JP2015171230A - Charger and charging method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charger capable of suppressing stratification of an electrolyte and excessive rise of temperature even in a state where SOC rises during charging.SOLUTION: A charging circuit provides a power storage device with a charging current. A voltage sensor measures an inter-terminal voltage of the power storage device. A control device detects generation of gassing at the power storage device on the basis of a measurement result of the voltage sensor. When generation of gassing is detected, a charging circuit is controlled and a charging current is lowered.

Description

  The present invention relates to a charging device that suppresses stratification of an electrolyte by causing a gassing state during charging, and a method for charging a power storage device.

  In an electric vehicle such as an electric forklift, charging is performed at night when the vehicle is not used. In the charging method disclosed in Patent Document 1, charging is performed to a fully charged state after the work is completed, and supplementary charging is started immediately before the work start time on the next day. By performing supplementary charging, the amount of charge reduced by self-discharge from the time when the fully charged state is reached to the time when the work is started is supplemented. Thereby, work can be started in a state where the power storage device is fully charged.

  In the conventional quasi-constant voltage charging method, the current changes as the voltage of the power storage device being charged changes. In the initial stage of charging, the voltage of the power storage device is low, so that the charging current is large. In the multi-stage constant current charging method, the charging current is reduced stepwise with time.

JP-A-9-271142

  As the state of charge (SOC) increases, the charging voltage also increases. As the SOC approaches 120%, the increase in charging voltage reaches its peak. The temperature of the electrolyte also gradually increases as the SOC increases, and when the SOC exceeds about 90%, the temperature rises sharply. This temperature rise is due to the electrolysis of water in addition to the charging reaction. Since hydrogen gas and oxygen gas generated by water electrolysis stir the electrolyte solution, stratification of the electrolyte solution can be suppressed. However, excessive charging in the gassing state causes excessive temperature rise, decrease in electrolyte solution, corrosion of the electrode, dropping of the active material, and the like.

  An object of the present invention is to provide a charging device and a charging method for a power storage device that can suppress stratification of the electrolyte and suppress an excessive temperature rise even when the SOC increases during charging. It is.

According to one aspect of the invention,
A charging circuit for supplying a charging current to the power storage device;
A voltage sensor for measuring a voltage between terminals of the power storage device;
When the occurrence of gassing in the power storage device is detected based on the measurement result of the voltage sensor, a charging device is provided that includes a control device that controls the charging circuit to reduce a charging current.

According to another aspect of the invention,
Starting charging the power storage device;
Measuring a voltage between terminals of the power storage device, and detecting occurrence of gassing in the power storage device based on a measurement result;
When the occurrence of gassing is detected, a method for charging a power storage device is provided that includes a step of reducing charging current and continuing charging.

  When gassing is occurring, an excessive increase in temperature of the power storage device can be suppressed by reducing the charging current.

FIG. 1A is a block diagram of a charging device according to an embodiment and an electric vehicle charged by the charging device, and FIG. 1B is a side view of a forklift shown as an example of the electric vehicle. FIG. 2A is a block diagram of a control device for a charging device according to the embodiment, and FIG. 2B is a chart illustrating an example of contents stored in a charging current target value storage unit. FIG. 3A is a graph showing measurement results of changes over time in charging voltage, charging current, and electrolyte solution temperature rise width of the power storage device when charging is performed by the quasi-constant voltage charging method, and FIG. It is a graph which shows the measurement result of the time change of the charging voltage at the time of charging with the charging method, a charging current, and the electrolyte solution temperature rise width of an electrical storage apparatus. FIG. 4 shows a case where the charge current of 0.05 C is continued even after the gashing state is reached, and the case where the charge current is reduced from 0.05 C to 0.04 C when the gashing state is reached. It is a graph which shows the measurement result of the time change of the temperature of the electrolyte solution of an apparatus. FIG. 5 is a block diagram of a control device used in a charging device according to another embodiment. FIG. 6 is a graph illustrating changes in voltage and current during a charging period of a power storage device in which deterioration has occurred and a power storage device in which deterioration has not occurred.

  FIG. 1A shows a block diagram of a charging device 20 according to an embodiment and an electric vehicle 30 charged by the charging device 20. Examples of the electric vehicle 30 include an electric forklift, an electric automatic guided vehicle (AGV), and an electric cleaning robot.

  The charging device 20 includes a charging circuit 21, a control device 22, an AC connector 23, a DC connector 24, a voltage sensor 25, and a current sensor 26. Electric vehicle 30 includes a power storage device 31, a DC connector 32, a relay 33, and an electric load 35. AC connector 23 of charging device 20 is connected to commercial power supply 15, and DC connector 24 is connected to DC connector 32 of electric vehicle 30. As the power storage device 31, a secondary battery, for example, a lead storage battery, is used that makes the specific gravity of the electrolytic solution uniform (prevents stratification) using a gassing state at the end of charging. Here, the “gassing state” means a state in which water in the electrolytic solution is electrolyzed at the end of charging to generate oxygen gas or hydrogen gas.

  Electric power, for example, three-phase AC power is supplied from the commercial power supply 15 to the AC connector 23. The charging circuit 21 includes a relay, a transformer, a rectifier, and the like, and converts an alternating current into a direct current. A direct current (charging current) output from the charging circuit 21 is supplied to the power storage device 31 via the DC connector 24 and the DC connector 32 of the electric vehicle 30. Voltage sensor 25 measures the voltage across terminals of power storage device 31. Current sensor 26 measures the charging current of power storage device 31. Measurement results from the voltage sensor 25 and the current sensor 26 are input to the control device 22. The control device 22 controls the charging circuit 21 based on the measurement results obtained by the voltage sensor 25 and the current sensor 26.

When the electric vehicle 30 is in operation, electric power is supplied from the power storage device 31 mounted on the electric vehicle 30 to the electric load 35 via the relay 33. When the power storage device 31 is charged, the relay 33 is turned off.

  FIG. 1B shows a side view of a forklift as an example of the electric vehicle 30. This forklift is a so-called counterbalance type forklift configured to balance the vehicle body by mounting a weight on the rear side of the vehicle body. The driver sits on the driver's seat 10 and operates the operation device 14 such as a lever. A front wheel 12 is disposed in front of the driver seat 10, and a rear wheel 13 is disposed in the rear of the driver seat 10. The front wheel 12 is a driving wheel, and the rear wheel 13 is a steering wheel. A fork 11 disposed in front of the driver's seat 10 raises and lowers the load. A DC connector 32 for connecting to the charging device 20 (FIG. 1A) is provided on the vehicle body. Furthermore, a power storage device 31 is mounted on the vehicle body. The electric load 35 (FIG. 1A) corresponds to a traveling electric motor that drives the front wheels 12 and a lifting electric motor that moves the fork 11 up and down.

  The charging device 20 (FIG. 1A) may be mounted on a forklift. In this case, the AC connector 23 (FIG. 1A) is provided on the forklift. The AC connector 23 of the forklift is connected to the commercial power supply 15 (FIG. 1A).

  FIG. 2A shows a block diagram of the control device 22 (FIG. 1A). The control device 22 includes a gashing state detection block 40, a voltage determination value storage unit 41, a non-gassing charge command block 42, a gashing charge command block 43, a charge current target value storage unit 44, and a charge command selection unit 45. The voltage determination value storage unit 41 stores a voltage (gassing voltage) at which gassing starts in the power storage device 31 (FIG. 1A) as a voltage determination value.

  The voltage between the terminals of the power storage device 31 (FIG. 1A) measured by the voltage sensor 25 is input to the gassing state detection block 40. The gassing state detection block 40 compares between the terminals of the power storage device 31 and the voltage determination value (gassing voltage) stored in the voltage determination value storage unit 41. When the voltage between the terminals of the power storage device 31 is equal to or higher than the voltage determination value, the gashing state detection block 40 determines that gassing has occurred in the power storage device 31 (FIG. 1A). As described above, the gassing state detection block 40 detects the occurrence of gassing in the power storage device 31 based on the voltage measured by the voltage sensor 25.

  The non-gushing charging command block 42 outputs a charging command based on the charging method applied during non-gassing to the charging circuit 21. As a charging method at the time of non-gassing, for example, a quasi-constant voltage charging method, a multistage constant current charging method, or the like is adopted.

  The charging command block 43 at the time of gassing outputs a charging command based on the charging method applied at the time of gassing to the charging circuit 21. Specifically, the charging circuit 21 is controlled such that a charging current equal to the charging current target value stored in the charging current target value storage unit 44 flows. The charging current target value storage unit 44 stores the relationship between the elapsed time from when the voltage between the terminals of the power storage device 31 (FIG. 1A) reaches the gassing voltage and the charging current target value.

  FIG. 2B shows an example of the contents stored in the charging current target value storage unit 44. In the example shown in FIG. 2B, the elapsed time from the time when the voltage between the terminals of the power storage device 31 reaches the gassing voltage is less than 1 hour, 1-2 hours, 2-3 hours, 3-4 hours, 4 hours or more. The charging current target values at the time of are 0.05C, 0.05C, 0.04C, 0.04C, and 0.04C, respectively. Here, the unit “C” represents a current value equal to the current capacity of the power storage device 31 (FIG. 1A). For example, when the current capacity of the power storage device 31 is 100 Ahr, a charging current of 1 C corresponds to 100 A, and a charging current of 0.1 C corresponds to 10 A.

FIG. 3A shows the measurement results of the charging voltage, the charging current, and the temperature rise of the electrolyte when charging is performed by the quasi-constant voltage charging method. The horizontal axis shows the elapsed time from the start of charging in the unit of “hour”
Represented by The vertical axis represents the temperature rise from the start of charging in the unit “° C.”, the charging voltage in the unit “V”, and the charging current in the unit “A”. The thick solid line in the figure indicates the charging voltage, the thin solid line indicates the charging current, and the broken line indicates the temperature rise width.

  As time elapses, the charging voltage gradually increases, the charging current gradually decreases, and the temperature rise increases. Charging ends at time t2. From time t1 when the charging voltage reaches the voltage determination value Vj0, the power storage device 31 (FIG. 1A) enters the gassing state. During the gassing period from the time t1 to the time t2, the temperature of the electrolytic solution of the power storage device 31 is rapidly increased.

  FIG. 3B shows measurement results of changes over time in the charging voltage, the charging current, and the increase in the electrolyte temperature of the power storage device when charging is performed by the charging method according to the embodiment. The horizontal and vertical axes in FIG. 3B are the same as those in FIG. 3A. Similarly to the graph of FIG. 3A, a thick solid line in the figure indicates the charging voltage, a thin solid line indicates the charging current, and a broken line indicates the temperature rise.

  At the start of charging, the charging command selection unit 45 (FIG. 2A) selects the non-gassing charging command block 42. The non-gashing charging command block 42 gives a charging command based on, for example, a constant current charging method to the charging circuit 21. During the period from the charging start time to time t3, constant current charging is performed with a charging current of 5A.

  At time t3, the voltage measured by the voltage sensor 25 (FIG. 1A) reaches the voltage determination value Vj0. When detecting that the inter-terminal voltage of the power storage device 31 (FIG. 1A) has reached the voltage determination value Vj0, the gassing state detection block 40 causes the charge command selection unit 45 to select the charge command block 43 during gassing.

  After time t3, a charging command is sent from the charging command block 43 at the time of gassing to the charging circuit 21, and charging is performed based on the charging method at the time of gassing. As shown in FIG. 2B, charging is performed at a charging current of 0.05 C for 2 hours from time t3 to t4, and charging is performed at a charging current of 0.04 C for 3 hours from time t4 to t5. Is done. The charging currents of 0.05C and 0.04C are smaller than the charging current during the period in which the constant current charging method until time t3 was applied. Furthermore, it is smaller than the charging current in the gassing state when the quasi-constant voltage charging method shown in FIG. 3A is applied.

  In the gassing state, the charging current is set so that the amount of heat generated by charging is smaller than the amount of natural heat dissipation. For this reason, during the period of the gassing state from time t3 to t5, the temperature gradually decreases. Charging ends at time t5.

  Comparing FIG. 3A and FIG. 3B, when charging is performed using the charging device according to the embodiment, the electrolytic solution of the power storage device 31 (FIG. 1A) is more than when charging is performed using a general quasi-constant voltage charging method. It can be seen that the maximum temperature reached is low. For this reason, deterioration of the electrical storage device 31 can be suppressed by using the charging device according to the embodiment. This is because the charging current is decreased after the gashing state is detected.

  In addition, the electrolyte solution is stirred in order to pass a small charging current even after the gashing state is reached. Thereby, stratification of electrolyte solution can be prevented.

In FIG. 3B, the constant current charging method is used during the period from the start of charging to the time t3 when the gashing state is reached, but other charging methods may be used. For example, a quasi-constant voltage charging method, a constant current constant voltage charging method, a multistage constant current charging method, or the like may be employed. In any case, after the voltage between the terminals of the power storage device 31 (FIG. 1A) reaches the gassing voltage, the charging current is made smaller than the charging current at that time. Thereby, the excessive temperature rise of the electrical storage apparatus 31 (FIG. 1A) can be suppressed. In order to obtain a sufficient effect of suppressing the temperature rise, when the voltage between the terminals of the power storage device 31 (FIG. 1A) reaches the gassing voltage, the charging current is set to ½ or less of the charging current at that time. Is preferred.

  In the example shown in FIG. 3B, the charging current is decreased from 0.05C to 0.04C at time t4. Next, the effect of reducing the charging current will be described with reference to FIG.

  In FIG. 4, the power storage device 31 (FIG. 1A) of the case where the charge current of 0.05C is continued after time t4 and the case where the charge current is decreased from 0.05C to 0.04C at time t4. The measurement result of the temperature of electrolyte solution is shown. In FIG. 4, the solid line shows the temperature rise when the charging current is decreased from 0.05C to 0.04C at time t4, and the broken line is the case where the charging current of 0.05C is maintained after time t4. Indicates the temperature rise. In the measurement results shown in FIG. 4, the temperature rise widths of the solid line and the broken line do not match during the period from time t3 to t4, but this difference is within the range of variation in measurement conditions.

  During the period from time t3 to t4, the temperature gradually decreases with time. If the 0.05 C charging current is maintained after time t4, the temperature starts to rise. This is because the heat generation amount is larger than the natural heat dissipation amount. When charging is finished at time t6, the temperature starts to decrease.

  When the charging current is decreased from 0.05C to 0.04C at time t4, the temperature also decreases with time after time t4. This is because the amount of heat generated by charging is smaller than the amount of natural heat dissipation. Thus, the charging current in the gashing state is preferably set so that the amount of heat generated by charging is smaller than the amount of natural heat dissipation. The magnitude of this charging current can actually be determined by conducting an evaluation experiment with various charging currents.

  In FIG. 3B, the charging current was reduced at times t3 and t4 during the period from the start of the gashing state to the end of charging. The number of times the charging current is lowered stepwise is not limited to two. The charging current may be reduced stepwise three or more times.

  Note that the charging current may be constant from the time t3 at which gashing is started to the charging end time. In this case, it is preferable to set the current value of the charging current so that the temperature of the electrolytic solution of the power storage device 31 (FIG. 1A) does not turn up.

  Next, another embodiment will be described with reference to FIGS. Hereinafter, differences from the embodiment shown in FIG. 2A will be described, and description of the same configuration will be omitted.

  In FIG. 5, the block diagram of the control apparatus 22 used for the charging device by another Example is shown. Measurement results of the voltage sensor 25 (FIG. 1A) and the current sensor 26 (FIG. 1A) are input to the deterioration degree calculation block 46. The deterioration degree calculation block 46 calculates the deterioration degree of the power storage device 31 (FIG. 1A) based on the input voltage and current measurement results. As the degree of deterioration, for example, the internal resistance of the power storage device 31 can be employed. As the power storage device 31 deteriorates, its internal resistance increases.

The internal resistance Ri of the power storage device 31 can be calculated by the following equation based on the open circuit voltage Vo of the power storage device 31 and the charging current Ic when the charging current starts to flow and the inter-terminal voltage Vc.
Ri = (Vc−Vo) / Ic

  The voltage determination value correction block 47 corrects the voltage determination value stored in the voltage determination value storage unit 41 based on the deterioration level calculated by the deterioration level calculation block 46. The gassing state detection block 40 detects the occurrence of gassing based on the voltage determination value corrected by the voltage determination value correction block 47, that is, the voltage determination value corresponding to the degree of deterioration. The subsequent processing is the same as the processing of the control device 22 shown in FIG. 2A.

  FIG. 6 shows changes in voltage and current during the charging period of the power storage device 31. The thick solid line and the thin solid line shown in FIG. 6 indicate the voltage and current when the power storage device 31 is not deteriorated, respectively. This is the same as the change in voltage and current shown in FIG. 3B. A thick broken line indicates a voltage when power storage device 31 is being deteriorated. A thin broken line indicates a current when the voltage determination value is not corrected even when the power storage device 31 is deteriorated.

  The measured value of the voltage by the voltage sensor 25 is represented by the sum of the open circuit voltage of the power storage device 31 and the voltage drop due to the internal resistance Ri. When the deterioration of the power storage device 31 (FIG. 1A) progresses and the internal resistance Ri increases, the voltage drop due to the internal resistance Ri increases, so the measured value of the voltage by the voltage sensor 25 is greater than the measured value when the deterioration has not progressed. Get higher. As a result, when the deterioration of power storage device 31 is progressing, the voltage across terminals of power storage device 31 reaches voltage determination value Vj0 at time t6 prior to time t3.

  If the voltage determination value is not corrected, it is determined that gassing has occurred at time t6. At this time, if the charging current is decreased, the power storage device 31 may not be fully charged. In the embodiment shown in FIG. 5, the voltage determination value correction block 47 corrects the voltage determination value from Vj0 to Vj1 according to the degree of deterioration of the power storage device 31. The corrected voltage determination value Vj1 is equal to the voltage between the terminals of the power storage device 31 at time t3 when the voltage between the terminals of the power storage device 31 reaches the voltage determination value Vj0 when the power storage device 31 has not deteriorated. Is set to be Thereby, even if deterioration has advanced, the determination system of whether the gas storage has generate | occur | produced in the electrical storage apparatus 31 can be improved.

  In this way, by correcting the voltage determination value, it is possible to avoid the occurrence of insufficient charging even when the power storage device 31 is deteriorated.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 Driver's seat 11 Fork 12 Front wheel 13 Rear wheel 14 Controller 15 Commercial power supply 20 Charging device 21 Charging circuit 22 Control device 23 AC connector 24 DC connector 25 Voltage sensor 26 Current sensor 30 Electric vehicle 31 Power storage device 32 DC connector 33 Relay 35 Electricity Load 40 Gasing state detection block 41 Voltage determination value storage unit 42 Non-gashing charging command block 43 Gasing charging command block 44 Charging current target value storage unit 45 Charging command selection unit 46 Degradation degree calculation block 47 Voltage determination value correction block

Claims (7)

A charging circuit for supplying a charging current to the power storage device;
A voltage sensor for measuring a voltage between terminals of the power storage device;
And a control device configured to control the charging circuit to reduce a charging current when occurrence of gassing in the power storage device is detected based on a measurement result of the voltage sensor.   The control device stores a time change of a target value of the charging current when the gassing occurs, and when the occurrence of the gashing is detected, the charging is performed so that the charging current becomes the target value. The charging device according to claim 1 which controls a circuit.   The charging device according to claim 2, wherein the target value of the charging current decreases stepwise as time elapses.   4. The charging device according to claim 2, wherein the target value of the charging current is determined such that the amount of heat released by natural heat dissipation is larger than the amount of heat generated by charging, and the temperature of the power storage device decreases. .   5. The charging device according to claim 1, wherein the control device calculates a degree of deterioration of the power storage device and detects occurrence of the gassing according to the degree of deterioration of the power storage device. Starting charging the power storage device;
Measuring a voltage between terminals of the power storage device, and detecting occurrence of gassing in the power storage device based on a measurement result;
A charging method for a power storage device, comprising: a step of reducing charging current and continuing charging when occurrence of gassing is detected.   The method for charging a power storage device according to claim 6, wherein after the occurrence of gassing is detected, the charging current is set so that the amount of heat generated by charging satisfies a condition smaller than the amount of natural heat dissipation.

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