JP2014147261A - Secondary battery system and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery system that can be manufactured at a low cost and can properly charge a plurality of secondary batteries constituting a battery pack to full, and an image forming apparatus.SOLUTION: A secondary battery system includes a battery pack comprising a plurality of secondary batteries connected in series. The battery pack is connected with a voltage detection unit that detects the entire voltage of the battery pack. The secondary battery system recognizes, during charging, the number of secondary batteries of the battery pack that have reached full charge on the basis of the entire voltage of the battery pack obtained by the voltage detection unit. When all the secondary batteries have reached full charge, the secondary battery system ends the charging of the battery pack. On the other hand, in the case of the presence of the secondary batteries that have not reached full charge, the secondary battery system continues the charging of the battery pack, while regulating a current for charging the battery pack according to the number of the secondary batteries that have not reached full charge.

Description

  The present invention relates to a secondary battery system including a plurality of secondary batteries and an image forming apparatus. More specifically, the present invention relates to a secondary battery system having an assembled battery formed by connecting a plurality of secondary batteries in series, and an image forming apparatus including the secondary battery system.

  In recent years, secondary batteries such as nickel metal hydride secondary batteries have been used as power sources for various electronic devices such as portable electronic devices such as mobile phones and notebook computers. Further, when used as a power source for various purposes, it is used as an assembled battery in which a plurality of secondary batteries are combined in order to obtain an output corresponding to the intended use.

  Here, the battery characteristics such as the full charge capacity and the internal resistance of the secondary battery may differ depending on the quality variation at the time of manufacturing the secondary battery. In addition, the temperature of the secondary battery in the assembled battery may vary depending on the arrangement. Further, the degree of deterioration of the secondary battery varies depending on the temperature. Therefore, by repeatedly charging and discharging the assembled battery, the secondary battery constituting the assembled battery may vary in the storage rate, which is the ratio of the remaining battery capacity to the full charge capacity.

  When charging an assembled battery in which the storage rate of each secondary battery varies, the timing of full charge differs for each secondary battery. When charging of the assembled battery was stopped in accordance with the timing of full charging of the secondary battery, which had a low storage rate at the start of charging of the assembled battery, the storage rate was high at the start of charging of the assembled battery. The secondary battery will be overcharged.

  On the other hand, when charging of the assembled battery was stopped in accordance with the timing of full charge of the secondary battery, which had a high storage rate at the start of charging of the assembled battery, the storage rate was low at the start of charging of the assembled battery. The secondary battery cannot be fully charged. Therefore, Patent Document 1 is cited as a prior art that can appropriately fully charge all the secondary batteries even for an assembled battery in which the storage rates of the secondary batteries vary.

  In Patent Document 1, the battery pack is charged while individually monitoring the voltages of a plurality of secondary batteries constituting the battery pack, and when it is detected that at least one secondary battery is fully charged, A charging device is disclosed in which charging is continued by lowering the charging current of the battery. As a result, it is possible to fully charge a secondary battery having a low storage rate at the start of charging of the assembled battery while suppressing overcharging of the secondary battery having a high storage rate at the start of charging of the assembled battery. Has been.

JP 2010-68571 A

  By the way, in the above prior art, full charge of each secondary battery constituting the assembled battery is detected by detecting the voltage of each secondary battery. Therefore, a circuit for detecting the voltage is required for each of the plurality of secondary batteries constituting the assembled battery. For this reason, there is a problem that the area of the circuit for detecting the voltage becomes large. Furthermore, since a circuit for detecting a voltage for each of a plurality of secondary batteries is required, there is a problem that a system for charging the assembled battery becomes expensive.

  The present invention has been made for the purpose of solving the problems of the prior art described above. That is, the problem is to provide a secondary battery system and an image forming apparatus that are inexpensive and can fully charge a plurality of secondary batteries constituting an assembled battery.

  The secondary battery system of the present invention made for the purpose of solving this problem includes a secondary battery having an assembled battery formed by connecting a plurality of secondary batteries in series, and a battery control unit for controlling charging / discharging of the assembled battery. In the battery system, the voltage of each of the secondary batteries increases as it approaches full charge during charging, and the low rise period during which the voltage increase rate is lower during the charging period from the start of charging to full charging. And a high rise period with a higher voltage rise rate after the low rise period, and a voltage drop when the battery is further charged beyond full charge. A voltage detection unit that detects the overall voltage of the battery is connected, and the battery control unit obtains the voltage detection unit after the start of the high rise when the high rise period is started in at least one of the plurality of secondary batteries. Battery pack based on the change in voltage value A full charge value deriving unit for deriving a full charge value, which is a value indicating the number of secondary batteries that have newly reached full charge after the start of high rise, and a full charge value deriving unit Each time the value is derived, the full charge value is integrated to calculate the full charge value integrated value, and the assembled battery is charged based on the full charge value integrated value calculated by the full charge value integrated unit. A charging current regulating unit that regulates the charging current, and the charging current regulating unit reduces the charging current and the full charge value when the full charge value integrated value is equal to or greater than a predetermined first threshold value. In the secondary battery system, the charging current is terminated when the integrated value is equal to or higher than a predetermined second threshold value higher than the first threshold value.

  The secondary battery system of the present invention includes an assembled battery formed by connecting a plurality of secondary batteries in series. And a battery control part charges an assembled battery based on the voltage value of the whole assembled battery which a voltage detection part detects. That is, the secondary battery system of the present invention is inexpensive because it does not have a configuration for detecting the voltage of each secondary battery constituting the assembled battery.

  In addition, the battery control unit calculates a full charge value integrated value based on the entire voltage of the assembled battery during charging. The full charge value integrated value is a value indicating the total number of secondary batteries that have reached full charge after the start of charging of the assembled battery. Then, when it is determined that all the secondary batteries constituting the assembled battery have reached full charge because the full charge value integrated value is equal to or greater than the second threshold value, the charging of the assembled battery is terminated. On the other hand, when it is determined that all the secondary batteries have not reached full charge because the full charge value integrated value is not less than the first threshold value but has not reached the second threshold value. The charging of the assembled battery is continued while the charging current regulating unit regulates the charging current for charging the assembled battery. Thus, charging of the assembled battery can be continued until all the secondary batteries constituting the assembled battery reach full charge without degrading the secondary battery that has reached full charge.

  In the secondary battery system described above, the battery control unit includes an increase rate acquisition unit that acquires an increase rate of the overall voltage of the assembled battery based on a voltage value acquired by the voltage detection unit during charging, and an increase rate Has a high rise start time determination unit that determines that the high rise start time is when the value becomes less than or equal to a predetermined first reference value, and the full charge value deriving unit has a peak voltage value from the start of the high rise. When the rate of increase at a predetermined reference time until reaching the point is higher than a predetermined second reference value that is higher than the first reference value, the degree of the decrease when a decrease after the peak is observed If the rate of increase at the reference time is less than or equal to the second reference value, the fully charged value is derived based on the integrated value of the voltage value from the start of the high increase to the decrease. It is preferable that This is because the full charge value can be accurately calculated.

  In the secondary battery system described above, the first reference value is equal to or greater than the maximum voltage increase rate during the low rise period of the secondary battery alone, and the voltage rise at the initial stage of the secondary battery high rise period. The second reference value is higher than the rate of voltage increase at the beginning of the high rise period of the single secondary battery, and is the value of the high rise period when the high rise periods of the two secondary batteries overlap. It is preferably a value lower than the rate of increase in voltage of the assembled battery in the initial stage. That is, when the rate of increase in the voltage of the assembled battery becomes less than the first reference value or more, it is properly detected that any of the secondary batteries in the assembled battery is nearing full charge. Because you can.

  Further, when the rate of increase at the reference time is higher than the second reference value, the plurality of secondary batteries are close to reaching full charge at the same time. Therefore, the number of secondary batteries that are fully charged at the same time can be appropriately determined based on the subsequent decrease in the overall voltage of the assembled battery. On the other hand, when the rate of increase at the reference time is less than or equal to the second reference value, one secondary battery is about to reach full charge, or a plurality of secondary batteries are about to shift to a full charge soon. It may be. Therefore, in these cases, the number of fully charged secondary batteries can be appropriately determined from the integrated value of the voltage value from the start of the rise to the drop. This is because the integrated voltage value of the assembled battery becomes higher as the number of fully charged secondary batteries increases.

  In the secondary battery system described above, the secondary battery may be a nickel hydride secondary battery.

  The present invention also extends to an image forming apparatus comprising: a power supply unit having the secondary battery system described above; and an image forming unit that operates by receiving power from the power supply unit.

  According to the present invention, there are provided a secondary battery system and an image forming apparatus which are inexpensive and can appropriately fully charge a plurality of secondary batteries constituting an assembled battery.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. It is a figure which shows the charge characteristic of the secondary battery which concerns on this form. It is a figure which shows the temperature change at the time of charge of the secondary battery which concerns on this form. It is a figure which shows the charge characteristic of an assembled battery when all the electrical storage rates of the secondary battery before charge of an assembled battery are the same. It is a figure for demonstrating the charging characteristic of an assembled battery when the electrical storage rate of one secondary battery differs before the assembled battery is charged. It is a figure for demonstrating the charging characteristic of an assembled battery when the electrical storage rate of the secondary battery before charge of an assembled battery is all different. It is a figure for demonstrating the charging characteristic of an assembled battery when the electrical storage rate of the secondary battery before charge of an assembled battery has shifted | deviated slightly. It is a flowchart which shows the process sequence of charge of an assembled battery by a charge control part.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is embodied in an image forming apparatus as an example of an electronic apparatus.

  FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a device control unit 10, a power supply device 20, and a processing unit 40. In FIG. 1, a path related to power supply is indicated by a solid line arrow, and a path of a control signal related to control of each part is indicated by a broken line arrow.

  As illustrated in FIG. 1, the processing unit 40 includes an image forming unit 41, an operation unit 42, and a display unit 43. The image forming unit 41 is for performing image formation. That is, the image forming unit 41 includes various units for performing image formation, a driving unit for operating them, a fan for exhausting and cooling the inside of the apparatus, and the like.

  The operation unit 42 is used by the user to input various instructions, data such as characters and numbers, using operation keys. Further, the operation unit 42 has a return switch 44 for returning from a standby mode, which will be described later, to an operation mode. The display unit 43 is a liquid crystal panel on which a menu or the like selected by the user is displayed. The image forming unit 41, the operation unit 42, and the display unit 43 are all operation units that operate upon receiving power supply.

  The power supply device 20 includes a power supply control unit 21, an AC / DC conversion unit 22, a relay 23, a power sensor 24, an assembled battery A, a charge control unit 25, and a discharge control unit 26. Further, the power supply device 20 is connected to the device control unit 10 and the processing unit 40.

  Furthermore, an external power supply 200 is connected to the power supply device 20. The external power source 200 is, for example, a commercial power source for supplying AC power to the image forming apparatus 1. The power supplied from the external power source 200 is input to the power source control unit 21 via the power sensor 24, the relay 23, and the AC / DC conversion unit 22 in this order.

  The power sensor 24 is for measuring the amount of power supplied from the external power source 200 to the power supply device 20. Therefore, the power sensor 24 can determine whether or not power is supplied from the external power source 200. The relay 23 is for switching power supply from the external power supply 200 into the power supply device 20 by switching between conduction and non-conduction at the connection position in the electric circuit. The AC / DC converter 22 is for converting AC power from the external power source 200 into DC power.

  The power control unit 21 is for controlling power supplied to each unit of the image forming apparatus 1 based on an instruction from the processing management unit 11. Specifically, the power supply control unit 21 receives the operation state and operation mode of the image forming apparatus 1 from the process management unit 11. And the power supply control part 21 supplies the electric power which they require with respect to the apparatus control part 10 and the process part 40 based on the operation state and operation mode. Therefore, the power control unit 21 controls each unit of the power supply device 20.

  The assembled battery A is formed by connecting three secondary batteries B1, B2, and B3 in series. The secondary batteries B1, B2, and B3 in this embodiment are all nickel-hydrogen secondary batteries having the same specifications. Therefore, hereinafter, the secondary batteries B1, B2, B3 will be described as the secondary battery B unless otherwise distinguished.

  In addition, the AC / DC conversion unit 22 has a power supply path to the charge control unit 25 separately from the power supply path to the power supply control unit 21. The charging control unit 25 is for charging the assembled battery A with the electric power of the external power source 200. Furthermore, the assembled battery A is connected to the power supply control unit 21 via the discharge control unit 26. The discharge control unit 26 is for controlling the discharge of the assembled battery A.

  A voltage detection unit 27 is connected to the assembled battery A. The voltage detection unit 27 of the present embodiment is for detecting the entire voltage of the assembled battery A formed by connecting the secondary batteries B1, B2, and B3 in series. The voltage detection unit 27 detects the voltage of the assembled battery A at a predetermined time interval, and outputs the detected value to the charge control unit 25. The time interval for detecting the voltage of the assembled battery A by the voltage detector 27 can be set to 1 second, for example.

  FIG. 2 shows a graph of charging characteristics of the secondary battery B alone. In FIG. 2, the vertical axis represents battery voltage and the horizontal axis represents time. FIG. 2 shows the transition of voltage when the secondary battery B is charged with a constant current value from the state where the storage rate, which is the ratio of the remaining battery capacity to the full charge capacity, is 0%. . That is, the storage rate of the secondary battery B at time T0 when charging is started is 0%. Note that FIG. 2 shows that charging of the secondary battery B is 0 at a C rate where the current value (A) that can charge or discharge the full charge capacity (Ah) of the secondary battery B in 1 hour is 1 C. When it is performed at a constant current value of .5 to 1.0C. Moreover, the full charge capacity of the secondary battery B of this embodiment is 2000 mA.

  As shown in FIG. 2, the battery voltage of the secondary battery B at the time of charging increases from time T0 to time T3, and reaches a maximum value Vmax at time T3. This time T3 when the battery voltage becomes Vmax is when the secondary battery B is in a fully charged state with a storage rate of 100%. The battery voltage of the secondary battery B decreases to the time T4 after reaching the maximum value Vmax at the time T3. FIG. 2 shows the amount of decrease in the battery voltage from Vmax as Y. After the decrease of the Y voltage, the battery voltage is almost constant.

  Further, the battery voltage of the secondary battery B rises with a large slope in a section from the initial time T0 to time T1 when charging is started and a section from the time T2 to the time T3 immediately before the fully charged state is reached. doing. On the other hand, in the interval from time T1 to time T2 in the meantime, the battery voltage of the secondary battery B only rises with a slight slope.

  A section from T0 to T1 is an initial part IE, a section from T1 to T2 is a low rise part IL, and a section from T2 to T3 is a high rise part IH. Therefore, the voltage increase rate of the secondary battery B is higher in the initial portion IE and the high increase portion IH than in the low increase portion IL. The time of the high ascending portion IH is about 10 minutes.

  Further, as shown in FIG. 2, a point on the graph at T2 from the low ascending portion IL to the high ascending portion IH is defined as a feature point X. In the secondary battery B of this embodiment, the storage rate at the feature point X is about 90%. Further, a section from T3 to T4 in which the Y voltage drop occurs is defined as a descending portion D. Further, in FIG. 2, a section from time T <b> 2 indicating the feature point X to time T <b> 4 when the voltage drop at Y occurs is shown as a convex portion Z.

  FIG. 3 shows a graph of temperature change during charging of the secondary battery B. In FIG. 3, the vertical axis represents the battery temperature and the horizontal axis represents the charging time. The temperature change shown in FIG. 3 is also when the secondary battery B with the charged amount of 0% is charged at a constant current value of 0.5 to 1.0 C as in FIG.

  As shown in FIG. 3, the temperature of the secondary battery B slightly increases immediately after the start of charging, and thereafter remains substantially constant until time T2. And it turns out that it is rising rapidly from the time T2 to the time T3, ie, the secondary battery B just before full charge. This is because the energy consumed for charging while the storage rate of the secondary battery B is low is not consumed for charging due to the increase of the storage rate of the secondary battery B, but is consumed as thermal energy. Is due to. Note that the temperature drop after the peak value after time T3 is associated with the end of charging.

  Therefore, it is not preferable to continue charging the secondary battery B with a constant current value of 0.5 to 1.0 C as it is even after full charging. If the fully charged secondary battery B continues to be overcharged at a current value as high as 0.5 to 1.0 C, the battery temperature of the secondary battery B deteriorates due to excessive rise in battery temperature. This is because there is a risk of it. In addition, about the secondary battery B of this form, even if it is after a full charge, if it is a current value lower than about 0.25 C, an electric current can be sent, without raising a battery temperature excessively. That is, if the current value is lower than about 0.25 C, the current can be passed through the fully charged secondary battery B while suppressing the deterioration of the battery performance of the secondary battery B.

  The apparatus control unit 10 includes a process management unit 11, a process management storage unit 12, a reception unit 13, and a communication interface (I / F) unit 14. The I / F unit 14 is for connecting to the LAN 100 such as a LAN card or a LAN board, for example, and is for receiving image data or the like sent via the LAN 100 from an external PC or the like. The LAN 100 may be wired or wireless. The external I / F unit 14 receives the image data, and the image data is input to the process management unit 11 via the reception unit 13, whereby a print job is generated in the image forming apparatus 1.

  The process management storage unit 12 stores various programs executed in the image forming apparatus 1. The processing management storage unit 12 of this embodiment stores an operation mode and a standby mode as operation modes of the image forming apparatus 1.

  The process management unit 11 is for performing control processing of the entire apparatus. That is, the process management unit 11 controls the image forming unit 41 to execute an image forming operation based on the image data received by the I / F unit 14, for example. Also, switching between operation modes stored in the process management storage unit 12 is performed.

  The operation mode is, for example, a mode when image formation is performed by the image forming unit 41. The operation mode includes a case where a menu is displayed to the user by the display unit 43 and a READY state in which an image forming operation can be performed immediately. For this reason, the image forming apparatus 1 in the operation mode requires a large amount of power. The power supply control unit 21 in the operation mode basically supplies power from the external power supply 200 to each unit of the image forming apparatus 1 while keeping the relay 23 in a conductive state.

  When the power control unit 21 in the operation mode is not supplied with power from the external power source 200 due to, for example, a power failure such as a disaster, the discharge control unit 26 discharges the assembled battery A, and the power generated by the discharge is imaged. It can also be supplied to each part of the forming apparatus 1. For example, when the image data is not received by the I / F unit 14 or the operation of the operation unit 42 is not performed by the user for a certain time in the operation mode, the process management unit 11 shifts the operation mode to the standby mode. . The operation unit 42 can be provided with a switch to standby mode, and the operation mode can be shifted to the standby mode by a user operation instruction using the switch.

  The standby mode is a mode for reducing power consumption in the image forming apparatus 1 as compared with the operation mode. In the standby mode, for example, the image forming unit 41 and the display unit 43 are in a non-operating state. Therefore, the power supply control unit 21 in the standby mode cuts off the supply of power to the image forming unit 41, the display unit 43, and the like that are in a non-operating state. Thereby, in the image forming apparatus 1 in the standby mode, power consumption is reduced as compared with the operation mode.

  The power supply control unit 21 in the standby mode supplies power from the assembled battery A to each unit of the image forming apparatus 1 while the relay 23 is in a non-conductive state. For this reason, in the standby mode, the power of the external power source 200 is not required, and the standby power is zero. In the standby mode, when the I / F unit 14 receives image data or when the return switch 44 of the operation unit 42 is operated by the user, the operation mode is shifted to. Therefore, the power supply control unit 21 in the standby mode supplies power to at least the I / F unit 14, the reception unit 13, the process management unit 11, and the return switch 44.

  In addition, when the remaining battery capacity of the assembled battery A decreases, the power supply control unit 21 causes the charging control unit 25 to charge the assembled battery A with the electric power of the external power supply 200. The remaining battery capacity of the assembled battery A at the start of charging can be set to 50% of the full charge capacity, for example. Then, when all of the secondary batteries B1, B2, B3 of the assembled battery A are fully charged, the charging control unit 25 determines that the charging of the assembled battery A is completed, and stops the charging of the assembled battery A. Note that when the battery pack A is charged in the standby mode, the relay 23 is temporarily turned on. In the standby mode, after the battery pack A is completely charged, the relay 23 is turned off again.

  Here, the charging characteristics during charging of the battery pack A are shown in FIG. In FIG. 4, the secondary batteries B1, B2, and B3 are shown by a single battery voltage, and the assembled battery A is shown by the entire battery voltage of the assembled battery A. FIG. 4 shows an example in which the secondary batteries B1, B2, and B3 constituting the assembled battery A all have the same storage rate before charging.

  Therefore, the timing at which the feature point X on the graph of the secondary batteries B1, B2, B3 appears is the same at T5. In addition, the full charge timings at which the battery voltages of the secondary batteries B1, B2, and B3 indicate Vmax are all the same at T6. Further, all the timings at which the Y voltage drops in the secondary batteries B1, B2, B3 are the same at T7.

  For this reason, also in the graph of the assembled battery A, the voltage is greatly increased from T5. And the point on the graph of the assembled battery A in T5 is shown as the feature point XA1. Note that the voltage increase rate immediately after the characteristic point XA1 of the assembled battery A is higher than the maximum value of the voltage increase rate in the low increase portion IL of the secondary battery B alone. Furthermore, the voltage increase rate immediately after the feature point XA1 of the assembled battery A is higher than the voltage increase rate immediately after the feature point X of the secondary battery B alone.

  Further, the voltage of the assembled battery A shows the maximum value at T6. Further, the voltage decreases from T6 to T7. The voltage decrease amount of the assembled battery A is 3Y, which is three times the voltage decrease amount Y of the secondary battery B alone. Further, the convex portion ZA1 from when the voltage drops from the characteristic point XA1 of the assembled battery A is a portion where all the convex portions Z of the secondary batteries B1, B2, and B3 overlap.

  Further, the storage rates of the secondary batteries B1, B2, B3 constituting the assembled battery A are not always the same. Battery characteristics such as the full charge capacity and internal resistance of the secondary batteries B1, B2, and B3 may be different due to quality variations during manufacturing. In addition, the temperatures of the secondary batteries B1, B2, and B3 in the assembled battery A may be different depending on the positions of the batteries. For example, when the secondary batteries B1, B2, B2 are arranged in close contact in this order, the temperature of the secondary battery B2 arranged between the secondary batteries B1, B3 is the secondary batteries B1, B3. It tends to rise above the temperature. The progress of deterioration of the secondary batteries B1, B2, and B3 varies depending on the temperature. Therefore, when the assembled battery A is repeatedly charged and discharged, the storage rates of the secondary batteries B1, B2, and B3 constituting the assembled battery A may vary.

  FIG. 5 shows the charging characteristics of the assembled battery A when the storage rate of the secondary batteries B2 and B3 at the start of charging of the assembled battery A is lower than that of the secondary battery B1. In the example of FIG. 5, the storage rate of the secondary battery B1 at the start of charging of the assembled battery A is the same as in FIG. Further, the storage rates of the secondary batteries B2 and B3 at the start of charging of the assembled battery A are the same. For the secondary batteries B2 and B3, the timing at which the feature point X appears, the timing at which the battery voltage indicates Vmax, and the timing at which the voltage drop at Y occurs are shown as T8, T9, and T10 in FIG.

  In the graph of the assembled battery A, first, the first feature point XA2 appears at T5. Thereafter, the first voltage drop occurs from T6 to T7. The convex portion ZA2 from the first feature point XA2 of the assembled battery A until the voltage drop occurs is due to only the convex portion Z of the secondary battery B1. That is, the first feature point XA2 and the voltage drop are due to the fact that only the secondary battery B1 has reached full charge. Therefore, the first voltage decrease amount of the assembled battery A is Y.

  In the section from T6 to T8, the voltage value of the secondary batteries B2 and B3 indicates the low rise portion IL. That is, the voltage values of the secondary batteries B2 and B3 increase from T6 to T8. However, since the degree of increase in the voltage value of the secondary batteries B2 and B3 is slight, the influence on Y, which is the amount of decrease in the overall voltage of the assembled battery A, is slight. Therefore, for simplification of description, the influence of the low rise portion IL on the voltage value of the assembled battery A is omitted. This also applies to FIG. 6 below.

  At T8, a second feature point XA3 appears. Thereafter, the second voltage drop occurs from T9 to T10. The convex portion ZA3 from the second feature point XA3 of the assembled battery A until the voltage drop occurs is a portion where the convex portions Z of the secondary batteries B2 and B3 overlap. That is, the second feature point XA3 and the voltage drop are due to the full charge of the secondary batteries B2 and B3. Therefore, the amount of decrease in the second voltage of the assembled battery A is 2Y.

  FIG. 6 shows the charging characteristics of the assembled battery A when all the storage rates of the secondary batteries B1, B2, and B3 at the start of charging of the assembled battery A are different. In the example of FIG. 6, the storage rates of the secondary batteries B1 and B2 at the start of charging of the assembled battery A are the same as those in FIG. Further, the storage rate of the secondary battery B3 at the start of charging of the assembled battery A is lower than that in FIG. In FIG. 6, the timing at which the feature point X of the secondary battery B3 appears, the timing at which the battery voltage indicates Vmax, and the timing at which the voltage drop at Y occurs are indicated as T11, T12, and T13, respectively.

  In the graph of the assembled battery A, first, the first feature point XA4 appears at T5. Thereafter, the first voltage drop occurs from T6 to T7. The convex portion ZA4 from the first feature point XA4 of the assembled battery A until the voltage drop occurs is due to only the convex portion Z of the secondary battery B1. That is, the first feature point XA2 and the voltage drop are due to the full charge of only the secondary battery B1. Therefore, the first voltage decrease amount of the assembled battery A is Y.

  At T8, the second feature point XA5 appears. Thereafter, the second voltage drop occurs from T9 to T10. The convex portion ZA5 from the second feature point XA5 of the assembled battery A until the voltage drop occurs is due only to the convex portion Z of the secondary battery B2. That is, the second feature point XA5 and the voltage drop are due to full charge of only the secondary battery B2. Therefore, the amount of decrease in the second voltage of the assembled battery A is Y.

  Furthermore, a third feature point XA6 appears at T11. Thereafter, a third voltage drop occurs from T12 to T13. The convex portion ZA6 from the third feature point XA6 of the assembled battery A until the voltage drop occurs is due to only the convex portion Z of the secondary battery B3. That is, the third feature point XA6 and the voltage drop are due to the full charge of only the secondary battery B3. Therefore, the amount of decrease in the third voltage of the battery pack A is Y.

  In addition, the charging characteristics of the assembled battery A shown in FIGS. 4 to 6 described above are such that at least two or more of the convex portions Z of the secondary batteries B1, B2, and B3 are almost completely overlapped or overlapped at all. It is when there is no state. However, due to variations in the storage rates of the secondary batteries B1, B2, and B3, the convex portions Z of the two or more secondary batteries B may overlap with each other at the time of charging. FIG. 7 shows an example in which the convex portions Z of the two secondary batteries B1 and B2 are overlapped in a shifted state.

  FIG. 7 shows a case where the storage rate of the secondary battery B2 is slightly lower than the storage rate of the secondary battery B1 at the start of charging of the assembled battery A. In FIG. 7, for the secondary battery B1 indicated by a solid line, the characteristic point X is shown at T14, and the voltage of Y is reduced at T16. On the other hand, for the secondary battery B2 indicated by a broken line, the feature point X is shown at T15, and the voltage of Y is reduced at T17.

  Further, as shown in FIG. 7, the time from T14 to T15 is assumed to be t1. The time of t1 is shorter than the time of the convex part Z. For this reason, the convex part Z of the secondary battery B1 and the convex part Z of the secondary battery B2 are overlapped with each other while being shifted by t1. In FIG. 7, the convex portion Z of the secondary battery B3 does not overlap with any convex portion Z of the secondary batteries B1 and B2, and does not appear in the drawing.

  Further, in the graph of the assembled battery A indicated by a thick solid line in FIG. 7, a feature point XA7 appears at T14, and a voltage drop occurs at T17. The amount of voltage drop of the assembled battery A is YA. Further, a section from T14 in which the graph of the assembled battery A indicates the feature point XA7 to when the voltage drop of YA occurs is shown as a convex portion ZA7.

  Here, the voltage increase rate immediately after the feature point XA7 of the assembled battery A is equal to or higher than the voltage increase rate immediately after the feature point X of the secondary battery B alone. This is because immediately after the assembled battery A shows the characteristic point XA7, the secondary battery B2 shows the low rise portion IL. That is, the voltage of the secondary battery B2 is slightly increased. Further, the time during which the assembled battery A exhibits the convex portion ZA is naturally longer than the time during which the secondary battery B alone exhibits the convex portion Z. Further, the YA of the assembled battery A differs depending on the overlapping state of the convex portions Z of the secondary batteries B1 and B2 that differ depending on the time t1. However, YA of the assembled battery A is at least larger than Y of the secondary battery B alone.

  Next, the processing procedure of charging the assembled battery A by the charging control unit 25 will be described with reference to the flowchart of FIG. In the present embodiment, charging of the assembled battery A starts with a current value of 0.5 to 1.0 C. First, the charging control unit 25 during charging calculates the voltage increase rate from the voltage value of the assembled battery A detected by the voltage detection unit 27 (S101). Then, it is determined whether or not the calculated voltage increase rate is equal to or higher than a predetermined first reference increase rate (S102).

  The first reference increase rate is determined to be not less than the maximum value of the voltage increase rate in the low increase portion IL of the secondary battery B alone and not more than the voltage increase rate immediately after the inflection point X of the secondary battery B alone. . That is, the first reference increase rate is a value that is lower than any of the voltage increase rates that the assembled battery A exhibits immediately after the feature points XA1 to XA7. Thereby, it is possible to appropriately detect that any secondary battery B of the assembled batteries A has reached the feature point X.

  Next, when the calculated voltage increase rate of the assembled battery A is equal to or higher than the first reference increase rate (S102: YES), the voltage increase rate of the assembled battery A becomes less than or equal to the first reference increase rate. Sometimes, it is determined that the assembled battery A has reached the feature point (S103). Further, it is determined whether the voltage increase rate immediately after the feature point is higher than a predetermined second reference increase rate (S104).

  The second reference increase rate is determined based on the voltage increase rate at the feature point X of the secondary battery B. That is, the second reference increase rate is determined to be higher than the voltage increase rate immediately after the feature point X of the secondary battery B alone. For this reason, the second reference increase rate is set to a value higher than the first reference increase rate. Further, the second reference increase rate is set to a value lower than the voltage increase rate that the assembled battery A shows immediately after the feature point when the convex portions Z of the two secondary batteries completely overlap.

  Note that the determination in step S104 is not limited to the determination based on the voltage increase rate immediately after the assembled battery A reaches the feature point. As described above, the voltage of the secondary battery B exhibits a high voltage rise rate in the high rise portion IH of about 10 minutes after showing the feature point X. Therefore, after the assembled battery A reaches the feature point, the second reference increase rate is determined by the voltage increase rate of the assembled battery A at the time corresponding to the section showing the high voltage increase rate of the high increase portion IH of the secondary battery B. The determination in step S104 related to the comparison may be made. Specifically, for example, after the assembled battery A reaches the feature point, the determination in step S104 related to the comparison with the second reference increase rate may be made based on the voltage increase rate of the assembled battery A two minutes later. Good.

  When the voltage increase rate immediately after the feature point of the assembled battery A is higher than the second reference increase rate (S104: YES), the secondary battery B1, B2, B3 constituting the assembled battery A is selected. It is determined that two or more secondary batteries B are nearing full charge at the same time (S105). That is, it is determined that the secondary batteries B are in a state where the convex portions Z of the two or more secondary batteries B are almost completely overlapped, and those secondary batteries B are just before reaching full charge.

  Subsequently, it is determined whether or not there is a voltage drop in the voltage value of the assembled battery A detected by the voltage detector 27 (S106). If the battery pack A has a voltage drop (S106: YES), the fully charged battery is the ratio of the secondary battery B in the battery pack A that has been fully charged based on the voltage drop amount. The ratio is calculated (S107). For example, when the amount of voltage decrease is 2Y, the number of secondary batteries B in a fully charged state is 2, so the full charge ratio of the assembled battery A is 2/3.

  It should be noted that the battery voltage of the secondary battery B of this embodiment may increase again within about 2 to 5 minutes after exhibiting the behavior of the descending portion D when the secondary battery B is deteriorated. For this reason, when the voltage value of the assembled battery A decreases, the charge control unit 25 of the present embodiment subsequently reduces the voltage of the assembled battery A when the voltage value does not increase again in about 2 to 5 minutes. It is determined that there is (S106: YES).

  On the other hand, when the voltage increase rate immediately after the feature point of the assembled battery A is equal to or less than the second reference increase rate (S104: NO), one of the secondary batteries B1, B2, and B3 is selected. It is determined that B is about to reach full charge or that it is about to reach full charge when two or more secondary batteries B are scattered (S109). Nearly reaching full charge when two or more secondary batteries B are scattered means when two or more secondary batteries B are nearing full charge with their convex portions Z shifted and overlapped. is there.

  In this case, the charging control unit 25 starts calculating the integrated value of the voltage value of the assembled battery A detected by the voltage detecting unit 27 from when the feature point appears in the assembled battery A (S110). Then, while calculating the integrated value of the voltage value of the assembled battery A, it is determined whether or not there is a voltage drop in the voltage value of the assembled battery A detected by the voltage detection unit 27 (S111). When the battery pack A has a voltage drop (S111: YES), the full charge ratio of the battery pack A is calculated from the integrated value of the voltage values until the voltage drop (S112).

  Here, the integrated value of the voltage value of the assembled battery A when the secondary batteries B are fully charged in a state where the convex portions Z of the plurality of secondary batteries B are shifted from each other and overlapped with each other is naturally one two. It becomes a value higher than the integrated value of the voltage value of the assembled battery A when only the secondary battery B is fully charged. As described above in the example of FIG. 7, the time for the assembled battery A to show the convex portion ZA7 is longer than the time for the secondary battery B to show the convex portion Z. Furthermore, it is because the voltage drop amount YA of the assembled battery A is at least larger than the voltage drop amount Y of the secondary battery B alone.

  Further, when the secondary batteries B are fully charged in a state where the convex portions Z of the plurality of secondary batteries B are shifted from each other and overlapped, the assembled battery A is determined according to the number of the overlapping convex portions Z. The integrated values of the voltage values are different. This is because the integrated value of the voltage value of the assembled battery A at that time becomes higher as the number of convex portions Z overlapping each other increases. Therefore, the full charge ratio of the assembled battery A can be calculated from the integrated value of the voltage values from when the characteristic point appears in the assembled battery A to when the voltage drops.

  The full charge ratio of the assembled battery A is based on the slope of the portion where the secondary battery B before the feature point appears in the assembled battery A exhibits the low rise portion IL, and is the integrated value of the higher voltage value portion. It is good also as calculating using. That is, in the example of FIG. 7, the full charge ratio of the assembled battery A is determined by the integrated value of only the convex portion ZA7 showing a high voltage value with respect to the straight line having the voltage increase rate immediately before the feature point XA7 as a slope. You may make it calculate.

  Next, it is determined whether or not all of the secondary batteries B1, B2, and B3 constituting the assembled battery A are fully charged (S108). That is, when the calculation of the full charge ratio of the assembled battery A in step S107 or step S112 is the first time, when the value is 1, all of the secondary batteries B1, B2, B3 are in a fully charged state. Judge that there is. Further, when the calculation of the full charge ratio of the assembled battery A in step S107 or step S112 is the second time or later, the full charge of the assembled battery A calculated this time is set to the full charge ratio of the assembled battery A calculated before that. Add the ratio. When the value of the full charge ratio of the assembled battery A after the addition is 1, it is determined that all of the secondary batteries B1, B2, and B3 are in a fully charged state.

  When all of the secondary batteries B1, B2, B3 are fully charged (S108: YES), the charging control unit 25 stops the charging of the assembled battery A when the charging of the assembled battery A is completed. . On the other hand, when even one of the secondary batteries B1, B2, B3 is not in a fully charged state (S108: NO), it is the ratio of the secondary batteries B in the assembled battery A that are not fully charged. The non-full charge ratio of the assembled battery A is calculated, and the current value for charging the assembled battery A is switched to a predetermined current value according to the non-full charge ratio (S113). Then, the secondary battery B that has not reached full charge is charged by returning to step S101 and continuing charging of the assembled battery A with the current value after switching.

  The current value after switching according to the non-full charge ratio of the assembled battery A is a current value lower than the current value that was 0.5 to 1.0 C at the start of charging. Furthermore, the current value after switching is determined in accordance with the ratio of the secondary batteries B that have not reached full charge so that the fully charged secondary battery B of the assembled battery A does not generate excessive heat. ing. This is because the secondary battery B that has reached full charge is not deteriorated. Specifically, for example, when the non-full charge ratio of the assembled battery A is 1/3, the current value after switching can be set to 0.25C.

  As described above in detail, the power supply device 20 of the image forming apparatus 1 according to the present invention includes the assembled battery A formed by connecting three secondary batteries B in series. The charging control unit 25 charges the assembled battery A based on the voltage value of the assembled battery A detected by the voltage detection unit 27. The voltage detector 27 detects the entire voltage value of the assembled battery A. That is, since there is no configuration for detecting the voltage for each secondary battery B constituting the assembled battery A, it is inexpensive. In addition, when charging the assembled battery A, the charging control unit 25 determines whether all of the secondary batteries B constituting the assembled battery A have reached full charge based on the overall voltage of the assembled battery A. . And when there exists the secondary battery B which has not reached full charge, the electric current value which charges the assembled battery A is reduced. Thereby, the charging of the assembled battery A can be continued until all the secondary batteries B are fully charged without degrading the secondary batteries B that have reached full charge.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the assembled battery A is not limited to one in which three secondary batteries B are connected in series. The assembled battery A may be one in which two secondary batteries B are connected in series, or may be one in which four or more secondary batteries B are connected in series.

  For example, the external power source 200 that supplies power to the power source device 20 of the image forming apparatus 1 is not limited to a commercial power source, and a solar cell, a thermoelectric conversion element, or the like can be used in combination. In that case, the power supplied from the solar cell and the thermoelectric conversion element may be directly input to the charge control unit 25 without going through the AC / DC conversion unit. If it does in this way, assembled battery A can be charged with the electric power supplied from a solar cell and a thermoelectric conversion element.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 20 ... Power supply device 21 ... Power supply control part 25 ... Charge control part A ... Assembly battery B1, B2, B3 ... Secondary battery

Claims (5)

In a secondary battery system having an assembled battery formed by connecting a plurality of secondary batteries in series, and a battery control unit that controls charging and discharging of the assembled battery,
The plurality of secondary batteries are all
When charging, the voltage increases as it approaches full charge,
A low rise period with a lower voltage rise rate during a charge period from the start of charging to full charge, and a high rise period with a higher voltage rise rate after the low rise period;
Satisfying that the voltage drops when the battery is further charged beyond full charge.
The assembled battery is connected to a voltage detector that detects the entire voltage of the assembled battery,
The battery controller is
The secondary battery that constitutes the assembled battery based on a change in voltage value acquired by the voltage detection unit after the start of the high rise, which is when the high rise period starts in at least one of the plurality of secondary batteries. A full charge value deriving unit for deriving a full charge value that is a value indicating the number of batteries that have newly reached full charge after the start of the high rise;
A full charge value integration unit for calculating a full charge value integrated value by integrating the full charge value each time the full charge value deriving unit derives a full charge value;
A charging current regulating unit that regulates a charging current for charging the assembled battery based on a full charging value integrated value calculated by the full charging value integrating unit;
The charging current regulating unit is
When the full charge value integrated value is equal to or greater than a predetermined first threshold value, the charging current is decreased,
The secondary battery system, wherein the charging current is terminated when the full charge value integrated value is equal to or higher than a predetermined second threshold value higher than the first threshold value. The secondary battery system according to claim 1,
The battery controller is
An increase rate acquisition unit that acquires an increase rate of the overall voltage of the assembled battery based on a voltage value acquired by the voltage detection unit during charging;
A high rise start time determination unit that determines when the rise rate is less than or equal to a predetermined first reference value as the high rise start time;
The full charge value deriving unit
When the rate of increase at a predetermined reference time from the start of the high rise to the peak of the voltage value is higher than a predetermined second reference value higher than the first reference value,
When a decrease after the peak is observed, a full charge value is derived based on the degree of the decrease,
If the rate of increase at the reference time is less than or equal to the second reference value,
A secondary battery system, wherein a fully charged value is derived based on an integrated value of voltage values from the start of the high rise to the drop. The secondary battery system according to claim 2,
The first reference value is
A value that is not less than the maximum value of the voltage increase rate during the low rise period of the secondary battery alone and not more than the voltage rise rate at the initial stage of the high rise period of the secondary battery alone,
The second reference value is
The voltage rise rate of the assembled battery at the initial stage of the high rise period when the high rise period of the two secondary batteries overlaps is higher than the voltage increase rate at the initial stage of the high rise period of the secondary battery alone. A secondary battery system having a value lower than the rate of increase. The secondary battery system according to any one of claims 1 to 3,
The secondary battery is a nickel metal hydride secondary battery. An image forming apparatus comprising: a power supply unit having the secondary battery system according to any one of claims 1 to 4; and an image forming unit that operates by receiving power supply from the power supply unit.

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