Secondary battery output control method and secondary battery output control system

Abstract

The present invention provides a secondary battery output control method for determining the outputtable power that a secondary battery composed of multiple single cells can output, and controlling the secondary battery's output power based on the outputtable power. In this output control method, a deviation indicative value related to the magnitude of the deviation in the charge-discharge characteristics between the multiple single cells is calculated based on a charge-discharge characteristic indicative value that varies according to the charge-discharge characteristics of each of the multiple single cells. When the deviation indicative value exceeds a predetermined reference value, it is determined that a deviation has occurred, and the outputtable power is set based on the determination that a deviation has occurred. Furthermore, if no deviation has occurred, the basic outputtable power determined based on the charge-discharge characteristic indicative value is set as the outputtable power. If a deviation has occurred, a corrected outputtable power, which is lower than the basic outputtable power, is set as the outputtable power.

Description

Technical Field

[0001] The present invention relates to an output control method and an output control system for controlling the output of a secondary battery. Background Art

[0002] Conventional technologies exist for controlling the output of secondary batteries, such as lithium-ion batteries. For example, some technologies determine the upper limit of output power based on the secondary battery's temperature. For example, JP2007-165211A discloses a technique that calculates the maximum allowable discharge power of a secondary battery for both its maximum and minimum temperatures, and selects the lower of these two maximum allowable discharge power levels. Summary of the Invention

[0003] In the aforementioned prior art, temperature sensors within the battery pack are used to detect the maximum and minimum temperatures of the secondary battery. However, unless temperature sensors are installed for all of the secondary battery's cells, variations in the secondary battery's temperature cannot be properly detected. This can cause the voltage of the low-temperature cells to drop beyond the permissible range, resulting in overdischarge. On the other hand, installing temperature sensors for all of the secondary battery's cells may be difficult due to layout limitations within the battery pack or increased manufacturing costs. Therefore, it is important to control the output of the secondary battery by appropriately setting the output power of the secondary battery while reducing manufacturing costs.

[0004] Therefore, an object of the present invention is to appropriately control the output of a secondary battery.

[0005] A secondary battery output control method according to one embodiment of the present invention is used to determine the outputtable power that a secondary battery composed of multiple cells can output, and to control the secondary battery's output power based on this outputtable power. In this output control method, a deviation indicative value related to the magnitude of variation in the charge-discharge characteristics between the cells is calculated based on an indicative charge-discharge characteristic value that varies according to changes in the charge-discharge characteristics of each of the multiple cells. When this indicative deviation value exceeds a predetermined reference value, it is determined that a deviation has occurred, and the outputtable power is set based on the determination that a deviation has occurred. Furthermore, if no deviation has occurred, the basic outputtable power determined based on the indicative charge-discharge characteristic value is set as the outputtable power. If a deviation has occurred, a corrected outputtable power, which is lower than the basic outputtable power, is set as the outputtable power. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is a block diagram showing a configuration example of a battery output control system in the first embodiment.

[0007] Figure 2This is a diagram showing an example of the relationship between CCV and OCV used in the OCV calculation process.

[0008] Figure 3 This is a diagram showing the relationship between battery temperature and internal resistance used in the OCV calculation process.

[0009] Figure 4 This is a timing chart showing an example of the relationship between the output power of a lithium-ion battery and the cell voltage.

[0010] Figure 5 It is a graph showing the rate characteristics of a lithium-ion battery.

[0011] Figure 6 This is a graph showing output characteristics of a lithium-ion battery.

[0012] Figure 7 This is a flowchart showing an example of a processing procedure of an output control process executed by the battery output control system.

[0013] Figure 8 This is a block diagram showing a functional configuration example of a battery output control system in the second embodiment.

[0014] Figure 9 This is a flowchart showing an example of a processing procedure of an output control process executed by the battery output control system.

[0015] Figure 10 This is a block diagram showing a functional configuration example of a battery output control system in the third embodiment.

[0016] Figure 11 It is a diagram schematically showing a temperature correction method performed by the temperature correction unit.

[0017] Figure 12 This is a diagram showing an example of a method for calculating an initial SOC (state of charge) from an initial OCV.

[0018] Figure 13 This is a diagram showing an example of a method for calculating OCV by the OCV calculation unit.

[0019] Figure 14 This is a diagram showing an example of setting the power limit followability by the power limit followability setting unit.

[0020] Figure 15 It is a time chart showing changes in SOC and outputtable power Pout.

[0021] Figure 16 This is a flowchart showing an example of a processing procedure of an output control process executed by the battery output control system.

[0022] Figure 17 This is a block diagram showing a functional configuration example of a battery output control system in a fourth embodiment.

[0023] Figure 18 This is a diagram showing an example of an outputtable power calculation map indicating the relationship between SOC, temperature, and outputtable power. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] [First embodiment]

[0026] [Configuration example of battery output control system]

[0027] Figure 1 This is a block diagram illustrating an example configuration of a battery output control system 100 in the first embodiment. Battery output control system 100 controls the output of a lithium-ion battery 1 installed in a vehicle such as an electric vehicle or hybrid vehicle. Lithium-ion battery 1 supplies power to onboard equipment such as the vehicle's drive motor and auxiliary equipment. Lithium-ion battery 1 can also be charged using an onboard charger or an external charging device.

[0028] like Figure 1 As shown, the battery output control system 100 includes a lithium-ion battery 1, a single cell voltage detection unit 2, a current detection unit 3, a temperature detection unit 4, a state determination unit 5, a switching unit 6, an OCV (Open circuit voltage) calculation unit 7, an output power calculation unit 8, a vehicle controller 30, and a meter 40. In addition, the single cell voltage detection unit 2, the current detection unit 3, and the temperature detection unit 4 function as an internal state detection unit 10 for detecting the internal state of the lithium-ion battery 1. In addition, the state determination unit 5, the switching unit 6, the OCV calculation unit 7, and the output power calculation unit 8 are implemented by the LBC (Lithium Battery Controller) 20. In addition, for each structure of the battery output control system 100, refer to Figures 2 to 4 Provide explanation.

[0029] The LBC 20 is a control device that controls the charging and discharging of the lithium-ion battery 1. It is comprised of, for example, a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input / output (I / O) interfaces. The LBC 20 functions as a control unit that controls the operation of the lithium-ion battery 1 by executing a specific program. Alternatively, the LBC 20 may be comprised of multiple microcomputers rather than a single microcomputer.

[0030] Figure 2 This diagram shows an example of the relationship between CCV (Closed Circuit Voltage) and OCV used in the OCV calculation process of the OCV calculation unit 7. The vertical axis represents voltage V, and the horizontal axis represents current I. A solid curve 501 represents CCV, and a dashed curve 502 represents OCV.

[0031] like Figure 2 As shown, when current I flows from the lithium ion battery 1, the voltage CCV drops. The relationship between OCV and CCV can be obtained by the following formula 1. The dashed arrow 503 represents current I×internal resistance R.

[0032] OCV=CCV+I×R…Equation 1

[0033] Figure 3 : is a graph showing the relationship between battery temperature and internal resistance used in the OCV calculation process of the OCV calculation unit 7. The vertical axis represents the internal resistance R, and the horizontal axis represents the battery temperature ° C. Figure 3 As shown in the curve 504, the lower the battery temperature ℃, the higher the internal resistance R. Figure 2 、 Figure 3 , refer to the OCV calculation unit 7 for explanation.

[0034] Figure 4This is a time chart showing an example of the relationship between the output power and cell voltage of a lithium-ion battery 1. The vertical axis of the upper graph represents the output power, and the vertical axis of the lower graph represents the cell voltage. The horizontal axis of both graphs represents the time axis. Furthermore, "Pout" represents, for example, the upper limit of the output power, set so as not to significantly degrade the battery characteristics of the lithium-ion battery 1 (so as to prevent overdischarge). This is hereinafter referred to as "outputtable power Pout." Furthermore, in this embodiment, outputtable power Pout, set so as not to overdischarge the lithium-ion battery 1 without causing variations in the charge-discharge characteristics of the individual cells comprising the lithium-ion battery 1 (described later), is also referred to as "basic outputtable power Pout1." Furthermore, "Vr" represents the cell voltage value (lower limit) when the output power reaches the outputtable power Pout. This is hereinafter referred to as "target lower limit cell voltage Vr." When power is drawn from the lithium-ion battery 1 as shown by curve 505, the cell voltage decreases as shown by curve 506. Therefore, by limiting the power taken out from the lithium-ion battery 1 to the outputtable power Pout, the cell voltage can be maintained at the target lower limit cell voltage Vr. Figure 4 , and the description will be made with reference to the output power calculation unit 8.

[0035] Lithium-ion battery 1 is a battery that charges and discharges by the movement of lithium ions between a positive electrode and a negative electrode. It is constructed by electrically connecting multiple single cells in series. Lithium-ion battery 1 is used, for example, as a vehicle power source and is connected to a drive motor via an inverter. While this embodiment uses a lithium-ion battery as an example, this embodiment can also be applied to other secondary batteries, such as lead batteries and nickel-metal hydride batteries, that have a certain correlation between operating temperature and output characteristics.

[0036] The cell voltage detection unit 2 is a cell voltage sensor that detects the voltage (CCV) of each cell constituting the lithium-ion battery 1 and outputs the detection result to the state determination unit 5 and the switching unit 6. Specifically, the cell voltage detection unit 2 is provided for all cells constituting the lithium-ion battery 1, and the cell voltage detection unit 2 detects the voltage of each cell. Furthermore, in the first embodiment, the voltage of each cell serves as a charge-discharge characteristic indicator that changes according to changes in the charge-discharge characteristics of each cell.

[0037] The current detection unit 3 is a current sensor that detects currents serving as charging current and discharging current of the lithium-ion battery 1 , and outputs the detection result to the OCV calculation unit 7 .

[0038] The temperature detection unit 4 is a temperature sensor that detects the temperature inside the battery pack of the lithium-ion battery 1, and outputs the detection result to the OCV calculation unit 7 and the output power calculation unit 8. In addition, for the lithium-ion battery 1, either one temperature sensor or multiple temperature sensors can be provided. For example, in the case of providing one temperature sensor, it is preferably provided at a position where the temperature of the lithium-ion battery 1 is most likely to rise, such as the center. In addition, in the case of providing multiple temperature sensors, it is preferably provided at a position where the temperature of the lithium-ion battery 1 is most likely to rise, and a position where the temperature is most likely to drop, such as the end. In addition, in the case of providing multiple temperature sensors, it is also possible to provide them at the position where the temperature of the lithium-ion battery 1 is most likely to rise and at positions around it. In addition, in the case of providing multiple temperature sensors for the lithium-ion battery 1, it is also possible to provide the internal resistance calculation unit with the lowest value among the temperatures detected by these temperature sensors to calculate the internal resistance of the lithium-ion battery 1.

[0039] In this manner, the internal state detection unit 10 outputs an internal state detection value indicating the internal state of the lithium ion battery 1 .

[0040] Based on the cell voltages output from the cell voltage detection unit 2, the state determination unit 5 determines differences in the state of the lithium-ion battery 1, i.e., variations in the charge and discharge characteristics (charge and discharge performance) of each cell, and outputs the determination result to the switching unit 6. Specifically, the state determination unit 5 determines the average cell voltage, i.e., the average value of the voltages of all the cells comprising the lithium-ion battery 1. Furthermore, the state determination unit 5 determines the lowest cell voltage, i.e., the lowest cell voltage, of the cell voltages comprising all the cells comprising the lithium-ion battery 1. The state determination unit 5 then calculates a cell voltage difference, which is the difference between the average cell voltage and the lowest cell voltage. The state determination unit 5 then determines whether the cell voltage difference has deviated from a predetermined voltage difference threshold value, which serves as a reference value for determination.

[0041] The voltage difference threshold used in the determination process by the state determination unit 5 is a value capable of determining a predetermined degree of variation in the charge-discharge characteristics (charge-discharge performance) of the individual cells comprising the lithium-ion battery 1. For example, the voltage difference threshold can be set to a value approximately 10 times the variation range that is unavoidably caused by factors such as sensor errors and the operating environment of the lithium-ion battery 1. For example, the voltage difference threshold can be set to a value that results in a cell voltage difference of approximately 15%. These values can be set using various experimental data.

[0042] Switching unit 6 switches the cell voltage used in the OCV calculation based on the state difference determination result outputted from state determination unit 5, and outputs the switching result to OCV calculation unit 7. Specifically, when the cell voltage difference is less than the voltage difference threshold, switching unit 6 sets the cell voltage used in the OCV calculation to the average cell voltage. Alternatively, when the cell voltage difference is greater than the voltage difference threshold, switching unit 6 sets the cell voltage used in the OCV calculation to the minimum cell voltage.

[0043] OCV calculation unit 7 calculates the OCV of each cell based on the cell voltage output from switching unit 6, the current output from current detection unit 3, and the temperature output from temperature detection unit 4, and outputs the calculation result, i.e., the OCV, to outputtable power calculation unit 8. Specifically, OCV calculation unit 7 calculates the OCV based on the cell voltage value CCV, the current value I, and the internal resistance R. That is, OCV calculation unit 7 calculates the OCV using Equation 1 described above.

[0044] In addition, if Figure 3 As shown in FIG. 1 , the internal resistance R can be obtained based on the temperature output from the temperature detection unit 4. Therefore, the OCV calculation unit 7 preliminarily calculates Figure 3 The information shown is set as table values or the like, and is used to calculate the internal resistance R. That is, the OCV calculation unit 7 also functions as an internal resistance calculation unit that calculates the internal resistance of the lithium ion battery 1 based on the temperature detected by the temperature detection unit 4 .

[0045] When the cell voltage set by the switching unit 6 is the average cell voltage, the OCV calculation unit 7 calculates the OCV using the average cell voltage according to the aforementioned equation 1. Furthermore, when the cell voltage set by the switching unit 6 is the minimum cell voltage, the OCV calculation unit 7 calculates the OCV using the minimum cell voltage according to the aforementioned equation 1.

[0046] The outputtable power calculation unit 8 calculates the outputtable power based on the OCV output from the OCV calculation unit 7 and the temperature output from the temperature detection unit 4 , and outputs the calculation result, ie, the outputtable power, to the vehicle controller 30 .

[0047] Specifically, similar to the internal resistance calculation process described above, the output power calculation unit 8 calculates the internal resistance R based on the temperature output from the temperature detection unit 4. The output power calculation unit 8 then calculates the output power Pout_c for each cell based on the internal resistance R, the target lower-limit cell voltage Vr, and the OCV calculated by the OCV calculation unit 7. Specifically, the output power calculation unit 8 calculates the output power Pout_c for each cell using the following equation 2.

[0048] Pout_c=I×Vr=(OCV-Vr) / R×Vr…Equation 2

[0049] For example, the target lower limit cell voltage Vr is set to provide a margin above the overdischarge voltage. In the first embodiment, the target lower limit cell voltage Vr is set to 2.5V. In this case, the output power calculation unit 8 calculates (OCV - 2.5V) / R × 2.5V using the aforementioned equation 2. The output power calculation unit 8 then multiplies the output power Pout_c per cell obtained by this calculation by the number of cells to determine the output power Pout for the entire battery pack of lithium-ion batteries 1.

[0050] Thus, the output power calculation unit 8 calculates the output power Pout in consideration of variations in the charge and discharge characteristics of each cell of the lithium ion battery 1. The LBC 20 also functions as an output power calculation device for the lithium ion battery 1.

[0051] The vehicle controller 30 is a control device that controls various devices and is comprised of, for example, a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input / output interfaces (I / O interfaces). The vehicle controller 30 functions as a control unit that controls the operation of various devices included in the vehicle, such as the engine, motor, inverter, and battery, by executing a specific program. Alternatively, the vehicle controller 30 may be comprised of multiple microcomputers rather than a single microcomputer.

[0052] The vehicle controller 30 also limits the power extracted from the lithium-ion battery 1 based on the outputtable power Pout outputted from the outputtable power calculation unit 8. For example, the vehicle controller 30 limits the upper limit of power consumption of the drive motor and auxiliary equipment to the outputtable power Pout. Furthermore, the vehicle controller 30 causes the meter 40 to display various information.

[0053] As described above, when power is extracted from the lithium ion battery 1, the cell voltage drops. However, by limiting the extracted power to the outputtable power, the cell voltage can be maintained at the target lower limit cell voltage Vr, for example, 2.5V. Figure 4 As shown, by limiting the electric power extracted from the lithium-ion battery 1 to the outputtable electric power Pout1 , the cell voltage can be maintained at the target lower limit cell voltage Vr.

[0054] The meter 40 displays various information based on control from the vehicle controller 30. For example, the meter 40 displays the outputtable power Pout, the actual power consumption, and the like to the driver.

[0055] Figure 5This is a graph showing the rate characteristics of a lithium-ion battery. The vertical axis represents the cell voltage, and the horizontal axis represents the SOC. Furthermore, solid curve 511 represents the output characteristics at a high temperature of approximately 25 degrees Celsius, while dashed curves 512 and 513 represent the output characteristics at a low temperature of approximately -25 degrees Celsius. Furthermore, dashed curve 513 represents the output characteristics of the lithium-ion battery when the discharge current is higher than that of dashed curve 512. As indicated by arrow 514, the output characteristics decrease at low temperatures compared to room temperature. In particular, at low temperatures, as shown by dashed curves 512 and 513, if the discharge current is high, the discharge capacity, i.e., the SOC amplitude, decreases, causing the cell voltage to drop sharply.

[0056] Figure 6 : is a graph showing the output characteristics of lithium-ion batteries. The vertical axis represents the output power, and the horizontal axis represents the SOC. In addition, the dotted line curve 515 represents the output characteristics at high temperature, the solid line curve 516 represents the output characteristics at room temperature, and the dotted line curve 517 represents the output characteristics at low temperature. Figure 6 As shown, the output power is determined by the temperature and SOC of the lithium-ion battery. Specifically, as indicated by arrow 518, the lower the temperature of the lithium-ion battery, the higher the internal resistance, the more significant the voltage drop corresponding to the current flowing through the lithium-ion battery, and the lower the output power. Furthermore, the lower the SOC, the lower the voltage, and therefore the lower the output power.

[0057] Here, when the outside air temperature is low and the battery temperature is low, if the vehicle is traveling at high speed, the temperature of the center side of the battery pack will rise due to the high power extraction. The end plate side is closer to the outside air and is easily cooled, so the temperature rise will be slower, and there is a high possibility of a temperature difference occurring within the battery pack. In this case, if power is extracted in conjunction with the state of the cell with a rising temperature, the capacity characteristics and voltage of the low-temperature cell will drop sharply. In other words, the charge and discharge characteristics will deviate between the high-temperature cell and the low-temperature cell. For example, Figure 5 、 Figure 6 As shown, the rate characteristics of low-temperature cells are significant, causing a sharp drop in SOC and cell voltage, potentially reducing the drivable range. Specifically, since the discharge allowable power is low in low-temperature conditions, exceeding the allowable power of the low-temperature cells can lead to overdischarge. Therefore, to prevent overdischarge, setting the allowable power based on battery temperature is a possible approach. However, the placement of temperature sensors within the battery pack is often difficult due to layout and cost constraints.

[0058] Therefore, in this embodiment, when there is variation in the charge-discharge characteristics between individual cells, output limits are appropriately applied based on the variation, thereby preventing a decrease in the cell capacity and voltage. For example, in the first embodiment, when the cell voltage difference, an indicative amount of variation related to the magnitude of the variation in the charge-discharge characteristics between the individual cells constituting the lithium-ion battery 1, exceeds a reference value (voltage difference threshold), the output power Pout is switched from the base output power Pout1, which is normally set (when there is no variation), to the corrected output power Pout2. More specifically, the cell voltage used to calculate the output power Pout is switched from the average cell voltage corresponding to the base output power Pout1 to the minimum cell voltage corresponding to the corrected output power Pout2. This prevents the cell capacity and voltage from dropping below their lower limits. Furthermore, power can be continuously extracted from the lithium-ion battery 1, maintaining vehicle travel.

[0059] [Operation Example of Battery Output Control System 100]

[0060] Figure 7 1 is a flowchart showing an example of a processing procedure of an output control process executed by the battery output control system 100. Note that this processing procedure is executed based on a program stored in a storage unit (not shown) of the battery output control system 100.

[0061] In step S201 , the cell voltage detection unit 2 detects the voltage of each cell of the lithium-ion battery 1 .

[0062] In step S202 , the current detection unit 3 detects the current flowing in the lithium-ion battery 1 .

[0063] In step S203 , the temperature detection unit 4 detects the temperature inside the battery pack of the lithium-ion battery 1 .

[0064] In step S204, the state determination unit 5 calculates the average cell voltage and the minimum cell voltage based on the individual cell voltages detected by the cell voltage detection unit 2, and determines whether the cell voltage difference, which is the difference between the average cell voltage and the minimum cell voltage, is greater than a voltage difference threshold. Based on this determination result, the switching unit 6 then switches the cell voltage used for OCV calculation as needed. If the cell voltage difference is greater than the voltage difference threshold, the switching unit 6 switches the cell voltage used for OCV calculation to the minimum cell voltage, and the process proceeds to step S206. If the cell voltage difference is less than the voltage difference threshold, the switching unit 6 sets the average cell voltage to the cell voltage used for OCV calculation, and the process proceeds to step S205.

[0065] In step S205 , the OCV calculation unit 7 calculates the OCV of each cell based on the average cell voltage set by the switching unit 6 , the current detected by the current detection unit 3 , and the temperature detected by the temperature detection unit 4 .

[0066] In step S206 , the OCV calculation unit 7 calculates the OCV of each cell based on the minimum cell voltage set by the switching unit 6 , the current detected by the current detection unit 3 , and the temperature detected by the temperature detection unit 4 .

[0067] In step S207 , the outputtable power calculation unit 8 calculates the outputtable power of the entire battery pack of the lithium-ion batteries 1 based on the OCV calculated by the OCV calculation unit 7 and the temperature detected by the temperature detection unit 4 .

[0068] In step S208 , the vehicle controller 30 limits the upper limit of the electric power extracted from the lithium-ion battery 1 to the outputtable electric power obtained in step S207 .

[0069] In step S209 , the vehicle controller 30 causes the meter 40 to display the outputtable power obtained in step S207 and the actual power consumption of the lithium-ion battery 1 .

[0070] Furthermore, while the above example illustrates switching the cell voltage used in the OCV calculation to the lowest cell voltage when the cell voltage difference (indicative deviation amount), which is the difference between the average cell voltage and the lowest cell voltage, exceeds a voltage difference threshold, other criteria may be used. For example, the indicative deviation amount may be set as the difference between the highest cell voltage and the lowest cell voltage, and a determination may be made as to whether the difference is greater than a suitably determined criterion value. If the difference is greater than the criterion value, the cell voltage used in the OCV calculation may be switched to the lowest cell voltage.

[0071] [Effects of the First Embodiment]

[0072] The output control method for a lithium-ion battery 1 (an example of a secondary battery) according to the first embodiment is for determining the outputtable power Pout that can be output by the lithium-ion battery 1, which is composed of a plurality of cells, and controlling the output power of the lithium-ion battery 1 based on the outputtable power Pout. The output control method includes the following steps: an indicative quantity calculation step (step S204) for calculating an indicative quantity of deviation (cell voltage difference) related to the magnitude of deviation in charge and discharge characteristics between the cells based on an indicative quantity of charge and discharge characteristics (the voltage of each cell or the average cell voltage) that varies according to the charge and discharge characteristics of the plurality of cells; a determination step (step S204) for determining that a deviation has occurred when the indicative quantity of deviation is greater than a predetermined determination reference value (voltage difference threshold); and an outputtable power setting step (steps S205 to S207) for setting the outputtable power Pout based on the determination that a deviation has occurred. Moreover, in the output power setting step, when no deviation occurs, the basic output power Pout1 determined based on the charge and discharge characteristic indicative quantity (especially the average single cell voltage) is set as the output power Pout. When a deviation occurs, the corrected output power Pout2 having a value lower than the basic output power Pout1 is set as the output power Pout.

[0073] According to such an output control method, it is possible to appropriately impose output restrictions according to variations in charge and discharge characteristics of the individual cells of the lithium ion battery 1 , thereby preventing a decrease in the capacity or voltage of the cells.

[0074] Furthermore, in the output control method for the lithium-ion battery 1 according to the first embodiment, in the indicative quantity calculation step (step S204), the voltages of each of the plurality of cells (the cell voltages detected by the cell voltage detection unit 2) are acquired as indicative quantities of charge and discharge characteristics, and the cell voltage difference is calculated as the deviation indicative quantity. This cell voltage difference is the difference between the average cell voltage and the minimum cell voltage of the cells. Furthermore, in the determination step (step S204), a predetermined voltage difference threshold is set as the aforementioned determination reference value. Furthermore, in the output power setting step (steps S205-S207), the basic output power Pout1 is calculated based on the average cell voltage, and the corrected output power Pout2 is calculated based on the minimum cell voltage.

[0075] According to such an output control method, it is possible to obtain appropriate outputtable power based on variations in the charge and discharge characteristics of the individual cells of the lithium-ion battery 1 .

[0076] Furthermore, a battery output control system 100 (an example of a secondary battery output control system) according to this embodiment controls the output power of a lithium-ion battery 1 composed of multiple cells. The battery output control system 100 includes an LBC 20 (an example of a controller). This LBC 20 acquires an indicative charge-discharge characteristic quantity (the voltage of each cell) that changes according to the charge-discharge characteristics of each of the multiple cells. Based on the acquired indicative charge-discharge characteristic quantity, the LBC 20 calculates the output power Pout that the lithium-ion battery 1 can output, and controls the output power of the lithium-ion battery 1 based on this output power Pout. Based on the indicative charge-discharge characteristic quantity, the LBC 20 calculates an indicative deviation quantity (cell voltage difference) that correlates with the magnitude of the deviation in the charge-discharge characteristic between the cells. When this indicative deviation quantity exceeds a predetermined reference value (voltage difference threshold), the LBC 20 determines that a deviation has occurred. Furthermore, when there is no deviation, the LBC 20 sets the basic outputtable power Pout1 determined based on the charge and discharge characteristic indicative amount as the outputtable power Pout. When there is a deviation, the LBC 20 sets the corrected outputtable power Pout2, which is lower than the basic outputtable power Pout1, as the outputtable power.

[0077] According to such a battery output control system 100 , output limitation can be appropriately applied according to variations in charge and discharge characteristics of each cell of the lithium-ion battery 1 , thereby preventing a decrease in the capacity or voltage of the cell.

[0078] [Second embodiment]

[0079] The second embodiment shows an example in which an average OCV calculation unit 51 and a minimum OCV calculation unit 52 are provided in place of the OCV calculation unit 7 in the battery output control system 100 shown in the first embodiment. The second embodiment is a partial modification of the first embodiment; thus, identical components to those in the first embodiment are denoted by the same reference numerals, and their descriptions are partially omitted.

[0080] [Configuration example of battery output control system]

[0081] Figure 8 2 is a block diagram showing a functional configuration example of a battery output control system 200 in the second embodiment. The battery output control system 200 includes an average OCV calculation unit 51 and a minimum OCV calculation unit 52 in the LBC 50 .

[0082] Average OCV calculation unit 51 calculates an average OCV, corresponding to the average value of the OCVs of each cell, based on the average value of the cell voltages detected by cell voltage detection unit 2, the current detected by current detection unit 3, and the temperature detected by temperature detection unit 4. Specifically, the average OCV is calculated by applying the average cell voltage value to the CCV in equation 1 above.

[0083] The minimum OCV calculation unit 52 calculates the minimum OCV, corresponding to the minimum value among the OCVs of the individual cells comprising the lithium-ion battery 1, based on the minimum value of the cell voltage detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4. Specifically, the minimum OCV is calculated according to the above-mentioned equation 1, using the minimum cell voltage as the CCV. Thus, in the second embodiment, the average OCV calculation unit 51 uses the average value of all cell voltages detected by the cell voltage detection unit 2, while the minimum OCV calculation unit 52 uses only the minimum value among the cell voltages detected by the cell voltage detection unit 2. Furthermore, the average OCV calculation unit 51 and the minimum OCV calculation unit 52 also function as internal resistance calculation units that calculate the internal resistance of the lithium-ion battery 1 based on the temperature detected by the temperature detection unit 4. Furthermore, in the second embodiment, OCV is an indicative quantity of charge-discharge characteristics that changes with changes in the charge-discharge characteristics of each cell.

[0084] The state determination unit 5 determines the difference in charge and discharge characteristics between the individual cells comprising the lithium-ion battery 1 based on the average OCV output from the average OCV calculation unit 51 and the minimum OCV output from the minimum OCV calculation unit 52. Specifically, the state determination unit 5 calculates an OCV difference, which is the difference between the average OCV and the minimum OCV. The state determination unit 5 then determines whether a deviation has occurred such that the OCV difference exceeds an OCV difference threshold value, which is a predetermined reference value for determination.

[0085] Here, similar to the voltage difference threshold described in the first embodiment, the OCV difference threshold used in the determination process of the state determination unit 5 is set to a value that is preferred from the perspective of determining whether a predetermined variation has occurred in the charge and discharge characteristics (charge and discharge performance) of each cell constituting the lithium-ion battery 1. For example, the OCV difference threshold can be set to a value that results in an OCV difference of approximately 15%. These values can be set using various experimental data.

[0086] Switching unit 6 switches the OCV used in outputtable power calculation based on the state difference determination result outputted from state determination unit 5, and outputs the switching result to outputtable power calculation unit 8. Specifically, when the OCV difference is less than the OCV difference threshold, switching unit 6 sets the OCV used in outputtable power calculation to the average OCV. Alternatively, when the OCV difference is greater than the OCV difference threshold, switching unit 6 sets the OCV used in outputtable power calculation to the minimum OCV.

[0087] The output power calculation unit 8 calculates the output power of the entire battery pack of lithium-ion batteries 1 based on the OCV (average OCV or minimum OCV) output from the switching unit 6 and the temperature output from the temperature detection unit 4. The method of calculating the output power is the same as that of the first embodiment.

[0088] [Battery output control system operation example]

[0089] Figure 9 1 is a flowchart showing an example of a processing procedure of the output control process executed by the battery output control system 200. In addition, this processing procedure is executed based on a program stored in a storage unit (not shown) of the battery output control system 200. Figure 9 The treatment shown is for Figure 7 An example obtained by deforming a portion of the processing shown, Figure 9 Steps S301 to S303, S308, and S309 shown are the same as Figure 7 The steps S201 to S203, S208, and S209 shown in FIG are the same. Figure 7 The description of the same parts of the processes shown will be partially omitted.

[0090] In step S304, the average OCV calculation unit 51 calculates the average OCV of each cell based on the average value of the cell voltages detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4. Furthermore, the minimum OCV calculation unit 52 calculates the minimum OCV of each cell based on the minimum value of the cell voltage detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4.

[0091] In step S305, the state determination unit 5 determines whether the OCV difference (the difference between the average OCV and the minimum OCV calculated in step S304) is greater than the OCV difference threshold. Then, based on the determination result, the switching unit 6 switches the OCV used for outputtable power calculation as needed. If the OCV difference is greater than the OCV difference threshold, the switching unit 6 switches the OCV used for outputtable power calculation to the minimum OCV, and the process proceeds to step S307. If the OCV difference is less than the OCV difference threshold, the switching unit 6 sets the average OCV as the OCV used for outputtable power calculation, and the process proceeds to step S306.

[0092] In step S306 , the output power calculation unit 8 calculates the output power of the entire battery pack of lithium-ion batteries 1 based on the average OCV set by the switching unit 6 and the temperature output from the temperature detection unit 4 .

[0093] In step S307 , the output power calculation unit 8 calculates the output power of the entire battery pack of the lithium-ion batteries 1 based on the minimum OCV set by the switching unit 6 and the temperature output from the temperature detection unit 4 .

[0094] Furthermore, the second embodiment illustrates an example in which the OCV used in calculating the outputtable power is switched to the lowest OCV when the OCV difference (indicative deviation amount), which is the difference between the average OCV and the lowest OCV, is equal to or greater than the OCV difference threshold (determination reference value). However, other determination criteria may also be used. For example, the OCV used in calculating the outputtable power may be switched to the lowest OCV when both the determination process for determining whether the cell voltage difference is equal to or greater than the voltage difference threshold (determination reference value) or the determination process for determining whether the difference between the highest cell voltage and the lowest cell voltage is equal to or greater than the determination reference value, and the determination process for determining whether the OCV difference is equal to or greater than the OCV difference threshold, described in the first embodiment, are affirmative.

[0095] [Operation and Effect of the Second Embodiment]

[0096] In the output control method for a lithium-ion battery 1 (an example of a secondary battery) according to the second embodiment, in the indicative quantity calculation step (step S305), the OCVs of each of the plurality of cells (the average OCV calculated by the average OCV calculation unit 51 and the minimum OCV calculated by the minimum OCV calculation unit 52) are obtained as indicative quantities of charge and discharge characteristics. The OCV difference is calculated as the deviation indicative quantity. This OCV difference is the difference between the average OCV and the minimum OCV of the plurality of cells. Furthermore, in the determination step (step S305), a predetermined OCV difference threshold is set as the aforementioned determination reference value. Furthermore, in the output power setting step (steps S306 and S307), the basic output power Pout1 is calculated based on the average OCV, and the corrected output power Pout2 is calculated based on the minimum OCV.

[0097] According to such an output control method, it is possible to obtain appropriate outputtable power based on variations in the charge and discharge characteristics of the individual cells of the lithium-ion battery 1 .

[0098] [Third embodiment]

[0099] The third embodiment shows an example in which the battery output control system 200 shown in the second embodiment is replaced with an average SOC calculation unit 61, a minimum SOC calculation unit 62, and a calculation unit 70, in place of the average OCV calculation unit 51, the minimum OCV calculation unit 52, and the outputtable power calculation unit 8. Furthermore, a temperature correction unit 63 and a power limit followability setting unit 64 are added. The third embodiment is a partial modification of the first and second embodiments. Components identical to those in the first and second embodiments are denoted by the same reference numerals, and their descriptions are partially omitted.

[0100] [Configuration example of battery output control system]

[0101] Figure 10 This is a block diagram showing an example of the functional configuration of the battery output control system 300 in the third embodiment. The battery output control system 300 includes an average SOC calculation unit 61, a minimum SOC calculation unit 62, a temperature correction unit 63, a power limit followability setting unit 64, and a calculation unit 70 in the LBC 60. The calculation unit 70 also includes an OCV calculation unit 71, an internal resistance calculation unit 72, and an output power calculation unit 73. Regarding the various components of the battery output control system 300, please refer to the relevant references as appropriate. Figures 11 to 15 To explain.

[0102] Figure 11 1 is a diagram schematically showing a temperature correction method performed by the temperature correction unit 63 .

[0103] Figure 12This diagram illustrates an example of a method for calculating the initial SOC based on the initial OCV. The initial OCV is the open-circuit terminal voltage of the lithium-ion battery 1, calculated based on the cell voltage at vehicle startup. Furthermore, the initial SOC, as shown by curve 521, is the value calculated based on the initial OCV.

[0104] Figure 13 1 is a diagram showing an example of a method for calculating OCV by the OCV calculation unit 71 .

[0105] Figure 14 1 and 2 are diagrams showing an example of setting the electric power limit followability by the electric power limit followability setting unit 64 .

[0106] Figure 15 It is a time chart showing the changes in SOC and output power Pout. The vertical axis of the upper graph represents SOC, and the vertical axis of the lower graph represents output power Pout. In addition, the horizontal axis of both graphs is a time axis. In addition, curve 531 represents the average SOC, and curve 532 represents the minimum SOC. In addition, the minimum SOC corresponding to curve 532 is displayed on the meter 40. In addition, curve 534 represents the output power Pout calculated using the average SOC, and curve 535 represents the output power Pout calculated using the minimum SOC. In addition, as shown by arrow 533, time t1 represents the moment when a deviation of more than a specified value occurs between the average SOC and the minimum SOC.

[0107] The average SOC calculation unit 61 calculates the average SOC corresponding to the average value of the SOC of each cell based on the cell voltage detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4. Specifically, the average SOC calculation unit 61 uses Figure 2 The open circuit terminal voltage (initial OCV) of the lithium ion battery 1 is detected based on the single cell voltage when the vehicle is started. Next, the average SOC calculation unit 61 calculates the following: Figure 12 The initial SOC corresponding to the initial OCV is calculated as shown by curve 521. Then, based on the current detected by the current detection unit 3, the average SOC calculation unit 61 subtracts the current flowing from the lithium-ion battery 1 from the initial SOC to calculate the average SOC. While this example shows the calculation of the average SOC by subtracting the integrated current from the initial SOC, the average SOC may also be calculated using the average value of the cell voltages detected by the cell voltage detection unit 2, similar to the calculation process for the minimum SOC described below.

[0108] The minimum SOC calculation unit 62 calculates the minimum OCV corresponding to the minimum value of the SOC of each cell constituting the lithium ion battery 1 based on the minimum value of the cell voltage detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4. Specifically, the minimum OCV is calculated according to the above-mentioned formula 1 by applying the minimum cell voltage to the CCV. In addition, the following formula is calculated: Figure 13 The lowest SOC corresponding to the lowest OCV is shown in curve 523 of FIG. Thus, in the third embodiment, the average SOC calculation unit 61 uses the average value of the cell voltages detected by the cell voltage detection unit 2, while the lowest SOC calculation unit 62 uses only the lowest value of the cell voltages detected by the cell voltage detection unit 2. Furthermore, the average SOC calculation unit 61 and the lowest SOC calculation unit 62 also function as internal resistance calculation units that calculate the internal resistance of the lithium-ion battery 1 based on the temperature detected by the temperature detection unit 4. Furthermore, in the third embodiment, the SOC is a charge-discharge characteristic indicator that changes according to changes in the charge-discharge characteristics of each cell.

[0109] State determination unit 5 determines differences in the charge and discharge characteristics of the individual cells comprising lithium-ion battery 1 based on the average SOC output from average SOC calculation unit 61 and the minimum SOC output from minimum SOC calculation unit 62. Specifically, state determination unit 5 calculates an SOC difference, which is the difference between the average SOC and the minimum SOC. State determination unit 5 then determines whether a deviation has occurred such that the SOC difference exceeds an SOC difference threshold value, which is a predetermined reference value.

[0110] Here, similar to the OCV difference threshold described in the second embodiment, the SOC difference threshold used in the determination process of the state determination unit 5 is set to a value that is preferred from the perspective of determining whether a predetermined deviation has occurred in the charge and discharge characteristics of each cell of the lithium-ion battery 1. For example, the SOC difference threshold can be set to a value that results in an SOC difference of approximately 15%. These values can be set using various experimental data.

[0111] Switching unit 6 switches the SOC used in the OCV calculation based on the state difference determination result outputted from state determination unit 5, and outputs the switching result to OCV calculation unit 71. Specifically, when the SOC difference is less than the SOC difference threshold, switching unit 6 sets the SOC used in the OCV calculation to the average SOC. Alternatively, when the SOC difference is greater than the SOC difference threshold, switching unit 6 sets the SOC used in the OCV calculation to the minimum SOC.

[0112] The temperature correction unit 63 corrects the temperature output from the temperature detection unit 4 based on the minimum SOC output from the minimum SOC calculation unit 62, and outputs the corrected temperature to the internal resistance calculation unit 72. Specifically, Figure 11 As shown, the temperature correction unit 63 extracts a value corresponding to the minimum SOC output from the minimum SOC calculation unit 62 from the minimum SOC value 65, and subtracts the value of the correction amount 66 corresponding to the extracted value from the temperature output from the temperature detection unit 4. For example, when the minimum SOC output from the minimum SOC calculation unit 62 is a value within the range of 21 to 30, 10 is used as the correction amount 66.

[0113] In this way, by pre-checking the deviation between the detected temperature value of the lithium-ion battery 1 inside the battery pack and the actual minimum temperature value and correcting the detected value toward the lower side, it is possible to predict the actual minimum temperature and improve the accuracy of the output power calculation, thereby achieving output power calculation using fewer temperature sensors.

[0114] In addition, if Figure 11 As shown, the lower the minimum SOC 65, the larger the correction amount 66 is set, thereby applying a stronger output restriction and mitigating capacity and voltage drops. This allows lithium-ion battery 1 to continuously output power, allowing the vehicle system to maintain driving. While this example shows temperature correction based on the minimum SOC, temperature correction can also be performed based on the average SOC. In this case, it is preferable to set correction amount 66 larger than when using the minimum SOC.

[0115] The OCV calculation unit 71 calculates the OCV of each battery cell based on the SOC (average SOC or minimum SOC) output from the switching unit 6, and outputs the calculation result, that is, the OCV, to the output power calculation unit 73. Specifically, the OCV calculation unit 71 calculates the following: Figure 13 The OCV corresponding to the SOC output from the switching unit 6 is as shown by the curve 523 .

[0116] The internal resistance calculation unit 72 calculates the internal resistance of the lithium-ion battery 1 based on the temperature output from the temperature correction unit 63, and outputs the calculation result, i.e., the value of the internal resistance, to the outputtable power calculation unit 73. The internal resistance calculation method is the same as that of the first embodiment. Furthermore, the internal resistance calculation units shown in the first and second embodiments may also calculate the internal resistance of the lithium-ion battery 1 using the corrected temperature.

[0117] The output power calculation unit 73 calculates the output power of the entire battery pack of lithium ion batteries 1 based on the OCV output from the OCV calculation unit 71 and the internal resistance output from the internal resistance calculation unit 72. The method of calculating the output power is the same as that of the first embodiment.

[0118] The power limit followability setting unit 64 sets the power limit followability based on the state difference determination result outputted from the state determination unit 5 and the minimum SOC outputted from the minimum SOC calculation unit 62, and outputs the setting information to the vehicle controller 30. Specifically, the power limit followability setting unit 64 switches the output power status indicating how to follow the outputtable power calculated by the outputtable power calculation unit 73. In other words, the power limit followability setting unit 64 sets the degree of followability so that the actual power consumed by the lithium-ion battery 1, such as by the vehicle system's drive motor, follows the outputtable power.

[0119] For example, Figure 14 As shown, if the state determination unit 5 does not detect a state difference, the output power setting is followed at a predetermined rate of change. In other words, under normal circumstances, the amount of power change is determined based on the vehicle speed, taking into account the driver's drivability. By setting the followability to slow, the output limit of the lithium-ion battery 1 is relaxed, thus prioritizing the driver's drivability.

[0120] On the other hand, when a state difference is detected by the state determination unit 5, the followability of the power limit of the outputtable power is set to be faster. In other words, the followability of limiting the outputtable power calculated by the calculation unit 70 is set to be faster. For example, when the minimum SOC is between 30% and 60%, the followability of the power limit of the outputtable power is set to be approximately three times faster than when no state difference is detected. Furthermore, when the minimum SOC is between 0% and 30%, the followability is set to be immediate according to the outputtable power. Thus, when a state difference is detected, the degree of followability is set to make the actual power follow the followability of the outputtable power faster than before the state difference was detected. In other words, the followability of the power limit is set to be faster by switching the output power status. Furthermore, by immediately following the minimum SOC when it decreases, the capacity and voltage of the lithium-ion battery 1 can be suppressed.

[0121] The vehicle controller 30 limits the power extracted from the lithium-ion battery 1 to the outputtable power outputted from the computing unit 70. Furthermore, during this limitation, the vehicle controller 30 adjusts the power extraction speed limit based on the followability set by the power limit followability setting unit 64, as described above. Specifically, the vehicle controller 30 limits the outputtable power at the power limit change rate according to the power limit followability set by the power limit followability setting unit 64. In this manner, the vehicle controller 30 functions as a power limiter that limits the output power of the lithium-ion battery 1 based on the degree of followability set by the power limit followability setting unit 64.

[0122] Meter 40 displays the minimum SOC output from minimum SOC calculation unit 62 to the driver, along with the available output power and actual power consumption. Displaying the minimum SOC on meter 40 in this manner allows the driver to quickly recognize a decrease in SOC. This allows the available output power to be limited after the driver recognizes the decrease in SOC, resulting in a less abrupt or unnatural feeling.

[0123] As described above, in the third embodiment, when the deviation indicative amount, i.e., the SOC difference, is greater than the determination reference value (SOC difference threshold), the SOC used when calculating the outputtable power Pout is switched from the average SOC corresponding to the basic outputtable power to the minimum SOC corresponding to the corrected outputtable power. By using the minimum SOC to reduce the outputtable power Pout as quickly as possible, a sudden drop in the cell voltage can be suppressed.

[0124] For example, Figure 15 As shown in the curve 534 , when the outputtable power Pout is obtained using the average SOC, since the outputtable power Pout is a high value, the minimum cell voltage drops at high output, and the outputtable power Pout may decrease suddenly.

[0125] On the other hand, in the third embodiment, when the SOC difference is equal to or greater than the SOC difference threshold, the control is limited to Figure 15 The outputtable power Pout obtained using the minimum SOC is shown in the curve 535. This can suppress a rapid drop in the cell voltage.

[0126] [Battery output control system operation example]

[0127] Figure 16 1 is a flowchart showing an example of a processing procedure of the output control process executed by the battery output control system 300. In addition, this processing procedure is executed based on a program stored in a storage unit (not shown) of the battery output control system 300. Figure 16 The treatment shown is for Figure 7 An example obtained by deforming a portion of the processing shown, Figure 9 Steps S401 to S403 shown are similar to Figure 7 The steps S201 to S203 are the same as those shown in FIG. Figure 7 The description of the same processing parts will be partially omitted.

[0128] In step S404, the average SOC calculation unit 61 calculates the average SOC of each cell based on the cell voltage detected by the cell voltage detection unit 2 and the current detected by the current detection unit 3. Furthermore, the minimum SOC calculation unit 62 calculates the minimum SOC of each cell based on the minimum value of the cell voltage detected by the cell voltage detection unit 2, the current detected by the current detection unit 3, and the temperature detected by the temperature detection unit 4.

[0129] In step S405, the state determination unit 5 determines whether the SOC difference (the difference between the average SOC and the minimum SOC, calculated in step S404) is greater than the SOC difference threshold. Then, based on the determination result, the switching unit 6 switches the SOC used in the OCV calculation as needed. If the SOC difference is greater than the SOC difference threshold, the switching unit 6 switches the SOC used in the OCV calculation to the minimum SOC, and the process proceeds to step S407. If the SOC difference is less than the SOC difference threshold, the switching unit 6 sets the average SOC as the SOC used in the OCV calculation, and the process proceeds to step S406.

[0130] In step S406 , the OCV calculation unit 71 calculates the OCV of each cell based on the average SOC set by the switching unit 6 .

[0131] In step S407 , the OCV calculation unit 71 calculates the OCV of each cell based on the minimum SOC set by the switching unit 6 .

[0132] In step S408 , the power limit followability setting unit 64 sets the degree of followability for causing the actual power of the lithium ion battery 1 to follow the outputtable power based on the minimum SOC set by the switching unit 6 .

[0133] In step S409 , the temperature correction unit 63 corrects the temperature detected by the temperature detection unit 4 based on the lowest SOC set by the switching unit 6 .

[0134] In step S410 , the internal resistance calculation unit 72 calculates the internal resistance of the lithium-ion battery 1 based on the temperature correction value corrected by the temperature correction unit 63 .

[0135] In step S411 , the output power calculation unit 73 calculates the output power of the entire battery pack of lithium-ion batteries 1 based on the OCV calculated by the OCV calculation unit 71 , the internal resistance calculated by the internal resistance calculation unit 72 , and the cell voltage lower limit target value.

[0136] In step S412 , the vehicle controller 30 limits the upper limit of the power extracted from the lithium-ion battery 1 to the outputtable power according to the degree of the power limit followability set by the power limit followability setting unit 64 .

[0137] In step S413 , meter 40 displays the minimum SOC obtained by minimum SOC calculation unit 62 , the outputtable power obtained by outputtable power calculation unit 73 , and the actual power consumption of lithium-ion battery 1 .

[0138] Furthermore, the third embodiment illustrates an example in which the SOC used in outputtable power calculation is switched to the minimum SOC when the SOC difference (indicative deviation amount), which is the difference between the average SOC and the minimum SOC, is equal to or greater than the SOC difference threshold. However, other criteria may also be used. For example, the SOC used in outputtable power calculation may be switched to the minimum SOC when both the determination process for determining whether the cell voltage difference is equal to or greater than the voltage difference threshold (determination reference value) or the determination process for determining whether the difference between the highest cell voltage and the lowest cell voltage is equal to or greater than the determination reference value, as described in the first embodiment, and the determination process for determining whether the SOC difference is equal to or greater than the SOC difference threshold, are affirmative.

[0139] [Effects of the Third Embodiment]

[0140] In the output control method for a lithium-ion battery 1 (an example of a secondary battery) according to the third embodiment, in the indicative quantity calculation step (step S405), the SOCs of each of the plurality of cells (the average SOC calculated by the average SOC calculation unit 61 and the minimum SOC calculated by the minimum SOC calculation unit 62) are obtained as indicative quantities of charge and discharge characteristics, and the SOC difference, which is the difference between the average SOC and the minimum SOC of the plurality of cells, is calculated as the indicative quantity of deviation. Furthermore, in the determination step (step S405), a predetermined SOC difference threshold is set to the aforementioned determination reference value. Furthermore, in the output power setting steps (steps S406 to S411), the basic output power Pout1 is calculated based on the average SOC, and the corrected output power Pout2 is calculated based on the minimum SOC.

[0141] According to such an output control method, it is possible to appropriately impose output restrictions according to variations in charge and discharge characteristics of the individual cells of the lithium ion battery 1 , thereby preventing a decrease in the capacity or voltage of the cells.

[0142] The output control method for the lithium-ion battery 1 according to the third embodiment further includes the following steps: a temperature detection step (step S403) for detecting the temperature of the lithium-ion battery 1; a temperature correction step (step S409) for correcting the detected temperature based on the charge-discharge characteristic indicator (SOC); and a step for calculating the output power Pout using the corrected temperature (step S411). Furthermore, in the output power setting step (steps S406 to S411), the corrected temperature is used to calculate the corrected output power Pout2.

[0143] According to such an output control method, the calculation accuracy of the outputtable power can be improved, and the outputtable power calculation can be realized with a smaller number of temperature sensors.

[0144] Furthermore, in the output control method of the lithium ion battery 1 according to the third embodiment, in the temperature correction step (step S409 ), the detected temperature is corrected based on the lowest SOC among the SOCs of the plurality of cells, which are indicative quantities of charge and discharge characteristics.

[0145] According to such an output control method, the calculation accuracy of the outputtable power can be improved, and the outputtable power calculation can be realized with a smaller number of temperature sensors.

[0146] The output control method for lithium-ion battery 1 according to the third embodiment further includes a followability setting step (step S408) for setting a degree of followability for the actual power of lithium-ion battery 1 to follow the outputtable power Pout. In this followability setting step, when a deviation occurs, the followability setting step is used to set a degree of followability that allows the actual power to follow the outputtable power more quickly than before the deviation occurred. Furthermore, in this output control method, the output power of lithium-ion battery 1 is controlled to be limited based on the set followability degree.

[0147] According to such an output control method, it is possible to suppress a decrease in capacity and a decrease in voltage of the lithium ion battery 1 .

[0148] [Fourth embodiment]

[0149] The fourth embodiment shows an example in which, in the battery output control system 300 shown in the third embodiment, the state determination unit 5 uses the temperature detected by the temperature detection unit 4 to perform state difference determination. The fourth embodiment is a partially modified example of the third embodiment; components identical to those in the third embodiment are denoted by the same reference numerals, and their descriptions are partially omitted.

[0150] [Configuration example of battery output control system]

[0151] Figure 17 This is a block diagram showing an example of the functional configuration of the battery output control system 400 in the fourth embodiment. Figure 10 The structures shown are substantially the same, but the difference is that the temperature value detected by the temperature detection unit 4 is output to the state determination unit 5 .

[0152] The state determination unit 5 determines whether to determine the state difference of the lithium-ion battery 1 (the difference in the charge and discharge characteristics of each single cell) based on the temperature detected by the temperature detection unit 4. For example, the state determination unit 5 determines whether to determine the state difference of the lithium-ion battery 1 while the startup state continues (during one mileage) based on the temperature detected by the temperature detection unit 4 when the vehicle is started. For example, when the temperature detected by the temperature detection unit 4 when the vehicle is started is below a specified temperature, for example, below 0°C, the state determination unit 5 decides to continue to determine the state difference of the lithium-ion battery 1. On the other hand, when the temperature detected by the temperature detection unit 4 when the vehicle is started exceeds a specified temperature, the state determination unit 5 decides not to determine the state difference of the lithium-ion battery 1. In this case, Figure 16 In the determination of step S405, the process always proceeds to step S406. The other structures are the same as those of the third embodiment.

[0153] Here, variations in temperature and voltage occur among the individual cells of lithium-ion battery 1 most often when the temperature rises from a low temperature. Therefore, by limiting the determination by state determination unit 5 to low temperatures, output limitations based on these variations are not applied at normal temperatures. This allows calculation of the output power available without sacrificing the vehicle's power performance at normal temperatures. Furthermore, limiting output limitations based on these variations to low temperatures prevents malfunctions at normal temperatures.

[0154] [Functions and Effects of the Fourth Embodiment]

[0155] The output control method of the lithium ion battery 1 according to the fourth embodiment further includes a temperature detection step (step S403) for detecting the temperature of the lithium ion battery 1. In the determination step (step S405), if the detected temperature is below a predetermined value, it is determined whether a deviation has occurred.

[0156] According to such an output control method, the calculation of the outputtable electric power can be realized without sacrificing the power performance of the vehicle at normal temperature, and malfunction at normal temperature can be prevented.

[0157] [Fifth embodiment]

[0158] In the third and fourth embodiments, examples are shown in which the calculation unit 70 calculates the output power based on the SOC and temperature. However, a mapping table representing the relationship between the SOC, temperature, and output power may be stored in advance and used to calculate the output power. Therefore, in the fifth embodiment, an example is shown in which the output power is calculated using a mapping table representing the relationship between the SOC, temperature, and output power.

[0159] [Example of output power calculation map]

[0160] Figure 18 This is a diagram showing an example of an output power calculation map showing the relationship between SOC, temperature and output power. The output power calculation map can be created by performing calculations in advance by testing the relationship between SOC, temperature and output power offline. For example, Figure 6 The output power calculation map is created based on the output characteristics of the lithium-ion battery shown.

[0161] The battery output control system in the fifth embodiment can Figure 18 The output power calculation map shown is pre-stored in a storage unit (not shown). The output power calculation map is referenced to determine the output power corresponding to the SOC and temperature. For example, at an SOC of 20% and a temperature of 10°C, the output power is calculated as 70 kW. Alternatively, at an SOC of 60% and a temperature of 0°C, the output power is calculated as 75 kW.

[0162] Furthermore, the respective processes described in the first to fifth embodiments can be appropriately combined and implemented within a possible range.

[0163] Furthermore, in the first to fifth embodiments, an example is shown in which the state determination unit 5 calculates an indicative deviation amount (cell voltage difference, SOC difference, OCV difference) based on the indicative quantities of charge and discharge characteristics (cell voltage, SOC, OCV), and determines that a deviation has occurred when the indicative deviation amount exceeds a predetermined reference value. Furthermore, an example is shown in which, when a deviation occurs, the switching unit 6 switches to using the lowest value (lowest cell voltage, lowest SOC, lowest OCV) to calculate the output power. However, the switching unit 6 may also be configured to further limit the output power based on the magnitude of the indicative deviation amount (cell voltage difference, SOC difference, OCV difference). For example, the state determination unit 5 may calculate a ratio of the difference values with respect to the indicative deviation amount. The switching unit 6 then sets a setting to change the method for calculating the output power based on this ratio, i.e., the magnitude of the indicative deviation amount. For example, the switching unit 6 may be configured to calculate a method for further limiting the output power in response to an increase in the ratio, and the output power calculation unit may calculate the further limited output power in accordance with this setting.

[0164] Furthermore, each process described in the first through fifth embodiments is executed based on a program that causes a computer to execute each process. Therefore, the first through fifth embodiments can also be understood as embodiments of a program that implements the functions of executing each process and a recording medium storing the program. For example, the program can be updated and stored in the vehicle's storage device when a new function is added to the vehicle. This update can be performed, for example, during a regular vehicle inspection. Alternatively, the program can be updated via wireless communication.

[0165] The embodiments of the present invention have been described above. However, the above embodiments merely illustrate a part of application examples of the present invention and are not intended to limit the technical scope of the present invention to the specific structures of the above embodiments.

Claims

1. A secondary battery output control method for determining the output power that a secondary battery composed of a plurality of single cells can output and controlling the output power of the secondary battery based on the output power, the secondary battery output control method comprising the following steps: an indicative quantity calculation step of calculating, based on the indicative quantity of charge and discharge characteristics that changes according to changes in the charge and discharge characteristics of each of the plurality of single cells, a deviation indicative quantity related to the magnitude of deviation in the charge and discharge characteristics between the single cells; a determination step of determining that the deviation has occurred when the deviation indication amount is equal to or greater than a predetermined determination reference value; an outputtable power setting step of setting the outputtable power based on a determination result that the deviation has occurred; as well as a temperature detection step of detecting the temperature of the secondary battery, In the output power setting step, When the deviation does not occur, the basic outputtable power determined based on the charge-discharge characteristic indicative quantity is set as the outputtable power; When the deviation occurs, a corrected output power lower than the basic output power is determined using the charge and discharge characteristic indicative amount and the temperature of the secondary battery, and the corrected output power is set as the output power.

2. The output control method of a secondary battery according to claim 1, wherein: In the indicative quantity calculation step, the voltage of each of the plurality of single cells is obtained as the charge-discharge characteristic indicative quantity, and a single cell voltage difference is calculated as the deviation indicative quantity. The single cell voltage difference is the difference between the average single cell voltage of the plurality of single cells and the lowest single cell voltage. In the determination step, a predetermined voltage difference threshold is set as the determination reference value. In the outputtable power setting step, the basic outputtable power is calculated based on the average cell voltage, and the corrected outputtable power is calculated based on the minimum cell voltage.

3. The output control method of a secondary battery according to claim 1, wherein: In the indicative quantity calculation step, the open circuit voltage of each of the plurality of single cells is obtained as the charge-discharge characteristic indicative quantity, and the open circuit voltage difference is calculated as the deviation indicative quantity. The open circuit voltage difference is the difference between the average open circuit voltage and the lowest open circuit voltage of the plurality of single cells. In the determination step, a predetermined open circuit voltage difference threshold is set as the determination reference value, In the outputtable power setting step, the basic outputtable power is calculated based on the average open-circuit voltage, and the corrected outputtable power is calculated based on the minimum open-circuit voltage.

4. The output control method of a secondary battery according to claim 1, wherein: In the indicative quantity calculation step, the state of charge of each of the plurality of single cells is obtained as the charge-discharge characteristic indicative quantity, and the state of charge difference is calculated as the deviation indicative quantity. The state of charge difference is the difference between the average state of charge of the plurality of single cells and the lowest state of charge. In the determination step, a predetermined state of charge difference threshold is set as the determination reference value, In the outputtable power setting step, the basic outputtable power is calculated based on the average state of charge, and the corrected outputtable power is calculated based on the minimum state of charge.

5. The output control method of a secondary battery according to any one of claims 1 to 4, wherein: In the determination step, when the detected temperature is equal to or lower than a predetermined value, it is determined whether the deviation has occurred.

6. The output control method of a secondary battery according to any one of claims 1 to 4, wherein: The following steps are also included: a temperature correction step of correcting the detected temperature based on the charge-discharge characteristic indicative quantity; as well as The output power is obtained using the corrected temperature. In the outputtable power setting step, the corrected outputtable power is obtained using the corrected temperature.

7. The output control method of a secondary battery according to claim 6, wherein: In the temperature correction step, the detected temperature is corrected based on the lowest state of charge among the states of charge of the plurality of battery cells serving as the charge-discharge characteristic indicator.

8. The output control method of a secondary battery according to claim 1, wherein: The method further includes a followability setting step of setting a followability level so that the actual power of the secondary battery follows the outputtable power. In the followability setting step, when the deviation occurs, the followability level is set so that the actual power follows the outputtable power faster than before the deviation occurs. In the secondary battery output control method, control is performed so as to limit the output power of the secondary battery based on the set degree of followability.

9. A secondary battery output control system for controlling the output power of a secondary battery composed of a plurality of single cells, wherein: The output control system of the secondary battery comprises: a temperature detection unit configured to detect a temperature in the secondary battery; as well as a controller that obtains a charge-discharge characteristic indicative quantity that changes according to a change in the charge-discharge characteristic of each of the plurality of single cells, calculates an outputtable power that can be output by the secondary battery based on the obtained charge-discharge characteristic indicative quantity, and controls the output power of the secondary battery based on the outputtable power; The controller performs the following processing: calculating, based on the charge-discharge characteristic indicative quantity, a deviation indicative quantity related to the magnitude of deviation in the charge-discharge characteristic between the single cells; When the deviation indication amount is equal to or greater than a predetermined determination reference value, it is determined that the deviation has occurred; When the deviation does not occur, the basic outputtable power determined based on the charge-discharge characteristic indicative quantity is set as the outputtable power; When the deviation occurs, a corrected output power lower than the basic output power is determined using the charge and discharge characteristic indicative amount and the temperature of the secondary battery, and the corrected output power is set as the output power.

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