Patent ID: 12196811

DETAILED DESCRIPTION

The present application will be described below in further detail including with reference to the figures according to an embodiment.

FIG.1is a block diagram illustrating an example of a configuration of a power supply device10according to an embodiment. The power supply device10is a power supply device having the neural network realized by an information processing device. The power supply device10includes a secondary battery11, a temperature measurement unit12, a current measurement unit13A, a current peak detection unit13B, a voltage measurement unit14A, a voltage peak detection unit14B, a determination unit15, a positive electrode terminal16A, and a negative electrode terminal16B. The power supply device10is preferably provided in electric vehicles (EV or PHV) or electric aircrafts.

The secondary battery11is a lithium ion battery. The positive electrode terminal of the secondary battery11is connected to the positive electrode terminal of a power supply source via the positive electrode terminal16A. Furthermore, the negative electrode terminal of the secondary battery11is connected to the negative electrode terminal of the power supply source via the negative electrode terminal16B.

The temperature measurement unit12includes a temperature detection element such as a thermocouple or a thermistor. The temperature detection element is disposed on or near a surface of the secondary battery11. The temperature measurement unit12detects the temperature of the secondary battery11by the temperature detection element and outputs the temperature to the determination unit15.

The current measurement unit13A measures the current of the secondary battery11and outputs the current to the current peak detection unit13B. The current measurement unit13A is, for example, a current measurement circuit. The current peak detection unit13B keeps the maximum value of the current at regular time intervals from the current measured by the current measurement unit13A, and outputs the maximum value to the determination unit15. The current peak detection unit13B is an example of a current peak detection unit that detects the maximum value of the current at regular time intervals. As the current peak detection unit13B, a current peak holding unit (the peak hold circuit) configured to be able to perform the peak hold for the maximum value of the current as an analog signal is used. From a viewpoint of early detection of the failure of the secondary battery11, the regular time interval of the current holding is preferably 1 minute or less, more preferably 10 seconds or less, and still more preferably 1 second or less. A lower limit value of the regular time interval is not particularly limited, but is, for example, 10 milliseconds or more.

From the viewpoint of early detection of the failure of the secondary battery11, the current peak detection unit13B is preferably configured to be able to detect a current rise (the current peak) having a half-value width of 1 second or less. A detection target by the current peak detection unit13B is the micro-short circuit derived from metal lithium. An instantaneous rise of the current of the secondary battery11and behavior of immediately recovering thereafter are characteristic behaviors observed in the micro-short circuit caused by a dendrite generation. The dendrite generation can be detected by detecting these characteristic behaviors (waveforms) by the current peak detection unit13B. Accordingly, the determination unit15can determine whether the secondary battery11is normal or abnormal based on the maximum value of the current input from the current peak detection unit13B.

The voltage measurement unit14A measures the voltage of the secondary battery11and outputs the voltage to the voltage peak detection unit14B. The voltage measurement unit14A is, for example, a voltage measurement circuit. The voltage peak detection unit14B holds the minimum value of the voltage at regular time intervals from the voltage measured by the voltage measurement unit14A, and outputs the minimum value thereof to the determination unit15. The voltage peak detection unit14B is an example of a voltage peak detection unit that detects the minimum value of the voltage at regular time intervals. As the voltage peak detection unit14B, a voltage peak holding unit (the peak hold circuit) configured to be able to perform the peak hold for the minimum value of the voltage as the analog signal is used. The regular time interval of voltage holding is preferably 1 minute or less, more preferably 10 seconds or less, and still more preferably 1 second or less from the viewpoint of early detection of the failure of the secondary battery11. A lower limit value of the regular time interval is not particularly limited, but is, for example, 10 milliseconds or more.

From the viewpoint of early detection of the failure of the secondary battery11, the voltage peak detection unit14B is preferably configured to be able to detect a voltage drop (the voltage peak) having the half-value width of 1 second or less. The detection target by the voltage peak detection unit14B is the micro-short circuit derived from metal lithium. An instantaneous drop of the voltage of the secondary battery11and behavior of immediately recovering thereafter are characteristic behaviors observed in the micro-short circuit caused by the dendrite generation. The dendrite generation can be detected by detecting these characteristic behaviors (the waveforms) by the voltage peak detection unit14B. Accordingly, the determination unit15can determine whether the secondary battery11is normal or abnormal based on the minimum value of the voltage input from voltage peak detection unit14B.

The determination unit15determines the failure of the secondary battery11based on the temperature measured by the temperature measurement unit12, the current measured by the current measurement unit13A, the voltage measured by the voltage measurement unit14A, a maximum current value held by the current peak detection unit13B, and a minimum voltage value held by the voltage peak detection unit14B. The determination unit15is a processor that executes the above determination by the learned model using the neural network, or an integrated circuit such as an application specific integrated circuit (ASIC).

Specifically, the determination unit15includes a storage unit that stores the learned model using the neural network, and determines a failure of the secondary battery11using the learned model stored in the storage unit. The neural network includes an input layer and an output layer. Input data of the input layer is (1) the temperature measured by the temperature measurement unit12, (2) the current measured by the current measurement unit13A, (3) the voltage measured by the voltage measurement unit14A, (4) the maximum current value held by the current peak detection unit13B, and (5) the minimum voltage value held by the voltage peak detection unit14B. Output data of the output layer is presence or absence of the failure of the secondary battery11. The presence or absence of the failure of the secondary battery11is determined by inputting the data of (1) to (5) to the neural network. The storage unit included in the determination unit15is, for example, a nonvolatile memory.

Hereinafter, an example of a failure detection method for battery using the power supply device10having the configuration above will be described according to an embodiment.

To start with, the current measurement unit13A and the voltage measurement unit14A measure the voltage and the current of the secondary battery11respectively, and output the voltage and the current to the current peak detection unit13B as well as the voltage peak detection unit14B, and to the determination unit15. In addition, the temperature measurement unit12measures the temperature of the secondary battery11and outputs the temperature to the determination unit15.

Next, the current peak detection unit13B holds the maximum value of the current at regular time intervals from the current measured by the current measurement unit13A, and outputs the maximum value to the determination unit15. In addition, the voltage peak detection unit14B holds the minimum value of the voltage at regular time intervals from the voltage measured by the voltage measurement unit14A, and outputs the minimum value thereof to the determination unit15.

The determination unit15inputs, to the neural network, the temperature measured by the temperature measurement unit12, the current measured by the current measurement unit13A, the voltage measured by the voltage measurement unit14A, the maximum current value held by the current peak detection unit13B, and the minimum voltage value held by the voltage peak detection unit14B as data to determine the presence or absence of the failure of the secondary battery11, and outputs a determination result to an external device by, for example, serial communication.

Hereinafter, an example of a configuration of a data collection system used for generating the learned model will be described according to an embodiment.

FIG.2is a block diagram illustrating an example of a configuration of a data collection system. The data collection system includes a data collection device20, a source measure unit31, a timed internal short-circuit cell32, and a control PC33. The data collection device20and the timed internal short-circuit cell32are connected by a cable. The data collection device20and the source measure unit31are connected by a cable. The control PC33and the data collection device20are connected by a cable such as a universal serial bus (USB). The control PC33and the source measure unit31are connected by a cable such as a general purpose interface bus (GPIB).

In an abnormality detection technique using machine learning, when only time series data in the normal time is used as teacher data, it is possible to determine as not normal, but it is not possible to determine whether it leads to a thermal runaway. In order to reliably determine that the thermal runaway occurs, it is necessary to prepare the time series data of a case where the thermal runaway occurs as the teacher data and to perform the learning using the data. Thereupon, the timed internal short-circuit cell32in which an internal short-circuit will soon occur is produced.

Furthermore, the timed internal short-circuit cell32is not obviously different from a commercially available lithium ion battery, but is a cell subjected to processing for causing an internal short-circuit at a predetermined intended timing. There are several preparation methods thereof, and a battery cell can be prepared by, for example, performing continuous charging, high temperature storage, overcharge cycle, or the like, or processing a short source inside the battery cell when assembling the battery cell. The timed internal short-circuit cell32is housed within a refractory chamber32A.

FIG.3is a block diagram illustrating an example of a configuration of the data collection device20. The data collection device20measures a charge/discharge current, the voltage, and the temperature of the timed internal short-circuit cell32. In addition, the data collection device20detects the minimum value and the maximum value of the current of the timed internal short-circuit cell32at regular time intervals and the minimum value and the maximum value of the voltage of the timed internal short-circuit cell32at regular time intervals.

The data collection device20includes a microcontroller21as a control device, a display device22, positive electrode terminals23A1,24A1,23B1, and24B1, negative electrode terminals23A2,24A2,23B2, and24B2, a current measurement unit25A, an upper peak hold circuit25B, a lower peak hold circuit25C, a voltage measurement unit26A, an upper peak hold circuit26B, a lower peak hold circuit26C, a thermocouple27A as a temperature detection element, a temperature measurement unit27B, a USB connector28A, and a USB serial converter28B.

The positive electrode terminal23A1and the positive electrode terminal24A1are connected to each other. The negative electrode terminal23A2and the negative electrode terminal24A2are connected to each other. The positive electrode terminal23A1and the negative electrode terminal23A2are connected to a positive electrode terminal and a negative electrode terminal of the timed internal short-circuit cell32respectively, and the positive electrode terminal24A1and the negative electrode terminal24A2are connected to a positive electrode terminal and a negative electrode terminal for current control of the source measure unit31respectively.

The positive electrode terminal23B1and the positive electrode terminal24B1are connected to each other. The negative electrode terminal23B2and the negative electrode terminal24B2are connected to each other. The positive electrode terminal23B1and the negative electrode terminal23B2are connected to a positive electrode terminal and a negative electrode terminal of the timed internal short-circuit cell32respectively, and the positive electrode terminal24B1and the negative electrode terminal24B2are connected to a positive electrode terminal and a negative electrode terminal for a voltage control of the source measure unit31respectively.

The current measurement unit25A measures a current flowing between the positive electrode terminal23A1and the positive electrode terminal24A1, and outputs the current to the upper peak hold circuit25B, the lower peak hold circuit25C, and the microcontroller21. The upper peak hold circuit25B holds the maximum current value at regular time intervals from the current measured by the current measurement unit25A, and outputs the maximum current value to the microcontroller21. The lower peak hold circuit25C holds a minimum current value at regular time intervals from the current measured by the current measurement unit25A, and outputs the minimum current value to the microcontroller21.

The voltage measurement unit26A measures a voltage applied between the positive electrode terminal23B1and the negative electrode terminal23B2, and outputs the voltage to the upper peak hold circuit26B, the lower peak hold circuit26C, and the microcontroller21. The upper peak hold circuit26B holds a maximum voltage value at regular time intervals from the voltage measured by the voltage measurement unit26A, and outputs the maximum voltage value to the microcontroller21. The lower peak hold circuit25C holds the minimum voltage value at regular time intervals from the voltage measured by the voltage measurement unit26A, and outputs the minimum voltage value to the microcontroller21.

The thermocouple27A is disposed on or near a surface of the timed internal short-circuit cell32. The temperature measurement unit27B measures the temperature of the timed internal short-circuit cell32by the thermocouple27A and outputs the temperature to the microcontroller21.

A USB connector28A is connected to the microcontroller21via a USB serial converter28B. A USB cable is connected to the USB connector28A. The data collection device20and the control PC33are connected via the USB cable.

The microcontroller21acquires a voltage, a current, a temperature, a minimum voltage value at regular time intervals, the maximum voltage value at regular time intervals, the minimum current value at regular time intervals, and the maximum current value at regular time intervals, and outputs the acquired values to the control PC33. The microcontroller21resets each of the upper peak hold circuits25B and26B and the lower peak hold circuits25C and26C at regular time intervals. Accordingly, it is possible to read the minimum current value, the maximum current value, the minimum voltage value, and the maximum voltage value at a regular period after a previous reset. The display device22displays information related to collected data and the like.

The data collection device20is configured to be able to measure, for example, a peak value of a peak having a half-value width of 1 μs or more with an accuracy of 5% or less. The data collection device20is equipped with a continuous data transmission function. This is a function of transmitting (1) the value (Present) at that time, (2) the maximum value (Upper) in the latest 500 milliseconds, and (3) the minimum value (Lower) at regular time intervals (for example, every 500 milliseconds) (seeFIG.4).

The source measure unit31charges and discharges the timed internal short-circuit cell32.

The control PC33controls the source measure unit31to charge and discharge the timed internal short-circuit cell32. Furthermore, the control PC33controls the data collection device20to collect data on the timed internal short-circuit cell32.

Hereinafter, an example of a data collection method using the data collection system having the configuration above will be described according to an embodiment.

The control PC33controls the source measure unit31to perform a cycle test of the timed internal short-circuit cell32. Charge conditions in the cycle test are, for example, 1C charge, and discharge conditions are, for example, a current pattern actually applied to the battery in the electric aircrafts. Then, the data collection device20measures time-series data of the current, the voltage, the temperature, the minimum current value, the maximum current value, the minimum voltage value, and the maximum voltage value until the timed internal short-circuit cell32reaches the thermal runaway. The control PC33collects the time-series data measured by the data collection device20. This charge-discharge cycle test is performed until the timed internal short-circuit cell32undergoes an exothermic runaway. This series of data collection is performed using, for example, 200 timed internal short-circuit cells32.

The time series data of the current, the voltage, the temperature, the minimum current value, the maximum current value, the minimum voltage value, and the maximum voltage value collected by the data collection device20is used as the teacher data by using a machine learning platform TensorFlow to create a neural network for abnormality detection.

A neural network created on TensorFlow using Renesas integrated development environment e2 studio is converted into a source code for a microprocessor, and the source code is written into the microprocessor. Then, in combination with the current measurement unit13A, the current peak detection unit13B, the voltage measurement unit14A, the voltage peak detection unit14B, and the temperature measurement unit12, the power supply device10(seeFIG.1) on which the learned neural network is mounted is prepared.

The power supply device10is configured to be able to output (1) how many seconds after which an abnormality occurs and (2) the percentage of certainty of the abnormality.

For example, specifically when a data acquisition interval of the power supply device10is every 500 milliseconds, in a case where the current peak detection unit13B and the voltage peak detection unit14B capable of detecting the peak value of the peak having the half-value width of 1 μs or more are provided, the current abnormality and the voltage abnormality can be detected in an early stage.

In learning and estimation of the neural network, not only voltage but also current and temperature information are used. Since a voltage waveform for determining the presence or absence of the failure of the secondary battery11depends on an internal resistance, and the internal resistance depends on the current and the temperature, more accurate determination can be made by using these three physical quantities.

It is possible to determine whether the battery is normal or abnormal by detecting an instantaneous voltage drop and a voltage behavior that recovers immediately thereafter. However, in the technique described in the Background section (e.g., Japanese Patent Application Laid-Open No. 2003-009405), particularly when a lithium ion battery is to be used as a battery for the electric aircrafts, there are insufficient points, for example, (1) a specific detection means for detecting a voltage waveform thereof; and (2) a specific determination means for determining an obtained waveform.

(1) With Respect to Detection Means

Regarding the instantaneous voltage drop caused by the dendrite generation and the voltage behavior that immediately recovers thereafter, paragraph 0045 of Japanese Patent Application Laid-Open No. 2003-009405 describes that voltage measurement is performed every several tens of milliseconds.

However, specifically when the interval of the voltage measurement is every several tens of milliseconds, it cannot be said that the interval is sufficiently fast. This is because, in the internal short circuit caused by the dendrite, to start with, an extremely thin dendrite is connected between the positive and negative electrodes to cause an internal short circuit, which fuses in an extremely short time, then a slightly thick dendrite is connected between the positive and negative electrodes to cause an internal short circuit, which fuses after a slightly long short circuit time, and then a slightly thicker dendrite is connected, so that the dendrite gradually becomes thicker, and the short circuit time gradually becomes longer. In other words, an earlier dendrite growth can be found, the more it is possible to measure the initial abnormal voltage behavior in an extremely short time. At a measurement interval of several tens of milliseconds, it is difficult to detect such initial dendrite generation, and when the dendrite generation can be detected, there is not much time left until the thermal runaway, and the dendrite generation is detected after a relatively late stage. How much time is needed depends on a use application of the battery. For example, in a battery for electric aircrafts, a time on an order of several tens of minutes at the minimum and a time on an order of several hours when possible are needed as a postponed time from the detection of the internal short circuit to a safe landing of the aircrafts. The measurement interval of every several tens of milliseconds was insufficient for such applications that particularly has high requirement for safety.

In order to be able to measure a high-speed current change and a voltage change that are much shorter than several tens of milliseconds, for example, there is a method of increasing a sampling frequency of an AD converter that reads current behavior and voltage behavior. However, attempting to perform high-speed sampling on a large number of batteries required to drive an electric aircraft would increase an overall cost of the system. In Japanese Patent Application Laid-Open No. 2003-009405, the detection means for preventing the increase in cost is not sufficiently devised.

On the other hand, the power supply device10according to an embodiment includes the current peak detection unit13B and the voltage peak detection unit14B in order to solve the problem above. The current peak detection unit13B and the voltage peak detection unit14B are circuits that continue to hold the maximum value and the minimum value at a regular time interval. Accordingly, this makes it possible to detect the minimum voltage value without increasing the sampling frequency of the AD converter specifically when the current rise or the voltage drop has a very narrow half-value width.

The current peak detection unit13B configured by a first peak hold circuit and the voltage peak detection unit14B configured by the second peak hold circuit can be relatively easily constructed by an analog circuit using a rectifier element, and the cost of the circuit can also be suppressed. This is particularly effective in a case where a large number of batteries such as in the electric aircrafts are used.

(2) With Respect to Determination Means

Next is a base voltage. Japanese Patent Application Laid-Open No. 2003-009405 describes a threshold voltage for determining that the detection value of the voltage detection unit has instantaneously dropped. However, a degree of a voltage minimal value of the voltage drop due to the micro-short circuit depends on the internal resistance of the battery, and the internal resistance depends on the degree of deterioration, the temperature, and the like. Therefore, when the base voltage is used as a determination reference, it is necessary to separately prepare a measurement means of the internal resistance of the battery and the like, and sequentially change the base voltage using an obtained internal resistance value. However, Japanese Patent Application Laid-Open No. 2003-009405, such discussion is not sufficiently made, and a scientific basis for determination criteria is insufficient.

On the other hand, in the power supply device10according to an embodiment, a neural network is used to solve the above problems. When the neural network is learned, not only voltage information but also current and temperature information are used. The internal resistance of the battery is a physical quantity dependent on the voltage, the current, and the temperature. Therefore, by using these three pieces of data for learning and estimation, more accurate determination based on the internal resistance can be made.

The data used for learning and estimation of the neural network is not limited to the three pieces of data of the voltage, the current, and the temperature. Data obtained by the current peak detection unit13B and the voltage peak detection unit14B is also used as information on the voltage rise and the voltage drop having a very narrow half-value width. Accordingly, a determination accuracy can be further improved.

In an embodiment described above, the power supply device10may not include the temperature measurement unit12. In this case, the data collection device20may not include the thermocouple27A and the temperature measurement unit27B.

In an embodiment described above, the power supply device10may not include the current measurement unit13A and the current peak detection unit13B. In this case, the data collection device20may not include the current measurement unit25A, the upper peak hold circuit25B, and the lower peak hold circuit25C.

In an embodiment described above, the power supply device10may not include the voltage measurement unit14A and the voltage peak detection unit14B. In this case, the data collection device20may not include the voltage measurement unit26A, the upper peak hold circuit26B, and the lower peak hold circuit26C.

In an embodiment described above, an example in which the power supply device10includes one secondary battery11and the data collection system includes one timed internal short-circuit cell32has been described. However, the power supply device10may include a plurality of secondary batteries11and the data collection system may include a plurality of timed internal short-circuit cells32. In this case, the current measurement unit13A of the power supply device10may measure the currents of the plurality of secondary batteries11connected, and the voltage measurement unit14A of the power supply device10may measure the voltage of each secondary battery11. In addition, the current measurement unit25A of the data collection device20may measure the currents of the plurality of timed internal short-circuit cells32connected, and the voltage measurement unit26A of the data collection device20may measure the voltage of each timed internal short-circuit cell32.

In an embodiment described above, an example in which the power supply device10includes the current measurement unit13A, the current peak detection unit13B, the voltage measurement unit14A, and the voltage peak detection unit14B has been described. However, the sampling frequency of the AD converter that reads the current behavior and the voltage behavior may be increased to detect the maximum current value and the minimum voltage value.

Although an embodiment including the modification examples of the present application have been described above, the present application is not limited thereto and various modifications can be made.

For example, the configurations, methods, steps, shapes, materials, numerical values, and the like described in an embodiment and modification examples described above are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, and the like may be used as necessary.

In addition, the configurations, methods, steps, shapes, materials, numerical values, and the like of an embodiment including modification examples described above can be combined with each other without departing from the present application.

DESCRIPTION OF REFERENCE SYMBOLS

10: Power supply device11: Secondary battery12,27B: Temperature measurement unit13A,25A: Current measurement unit13B: Current peak detection unit14A,26A: Voltage measurement unit14B: Voltage peak detection unit15: Determination unit16A,23A1,23B1,24A1,24B1: Positive electrode terminal16B,23A2,23B2,24A2,24B2: Negative electrode terminal20: Data collection device21: Microcontroller22: Display device25B,26B: Upper peak hold circuit25C,26C: Lower peak hold circuit27A: Thermocouple28A: USB connector28B: USB serial converter31: Source measure unit32: Timed internal short-circuit cell32A: Refractory chamber33: Control PC

It should be understood that various changes and modifications to the presently preferred embodiments herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.