side by repeating charging and discharging, the battery 10 is allowed to be used according to the decrease in the deterioration evaluation value ΣD. Although the case where the charging power (Win) is reduced has been described as an example, the present invention has a characteristic that the deterioration evaluation value ΣD can be easily accumulated on the excessive discharge side where the deterioration evaluation value ΣD is repeated by repeating charging and discharging. It can also be applied to. In this case, instead of the map shown in FIG. 4, a map that reduces the allowable discharge power (Wout) corresponding to the increase in the degradation evaluation value ΣD in the memory 42 as shown in FIG. It may be stored and the allowable discharge power (Wout) may be reduced as the deterioration evaluation value ΣD increases using this map. When the map of FIG. 5 is used, when the deterioration evaluation value ΣD increases to a deterioration limit threshold ΣD3 that is a predetermined positive threshold for limiting the allowable discharge power (Wout) in order to suppress an increase in resistance of the battery 10. The allowable discharge power (Wout) of the battery 10 is rapidly reduced toward zero, and when the deterioration evaluation value ΣD increases to the upper limit value ΣD4, the allowable discharge power (Wout) of the battery 10 approaches zero. That is, when the deterioration evaluation value ΣD reaches the deterioration limit threshold ΣD3, the reduction amount is set to be larger than the reduction amount of the allowable discharge power (Wout).

  When the map shown in FIG. 5 is used, before the deterioration evaluation value ΣD increases to a deterioration limit threshold ΣD3 that is a predetermined threshold for limiting the allowable discharge power (Wout) in order to suppress an increase in battery resistance. Since the allowable discharge power (Wout) of the battery 10 is reduced as the deterioration evaluation value ΣD increases or as the deterioration evaluation value ΣD approaches the deterioration limit threshold ΣD3, the deterioration evaluation value ΣD As it increases, it is possible to suppress the generation of a large positive damage amount D due to discharge. For this reason, the rate of increase of the deterioration evaluation value ΣD due to discharge can be slowed down, and even when the electric vehicle is used for a long period of time, the deterioration evaluation value ΣD is prevented from increasing to the deterioration limit threshold ΣD3 during the use period. be able to. That is, deterioration of the battery 10 can be suppressed. Further, since it is possible to suppress the deterioration evaluation value ΣD from increasing to the deterioration limit threshold ΣD3 during the use period, the allowable discharge power (Wout) of the battery 10 is rapidly reduced during the use period, and the fuel consumption is suddenly increased. It can suppress that it falls. It should be noted that two maps as shown in FIGS. 4 and 5 are stored in the memory 42, and the allowable charging power (Win) according to the decrease in the deterioration evaluation value ΣD depending on the type of the battery 10 mounted on the vehicle. Or the allowable discharge power (Wout) may be limited in accordance with an increase in the deterioration evaluation value ΣD.

  DESCRIPTION OF SYMBOLS 10 Battery, 20 Motor generator, 31 Voltage sensor, 32 Current sensor, 33 Temperature sensor, 40 Battery control apparatus, 41 CPU, 42 Memory, 100 Battery apparatus.

Claims (1)

A battery control device that controls charging and discharging of a battery that supplies electric power to a vehicle drive motor,
Based on the charging / discharging current of the battery, the deterioration evaluation value due to the deviation of the salt concentration in the electrolyte of the battery is calculated,
Before the deterioration evaluation value reaches a predetermined threshold value that limits the allowable charge / discharge power in order to suppress an increase in resistance of the battery, the deterioration evaluation value is applied to the battery according to a change that approaches the predetermined threshold value. Limiting the allowable charge / discharge power;
A battery control device.

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