JP2018063115A - Charged state estimation system for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate properly a SOC of even a secondary battery with a wide plateau region in a charged state estimation system for a secondary battery.SOLUTION: A charged state estimation system 10 for a secondary battery includes a battery state detection unit that detects a charge and discharge current I, an inter-terminal voltage V and a battery temperature θ relating to a secondary battery 20, a storage unit 40 and an estimation device 30. The estimation device 30 includes a battery state acquisition section 32 that acquires I, V, and θ, and an internal resistance calculation section 34 that calculates internal resistance R of the secondary battery 20 from I and V. The estimating device 30 further searches the storage unit 40 using the internal resistance R as a retrieval key, acquires a corresponding SOC in a first charged state characteristic indicating relations between the internal resistance R and the SOC, and includes a charged state estimation section 36 for estimating a SOC of the secondary battery 20 based on the corresponding SOC.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a charging state estimation system for a secondary battery.

  Since the secondary battery mounted on the vehicle is frequently charged and discharged as the vehicle travels, it is important to estimate the remaining capacity or the state of charge (SOC) that is in a charged state. One of the estimation methods is a method in which the relationship between the open circuit voltage (Voltage of Open Circuit: VOC) of the secondary battery and the SOC is obtained in advance and mapped, and the SOC corresponding to the VOC is obtained. The other is a method in which the charge / discharge current of the secondary battery from the initial state is integrated and added to the initial value of the SOC.

  Patent Document 1 states that olivine iron-based lithium-ion batteries are cheaper and safer than lithium-ion batteries that use cobalt-based electrode materials, and that the battery voltage has a broad plateau region that is almost constant with respect to SOC. ing. If the plateau region is wide, the region where the change in VOC is small becomes wide, and it is difficult to estimate the SOC by VOC. Therefore, in the vehicle running, SOC estimation is normally performed by integrating the charge / discharge current, but the integration error increases as the integration of the charge / discharge current continues. Therefore, it is disclosed that when the charge / discharge current integration period exceeds a predetermined limit period, the SOC is moved higher or lower to correct the integration error, and the SOC is estimated by VOC with less error. .

JP 2010-283922 A

  In the method for estimating the SOC, the VOC method requires the secondary battery to be in an open state, and the current-voltage characteristics of the secondary battery have hysteresis, so whether the VOC is charged or discharged. The corresponding SOC may be different. Although the method by integrating the charging / discharging current can be performed while charging / discharging the secondary battery, the integration of the charging / discharging current over a long period may cause an error in the estimation of the SOC. When charging / discharging current integration is performed over a long period of time, even if an attempt is made to correct appropriately by the VOC method, the secondary battery mounted on the vehicle is prevented from being overcharged or overdischarged so that the SOC is within a predetermined range. Since charging / discharging is limited, charging / discharging outside the plateau region may be difficult. Therefore, a secondary battery charge state estimation system that can appropriately estimate the SOC of a secondary battery having a wide plateau region is desired.

  A charging state estimation system for a secondary battery according to the present disclosure includes a battery state detection unit that detects a charging / discharging current, a voltage between terminals, and a battery temperature related to the secondary battery, and an internal resistance and a charging state of the secondary battery. The first charging state characteristic is a storage unit that stores the first charging state characteristic for each battery temperature, and an estimation device that estimates the charging state of the secondary battery. At the acquisition time, the battery state detection unit acquires the charge / discharge current, the voltage between terminals, and the battery temperature related to the secondary battery, and determines the internal resistance of the secondary battery from the acquired charge / discharge current and the voltage between the terminals. The storage unit is searched using the calculated internal resistance of the secondary battery as a search key, the corresponding charging state in the first charging state characteristic of the corresponding battery temperature is acquired, and the acquired corresponding charging state is one. In the first case, the response In the second case where the state is estimated as the charge state of the secondary battery and the two corresponding charge states are acquired, the charge / discharge current is acquired during a predetermined time range immediately before the predetermined acquisition time. An integrated value is obtained, and one of the two corresponding charged states is estimated as the charged state of the secondary battery based on whether the internal resistance increases or decreases as the integrated value increases.

  According to the above configuration, the internal resistance of the secondary battery is calculated from the current and voltage at the time of charge / discharge without estimating the state of charge (SOC) by integrating the charge / discharge current that may cause an integration error. The SOC is estimated using the relationship between the SOC and the SOC. Since the voltage fluctuation at the time of charging / discharging is larger than the voltage fluctuation at rest, compared to the method of estimating the state of charge using VOC which is an open circuit voltage, the estimation accuracy of the SOC is less affected by the error of the voltage detection means. Will improve.

  As for how the internal resistance changes as the SOC increases, it is not only a simple increase or decrease in the internal resistance, but also when the internal resistance increases once and then decreases. May decrease and then increase. If it is not a simple increase and a simple decrease, there will be two corresponding SOCs for one internal resistance, and it is not possible to specify one SOC only by calculating the internal resistance. Since the SOC is closely related to the integrated value of the charging / discharging current, when the internal resistance increases when the integrated value of the charging / discharging current increases, it corresponds to the increase of the internal resistance when the SOC increases. Conversely, when the internal resistance decreases when the integrated value of the charge / discharge current increases, this corresponds to a decrease in the internal resistance when the SOC increases. Using this relationship, when there are two corresponding SOCs for one internal resistance, one of the two corresponding SOCs is set based on whether the internal resistance increases or decreases as the integrated value increases. Estimated as the SOC of the secondary battery. Thereby, SOC can be estimated appropriately also about a secondary battery with a wide plateau area.

  Further, in the charging state estimation system for the secondary battery according to the present disclosure, the storage unit uses the relationship between the integrated value of the charging / discharging current from the initial value of the secondary battery and the charging state as the second charging state characteristic, The second charging state for each battery temperature is stored, and the estimation device estimates the first estimated charging state estimated based on the first charging state characteristic and the second estimated charging state estimated based on the second charging state characteristic. For the first term obtained by multiplying the first estimated charge state by a weighting factor determined based on any one of the charge / discharge current, the battery temperature, and the change rate of the internal resistance, 2 The second term multiplied by the estimated charge state is added to estimate the charge state of the secondary battery.

  According to the above configuration, the SOC of the secondary battery is calculated by using both the first estimated charge state estimated based on the internal resistance and the second estimated charge state estimated based on the integrated value of the charge / discharge current. presume. The estimation of the SOC based on the internal resistance is considered to have a relatively high estimation accuracy when the voltage fluctuation during charging and discharging is large. The voltage fluctuation during charging / discharging increases as the charging / discharging current increases, the battery temperature decreases, and the rate of change of internal resistance increases. Therefore, under the condition that the voltage fluctuation at the time of charging / discharging becomes large, by using a weighting factor that makes the contribution rate of the first estimated charge state higher than the contribution rate of the second estimated charge state, the SOC estimation accuracy is further increased. Can be improved.

  The secondary battery charge state estimation system according to the present disclosure can appropriately estimate the SOC even for a secondary battery having a wide plateau region.

It is a block diagram of the charge condition estimation system of the secondary battery which concerns on embodiment. It is a characteristic view which shows the relationship between SOC and VOC about the secondary battery to which the charge condition estimation system of the secondary battery which concerns on embodiment is applied suitably. It is a flowchart which shows the procedure of SOC estimation of the secondary battery in the charge condition estimation system of the secondary battery which concerns on embodiment. It is a figure which shows the example of the 1st charge condition characteristic memorize | stored in the memory | storage part of the charge condition estimation system of the secondary battery which concerns on embodiment. It is a figure which shows an example different from FIG. 4 about a 1st charge condition characteristic. FIG. 5A is a diagram corresponding to FIG. 4, and FIGS. 5B and 5C are relationships between the change in the integrated value of charge / discharge current and the change in internal resistance in B and C in FIG. 5, respectively. FIG. It is a figure which shows the example of the 2nd charge condition characteristic memorize | stored in the memory | storage part of the charge condition estimation system of the secondary battery which concerns on embodiment. The figure which shows four examples of the function form of the weighting coefficient regarding the magnitude of charging / discharging electric current when using together the 1st estimated charge state and the 2nd estimated charge state in the charge state estimation system of the secondary battery which concerns on embodiment. It is. In the charge state estimation system of the secondary battery which concerns on embodiment, it is a figure which shows four examples of the function form of the weighting coefficient regarding the height of battery temperature when using together a 1st estimated charge state and a 2nd estimated charge state. is there. FIG. 6 is a diagram illustrating an example of a function form of a weighting factor related to a rate of change in internal resistance when the first estimated charge state and the second estimated charge state are used in combination in the state estimation system of the secondary battery according to the embodiment. .

  Hereinafter, a charged state estimation system for a secondary battery according to an embodiment will be described in detail with reference to the drawings. Hereinafter, a secondary battery mounted on a hybrid vehicle will be described. However, this is an example for explanation, and any secondary battery in which a charge / discharge state frequently occurs may be used. For example, a stationary secondary battery It may be. Hereinafter, as a secondary battery, a lithium ion battery of a type in which a plateau region with a small change in VOC with respect to a change in SOC has a wide characteristic will be described, but this is an illustrative example. Any secondary battery that performs an operation in which the SOC control range for preventing overcharge and overdischarge is in the plateau region may be used. Below, the same code | symbol is attached | subjected to the same element in all the drawings, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a configuration diagram of a secondary battery charge state estimation system 10 according to the present embodiment. The secondary battery charging state estimation system 10 is a system that estimates the charging state of the secondary battery 20 mounted on the hybrid vehicle. Hereinafter, unless otherwise specified, the hybrid vehicle is simply referred to as a vehicle, and the secondary battery charge state estimation system 10 is referred to as an estimation system 10. The estimation system 10 includes a secondary battery 20, an estimation device 30, and a storage unit 40.

  Since the state of charge is referred to as SOC, in the following, “charged state” and “SOC” will be used as synonyms and described appropriately. For example, “estimated state of charge” is synonymous with “estimated SOC”, and “corresponding state of charge” is the same as “corresponding SOC”. However, the “charge state characteristics” are used as they are and are not called “SOC characteristics”.

  In FIG. 1, although not a component of the estimation system 10, an inverter 12 as a load of the secondary battery 20 and a rotating electrical machine 14 indicated by MG are illustrated. The inverter 12 is an AC / DC power conversion circuit provided between the secondary battery 20 and the rotating electrical machine 14. The inverter 12 converts the DC power discharged from the secondary battery 20 into AC power when the vehicle is running and supplies the AC power to the rotating electrical machine 14. When the vehicle is braking, the inverter 12 is AC that is regenerative energy of the rotating electrical machine 14. The secondary battery 20 is charged by converting electric power into DC power. The rotating electrical machine 14 is a motor / generator mounted on a vehicle, and is a three-phase synchronous rotating electrical machine that acts as an electric motor while the hybrid vehicle is traveling and acts as a generator when the vehicle is braked.

  The secondary battery 20 is an assembled battery in which a plurality of battery cells 22 are combined. As the battery cell 22, a lithium ion battery cell is used, and the secondary battery 20 is a lithium ion assembled battery. The cell voltage v which is a voltage between terminals of one battery cell 22 is about 3 to 4 V, and the secondary battery 20 is a high voltage which can output a predetermined high voltage and a large current by combining a plurality of them. It is a battery. An example of the voltage between the terminals of the secondary battery 20 is about 200 to 300V. In FIG. 1, the secondary battery 20 in which a plurality of battery cells 22 are connected in series is shown. However, the secondary battery 20 in which series connection and parallel connection are appropriately combined according to the output high voltage and large current specifications. It may be.

  FIG. 2 is a characteristic diagram showing the relationship between the SOC and VOC of the secondary battery 20. The horizontal axis is SOC, and the vertical axis is VOC. The secondary battery 20 has VOC = 0 V when SOC = 0%. However, as the SOC increases from 0%, the VOC also increases, and the VOC eventually saturates. Thereafter, even if the SOC increases, the VOC hardly changes and becomes a region called a plateau region. As the SOC further increases beyond the plateau region, the VOC also starts increasing, and reaches the maximum VOC when SOC = 100%. The hybrid vehicle controls charging / discharging of the secondary battery 20 while the vehicle is running so that the secondary battery 20 is not overcharged or overdischarged so that the SOC falls within a predetermined control range. An example of the SOC control range is about 30% to 80%. FIG. 2 shows the SOC control range, but the plateau region is wider than the SOC control range. In the plateau region, the SOC cannot be estimated based on the VOC. Therefore, the SOC is estimated by the charging / discharging current integration method. However, since the SOC control range during vehicle traveling is included in the plateau region, the SOC is estimated by the charging / discharging current integration method throughout the vehicle traveling. It will be. Since integration over a long period also accumulates errors, it is desired to correct with VOC as appropriate, but the area where the VOC method can be used on both sides of the plateau area is outside the SOC control range. In other words, when the vehicle is traveling and in the SOC control range, correction with VOC is difficult.

The following lithium ion batteries are known as the secondary battery 20 having the characteristic of having a wide plateau region including the SOC control range of the vehicle. It uses lithium iron phosphate (LiFePO ₄ ) or lithium manganate nickel oxide (LiMn _1.5 Ni _0.5 O ₄ ) as the positive electrode active material, and graphite or lithium titanate (Li ₄ Ti ₅ O ₁₂ ) as the negative electrode active material. It is what is used.

  Returning to FIG. 1, the cell voltage detection unit 23 is an assembly of a plurality of voltage detection means for detecting each cell voltage v of each battery cell 22. The voltage detection unit 24 is a voltage detection unit that detects the inter-terminal voltage V of the secondary battery 20 and is provided between the positive side bus and the negative side bus of the secondary battery 20 that is one assembled battery. The battery temperature detection unit 26 is a temperature detection unit that detects the battery temperature θ of each battery cell 22. Although the battery temperature detection unit 26 is provided for each battery cell 22, a predetermined number of the battery temperature detection units 26 may be provided over the entire secondary battery 20 in some cases. For example, you may provide in the three places of the both ends of the secondary battery 20, and an intermediate part. The charge / discharge current detection unit 28 is a current detection unit that detects the charge / discharge current I of the secondary battery 20, and is provided on the negative electrode bus of the secondary battery 20.

  The cell voltage detection unit 23, the voltage detection unit 24, the battery temperature detection unit 26, and the charge / discharge current detection unit 28 can be called a battery state detection unit for the secondary battery 20. The cell voltage v detected by the cell voltage detector 23, the inter-terminal voltage V of the secondary battery 20 detected by the voltage detector 24, the battery temperature θ detected by the battery temperature detector 26, and the charge / discharge current detector 28 detect. The charge / discharge current I is transmitted to the estimation device 30 via an appropriate signal line.

  The estimation device 30 is an arithmetic device that estimates the SOC of the secondary battery 20 having a wide plateau region as shown in FIG. As the estimation device 30, a computer suitable for mounting on a vehicle is used. The estimation device 30 may be an independent device, but may be included in another control device mounted on the vehicle. For example, the estimation device 30 may be included in a vehicle drive control device, a vehicle integrated control device, or the like.

  The estimation device 30 includes a battery state acquisition unit 32 that acquires the charge / discharge current I, the inter-terminal voltage V, and the battery temperature θ related to the secondary battery 20 from the battery state detection unit, and the charge / discharge current I and the inter-terminal voltage V. An internal resistance calculator 34 that calculates the internal resistance R of the secondary battery 20 is included. Furthermore, a charging state estimation unit 36 that estimates the SOC of the secondary battery 20 based on the internal resistance R is included. These functions of the estimation device 30 can be realized by the estimation device 30 executing software. Specifically, the estimation device 30 is realized by executing each processing procedure of the charging state estimation processing program. A part of the above functions may be realized by hardware.

  The storage unit 40 connected to the estimation device 30 is a memory that stores a program used in the estimation device 30 and temporarily stores a result of data processing. Here, several files used for estimating the SOC are stored. The first file 42 is a file in which the relationship between the internal resistance R and the SOC is the first charge state characteristic, and the first charge state characteristic is mapped for each battery temperature θ. The second file 44 is a file in which the relationship between the charge / discharge current integrated value ΣI and the SOC is set as the second charge state characteristic, and the first charge state characteristic is mapped for each battery temperature θ. The third file 46 is a first estimation when the state of charge is estimated using the first estimated SOC estimated based on the first state of charge characteristic and the second estimated SOC estimated based on the second state of charge characteristic. It is the file which mapped the weighting coefficient between SOC and 2nd estimation SOC.

  In the above description, the first file 42, the second file 44, and the third file 46 are mapped files. An example of a mapping file is a relationship map in the form of a lookup table. In addition to the mapping file, it may be a mathematical expression file. Alternatively, a ROM format in which an estimated value of SOC is output when an internal resistance R, a charge / discharge current integrated value ΣI, or the like is input may be used.

  The operation of the above configuration, in particular, each function of the estimation device 30 and the contents of each file stored in the storage unit 40 will be described in more detail with reference to FIGS.

  FIG. 3 is a flowchart showing a procedure for estimating the SOC of the secondary battery 20 in the estimation system 10. Each procedure corresponds to each processing procedure of the charging state estimation processing program. Since the secondary battery 20 has a wide plateau region, the SOC estimation based on the VOC cannot be performed, and the SOC control range is included in the plateau region. Therefore, if the SOC estimation based on the charge / discharge current integration is performed, the integration error Can occur, and it is difficult to use a VOC for correcting this. Therefore, the SOC is estimated using the relationship between the internal resistance R of the secondary battery 20 and the SOC. According to this method, the voltage fluctuation at the time of charging / discharging is larger than the voltage fluctuation at rest, so that it is less affected by the error of the voltage detection means than the method of estimating the SOC using the VOC which is an open circuit voltage. , SOC estimation accuracy is improved.

  The first of the SOC estimation procedures using the internal resistance R of the secondary battery 20 is acquisition of the charge / discharge current I, the voltage V between terminals, and the battery temperature θ (S10). This processing procedure is executed by the function of the battery state acquisition unit 32 of the estimation device 30. Specifically, the charging / discharging current I transmitted from the charging / discharging current detection unit 28, the inter-terminal voltage V of the secondary battery 20 transmitted from the voltage detection unit 24, and the battery temperature detection unit 26 are transmitted. Obtain the battery temperature θ. Since the secondary battery 20 is composed of a plurality of battery cells 22, it is preferable to obtain the cell voltage v of each battery cell 22 transmitted from the cell voltage detection unit 23. Let V be the cell voltage v of each battery cell 22.

  S10 is performed at a predetermined acquisition time. The predetermined acquisition time is a time for each predetermined acquisition cycle. The acquisition cycle is determined based on the SOC control cycle of the vehicle. When SOC control is always performed based on the latest estimated SOC, the SOC control cycle and the acquisition cycle of S10 are the same. As another example, when the estimated value of SOC is updated every 10 control cycles of SOC, the acquisition cycle of S10 is 10 times the SOC control cycle. The length of the above acquisition cycle is an example, and may be a length different from these.

  After S10, the internal resistance R of the secondary battery 20 is calculated from the obtained charge / discharge current I of the secondary battery 20 and the inter-terminal voltage V (S12). This processing procedure is executed by the function of the internal resistance calculation unit 34 of the estimation device 30. Specifically, the internal resistance R is calculated using the formula of internal resistance R = {(terminal voltage V) / (charge / discharge current I)}. Hereinafter, depending on the case, the internal resistance R is simply indicated as R.

Calculated internal resistance R when the R _1, searches the first state of charge characteristics of the first file 42 of the storage unit 40 a R = R ₁ as a search key (S14). Then, the corresponding SOC at the corresponding battery temperature θ is acquired. The first charge state characteristic is a characteristic that indicates a change in SOC with respect to a change in R. The secondary battery 20 has different first charge state characteristics depending on whether the type of the battery is different, or even if the type is the same, the change with time is different.

  Representative examples of the first charge state characteristics are shown in FIGS. 4 and 5A. In these figures, the horizontal axis is SOC, and the vertical axis is R. A characteristic 50 in FIG. 4 is a characteristic in which R simply increases as the SOC increases. A characteristic 52 in FIG. 5A is a characteristic having an upward convex function shape in the R-SOC plane, with R increasing and then increasing as the SOC increases. Although the characteristics 50 and 52 vary depending on the battery temperature θ, FIGS. 4 and 5A show the characteristics 50 and 52 under the condition of the battery temperature θ acquired in S10. In the following, although not particularly noted, the charge state characteristics such as the first charge state characteristic and the estimated SOC are under the battery temperature θ acquired in S10.

Since the internal resistance R = R ₁ calculated in S12 is shown, when a straight line R = R ₁ is drawn in FIG. 4, only one of the points A intersects with the characteristic 50, and the corresponding SOC at the point A is , SOC (A). On the other hand, with respect to FIG. 5A, when a straight line of R = R ₁ is drawn, two points B and C intersect with the characteristic 52. The corresponding SOC at point B is SOC (B), and the corresponding SOC at point C is SOC (B).

Thus, when the first charge state characteristic is a characteristic in which R is simply increased with respect to an increase in SOC, such as characteristic 50, since there is only one corresponding SOC when R = R ₁ is given, the SOC Can be estimated. Contrary to the characteristic 50, the same applies to the case where the first charge state characteristic is a characteristic in which R simply decreases as the SOC increases. On the other hand, in the case where the first charge state characteristic is a characteristic having a downward convex function shape in the R-SOC plane, such as the characteristic 52, if R = R ₁ is given, two corresponding SOCs appear. Then, the SOC cannot be estimated. In this case, it is necessary to specify which of the two corresponding SOCs is an appropriate estimated SOC. Contrary to the characteristic 52, the same applies to the case where the first state-of-charge characteristic has an upward convex function shape on the R-SOC plane.

Returning to FIG. 3, after searching for the first state-of-charge characteristic using R = R ₁ as a search key in S 14, it is determined whether or not the searched corresponding SOC is two instead of one (S 16). When the determination is negative, the retrieved corresponding SOC is one, and the corresponding SOC is estimated as the SOC of the secondary battery 20. This corresponds to the example of FIG. 4, and the retrieved SOC (A), which is one corresponding SOC, is estimated as the SOC of the secondary battery 20. Since the estimated SOC is the SOC estimated from the first charge state characteristic, it is referred to as a first estimated SOC (S20).

If the determination in S16 is affirmative, in order to identify which of the two corresponding SOCs is an appropriate estimated SOC, the relationship between the previous charge / discharge current integrated value ΣI and R is confirmed (S18). ). Since the SOC is closely related to the integrated value ΣI of the charge / discharge current, if the internal resistance R increases when the integrated value ΣI of the charge / discharge current increases, the internal resistance R increases when the SOC increases. It corresponds to. Conversely, when the internal resistance R decreases when the integrated value ΣI of the charge / discharge current increases, this corresponds to a decrease in the internal resistance R when the SOC increases. Using this relationship, when there are two corresponding SOCs for one internal resistance R = R ₁ , 2 is determined based on whether the internal resistance R increases or decreases with an increase in the integrated value ΣI of the charge / discharge current. Any one of the two corresponding SOCs is estimated as the SOC of the secondary battery 20.

  FIG. 5B and FIG. 5C show the relationship between the immediately preceding ΣI and R for each of the two corresponding SOCs, SOC (B) and SOC (C). 5B and 5C, the horizontal axis is ΣI, and the vertical axis is R. The immediately preceding ΣI is a value obtained by acquiring and integrating the charge / discharge current I during a predetermined time range immediately before the acquisition timing at which I, V, θ is acquired in S10. Since the acquisition of I, V, and θ is repeated at the acquisition cycle, the predetermined time range is a time range corresponding to the predetermined number of acquisition cycles. ΣI in the example of FIG. 6 goes back six acquisition cycles from the acquisition time at which I, V, θ was acquired at S10, and from there until the acquisition time at which I, V, θ was acquired at S10. Is obtained and the value obtained by integrating it. Going back six acquisition cycles is an example for explanation, and the number of acquisition cycles going back can be determined within a range where the integration error does not become so large. As an example, it can be in the range of 5 acquisition cycles to 10 acquisition cycles. ΣI over a long period has a large integration error. However, since ΣI in S18 is a short period of, for example, about 5 to 10 times the acquisition cycle, there is almost no integration error.

Since FIG. 5B relates to the point B where the internal resistance R decreases when the SOC increases, the internal resistance R decreases as the integrated value ΣI of the charge / discharge current increases. (C) relates to the point C at which the internal resistance R increases when the SOC increases, so that the internal resistance R increases as the integrated value ΣI of the charge / discharge current increases. Using this relationship, when two corresponding SOCs appear when R = R ₁ is given, the relationship between the charge / discharge current integrated value ΣI and R immediately before that is confirmed, and FIG. If so, the SOC (B) corresponding to the point B is an appropriate estimated SOC. On the contrary, when the relationship between the confirmed integrated value ΣI and R is the relationship of FIG. 5C, the SOC (C) corresponding to the point C is an appropriate estimated SOC. In this way, one of the two corresponding SOCs is identified as an appropriate estimated SOC. Since the estimated SOC is the SOC estimated based on the first charge state characteristic, it is the first estimated SOC (S20).

  Since there is a method for estimating the SOC in addition to the first charge state characteristic, the first estimated SOC is appropriately corrected in consideration of the SOC estimated by them to improve the estimation accuracy of the SOC of the secondary battery 20. be able to. Therefore, after S20, it is determined whether or not the SOC estimation accuracy is further improved (S22). Although this determination may be performed by the user, it is preferable to perform determination using a determination criterion predetermined by the estimation device 30. For example, based on the transition of the first estimated SOC estimated for each acquisition cycle, the determination in S22 is affirmed when the transition variation exceeds a predetermined variation.

  When the determination in S22 is negative, since the estimation accuracy of the first estimated SOC is sufficient for the SOC control, the first estimated SOC is estimated as the SOC of the secondary battery 20 (S32). When the determination in S22 is affirmative, an estimated SOC different from the first estimated SOC is obtained using another SOC estimation method of the first charge state characteristic. As another SOC estimation method of the first charge state characteristic, there is a method based on VOC, but as described with reference to FIG. 2, the secondary battery 20 having a wide plateau region is not very appropriate. Another method is a method of estimating the SOC based on the integrated value ΣI of the charge / discharge current. Here, the relationship between the integrated value ΣI of the charge / discharge current and the SOC is used as the second charge state characteristic, and the SOC estimated based on this is used.

FIG. 6 is a diagram illustrating an example of the second charge state characteristic. The horizontal axis is the integrated value ΣI of the charge / discharge current, and the vertical axis is the SOC. The characteristic 54 has SOC ₀ that is the SOC in the initial state as an initial value, and the SOC gradually increases as ΣI from the initial state increases. The second charge state characteristic is obtained in advance and stored in the second file 44 of the storage unit 40.

The initial value SOC ₀ can be the SOC at the start of vehicle operation. For example, the SOC is estimated based on the VOC of the secondary battery 20 at the time when the start switch such as an ignition switch is turned on in the vehicle, and this is set as SOC ₀ . From this point, S10 acquires I, V, and θ at a predetermined acquisition cycle. Since the acquired I, V, and θ are sequentially stored in a battery state data file (not shown) of the storage unit 40, ΣI in each acquisition cycle is calculated using the data (S24).

If the calculated integrated value of the charge / discharge current is (ΣI) ₁ , the second charge state characteristic of the second file 44 in the storage unit 40 is searched using ΣI = (ΣI) ₁ as a search key (S26). Then, the corresponding SOC at the corresponding battery temperature θ is acquired. When the characteristic 54 of FIG. 6 is used, the SOC of the point D that intersects the characteristic 54 by drawing a straight line of ΣI = (ΣI) ₁ is the corresponding SOC (D). This is referred to as a second estimated SOC as the estimated SOC based on the second state of charge characteristic (S28).

  When the second estimated SOC is obtained, next, weighted addition is performed with the first estimated SOC (S30), and the result is set as the estimated SOC of the secondary battery 20 (S32).

  The weighted addition in S30 is performed as follows using the weighting factor k. The weighting factor k is a value between 0 and 1. That is, the first estimated SOC of S20 is multiplied by k to be the first term, the second estimated SOC of S28 is multiplied by (1-k) to be the second term, and the first and second terms are added. To do. The added result is the estimated SOC of the secondary battery 20.

  The weighting factor k can be determined based on the characteristics of the SOC estimation based on the internal resistance R. In the estimation of the SOC based on the internal resistance R, it is considered that the estimation accuracy is relatively high when the voltage fluctuation during charging / discharging is large. The voltage fluctuation during charging / discharging increases as the charging / discharging current I increases, the battery temperature θ decreases, and the change rate ΔR of the internal resistance R increases. Therefore, the weighting factor k is determined so that the contribution rate of the first estimated SOC is higher than the contribution rate of the second estimated SOC under the condition that the voltage fluctuation during charging / discharging becomes large.

  FIG. 7 is a diagram showing four examples of the function form of the weighting coefficient k relating to the magnitude of the charging / discharging current I. In these figures, the horizontal axis is the charge / discharge current I, and the vertical axis is the weighting factor k. In FIG. 7A, the function form f1 of the weighting coefficient k increases and decreases linearly with respect to the increase and decrease of the charge / discharge current I. The function form f2 of (b) increases / decreases by a square to the increase / decrease of the charge / discharge current I. The function form f3 of (c) increases and decreases exponentially with the increase and decrease of the charge / discharge current I. The function form f4 of (d) increases or decreases stepwise with respect to the increase / decrease of the charge / discharge current I. Which function form is appropriate can be determined by experiments or the like. In any function form, the weight coefficient k increases as the charge / discharge current I increases, and the contribution rate of the first estimated SOC in the estimated SOC of the secondary battery 20 increases.

  FIG. 8 is a diagram illustrating four examples of the function form of the weight coefficient k relating to the level of the battery temperature θ. In these figures, the horizontal axis is the battery temperature θ, and the vertical axis is the weighting factor k. In FIG. 8A, the function form g1 of the weighting factor k increases linearly as the battery temperature θ decreases. The function form g2 of (b) increases inversely as the battery temperature θ decreases. The function form g3 in (c) increases exponentially as the battery temperature θ decreases. The function form g4 of (d) increases stepwise when the battery temperature θ becomes low. Which function form is appropriate can be determined by experiments or the like. In any function form, the weight coefficient k increases as the battery temperature θ decreases, and the contribution rate of the first estimated SOC in the estimated SOC of the secondary battery 20 increases.

  FIG. 9 is a diagram illustrating an example of a function form of the weighting coefficient k regarding the change rate ΔR of the internal resistance R. The horizontal axis is the rate of change ΔR of the internal resistance R, and the vertical axis is the weighting factor k. The function form h1 in FIG. 8 increases as ΔR increases. That is, as the change rate of the internal resistance R is larger, the weighting coefficient k is increased, and the contribution rate of the first estimated SOC in the estimated SOC of the secondary battery 20 is increased.

  Thus, in the combined use of the first estimated SOC and the second estimated SOC, by using an appropriate weighting factor k, the SOC estimation accuracy of the secondary battery 20 is further improved.

  The secondary battery charge state estimation system 10 according to the present embodiment includes a battery state detection unit that detects a charge / discharge current I, a voltage V between terminals, and a battery temperature θ related to the secondary battery 20. Furthermore, the relationship between the internal resistance R of the secondary battery 20 and the SOC that is the charged state is defined as a first charged state characteristic, and the storage unit 40 that stores the first charged state characteristic for each battery temperature θ, and the secondary battery And an estimation device 30 that estimates the SOC, which is 20 charged states. The estimation device 30 acquires the charge / discharge current I, the voltage V between terminals, and the battery temperature θ related to the secondary battery 20 from the battery state detection unit, and the acquired charge / discharge current I and voltage V between the terminals of the secondary battery 20. To calculate the internal resistance R of the secondary battery. Then, the storage unit 40 is searched using the calculated internal resistance R of the secondary battery 20 as a search key, and the corresponding SOC that is the corresponding charging state in the first charging state characteristic of the corresponding battery temperature θ is obtained. In the first case where the acquired corresponding charging state is one, the corresponding charging state is estimated as the SOC that is the charging state of the secondary battery 20. In the second case where there are two corresponding SOCs that are the acquired corresponding charging states, the charging / discharging current I is acquired within a predetermined time range from that time, and the integrated value ΣI is obtained. Then, based on whether the internal resistance R increases or decreases as the integrated value ΣI increases, one of the two corresponding charged states is estimated as the SOC that is the charged state of the secondary battery 20.

  10 (charged state of secondary battery) estimation system, 12 inverter, 14 rotating electrical machine, 20 secondary battery, 22 battery cell, 23 cell voltage detector, 24 voltage detector, 26 battery temperature detector, 28 charge / discharge current detection Unit, 30 estimation device, 32 battery state acquisition unit, 34 internal resistance calculation unit, 36 charge state estimation unit, 40 storage unit, 42 first file, 44 second file, 46 third file, 50, 52, 54 characteristics.

Claims (2)

A battery state detection unit for detecting a charge / discharge current, a voltage between terminals, and a battery temperature related to the secondary battery;
A storage unit that stores a first charge state characteristic for each of the battery temperatures, with a relationship between an internal resistance and a charge state of the secondary battery as a first charge state characteristic;
An estimation device for estimating the state of charge of the secondary battery;
With
The estimation device includes:
Obtaining the charge / discharge current, the voltage between the terminals, and the battery temperature related to the secondary battery from the battery state detection unit at a predetermined acquisition time set in advance;
The internal resistance of the secondary battery is calculated from the charge / discharge current of the acquired secondary battery and the inter-terminal voltage,
Search the storage unit using the calculated internal resistance of the secondary battery as a search key, and obtain a corresponding charge state in the first charge state characteristic of the corresponding battery temperature;
In the first case where the acquired corresponding charging state is one, the corresponding charging state is estimated as the charging state of the secondary battery,
In the second case where the acquired two corresponding charging states are obtained, the charge / discharge current is acquired during a predetermined time range immediately before the predetermined acquisition time, and the integrated value is obtained. A charging state estimation system for a secondary battery, wherein one of two corresponding charging states is estimated as the charging state of the secondary battery based on whether the internal resistance increases or decreases with increasing. The storage unit
The relationship between the integrated value of the charge / discharge current from the initial value of the secondary battery and the state of charge is a second state of charge characteristic, the second state of charge for each battery temperature is stored,
The estimation device includes:
For the first estimated charge state estimated based on the first charge state characteristic and the second estimated charge state estimated based on the second charge state characteristic, the charge / discharge current, the battery temperature, the internal A first term obtained by multiplying the first estimated charging state by a weighting factor determined based on any one of the resistance change rates, and a second term obtained by multiplying the second estimated charging state by (1-weighting factor). The charging state estimation system of the secondary battery according to claim 1, wherein the charging state of the secondary battery is estimated by adding the terms.

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