Battery management device and battery management method

Abstract

This system allows for a simple and highly accurate assessment of the degradation status of batteries that power electric work equipment, taking environmental conditions into consideration, while the equipment is in use. [Solution] The battery management device manages the degradation state of the battery that powers the electric work machine, and comprises an ambient temperature sensor that measures the ambient temperature around the battery, a battery temperature sensor that measures the surface temperature of the battery as the battery temperature, a voltage sensor that measures the voltage of the battery, and a controller that determines the degradation state of the battery based on the output of these sensors. The controller measures the charging capacity from the discharged state of the battery to the threshold voltage when the battery is being charged, and determines the degradation by comparing the measured charging capacity with the degradation standard capacity obtained by a preset estimation formula. The estimation formula estimates the charging capacity up to the threshold voltage in a specific degradation state as the degradation standard capacity, based on the ambient temperature and battery temperature measured when the battery is being charged.

Description

Technical Field

[0005]

[0001] The present invention relates to a battery management device and a management method for determining battery deterioration.

Background Art

[0002] In recent years, due to the increasing awareness of environmental issues, various engine-driven work machines tend to be electrified. The electrification of work machines inevitably requires the use of a battery as a power source. However, generally, the battery causes a decrease in the charging capacity due to deterioration by repeating charging and discharging. Therefore, in order to ensure the workability and safety of work machines, it is necessary to appropriately judge the deterioration of the battery and perform battery replacement at an appropriate timing.

[0003] Conventionally, as a method for estimating the degree of battery deterioration, the current battery characteristics including the internal resistance value are obtained for the battery, and the use condition data including the temperature-time distribution and the current value-time distribution during the estimation period, and the deterioration constant distribution with respect to the battery voltage and temperature are stored. Then, the deterioration degree is estimated by integrating the residence time in the battery voltage-temperature plane in the deterioration characteristic map based on the current battery characteristic data and the use condition data. Such a proposal has been made (see Patent Document 1 below).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The degradation of lithium-ion batteries commonly used in electric work equipment can be expressed by the degree of decrease in charge capacity. Generally, State of Health (SOH) is defined as the ratio (%) of the current charge capacity at 100% SOC (State of Charge) to the charge capacity at 100% SOC when the battery was new. However, since the charge capacity of a battery is highly dependent on environmental conditions such as temperature, it is difficult to measure the current charge capacity under the same environmental conditions as when the charge capacity of a new battery was measured. Therefore, a simple comparison of charge capacity does not allow for an accurate assessment of the degradation level. Furthermore, in order to measure the internal resistance, which is used as an indicator of degradation, it is necessary to measure the voltage between the positive and negative electrodes of the battery using a measuring instrument each time a degradation assessment is performed. This does not meet the requirement of easily understanding the degradation status of a battery while it is in use.

[0006] Furthermore, as with the conventional technology mentioned above, accurate estimation is possible by storing usage condition data and degradation characteristic maps and estimating the degree of degradation based on battery characteristic data and usage condition data. However, this requires a large memory capacity for data storage, and it is necessary to accumulate data and update maps according to the use of the work equipment, which inevitably leads to the problem of data acquisition and storage becoming complicated.

[0007] This invention was proposed to address these problems. Specifically, the objectives of this invention include enabling a highly accurate assessment of deterioration status, taking environmental conditions into account, to be easily performed while using work equipment. [Means for solving the problem]

[0008] To solve these problems, the present invention has the following configuration. A battery management device that provides power for an electric work machine and manages the deterioration state of the battery, comprising: an ambient temperature sensor for measuring the ambient temperature around the battery; a battery temperature sensor for measuring the surface temperature of the battery as the battery temperature; a voltage sensor for measuring the voltage of the battery; a current sensor for measuring the current being charged to the battery; and a controller for determining the deterioration state of the battery based on the outputs of the ambient temperature sensor, the battery temperature sensor, the voltage sensor, and the current sensor, wherein, when the battery is being charged, the controller measures the charging capacity from the discharged state of the battery to a threshold voltage based on the outputs of the voltage sensor and the current sensor, and performs a deterioration determination by comparing the measured charging capacity with a deterioration standard capacity determined by a preset estimation formula, wherein the estimation formula estimates the charging capacity up to the threshold voltage in a specific deterioration state as the deterioration standard capacity based on the ambient temperature and the battery temperature measured when the battery is being charged.

[0009] A battery management method for managing the degradation state of a battery that powers an electric work machine, comprising: measuring the actual charge capacity when charging the battery from a discharged state to a threshold voltage; measuring the ambient temperature of the battery and the surface temperature of the battery as the battery temperature during charging; substituting the measured ambient temperature and the battery temperature into a predetermined estimation formula to estimate the charge capacity up to the threshold voltage in a specific degradation state as the degradation standard capacity; and determining the degradation state of the battery by comparing the measured charge capacity with the degradation standard capacity. [Effects of the Invention]

[0010] The present invention, having these features, allows for easy and highly accurate assessment of the degradation status of a battery that powers an electric work machine, taking environmental conditions into consideration, while the work machine is in use. [Brief explanation of the drawing]

[0011] [Figure 1] Diagram illustrating a battery management device connected to a work machine. [Figure 2] A diagram illustrating the hardware configuration of the controller. [Figure 3] An explanatory diagram showing the battery charging method. [Figure 4] Diagram illustrating the battery degradation detection process (battery management method). [Figure 5] A graph showing the results of cycle tests on batteries and the regression line used to derive the degradation standard capacity. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same reference numerals in different figures indicate parts with the same function, and redundant explanations in each figure will be omitted as appropriate.

[0013] In Figure 1, the battery management device 1 is connected to the electric work implement 2 and is equipped with a battery 10 that powers the work implement 2. By connecting the battery management device 1 to the work implement 2, the load Ws of the work implement 2 is supplied with electricity from the battery 10.

[0014] The battery management device 1 includes a controller 20 that manages the degradation state of the battery 10. The battery management device 1 also includes an ambient temperature sensor 21 that measures the ambient temperature around the battery 10, a battery temperature sensor 22 that measures the surface temperature of the battery 10 as the battery temperature, a voltage sensor 23 that measures the voltage of the battery 10, and a current sensor 24 that measures the current being charged to the battery 10.

[0015] The controller 20 receives the outputs of the ambient temperature sensor 21, the battery temperature sensor 22, the voltage sensor 23, and the current sensor 24, respectively. Based on the outputs of these sensors, it determines the degradation state of the battery 10, and if it has reached a state where replacement is necessary, it displays a recommendation for replacement on the display device 25, prompting the user to replace the battery appropriately.

[0016] The power supply line L1 within the battery management device 1 is connected to the positive and negative electrodes of the battery 10. The power supply line L1 is connected to the power supply line L2, which is connected to the load Ws of the work machine 2, via a connection terminal C. The battery management device 1 is also provided with a charging line L3 that is connected to an external charger E, and both ends of the charging line L3 are connected to the power supply line L1. The battery 10 supplies power to the load Ws when the power switch SW1 on the power supply line L2 is turned on and the charging switch SW2 on the charging line L3 is turned off. Also, when the power switch SW1 is turned off and the charging switch SW2 is turned on, the external charger E is connected to the battery 10 and the battery 10 is charged.

[0017] The hardware configuration of the controller 20 is well-known and, for example, as shown in Figure 2, includes a processor 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and an interface (I / F) 104. Each of these components is connected to communicate with each other via the bus 100. The processor 101 is specifically a CPU (Central Processing Unit), MPU (Micro Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), SoC (System on a Chip), etc., and is composed of a single processor or multiple processors of the same or different types.

[0018] The processor 101 executes various arithmetic operations including control of each component and the deterioration determination described later. That is, the processor 101 reads a program from the ROM 102 or other storage unit, and executes the program using the RAM 103 as a working area, thereby performing control of each of the above components and various arithmetic operations.

[0019] The interface (I / F) 104 is an input unit that inputs a signal to the controller 20, and is also an output unit that outputs a signal from the controller 20. Through the interface (I / F) 104, the various sensors and the display device 25 described above are connected to the controller 20.

[0020] When the battery 10 is being charged while connected to the external charger E, the controller 20 controls the charging state of the battery 10 based on the output of the voltage sensor 23 (voltage V) and the output of the current sensor 24 (current I). FIG. 3 shows an example of the charging state control. Here, a charging method called CCCV (Constant Current Constant Voltage) charging is adopted. In CCCV charging, when charging from the discharged state (voltage V1: SOC0%) to the fully charged state (voltage V2: SOC100%), in the CC charging region which is the initial stage of the charging time T, the current I is made constant (I1), and the voltage V is gradually increased. Then, when the voltage V reaches V2, it shifts to the CV charging region, and the voltage V is kept constant (V2) until the end of charging, and the current I is gradually decreased. At this time, the controller 20 calculates the SOC (%) which is the charging state of the battery 10 as 100×(V - V1) / (V2 - V1) based on the output of the voltage sensor 23 (voltage V).

[0021] Also, when the battery 10 is being charged, the controller 20 measures the actual charging capacity. The actual measurement of the charging capacity can be easily performed, for example, within the CC charging region in the above-described CCCV charging method. The charging capacity W at this time can be calculated by the product of the current I1 which is controlled to be constant and the charging time T (I1×T).

[0022] Figure 4 illustrates the battery degradation detection process (battery management method) performed by the controller 20. When the degradation detection process is started, the controller 20 determines the state of charge (SOC) based on the output (voltage V) of the voltage sensor 23 and checks the discharge state of the battery 10 (step S1). If the battery 10 is not at SOC 0% (discharge state) (S2: NO), the controller 20 continues to check the discharge state (step S1), and when the SOC becomes 0% (discharge state) (step S2: YES), it starts charging the battery 10 (step S3).

[0023] Then, while charging the battery 10, the ambient temperature t and battery temperature (surface temperature) t1 of the battery 10 are measured by the ambient temperature sensor 21 and the battery temperature sensor 22 (step S4). Furthermore, the charging capacity W (= I1 × T) is measured according to the charging time T (step S5), and steps S3 to S4 described above are repeated until the voltage V reaches the threshold voltage Vs (set charging state) (step S6: NO).

[0024] The threshold voltage Vs here is set in the CC charging region of the CCCV charging method described above (see Figure 3). For example, if the set charging state is 80% SOC, the threshold voltage Vs is the voltage V at which the SOC reaches 80%. Steps S3 to S4 are repeated until the voltage V reaches the threshold voltage Vs through charging. When the threshold voltage Vs is reached (step S6: YES), the measured ambient temperature t and battery temperature t1 are saved (step S7), and the measured charging capacity W is saved (step S8). In this case, as shown in Figure 3, if the charging time until the threshold voltage Vs is reached is Ts, then 100 × (Vs - V1) / (V2 - V1) = 80, and the measured charging capacity W at that time is I1 × Ts.

[0025] Then, using the stored ambient temperature t and battery temperature t1, the degradation reference capacity Wp is calculated using the pre-set estimation formula Wp(t,t1) (step S9). The degradation reference capacity Wp is obtained by the estimation formula Wp(t,t1) described later, and is an estimate of the charge capacity up to the threshold voltage Vs mentioned above in a specific degradation state (for example, SOH 60%). The estimation formula is determined by the cycle test performed for each product type of battery 10 and is pre-stored in a memory unit such as the ROM 102 in the controller 20.

[0026] Battery degradation is determined by comparing the measured charging capacity W with the degradation standard capacity Wp calculated from the ambient temperature t and the battery temperature t1 (step S10). In this comparison, if the measured charging capacity W is higher than the degradation standard capacity Wp (step S10: NO), it is determined that the battery 10 has not degraded and is still usable, and the degradation determination is terminated. If, in the aforementioned comparison, the measured charging capacity W falls below the degradation standard capacity Wp (step S10: YES), it is determined that the battery 10 has degraded, and a message recommending battery replacement is displayed on the display device 25 (step S11), prompting the user to replace the battery.

[0027] The estimation formula for determining the degradation standard capacity Wp is described below. The aforementioned estimation formula is based on a regression equation created using correspondence data between ambient temperature and charge capacity obtained in cycle tests conducted for each product type of battery 10, and a correction based on battery temperature is applied to it. This is pre-stored in the memory unit (e.g., ROM 102) of the controller 20 of the battery management device 1, which will be the product. Cycle tests are not performed for each product of the battery management device 1; instead, the estimation formula obtained from a single cycle test is shared for batteries 10 of the same product type.

[0028] In the cycle test, multiple degradation states are experimentally created for the battery 10. The number of degradation states is determined according to the number of cycles, with one charge-discharge cycle for the battery 10 being considered one cycle. Then, data on the relationship between the charge capacity and ambient temperature is obtained for each degradation state. The test apparatus for the cycle test places the battery under test in a constant temperature chamber in which the ambient temperature can be set, and repeatedly charges and discharges the battery while the ambient temperature is set, sequentially changing the degradation state, and measuring the charge capacity from the discharge state to the threshold voltage Vs for each degradation state. Then, by changing the ambient temperature, for example, in increments of 10°C, and similarly sequentially changing the degradation state and measuring the charge capacity at each ambient temperature, data on the relationship between the charge capacity and ambient temperature is obtained.

[0029] An example of the results of a cycle test is shown in Figure 5. Here, the multiple degradation states are defined as new, first degradation state (e.g., 367 cycles), second degradation state (e.g., 744 cycles), third degradation state (e.g., 2465 cycles), and fourth degradation state (e.g., 4595 cycles). In Figure 5, the plot of charge capacity for each ambient temperature in each degradation state is indicated by "◎" for new, "〇" for first degradation state, "△" for second degradation state, "▲" for third degradation state, and "×" for fourth degradation state.

[0030] Looking at the results of the cycle test as shown in the figure, first, the plot of charge capacity against ambient temperature when the battery is new ("◎") shows that in the ambient temperature range of 0°C to 40°C, the charge capacity increases as the ambient temperature rises, but the change is not linear but nonlinear. Furthermore, in each degradation state, the plot of charge capacity against ambient temperature is generally nonlinear, similar to that of a new battery.

[0031] Here, in order to derive the degradation standard capacity Wp, it is necessary to set a specific degradation state that serves as the criterion for degradation determination. In the example shown, the specific degradation state is set between the second degradation state ("△") and the third degradation state ("▲"). The plot of the charging capacity against ambient temperature in the set specific degradation state becomes a regression line Re calculated based on the corresponding data obtained for each degradation state, and this regression line Re is expressed by the regression equation W(t) which finds the charging capacity W(Ah) with ambient temperature t(°C) as the variable.

[0032] This regression equation W(t) is based on the Arrhenius law, which describes the likelihood of chemical changes occurring at a given temperature. Using the Arrhenius law as the basic model results in a linear model of the corresponding data plot mentioned above. However, in reality, as the ambient temperature t rises, the internal resistance of the battery 10 increases, suppressing the charging capacity. As a result, the corresponding data plot becomes nonlinear, as shown in Figure 5. Taking this into consideration, the error between the linear model based on the Arrhenius law and the actual corresponding data is corrected by the nonlinear component to improve the estimation accuracy of the regression equation W(t).

[0033] Furthermore, as mentioned above, the regression equation W(t) cannot be uniquely determined unless a specific degradation state, which serves as the criterion for degradation judgment, is set. When setting a specific degradation state, if it is set to a degradation state with a small number of cycles (high SOH), the regression line Re shown in Figure 5 will shift upward as indicated by arrow a, and if it is set to a degradation state with a large number of cycles (low SOH), the regression line Re shown in Figure 5 will shift downward as indicated by arrow b.

[0034] Taking these factors into consideration, the regression equation W(t) can be expressed by the following equation (1).

[0035] W(t) = [Arrhenius term] + [Nonlinear correction term] + [Specific degradation state setting term] … (1)

[0036] Here, the "Arrhenius term" is a term that linearly models the plot of the corresponding data mentioned above according to the Arrhenius law. The "nonlinear correction term" is a term that corrects the error between the actual corresponding data and the linear model of the Arrhenius term using a nonlinear component. The "specific degradation state setting term" is a term that reflects the setting of a specific degradation state, which is the criterion for degradation judgment, into the regression equation W(t). As shown in equation (1) above, the regression equation W(t) is the sum of the "Arrhenius term", the "nonlinear correction term", and the "specific degradation state setting term".

[0037] Furthermore, in order to estimate the degradation standard capacity Wp with greater accuracy, the regression equation W(t), which is a function of the ambient temperature t, is corrected by the battery temperature t1. The battery temperature t1 may change independently of the ambient temperature t, and as degradation progresses when the battery 10 is charged and discharged under the same environmental conditions, the battery temperature t1 will rise. Also, as the battery temperature t1 rises, the internal resistance of the battery 10 increases, and the charging capacity is suppressed. For this reason, when the difference between the measured ambient temperature t and the battery temperature t1 becomes large, the regression equation W(t) is revised downward to determine the degradation standard capacity Wp. The calculation process for this downward revision is the temperature correction term.

[0038] The aforementioned temperature correction term is a term that corrects the effect of the internal resistance of battery 10 on the charging capacity based on the battery temperature, and is a function of ambient temperature t and battery temperature t1. If the temperature correction term is Tc(t,t1), the estimation formula Wp(t,t1) for determining the degradation standard capacity Wp is a function of ambient temperature t and battery temperature t1, and can be expressed by the following equation (2).

[0039] Wp(t,t1)=Tc(t,t1)×W(t) …(2)

[0040] Here, assuming that the results of the cycle test shown in Figure 5 are constant, one example of the estimation formula Wp(t,t1) for determining the degradation standard capacity Wp is calculated, and with Ar(t) as the Arrhenius term, Nl(t) as the nonlinear correction term, De(t) as the specific degradation state setting term, and Tc(t,t1) as the temperature correction term, it becomes as shown in equation (3) below.

[0041]

number

[0042] As described above, according to the battery management device 1 or battery management method using the embodiment of the present invention, when the battery management device 1 is connected to the work machine 2 and the work machine 2 is in use, it becomes possible to determine the degradation of the battery 10 when charging the battery 10. Furthermore, since the degradation standard capacity Wp, which is obtained by the estimation formula Wp(t,t1) with ambient temperature t and battery temperature t1 as variables, is used for this degradation determination, it becomes possible to determine the degradation while considering the change in the internal resistance of the battery 10 together with the environmental change, and a highly accurate determination result can be obtained.

[0043] Furthermore, since the estimation formula Wp(t,t1) includes a "specific degradation state setting term," the level of SOH used as the criterion for degradation determination can be appropriately changed by substituting the SOH value into the "specific degradation state setting term." This allows the degradation determination level of the degradation criterion capacity Wp to be changed as needed, enabling degradation determination that matches the purpose. [Explanation of symbols]

[0044] 1: Battery management device 2: Work equipment 10: Battery 20: Controller 21: Ambient temperature sensor 22: Battery temperature sensor 23: Voltage sensor 24: Current sensor 25: Display device 100: Bus 101: Processor 102: ROM 103: RAM 104: Interface Ws: Load L1, L2: Power supply line L3: Charging line SW1: Power switch SW2: Charging switch E: External charger

Claims

1. A battery management device equipped with a battery that powers an electric work machine, and which manages the deterioration state of the said battery, An ambient temperature sensor for measuring the ambient temperature of the battery, A battery temperature sensor that measures the surface temperature of the battery as the battery temperature, A voltage sensor for measuring the voltage of the aforementioned battery, A current sensor for measuring the current being charged to the aforementioned battery, The system includes a controller that determines the degradation state of the battery based on the outputs of the ambient temperature sensor, the battery temperature sensor, the voltage sensor, and the current sensor. The controller, when charging the battery, measures the charging capacity from the discharged state of the battery to the threshold voltage using the outputs of the voltage sensor and the current sensor. Degradation is determined by comparing the measured charging capacity with the degradation standard capacity determined by a predetermined estimation formula. The battery management device is characterized in that the estimation formula estimates the charging capacity up to the threshold voltage in a specific degradation state as the degradation reference capacity, based on the ambient temperature and the battery temperature measured during charging of the battery.

2. The estimation formula is obtained by creating multiple degradation states in cycle tests performed for each product type of the battery, acquiring correspondence data between the charging capacity up to the threshold voltage and the ambient temperature in each degradation state, and correcting the regression formula obtained from the acquired correspondence data by the battery temperature. The battery management device according to claim 1.

3. The estimation formula is obtained by multiplying the sum of an Arrhenius term, which linearly models the plot of the corresponding data; a nonlinear correction term, which corrects the error between the corresponding data and the linear model using a nonlinear component; and a specific degradation state setting term, which reflects the setting of a specific degradation state in the regression equation, by a temperature correction term, which corrects the effect of the battery's internal resistance on the charging capacity using the battery temperature. The battery management device according to claim 2.

4. A battery management method for managing the deterioration state of a battery that powers an electric work machine, The charging capacity is measured when the aforementioned battery is charged from a discharged state to a threshold voltage. During the charging process, the ambient temperature of the battery is measured, and the surface temperature of the battery is measured as the battery temperature. By substituting the measured ambient temperature and the battery temperature into a pre-set estimation formula, the charging capacity up to the threshold voltage in a specific degradation state is estimated as the degradation reference capacity. A battery management method for determining the degradation state of the battery by comparing the measured charging capacity with the degradation standard capacity.

5. The estimation formula is obtained by creating multiple degradation states in cycle tests performed for each product type of the battery, acquiring correspondence data between the charging capacity up to the threshold voltage and the ambient temperature in each degradation state, and correcting the regression formula obtained from the acquired correspondence data by the battery temperature. The battery management method according to claim 4.

6. The estimation formula is obtained by multiplying the sum of an Arrhenius term, which linearly models the plot of the corresponding data; a nonlinear correction term, which corrects the error between the corresponding data and the linear model using a nonlinear component; and a specific degradation state setting term, which reflects the setting of a specific degradation state in the regression equation, by a temperature correction term, which corrects the effect of the battery's internal resistance on the charging capacity using the battery temperature. The battery management method according to claim 5.

Images