Charging control device, charging system

Abstract

To charge a power storage cell while suppressing heat generation of a conductive component and the power storage cell.SOLUTION: A control device 120 of a power storage cell 62 calculates SOC or remaining capacity of the power storage cell 62 by a current integration method, and determines a command value of charging voltage of the power storage cell based on the SOC or the remaining capacity obtained by the current integration method. In this configuration, a charging voltage Vc and a charging current Ic can be precisely controlled according to the SOC or the remaining capacity of the power storage cell 62 as compared with the case where the charging voltage Vc is a fixed value. Therefore, it is possible to charge the power storage cell 62 while suppressing heat generation of a conductive component and the power storage cell 62 due to Joule heat.SELECTED DRAWING: Figure 8

Description

Technical Field

[0007] , , , , ,

[0001] The present invention relates to a technique for charging a storage cell.

Background Art

[0002] Patent Document 1 discloses constant current - constant voltage charging as a charging method for a storage cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During charging, the current - conducting components and the storage cell located on the current path may generate heat due to Joule heat caused by the charging current. The current - conducting components are, for example, electronic components such as relays, and structural members such as bus bars. This invention aims to charge the storage cell while suppressing the heat generation of the current - conducting components and the storage cell.

Means for Solving the Problems

[0005] The control device of the storage cell calculates the SOC or remaining capacity of the storage cell by the current integration method, and determines the command value of the charging voltage of the storage cell based on the SOC or remaining capacity obtained by using the current integration method.

[0006] This technology can be applied to a control device, a power storage device, a charging system, and a method for charging a storage cell.

Effects of the Invention

[0007] This configuration can charge the storage cell while suppressing the heat generation of the current - conducting components and the storage cell.

Brief Description of the Drawings

[0008] [Figure 1] Side view of a car [Figure 2] Battery disassembled perspective view [Figure 3] Plan view of a secondary battery cell [Figure 4] Cross-sectional view of a secondary battery cell [Figure 5] Battery circuit diagram [Figure 6] SOC-OCV characteristics of secondary batteries [Figure 7] Charging voltage curve [Figure 8] Reference Table [Figure 9] Charging voltage curve [Figure 10] Enlarged view of section B in Figure 9 [Figure 11] Mode transition diagram of the control device [Figure 12] Charging voltage control sequence [Figure 13] Diagram showing the relationship between a predetermined value of the charging voltage and range B. [Figure 14] Battery charging characteristics [Figure 15] Battery charging characteristics [Modes for carrying out the invention]

[0009] This section provides an overview of the control system for energy storage cells. The control device for the energy storage cell calculates the State of Charge (SOC) or remaining capacity of the energy storage cell using the current integration method, and determines the command value for the charging voltage of the energy storage cell based on the SOC or remaining capacity obtained using the current integration method. The current integration method estimates the SOC based on the integrated value of the current that can be measured at any time. Therefore, unlike the OCV method and the full-charge method, the current integration method allows for the sequential calculation of the SOC during charging. The OCV method is a method of estimating the SOC using the correlation between SOC and OCV, while the full-charge method assumes that the SOC at full charge is 100%. Since the charging voltage is determined based on the SOC calculated sequentially by the current integration method, precise charging voltage control in response to changes in SOC during charging is possible.

[0010] Therefore, compared with the case where the charging voltage is set to a fixed value regardless of the SOC, the charging current can be controlled with high precision. Thus, while suppressing heat generation of the current-carrying components and the storage battery cells due to Joule heat, the storage battery cells can be charged. Further, unlike the feedback control that increases or decreases the charging voltage according to the deviation of the charging current from the target value, this is a method of determining and controlling the charging voltage based on the SOC, so it is difficult for the charging current to oscillate due to positive feedback. The same effect can be achieved when determining the command value of the charging voltage of the storage battery cell based on the remaining capacity, not limited to the SOC.

[0011] When the charging current of the storage battery cell is smaller than a predetermined value, the control device may increase the command value of the charging voltage. In this configuration, when the charging current becomes smaller than the predetermined value due to the estimation error of the SOC or the remaining capacity by the current integration method, the charging current can be made closer to the predetermined value by increasing the command value of the charging voltage. By bringing the charging current closer to the predetermined value, it is possible to avoid the charging current becoming zero during charging and stopping the charging, and continue the charging. By continuing the charging, the storage battery cells can be charged up to the target SOC or the target remaining capacity.

[0012] When the duration of the state where the charging current is smaller than the predetermined value is less than the threshold value, the control device may not increase the command value of the charging voltage. In this configuration, when the charging current temporarily becomes smaller than the predetermined value due to the influence of the current measurement error or noise, it is possible to suppress the command value of the charging voltage from being increased. Therefore, it is possible to suppress heat generation of the current-carrying components and the storage battery cells due to an unintended increase in the charging voltage.

[0013] The SOC or remaining capacity calculated by the current integration method may be corrected to the SOC or remaining capacity when the power storage cell is fully charged. In this configuration, by correcting the SOC or remaining capacity calculated using the current integration method to the SOC (= 100 [%]) or remaining capacity (= full charge capacity [Ah]) at full charge, the estimation error of the SOC or remaining capacity by the current integration method can be eliminated. By eliminating the estimation error, the estimation accuracy of the SOC or remaining capacity can be improved.

[0014] The power storage device includes a power storage cell and a control device, and the control device may transmit a command value of the charging voltage to an external charging control device that controls the charging voltage of the power storage device. The "external charging control device" means, for example, a vehicle ECU in the case of an in-vehicle power storage device, and is a control device other than the power storage device that controls charging. In this configuration, the charging control device controls the charging voltage of the power storage device according to the command value transmitted from the power storage device. That is, the charging voltage of the power storage cell can be controlled by the cooperation of the control device and the charging control device. This configuration has an advantage in that this technology can be applied to a charging system that distributes the charging control function of the power storage device between the "control device of the power storage device" and the "external charging control device".

[0015] The power storage cell is a secondary battery cell having a low change region where the change amount of the OCV with respect to the change amount of the SOC is relatively low and a high change region where the change amount of the OCV with respect to the change amount of the SOC is relatively high in the SOC-OCV characteristic, or a secondary battery cell having a low change region where the change amount of the OCV with respect to the change amount of the remaining capacity is relatively low and a high change region where the change amount of the OCV with respect to the change amount of the remaining capacity is relatively high in the remaining capacity-OCV characteristic, and the control device compares the charging current of the power storage cell with a predetermined value at least in the high change region, and when the charging current of the power storage cell is smaller than the predetermined value, the command value of the charging voltage may be increased. In a secondary battery cell having a low change region and a high change region, due to the estimation error of the SOC or remaining capacity, the charging current becomes smaller than the predetermined value in the high change region and charging is likely to stop. By applying this configuration, in the high change region, the power storage cell can be charged to the target SOC or target remaining capacity without stopping in the middle.

[0016] The control device may compare the charging current of the energy storage cell with a predetermined value in both the low-variance region and the high-variance region, and may increase the command value of the charging voltage if the charging current of the energy storage cell is less than the predetermined value. In this configuration, if the charging current is less than the predetermined value in either the low-variance region or the high-variance region, the charging voltage is increased, so that the energy storage cell can be charged to the target SOC without stopping midway through the entire range, including the low-variance region and the high-variance region.

[0017] <Embodiment 1> 1. Battery 50 configuration Embodiment 1 illustrates an on-board battery 50. Figure 1 is a side view of an automobile. The automobile 10 has an engine 20 as a drive system. Figure 1 shows only the engine 20 and the battery 50, omitting other components that make up the automobile 10. The battery 50 is an example of an energy storage device.

[0018] As shown in Figure 2, the battery 50 comprises a battery pack 60, a circuit board unit 65, and a housing 71.

[0019] The container 71 comprises a body 73 and a lid 74 made of synthetic resin material. The body 73 is cylindrical with a bottom. The body 73 has a bottom portion 75 and four side portions 76. The four side portions 76 form an upper opening 77 at the upper end.

[0020] The housing 71 houses the battery pack 60 and the circuit board unit 65. The battery pack 60 has 12 secondary battery cells 62. The 12 secondary battery cells 62 are connected in 3 parallel and 4 series.

[0021] The circuit board unit 65 is located on top of the battery pack 60. The circuit board unit includes busbars 57, which are the power lines 55 of the battery pack 60. In the block diagram of Figure 5, three secondary battery cells 62 connected in parallel are represented by a single battery symbol. The secondary battery cell 62 is an example of an "energy storage cell".

[0022] The cover 74 closes the upper opening 77 of the main body 73. An outer peripheral wall 78 is provided around the cover 74. The cover 74 has a projection 79 that is roughly T-shaped in plan view. A positive external terminal 51 is fixed to one corner of the front part of the cover 74, and a negative external terminal 52 is fixed to the other corner.

[0023] The battery 50 supplies power to loads connected to the positive and negative external terminals 51 and 52. The battery 50 is charged by the generator 30 connected to the positive and negative external terminals 51 and 52.

[0024] As shown in Figures 3 and 4, the secondary battery cell 62 houses an electrode body 83 together with a non-aqueous electrolyte in a rectangular parallelepiped-shaped case 82. The case 82 has a case body 84 and a lid 85 that closes the opening at its top.

[0025] Although not shown in detail, the electrode body 83 consists of a negative electrode element made of a copper foil substrate coated with an active material and a positive electrode element made of an aluminum foil substrate coated with an active material, with a separator made of a porous resin film placed between them.

[0026] These are all in the form of strips, and are wound in a flattened shape so that they can be housed in the case body 84, with the negative electrode element and positive electrode element positioned on opposite sides in the width direction relative to the separator.

[0027] A positive electrode terminal 87 is connected to the positive electrode element via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode element via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 each consist of a flat base portion 90 and legs 91 extending from the base portion 90. Through holes are formed in the base portion 90. The legs 91 are connected to either the positive electrode element or the negative electrode element.

[0028] The positive terminal 87 and the negative terminal 89 each consist of a terminal body 92 and a shaft 93 that protrudes downward from the center of its lower surface. Of these, the terminal body 92 and shaft 93 of the positive terminal 87 are integrally molded from aluminum (a single material). In the negative terminal 89, the terminal body 92 is made of aluminum and the shaft 93 is made of copper, and these are assembled together.

[0029] The terminal bodies 92 of the positive terminal 87 and the negative terminal 89 are positioned on both ends of the cover 85 via gaskets 94 made of insulating material, and are exposed to the outside from these gaskets 94.

[0030] The cover 85 has a pressure relief valve 95. As shown in Figure 3, the pressure relief valve 95 is located between the positive terminal 87 and the negative terminal 89. The pressure relief valve 95 opens when the internal pressure of the case 82 exceeds a limit value, thereby reducing the internal pressure of the case 82.

[0031] Referring to Figure 5, the electrical configuration of the battery 50 will be explained. The battery 50 comprises a cutoff device 53, a battery pack 60, a current detection unit 54, a management device 100, and a temperature sensor 115.

[0032] The battery pack 60 is composed of a plurality of secondary battery cells 62 connected in series. In this embodiment, the number of cells connected in series is "4". The secondary battery cells 62 are an example of the "energy storage cells" of the present invention.

[0033] The positive terminal of the battery pack 60 is connected to the positive terminal's external terminal 51 by power line 55P. The negative terminal of the battery pack 60 is connected to the negative terminal's external terminal 52 by power line 55N.

[0034] The circuit breaker 53 is located at the positive terminal of the battery pack 60 and is provided on the positive terminal power line 55P. The circuit breaker 53 can use a relay or an FET.

[0035] The circuit breaker 53 is controlled to the CLOSE state (normally close) under normal circumstances. If there is an abnormality in the battery 50, the battery 50 can be protected by interrupting the current using the circuit breaker 53.

[0036] The current detection unit 54 detects the current I [A] of the battery pack 60. The current detection unit 54 may also be a resistor. A resistive current detection unit 54 can distinguish between discharge and charge based on the voltage polarity (positive or negative). The current detection unit 54 may also be a magnetic sensor. The temperature sensor 115 measures the temperature T [°C] of the battery pack 60, either by contact or non-contact.

[0037] The control device 100 is provided on the circuit board unit 65. The control device 100 includes a voltage detection circuit 110, a control device 120, and a power supply circuit 130.

[0038] The voltage detection circuit 110 is connected to each of the secondary battery cells 62 via signal lines and measures the cell voltage Vs of each secondary battery cell 62. It also measures the total voltage Vt of the battery pack 60 from the cell voltage Vs of each secondary battery cell 62. The total voltage Vt of the battery pack 60 is the sum of the voltages of the four secondary battery cells 62 connected in series.

[0039] The control device 120 includes a CPU 121 with calculation functions and a memory 123 which is a storage unit. The control device 120 monitors the current I of the battery pack 60, the cell voltage Vs of each secondary battery cell 62, the total voltage Vt of the battery pack 60, and the temperature T from the outputs of the current detection unit 54, the voltage detection circuit 110, and the temperature sensor 115. It can also detect the charging voltage Vc from the voltage of the external terminal 51.

[0040] Memory 123 is a non-volatile storage medium such as flash memory or EEPROM. Memory 123 stores a monitoring program that monitors the status of the battery pack 60 and data necessary for the execution of the monitoring program.

[0041] Memory 123 stores a control program that executes the control sequence for the charging voltage Vc of the battery 50 (Figure 12), and data necessary for executing the control program. The data necessary for executing the control program includes the data in the reference table shown in Figure 8.

[0042] The battery 50 is connected to the vehicle load 25 and the generator 30 via wiring 23. The vehicle load 25 may be the engine starter or auxiliary equipment. The engine starter is a motor that starts the engine. Auxiliary equipment includes headlights, power steering mechanism, air conditioning, audio system, etc.

[0043] The power generation device 30 includes a vehicle generator 31, a rectifier 33, and a voltage adjustment unit 35. The vehicle generator 31 is an AC generator that generates power using the engine 20. The rectifier 33 rectifies the power output by the vehicle generator 31 and converts it from AC to DC.

[0044] The voltage adjustment unit 35 adjusts the output voltage Vc of the generator 30. Voltage adjustment may be performed by controlling the excitation current of the vehicle generator 31 to adjust the output voltage Vc, or by controlling the output voltage Vc using PWM control.

[0045] If the amount of power generated by the generator 30 exceeds the electrical load of the vehicle load 25, the battery 50 can be charged by the generator 30. If the amount of power generated by the generator 30 is less than the electrical load of the vehicle load 25, the battery 50 will discharge to compensate for the insufficient power generation. The generator 30 is an example of a power device that outputs electricity.

[0046] The vehicle ECU (Electronic Control Unit) 40 is connected to the battery 50 via a communication line 41 and is connected to the generator 30 via a communication line 42.

[0047] The vehicle ECU 40 controls the output voltage Vc of the generator 30, i.e., the charging voltage Vc of the battery 50, by controlling the voltage adjustment unit 35 based on the command value of the charging voltage Vc transmitted from the battery 50. The vehicle ECU 40 corresponds to the "external charging control device" of the present invention. "External" means outside the battery.

[0048] 2. OCV characteristics and SOC estimation of secondary battery cell 62 Figure 6 shows the SOC-OCV correlation characteristic Yo of secondary battery cell 62, with SOC [%] on the horizontal axis and OCV [V] on the vertical axis. Hereafter, "Yo" will be referred to as the "OCV curve".

[0049] The State of Charge (SOC) is the ratio of remaining capacity to full charge capacity, and can be expressed by the following equation (1).

[0050] OCV is the open-circuit voltage of the secondary battery cell 62. The open-circuit voltage is the voltage across the terminals of the secondary battery cell 62 when there is no current or when it can be considered to be current-free.

[0051] SOC=(Cr / Co)×100 (1) Co represents the full charge capacity of the secondary battery cell, and Cr represents the remaining capacity of the secondary battery cell.

[0052] As shown in Figure 6, the secondary battery cell 62 has multiple charging regions, including a low-change region L in which the change in OCV is relatively low relative to the change in SOC, and a high-change region H in which the change in OCV is relatively high.

[0053] Specifically, it has two low-change regions L1 and L2, and three high-change regions H1, H2, and H3.

[0054] As shown in Figure 6, the low-change region L1 is located in the range of 35% to 62% of the SOC value, and the low-change region L2 is located in the range of 68% to 96% of the SOC value.

[0055] The low-change regions L1 and L2 are plateau regions where the change in OCV relative to the change in SOC is very small, and the OCV remains approximately constant at 3.3[V] and 3.35[V]. A plateau region is a region where the change in OCV relative to the change in SOC is below a certain threshold. The threshold is, for example, 2[mV / %].

[0056] The first high-change region H1 is located in the range of SOC values ​​greater than 62% but less than 68%, and lies between the two low-change regions L1 and L2. The second high-change region H2 is located in the range of SOC values ​​less than 35%, and lies lower than the low-change region L1. The third high-change region H3 is located in the range of SOC values ​​greater than 96%, and lies higher than the low-change region L2.

[0057] In the first to third high-change regions H1 to H3, the relationship between the change in OCV (the slope of the graph shown in Figure 6) and the change in SOC is relatively high compared to the low-change regions L1 and L2.

[0058] In terms of SOC-OCV correlation characteristics, a secondary battery cell 62 having the aforementioned plateau regions L1 and L2 is a lithium iron phosphate-based battery cell using lithium iron phosphate (LiFePO4) as the positive electrode active material and graphite as the negative electrode active material.

[0059] In plateau regions L1 and L2, the OCV hardly changes with respect to the SOC change. Therefore, it is difficult to estimate the SOC from the correlation with the OCV for secondary battery cells 62 that have plateau regions L1 and L2.

[0060] The control device 100 estimates the State of Charge (SOC) of the secondary battery cell 62 using the current integration method. As shown in (2), the current integration method estimates the SOC [%] based on the time integral of the current I. The sign of the current I is positive during charging and negative during discharge. In addition to SOC, the remaining capacity Cr can also be calculated using the current integration method.

[0061] SOC=SOCo+100×(∫Idt / Co)···(2) SOCo is the initial value of SOC, and I is the current.

[0062] 3. Determination of the command value for the charging voltage Vcs of the secondary battery cell 62 Figure 7 shows the charging voltage curve Yc. The charging voltage curve Yc shows the charging voltage Vcs of the secondary battery cell 62 for each SOC, with the horizontal axis being SOC [%] and the vertical axis being voltage [V].

[0063] The charging voltage curve Yc is higher than the OCV curve Yo at all SOCs, and the higher the SOC, the higher the charging voltage Vcs. The secondary battery cell 62 can be charged by the voltage difference ΔV between Vcs and OCV. The relationship between the voltage difference ΔV and the charging current Ic is as follows.

[0064] Ic = ΔV / r·····(3) "r" represents the internal resistance of the secondary battery cell.

[0065] By determining the voltage difference ΔV such that the charging current Ic does not exceed the maximum allowable current Im, Vcs can be determined as shown in equation (4). For each SOC, the charging voltage curve Yc can be determined by finding Vcs. Vcs = OCV + ΔV ·····(4)

[0066] The voltage difference ΔV can also be determined such that the charging current Ic is constant, except when the battery is nearly fully charged. ΔV / r = Const (where Im is less than)

[0067] Near full charge, the voltage of the secondary battery cell 62 rises sharply. Near full charge, the voltage difference ΔV becomes small, so the charging current Ic is smaller compared to other regions.

[0068] Memory 123 stores a reference table for the charging voltage curve Ycs. The reference table is a table that stores the correspondence between the State of Charge (SOC) and the charging voltage Vcs (see Figure 8).

[0069] The control device 100 estimates the State of Charge (SOC) of the secondary battery cells 62 using the current integration method, and determines the command value of the charging voltage Vcs per cell by referring the obtained SOC to a reference table.

[0070] Then, by controlling the output voltage Vc of the power generator 30 based on the command value of the charging voltage Vcs, the battery 50 can be charged while keeping the charging current Ic below the maximum allowable current value Im.

[0071] The charging voltage curve Ycs is set such that the voltage difference ΔV relative to the OCV is such that the charging current Ic is less than or equal to the maximum allowable current value Im. Therefore, heat generation in the conductive components and secondary battery cells 62 located in the current path can be suppressed during charging. Conductive components include the circuit breaker 53 and the busbar 57.

[0072] 4. Reduction of voltage difference ΔV due to SOC estimation error In the current integration method, the measurement error of the charge / discharge current Ic by the current detection unit 54 accumulates over time, resulting in an estimation error of the State of Charge (SOC).

[0073] When an error occurs in estimating the State of Charge (SOC), the voltage difference ΔV between the charging voltage Vcs and the OCV may fluctuate compared to when there is no SOC estimation error, and the voltage difference ΔV may become smaller. In addition, the relative magnitudes of the voltages may be reversed.

[0074] For example, if there is a negative estimation error in the SOC relative to the true value, the charging voltage curve Yc will shift to the right on the SOC axis (horizontal axis) by the amount of the estimation error, as shown in Figure 9. In the example in Figure 9, the estimation error of SOC is -10%, and the charging voltage curve Yd when the estimation error occurs is shifted 10% to the right from the charging voltage curve Yc when there is no estimation error. The point "V7" shifts to the point "V7'".

[0075] Comparing Yd-Yo (with estimation error) in Figure 9 with Yc-Yo (without estimation error) in Figure 7, the voltage difference ΔV fluctuates in the range of SOC 2% to 18% (part A in Figure 9) and the range of SOC 95% to 100% (part B in Figure 9).

[0076] Figure 10 is an enlarged view of section B in Figure 9. In the case of Yd-Yo (with estimation error) in Figure 9, compared to the case of Yc-Yo (without estimation error) in Figure 7, the voltage difference ΔV decreases after time t1, and the relative magnitudes of the voltages are reversed at time t2.

[0077] After time t1, when the voltage difference ΔV decreases, the charging current Ic becomes smaller compared to when there is no SOC estimation error, and charging may stop after time t2, when the relative magnitudes of the voltages reverse. Such fluctuations in the voltage difference ΔV are more likely to occur in the high-variability regions H1 and H2.

[0078] The control device 100 controls the charging voltage Vc to increase it when the charging current Ic is less than a predetermined value Ib1.

[0079] The predetermined value Ib1 is a value used to determine whether charging can continue without stopping, and is smaller than the expected value Ic0 of the charging current Ic. The expected value Ic0 is the theoretical value of the charging current Ic determined by equation (3). The predetermined value Ib1 may be a value common to each SOC, or it may be a unique value for each SOC.

[0080] By increasing the charging voltage Vc, the voltage difference ΔV between the charging voltage Vcs and OCV becomes larger than before, which brings the charging current Ic closer to the expected value Ic0. Therefore, it is possible to prevent the charging current Ic from becoming zero and stopping charging midway, and to continue charging.

[0081] The charging voltage Vc may be increased as long as it does not exceed the maximum value Vcm when converted to the charging voltage Vcs per cell. The maximum value Vcm is the charging voltage Vcs at SOC 100% (see Figures 7 and 9).

[0082] 5. Mode transitions of the control device 100 and control sequence of the charging voltage Vc As shown in Figure 11, the management device 100 has two modes: monitoring mode and sleep mode.

[0083] The monitoring mode is a mode in which the status of the battery 50 is monitored at a predetermined cycle N, and the sleep mode is a mode in which some of the monitoring functions are stopped to reduce the power consumption of the management device 100.

[0084] The management device 100 determines whether the battery 50 is in use or not based on the current I of the battery 50 and performs mode transitions accordingly. Specifically, if the current I is less than the current determination value (determined as not in use), it transitions to sleep mode, and if the current I is equal to or greater than the current determination value (determined as in use), it transitions to monitoring mode.

[0085] When the vehicle 10 is parked, the battery 50 is in an unused state, neither charging nor discharging, so the current I falls below the current threshold, and the management device 100 switches to sleep mode. On the other hand, when the vehicle is driving, stopped, or idling, or in any other state other than parking, the battery 50 is in use, charging and discharging with the vehicle 10. Therefore, the management device 100 switches to monitoring mode.

[0086] The control device 100 initiates a control sequence for the charging voltage Vc, triggered by a transition to monitoring mode.

[0087] The control sequence for the charging voltage Vc consists of seven steps, S10 to S70, as shown in Figure 12.

[0088] When the control sequence starts, the control device 100 uses measuring instruments such as the current detection unit 54, the voltage detection circuit 110, and the temperature sensor 115 to measure the current I of the battery pack 60, the cell voltage Vs of each secondary battery cell 62, the total voltage Vt of the battery pack 60, and the temperature T of the battery pack 60. Then, it estimates the state of charge (SOC) of the battery pack 60 using the current integration method (S10).

[0089] Next, the control device 100 determines a command value for the charging voltage Vcs per cell from the SOC obtained using the current integration method.

[0090] The charging voltage Vcs per cell can be determined by referencing the SOC in the reference table (Figure 8) stored in memory 123. For example, when SOC = 40%, the command value for the charging voltage Vcs equivalent to one cell is "V7".

[0091] The management device 100 then transmits a command value for the charging voltage Vc to the vehicle ECU 40 (S20). Along with the command value for the charging voltage Vc, it transmits the State of Charge (SOC) of the battery 50. By sending the SOC information, the vehicle ECU 40 can monitor the SOC of the battery 50.

[0092] The command value transmitted to the vehicle ECU 40 is the command value for the charging voltage Vc of the battery 50, which is the value obtained by multiplying the charging voltage Vcs per cell, determined from the reference table in Figure 8, by the number of cells, "4".

[0093] When the vehicle ECU 40 receives a command value for the charging voltage Vc, it controls the output voltage Vc of the generator 30 to the received command value.

[0094] The control device 100 determines the magnitude of the charging voltage Vc after transmitting the command value (S31). Specifically, it determines whether the difference between the command value Vco and the measured value Vct of the charging voltage Vc is smaller than the comparison value A. The charging voltage (measured value) Vct can be measured, for example, from the voltage at the external terminal 51 of the battery 50.

[0095] Vco-Vct≦A·····(4)

[0096] The measured value Vct of the charging voltage Vc will be smaller than the command value Vco due to voltage drop caused by wiring resistance, etc. If the difference between the command value Vco and the measured value Vct is smaller than the comparison value A (S31: YES), it can be determined that the generator 30 is outputting according to the command value and the battery 50 is being charged at the commanded charging voltage Vc.

[0097] If the result in S31 is YES, the control device 100 determines whether the charging current Ic is less than a predetermined value Ib1.

[0098] In this embodiment, the charging current Ic is compared with range B (see Figure 13). Range B is a range (Ib1 to Ib2) in which the current value is smaller than a predetermined value Ib1 and includes zero.

[0099] Ib2 <B<Ib1····(5) B may differ depending on the SOC, or it may be common to all SOCs.

[0100] If the charging current Ic falls within range B, it is determined that the charging current Ic is less than the predetermined value Ib1 (S33: YES).

[0101] If the charging current Ic is greater than or equal to a predetermined value Ib1 (S33: NO), the management device 100 determines whether or not there is a mode transition from monitoring mode to sleep mode (S60). If there is no mode transition and the monitoring mode continues (S60: NO), the process returns to S10.

[0102] After the start of the control sequence, if the power generator 30 is outputting according to the command value (S31: YES), the charging current Ic is a predetermined value Ib1 (S33: NO), and there is no mode transition from monitoring mode (S60: NO), then the processes of S10, S20, S31, and S60 are repeated with a predetermined period N (loop R).

[0103] As a result, the current I of the battery pack 60, the cell voltage Vs of each secondary battery cell, the total voltage Vt of the battery pack, and the temperature T are measured at a predetermined period N, and the state of charge (SOC) of the battery pack 60 is calculated sequentially based on the integrated value of the measured current I.

[0104] The control device 120 determines a command value for the charging voltage Vc of the battery 50 corresponding to each sequentially calculated SOC by referring to the reference table in Figure 8, based on the SOCs calculated sequentially using the current integration method. During charging, the control device 120 transmits information about each SOC, along with the command value of the charging voltage Vc corresponding to each SOC, to the vehicle ECU 40. The vehicle ECU 40 controls the generator 30 and controls the output voltage Vc of the generator 30 to the command value. This makes it possible to continuously change the charging voltage Vc in accordance with the continuously changing SOC during charging, and to charge the battery 50 while controlling the charging current Ic to a constant current below the maximum allowable current value Im.

[0105] Next, we will explain the case where the charging current Ic is less than a predetermined value Ib1 during charging (S33: YES).

[0106] If a YES determination is made in S33, the control device 100 counts the duration Ts of the state in which the charging current Ic is less than a predetermined value Ib1 (the state in which it is included in range B) and determines that the threshold D[s] is met (S40).

[0107] The threshold D is a value used to verify whether the charging current Ic remains below a predetermined value Ib1, in order to avoid false detections due to voltage measurement errors or noise.

[0108] If the duration Ts is longer than the threshold D, the management device 100 sends a command to the vehicle ECU 40 to increase the command value of the charging voltage Vc from the current value (S50).

[0109] By increasing the charging voltage Vc, the voltage difference ΔV between the charging voltage Vcs and OCV becomes larger than before the increase, allowing the charging current Ic to approach the expected value Ic0. Therefore, it is possible to prevent the charging current Ic from becoming zero and stopping charging during the process, and to continue charging the battery 50.

[0110] After increasing the command value of the charging voltage Vc, the process proceeds to S60, where it is determined whether or not there is a mode transition. If there is no mode transition, the process returns to S10.

[0111] Furthermore, if the duration Ts is less than the threshold D, the process proceeds to S60 instead of S50. Therefore, the command value of the charging voltage Vc is not increased, and the command value of the charging voltage Vc is maintained at its current value.

[0112] Then, as the vehicle 10 transitions from driving to parking, it switches from monitoring mode to sleep mode, and then proceeds to S70.

[0113] When the process moves to S70, the control device 100 resets the command value increase for the charging voltage Vc. The reset returns the command value of the charging voltage Vc to its initial state before the increase. This terminates the control sequence for the charging voltage Vc.

[0114] Even if battery 50 is charged to the target SOC, the process transitions to S70, resetting the command value increase for the charging voltage Vc, and the control sequence for the charging voltage Vc ends.

[0115] The target SOC may be full charge or something else. The target SOC and the end of charging may be determined and controlled by the vehicle ECU 40, or determined and controlled by the management device 100.

[0116] The control sequence shown in Figure 12 is always executed after charging begins, regardless of whether the secondary battery cell 62 is in the low-change region L1, L2, or the high-change region H1-H3.

[0117] By constantly executing the control sequence, it becomes possible to charge the secondary battery cell 62 at approximately the expected value Ic0, regardless of the region it is in, thereby suppressing heat generation in the secondary battery cell 62 and the conductive components 57 while charging the secondary battery cell 62.

[0118] Figures 14 and 15 show the charging characteristics of battery 50. Figures 14 and 15 show the change in state of charge (SOC) when the charging voltage Vc is controlled according to the charging voltage curve Yc. Due to the estimation error of SOC, charging stops (section C in the figure) approximately 95 seconds after the start of charging. The SOC at the start of charging is 96%.

[0119] If the charging voltage Vc is not increased (Figure 14), the device can only be charged to approximately 98.5% of its state of charge (SOC).

[0120] When the charging voltage Vc is increased (Figure 15), charging can be continued while preventing the charging from stopping.

[0121] In the example in Figure 15, the charging current Ic falls within range B (i.e., Ic falls below the upper limit Ib1 of range B) three times. Therefore, the command value of the charging voltage Vc is increased three times, and ultimately, the battery is fully charged, i.e., SOC 100% (section D). "Fully charged" is the state in which the secondary battery cell 62 has been charged to a predetermined charging termination condition, which is generally SOC = 100%. The predetermined charging termination condition can be, for example, the charging time after the secondary battery cell 62 reaches a predetermined upper limit voltage. For example, charging for 10 minutes after reaching the upper limit voltage may result in a full charge.

[0122] Furthermore, when the command value of the charging voltage Vc is increased, an inrush current flows through the battery 50, causing the current value to temporarily rise. This temporary increase in current causes polarization to occur inside the secondary battery cell 62, increasing its resistance. Therefore, the current decreases after passing its peak. As a result of the above, as the command value of the charging voltage Vc is increased, the waveform of the charging current Ic becomes a sharp wave (section E).

[0123] 6. Explanation of Effects In this configuration, the command value of the charging voltage Vc is determined according to the State of Charge (SOC) obtained using the current integration method. Compared to the case where the charging voltage Vc is a fixed value independent of the SOC (for example, Vcm when converted to a single cell), this configuration allows for precise control of the charging voltage Vc and charging current Ic of the battery 50 according to the SOC of the battery 50.

[0124] Specifically, within the range where the charging current Ic does not exceed the maximum allowable current Im, the charging voltage Vc is increased as the SOC increases, so that the secondary battery cells 62 can be charged for all SOCs from low to high while suppressing the heat generated by Joule heating in the conductive components and the secondary battery cells 62.

[0125] Battery 50 may manage the usage range of the State of Charge (SOC). For example, if the usage range is 60-80%, and charging starts at 70%, charging may be terminated when the SOC reaches 80%. This configuration uses the SOC, which is management information for controlling charging, to determine the charging voltage Vc, enabling precise charging control while minimizing the information required for charging control.

[0126] One possible method to suppress heat generation in the secondary battery cell 62 during charging is to feedback control the charging voltage Vc so that the charging current Ic matches the expected value Ic0. However, with feedback control, the charging current Ic, which is the target of control, may oscillate due to the influence of signal delays (for example, signal delays due to communication between the control device 120 and the vehicle ECU 40). This configuration has the advantage that the charging current Ic is more stable compared to feedback control because it changes the charging voltage Vc according to the SOC.

[0127] Methods for correcting the estimation error of the State of Charge (SOC) include correction methods using the OCV method and correction methods that involve fully charging the battery 50.

[0128] The OCV method is a method for determining the State of Charge (SOC) by utilizing the correlation between OCV and SOC. The correction method using the OCV method involves calculating the SOC using both the current integration method and the OCV method, and then correcting the SOC obtained by the current integration method to the SOC obtained using the OCV method. This correction of the SOC eliminates the estimation error of the SOC obtained by the current integration method. However, the OCV method has the drawback that it takes time to determine the OCV (open-circuit voltage) of the secondary battery cell 62 (a stabilization time is required until the voltage stabilizes).

[0129] The correction method for charging to full capacity involves charging battery 50 to full capacity and correcting the State of Charge (SOC) calculated by the current integration method to the SOC at full charge (SOC=100%). By correcting to the SOC at full charge (SOC=100%), the estimation error of the SOC by the current integration method can be eliminated.

[0130] In both correction methods, the corrected SOC is used as the initial value (SOC = 100% in the case of the correction method using full charge), and after correction, the SOC is estimated using the current integration method.

[0131] If the battery 50 is used within a range of less than full charge, for example, when the SOC is between 60 and 80%, then normally the battery 50 is charged within the usage range. When a predetermined period has elapsed since the last correction, or when an estimation error of the SOC has accumulated, the battery 50 is charged to full charge, thereby correcting the SOC calculated using the current integration method.

[0132] However, during charging to full charge, estimation errors for the State of Charge (SOC) accumulate. As explained with reference to Figure 14, charging may stop midway and fail to reach full charge, making it impossible to correct the SOC. In this case, because the SOC estimation method using current integration continues without eliminating the estimation error, the SOC estimation error expands beyond the acceptable limit.

[0133] In this configuration, as shown in Figure 15, if the charging current Ic falls below a predetermined value Ib1 due to an estimation error of the State of Charge (SOC), the command value of the charging voltage Vc is increased. By increasing the command value, the secondary battery cell 62 can be charged to full charge (SOC 100%) while suppressing the stopping of charging midway. Therefore, by correcting the SOC obtained by the current integration method to the SOC at full charge (SOC 100%), the estimation error of the SOC accumulated by the current integration method can be eliminated, and the estimation accuracy of the SOC can be maintained.

[0134] In this configuration, the command value of the charging voltage Vc is not increased if the duration Ts is less than the threshold D. This configuration prevents the command value of the charging voltage Vc from being increased when the charging current Ic temporarily becomes less than a predetermined value Ib1 due to current measurement errors or noise.

[0135] In this configuration, the control device 120 sends a command value for the charging voltage Vc to the vehicle ECU 40, and the vehicle ECU 40 adjusts the charging voltage Vc upon receiving the command value. In other words, the charging voltage Vc of the secondary battery cell 62 can be controlled through the cooperation of the control device 120 and the vehicle ECU 40. This configuration has the advantage that this technology can be applied to a charging system in which the charging control function of the battery 50 is shared between the "control device 120 of the energy storage device" and the "external charging control device (vehicle ECU 40)".

[0136] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.

[0137] (1) In the embodiment, as an example of an energy storage cell, a secondary battery cell having a low-change region L and a high-change region H in its SOC-OCV characteristics is shown. The secondary battery cell does not necessarily have to have characteristics with two change regions. A secondary battery cell having only one change region is also acceptable. Furthermore, the energy storage cell may be a capacitor or the like. The energy storage cell is not limited to multiple cells, but may be a single cell. Also, multiple cells may be connected in series and parallel.

[0138] (2) In the embodiment, an example of using the battery 50 in an automobile was shown. It can also be used for motorcycles and railways. Furthermore, the use of the battery 50 is not limited to mobile devices such as automobiles. It can also be used for stationary purposes such as uninterruptible power supplies and energy storage devices for power generation systems.

[0139] (3) In this embodiment, the command value of the charging voltage Vc was calculated by the battery management device 100. The command value of the charging voltage Vc may also be determined by the vehicle ECU 40. For example, the management device 100 may notify the vehicle ECU 40 of only the SOC information, and the vehicle ECU 40 may determine the command value of the charging voltage Vc by referring to the charging voltage Vc reference table (Figure 8). The control to increase the charging voltage Vc is also performed in the same manner.

[0140] (4) In this embodiment, the command value of the charging voltage was increased if the result in all three steps S31, S33, and S40 was YES. Steps S31 and S40 may be omitted, and only S33 may be executed. The command value of the charging voltage may be increased if the result in S33 is YES.

[0141] (5) In this embodiment, if the duration Ts of the time during which the charging current Ic is less than a predetermined value Ib1 is greater than or equal to a threshold D, the command value of the charging voltage Vc is increased. If the charging current Ic falls below the predetermined value Ib1, the command value of the charging voltage Vc may be increased immediately.

[0142] (6) In this embodiment, it is determined whether the charging current Ic is smaller than the predetermined value Ib1 by comparing it with range B. Alternatively, the difference between the charging current Ic and the predetermined value Ib1 may be calculated to determine whether it is smaller than the predetermined value Ib1. If the difference between Ic and Ic0 is outside the allowable range, it may be determined that the charging current Ic is smaller than the predetermined value Ib1.

[0143] (7) A reference table for the charging voltage Vc may be provided for each temperature of the battery 50. The command value for the charging voltage Vc may be determined by selecting the reference table to be used from the temperature information of the battery 50. Alternatively, the command value for the charging voltage Vc may be determined by storing the charging voltage curve Yc in memory 123 and referring to it, rather than using a reference table.

[0144] (8) In this embodiment, the control period of the charging voltage Vc is set to be the same as the measurement period N of the battery 50. The control period of the charging voltage Vc may be different from the measurement period N of the battery 50. For example, the control period of the charging voltage Vc may be set to be about 10 times the measurement period of the battery 50.

[0145] (9) In this embodiment, the reset of the command value increase for the charging voltage Vc (S70) was performed using the mode transition of the management device 100 as the trigger signal. The reset of the command value may also be performed using other signals as the trigger signal. For example, when the management device 100 outputs a full charge request signal to the vehicle ECU 40, that signal may be used as the trigger to reset the command value increase for the charging voltage Vc.

[0146] (10) In this embodiment, the charging current Ic of the battery 50 is compared with a predetermined value Ib1 in both the low-change region L and the high-change region H, and if the charging current Ic is less than the predetermined value Ib1, the command value of the charging voltage Vc is increased. In at least the high-change region H of the low-change region L and the high-change region H, the charging current Ic is compared with a predetermined value Ib1, and if the charging current Ic is less than the predetermined value, the command value of the charging voltage Vc may be increased. In other words, the process of increasing the command value of the charging voltage Vc is performed in the high-change region, but it is not necessary to perform it in the low-change region L. Whether a secondary battery cell is included in the high-change region or the low-change region can be determined by the SOC obtained by the current integration method.

[0147] (11) In this embodiment, an example in which the battery 50 is charged to full capacity has been described. The target state of charge is not limited to full charge (SOC = 100%), but may be other than full charge, such as 80% or 90%. Charging may also be performed within a plateau region.

[0148] (12) In this embodiment, the battery 50 was charged with power output from the power generator 30. However, the battery 50 is not limited to the output of the power generator 30. It may also be charged with the output of a charging device or a power converter (for example, a converter). In other words, the power device that charges the battery 50, which is an energy storage device, is not limited to the power generator 30, but may also be a charging device or a power converter.

[0149] (13) In this embodiment, the SOC[%] of the secondary battery cell 62 is calculated by the current integration method, and the command value for the charging voltage Vc of the secondary battery cell 62 is determined based on the SOC[%] obtained using the current integration method. Alternatively, the remaining capacity[Ah] of the secondary battery cell 62 may be calculated by the current integration method, and the command value for the charging voltage Vc of the secondary battery cell 62 may be determined based on the remaining capacity[Ah] obtained using the current integration method. In this case, the "remaining capacity-OCV correlation characteristic" can be used instead of the "SOC-OCV correlation characteristic," and the "remaining capacity-Vcs charging voltage curve" can be used instead of the "SOC-Vcs charging voltage curve." In this embodiment, an example of correcting the SOC by charging to full capacity has been described, but it is also possible to correct the remaining capacity Cr by charging to full capacity.

[0150] Cr = Cro + (∫Idt)···(6) Cr: remaining capacity, Cro: initial value of remaining capacity, I: current [Explanation of Symbols]

[0151] 10. Automobiles 30 Power generation systems 40. Vehicle ECU (corresponding to the "charging control device" of the present invention) 50. Battery (corresponding to the "energy storage device" of this invention) 60 battery packs 100 Management device 120 Control device

Claims

1. A charge control device for an energy storage cell, The state of charge (SOC) or remaining capacity of the aforementioned energy storage cell or a plurality of electrically connected energy storage cells is received. Based on the received SOC or remaining capacity, the command value for the charging voltage of the energy storage cell or the plurality of energy storage cells is determined. A charge control device for a storage cell, which increases the command value of the charging voltage when the charging current of the storage cell or the plurality of storage cells is less than a predetermined value.

2. A charge control device for an energy storage cell according to claim 1, A charge control device for an energy storage cell that does not increase the command value of the charging voltage if the duration of the state in which the charging current is less than a predetermined value is less than a threshold value.

3. It is a charging system, A power device that outputs electricity, A power storage device connected to the aforementioned power device, Includes a charging control device that controls the output of the power device, The aforementioned energy storage device is Energy storage cells and The control device includes a device that calculates the state of charge (SOC) or remaining capacity of the energy storage cell or a plurality of electrically connected energy storage cells by current integration and transmits it to the charging control device, The charging control device is Based on the received SOC or remaining capacity, the command value for the charging voltage of the energy storage cell or the plurality of energy storage cells is determined. A charging system that controls the output voltage of the power device to the command value to charge the energy storage cell or the plurality of energy storage cells.

4. A charging system according to claim 3, The charging control device fully charges the energy storage cell or the plurality of energy storage cells. The control device is a charging system that corrects the SOC or remaining capacity calculated by the current integration method to the SOC or remaining capacity when the energy storage cell or the plurality of energy storage cells are fully charged.

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