JP2019132780A - Chargeable battery state detecting device and chargeable battery state detecting method - Google Patents

Abstract

To detect a state of a chargeable battery at a sufficient frequency.SOLUTION: A chargeable battery state detecting device has: determination means (CPU 10a) which determines whether a chargeable battery is in a discharging state; measurement means (voltage sensor 11 and current sensor 12) which measures, when the determination means determines that the chargeable battery is being discharged, values of a current flowing in the chargeable battery and a terminal voltage thereof a plurality of times; calculation means (CPU 10a) which calculates, from the values of the current and terminal voltage measured by the measurement means, values of internal resistance of the chargeable battery at respective measurement timings; specification means (CPU 10a) which fits the values of internal resistance at the respective measurement timings calculated by the calculation means as a function including the current as an input variable, and specifies the internal resistance as a function including the current as an input variable; and detection means (CPU 10a) which detects the state of the chargeable battery based upon the function specified by the specification means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rechargeable battery state detection device and a rechargeable battery state detection method.

  As a technique for detecting the state of a rechargeable battery, for example, there is a technique disclosed in Patent Document 1.

  The technique disclosed in Patent Document 1 is a discharge unit that causes a battery to perform a pulse discharge of a substantially rectangular wave with a predetermined current value, and a rectangular wave that samples the response voltage when the battery is pulse-discharged and orthogonally intersects this. A rectangular wave expanding means for expanding the component; a pseudo impedance calculating means for calculating the pseudo impedance from the coefficient and current calculated by the rectangular wave expanding means; and a deterioration determining means for determining the deterioration state of the battery using the pseudo impedance. doing.

JP 2006-284537 A

  By the way, in the technique disclosed in Patent Document 1, battery deterioration is determined using pseudo impedance, but the value of the internal resistance constituting the pseudo impedance varies depending on the current flowing through the battery. For this reason, when the flowing current is governed by the demands of the vehicle and constantly fluctuates, such as an in-vehicle battery, a configuration in which a constant current flows is adopted, or the flowing current value is observed. It is necessary to determine whether or not the current value satisfies the condition for obtaining the internal resistance, and to calculate the internal resistance only when the condition is satisfied.

  In order to employ a configuration in which a constant current flows, it is necessary to add a discharging mechanism, a charging mechanism, and the like, which is a significant cost increase factor. In addition, when determining whether the current value satisfies the condition for obtaining the internal resistance, the timing for obtaining the internal resistance is governed by the situation of the current flow side of the vehicle, etc. There is a problem that it is difficult to assure that it is requested.

  If the internal resistance is calculated only when the condition is satisfied, the response voltage can be accurately estimated from the obtained internal resistance if the internal resistance is obtained at the timing when the same current as the requested current to be predicted flows. . However, in many cases, since the required current is set assuming severe conditions, the frequency of the requested current flowing is extremely rare, so it is possible to ensure that the internal resistance is obtained with sufficient frequency. There is a problem of difficulty.

  The present invention has been made in view of the above situation, and provides a rechargeable battery state detection device and a rechargeable battery state detection method capable of detecting the state of a rechargeable battery with sufficient frequency. The purpose is that.

In order to solve the above problems, the present invention provides a rechargeable battery state detection device that detects a state of a rechargeable battery, a determination unit that determines whether or not the rechargeable battery is in a discharged state, and the determination unit If it is determined that the battery is being discharged by the measurement means for measuring the current flowing through the rechargeable battery and the value of the terminal voltage a plurality of times, and the current measured by the measurement means and the value of the terminal voltage, respectively. A calculation means for calculating the value of the internal resistance of the rechargeable battery at the measurement timing, and the value of the internal resistance at each measurement timing calculated by the calculation means is fitted as a function using the current as an input variable, A specifying means for specifying the internal resistance as the function having an electric current as an input variable, and the function specified by the specifying means Based and having a detecting means for detecting a state of the rechargeable battery.
According to such a configuration, the state of the rechargeable battery can be detected with sufficient frequency.

Further, the present invention is characterized in that the function used by the specifying means has at least one exponential function term.
According to such a configuration, the value of the internal resistance can be accurately fitted as a function with the current as an input variable.

Further, the present invention is characterized in that the specifying means fits the function by arithmetic processing using a least square method, a Kalman filter, or a neural network.
According to such a configuration, the coefficient of the function can be obtained with high accuracy.

In the invention, it is preferable that the specifying unit calculates at least one of the coefficients of the function based on at least one of an ambient temperature or an electrolyte temperature of the rechargeable battery, an SOC, and an elapsed time from the start of discharge. It is characterized by correcting.
According to such a configuration, the state of the rechargeable battery can be accurately detected regardless of the situation where the rechargeable battery is placed.

Further, the present invention is characterized in that the detection means obtains SOF as a response voltage when a predetermined current flows through the rechargeable battery based on the function.
According to such a configuration, the SOF of the rechargeable battery can be obtained with sufficient frequency.

Further, the present invention is characterized in that the detection means obtains SOH as a deterioration degree of the rechargeable battery based on the function.
According to such a configuration, the SOH of the rechargeable battery can be obtained with sufficient frequency.

Further, the present invention provides a rechargeable battery state detection method for detecting a state of a rechargeable battery, wherein a determination step for determining whether or not the rechargeable battery is in a discharged state and a discharge in the determination step If determined, the measurement step of measuring the current and terminal voltage values flowing through the rechargeable battery a plurality of times, and the current and terminal voltage values measured in the measurement step, at each measurement timing A calculation step of calculating a value of the internal resistance of the rechargeable battery, and fitting the internal resistance value at each measurement timing calculated in the calculation step as a function using the current as an input variable; As a function having the current as an input variable, and the specific step. And having a detection step of detecting a state of the rechargeable battery based on the function specified in.
According to such a method, the state of the rechargeable battery can be detected with sufficient frequency.

  According to the present invention, it is possible to provide a rechargeable battery state detection device and a rechargeable battery state detection method capable of detecting the state of a rechargeable battery with sufficient frequency.

It is a figure which shows the structural example of the rechargeable battery state detection apparatus which concerns on embodiment of this invention. It is a block diagram which shows the detailed structural example of the control part of FIG. It is a figure which shows the time change of the electric current which flows into a rechargeable battery at the time of cranking by a starter motor, and a terminal voltage. It is a figure which shows the time change of the internal resistance calculated | required from the voltage and electric current which are shown in FIG. It is a figure which shows the electrical equivalent circuit model of a rechargeable battery. It is the figure which rearranged and displayed the measurement result shown in FIG. 4 by making a horizontal axis into an electric current. It is a figure which shows the relationship between the estimated value and the measured value by the fitted function. It is a figure which shows the relationship between internal resistance and SOF. It is a flowchart for demonstrating an example of the process performed in embodiment of this invention. It is a flowchart for demonstrating an example of the deformation | transformation embodiment of the flowchart shown in FIG.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of Embodiment of the Present Invention FIG. 1 is a diagram showing a power supply system of a vehicle having a rechargeable battery state detection device according to an embodiment of the present invention. In this figure, the rechargeable battery state detection device 1 includes a control unit 10, a voltage sensor 11, a current sensor 12, and a temperature sensor 13 as main components, and detects the occurrence of an abnormality in the rechargeable battery 14. To do. Note that the control unit 10, the voltage sensor 11, the current sensor 12, and the temperature sensor 13 are not separately configured, and a part or all of them may be combined.

  Here, the control unit 10 refers to the outputs from the voltage sensor 11, the current sensor 12, and the temperature sensor 13, detects the state of the rechargeable battery 14, and controls the power generation voltage of the alternator 15 to perform charging. The charge state of the possible battery 14 is controlled. The voltage sensor 11 detects the terminal voltage of the rechargeable battery 14 and notifies the control unit 10 of it. The current sensor 12 detects the current flowing through the rechargeable battery 14 and notifies the control unit 10 of the current. The temperature sensor 13 detects the electrolyte solution of the rechargeable battery 14 or the temperature around the rechargeable battery 14 and notifies the control unit 10 of the detected temperature. Note that the control unit 10 does not control the charging state of the rechargeable battery 14 by controlling the power generation voltage of the alternator 15, but for example, an unillustrated ECU (Electric Control Unit) controls the charging state. Good.

  The rechargeable battery 14 is constituted by a rechargeable battery having an electrolytic solution, such as a lead storage battery, a nickel cadmium battery, or a nickel metal hydride battery. The rechargeable battery 14 is charged by the alternator 15 and drives the starter motor 17 to start the engine. At the same time, power is supplied to the load 18. The rechargeable battery 14 is configured by connecting a plurality of cells in series. The alternator 15 is driven by the engine 16 to generate AC power, convert it into DC power by a rectifier circuit, and charge the rechargeable battery 14. The alternator 15 is controlled by the control unit 10 and can adjust the generated voltage.

  The engine 16 is constituted by, for example, a reciprocating engine such as a gasoline engine and a diesel engine, a rotary engine, or the like, and is started by a starter motor 17 to drive driving wheels via a transmission to provide propulsive force to the vehicle. To generate electric power. The starter motor 17 is constituted by, for example, a DC motor, and generates a rotational force by the electric power supplied from the rechargeable battery 14 to start the engine 16. The load 18 is composed of, for example, an electric steering motor, a defogger, a seat heater, an ignition coil, a car audio, a car navigation, and the like, and operates with electric power supplied from the rechargeable battery 14. In the example of FIG. 1, only the engine 16 outputs driving force. However, for example, a hybrid vehicle including an electric motor that assists the engine 16 may be used. In the case of a hybrid vehicle, the rechargeable battery 14 activates a high-pressure system (system that drives an electric motor) constituted by a lithium battery or the like, and the high-pressure system starts the engine 16.

  FIG. 2 is a diagram illustrating a detailed configuration example of the control unit 10 illustrated in FIG. 1. As shown in this figure, the control unit 10 includes a CPU (Central Processing Unit) 10a, a ROM (Read Only Memory) 10b, a RAM (Random Access Memory) 10c, a communication unit 10d, an I / F (Interface) 10e, A bus 10f is provided. Here, the CPU 10a controls each unit based on the program 10ba stored in the ROM 10b. The ROM 10b is configured by a semiconductor memory or the like, and stores a program 10ba or the like. The RAM 10c is configured by a semiconductor memory or the like, and stores data generated when the program 10ba is executed and data 10ca such as a table to be described later. The communication unit 10d communicates with an upper device such as an ECU (Electronic Control Unit) and notifies the detected information or control information to the upper device. The I / F 10e converts the signals supplied from the voltage sensor 11, the current sensor 12, and the temperature sensor 13 into digital signals and fetches them, and supplies drive current to the alternator 15, the starter motor 17 and the like. To control. The bus 10f is a signal line group for mutually connecting the CPU 10a, the ROM 10b, the RAM 10c, the communication unit 10d, and the I / F 10e so that information can be exchanged between them.

(B) Description of Operation of the Embodiment of the Present Invention Next, the operation of the embodiment of the present invention will be described. In the following, after describing the operation principle of the embodiment of the present invention, the detailed operation will be described.

  First, the operation principle of the embodiment of the present invention will be described. FIG. 3 is a diagram showing temporal changes in the current flowing from the rechargeable battery 14 to the starter motor 17 and the terminal voltage of the rechargeable battery 14 when the engine 16 is started by the starter motor 17. In FIG. 3, solid squares indicate temporal changes in the terminal voltage of the rechargeable battery 14, and hollow squares indicate temporal changes in the current flowing through the rechargeable battery 14. In FIG. 3, the case where the rechargeable battery 14 is charged is positive, and the case where it is discharged is negative. As shown in FIG. 3, when the starter motor 17 is energized at time 0, an inrush current exceeding 400A flows and the terminal voltage of the rechargeable battery 14 decreases. When cranking the engine 16 (rotating the crankshaft of the engine 16), a large current flows at the timing when the piston of the engine 16 reaches top dead center. Further, as the rotational speed of the engine 16 increases, the current decreases and the terminal voltage also increases.

  FIG. 4 is a diagram showing temporal changes in internal resistance in FIG. In FIG. 4, the filled squares indicate temporal changes in the internal resistance R (= Rohm + Rct) including both the conductive resistance / liquid resistance Rohm and the reaction resistance Rct, and the hollow squares indicate only the reaction resistance Rct. It shows the time variation of internal resistance.

  FIG. 5 shows an example of an electrical equivalent circuit model of the rechargeable battery 14. In the equivalent circuit model shown in FIG. 5, the reaction resistance Rct1 and electric double layer capacitance C1 connected in parallel, the reaction resistance Rct2 and electric double layer capacitance C2 connected in parallel, and the conductive resistance / liquid resistance Rohm are connected in series. Connected and configured. The conductive resistance / liquid resistance Rohm is a resistance having no current dependence, and the reaction resistances Rct1 and Rct2 are resistances having a current dependence. Hereinafter, the reaction resistances Rct1 and Rct2 connected in series are represented as reaction resistance Rct (= Rct1 + Rct2).

  The internal resistance R is obtained by R = (V−OCV) / I, where V is the measured terminal voltage, I is the measured current, and OCV (Open Circuit Voltage) is the open circuit voltage. Can do. In addition, the conductive resistance / liquid resistance Rohm causes the rechargeable battery 14 to be pulse-discharged by a rectangular wave having a period of 100 Hz or less, for example, and the difference between the voltage V1 before the discharge and the voltage V2 after the discharge (V1−V2) The value obtained by dividing by the current I can be defined as the conductive resistance / liquid resistance Rohm. Of course, other methods may be used. In FIG. 4, in the graph of only the reaction resistance Rct indicated by the hollow square, the filled square is translated downward in the internal resistance graph including both the conductive resistance / liquid resistance Rohm and the reaction resistance Rct. It has become a thing.

  FIG. 6 is a diagram in which the measurement results shown in FIG. 4 are rearranged with the horizontal axis as the current value and the vertical axis as the resistance value. In the example of FIG. 6, the value of the internal resistance increases as the discharge current decreases. In addition, the reaction resistance Rct graph indicated by a hollow square is obtained by translating the internal resistance graph including both the conductive resistance / liquid resistance Rohm and the reaction resistance Rct indicated by a filled square downward. Yes.

  In the present embodiment, the coefficients I, t, and y are obtained by fitting the current I and the reaction resistance Rct at each measurement point constituting the graph of the reaction resistance Rct shown in FIG. 6 using the following equation (1). .

  Rct (I) = a × exp (I / t) + y (1)

  By obtaining the above equation (1), the relationship between the reaction resistance Rct having current dependency and the current can be obtained. FIG. 7 is a diagram illustrating a relationship between an estimated value (solid line) according to Expression (1) and an actual measurement value (rectangle). As shown in FIG. 7, since the estimated value and the actually measured value are in good agreement, it can be understood that the estimation using Expression (1) is appropriate.

  By obtaining the above equation (1), the reaction resistance Rct at an arbitrary current value can be obtained. By using the reaction resistance Rct, for example, as shown in FIG. 8, an SOF (State of Function) having a high correlation with the internal resistance R can be obtained at an arbitrary current value. In FIG. 8, the horizontal axis indicates internal resistance, and the vertical axis indicates SOF. A solid line indicates an estimated value, and a circle indicates an actually measured value.

  Further, the value of the reaction resistance Rct with respect to a predetermined current value at an arbitrary time point is an initial value Rct0 of the internal resistance at the predetermined current value (for example, the value of the internal resistance when the rechargeable battery 14 is new or replaced). By dividing and expressing it as a percentage (= Rct / Rct0 × 100), SOH (State of Health) can be obtained.

  In the example described above, SOF and SOH are obtained from only the reaction resistance Rct, but may be obtained from Rct + Rohm. In addition, when overcharge or overdischarge is performed or charging / discharging is repeated in a short cycle, variation in deterioration occurs between cells of the rechargeable battery 14. For this reason, the history of the use state of the rechargeable battery 14 is stored, and when the use history has such a use history that induces variation in deterioration between cells of the rechargeable battery 14, the SOH obtained by the above-described formula is corrected. You may do it. As the correction formula, the following formula (2) can be used. Here, g () is a function having a value of 1 or less, a value close to 1 when there is little variation in deterioration between cells, and a function that decreases as the variation in deterioration between cells increases. It is. That is, g () = 1 when the rechargeable battery 14 is new, and g () = 1 when there is no variation in the rechargeable battery 14 even when deterioration is advanced. On the other hand, when the deterioration of the rechargeable battery 14 varies, g () is a value close to, for example, “the capacity of the most deteriorated cell / the average value of the capacities of all cells”.

  SOH = f (Rohm, Rct1, Rct2, C1, C2) × g (one or a plurality of variables according to usage history) (2)

  In this embodiment, since the value of the internal resistance at an arbitrary current value can be obtained by using the expression (1), it is not necessary to add a configuration for flowing a constant current, and the cost of the apparatus increases. Can be prevented. Further, since it is not necessary to perform measurement after waiting for a predetermined current, internal resistance can be obtained at a desired timing, and states such as SOH and SOF can be obtained.

  Next, an example of processing executed in the embodiment of the present invention will be described with reference to FIG. When the processing of the flowchart shown in FIG. 9 is started, the following steps are executed.

  In step S <b> 10, the CPU 10 a calculates the conductive resistance / liquid resistance Rohm of the rechargeable battery 14. Specifically, for example, the CPU 10a controls a discharge circuit (not shown), discharges the rechargeable battery 14 with a pulse wave having a rectangular wave shape at a repetition frequency of 100 Hz or less, and discharges the voltage V1 and the discharge voltage before discharge. A value obtained by dividing the difference (V1−V2) of the subsequent voltage V2 by the current I can be defined as the conductive resistance / liquid resistance Rohm. Of course, other methods may be used.

  In step S11, the CPU 10a refers to the output of the current sensor 12, determines whether or not the rechargeable battery 14 is in a discharged state, and proceeds to step S12 if determined to be in a discharged state (step S11: Y). In other cases (step S11: N), the process ends. For example, when the engine 16 is started by the starter motor 17, it is determined as Y and the process proceeds to step S12. Note that the following steps may be executed when a current is supplied to a load other than the starter motor 17 (for example, a steering motor). Any load that can supply a certain amount of current can be measured.

  In step S <b> 12, the CPU 10 a refers to the output of the voltage sensor 11 and obtains the terminal voltage V of the rechargeable battery 14.

  In step S <b> 13, the CPU 10 a refers to the output of the current sensor 12 and obtains the current I flowing through the rechargeable battery 14.

  In step S14, the CPU 10a acquires the OCV. For example, refer to the output of the voltage sensor 11 when the rechargeable battery 14 is stable (for example, when a predetermined time (for example, several hours to several tens of hours) has elapsed since the vehicle was stopped and the engine 16 was stopped). The OCV acquired and stored in the RAM 10c is acquired.

  In step S15, the CPU 10a obtains the internal resistance R by R = (V−OCV) / I based on the terminal voltage V measured in step S12, the current I measured in step S13, and the OCV acquired in step S14.

  In step S16, the CPU 10a sets the value obtained by subtracting the conductive resistance / liquid resistance Rohm obtained in step S10 from the internal resistance R obtained in step S15 as the value of the reaction resistance Rct.

  In step S17, the CPU 10a stores the reaction resistance Rct obtained in step S16 and the value of the current I measured in step S13 in the RAM 10c.

  In step S18, for example, the CPU 10a refers to the output of the current sensor 12 to determine whether or not the discharge has ended. If it is determined that the discharge has ended (step S18: Y), the process proceeds to step S19. In this case (step S18: N), the process returns to step S12 and the same process as described above is repeated. Note that instead of the end of the discharge, the process may proceed to step S19 when a predetermined time has elapsed, or may proceed to step S19 when the current value becomes equal to or less than a predetermined threshold value.

  In step S19, the CPU 10a executes a process of fitting the above-described equation (1) using the values of Rct, I stored in the RAM 10c by the processes of steps S12 to S18. In addition, as a method for obtaining the coefficients a, t, and y in the equation (1), there are calculation methods such as a least square method, a Kalman filter, and a neural network, and an optimum coefficient is determined by appropriately using these calculation methods. can do.

  In step S20, the CPU 10a corrects the values of the coefficients a, t, y in the equation (1) obtained in step S19 with reference to the output of the temperature sensor 13. Specifically, for example, the CPU 10 a estimates the temperature of the electrolytic solution of the rechargeable battery 14 based on the external temperature of the rechargeable battery 14 detected by the temperature sensor 13 and the thermal equivalent circuit model of the rechargeable battery 14. To do. The CPU 10a uses a conversion formula stored in the ROM 10b for converting the values of the coefficients a, t, y at that time into the values of the coefficients a, t, y at a reference temperature (for example, 25 ° C.), The values of the coefficients a, t, y at the reference temperature are obtained. A table may be used instead of the conversion formula.

  In step S21, the CPU 10a corrects the coefficients a, t, and y corrected by the temperature in step S20 based on the SOC at that time. Specifically, for example, the CPU 10a obtains the SOC at that time by cumulatively adding the current value flowing into and out of the rechargeable battery 14 to the SOC obtained based on the relationship between the OCV and the SOC. The CPU 10a uses a conversion formula for converting the values of the coefficients a, t, y at that time stored in the ROM 10b into the values of the coefficients a, t, y in the reference SOC (for example, 100%), The values of the coefficients a, t, y in the reference SOC are obtained. A table may be used instead of the conversion formula.

  In step S22, the CPU 10a corrects the values of the coefficients a, t, and y corrected by the SOC in step S21 based on the time from the start of discharge. Specifically, for example, the CPU 10a measures the time from the start to the end of discharge, and stores the values of the coefficients a, t, y at that time stored in the ROM 10b as a reference time (for example, 1). The values of the coefficients a, t, and y in the reference SOC are obtained using a conversion formula for converting the values into the values of the coefficients a, t, and y in seconds). A table may be used instead of the conversion formula.

  In step S23, the CPU 10a obtains the SOF using Rct (I) whose coefficients have been corrected in steps S20 to S22. More specifically, the value of the reaction resistance Rct at a predetermined current I is obtained using Rct (I), and the SOF at the predetermined current I can be obtained from the relationship between Rct and SOF. Note that SOF may be obtained using a value obtained by adding Rohm to Rct.

  In step S24, the CPU 10a obtains SOH using Rct (I) whose coefficients have been corrected in steps S20 to S22. More specifically, the value of the reaction resistance Rct at a predetermined current value is obtained using Rct (I), and is expressed as a percentage by dividing by the initial value Rct0 of the reaction resistance at the predetermined current value (= Rct / Rct0 × 100), SOH can be obtained. Note that SOH may be obtained using a value obtained by adding Rohm to Rct.

  According to the above processing, the above-described operation can be realized.

(C) Description of Modified Embodiment It goes without saying that the above embodiment is merely an example, and the present invention is not limited to the case described above. For example, in the above embodiment, the relationship between the current and the reaction resistance is obtained using the equation (1), but other equations may be used. For example, in the formula (1), the exponential function term is only one term, but it may have two or more terms. Alternatively, the fitting may be performed using a polynomial (Rct (I) = a ₀ + a ₁ I + a ₂ I ² +... A _n I ⁿ ) (n ≧ 1) whose indefinite element is I.

  Further, in the above embodiment, the values of the coefficients a, t, and y in the equation (1) are set according to the temperature, the SOC, and the elapsed time from the start of discharge by the processing of step S20 to step S22 in the flowchart shown in FIG. I corrected it. In addition to this, for example, as shown in steps S30 to S32 of FIG. 10, the value of the reaction resistance Rct may be corrected according to the temperature, the SOC, and the elapsed time from the start of discharge. In FIG. 10, steps S20 to 22 are excluded and steps S30 to S32 are added as compared to FIG. The other processes are the same as those in FIG.

  More specifically, in the flowchart shown in FIG. 10, the following processing is executed in steps S30 to S32.

  In step S30, the CPU 10a corrects the value of the reaction resistance Rct obtained in step S16 with reference to the output of the temperature sensor 13. Specifically, for example, the CPU 10 a estimates the temperature of the electrolytic solution of the rechargeable battery 14 based on the external temperature of the rechargeable battery 14 detected by the temperature sensor 13 and the thermal equivalent circuit model of the rechargeable battery 14. To do. The CPU 10a uses the conversion equation for converting the value of the reaction resistance Rct at that time stored in the ROM 10b into the value of the reaction resistance Rct at the reference temperature (for example, 25 ° C.), and the reaction resistance Rct at the reference temperature. Get the value of. A table may be used instead of the conversion formula.

  In step S31, the CPU 10a corrects the value of the reaction resistance Rct corrected by the temperature in step S30 based on the SOC at that time. Specifically, for example, the CPU 10a obtains the SOC at that time by cumulatively adding the current value flowing into and out of the rechargeable battery 14 to the SOC obtained based on the relationship between the OCV and the SOC. The CPU 10a uses the conversion equation for converting the value of the reaction resistance Rct at that time stored in the ROM 10b into the value of the reaction resistance Rct in the reference SOC (for example, 100%), and the reaction resistance Rct in the reference SOC. Get the value of. A table may be used instead of the conversion formula.

  In step S32, the CPU 10a corrects the value of the reaction resistance Rct corrected by the SOC in step S31 based on the time from the start of discharge. Specifically, for example, the CPU 10a measures the time from the start of discharge, and the value of the reaction resistance Rct at that time stored in the ROM 10b is the reaction resistance at the reference time (for example, 1 second) from the start of discharge. The value of the reaction resistance Rct at the reference SOC is obtained using a conversion formula for converting into the value of Rct. A table may be used instead of the conversion formula.

  Also in the flowchart shown in FIG. 10, the influence of the error on the equation (1) can be reduced by the temperature, the SOC, and the elapsed time from the start of discharge.

  In the above embodiment, the case where the current flows through the starter motor 17 has been described as an example. However, the measurement is performed when the current flows through a load (for example, a steering motor) other than the starter motor 17. Also good.

  Further, in the processes of FIGS. 9 and 10, correction is made for all of the temperature, the SOC, and the elapsed time from the start of discharge, but correction is made for at least one of these. Also good.

  In the above embodiment, the open circuit voltage is measured when the rechargeable battery 14 is stable. However, the open circuit voltage may be obtained based on the estimated value. For example, the open circuit voltage when the rechargeable battery 14 is stable can be estimated by using a voltage characteristic equation that can approximate the temporal variation of the open circuit voltage. By using an approximate expression including a high-order (for example, fourth-order or higher) exponential decay function as the voltage characteristic expression, it is possible to estimate the time variation of the open circuit voltage with high accuracy.

  Further, the flowcharts shown in FIGS. 9 and 10 are examples, and the present invention is not limited only to the processes of these flowcharts. For example, in the flowcharts shown in FIGS. 9 and 10, Rohm is obtained in step S10, but may be arranged after step S11 if it is before the process of step S16. Also, the process of acquiring the OCV in step S14 may be arranged before step S13 as long as it is before the process of step S15.

  Moreover, the electrical equivalent circuit model shown in FIG. 5 is an example, and is not limited to this model. For example, the number of RC parallel circuits may be one, three or more, and an equivalent circuit model having at least one RC parallel circuit may be used.

DESCRIPTION OF SYMBOLS 1 Chargeable battery state detection apparatus 10 Control part 10a CPU
10b ROM
10c RAM
10d Communication unit 10e I / F
DESCRIPTION OF SYMBOLS 11 Voltage sensor 12 Current sensor 13 Temperature sensor 14 Rechargeable battery 15 Alternator 16 Engine 17 Starter motor 18 Load

Claims (7)

In the rechargeable battery state detection device that detects the state of the rechargeable battery,
Determining means for determining whether or not the rechargeable battery is in a discharged state;
When the determination means determines that the battery is being discharged, the measurement means measures the current flowing through the rechargeable battery and the value of the terminal voltage a plurality of times;
Calculation means for calculating the value of the internal resistance of the rechargeable battery at each measurement timing from the values of the current and terminal voltage measured by the measurement means;
A specifying means for fitting the value of the internal resistance at each measurement timing calculated by the calculating means as a function having an electric current as an input variable, and specifying the internal resistance as the function having an electric current as an input variable;
Detecting means for detecting a state of the rechargeable battery based on the function specified by the specifying means;
A rechargeable battery state detection device comprising:   The rechargeable battery state detection device according to claim 1, wherein the function used by the specifying unit includes at least one exponential function term.   3. The rechargeable battery state detection device according to claim 1, wherein the specifying unit fits the function by a calculation process using a least square method, a Kalman filter, or a neural network.   The specifying means corrects at least one of the coefficients of the function based on at least one of an ambient temperature or an electrolyte temperature of the rechargeable battery, an SOC, and an elapsed time from the start of discharge. The rechargeable battery state detection device according to any one of claims 1 to 3.   5. The chargeable device according to claim 1, wherein the detecting unit obtains SOF as a response voltage when a predetermined current flows through the rechargeable battery based on the function. Battery state detection device.   5. The rechargeable battery state detection device according to claim 1, wherein the detection unit obtains SOH as a degree of deterioration of the rechargeable battery based on the function. In the rechargeable battery state detection method for detecting the state of the rechargeable battery,
A determination step of determining whether or not the rechargeable battery is in a discharged state;
If it is determined that the battery is being discharged in the determination step, a measurement step of measuring the current flowing through the rechargeable battery and the value of the terminal voltage a plurality of times;
A calculation step of calculating a value of an internal resistance of the rechargeable battery at each measurement timing from the value of the current and the terminal voltage measured in the measurement step;
A specific step of fitting the value of the internal resistance at each measurement timing calculated in the calculation step as a function using the current as an input variable, and specifying the internal resistance as the function using the current as an input variable When,
A detecting step for detecting a state of the rechargeable battery based on the function specified in the specifying step;
A rechargeable battery state detection method characterized by comprising:

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