JP7500404B2 - Storage element charge rate estimator - Google Patents

Description

The present invention relates to a device and method for estimating the charging rate of a storage element in which a flat region with small open circuit voltage changes and a region with large changes appear in response to changes in the charging rate.

Conventional examples of this type of charging rate estimation device and charging rate estimation method include the state estimation device and state estimation method disclosed in Patent Document 1.

The state estimation device and the state estimation method disclosed in the document utilize the SOC-OCV characteristics of the secondary battery shown in FIG. 2 of the document. The SOC-OCV characteristics are expressed with the horizontal axis representing SOC (charging rate) and the vertical axis representing OCV (open circuit voltage), and the OCV change relative to the SOC change is expressed as the open circuit voltage characteristics of the secondary battery. As shown in the SOC-OCV characteristics, the secondary battery has a flat region where the OCV change relative to the SOC change is relatively small, and a large change region. In the state estimation device and the state estimation method disclosed in the document, as shown in FIG. 6 of the document, in the change region where the OCV change relative to the SOC change is large, the SOC estimated by the current integration method is corrected using a Kalman filter. Also, in the flat region where the OCV change relative to the SOC change is small, the SOC estimated by the current integration method is not corrected, and the SOC estimated by the current integration method is taken as the SOC at that time.

In addition, in the actual operation of a battery pack using such a secondary battery as a storage element, the OCV may be measured at the timing of transition from the charging or discharging period to the resting period in each charge/discharge cycle in which charging and discharging are repeated with resting periods in between. Then, the SOC corresponding to the measured OCV may be identified from a pre-stored SOC-OCV correspondence table, and the identified SOC may be estimated as the SOC at the end of the resting period, and the initial SOC at the transition to the resting period may be corrected.

Patent No. 6657967

However, in the plateau region of the SOC-OCV characteristics of a secondary battery, where the change in OCV relative to the change in SOC is relatively small, the SOC changes significantly in response to a small change in OCV. Furthermore, the OCV value is subject to hysteresis due to the charge/discharge history of the secondary battery, and the measured value changes depending on the number of charge/discharge cycles that have elapsed due to this hysteresis. Therefore, in the plateau region where the change in OCV is relatively small, if the SOC is estimated based on the SOC-OCV characteristics from the measured OCV value, an error will occur in the estimated SOC. This error occurs significantly in the estimated SOC due to the influence of the above-mentioned hysteresis for each charge/discharge cycle.

This phenomenon is particularly noticeable in olivine-based lithium-ion secondary batteries, and in the plateau region of the SOC-OCV characteristics of olivine-based lithium-ion secondary batteries, a deviation of just a few mV in OCV can cause an error of several tens of percent in the SOC. For this reason, in the plateau region where OCV change is relatively small, if the SOC is estimated based on the SOC-OCV characteristics from the measured OCV value, and a determination is made based on the estimated SOC as to whether the OCV characteristics of the secondary battery at that time are in the plateau region or the changing region, then an accurate determination cannot be made.

Therefore, the state estimation device and state estimation method disclosed in the above-mentioned conventional Patent Document 1, which estimate the SOC based on whether the olivine-based lithium-ion secondary battery is in the plateau region or the change region of the SOC-OCV characteristics, cannot reliably estimate the SOC.
Furthermore, in actual operation of the above-described conventional battery pack, when the OCV value is measured in a flat region where the OCV change is relatively small, the SOC specified by the measured OCV value from the pre-stored SOC-OCV correspondence table contains a large error.

The present invention has been made in consideration of the above points, and aims to provide a charging rate estimation device and a charging rate estimation method that can reliably estimate the SOC for a storage element in which a flat region with small OCV changes and a region with large changes appear in response to SOC changes.

For this purpose, the present invention provides
a current measuring unit for measuring a current flowing through an energy storage element having an open circuit voltage characteristic in which a relatively small flat region and a relatively large change region of the open circuit voltage appear with respect to a change in the charging rate;
A voltage measuring unit for measuring a terminal voltage of the storage element;
A charging rate estimating unit that estimates a charging rate of the storage element;
a charging rate correction unit that corrects the charging rate of the storage element estimated by the charging rate estimation unit;
an idle period determination unit that determines whether the storage element has entered an idle period because the current flowing through the storage element has not been measured by the current measurement unit for a predetermined period;
an estimated charging rate storage unit that stores, as an initial charging rate, a charging rate estimated by the charging rate estimation unit when the idle period determination unit determines that the storage element has entered an idle period;
a suspension period end determination unit that determines whether the suspension period has ended by measuring, by a current measurement unit, when a current starts to flow through the storage element during the suspension period;
an internal resistance value calculation unit that calculates an internal resistance value of the storage element from a current that starts to flow through the storage element during the pause period and a terminal- to- terminal voltage of the storage element measured by a voltage measurement unit at that time;
The present invention provides a charging rate estimating device for a storage element that includes a charging rate correction unit that, when the internal resistance value calculated by the internal resistance value calculation unit is equal to or lower than a predetermined value, sets the initial charging rate stored in the estimated charging rate memory unit as the charging rate of the storage element at the end of the rest period .

According to this configuration, when the internal resistance calculated by the internal resistance calculation unit is equal to or less than a predetermined value, the storage element is determined to be in a plateau region where the open circuit voltage characteristic versus the charging rate has a small open circuit voltage change. In the plateau region where the open circuit voltage characteristic versus the charging rate has a small open circuit voltage change, the internal resistance of the storage element is smaller than in the region where the open circuit voltage change is large. Moreover, the internal resistance of the storage element does not have a large hysteresis due to the charge and discharge history, unlike the charging rate.

Therefore, according to this configuration, the calculated internal resistance value is compared with a predetermined value, and the charging rate correction unit accurately determines whether the open circuit voltage characteristic with respect to the charging rate is in a plateau region where the open circuit voltage change is small or in a region where the change is large. If it is determined that the open circuit voltage characteristic is in a plateau region where the open circuit voltage change is small, the corrected charging rate obtained by correction by the charging rate correction unit is deemed to contain a large error, and the charging rate estimated by the charging rate estimation unit is deemed to be the charging rate of the storage element.

It is therefore possible to provide a state of charge estimation device that can reliably estimate the state of charge of a storage element in which a flat region with small open circuit voltage changes and a region with large changes appear in relation to the state of charge change.

According to this configuration, when the suspension period determination unit determines that the storage element has entered a suspension period, the suspension rate estimated by the suspension rate estimation unit is stored in the estimated suspension rate storage unit as an initial suspension rate. Also, the internal resistance value when the suspension period end determination unit determines that the suspension period has ended is calculated by the internal resistance value calculation unit , and it is determined whether the calculated internal resistance value is equal to or less than a predetermined value. If it is determined that the internal resistance value is equal to or less than the predetermined value, the suspension rate correction unit sets the initial suspension rate stored in the estimated suspension rate storage unit as the suspension rate of the storage element at the end of the suspension period.

As a result, in the actual operation of a battery pack that is composed of a storage element in which a flat region with small open circuit voltage changes and a region with large changes appear in response to changes in the charging rate, it becomes possible to reliably estimate the charging rate at the end of the rest period of the battery pack.

According to the present invention, as described above, it is possible to provide a charging rate estimation device that can reliably estimate the charging rate for a storage element in which a flat region with small open circuit voltage change and a region with large change appear in relation to charging rate change.

1 is a block diagram showing a schematic configuration of a battery pack including a storage element state of charge estimation device according to an embodiment of the present invention; 1 is a graph showing SOC-OCV characteristics of a secondary battery referenced in a storage element state of charge estimation device and state of charge estimation method according to an embodiment; 3 is a diagram showing an SOC-OCV table corresponding to the SOC-OCV characteristics shown in FIG. 2, which is stored in the storage element state-of-charge estimation device according to the embodiment; 3 is a graph showing the SOC-OCV curve shown in FIG. 2 superimposed with the SOC-DCR curve of a secondary battery. 4 is a flowchart showing an outline of a process in a method for estimating a charging rate of a storage element according to an embodiment of the present invention.

Next, we will explain a storage element charging rate estimation device and charging rate estimation method according to one embodiment of the present invention.

Figure 1 is a block diagram showing the schematic configuration of a battery pack 2 equipped with a storage element charging rate estimation device 1 according to one embodiment.

The battery pack 2 supplies power to a power source that runs on electrical energy, for example in an electric vehicle or a small boat. The battery pack 2 has a battery pack 3, a current sensor 4, and a battery management unit (BMU) 5 that manages the battery pack 3. The current sensor 4 and BMU 5 constitute the charging rate estimation device 1.

The battery pack 3 is configured by stacking and connecting multiple laminated cells made up of secondary batteries 31 in series, and each secondary battery 31 serves as a power storage element. In this embodiment, each secondary battery 31 is an olivine (iron phosphate) lithium ion secondary battery (LFP), and the change in open circuit voltage (OCV) relative to the change in state of charge (SOC) shows the SOC-OCV characteristics shown in the graph of FIG. 2. The horizontal axis of the graph is SOC [%], the vertical axis is OCV [mV], and the graph shows SOC-OCV curve A. As shown in the SOC-OCV characteristics, each secondary battery 31 shows open circuit voltage characteristics having a flat region L where the change in OCV relative to the change in SOC is relatively small, and a large change region H. The flat region L is set to a region where the change in OCV relative to the change in SOC is, for example, 0.5 [mV/%] or less.

The charging rate is the ratio [%] of the remaining capacity to the fully charged capacity of the secondary battery 31, and is called the SOC (State Of Charge). The open circuit voltage is the voltage between the terminals of the secondary battery 31 when no current flows through the secondary battery 31, and is called the OCV (Open Circuit Voltage).

Each secondary battery 31 and current sensor 4 are connected in series via wiring 6 and connected to a load 7, such as a charger 7 mounted on an electric vehicle or the like, or a power source provided inside an electric vehicle or the like. The charger 7 charges the battery pack 3, and the load 7 receives power from the battery pack 3 and consumes it.

The current sensor 4 constitutes a current measuring unit that measures the current flowing through each secondary battery 31. The current sensor 4 measures the current value of each secondary battery 31 at regular intervals and transmits the measured current measurement value data to the control unit 51 in the BMU 5. The BMU 5 includes a control unit 51, a voltage detection circuit 52, and a temperature sensor 53. The control unit 51 includes a central processing unit (CPU) 51a, a memory 51b, and a communication unit 51c. The communication unit 51c communicates with an ECU (Electronic Control Unit) 8 mounted on an electric vehicle, a small boat, etc., and transmits information about the secondary battery 31 to the ECU 8. The voltage detection circuit 52 constitutes a voltage measuring unit that is connected to both ends of each secondary battery 31 via a detection line and measures the terminal voltage of each secondary battery 31 in response to an instruction from the control unit 51. The temperature sensor 53 is a contact type or a non-contact type that measures the temperature T [°C] of each secondary battery 31.

The memory 51b in the control unit 51 stores in advance a computer program for executing a method for estimating the charging rate of a storage element according to one embodiment, and data necessary to execute the program. Various functional blocks are configured in the control unit 51 by the CPU 51a controlling each part of the circuit according to this computer program. These functional blocks include a charging rate estimation unit 51d, a charging rate correction unit 51e, an internal resistance calculation unit 51f, and a charging rate correction unit 51g.

The charging rate estimation unit 51d estimates the charging rate of each secondary battery 31. The charging rate correction unit 51e corrects the charging rate of each secondary battery 31 estimated by the charging rate estimation unit 51d. The internal resistance value calculation unit 51f calculates the direct current internal resistance (DCR) value of each secondary battery 31 from the current flowing through the secondary battery 31 measured by the current sensor 4 and the terminal voltage of the secondary battery 31 measured by the voltage detection circuit 52. The charging rate correction unit 51g sets the charging rate estimated by the charging rate estimation unit 51d as the charging rate of the secondary battery 31 when the direct current internal resistance value calculated by the internal resistance value calculation unit 51f is equal to or less than a predetermined value y described later.

The memory 51b also constitutes an estimated charging rate storage section that stores the charging rate estimated by the charging rate estimation section 51d, and a corrected charging rate storage section that stores the charging rate corrected by the charging rate correction section 51e. The memory 51b also constitutes an open circuit voltage characteristic storage section that stores the open circuit voltage characteristic shown in FIG. 2, and the memory 51b prestores an SOC-OCV table that associates the open circuit voltage OCV [mV] value with each charging rate (SOC [%]) value, as shown in FIG. 3. The flat region L shown in FIG. 2 corresponds to the characteristic represented by each OCV [mV] value when the SOC is 40 to 70 [%] shown in the table. The memory 51b also prestores an SOC-DCR table (not shown) that stores the direct current internal resistance (DCR) [mΩ] value measured for each charging rate (SOC [%]).

In the graph shown in FIG. 4, SOC-DCR curve B, which is plotted using each value in the SOC-DCR table stored in memory 51b, is shown superimposed on SOC-OCV curve A shown in FIG. 2. SOC-OCV curve A is shown as a solid line, and SOC-DCR curve B is shown as a dashed line. The horizontal axis of the graph is SOC [%], the vertical axis on the left is OCV [mV], and the vertical axis on the right is DCR [mΩ]. The arrows in the graph indicate which vertical axis curve A or B corresponds to.

From the SOC-DCR curve B shown in the graph, it can be seen that the DC internal resistance value of the secondary battery 31 is smaller in the flat region L of the open circuit voltage than in the change region H of the open circuit voltage, and is smaller than the constant value y [mΩ]. The flat region L is set in the SOC-OCV curve A in a region where the change in open circuit voltage relative to the change in the charging rate is within a predetermined range, for example, 0.5 [mV/%] or less. The constant value y [mΩ] defines the flat region L set in the SOC-OCV curve A in the SOC-DCR curve B, and in this embodiment, it is set as the predetermined value of the DC internal resistance value compared by the charging rate correction unit 51g. However, the method of determining the predetermined value of the DC internal resistance value in the present invention is not limited to this, and the predetermined value of the DC internal resistance value may be changed as necessary from the DC internal resistance value in a range smaller than the constant value y [mΩ] that the secondary battery 31 exhibits in response to the change in the charging rate in the flat region L in the SOC-DCR curve B.

In addition, in this embodiment, the charging rate estimation unit 51d estimates the charging rate of the secondary battery 31 using a current integration method. The charging rate correction unit 51e corrects the charging rate of the secondary battery 31 estimated by the charging rate estimation unit 51d to the charging rate (see FIG. 3) stored in the open circuit voltage characteristic storage unit corresponding to the value of the open circuit voltage measured by the voltage detection circuit 52.

In this embodiment, the computer program stored in the memory 51b configures the control unit 51 with functional blocks of a pause period determination unit 51h and a pause period end determination unit 51i as shown in FIG. 1. The pause period determination unit 51h performs the function of determining whether the secondary battery 31 has entered a pause period when the current flowing through the secondary battery 31 is not measured by the current sensor 4 for a predetermined period. The pause period end determination unit 51i performs the function of determining whether the pause period has ended when the current sensor 4 measures the start of current flowing through the secondary battery 31 during the pause period.

The estimated charging rate storage unit stores the charging rate estimated by the charging rate estimation unit 51d when the suspension period determination unit 51h determines that the secondary battery 31 has entered a suspension period as the initial charging rate. The internal resistance value calculation unit 51f calculates the DC internal resistance value of the secondary battery 31 from the current that starts to flow to the secondary battery 31 during the suspension period and the terminal voltage of the secondary battery 31 measured by the voltage detection circuit 52 at that time. When the internal resistance value calculated by the internal resistance value calculation unit 51f is equal to or less than a predetermined value y, the charging rate correction unit 51g sets the initial charging rate stored in the estimated charging rate storage unit as the charging rate of the secondary battery 31 at the end of the suspension period.

Figure 5 is a flowchart outlining the process of a method for estimating the charge rate of a storage element according to one embodiment.

First, the CPU 51a acquires the current SOC value of each secondary battery 31 (see step 101). Next, the charging rate estimation unit 51d estimates the SOC value of each secondary battery 31 by the current integration method (see step 102). The charging rate estimated in this charging rate estimation step of step 102 is stored in the estimated charging rate storage unit. Next, the current value flowing through each secondary battery 31 is measured and acquired by the current sensor 4 (see step 103). Then, the rest period determination unit 51h determines whether or not the current flowing through each secondary battery 31 has become zero for a predetermined period and is not measured by the current sensor 4, and each secondary battery 31 has entered a rest period (see step 104). In this embodiment, whether or not the current value acquired in step 103 is zero for a certain period or more, for example, for two hours or more, is determined by a clock generated by a clock unit (not shown) in the control unit 51. If the current value acquired in step 103 is not zero for a certain period of time or more, and the judgment result in step 104 is No, the process returns to step 102 and the processes in steps 102 to 104 are repeated.

On the other hand, if the current value acquired in step 103 becomes zero for a certain period of time or more and the judgment result in step 104 becomes Yes, it is next judged whether or not it has been judged that each secondary battery 31 has already entered a sleep period (see step 105). When the processing of this step 105 is executed for the first time, it has not been judged that each secondary battery 31 has already entered a sleep period, so the judgment result in step 105 is No. In this case, it is judged that each secondary battery 31 has entered a sleep period in the sleep period judgment step of step 105. Then, the charging rate estimated in the charging rate estimation step of step 102 is acquired as the charging rate at the time of entering the sleep period, and this acquired charging rate is stored in the estimated charging rate storage unit as the initial charging rate RSOC (see step 106). By this processing of step 106, the charging rate SOC stored in the estimated charging rate storage unit is set to the initial charging rate RSOC (SOC = RSOC).

On the other hand, if it has been determined that each secondary battery 31 has already entered the rest period and the determination result of step 105 is Yes, then an open circuit voltage (OCV) value is obtained from the terminal voltage of the secondary battery 31 measured by the voltage detection circuit 52 (see step 107). Next, the charging rate of each secondary battery 31 estimated in the charging rate estimation step of step 102 is corrected to the charging rate VSOC stored in the open circuit voltage characteristic storage unit as the SOC-OCV characteristic corresponding to the value of the open circuit voltage acquired in step 107 (see step 108). By this process of step 108, the charging rate SOC stored in the corrected charging rate storage unit is set to the corrected charging rate VSOC (SOC = VSOC). Step 108 constitutes a charging rate correction step for correcting the charging rate of the secondary battery 31 estimated in the charging rate estimation step of step 102, and a corrected charging rate storage step for storing the charging rate corrected in this charging rate correction step in the corrected charging rate storage unit. In addition, in an open circuit voltage characteristics storage step (not shown), the open circuit voltage values for each charging rate value for each secondary battery 31 are stored in advance as open circuit voltage characteristics in the open circuit voltage characteristics storage unit.

Next, the current sensor 4 measures the start of current flowing through each secondary battery 31 during the idle period, and determines whether or not a starting current has flowed through each secondary battery 31 (see step 109). This step 109 constitutes an idle period end determination step for determining whether or not the idle period of each secondary battery 31 has ended. If no starting current is detected flowing through each secondary battery 31, and the determination result of step 109 is No, the process returns to step 105, and steps 105 to 109 are repeated.

When a transient response caused by the starting current flowing through each secondary battery 31 is detected and the judgment result in step 109 is Yes, it is judged that the rest period of each secondary battery 31 has ended. In this case, the DC internal resistance value of the secondary battery 31 is then calculated by the internal resistance value calculation unit 51f from the current flowing through the secondary battery 31 measured by the current sensor 4 and the terminal voltage of the secondary battery 31 measured by the voltage detection circuit 52 (see step 110).

Next, it is determined whether the internal resistance value calculated in this internal resistance value calculation step of step 110 is equal to or less than a predetermined value y selected from the range of internal resistance values exhibited by the secondary battery 31 in response to the change in the charging rate in the flat region L (see step 111). If the internal resistance value calculated in step 110 is equal to or less than the predetermined value y, the determination result of step 111 is Yes, and the charging rate SOC of the secondary battery 31 is set to the initial charging rate RSOC stored in the estimated charging rate storage unit by the charging rate correction unit 51g (see step 112). Also, if the internal resistance value calculated in step 110 is not equal to or less than the predetermined value y, the determination result of step 111 is No, and the charging rate SOC of the secondary battery 31 is set to the corrected charging rate VSOC stored in the corrected charging rate storage unit by the charging rate correction unit 51g (see step 113). Steps 111 and 112 constitute a charging rate correction step in which, if the internal resistance value calculated in the internal resistance value calculation step of step 110 is equal to or less than a predetermined value y, the charging rate estimated in the charging rate estimation step of step 102 is set as the charging rate of the secondary battery 31.

According to the storage element charging rate estimation device and charging rate estimation method of this embodiment, when the internal resistance calculated by the internal resistance calculation unit 51f and the internal resistance calculation step of step 110 is equal to or less than a predetermined value y, the secondary battery 31 is determined to be in a plateau region L where the open circuit voltage characteristic versus charging rate is small. In the plateau region L where the open circuit voltage characteristic versus charging rate is small, the internal resistance of the secondary battery 31 is smaller than the region H where the open circuit voltage is large, as shown in the graph of FIG. 4. Furthermore, the internal resistance of the secondary battery 31 does not have large hysteresis due to the charge and discharge history, unlike the charging rate.

Therefore, according to the storage element charging rate estimation device and charging rate estimation method of this embodiment, the calculated internal resistance value is compared with a predetermined value y, and whether the open circuit voltage characteristic with respect to the charging rate is in a plateau region L where the open circuit voltage change is small or in a large change region H is accurately determined by the charging rate correction unit 51g and the charging rate correction step of steps 111 and 112. The charging rate estimated by the current integration method in step 102 accumulates an error over time. In the present invention, the accuracy of the region determination can be improved compared to the case where the SOC-OCV characteristic is referenced from the estimated charging rate and whether it is in the plateau region L or the change region H, as in Patent Document 1, for example. Then, when it is determined that the open circuit voltage characteristic is in the plateau region L where the open circuit voltage change is small, the corrected charging rate obtained by correction by the charging rate correction unit 51e and the charging rate correction step of step 108 is considered to include a large error, and the charging rate estimated by the charging rate estimation unit 51d and the charging rate estimation step of step 102 is considered to be the charging rate of the secondary battery 31 at that time.

This makes it possible to provide a charging rate estimation device and a charging rate estimation method that can reliably estimate the charging rate for a secondary battery 31 in which a flat region L of small open circuit voltage change and a region H of large change appear in response to charging rate change.

If the open circuit voltage characteristic is in the flat region L where the open circuit voltage change is small, and the corrected charging rate obtained by correction by the charging rate correction unit 51e and the charging rate correction step of step 108 is adopted, the corrected charging rate will contain a large error. In other words, from the table shown in FIG. 3, if the OCV is measured to be, for example, 3320 mV at the timing when the charging or discharging period transitions to the resting period, the SOC will be corrected to 70%, and if the OCV is measured to be, for example, 3306 mV at the timing when the resting period ends after the secondary battery 31 is charged and discharged a certain number of cycles, the SOC will be corrected to 40%, resulting in a large error of 30% in the corrected charging rate. This SOC error is due to the occurrence of a deviation in the OCV in the flat region L due to hysteresis every charge and discharge cycle.

In addition, according to the storage element charging rate estimation device and charging rate estimation method of this embodiment, when the secondary battery 31 is determined to have entered a pause period by the pause period determination unit 51h and the pause period determination step of step 105, the charging rate estimated by the charging rate estimation unit 51d and the charging rate estimation step of step 102 is stored as an initial charging rate RSOC in the estimated charging rate storage unit. In addition, the internal resistance value when the pause period end determination unit 51i and the pause period end determination step of step 109 determine that the pause period has ended is calculated by the internal resistance value calculation unit 51f and the internal resistance value calculation step of step 108, and it is determined whether the calculated internal resistance value is equal to or less than a predetermined value y. If it is determined that the internal resistance value is equal to or less than the predetermined value y, the charging rate correction unit 51g and the charging rate correction steps of steps 111 and 112 make the initial charging rate RSOC stored in the estimated charging rate storage unit the charging rate of the secondary battery 31 at the end of the pause period.

As a result, in the actual operation of a battery pack 20 that is configured using a secondary battery 31 in which a flat region L of small open circuit voltage change and a region H of large change appear in response to changes in the charging rate, it becomes possible to reliably estimate the charging rate of the battery pack 20 at the end of a rest period.

In the above embodiment, the correction of the charging rate by the charging rate correction unit 51e and the charging rate correction step of step 108 is performed by making the charging rate of the secondary battery 31 estimated by the charging rate estimation unit 51d and the charging rate estimation step of step 102 using the current integration method into the charging rate stored in the open circuit voltage characteristic storage unit corresponding to the value of the open circuit voltage measured by the voltage detection circuit 52. However, the correction of the charging rate by the charging rate correction unit 51e and the charging rate correction step of step 108 may be performed by correcting the charging rate of the secondary battery 31 estimated by the charging rate estimation unit 51d and the charging rate estimation step of step 102 using the current integration method using a Kalman filter. In this case, the "pre-estimated value of SOC" is corrected by adding the product of the "Kalman gain" and the "terminal voltage prediction error" by the Kalman filter to the "pre-estimated value of SOC" which is the charging rate estimated by the charging rate estimation unit 51d and the charging rate estimation step. With this configuration, the same effects as those of the storage element charging rate estimation device and charging rate estimation method according to the above embodiment can be achieved.

The above embodiment of the charging rate estimation device and charging rate estimation method for a storage element has been described for the case where the secondary battery 31 is an LFP. However, the present invention is not limited to the case where the secondary battery 31 is an LFP, and can be similarly applied to other storage elements having open circuit voltage characteristics in which a relatively small flat region and a large change region of the open circuit voltage change appear with respect to the charging rate change. Even in such cases, the same effects as those of the above embodiment of the charging rate estimation device and charging rate estimation method for a storage element are achieved.

1: Charging rate estimation device 2: Battery pack 3: Assembled battery 31: Secondary battery (storage element)
4: Current sensor (current measurement unit)
5: Battery Management Unit (BMU)
51: Control unit 51a: CPU
51b: Memory (estimated charging rate storage unit, corrected charging rate storage unit, open circuit voltage characteristic storage unit)
51d: charging rate estimation unit 51e: charging rate correction unit 51f: internal resistance calculation unit 51g: charging rate correction unit 51h: idle period determination unit 51i: idle period end determination unit

Claims (2)

a current measuring unit for measuring a current flowing through a storage element having an open circuit voltage characteristic in which a relatively small flat region and a relatively large change region of the open circuit voltage appear with respect to a change in the charging rate;
A voltage measuring unit for measuring a terminal voltage of the storage element;
A charging rate estimation unit that estimates a charging rate of the storage element;
a charging rate correction unit that corrects the charging rate of the storage element estimated by the charging rate estimation unit;
an idle period determination unit that determines whether the storage element has entered an idle period because the current flowing through the storage element has not been measured by the current measurement unit for a predetermined period;
an estimated charging rate storage unit that stores, as an initial charging rate, a charging rate estimated by the charging rate estimation unit when the idle period determination unit determines that the storage element has entered the idle period;
a suspension period end determination unit that determines whether the suspension period has ended by measuring, by the current measurement unit, when a current starts to flow through the storage element during the suspension period;
an internal resistance value calculation unit that calculates an internal resistance value of the storage element from the current that starts to flow through the storage element during the pause period and the inter-terminal voltage of the storage element measured by the voltage measurement unit at that time ;
and a charging rate correction unit that, when the internal resistance value calculated by the internal resistance value calculation unit is equal to or lower than a predetermined value, sets the initial charging rate stored in the estimated charging rate storage unit as the charging rate of the storage element at the end of the idle period . a corrected charging rate storage unit that stores the charging rate corrected by the charging rate correction unit as a corrected charging rate ,
The charging rate correction unit is configured to set the corrected charging rate stored in the corrected charging rate storage unit as the charging rate of the storage element at the end of the rest period when the internal resistance value calculated by the internal resistance value calculation unit exceeds the predetermined value.

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