Battery system

Abstract

An ECU of a battery system according to the present invention executes a process including: a step of acquiring a parameter; a step for calculating an integrated value (Q1) of the charging current when it is not determined that the step has been detected; a step of acquiring a battery temperature of each single battery when it is determined that the step has been detected; a step for calculating an integrated value (Q2) of the charging current until the charging is completed; a step for calculating a correction factor (C) when the charging is completed; and a step of calculating a full charge capacity.

Description

Technical Field

[0001] This disclosure relates to battery systems. Background Technology

[0002] For example, Japanese Patent Application Publication No. 2003-164006 discloses the following technology: calculating the degree of degradation of a battery based on voltage and current values, correcting the capacity adjustment range based on the calculated degree of degradation, and displaying the current battery capacity in a segmented manner.

[0003] When calculating the capacity of a current battery using the techniques described above, the full-charge capacity is estimated based on the step change of the battery's open circuit voltage (OCV). However, under conditions such as low temperatures, the accuracy of the full-charge capacity estimation may decrease due to variations in the position of the step change. Summary of the Invention

[0004] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a battery system that can accurately estimate the full charge capacity even at low temperatures.

[0005] One aspect of this disclosure relates to a battery system equipped with a control device for controlling the charging of a battery, including a lithium iron phosphate battery. If the control device detects a step difference in the change of the battery's open voltage (OCV) during charging, it sets a correction factor using a first cumulative value of the current flowing into the battery from the start of charging until the step difference is detected, and the battery temperature. A predetermined value is added to a second cumulative value of the current flowing into the battery from the detection of the step difference until charging is complete, and the sum is multiplied by the correction factor to calculate the battery's full charge capacity.

[0006] In this way, by using a correction factor set by the first cumulative value and the battery temperature to correct the sum of the second cumulative value and the fixed value, and calculating the full charge capacity of the battery, the full charge capacity can be estimated with high accuracy.

[0007] In one implementation, the control device sets a correction factor such that when the battery temperature is low, the full charge capacity is less than the sum of a predetermined value and a second cumulative value compared to when the battery temperature is high.

[0008] By setting an appropriate correction factor based on the battery temperature, the full charge capacity can be estimated with high accuracy.

[0009] In another embodiment, the control device uses the degree of battery degradation to set a correction factor, in addition to the first cumulative value and the battery temperature.

[0010] In this way, by using a correction factor that takes into account the degree of battery degradation in addition to the first cumulative value and the battery temperature, the full charge capacity of the battery can be estimated with greater accuracy.

[0011] In another embodiment, the control device sets a correction coefficient such that, when the battery degradation is high, the full charge capacity is less than the sum of a predetermined value and a second cumulative value compared to when the battery degradation is low.

[0012] By appropriately setting correction factors based on the degree of battery degradation, the full charge capacity can be estimated with high accuracy.

[0013] In another embodiment, the predetermined value is equivalent to the first cumulative value of the battery when it is not deteriorated and at room temperature.

[0014] In this way, the full charge capacity can be estimated with high accuracy using a second cumulative value and a correction factor during the period from the detection of the step difference to the completion of battery charging.

[0015] According to this disclosure, a battery system can be provided that can accurately estimate the full charge capacity even at low temperatures. Attached Figure Description

[0016] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements, wherein,

[0017] Figure 1 This is a diagram showing an example of the overall configuration of an electric vehicle equipped with the battery system according to this embodiment;

[0018] Figure 2 This is a graph showing the relationship between OCV and remaining capacity in a single cell of this embodiment;

[0019] Figure 3 This is a graph showing an example of how the OCV changes relative to the remaining capacity at each temperature;

[0020] Figure 4 This is a flowchart illustrating an example of a process performed by an ECU;

[0021] Figure 5 This indicates the relationship between battery temperature, cumulative value, and correction factor.

[0022] Figure 6 This is a diagram used to illustrate the relationship between the degree of battery degradation and the position of the step difference. Detailed Implementation

[0023] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0024] Figure 1 This diagram illustrates an example of the overall configuration of an electric vehicle 1 equipped with the battery system S according to this embodiment. In this embodiment, the electric vehicle 1 is, for example, a battery electric vehicle. The electric vehicle 1 includes a motor generator 10 as a rotary motor, a power transmission gear 20, a drive wheel 30, a power control unit (PCU) 40, a system main relay (SMR) 50, a battery 100, a monitoring unit 200, and an electronic control unit (ECU) 300 as an example of a control device.

[0025] MG10 is, for example, an embedded permanent magnet synchronous motor (IPM motor), which functions as both a motor and a generator. The output torque of MG10 is transmitted to the drive wheel 30 via a power transmission gear 20, which includes a reducer and a differential device.

[0026] When the electric vehicle 1 brakes, the MG10 is driven by the drive wheel 30, and the MG10 functions as a generator. Thus, the MG10 also functions as a braking device that performs regenerative braking, converting the kinetic energy of the electric vehicle 1 into electrical energy. The regenerative power generated by the regenerative braking force in the MG10 is stored in the battery 100.

[0027] PCU40 is a power conversion device that bidirectionally converts power between MG10 and battery 100. PCU40 includes, for example, an inverter and a converter that operate based on control signals from ECU300.

[0028] The converter boosts the voltage supplied from the battery 100 when the battery 100 discharges and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG10.

[0029] The inverter converts the AC power generated by MG10 into DC power and supplies it to the converter while the battery 100 is charging. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging the battery 100 and supplies it to the battery 100.

[0030] SMR50 is electrically connected to the power line connecting battery 100 and PCU40. When SMR50 is closed (ON) according to a control signal from ECU300, power can be transferred between battery 100 and PCU40. On the other hand, when SMR50 is opened (OFF) according to a control signal from ECU300, the electrical connection between battery 100 and PCU40 is disconnected.

[0031] The storage battery 100 stores the power used to drive the MG10. The storage battery 100 is a rechargeable DC power source (secondary battery) and is constructed by stacking multiple individual cells (battery cells) 100a, for example, by electrically connecting them in series. Each individual cell 100a can be, for example, a lithium-ion battery. In this embodiment, a lithium iron phosphate (LFP) battery using lithium iron phosphate as the positive electrode active material is used as the individual cell 100a.

[0032] The monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. The voltage sensor 210 detects the voltage VB of the individual battery 100a (the voltage VB between the terminals of the individual battery 100a). The current sensor 220 detects the current IB input to and output to the battery 100 (individual battery 100a). For the current IB, the current charging the battery 100 can be positive (+), and the current discharging from the battery 100 can be negative (-). The temperature sensor 230 detects the temperature TB of each individual battery 100a. The monitoring unit 200 outputs the detection results from each sensor to the ECU 300.

[0033] The electric vehicle 1 is equipped with a DC socket 60, enabling the battery 100 to be fast-charged from an external direct current (DC) power source, which serves as a charging device. The DC socket 60 is configured to connect to a connector 420 at the front end of a charging cable 410 located on the external DC power source (charging device) 400. A charging relay 70 is electrically connected to the power line connecting the DC socket 60 and the battery 100. The charging relay 70 switches the supply and disconnection of power between the DC socket 60 and the battery 100 based on a control signal from the ECU 300. External charging (fast charging) of the battery 100 is performed by closing the charging relay 70.

[0034] Electric vehicle 1 is equipped with an AC socket 80, allowing battery 100 to be normally charged from an external AC power source, which serves as a charging device. The AC socket 80 is configured to allow connection to a connector 520 at the front end of a charging cable 510 located at an external AC power source (charging device) 500. An on-board charger 130 is installed on the power line between the AC socket 80 and the battery 100, converting the AC power supplied from the external AC power source 500 into DC power, and then into a voltage capable of charging the battery 100. A charging relay 90 is electrically connected to the power line connecting the on-board charger 130 and the battery 100. The charging relay 90 switches the power supply and disconnection between the on-board charger 130 and the battery 100 according to a control signal from the ECU 300. External charging (normal charging) of the battery 100 is performed by closing the charging relay 90.

[0035] The ECU 300 includes a central processing unit (CPU) 301 and a memory (e.g., including read-only memory (ROM) and random access memory (RAM)) 302. The ECU 300 controls various devices based on signals received from the monitoring unit 200, signals from various sensors (not shown) (e.g., accelerator opening signal, vehicle speed signal, etc.), mappings stored in the memory 302, and program information, to bring the electric vehicle 1 into a desired state. Additionally, the ECU 300 performs processes such as estimating the full charge capacity during charging. Furthermore, the battery system S consists of a battery 100 (single battery 100a), the monitoring unit 200, and the ECU 300.

[0036] Figure 2 This is a graph showing the relationship between the OCV (Open Circuit Voltage) and the remaining capacity in the single cell 100a (LFP cell) of this embodiment. Figure 2 In section (A), the vertical axis represents the OCV [V] of a single 100a battery, and the horizontal axis represents the remaining capacity (charging capacity) [Ah] of a single 100a battery. Figure 2 As shown in part (A), the relationship between OCV and residual capacity (hereinafter also referred to as the OCV curve) is characterized by a wide range of regions where the OCV curve changes very little (voltage flat region). If the part of the OCV curve that increases from the voltage flat region and becomes a voltage flat region again is called a "step difference", then in the single cell 100a of this embodiment, there are two steps difference P1 and P2.

[0037] The first stage (OCV is the low-voltage side) step difference P1 exists around 30% of the SOC (State of Charge) of a new 100a single cell. The second stage (OCV is the high-voltage side) step difference P2 exists around 60% of the SOC of a new 100a single cell.

[0038] Figure 2 Part (B) represents the relationship between the voltage change ΔVB of the battery during charging (VB) and the remaining capacity, indicating the relationship during constant current charging or discharging. The voltage change ΔVB is the change in voltage VB relative to the remaining capacity (charging capacity) [V / Ah], or the change in voltage VB relative to time (charging time or discharging time) [V / s]. For example... Figure 2 As shown in section (B), the voltage change ΔVB has a maximum value M1 at the residual capacity corresponding to step P1, and a maximum value M2 at the residual capacity corresponding to step P2. Therefore, the remaining capacity at which the voltage change ΔVB becomes the maximum value M2 is stored as the reference capacity C2. The charging current from when the voltage change ΔVB becomes the maximum value M2 until it is fully charged is accumulated, and this accumulated value is added to the reference capacity C2. Thus, the full charge capacity of the battery 100 (single cell 100a) can be estimated.

[0039] However, under conditions such as low temperature, there may be changes in the position of the step difference, which can reduce the accuracy of the estimated full charge capacity.

[0040] Figure 3 This is a graph showing an example of how the OCV changes relative to the remaining capacity at each temperature. Figure 3 The vertical axis represents OCV. Figure 3 The horizontal axis represents SOC. Figure 3 LN1 represents an example of the change in OCV relative to the change in SOC at room temperature (25°C). Figure 3 LN2 represents an example of the change in OCV relative to the change in SOC at a temperature 10°C lower than normal. For example... Figure 3 As shown in LN1 and LN2, at low temperatures, compared to high temperatures, the position of the OCV relative to SOC tends to shift towards the lower SOC side, exhibiting a step-like change. Therefore, when estimating the full charge capacity based on the step difference P2, the estimation accuracy may decrease due to temperature variations.

[0041] Therefore, in this embodiment, during the charging of the battery 100, if the ECU 300 detects a step difference in the change of the OCV of the battery 100, it uses a first cumulative value Q1 (hereinafter referred to as cumulative value Q1) of the current flowing to the battery 100 during the period from the start of charging of the battery 100 to the detection of the step difference, and the temperature TB of the battery 100 to set a correction coefficient C. It adds a predetermined value to a second cumulative value Q2 (hereinafter referred to as cumulative value Q2) of the current flowing to the battery 100 during the period from the detection of the step difference to the completion of charging of the battery 100, and multiplies the sum by the correction coefficient C to calculate the full charge capacity of the battery 100.

[0042] In this way, by using the first cumulative value Q1 and the temperature TB of the battery 100 to set a correction coefficient C, the sum of the second cumulative value Q2 and the predetermined value is corrected, and the full charge capacity of the battery 100 is calculated. Therefore, the full charge capacity of the battery 100 can be estimated with high accuracy.

[0043] The following is for reference Figure 4 An example of a process performed in ECU300 is illustrated. Figure 4 This is a flowchart illustrating an example of the processing performed by ECU 300. If connector 420 is connected to DC socket 60, or connector 520 is connected to AC socket 80, external charging of battery 100 begins. This flowchart is executed for each individual battery 100a when external charging of battery 100 begins.

[0044] In step (hereinafter referred to as step S) 100, the ECU 300 acquires parameters. These parameters may include, for example, voltage VB, current IB, temperature TB, etc., detected by the monitoring unit 200. Afterwards, the processing proceeds to S102.

[0045] In S102, ECU 300 determines whether a detected step difference has been determined. ECU 300 determines whether the detected step difference P2 of the second stage (OCV is the high-voltage side) has been determined. When a maximum value corresponding to the step difference P2 is detected in the OCV, ECU 300 determines that a detected step difference has been determined. More specifically, ECU 300 can also calculate the change in OCV ΔOCV, and determine that a maximum value has been detected when the current change ΔOCV(n) is smaller than the previous change ΔOCV(n-1). Alternatively, ECU 300 can also detect a maximum value when the sign of the derivative of the change ΔOCV changes from positive to negative. When the SOC of the single cell 100a that detects the maximum value is greater than a specified value (e.g., 50%), ECU 300 determines that the detected step difference P2 has been determined. Furthermore, SOC can be measured, for example, by coulomb counting. If it is determined that a step difference has been detected ("Yes" in S102), the process moves to S104.

[0046] In S104, ECU300 obtains the battery temperature TB of each individual cell 100a. Then, the process moves to S108. If it is determined that no step difference was detected (not in S102), the process moves to S106.

[0047] In S106, ECU300 accumulates the cumulative value Q1 of the charging current since charging began. More specifically, ECU300 calculates the current cumulative value Q1(n) by adding the cumulative amount ΔQ1 of the charging current from the previous calculation time to the current calculation time to the previous cumulative value Q1(n-1). Then, the process returns to S102.

[0048] In S108, ECU 300 determines whether charging has ended. ECU 300 determines charging has ended when battery 100 is fully charged. For example, when battery 100 is undergoing CCCV (Constant Current-Constant Voltage) charging, ECU 300 may determine that battery 100 is fully charged when the charging current falls below a set value. Alternatively, ECU 300 may determine that battery 100 is fully charged when the voltage VB of any single cell 100a reaches the charging end voltage. If charging is determined to be complete (S108: Yes), the process proceeds to S110.

[0049] In S110, ECU300 calculates the correction factor C based on a mapping that represents the relationship between battery temperature TB, cumulative value Q1, and correction factor C. Figure 5 This represents the relationship between battery temperature TB, cumulative value Q1, and correction factor C. Figure 5The diagram shows correction factors C set for combinations of multiple battery temperatures (-10°C, 0°C, 10°C, and 20°C) and multiple cumulative current values ​​(40Ah, 50Ah, 60Ah, and 70Ah). The cumulative current value represents the accumulated current from the start of charging until the step difference is detected.

[0050] For example, when the battery temperature TB is 20°C, "1.0" is set as the correction factor C for each current accumulation value.

[0051] On the other hand, when the battery temperature TB is 10°C, when the cumulative current value is 40Ah or 50Ah, "1.0" is set as the correction factor C, and when the cumulative current value is 60Ah or 70Ah, "0.98" is set as the correction factor C.

[0052] Furthermore, when the battery temperature TB is 0℃, the correction factor C is set to "0.97" when the cumulative current value is 40Ah, "0.96" when the cumulative current value is 50Ah, "0.95" when the cumulative current value is 60Ah, and "0.94" when the cumulative current value is 70Ah.

[0053] Furthermore, with a battery temperature TB of -10℃, the correction factor C is set to "0.97" for a cumulative current value of 40Ah, "0.95" for 50Ah, "0.93" for 60Ah, and "0.89" for 70Ah. Additionally, [the following text is incomplete and likely refers to a different context:] ...and... Figure 5 The values ​​of correction factor C for each parameter shown (battery temperature TB and cumulative current) are listed in an example. Values ​​matched through experiments, etc., can also be set as values ​​representing correction factor C.

[0054] ECU300 uses the obtained battery temperature TB, the calculated cumulative value Q1, and Figure 5 The mapping shown is used to calculate the correction coefficient C corresponding to the battery temperature TB obtained through linear interpolation and the calculated cumulative value Q1. Then, the process is moved to S112.

[0055] In S112, ECU300 multiplies the value obtained by adding the fixed value to the cumulative value Q2 by a correction factor C to calculate the estimated full-charge capacity. The fixed value is a value equivalent to the cumulative value Q1 of the battery 100 (single battery 100a) under normal temperature conditions without degradation, and is a predetermined value matched through experiments, etc. After that, the process ends. Furthermore, if it is determined that charging has not ended (not in S108), the process moves to S114.

[0056] In S114, ECU300 accumulates the cumulative value Q2 of the charging current since the step difference was detected. More specifically, ECU300 calculates the current cumulative value Q2(n) by adding the cumulative amount ΔQ2 of the charging current from the previous calculation time to the current calculation time to the previous cumulative value Q2(n-1). Then, the process returns to S108.

[0057] The operation of the ECU300 of the battery system S according to this embodiment, based on the above-described configuration and flowchart, will be explained.

[0058] For example, if external charging begins and the battery 100 is charged, the OCV in each individual cell 100a increases. Various parameters of the individual cell 100a are obtained (S100), and the SOC is calculated using the obtained parameters. In addition, during the period until the step difference is detected (not in S102), the cumulative value Q1 of the charging current supplied since the start of external charging is accumulated (S106).

[0059] Furthermore, if, when the SOC exceeds 50%, the sign of the change in OCV (differential value) relative to the change in SOC changes from positive to negative and a maximum value is detected, then a step difference is determined to have been detected (in S102). If a step difference is determined to have been detected, the cell temperature TB of the single cell 100a is obtained (S104).

[0060] Before charging ends (No in S108), the cumulative value Q2 of the charging current from the moment the step difference is detected is calculated (S114). Furthermore, if the battery 100 reaches a fully charged state, charging ends (Yes in S108), and the obtained battery temperature TB, cumulative value Q1, and... Figure 5 The mapping shown is used to calculate the correction factor C. The estimated full-charge capacity of a single battery 100a is calculated by multiplying the value obtained by adding the fixed value and the cumulative value Q2 by the correction factor C (S110). Thus, the estimated full-charge capacity of each single battery 100a constituting the storage battery 100 is calculated.

[0061] As described above, according to the battery system S of this embodiment, the sum of the cumulative value Q2 and a fixed value is corrected using a correction coefficient C set using the cumulative value Q1 and the battery temperature TB, and the full charge capacity of a single battery 100a is calculated. Therefore, the full charge capacity of the battery 100 can be estimated with high accuracy. Thus, a battery system that can accurately estimate the full charge capacity even at low temperatures can be provided.

[0062] Furthermore, the ECU300 sets a correction factor so that when the battery temperature TB is low, the full charge capacity is less than the sum of a predetermined value and the cumulative value Q2 compared to when the battery temperature TB is high. Therefore, the full charge capacity can be estimated with high accuracy based on the battery temperature TB.

[0063] Furthermore, a predetermined value equivalent to the cumulative value Q1 of the battery when it is not deteriorated and at room temperature is set as a fixed value. Therefore, the full charge capacity can be estimated with high accuracy based on the cumulative value Q2 and the correction factor C during the period from the detection of the step difference to the completion of charging of the battery 100.

[0064] The following is an explanation of the variations.

[0065] In the above embodiment, the case in which the correction factor C is set using the battery temperature TB and the cumulative current value from the start of charging to the detection of the step difference is used as an example. However, in addition to the battery temperature TB and the cumulative current value, the degradation degree of a single cell 100a can also be used to set the correction factor C.

[0066] Figure 6 This is a diagram used to illustrate the relationship between the degree of battery degradation and the position of the step difference. Figure 6 The vertical axis represents the voltage change ΔVB. Figure 6 The horizontal axis represents the charging capacity (remaining capacity). Figure 6 LN1 represents the relationship between the voltage change ΔVB and the charging capacity in a new 100a single battery. Figure 6 LN2 indicates that it is more than Figure 6 The relationship between voltage change ΔVB and charging capacity in a degraded LN1 single cell 100a. Figure 6 LN3 indicates that it is more than Figure 6 The relationship between voltage change ΔVB and charging capacity in a 100a LN2 degraded single cell. Figure 6 LN4 indicates that it is more than Figure 6 The relationship between voltage change ΔVB and charging capacity in a 100a LN3 degraded single cell. Figure 6 LN5 indicates that it is more than Figure 6 The relationship between voltage change ΔVB and charging capacity in a 100a LN4 degraded single cell. Figure 6 LN6 indicates that it is more than Figure 6 The relationship between voltage change ΔVB and charging capacity in a degraded LN5 single cell (100a). Figure 6 The position of the maximum value on the side with the higher charging capacity of LN1 to LN6 is the step difference P2.

[0067] like Figure 6 As shown in LN1 to LN6, the higher the degradation degree of single cell 100a, the more the step P2 changes towards the side with lower charging capacity. Therefore, if the degradation degree of single cell 100a is taken into account in the setting of the correction factor C, the estimation accuracy of the full charge capacity can be further improved.

[0068] For example, the representation is set according to each degree of degradation. Figure 5 The mapping shown represents the relationship between battery temperature TB, cumulative current, and correction factor C. By using an appropriate mapping based on the degree of degradation and setting the correction factor C according to the battery temperature TB and cumulative current, the full charge capacity can be estimated with high accuracy.

[0069] Furthermore, regarding the correction factor C, for example, when the battery temperature and cumulative current are the same, it is preferable to set the correction factor so that when the degradation degree is high, the full charge capacity is less than the sum of the cumulative value Q2 and the fixed value compared to when the degradation degree is low. In this way, by setting an appropriate correction factor C based on the degradation degree of a single battery 100a, the full charge capacity can be estimated with high accuracy.

[0070] All points in the embodiments disclosed herein should be considered illustrative and not intended to limit the invention. The scope of the invention is not limited by the foregoing description, but is defined by the technical solutions and is intended to include equivalents and all modifications within that scope.

Claims

1. A battery system comprising a control device for controlling the charging of a rechargeable battery, including a lithium iron phosphate battery, characterized in that, The control device is configured as follows: If a step difference is detected in the change of the battery's OCV during the charging of the battery, a correction factor is set using a first cumulative value of the current flowing into the battery from the start of charging until the step difference is detected, and the temperature of the battery. The full charge capacity of the battery is calculated by adding a predetermined value to a second cumulative value of the current flowing into the battery during the period from the detection of the step difference to the completion of the battery charging, and multiplying the sum by the correction factor.

2. The battery system according to claim 1, characterized in that, The control device sets the correction coefficient so that when the battery temperature is low, the full charge capacity is less than the sum of the predetermined value and the second cumulative value compared to when the battery temperature is high.

3. The battery system according to claim 1, characterized in that, In addition to the first cumulative value and the temperature of the battery, the control device also uses the degree of battery degradation to set the correction coefficient.

4. The battery system according to claim 3, characterized in that, The control device sets the correction coefficient such that, when the battery has a high degree of degradation, the full charge capacity is less than the sum of the predetermined value and the second cumulative value compared to when the battery has a low degree of degradation.

5. The battery system according to any one of claims 1 to 4, characterized in that, The predetermined value is equivalent to the first cumulative value of the battery when it is not deteriorated and at room temperature.

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