Method and apparatus for diagnosing battery cell

Abstract

The present application provides a kind of battery unit diagnostic method and diagnostic device capable of mastering internal state per battery unit. Battery pack in the state that multiple battery units are not charged and discharged, multiple battery units are warmed up by ripple current, resistance values under multiple frequencies are calculated, based on the relationship information indicating the relationship between the resistance values at the time of pre-acquired alternating current impedance and the frequency of positive electrode resistance reaction region and the frequency of negative electrode resistance reaction region, and the calculated resistance values, positive electrode resistance value and negative electrode resistance value are estimated, and based on the positive electrode resistance value and the negative electrode resistance value, the state of each of multiple battery units is diagnosed.

Description

Technical Field

[0001] This invention relates to a diagnostic method and device for battery cells. Background Technology

[0002] Patent Document 1 discloses a technology for an internal resistance estimation device, which estimates the internal resistance of the energy storage device based on the ripple current detected by a current detection unit connected to the energy storage device, the temperature detected by a temperature detection unit, and the correlation between the ripple current and the temperature stored in the storage unit.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2011-122835 Summary of the Invention

[0004] In Patent Document 1, the positive and negative resistances of the energy storage device change due to deterioration, making it difficult to predict the resistance values ​​of the positive and negative electrodes based on the relationship between frequency and internal resistance, leaving room for improvement.

[0005] The present invention was made in view of the above, and its object is to provide a diagnostic method and diagnostic device for battery cells that can grasp the internal state of each battery cell.

[0006] The battery cell diagnostic method of the present invention involves, in a state where multiple battery cells are not charged or discharged, heating the multiple battery cells by means of ripple current, calculating resistance values ​​at multiple frequencies, estimating positive and negative resistance values ​​based on the relationship information between the resistance values ​​representing the pre-acquired AC impedance and the frequencies of the positive and negative resistance reaction regions, and the calculated resistance values, and diagnosing the state of each of the multiple battery cells based on the positive and negative resistance values.

[0007] Furthermore, the diagnostic device according to the present invention comprises: a battery pack consisting of multiple battery cells; a ripple generating device that heats the multiple battery cells by supplying a ripple current to the multiple battery cells when the multiple battery cells are not charged or discharged; a voltage detection device that detects the voltage of the multiple battery cells when the multiple battery cells are heated; a relationship information recording unit that records relationship information indicating the relationship between the resistance value at a pre-acquired AC impedance and the frequency of the positive electrode resistance response region and the frequency of the negative electrode resistance response region; and a control device that performs the following processing: heating the multiple battery cells by the ripple current when the multiple battery cells are not charged or discharged, calculating the resistance value at multiple frequencies, estimating the positive electrode resistance value and the negative electrode resistance value based on the relationship information and the calculated resistance value, and diagnosing the state of each of the multiple battery cells based on the positive electrode resistance value and the negative electrode resistance value.

[0008] Invention Effects

[0009] According to the present invention, it is possible to understand the internal state of each battery cell. Attached Figure Description

[0010] Figure 1 This is a diagram showing a schematic structure of a diagnostic device according to an embodiment of the present invention.

[0011] Figure 2 This is a graph showing the relationship between the resistance value under AC impedance and the resistance value under ripple current in the relational information recorded by the relational information recording unit of the diagnostic device according to an embodiment of the present invention.

[0012] Figure 3 This is a flowchart illustrating the process of an on-board battery cell diagnostic method performed by a control device according to an embodiment of the present invention.

[0013] Figure 4 This is a graph showing the relationship between the resistance value calculated by the control device of the diagnostic device according to an embodiment of the present invention and the resistance value when AC impedance is applied. Detailed Implementation

[0014] Hereinafter, a diagnostic method and diagnostic apparatus for a battery cell according to an embodiment of the present invention will be described with reference to the accompanying drawings. Furthermore, the constituent elements in the following embodiments include constituent elements that can be substituted and easily implemented by those skilled in the art, or substantially the same constituent elements.

[0015] [Structure of the diagnostic device]

[0016] Figure 1 This is a diagram showing a schematic structure of a diagnostic device according to an embodiment of the present invention. Figure 1 The diagnostic device 1 shown includes a secondary battery 10, a ripple generating device 20, a voltage detection device 30, a relational information recording unit 40, and a control device 50.

[0017] The secondary battery 10 is a battery pack composed of multiple battery cells 11 and is mounted in a vehicle. The secondary battery 10 is constructed using rechargeable batteries such as lithium-ion batteries or nickel-metal hydride batteries. Furthermore, the secondary battery 10 has an internal resistance 12. This internal resistance 12 is temperature-dependent and exhibits a characteristic that varies significantly depending on the frequency of the current flowing through the secondary battery 10.

[0018] The ripple generating device 20 is electrically connected to the secondary battery 10. Under the control of the control device 50, the ripple generating device 20 causes the secondary battery 10 to generate a ripple current of a predetermined frequency. Specifically, the ripple generating device 20 causes the secondary battery 10 to heat up internally (ripple heating) by generating a ripple current. The ripple generating device 20 is constructed using at least one power semiconductor switching element, and under the control of the control device 50, it causes the secondary battery 10 to generate a ripple current by switching the power semiconductor switching element on or off.

[0019] The voltage detection device 30 is constructed using a voltage sensor and the like, detects the voltage of the secondary battery 10, and outputs the detection result to the control device 50.

[0020] The relationship information recording unit 40 records, for each battery cell 11, relationship information relating the resistance value at the pre-acquired AC impedance to the frequency of the positive electrode resistance reaction region and the frequency of the negative electrode resistance reaction region. Figure 2 This is a graph showing the relationship between the resistance value under AC impedance and the resistance value under ripple current in the relational information recorded by the relational information recording unit 40. Figure 2 In the diagram, the vertical axis represents the resistance value ([Z][Ω]) at AC impedance, and the horizontal axis represents the frequency (Hz). Furthermore, in... Figure 2 In the diagram, curve L1 represents the resistance value caused by AC impedance (weak current), straight line D1 represents the positive electrode DC resistance reaction region, and straight line D2 represents the negative electrode DC resistance reaction region. Furthermore, from the viewpoint of the safety or durability of the capacitor constituting the ripple generating device 20, the heat generation Q of the secondary battery 10 is described under the condition that the self-heating (operating temperature) is within 20 degrees Celsius. In addition, in Figure 2 The image shows an example of the relationship between the resistance value of a battery cell 11 at AC impedance and the frequency of the positive electrode resistance reaction region and the frequency of the negative electrode resistance reaction region.

[0021] like Figure 2 As shown by curve L1, the resistance value at AC impedance is correlated with frequency. Furthermore, as shown by lines D1 and D2, the resistance values ​​of the positive and negative DC resistance response regions of battery cell 11 at each frequency are correlated. Additionally, in Figure 2 In this example, for each state of charge (SOC), temperature, cell design factor tolerance (weight or density per unit area, etc.) and degradation state of battery cell 11, data of the positive electrode DC resistance reaction region and the negative electrode DC resistance reaction region are obtained in advance as relational information and recorded in the relational information recording unit 40.

[0022] return Figure 1 The structure of diagnostic device 1 will be further explained.

[0023] The control device 50 is constructed using hardware such as a memory and a central processing unit (CPU). The control device 50 generates ripple current in the secondary battery 10 by controlling the ripple generating device 20, thereby causing the secondary battery 10 to heat up internally. Specifically, the ripple generating device 20 is controlled based on the frequency characteristics of the impedance of the secondary battery 10, in a manner that generates ripple current in the frequency region where the absolute value of the impedance of the secondary battery 10 is relatively lower.

[0024] Here, the heat generated by the secondary battery 10 when the ripple current flows through it will be explained. When the heat generated by the secondary battery 10 is set to Q, the ripple current is set to I, and the resistance value of the internal resistor 12 is set to R, the following equation (1) holds.

[0025] Q=I 2 ×R……(1)

[0026] By using equation (1), the control device 50 can further increase the temperature of the secondary battery 10 by increasing the ripple current I generated by the ripple generating device 20.

[0027] Furthermore, the control device 50 controls the ripple generating device 20 when the multiple battery cells 11 are not being charged or discharged, thereby raising the temperature of the multiple battery cells 11 through the ripple current of the ripple generating device 20 and calculating the resistance values ​​at multiple frequencies. Then, the control device 50 estimates the positive electrode resistance value and the negative electrode resistance value based on the relationship information recorded by the relationship information recording unit 40 and the resistance value calculated therefrom, and diagnoses the state of each of the multiple battery cells 11 based on the positive electrode resistance value and the negative electrode resistance value.

[0028] [Diagnostic methods for vehicle battery cells]

[0029] Next, the diagnostic process for the on-board battery cell executed by the control device 50 will be explained. Figure 3 This is a flowchart outlining the process of the on-board battery cell diagnostic method executed by the control device 50.

[0030] like Figure 3As shown, firstly, the control device 50 controls the ripple generating device 20 to heat up the secondary battery 10 while the multiple battery cells 11 of the secondary battery 10 are not being charged or discharged. The control device 50 then acquires the voltage (voltage fluctuation) at each frequency of the multiple battery cells 11 of the secondary battery 10 during the heating process, as detected by the voltage detection device 30 (step S101). Here, the state where the multiple battery cells 11 of the secondary battery 10 are not being charged or discharged refers to the state where the vehicle equipped with the secondary battery 10 is stationary.

[0031] Next, the control device 50 calculates the resistance value based on the voltage of each frequency of the plurality of battery cells 11 of the secondary battery 10 obtained from the voltage detection device 30 (step S102). Specifically, the control device 50 calculates the resistance value (voltage ÷ (amplitude / 2)) by dividing the voltage of the battery cells 11 obtained from the voltage detection device 30 by 2. Figure 4 As shown in curve L2, the control device 50 calculates the resistance value based on the voltage change under ripple current (high current) at each frequency. Here, each frequency is, for example, 100Hz, 500Hz, 10000Hz, etc.

[0032] Then, the control device 50 checks the resistance value calculated in step S102 against the relationship information recorded by the relationship information recording unit 40 (step S103). Specifically, the control device 50 checks the relationship information of each battery cell 11 recorded by the relationship information recording unit 40 to see if the characteristics of the resistance value calculated in step S102 at each frequency are consistent with the characteristics of the resistance value based on AC impedance (weak current). For example, in Figure 4 In the case shown, the control device 50 checks whether the relationship information with the characteristics of curve L1 is consistent with the characteristics of curve L2 (curve characteristics) based on the characteristics of curve L2.

[0033] Next, the control device 50 estimates the positive and negative resistance values ​​based on the relationship information recorded by the relationship information recording unit 40 and the resistance value calculated in step S102 (step S104). Specifically, the control device 50 estimates the positive and negative resistance values ​​based on the relationship information recorded by the relationship information recording unit 40 and the resistance value calculated in step S102. Figure 4 Curve L1 is used to establish the corresponding positive electrode DC resistance response regions of straight line D1 and straight line D2 to estimate the positive and negative electrode resistance values ​​of battery cell 11. Figure 4 In the case shown, the control device 50 estimates the positive resistance value as 15 ([Z][Ω]) and the negative resistance value as 10 ([Z][Ω]).

[0034] Then, based on the positive and negative electrode resistance values ​​of the battery cell 11 estimated in step S104, the control device 50 diagnoses the state of the battery cell 11 (step S105) and performs optimization for each battery cell (step S106). Specifically, based on the positive and negative electrode resistance values ​​of the battery cell 11, the control device 50 diagnoses the degree of positive electrode degradation of the battery cell 11 as the state of the battery cell 11 and performs optimization to homogenize the energy capacity of each of the multiple battery cells 11. Thus, by separating the negative electrode resistance value of the battery cell 11, the control device 50 can predict the negative electrode potential and optimize the charging current value used to control the battery cell 11. Moreover, by separating the positive electrode resistance value of the battery cell 11, the control device 50 can estimate the degree of positive electrode degradation and optimize the safety control and Li deposition control corresponding to the degradation state. After step S106, the control device 50 ends this process.

[0035] According to one embodiment described above, the control device 50 estimates the positive and negative resistance values ​​based on the relationship information between the resistance value representing the pre-acquired AC impedance and the frequency of the positive and negative resistance reaction regions, and the resistance values ​​calculated at multiple frequencies by heating the multiple battery cells 11 with ripple current when the multiple battery cells 11 are not charged or discharged. Based on these positive and negative resistance values, the control device 50 diagnoses the state of each of the multiple battery cells 11, thus enabling it to grasp the internal state of each battery cell 11.

[0036] Furthermore, according to one embodiment, by separating the positive electrode resistance value of the battery cell 11, the amount of positive electrode degradation can be estimated, and safety control corresponding to the degradation state can be implemented.

[0037] Further effects or variations can be readily derived by those skilled in the art. The invention is not limited to the specific details and representative embodiments shown and described above. Therefore, various modifications can be made without departing from the spirit or scope of the general invention as defined by the appended claims and their equivalents.

[0038] The above description of several embodiments of the present application is based on the accompanying drawings. However, these are merely illustrative examples. Based on the methods described in the disclosure section of the present invention, various modifications and improvements can be implemented in other ways based on the knowledge of those skilled in the art.

[0039] Symbol Explanation

[0040] 1-Diagnostic device, 10-Secondary battery, 20-Ripple generating device, 30-Voltage detection device, 40-Relationship information recording unit, 50-Control device, 11-Battery unit.

Claims

1. A method for diagnosing a battery cell, characterized in that, With multiple battery cells not being charged or discharged, the cells are heated by ripple current, and the resistance values ​​at multiple frequencies are calculated. Based on the relationship information between the resistance value representing the pre-obtained AC impedance and the frequencies of the positive and negative electrode resistance response regions, and the calculated resistance values, the positive and negative electrode resistance values ​​are estimated. Based on the positive electrode resistance value and the negative electrode resistance value, the state of each of the plurality of battery cells is diagnosed.

2. The diagnostic method for a battery cell according to claim 1, characterized in that, The state in which the multiple battery cells are not being charged or discharged is the state in which the vehicle is stationary.

3. The diagnostic method for a battery cell according to claim 1, characterized in that, Based on the diagnosed states of the plurality of battery cells, optimization is performed to homogenize the energy capacity of each of the plurality of battery cells.

4. A diagnostic device, characterized in that, have: A battery pack, which consists of multiple battery cells; A ripple generating device that heats up the plurality of battery cells by supplying ripple current to the plurality of battery cells when the plurality of battery cells are not being charged or discharged. A voltage detection device that detects the voltage of the plurality of battery cells when the plurality of battery cells are heated; The relationship information recording unit records relationship information indicating the relationship between the resistance value at the pre-acquired AC impedance and the frequencies of the positive and negative electrode resistance response regions; and Control device, The control device performs the following processing: With the battery cells not being charged or discharged, the ripple current is used to heat the battery cells, and the resistance values ​​at multiple frequencies are calculated. Based on the aforementioned relationship information and the calculated resistance values, the positive and negative electrode resistance values ​​are estimated. Based on the positive electrode resistance value and the negative electrode resistance value, the state of each of the plurality of battery cells is diagnosed.

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