JP5004557B2 - How to detect battery deterioration - Google Patents

Description

  The present invention relates to a method for detecting the degree of deterioration of a battery, and more particularly to a method for detecting the degree of deterioration of a battery that is optimal for detecting the degree of deterioration of a battery built in a power supply device that drives an electric vehicle.

  A battery mounted on an electric vehicle such as a hybrid car deteriorates as time elapses and charging / discharging is repeated. A deteriorated battery has low output power. A battery whose output is reduced cannot start the engine of a hybrid car, and the acceleration characteristics are deteriorated. The battery used for this purpose has a degree of deterioration specified from the maximum output power. The battery life can be estimated by detecting the degree of deterioration. For example, it can be estimated that a battery having a degradation degree of 50% after 5 years can be used for the next 5 years using the same charge / discharge characteristics. However, it can be estimated that a battery whose deterioration degree after 4 years is 80% can only be used for about 2 years thereafter. From this, it is possible to detect the degree of deterioration of the battery, control the charge / discharge power of the battery from the degree of deterioration, and control the life of the battery in a specific period. However, in order to realize this, it is important to accurately detect the deterioration degree of the battery.

A method for determining the degree of deterioration of the battery from the internal resistance is described in Patent Document 1. However, the method of determining the degree of deterioration of the battery from the internal resistance has a drawback that it cannot be accurately determined except at the end when the internal resistance increases. A method for solving this problem is described in Patent Document 2. The method of Patent Document 2 calculates a current capacity, which is the amount of electric power that can be discharged from a fully charged state to a predetermined discharge voltage value, based on the discharge voltage V and the discharge amount Ah. The degree of deterioration of the battery is calculated as a ratio with the initial capacity that is the amount of electric power that can be discharged from the fully charged state up to the predetermined discharge voltage value.
JP-A-8-254573 JP 2000-131404 A

  The method of Patent Document 2 can detect the initial deterioration degree more accurately than the method based on the internal resistance. However, in this method, since the battery is discharged from the fully charged state and the degree of deterioration is detected, it is difficult to detect the degree of deterioration of the battery in the traveling state of the hybrid car. This is because the hybrid car controls the remaining capacity of the battery to about 50% and keeps the vehicle running in order to keep the battery deterioration as much as possible and to be able to always output and regenerate. Batteries tend to deteriorate when fully charged. Therefore, when the battery is fully charged in order to detect the degree of deterioration of the battery, the deterioration in this state increases. In addition, since the hybrid car controls the charging and discharging of the battery in the running state, in order to fully charge the battery, the power supply from the battery to the motor is limited, the generator is driven by the engine, and the battery is charged. There is a need to. This condition limits the vehicle's driving condition, particularly lowering acceleration and climbing ability, giving the tribar a sense of incongruity, and also different from the normal driving condition, which also reduces safety. There is.

  The present invention has been developed for the purpose of solving this drawback. An important object of the present invention is to provide a method for detecting the degree of deterioration of a battery that can accurately detect the degree of deterioration without limiting the charging / discharging of the battery.

The battery degradation level detection method of the present invention has the following configuration in order to achieve the above-described object.
Detection method for the degree of deterioration of the battery according to claim 1 of the present invention, the battery current, the deterioration degree SOH1 obtained from the temperature, calculates the battery deterioration degree SOH from both deterioration degree SOH2 obtained from the internal resistance of the battery .

In addition to claim 1, the detection method according to claim 2 of the present invention calculates the deterioration degree SOH of the battery by the following expression.
Degradation degree SOH = weight 1 × degradation degree SOH1 + weight 2 × degradation degree SOH2
However, weight 1 + weight 2 = 1.
In this method, the deterioration degree SOH can be accurately determined by changing the ratio of the weight 1 and the weight 2.

  In particular, the detection method of claim 3 of the present invention, in addition to claim 2, increases the weight 2 as the internal resistance of the battery increases. Can be determined accurately.

  Further, in addition to claim 1, the detection method of claim 4 of the present invention sets the battery degradation degree SOH to 0% when the output power becomes the minimum output power. Can be determined accurately.

Furthermore, in the detection method of claim 5 of the present invention, the deterioration degree SOH1 obtained from the current and temperature is calculated by the following equation.
Deterioration degree SOH1 = previous deterioration degree SOH + α (coefficient specified by current value)
+ Β (coefficient specified by temperature)
However, α and β are negative values.
In this method, the degree of deterioration SOH1 can be easily and accurately determined from the current and temperature at which the battery is charged and discharged.

  In the detection method according to claim 6 of the present invention, the deterioration degree SOH2 specified from the internal resistance of the battery is estimated using the LUT, and therefore the deterioration degree SOH2 can be easily obtained from the internal resistance.

  In the detection method of claim 7 of the present invention, since the battery for calculating the deterioration degree SOH is a battery for running an electric vehicle, it is possible to accurately estimate how long the battery mounted in the hybrid car or the like can be used. There are features.

The method for detecting the degree of deterioration of the battery according to the present invention is characterized in that the degree of deterioration can be accurately detected without limiting the charging / discharging of the battery. It is because the detection method of the present invention, the battery current, the deterioration degree SOH1 obtained from the temperature, calculates the degradation degree SOH from both deterioration degree SOH2 obtained from the internal resistance of the battery.

  Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify battery deterioration level detection methods for embodying the technical idea of the present invention, and the present invention uses battery deterioration level detection methods as follows. Not specified. Further, this specification does not limit the members shown in the claims to the members of the embodiments.

  FIG. 1 is a block diagram of a power supply device used in the method for detecting the degree of battery deterioration according to the present invention. This figure shows a block diagram for determining the degree of deterioration of the battery 1 mounted in the hybrid car. The battery 1 is discharged by supplying electric power to a motor 6 for driving the vehicle, and is charged by a generator 7 so that the remaining capacity is maintained in the vicinity of about 50%. The deterioration level SOH (State of Health) of the battery 1 is detected by the determination circuit 2. The determination circuit 2 includes a current detection circuit 3 that detects a charge / discharge current flowing through the battery 1, a temperature sensor 4 that detects the temperature of the battery 1, and a voltage of the battery 1 in order to detect the deterioration degree SOH of the battery 1. Is connected to a voltage detection circuit 5 for detecting

  The vehicle side includes a bidirectional power converter 8 that supplies electric power supplied from the battery 1 to the motor 6 and supplies electric power from the generator 7 to the battery 1. The bidirectional power converter 8 converts the DC power of the battery 1 into three-phase AC power and supplies it to the motor 6, and converts the AC output from the generator 7 into DC and supplies it to the battery 1. The bidirectional power converter 8 is controlled by the control circuit 9 to control the power supplied from the battery 1 to the motor 6 and the charging power from the generator 7 to the battery 1. The control circuit 9 controls the bidirectional power conversion device 8 in consideration of the deterioration degree SOH of the battery 1 transmitted from the determination circuit 2 on the power supply device side via the communication line 10. When the deterioration degree SOH of the battery 1 is in the expected normal state, the control circuit 9 controls the bidirectional power converter 8 in the normal mode. However, when the degree of deterioration SOH of the battery 1 is smaller than the expected normal state, the control circuit 9 controls the bidirectional power converter 8 in a limiting mode in which the charge / discharge power is smaller than in the normal mode. On the other hand, when the deterioration degree SOH of the battery 1 is larger than the expected normal state, the control circuit 9 sets the bidirectional power converter 8 in the acceleration mode in which the charge / discharge power is larger than in the normal mode or in the normal mode. To control. As described above, the control circuit 9 controls the output of the motor 6 and the generator 7 via the bidirectional power conversion device 8, whereby the life of the battery 1 can be brought close to the target year.

The determination circuit 2 incorporates an EEPROM, stores the deterioration degree SOH1, the deterioration degree SOH2, and the deterioration degree SOH in the EEPROM, and transmits the stored deterioration degree SOH to the control circuit 9 on the vehicle side via the communication line 10. To do. A deterioration degree SOH1 resulting from charge and discharge current and the temperature of the battery 1, calculates a degradation degree SOH from both deterioration degree SOH2 obtained from the internal resistance of the battery 1. The determination circuit 2 calculates the deterioration degree SOH of the battery 1 using the following equation.
Degradation degree SOH = weight 1 × degradation degree SOH1 + weight 2 × degradation degree SOH2
However, weight 1 + weight 2 = 1.

  The weight 1 and the weight 2 are specified by the internal resistance of the battery 1 as shown in the graph shown in FIG. In this figure, the horizontal axis represents the relative value of the internal resistance of the battery 1, and the vertical axis represents weight 1 and weight 2. However, in this figure, the internal resistance of the battery 1 whose lifetime has been exhausted is set to 100 in a state where the degradation degree SOH of the battery 1 is 0%. As shown in this figure, as the deterioration of the battery 1 progresses and the deterioration degree SOH decreases, the weight 1 is decreased and the weight 2 is increased. This is because, in the battery 1, the internal resistance accurately specifies the deterioration degree SOH in a state where the internal resistance is large and the deterioration is advanced. In this method, the weight 1 and the weight 2 are specified from the internal resistance of the battery 1. However, in the detection method of the present invention, the weight 1 and the weight 2 are specified from the deterioration degree SOH2 specified from the internal resistance of the battery 1, or the weight 1 from the deterioration degree SOH determined from the deterioration degree SOH1 and the deterioration degree SOH2. And weight 2 can be specified. Also in this case, the deterioration degree SOH2 is reduced or the deterioration degree SOH is reduced. In other words, the weight 1 is reduced and the weight 2 is increased as the end of life is approached.

Further, the determination circuit 2 determines the deterioration degree SOH1 by the following equation.
Deterioration degree SOH1 (%) = previous deterioration degree SOH1 (%)
+ Α {coefficient specified by current value (%)}
+ Β {coefficient specified by temperature (%)}
However, α and β are negative values.

The deterioration of the battery 1 proceeds as the charged / discharged current increases. Therefore, the negative coefficient α (%) specified by the current value is set as follows, for example, and is increased as charging / discharging with a large current is performed. The determination circuit 2 detects the current and temperature of the battery 1 for 1 second, and calculates the deterioration degree SOH1 from the detected current with α1 (%) to α4 (%) in 1 second as the following values.
α1 (current value is 0 A or more and less than 20 A) = − 132 × 0.00001 / 3600 (%)
α2 (current value is 20 A or more and less than 40 A) = − 528 × 0.00001 / 3600 (%)
α3 (current value is 40 A or more and less than 100 A) = − 2460 × 0.00001 / 3600 (%)
α4 (current value is 100A or more) = −5280 × 0.00001 / 3600 (%)

  In the battery 1 described above, for example, when a current 100A flows for 1 second, the degree of deterioration (%) for 1 second becomes 5280 × 0.00001 / 3600%.

Furthermore, the deterioration of the battery 1 proceeds as the battery temperature increases. Therefore, the negative coefficient β (%) specified by the battery temperature is set as follows, for example, and is increased as the battery is charged / discharged at a higher temperature. The determination circuit 2 detects the current and temperature of the battery 1 for 1 second, and calculates the deterioration degree SOH1 from the detected temperature with β1 (%) to β4 (%) in 1 second as the following values.
β1 (temperature is −40 ° C. or higher and lower than 0 ° C.) = − 3.3 × 0.00001 / 3600 (%)
β2 (temperature is 0 ° C. or higher and lower than 20 ° C.) = − 13.3 × 0.00001 / 3600 (%)
β3 (temperature is 20 ° C. or higher and lower than 40 ° C.) = − 53.3 × 0.00001 / 3600 (%)
β4 (temperature is 40 ° C. or higher) = − 426.7 × 0.00001 / 3600 (%)

  In the battery 1 described above, for example, when the battery temperature is 30 ° C. for 1 second, the deterioration degree (%) for 1 second is 53.3 × 0.00001 / 3600%.

  The battery has different α and β depending on the type. Therefore, the values of α and β are specified by actually charging / discharging the battery, detecting the battery temperature, and measuring the current and temperature.

  The determination circuit 2 detects the current and temperature of the battery 1 at intervals of 1 second when the ignition switch of the hybrid car is on and the vehicle is in a running state. Deterioration degree SOH1 is calculated. However, the timing at which the determination circuit 2 calculates the deterioration degree SOH1 is not specified as 1 second, but is shorter or longer than 1 second, for example, 0.1 seconds to 10 seconds, preferably 0.3 seconds to 5 seconds. More preferably, it may be 0.3 seconds to 3 seconds. In a state where the ignition switch is switched off, the determination circuit 2 detects the average temperature of the battery 1 every several hours, for example, every 1 to 5 hours, and calculates the deterioration degree SOH1. Since the current of the battery 1 does not flow when the ignition switch is off, the deterioration degree SOH1 is calculated only from β1 to β4 without calculating α.

Furthermore, the determination circuit 2 detects the internal resistance of the battery 1 and determines the deterioration degree SOH2 from the internal resistance. FIG. 3 shows an equivalent circuit of the battery 1 having an internal resistance. When the battery 1 of this equivalent circuit is charged and discharged and the current I and the output voltage VL are detected, the result is as shown in FIG. In FIG. 4, the internal resistance R 0 is calculated from the slope of the line A indicating the current-voltage characteristics of the battery 1.
If the open voltage of the battery 1 is Vo and the voltage is VL when the current is I,
VL = Vo-R0 × I
From this formula:
R0 = (Vo-VL) / I

  The deterioration degree SOH2 of the battery 1 with respect to the internal resistance of the battery 1 is measured in advance and stored in the LUT of the determination circuit 2, or the determination circuit 2 stores the deterioration degree SOH2 with respect to the internal resistance as a function. The deterioration degree SOH2 with respect to the internal resistance, which is stored in the LUT or stored as a function, is a value shown in FIG. From this figure, for example, when the internal resistance of the battery 1 is 300 mΩ, the deterioration degree SOH2 is set to 60%.

The determination circuit 2 calculates the deterioration degree SOH1 and the deterioration degree SOH2 by the above method, specifies the weight 1 and the weight 2 from the calculated deterioration degree SOH1 and deterioration degree SOH2, and determines the deterioration degree SOH of the battery 1. . FIG. 6 shows a flowchart in which the determination circuit 2 calculates the deterioration degree SOH.
[Step of n = 1]
In this step, the determination circuit 2 initializes the deterioration degree SOH1, the deterioration degree SOH2, and the deterioration degree SOH from the built-in EEPROM data.
[Step of n = 2]
In this step, the determination circuit 2 calculates the internal resistance from the current and voltage of the battery 1. At this time, filtering by temperature is performed to increase measurement accuracy. This is because the internal resistance changes with temperature. The filtering by temperature detects the battery temperature when detecting the internal resistance of the battery 1 and converts the detected internal resistance into an internal resistance at a set temperature as a function of temperature. The determination circuit 2 that filters the internal resistance stores the change of the internal resistance with respect to the temperature as a function or in the LUT. From this stored value, the internal resistance is filtered and corrected to the internal resistance at the set temperature.
[Step n = 3]
Measure the current and temperature of the battery 1 is charged and discharged, to filter them.
[Step n = 4]
The steps of n = 2 to 4 are looped until 1 second elapses.
[Step n = 5]
When one second has elapsed, in this step, the average current, average temperature, and internal resistance in one second are calculated.
[Step n = 6]
In this step, the determination circuit 2 calculates the deterioration degree SOH1 from the average current for one second and the battery temperature. The determination circuit 2 calculates the deterioration degree SOH1 using the following equation.
Deterioration degree SOH1 (%) = previous deterioration degree SOH1 (%)
+ Α {coefficient specified by current value (%)}
+ Β {coefficient specified by temperature (%)}
[Step n = 7]
Further, the determination circuit 2 calculates the deterioration degree SOH2 from the internal resistance based on the stored LUT and function.
[Step n = 8]
In this step, the determination circuit 2 specifies weight 1 and weight 2 of the deterioration level SOH1 and the deterioration level SOH2. Weight 1 and weight 2 are specified from FIG.
[Step n = 9]
The determination circuit 2 calculates the degree of degradation SOH from the weight 1 and the degree of degradation SOH1, and from the weight 2 and the degree of degradation SOH2.
As a guideline, although depending on the battery usage conditions, the deterioration degree is about 100% to about 70% after 2 hours of operation for 5 years.
[Step n = 10]
In order to bring the deterioration degree SOH1 closer to the deterioration degree SOH, the deterioration degree SOH1 is corrected from the calculated deterioration degree SOH.

The determination circuit 2 determines the deterioration degree SOH of the battery 1 as described above, and transmits the determined deterioration degree SOH to the vehicle-side control circuit 9 via the communication line 10.
By detecting such a deterioration degree SOH, the life of the battery can be known. In addition, various parameters in each deterioration degree SOH (for example, the relationship between the voltage and the battery capacity (SOC) at the deterioration degree, the full charge capacity at the deterioration degree, etc.) are stored in advance, and are determined and detected. Such stored parameters can be used according to the degree of degradation SOH at the time.

In the present embodiment, the following are used as the degree of deterioration.
Degradation degree SOH (%) = {1- [Initial MAXPOWER (at time of SOC 50%) − MAXPOWER at that time (at time of SOC 50%)] / [Initial MAXPOWER (at time of SOC 50%) − Maximum MAXPOWER (at time of SOC 50%) ]} × 100
That is, the deterioration degree SOH is set to 100% in the initial state, and decreases with time to 0%. The end of MAXPOWER (SOC 50%) is the minimum MAXPOWER required during the design life (SOC 50%), and MAXPOWER decreases from the beginning of life to the end of life. %) Is the minimum value of MAXPOWER (SOC 50%) during the design life.

By the way, as an example of the deterioration degree SOH, it can be exemplified as follows with specific numbers at the beginning of use, around the middle of use, and around the end of use.
(1) Around the beginning of use Initial MAXPOWER (SOC 50%) = 40 kW
MAXPOWER at that time (SOC 50%) = 40 kW
Assuming that MAXPOWER (SOC 50%) = 20 kW at the end of the period Deterioration degree SOH = {1− (40−40) / (40−20)} × 100 = 100 (%)
(2) Middle period of use Initial MAXPOWER (SOC 50%) = 40 kW
MAXPOWER (SOC50%) at that time = 30kW
Assuming MAXPOWER (SOC 50%) = 20 kW at the end of the period Deterioration degree SOH = {1− (40−30) / (40−20)} × 100 = 50 (%)
(3) Around the end of use Initial MAXPOWER (SOC 50%) = 40 kW
MAXPOWER at that time (SOC 50%) = 20 kW
Assuming MAXPOWER (SOC 50%) = 20 kW at the end of the period Deterioration degree SOH = {1- (40-20) / (40-20)} × 100 = 0 (%)

  Here, MAXPOWER is obtained by changing the power (or current) to discharge (or charge) at a constant power (or current) for a specific duration when the battery capacity (SOC) is 50%. . In this embodiment, the battery is actually used, or the battery is accelerated under accelerated test conditions, and the MAXPOWER of the battery is measured to obtain the degree of deterioration of the battery. By calculating the degradation degree SOH (= weight 1 × degradation degree SOH1 + weight 2 × degradation degree SOH2) of the present embodiment, the SOH determined in the present embodiment and the SOH by MAXPOWER or the like measured in an actual battery Consistency with was obtained.

The deterioration degree SOH of the present embodiment can be used not only for the above-described deterioration degree but also for the battery capacity deterioration degree described below.
(Deterioration degree of battery capacity SOH) = {(battery capacity at that time) / (initial battery capacity)} × 100 (%)

It is a block diagram of the power supply device used for the detection method of the deterioration degree of the battery concerning one Example of this invention. It is a graph which shows weight 1 and weight 2. It is a figure which shows the equivalent circuit of the battery which has internal resistance. It is a graph which shows the current-voltage characteristic at the time of charging / discharging of a battery. It is a graph which shows deterioration degree SOH2 with respect to internal resistance. It is a flowchart in which the determination circuit calculates the deterioration degree SOH.

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Determination circuit 3 ... Current detection circuit 4 ... Temperature sensor 5 ... Voltage detection circuit 6 ... Motor 7 ... Generator 8 ... Bidirectional power converter 9 ... Control circuit 10 ... Communication line

Claims (7)

A method for detecting the degree of deterioration of a battery, which calculates the degree of deterioration SOH from both the degree of deterioration SOH1 obtained from the current and temperature of the battery and the degree of deterioration SOH2 obtained from the internal resistance of the battery. The battery deterioration degree detection method according to claim 1, wherein the battery deterioration degree SOH is calculated by the following equation.
Degradation degree SOH = weight 1 × degradation degree SOH1 + weight 2 × degradation degree SOH2
However, weight 1 + weight 2 = 1.   The battery deterioration detection method according to claim 2, wherein the weight 2 is increased as the internal resistance increases.   The battery deterioration degree detection method according to claim 1, wherein the battery deterioration degree SOH is set to 0% in a state where the output power becomes the minimum output power. The battery deterioration degree detection method according to claim 1, wherein the deterioration degree SOH1 obtained from the current and the temperature is calculated by the following equation.
Deterioration degree SOH1 = previous deterioration degree SOH1 + α (coefficient specified by current value)
+ Β (coefficient specified by temperature)
However, α and β are negative values.   The method for detecting the degree of deterioration of a battery according to claim 1, wherein the degree of deterioration SOH2 is estimated from the internal resistance of the battery using an LUT.   The battery deterioration degree detection method according to claim 1, wherein the battery for which the deterioration degree SOH is calculated is a battery for running an electric vehicle.

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