WO2012164947A1

WO2012164947A1 - Rechargeable battery degradation level estimation device and method

Info

Publication number: WO2012164947A1
Application number: PCT/JP2012/003603
Authority: WO
Inventors: Ryosuke Ozeki
Original assignee: Kabushiki Kaisha Toyota Jidoshokki
Priority date: 2011-06-01
Filing date: 2012-05-31
Publication date: 2012-12-06
Also published as: JP2012252823A

Abstract

A controller calculates an evaluation value for each abnormal degradation factor from a degradation function corresponding to an abnormal degradation factor causing a prescribed abnormality that is not under a specified control state of the rechargeable battery by using a time corresponding to the prescribed abnormality. Then, the controller stores the evaluation value for each abnormal degradation factor for accumulating and storing the evaluation value for each abnormal degradation factor for each degradation factor in a non-volatile area in a memory.

Description

RECHARGEABLE BATTERY DEGRADATION LEVEL ESTIMATION DEVICE AND METHOD

Field

The present invention relates to the technique of evaluating the degradation level of a rechargeable battery loaded into equipment.

Background

Presently, a rechargeable battery which can be used repeatedly after a recharging operation is used after loaded into various types of equipment. Especially, with an increasing use of an electric vehicle, a hybrid vehicle, etc., there are a number of vehicles loaded with a large capacity secondary battery etc. such as a lithium ion secondary battery etc.

A large capacity rechargeable battery for use in an electric vehicle, a hybrid vehicle, etc. is normally loaded into a vehicle as a combination of a plurality of rechargeable batteries.

A rechargeable battery gradually degrades as charge and discharge are repeated during the service, and reduces its charging capacity.

To solve the problem, there are a number of methods proposed to detect the state of a rechargeable battery loaded into a vehicle.

For example, the patent document 1 (Japanese Laid-open Patent Publication No. 2000-12098) discloses the technique of detecting whether or not the rechargeable batteries loaded into a vehicle includes a battery inferior in degradation characteristic. In the method according to the patent document 1, the capacity degradation rate of the rechargeable battery is calculated during the drive of the vehicle. In addition, the cycle degradation rate and the storage degradation rate are calculated from the charge/discharge frequency and the retention time out of service, and the sum of the cycle degradation rate and the storage degradation rate is defined as a characteristic degradation rate. By comparing the capacity degradation rate with the characteristic degradation rate, it is determined whether or not the degradation of the rechargeable battery is much conspicuous than normal degradation characteristic.

The patent document 2 (Japanese Laid-open Patent Publication No. 2004-14205) discloses the technique of detecting the abnormal degradation of a rechargeable battery with high accuracy. The battery abnormal degradation detection device according to the patent document 2 corrects the charge/discharge frequency of a rechargeable battery based on the history of the charge/discharge state, and calculates the cycle degradation rate of a standard battery based on the corrected charge/discharge frequency. Then, based on the calculated cycle degradation rate of the standard battery and the capacity degradation rate, the abnormality of the degradation state of a battery is detected. That is, the abnormality in degradation state is detected by comparing the actual degradation state of the battery with the degradation state of the standard battery which has been used like the battery.

Furthermore, the patent document 3 (Japanese Laid-open Patent Publication No. 2010-209733) discloses the method of estimating the state of a on-board battery with high accuracy. According to the method of the patent document 3, the internal resistance is obtained from the voltage and the current of the battery at the start of the drive of an engine, or the available capacity of a battery is obtained from the accumulation value of the battery current during the charging process and the temperature of the battery, and the remaining capacity and the degradation level of the battery are obtained from the internal resistance and the available capacity.

The rechargeable battery is also degraded by various factors such as a battery temperature etc. other than the charge/discharge operations.

The conventionally proposed method of obtaining the degradation level of a rechargeable battery is to detect whether or not a rechargeable battery has been degraded or to obtain the degradation level of the entire rechargeable battery.

However, in developing a vehicle such as an electric vehicle, a hybrid vehicle, etc. into which a large capacity rechargeable battery is loaded or developing a rechargeable battery itself, it is important to know which factor causes to what extent the degradation of the rechargeable battery.

Summary

The present invention aims at providing a rechargeable battery degradation level estimation device and estimating method capable of estimating the level of the degradation of a rechargeable battery for each degradation factor.

The rechargeable battery degradation level estimation device according to the present invention which estimates the degradation level of a rechargeable battery loaded into equipment includes: a unit calculating an evaluation value for each abnormal degradation factor for calculating an evaluation value for each abnormal degradation factor from a degradation function corresponding to an abnormal degradation factor causing a prescribed abnormality that is not under a specified control state of the rechargeable battery by using a time corresponding to the prescribed abnormality; and a unit storing an evaluation value for each abnormal degradation factor for accumulating and storing the evaluation value for each abnormal degradation factor for each degradation factor.

The rechargeable battery degradation level estimating method according to the present invention estimates the degradation level of a rechargeable battery loaded into equipment, and measures state information about the state of the rechargeable battery during the operation of the equipment, and calculating an evaluation value for each abnormal degradation factor from a degradation function corresponding to an abnormal degradation factor causing a prescribed abnormality that is not under a specified control state of the rechargeable battery by using a time corresponding to the prescribed abnormality, accumulates the evaluation value for each abnormal degradation factor for each degradation factor, and stores the evaluation value in a memory.

[FIG. 1]FIG. 1 is a configuration of a rechargeable battery degradation level estimation device according to an embodiment of the present invention;
[FIG. 2]FIG. 2 is an example of a method of deriving a degradation function of an abnormal degradation factor; and
[FIG. 3]FIG. 3 is a flowchart of the operation performed by a controller using a degradation function of a temperature abnormality and a voltage abnormality in the evaluating process on a rechargeable battery.

An embodiment of the present invention is described below with reference to the attached drawings.

FIG. 1 is a configuration of a rechargeable battery degradation level estimation device according to an embodiment of the present invention.

The configuration in FIG. 1 exemplifies the case in which a rechargeable battery is loaded into a vehicle, but the equipment into which the rechargeable battery degradation level estimation device according to the present embodiment is loaded is not limited to a vehicle, but can be any type of equipment which can be loaded with a rechargeable battery.

In the configuration illustrated in FIG. 1, a plurality of rechargeable batteries 10-1 through 10-n are serially connected and loaded, and temperature sensors 20-1 through 20-n are provided near each of the rechargeable batteries 10-1 through 10-n for measuring the battery temperature. The battery temperature of each of the rechargeable batteries 10-1 through 10-n measured by the temperature sensors 20-1 through 20-n is reported to a controller 60. In addition, both ends of each of the rechargeable batteries 10-1 through 10-n are connected to a multiplexer (MUX) 30, and a voltmeter 50 is connected to the multiplexer (MUX) 30. The multiplexer (MUX) 30 selects one or a plurality of rechargeable batteries from among the rechargeable batteries 10-1 through 10-n at an instruction from the controller 60, and the voltages at both ends of the selected batteries are measured by the voltmeter 50, and the measurement result is reported to the controller 60. An ammeter 40 measures the current passing from the serially connected rechargeable batteries 10-1 through 10-n, and notifies the controller 60 of the measurement result.

The controller 60 calculates the degradation level for each factor about the rechargeable batteries 10-1 through 10-n based on the information from the temperature sensors 20-1 through 20-n, the ammeter 40, and the voltmeter 50, and the measurement result of a timer 62. The controller 60 includes memory 61 and a timer 62. The memory 61 stores a control program to be executed by the controller 60, and functions as work memory when the controller 60 is operated. The memory 61 stores the information about the degradation level of each factor obtained by the controller 60. The timer 62 measures the time in which the rechargeable batteries 10-1 through 10-n are placed in an abnormal stage.

With the configuration above, a rechargeable battery degradation level estimation device 1 according to the present embodiment obtains the degradation evaluation values of each of the factors of the rechargeable batteries 10-1 through 10-n.

In this case, the rechargeable battery degradation level estimation device 1 prepares a model by assuming that the degradation of the rechargeable batteries 10-1 through 10-n proceeds in proportion to the operation time, and evaluates the degradation level. As an example, the degradation of the rechargeable batteries 10-1 through 10-n under a specified control state is defined as normal degradation, and a normal degradation value representing the level of the normal degradation is obtained. In addition, evaluation values for abnormal degradation factors corresponding to the abnormal degradations caused by prescribed degradation factors that are not under the control state are obtained and each of the evaluation values for each abnormal degradation factor is added to the normal degradation value to obtain the degradation evaluation values.

In the rechargeable battery degradation level estimation device 1 according to the present embodiment, D = F(t) + D_f that is, the degradation evaluation value D is obtained by the normal degradation function F(t) as a time function for the normal degradation and the evaluation value D_fof the abnormal degradation factor. The expression can be replaced with another expression so far as the replacing expression indicates that the degradation evaluation value D increases with the increase of the normal degradation function F(t) and the abnormal degradation factor D_f, and the degradation evaluation value D decreases with the decrease of the normal degradation function F(t) and the abnormal degradation factor D_f, and can be defined as D = F(t) * D_f.

The normal degradation function F(t) is a model of the degradation level variable depending on the operation time when the rechargeable batteries 10-1 through 10-n is maintained in a state within the range of a specified electronic control rule with respect to the abnormal degradation factor described later.

The abnormal degradation factor D_f is defined as a plurality of functions having a specified abnormal degradation factor as a variable.

In the present embodiment, the rechargeable battery degradation level estimation device 1 defines four abnormal degradation factors, that is, a battery temperature abnormality, a battery voltage abnormality, an overcharge abnormality, and an overdischarge abnormality, of the rechargeable batteries 10-1 through 10-n, and defines and models each abnormality as a degradation function. For example, the degradation function of the battery temperature abnormality is defined as F_T(t, T) where T indicates a battery temperature, and t indicates the duration of the battery temperature abnormal state. The degradation function of the battery voltage abnormality is defined as F_V (t, V) where V indicates a battery voltage, and t indicates the duration of the battery voltage abnormal state. Furthermore, the degradation function of an overcharge abnormality is defined as F_Iin (t, I) where I indicates a charge current passing through a rechargeable battery during a charging operation, and t indicates the duration of the overcharge abnormal state. Then, the degradation function of an overdischarge abnormality is defined as F_Iout (t, T) where I indicates a discharge current passing through a rechargeable battery during a discharging operation, and t indicates the duration of the overdischarge abnormality state.

Each of the four abnormal degradation factors are different in influence on the degradation proceeding speed. Therefore, each factor has a different function. An abnormal degradation factor D_f is obtained by combining the accumulation values of the functions after equalizing or weighting the accumulation values and acquiring the sum of them.

With the degradation functions of these abnormal degradation factors, the frequency or time at which the events (degradation factors) having an influence on the battery degradation is counted, and the value depending on the count value or time is generated.

FIG. 2 is an example of a method of deriving a degradation function of an abnormal degradation factor. FIG. 2 illustrates an example of deriving the degradation function F_T (t, T) of the temperature abnormality.

The vertical axis in FIG. 2 illustrates the degradation level of a rechargeable battery and "1" indicates no degradation and "0" indicates full degradation. The horizontal axis in FIG. 2 indicates the time in which the rechargeable battery is in the abnormal temperature state.

A plurality of dots 71 in FIG. 2 are plotted to express the relationship between the degradation level and the time in which a rechargeable battery is continuously used after measuring the degradation level of the rechargeable battery in the state in which the battery temperature is maintained at a constant level (T) (in the present embodiment, at a normal temperature (25 degrees), 50 degrees, 60 degrees, and 70 degrees). By performing polynomial approximation on these measurement values for each battery temperature, degradation characteristics 72a through 72c are obtained at each battery temperature. Then, from the degradation characteristics 72a through 72c, a degradation function F_T (t, T) indicating the degradation level of the rechargeable battery at a temperature abnormality is obtained.

Similarly, based on the measurement value of the relationship between the degradation level of the rechargeable battery and the duration t in the abnormal state with the application value, the overcharge current, and the overdischarge current fixed, degradation functions F_V (t, V), F_Iin (t, I), and F_Iout (t, T) are obtained.

Described next is the method of obtaining the estimate value of the practical degradation level of the rechargeable battery degradation level estimation device 1. In the example below, the case in which only the battery temperature abnormality and the inter-terminal voltage abnormality are processed as the abnormal degradation factors is described as an example for simple explanation. However, it is obvious that the rechargeable battery degradation level estimation device 1 can regard all of the above-mentioned temperature abnormality, voltage abnormality, overcharge abnormality, and overdischarge abnormality as abnormal degradation factors, regard five or more abnormal degradation factors by including other abnormal degradation factors, or regard three or less of the above-mentioned abnormalities as abnormal degradation factors. Additional degradation factors can be the level of precipitation of lithium in the rechargeable batteries 10-1 through 10-n when the rechargeable batteries 10-1 through 10-n are lithium ion secondary batteries, etc.

FIG. 3 is a flowchart of the operation performed by a controller 60 illustrated in FIG. 1 using a degradation function of a temperature abnormality and a voltage abnormality in the evaluating process on the rechargeable batteries 10-1 through 10-n. The process in FIG. 1 is realized by the operation unit in the controller 60 not illustrated in the attached drawings executing the control program stored in the non-volatile area in the memory 61.

The process in FIG.3 is started when the equipment into which the rechargeable battery degradation level estimation device 1 is loaded operates, for example, when the equipment enters the ignition-on state if the equipment is a vehicle. Then, during the activation of the equipment, the measurement values by the temperature sensors 20-1 through 20-n, the ammeter 40, and the voltmeter 50 are collected in the controller 60. The controller 60 updates the degradation evaluation value using the state information about the rechargeable batteries 10-1 through 10-n which changes during the activation of the equipment.

When the process in FIG. 3 starts, the controller 60 reads degradation evaluation values D (D(1), D(2), ..., D(n)) stored in the non-volatile area of the memory 61 to the work area of the memory 61 first in step S1. Similarly, the controller 60 reads degradation factor accumulation values T_FV (T_FV (1), T_FV(2), ..., T_FV (n)) and T_FT (1), T_FT (2), ..., T_FT(n) stored in the non-volatile area of the memory 61 to the work area of the memory 61 in step S2. The degradation factor accumulation value T_FV indicates the value obtained by accumulating the values obtained from the degradation function of the voltage abnormality, and the degradation factor accumulation value T_FTindicates the value obtained by accumulating the values obtained from the degradation function of the temperature abnormality.

Next, the controller 60 measures the battery temperatures of the rechargeable batteries 10-1 through 10-n from the temperature sensors 20-1 through 20-n, and measures the inter-terminal voltage or each of the rechargeable batteries 10-1 through 10-n from the voltmeter 50 while controlling the multiplexer (MUX) 30.

Next, in step S4, the controller 60 obtains inter-terminal voltages V (V(1), V(2), ..., V(n)) of each of the rechargeable batteries 10-1 through 10-n, which are measured in the voltmeter 50. The controller 60 determines whether or not the obtained inter-terminal voltages V (V(1), V(2), ..., V(n)) of each of the rechargeable batteries 10-1 through 10-n is in a specific range, that is, V1 < V < Vh (a specified control state). As a result, if the inter-terminal voltage V (V(1), V(2), ..., V(n)) equals or falls short of a voltage V1, or exceeds a voltage Vh (NO in step S4), the controller 60 calculates the voltage abnormality degradation function FV(V, t1) and obtains an evaluation value for each abnormal degradation factor using the time t1 in which a voltage abnormality is detected in step S5, and adds the evaluation value to the degradation evaluation values D(1), D(2), ..., D(n) corresponding to the rechargeable battery 10 having the voltage abnormal value. Also in step S5, the controller 60 similarly adds the evaluation value for each abnormal degradation factor indicating the voltage abnormality which is obtained from the calculation of the voltage abnormality degradation function FV (V) to the voltage abnormal degradation factor accumulation values TFV (1), TFV (2), ..., TFV (n) corresponding to the rechargeable battery 10 having the voltage abnormal value. On the other hand, if the inter-terminal voltages V (V(1), V(2), ..., V(n)) is V1 < V < Vh in step S4 (YES in step S4), the controller 60 skips the processes in steps S5 and S6.

Next, in step S7, the controller 60 obtains battery temperature (T(1), T(2), ..., T(n)) of each of the rechargeable batteries 10-1 through 10-n, which was measured by the temperature sensors 20-1 through 20-n. The controller 60 checks whether or not the obtained battery temperatures T(1), T(2), ..., T(n) of each of the rechargeable batteries 10-1 through 10-n is in the specific range, that is, T1 < T < Th (a specified control state). As a result, if the battery temperature T(T(1), T(2), ..., T(n)) equals or falls short of the temperature T1 or exceeds the temperature Th (NO in step S7), then the controller 60 calculates the temperature abnormality degradation function FT (T, t2) using the time t2 indicating the temperature abnormality and obtains an evaluation value for each abnormal degradation factor indicating the temperature abnormality, and adds the evaluation value to the degradation evaluation values D(1), D(2), ..., D(n) corresponding to the rechargeable battery 10 having the temperature abnormal value in step S8. In step S9, the controller 60 adds the evaluation value for each abnormal degradation factor indicating the temperature abnormality which is obtained from the calculation of the temperature abnormality degradation function FT (T) to the temperature abnormal degradation factor accumulation values TFT (1), TFT (2), ..., TFT (n) corresponding to the rechargeable battery 10 having the temperature abnormal value. On the other hand, when the battery temperatures T(T(1), T(2), ..., T(n)) indicate T1 < T < Th in step S7 (YES in step S7), the controller 60 skips the processes in steps S8 and S9.

Next, the controller 60 obtains a normal degradation value using the elapsed time t3 from the previous process for the normal degradation function F(t) in step S10, and adds the value to the degradation evaluation value D. Finally, the controller 60 stores the degradation evaluation value D, the degradation factor accumulation value T_FVand T_FT in a specified position in a non-volatile area, and updates the values, thereby terminating the process.

Thus, in the rechargeable battery degradation level estimation device 1 according to the present embodiment, in addition to the entire degradation evaluation values D (D(1), ..., D(n)) for each of the rechargeable batteries 10-1 through 10-n, the accumulation values T_FVandT_FTindicating the value contributing to the degradation of each abnormal degradation factor are also obtained. Therefore, how each abnormal degradation factor has contributed to the degradation of each of the rechargeable batteries 10-1 through 10-n can be and using these values T_FVandT_FT. Based on the analysis result, the system of a rechargeable battery which is not easily degraded, and the configuration of equipment which doe not easily degrade a rechargeable battery can be obtained.

In the explanation above, a plurality of rechargeable batteries are serially connected to equipment, but the application of a rechargeable battery degradation level estimation device according to the present embodiment is not limited to the method of loading of the rechargeable battery as described above. The rechargeable battery degradation level estimation device according to the present embodiment can also be applied when rechargeable batteries are connected in parallel and loaded into equipment, when they are connected in parallel and also in series, and when one rechargeable battery is loaded.

Thus, the level of contribution to the degradation can be estimated for each degradation factor for a rechargeable battery.

Furthermore, the level for each degradation factor can be obtained according to the state information about the state of the rechargeable battery variable during the operation of equipment.

Claims

A rechargeable battery degradation level estimation device which estimates a degradation level of a rechargeable battery loaded into equipment, comprising:
a unit calculating an evaluation value for each abnormal degradation factor for calculating an evaluation value for each abnormal degradation factor from a degradation function corresponding to an abnormal degradation factor causing a prescribed abnormality that is not under a specified control state of the rechargeable battery by using a time corresponding to the prescribed abnormality
; and
a unit storing an evaluation value for each abnormal degradation factor for accumulating and storing the evaluation value for each abnormal degradation factor for each degradation factor.
The device according to claim 1, further comprising
a sensor unit measuring state information about a state of the rechargeable battery during an operation of the equipment, wherein
the unit calculating an evaluation value for each abnormal degradation factor calculates the evaluation value for each abnormal degradation factor for each abnormal degradation factor according to the state information.
The device according to claim 1, wherein
the abnormal degradation factor includes at least one of an abnormality of an inter-terminal voltage of the rechargeable battery, a battery temperature abnormality of the rechargeable battery, and an overdischarge abnormality of the rechargeable battery.
A rechargeable battery degradation level estimating method for estimating a degradation level of a rechargeable battery loaded into equipment, comprising:
measuring state information about a state of the rechargeable battery during an operation of the equipment;
calculating an evaluation value for each abnormal degradation factor from a degradation function corresponding to an abnormal degradation factor causing a prescribed abnormality that is not under a specified control state of the rechargeable battery by using a time corresponding to the prescribed abnormality; and
accumulating the evaluation value for each abnormal degradation factor for each degradation factor, and storing the evaluation value in a memory.