JP2014033580A - Charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charger for rapidly charging secondary batteries with appropriate charge current Ic depending on battery capacity, even when the secondary batteries have different battery capacity, without executing capacity measurement processing for detecting battery capacity of the secondary batteries before the rapid charge.SOLUTION: A charger performs variable control of charge current of DC power so that a voltage rise change rate calculated by calculation means is to be a predetermined set rise change rate, while setting charge voltage of the DC power to be terminal voltage of a secondary battery; while a power supply unit charges the secondary battery with the DC power.

Description

  The present invention relates to a charging device for charging a secondary battery, and more specifically, in a quick charge mode, even when the battery capacity of a secondary battery to be charged is different, charging is performed with an optimal charging current according to the battery capacity. The present invention relates to a charging device.

  Conventionally, a secondary battery such as lithium ion is normally charged by a CCCV (constant current constant voltage) charging method shown in FIG. In the CCCV charging method, as shown in FIG. 4B, after a pre-charge is performed to confirm a rise in voltage Vb between the terminals of the secondary battery (referred to as terminal voltage) Vb by adding a minute charging current Ic, a constant value is obtained. Rapid charging is performed with the charging current Ic of the current Ik1, and the terminal voltage Vb (t) near the maximum charging voltage Ve is just before or until the terminal voltage Vb (t) reaches the maximum charging voltage Ve determined by the secondary battery. ) Is maintained at a constant voltage that gradually decreases the charging current Ic (t). Here, the maximum charging voltage Ve is the maximum charging voltage that is allowed when the secondary battery is charged. If charging is performed at a voltage exceeding this, the secondary battery is deteriorated or destroyed. There is danger. The maximum charging voltage Ve of the secondary battery is substantially constant depending on the type regardless of the battery capacity, and is 4.2 V in the case of a lithium ion battery.

  On the other hand, the rate of increase (inclination) of the terminal voltage Vb (t) that rises at a constant charging current Ik1 during rapid charging differs depending on the battery capacity of the secondary battery to be charged, and the charging current Ik1 compared to the battery capacity. If it is small, the charging time of rapid charging will be extended. Conversely, if it is large, the battery will be charged beyond the natural chemical change rate of the secondary battery, so that the secondary battery will have a shorter service life. Therefore, the secondary battery fully charged with the nominal capacity value is discharged with constant current, and the discharge current value when the discharge is completed in 1 hour (SOC (State of Charge) is 0%) is 1 C (C is the rated discharge capacity value). ), A constant current Ik1 shown in FIG. 3 (a) is set to 1C determined for each battery capacity of the secondary battery to be charged, and a charging device that outputs a constant current Ic around 1C is used. So-called 1C charging is performed during rapid charging. If rapid charging is performed by 1C charging, the battery can be fully charged in the shortest time without exceeding the natural chemical change rate of the secondary battery.

  However, a dedicated charging device for setting Ik1 must be prepared for each battery capacity of the secondary battery to be charged. In order to solve this problem, the charging current Ic for constant current control during the rapid charging is set. A constant current Ik2 that matches the battery capacity of the secondary battery is set from the secondary battery side, and even with a general-purpose charging device, a secondary battery with a different battery capacity is set to an appropriate value for each battery capacity. A charging method for charging with a charging current Ik2 is also known. In this charging method, as shown in FIG. 4, a charging device that outputs a constant voltage as a charging voltage Vc using a DC voltage Vk that is sufficiently higher than the maximum charging voltage Ve of the secondary battery is used. In the constant current control circuit, the constant current control is performed so that the charging current Ik2 during the rapid charging becomes 1C according to the battery capacity of the secondary battery. Therefore, during the rapid charging, the secondary battery is charged by 1C, and after approximately 1 hour, when the terminal voltage Vb (t) reaches the maximum charging voltage Ve, the charging current Ic (t) is decreased to reduce the terminal voltage Vb. Constant voltage charging is performed to maintain the maximum charging voltage Ve.

  In addition, a capacity measurement process for detecting a battery capacity of a secondary battery to be charged in advance before the quick charge is performed, and a constant current charge process is performed during the quick charge with a charge current Ic set based on the detected battery capacity. An apparatus is also known (Patent Document 1). The battery capacity of the secondary battery is controlled by opening and closing a charging path through which a known charging current Io for capacity detection is passed from the charging device to the secondary battery during the capacity measurement process, and at intervals of a certain time Δt in which the charging current Io flows. Obtained from the two SOC1 and SOC2 (unit:%) detected.

That is, the battery capacity of the secondary battery is
Battery capacity = charging current Io · fixed time Δt · 100 / (SOC2-SOC1)
Calculated from Here, the SOC (State of Charge), which is the remaining battery level, increases or decreases in proportion to the change in the open-circuit voltage between the terminals of the secondary battery, assuming that the secondary battery is fully charged as 100%. And SOC2 are obtained from the open voltage of the secondary battery that controls the opening of the charging path before and after the charging time Δt.

JP 2008-61373 A

  In the conventional CCCV charging method shown in FIG. 3 described above, it is necessary to prepare a dedicated charging device for each battery capacity of the secondary battery, and if an excessive charging current Ic is passed compared to the battery capacity during rapid charging, This causes deterioration of the secondary battery and shortens the service life. On the other hand, if constant current charging is performed with a charging current Ic that is smaller than the battery capacity, the charging time until full charging is extended and rapid charging cannot be performed.

  On the other hand, in accordance with the battery capacity of the secondary battery, the charging current Ic (t) during the rapid charging is controlled to a constant current Ik2 from the side of the secondary battery to be charged or the device containing the secondary battery, as shown in FIG. In the method, even if the terminal voltage Vb (t) of the secondary battery increases during the rapid charging, the charging voltage Vc output from the charging device from the secondary battery or device side cannot be controlled. A DC voltage Vk sufficiently higher than the maximum charging voltage Ve of the battery is output at a constant voltage. As a result, particularly in the initial stage of rapid charging, the potential difference between the DC voltage Vk, which is the charging voltage Vc, and the terminal voltage Vb (t) of the secondary battery is large, and the constant current Ik2 flows, resulting in a large power loss. In addition, the loss energy is replaced with thermal energy, and an unintended temperature rise occurs.

  Further, in the charging device described in Patent Document 1, it is necessary to perform a capacity measurement process for detecting the battery capacity of the secondary battery before rapid charging. In the capacity measurement process, the charging path is controlled to open and close multiple times. There is the trouble of measuring the open-circuit voltage of the secondary battery, and its control is complicated.

  Furthermore, every time the remaining battery level (SOC) is detected, the charging path is controlled to open and the terminal voltage of the secondary battery greatly decreases, so that charging does not proceed substantially during the capacity measurement process, and charging efficiency is improved. There was a problem of being bad.

  The present invention does not execute the capacity measurement process for detecting the battery capacity of the secondary battery before rapid charging, and even if the secondary battery has a different battery capacity, an appropriate charging current Ic ( It is an object of the present invention to provide a charging device that performs quick charging at t).

  It is another object of the present invention to provide a charging device that performs rapid charging with no power loss because the charging voltage Vc output from the charging device during rapid charging matches the terminal voltage Vb (t) of the secondary battery.

  In order to achieve the above-described object, the charging device according to claim 1 includes a power supply unit that charges a secondary battery with DC power, and the power supply unit until a terminal voltage of the secondary battery reaches a predetermined end voltage. A power supply control unit that controls the charging operation of the battery, wherein the power supply control unit includes a voltage detection unit that detects a terminal voltage of the secondary battery, a timer unit that measures an elapsed time, and a minute unit Calculation means for successively calculating a rate of change in voltage expressed by a terminal voltage increase ΔV during the elapsed time, and while the power supply unit charges the secondary battery with DC power, the charging voltage of the DC power is The charging current of the DC power is variably controlled so that the voltage rise change rate calculated by the calculation means becomes a preset rise change rate while using the terminal voltage of the secondary battery.

  The power supply control unit increases the terminal voltage from the potential difference of the secondary battery terminal voltage detected by the voltage detection unit before and after the minute unit elapsed time measured by the timer means while the power supply unit charges the secondary battery with DC power. The minute ΔV is obtained, and the voltage increase rate during the minute unit elapsed time is calculated. The calculated voltage rise change rate represents the charging speed of the secondary battery and is proportional to the charging current. Therefore, the secondary battery is variably controlled so that the voltage rise change rate becomes the set rise change rate. Regardless of the battery capacity, the battery can be charged at the optimum charging speed suitable for the secondary battery.

  The charging device according to claim 2, wherein the end voltage is a maximum charging voltage allowed for the secondary battery, and the power supply control unit rapidly increases until the terminal voltage of the secondary battery reaches a target voltage slightly lower than the maximum charging voltage. The charging operation of the power supply unit is controlled in the charging mode, and the set increase rate in the rapid charging mode is set to 1C, where the secondary battery having the nominal capacity value is discharged at a constant current, and the current value at which discharge ends in 1 hour is 1C. It is characterized in that it is determined in the vicinity of the rate of change in voltage rise when charged with a charging current of 1C.

  Until the terminal voltage of the secondary battery reaches a target voltage that is slightly lower than the maximum charging voltage, the terminal voltage of the secondary battery increases at a rate of change in voltage increase when charging with a charging current of approximately 1C. In the fast charge mode, the secondary battery is charged at a charge rate approximately equal to the natural discharge rate regardless of the battery capacity.

  The charging device according to claim 3 is characterized in that the target voltage is an inflection point voltage at which a rate of change in voltage increase proportional to the charging current starts to decrease.

  If the terminal voltage of the secondary battery exceeds the inflection point voltage, the rate of increase of the terminal voltage will drop rapidly even if the same charging current is applied, and the electrical energy supplied to the secondary battery will be converted into thermal energy. The rate increases and charging efficiency deteriorates. Therefore, when the inflection point voltage is reached immediately before the charging efficiency deteriorates, the quick charge mode in which the terminal voltage is increased at the rate of voltage increase when charging with a charging current of approximately 1 C is terminated.

  According to a fourth aspect of the present invention, the power supply control unit controls the charging operation of the power supply unit in the fine adjustment charging mode until the maximum charging voltage is reached after the terminal voltage of the secondary battery reaches the target voltage. The set increase rate of change in the adjustment charge mode is set to a value sufficiently lower than the set increase rate of change in the quick charge mode.

  After the terminal voltage of the secondary battery reaches the target voltage, until the maximum charging voltage is reached, the rate of change in the voltage of the secondary battery terminal voltage is sufficiently lower than in the quick charge mode. The maximum charging voltage is approached and the terminal voltage does not become overcharged exceeding the maximum charging voltage.

  If the target voltage is the inflection point voltage, the charging current decreases after reaching the inflection point voltage, so that the terminal voltage reaches the maximum charging voltage while suppressing heat generation.

  The charging device according to claim 5, wherein the power supply unit outputs the DC power between the charging terminals of the secondary battery by opening and closing a switching element connected in series between the DC input voltages having a DC voltage higher than the end voltage. The power step-down converter increases or decreases the ON duty of the pulse width modulation signal that controls opening and closing of the switching element so that the voltage increase change rate calculated by the calculating means matches the set increase change rate. The charging device according to claim 1, wherein the rate of change in voltage rise is adjusted.

  Since the magnitude of the DC power output from the chopper type step-down converter depends on the ON duty of the pulse width modulation signal for closing and controlling the switching element, the DC power for charging the secondary battery increases and decreases according to the increase and decrease of the ON duty. To do. Since the output voltage of the chopper type step-down converter is the terminal voltage of the secondary battery, the increase / decrease in DC power appears as an increase / decrease in charging current, and the rate of increase in voltage proportional to the charging current also increases / decreases. Therefore, by adjusting the ON duty of the pulse width modulation signal, the voltage increase change rate calculated by the calculating means can be matched with the set increase change rate.

  According to the first aspect of the present invention, it is possible to arbitrarily set the rate of increase in setting even for secondary batteries having different battery capacities without executing the capacity measurement process for detecting the battery capacity of the secondary battery before the quick charge. By setting, the secondary battery can be charged at an optimal charging speed according to the battery capacity. Therefore, it can be widely used as a charging device for charging a plurality of types of secondary batteries without preparing a dedicated charging device for each secondary battery to be charged.

  Further, since the secondary battery is charged while making the charging voltage coincide with the terminal voltage of the secondary battery, the power loss due to the voltage difference between the two is small, and the battery can be charged without causing unnecessary heat generation.

  According to invention of Claim 2, it can charge with the fastest charging speed which does not degrade a secondary battery irrespective of the battery capacity of the secondary battery to charge.

  According to the third aspect of the present invention, when the inflection point voltage is reached, the rapid charging mode with a high rate of change in voltage rise is terminated, so that a reduction in charging efficiency can be prevented.

  According to the invention of claim 4, there is no fear that the secondary battery is deteriorated by overcharge.

  In addition, if the target voltage is the inflection point voltage, the charging voltage is sufficiently reduced in the fine adjustment charging mode that exceeds the inflection point voltage, so heat generation is suppressed and maximum charging is performed without significantly reducing charging efficiency. Can charge up to voltage.

  According to the fifth aspect of the present invention, the voltage increase rate can be made to coincide with the set increase rate only by adjusting the ON duty of the pulse width modulation signal for controlling opening and closing of the switching element while using the charging voltage as the terminal voltage. it can.

1 is a circuit diagram of a charging device 1 according to an embodiment of the present invention that charges a secondary battery 10. FIG. During charging of the secondary battery 10 with the charging device 1, (a) shows the relationship between the charging voltage Vc and the charging current Ic output from the charging device 1, and (b) shows the charging with the terminal voltage waveform Vb (t). It is a graph which shows current waveform Ic (t). During charging of the secondary battery by the conventional CCCV charging method, (a) shows the relationship between the charging voltage Vc and charging current Ic output from the charging device, and (b) shows the terminal voltage waveform Vb (t) and charging. It is a graph which shows current waveform Ic (t). While charging the secondary battery by another conventional charging method, (a) shows the relationship between the charging voltage Vc and charging current Ic output from the charging device, and (b) shows the terminal voltage waveform Vb (t). It is a graph which shows charging current waveform Ic (t).

  Hereinafter, a charging device 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the charging device 1 includes a power supply unit 2 that charges the secondary battery 10 with DC power and a power supply control unit 3 that controls the output of the power supply unit 2.

  The power supply unit 2 is a chopper type step-down converter that steps down the input voltage Vin of the DC power supply 20 smoothed by the smoothing capacitor 11 connected between the pair of inputs 2a and 2b and outputs the voltage between the pair of outputs 2c and 2d. The switch element 4 configured between the low-voltage side input 2b and the low-voltage side output 2d, the inductor 6 connected between the high-voltage side input 2a and the high-voltage side output 2c, and the pair of outputs 2c and 2d. And a capacitor 7 and a backflow prevention switch element connected between the high voltage side input 2a and the low voltage side output 2d.

  The switch element 4 is a three-terminal field effect transistor in which a drain and a source are connected to a low-voltage side output 2d and a low-voltage side input 2b, respectively, and a gate is connected to a drive circuit 17 described later of the power supply control unit 3. The open / close control is performed between the drain and the source by the forward switch control signal.

  The backflow prevention switch element is also a three-terminal field effect transistor in which the drain is connected to the high-voltage side input 2 a, the source is connected to the low-voltage side output 2 d, and the gate is connected to the drive circuit 17 of the power supply control unit 3. While the switch element 4 is controlled to be closed by the flyback control signal, the drain-source is controlled to be cut off so that the current flowing from the high-voltage side input 2a to the low-voltage side input 2b is blocked, and the switch element 4 is opened. While being controlled, conduction between the drain and the source is controlled so that a discharge current from the low voltage side output 2d side to the high voltage side output 2c caused by the flyback operation of the inductor 6 flows. Therefore, a diode having a forward direction from the low voltage side input 2b to the high voltage side input 2a may be used instead of the backflow prevention switch element.

  The high-voltage side output 2c and the low-voltage side output 2d are directly connected to the pair of terminals 10a and 10b of the secondary battery 10 through the high-voltage side charging line 8a and the low-voltage side charging line 8b, respectively. Thereby, the output voltage between the pair of outputs 2c and 2d of the power supply unit (chopper type step-down converter) 2 matches the terminal voltage Vb between the pair of terminals 10a and 10b of the secondary battery 10 charged by the power supply unit 2. Yes.

  The secondary battery 10 charged with the DC power of the power supply unit 2 is a lithium ion battery having a maximum charging voltage of 4.2 V and a nominal voltage of 3.7 V, and the lithium ion battery is vulnerable to an overvoltage exceeding the maximum charging voltage. Here, the end voltage for stopping charging is set to the maximum charging voltage of 4.2 V, and the power supply control unit 3 charges when the output voltage between the pair of outputs 2 c and 2 d, that is, the terminal voltage Vb reaches 4.2 V. The charging control is stopped. As described above, since the chopper type step-down converter that steps down the input voltage Vin is used for the power supply unit 2, the input voltage Vin of the DC power supply 20 is at least higher than the maximum value 4.2V of the terminal voltage Vb. .

  As shown in FIG. 1, the power supply controller 3 includes a microprocessor 9, a terminal voltage detection circuit 12 that detects the terminal voltage Vb between the outputs 2 c and 2 d at a cycle of several milliseconds and outputs the detected voltage to the microprocessor 9, In addition to the execution program of the processor 9, a ROM 13 that stores a final voltage, a target voltage, a set increase rate of change, and the like that are determined for each secondary battery 10 to be charged, and a shunt resistor 18 that is interposed in the low-voltage side charging line 8b A charging current detection circuit 14 that constantly monitors the charging current Ic flowing in the low-voltage side charging line 8b from the voltage drop and outputs the charging current Ic to the microprocessor 9, a timer circuit 15 that outputs timing information to the microprocessor 9, and an input of the DC power source 20 The input voltage detection circuit 16 that detects the voltage Vin and outputs it to the microprocessor 9, the switch element 4, and the backflow prevention switch element And a drive circuit 17 for controlling the work. The microprocessor 9 is further connected to a temperature sensor 19 disposed in the vicinity of the secondary battery 10 and inputs temperature information of the secondary battery 10 from the temperature sensor 19.

  A forward switch control signal for controlling opening / closing of the switch element 4 (the gate of the FET) from the drive circuit 17 in a high-speed charging mode, which will be described later, is a rectangular wave signal that repeats an H level and an L level at a cycle of 1 μsec. When it is at the H level, the low voltage side output 2d and the low voltage side input 2b are conducted. Further, the flyback control signal for opening / closing the backflow prevention switch element 5 (the gate of the FET) from the drive circuit 17 is output in synchronization with the forward switch control signal by inverting the polarity of the forward switch control signal. Thus, while the switch element 4 is closed, an L level rectangular wave signal is output to the backflow prevention switch element 5 and the high voltage side input 2a and the low voltage side output 2d are blocked. Therefore, during the ON period in which the switch element 4 is closed and controlled, the differential voltage between the input voltage Vin of the DC power supply 20 and the terminal voltage Vb is applied to the inductor 6 to charge the inductor 6 and the electric energy is converted into magnetic field energy. The

  On the other hand, an L-level rectangular wave signal is output to the switch element 4, and an H-level rectangular wave signal is output to the backflow prevention switch element 5 during the OFF period in which the switch element 4 is controlled to open. And the secondary battery 10 connected in parallel to both ends of the inductor 6, the magnetic energy stored in the inductor 6 during the ON period becomes the charging current Ic which is electric energy. The capacitor 7 is charged.

  Here, the electrical energy generated in the outputs 2c and 2d of the power supply unit 2 in one cycle (1 μsec) that is the sum of the ON period and the OFF period is proportional to the ratio of the ON period in one cycle, that is, the ON duty. The electrical energy generated at the outputs 2c and 2d charges the secondary battery 10 as DC power, but the outputs 2c and 2d are connected to the pair of terminals 10a and 10b of the secondary battery 10, so the output 2c, The output voltage between 2d is equal to the terminal voltage Vb between the terminals 10a and 10b, and the DC power increasing or decreasing in proportion to the ON duty appears as an increase or decrease in the charging current Ic for charging the secondary battery 10.

  Therefore, in the present embodiment, the forward switch control signal, which is a rectangular wave signal, is converted into a PWM (pulse width modulation) signal modulated by predetermined control data output from the microprocessor 9, and the secondary battery 10 is charged according to the charging status. The control data output from the microprocessor 9 to the drive circuit 17 varies the ON duty of the forward switch control signal and controls the charging current Ic to increase or decrease.

  Hereinafter, the charging process of the charging device 1 that charges the secondary battery 10, which is a lithium ion battery, to the end voltage Ve is divided into precharge, quick charge, and fine adjustment charge modes shown in FIG. The operation of the processor 9 will be mainly described.

(Pre-charge mode A)
In the precharge mode, before charging the secondary battery 10, it is determined whether there is an abnormality in the secondary battery 10 or the charging circuit. If the abnormality is recognized, the charging is performed without shifting to the quick charge mode. Discontinue.

The microprocessor 9 is sometimes t ₀ starts pre-charging mode, the terminal voltage detection circuit 12, the charging current detection circuit 14, the input voltage detection circuit 16, the temperature sensor 19 detects each terminal voltages Vb, charging current Ic, input The voltage Vin and the temperature Tb of the secondary battery 10 are recorded, and at the same time, control data for outputting a forward switch control signal and a flyback control signal is output to the drive circuit 17 to operate the power supply unit 2. Here, the control data output to the drive circuit 17 is the one in which the ON period of the forward switch control signal is shortened by pulse width modulation. Therefore, as shown in FIG. The secondary battery 10 is charged with the charging current Ic (t).

After that, the microprocessor 9 counts the terminal voltage Vb, the charging current I, the input voltage Vin, and the temperature Tb of the secondary battery 10 at t ₁ after a predetermined time counted by the timer circuit 15, respectively, current detection circuit 14, the input voltage detection circuit 16, and input from the temperature sensor 19 is compared with the value of the time t _0, when there is an abnormal value in any of the detected value, for example, the terminal voltage Vb (t) does not rise If the charging current Ic (t) is not in the range predicted by the control data, the input voltage Vin is lower than the end voltage, or the temperature Tb of the secondary battery rises abnormally, the charging is performed. Discontinue. To stop charging, the forward switch control signal output from the drive circuit 9 is always set to L level, and the switch element 4 is controlled to open.

(Quick charge mode B → B ′ → C)
If there is no abnormality in t detected value of _1:00 shifts to rapid charging mode. In the quick charge mode, the secondary battery 10 is turned on until t ₂ when the terminal voltage Vb (t) reaches a target voltage Ve ′ that is slightly lower than the maximum charge voltage Ve at a charge rate substantially equal to the rated discharge rate of the secondary battery 10. Charge. Here, the charge rate substantially equal to the rated discharge rate of the secondary battery 10 is a constant current discharge of the fully charged secondary battery 10 having a nominal capacity value, and the current value at which discharge ends in 1 hour is 1C. The terminal voltage Vb (t) is approximately equal to the rate of change in voltage (the difference voltage between the terminal voltages Vb (t) per unit time) when the secondary battery 10 is charged with a charging current of Is the rate of rising. In the present embodiment, the target voltage Ve ′ for ending the quick charge mode is an inflection point voltage at which the rate of change in voltage increase proportional to the charge current Ic (t) starts to decrease, and the maximum charge voltage Ve of 4. The voltage is 4.0 V, which is slightly lower than 2V.

  In the ROM 13, as a charging information of the secondary battery 10 that is a lithium ion battery, a rate of change in voltage rise when the secondary battery 10 to be charged is charged by 1 C (different for each battery type of the secondary battery 10) is also stored. The first set increase rate of change (here, set to the change rate in the case of a lithium ion battery), the second set increase rate of change set to a value sufficiently lower than the first set increase rate, and the target voltage Ve '(4.0 V), the maximum charging voltage Ve (4.2 V) as the end voltage is stored.

The microprocessor 9 outputs control data for setting the ON duty of the forward switch control signal to a predetermined value to the drive circuit 17 at t ₁ when the quick charge mode is started, and inverts the polarity of the forward switch control signal from the drive circuit 17. The generated flyback control signal is output, and the power supply unit 2 is operated. Thereafter, a terminal voltage increase ΔV is obtained from the difference voltage between the terminal voltages Vb (t) detected by the terminal voltage detection circuit 12 before and after (B, B ′) of a minute time Δt of several milliseconds, and per minute time Δt. The rate of change in voltage rise, which is the terminal voltage increase ΔV, is calculated.

  Subsequently, the calculated voltage rise change rate is compared with the first set rise change rate read from the ROM 13, and the ON duty of the forward switch control signal is set so that the calculated voltage rise change rate matches the first set rise change rate. The control data to be changed is output to the drive circuit 17. That is, when the calculated voltage increase rate is equal to or less than the first set rate of increase, the control data for increasing the ON duty of the forward switch control signal is output to the drive circuit 17 and the charging current Ic (t) is increased. Conversely, when the calculated rate of change in voltage increase is equal to or greater than the first set rate of increase, control data for reducing the ON duty of the forward switch control signal is output to the drive circuit 17, and the charging current Ic (t) Decrease. Since the rate of increase in voltage of the terminal voltage Vb (t) increases or decreases as the charging current Ic (t) increases / decreases, the secondary battery 10 can be recharged by repeating the above processing at a cycle of, for example, several milliseconds during the quick charging mode. Regardless of the size of the battery capacity, the battery can be charged at a charge rate substantially equal to the rated discharge rate. Note that the length of the minute time Δt, that is, the cycle in which the above-described processing is repeated is set to several msec in this embodiment, but it is not necessarily such a length, and it is not necessarily several seconds to several tens of seconds. The present invention can be implemented even with a length of about.

  The charging current Ic (t) in the rapid charging mode ideally varies in the vicinity of a charging current value 1C determined from the type of the secondary battery 10 to be charged and its battery capacity. As in the case of the device, the constant current control is not performed with the charging current value 1C determined for the known secondary battery 10, so that the charging conditions such as the secular change of the internal resistance of the secondary battery 10 and the change of the resistance value of the charging line are included. Even if the charging current changes, the charging current Ic is automatically changed and set, and charging can be performed while maintaining an optimal charging speed for the charging conditions in each case.

In addition, the microprocessor 9 compares the terminal voltage Vb (t) detected by the terminal voltage detection circuit 12 with the target voltage Ve ′ (4.0 V) read from the ROM 13 in the process of repeating the above process at a cycle of several milliseconds. Then, at time t ₂ when the target voltage Ve ′ (4.0 V) is reached, the quick charge mode is shifted to the fine adjustment charge mode.

(Fine adjustment charging mode D)
In the fine adjustment charging mode, since the terminal voltage Vb (t) exceeds the inflection point voltage at which the charging efficiency of the secondary battery 10 rapidly decreases, the charging current Ic (t) of the secondary battery 10 is decreased. The charging speed is reduced and excessive charging current Ic (t) is converted into thermal energy to prevent the charging efficiency from deteriorating. At the same time, the terminal voltage Vb exceeds the maximum charging voltage, and the secondary battery 10 deteriorates. To prevent damage.

  The microprocessor 9 detects the terminal voltage Vb (t) before and after the minute time Δt of several milliseconds after the quick charge mode, and calculates the rate of change in voltage increase that is the terminal voltage increase ΔV per minute time Δt. The control data for changing the ON duty of the forward switch control signal is output to the drive circuit 17 so that the calculated voltage rise change rate matches the second set rise change rate read from the ROM 13.

  The second set increase rate of change is sufficiently lower than the first set increase rate of change and is close to 0. Therefore, as shown in FIG. 2B, the voltage increase rate of change is changed to the second set increase rate of change. The charging current Ic to be matched with the voltage rapidly decreases from the charging current Ic (t) in the rapid charging mode, and the terminal voltage Vb (t) increases with a very gentle slope.

The microprocessor 9 repeats the above process at a cycle of several milliseconds, and the terminal voltage Vb (t) detected by the terminal voltage detection circuit 12 is the maximum charging voltage Ve (4.2 V) that is the final voltage read from the ROM 13. compared to, at t ₃ reaches the end voltage (4.2 V), as always L level forward switch control signal output from the drive circuit 9, and opening control of the switching element 4, to stop the charging.

In the above charging process of the rechargeable battery 10, the drive after the time t ₃ when the terminal voltage Vb (t) has reached the final voltage (4.2 V), the microprocessor 9 sets the control data to 0 voltage rise rate of change The output may be made to the circuit 17 and a minute charging current Ic (t) may be supplied to maintain the terminal voltage Vb at the end voltage (4.2 V).

  Even in the quick charge mode or the fine adjustment charge mode, when the temperature of the secondary battery 10 detected by the temperature sensor 19 rises abnormally or the input voltage Vin becomes less than the end voltage (4.2 V) In this case, the switch element 4 is controlled to be opened and charging is stopped.

  The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the first set increase change rate that matches the voltage increase change rate in the quick charge mode is not necessarily a charging current of 1C. It is not necessary to set the rate of change in voltage rise when charging, and it can be set according to an arbitrary charging rate such as 2C charging or 1 / 2C charging.

  In addition, the set increase change rate that matches the voltage increase change rate does not need to be the same in the quick charge mode, and is set to one of a plurality of set increase change rates set to different change rates according to the change in the charging state. The rate of change in voltage increase may be matched. For example, as the temperature of the secondary battery 10 detected by the temperature sensor 19 is increased, the set increase change rate for matching the voltage increase change rate is changed to a set increase change rate set to a lower value.

  Further, the terminal voltage detected before and after the minute unit elapsed time may be specified by performing a calculation process such as removing an abnormal value or averaging the correlation from a plurality of terminal voltages detected continuously.

  The power supply unit 2 is not limited to a chopper type step-down converter as long as the output current (charging current) for charging the secondary battery can be variably controlled while interlocking the output voltage with the terminal voltage. Can be used.

  Furthermore, the secondary battery is not limited to the lithium ion battery, and may be another secondary battery such as a nickel cadmium battery as long as the secondary battery has a characteristic that the charging speed changes according to the charging current.

  The present invention is suitable for a charging device using a reversing leaf spring as a movable contact plate.

DESCRIPTION OF SYMBOLS 1 Charging apparatus 2 Power supply part 3 Power supply control part 4 Switch element (switching element)
9 Microprocessor (calculation means)
10 Secondary battery 12 Terminal voltage detection circuit (voltage detection unit)
15 Timer circuit (timer means)

Claims (5)

A power supply unit for charging the secondary battery with DC power;
A charging device including a power supply control unit that controls a charging operation of the power supply unit until a terminal voltage of the secondary battery reaches a predetermined end voltage,
The power control unit
A voltage detector for detecting a terminal voltage of the secondary battery;
Timer means for measuring elapsed time;
A calculation means for sequentially calculating a voltage increase change rate represented by a terminal voltage increase ΔV during a minute unit elapsed time;
While the power supply unit charges the secondary battery with DC power, the voltage increase change rate calculated by the calculating means is set to a predetermined increase increase rate while the charging voltage of the DC power is the terminal voltage of the secondary battery. The charging device is characterized by variably controlling the charging current of the DC power. The end voltage is the maximum charging voltage allowed for the secondary battery,
The power supply control unit controls the charging operation of the power supply unit in the quick charge mode until the terminal voltage of the secondary battery reaches a target voltage slightly lower than the maximum charging voltage.
The rate of change in voltage increase when charging with a charging current of 1 C, assuming that the set rate of increase in the quick charge mode is constant current discharge of a secondary battery having a nominal capacity value and the current value at which discharge ends in 1 hour is 1 C. The charging device according to claim 1, wherein the charging device is determined in the vicinity of the rate.   The charging device according to claim 2, wherein the target voltage is an inflection point voltage at which a rate of change in voltage increase proportional to the charging current starts to decrease. The power supply control unit controls the charging operation of the power supply unit in the fine adjustment charging mode until the maximum charging voltage is reached after the terminal voltage of the secondary battery reaches the target voltage,
4. The method according to claim 2, wherein the set increase rate of change in the fine adjustment charging mode is set to a value sufficiently lower than the set increase rate of change in the quick charge mode. 5. Charging device. The power supply unit is a chopper type step-down converter that outputs the DC power between the charging terminals of the secondary battery by opening and closing a switching element connected in series between the DC input voltages of the DC voltage that is at least higher than the cut-off voltage. The unit adjusts the voltage rise change rate by increasing / decreasing the ON duty of the pulse width modulation signal for controlling the opening / closing of the switching element so that the voltage rise change rate calculated by the calculating means matches the set rise change rate. The charging device according to any one of claims 1 to 4, wherein the charging device is provided.

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