JP2012050281A - Battery charging system of electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a travel distance per charge by optimizing energy balance between a high voltage battery and a low voltage battery in an electric vehicle.SOLUTION: The battery charging system of an electric vehicle includes a chargeable/dischargeable high voltage battery 18 supplying travel electric power, a low voltage battery 20 charged by the electric power from the high voltage battery 18 and supplying drive electric power to vehicle-mounted auxiliary devices 44, and a control device 22 controlling each state of charge of the high voltage battery 18 and the low voltage battery 20. The control device 22 sets a charging target value during the charging of the low voltage battery 20 when the SOC of the high voltage battery 18 is low to a value lower than that when the SOC of the high voltage battery is high.

Description

  The present invention relates to a battery charging system for an electric vehicle, and more particularly to a battery charging system for an electric vehicle equipped with a high voltage battery that supplies electric power for traveling and a low voltage battery that supplies auxiliary machinery driving power.

  Conventionally, a high-voltage battery that supplies high-voltage power for driving a motor that outputs driving power, and a low-voltage battery that supplies low-voltage power for driving auxiliary equipment such as an air conditioner, audio equipment, and lighting mounted on the vehicle, An electric vehicle such as a hybrid vehicle or an electric vehicle equipped with is known.

  For example, Japanese Patent Laid-Open No. 2000-50404 (Patent Document 1) describes a generator driven by an engine (engine starting motor), a high-voltage main battery that charges the power generated by the generator, and a low-voltage auxiliary. In a hybrid electric vehicle equipped with a machine battery, the power from the main battery is usually stepped down by a DC / DC converter to charge the auxiliary battery, but when the voltage of the main battery drops to such an extent that the engine cannot be started, the auxiliary machine It describes that the power from the battery is boosted by the DC / DC converter to charge the main battery.

JP 2000-50404 A

  In the electric vehicle as described above, when the charge amount of the low voltage battery decreases and there is a request for charging the low voltage battery, it is assumed that the battery is always charged up to a certain charge state value (hereinafter referred to as SOC as appropriate). There is a problem that the amount of electric power taken out from the battery increases, and the cruising distance that can be EV traveled by one full charge is shortened. This is used not only for electric vehicles that do not have an engine for driving a generator, but also for being charged by being connected to an external power source after EV traveling for a limited distance without operating the engine. This is also true for plug-in hybrid vehicles.

  In addition, the SOC of the high voltage battery is lowered to near the lower limit of the control range due to the discharge of the electric power for traveling, but the SOC of the low voltage battery is maintained at a high level because almost no auxiliary equipment is used. May occur, and the energy balance between the high voltage battery and the low voltage battery may be poor.

  An object of the present invention is to provide a battery charging system and a battery charging method for an electric vehicle capable of optimizing the energy balance between the high voltage battery and the low voltage battery and extending the travel distance per charge.

  A battery charging system for an electric vehicle according to the present invention includes a first battery capable of charging / discharging that supplies electric power for traveling, a first battery that is charged by electric power from the first battery and that supplies driving electric power to in-vehicle accessories. A battery charging system for an electric vehicle comprising two batteries and a control device for controlling the respective charging states of the first battery and the second battery, wherein the control device has a high charging state value of the first battery. The charge state target value at the time of charging the second battery is set lower when it is lower than the time.

  In the battery charging system for an electric vehicle according to the present invention, the control device may perform charging from the first battery to the second battery after the charging state of the second battery reaches a charging state lower limit value. Good.

  In the battery charging system for an electric vehicle according to the present invention, the control device reduces the target state value of the second battery in accordance with the state of charge value of the first battery. Battery charging system.

  Further, in the battery charging system for an electric vehicle according to the present invention, when the charging state value of the first battery is reduced to a first threshold value or less, the control device sets the charging state target value at the time of charging the second battery. You may set to a value lower than the charge condition value of a 1st battery.

  Furthermore, in the battery charging system for an electric vehicle according to the present invention, the control device prohibits charging from the first battery to the second battery when a charging state value of the first battery decreases to a second threshold value or less. May be.

  A battery charging method for an electric vehicle according to the present invention includes a first battery capable of charging / discharging for supplying electric power for traveling, charging with electric power from the first battery, and supplying driving electric power to in-vehicle accessories. A battery charging method for an electric vehicle comprising two batteries and a control device that controls the respective charging states of the first battery and the second battery, and is lower than when the charging state value of the first battery is high The time sets the target state of charge at the time of charging the second battery to be lower.

  According to the battery charging system and the battery charging method for an electric vehicle according to the present invention, the auxiliary device driving power is supplied when the charging state value of the first battery that supplies the running power is lower than when the charging state value is high. Since the charging state target value at the time of charging the second battery is set low, the amount of power taken out from the first battery to charge the second battery can be suppressed, and as a result, the travel distance per charge Can be stretched.

1 is a schematic configuration diagram of an electric vehicle on which a battery charging system according to an embodiment of the present invention is mounted. It is a flowchart which shows the process sequence of the battery charge control routine performed in a control apparatus. FIG. 3 is a diagram schematically showing the control shown in FIG. 2. It is a flowchart which shows the process sequence of another battery charge control routine performed in a control apparatus. It is a figure which shows the control of FIG. 4 typically. It is a flowchart which shows the process sequence of another battery charge control routine performed in a control apparatus. It is a figure which shows the control of FIG. 6 typically.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. In this description, specific shapes, materials, numerical values, directions, and the like are examples for facilitating the understanding of the present invention, and can be appropriately changed according to the application, purpose, specification, and the like.

  The electric vehicle on which the battery charging system described below is mounted may be an electric vehicle not mounted with the internal combustion engine as a power source, or the internal combustion engine is mounted as a power source for driving or driving the generator. It may be a hybrid vehicle.

  FIG. 1 shows a schematic configuration of an electric vehicle 100 equipped with a battery charging system 10 of the present embodiment. The electric vehicle 100 includes a battery charging system 10, an inverter (indicated as INV in the figure) 12 as a power converter, and a motor (indicated as MG in the figure) 14 as a driving power source connected to the inverter 12. And a charging device 16 that receives power supplied from an external power source.

  The battery charging system 10 includes a high voltage battery (first battery, indicated as BAT1 in the figure) 18, a low voltage battery (second battery, indicated as BAT2 in the figure) 20, and the charge states of these batteries 18, 20. And a control device 22 (indicated as ECU in the figure).

  The high voltage battery 18 is preferably configured by a secondary battery such as lithium ion. The high voltage battery 18 is connected to the inverter 12 by two power lines 24 and 26. A voltage sensor 28 for detecting a voltage between terminals of the high voltage battery 18 is provided between the power lines 24 and 26, and a current sensor 30 for detecting a current flowing into and out of the high voltage battery 18 is provided on the power line 24. Is provided. The detection values by the sensors 28 and 30 are transmitted to the control device 22.

  A smoothing capacitor 32 is connected between the two power lines 24 and 26. Direct current power (traveling power) is supplied from the high voltage battery 18 to the inverter 12 through the smoothing capacitor 32. A step-up / step-down converter may be connected to the power lines 24 and 26 between the high-voltage battery 18 and the smoothing capacitor 32.

  The inverter 12 is a known one that converts DC power supplied from the high voltage battery 18 into AC power and outputs the AC power. When the AC power output from the inverter 12 is applied to the motor 14, the motor 14 is rotationally driven. The rotor shaft of the motor 14 is connected to a wheel (not shown), and the power from the motor 14 is transmitted to the wheel so that the vehicle can run. As the motor 14, a three-phase synchronous AC motor is preferably used. However, the present invention is not limited to this, and a DC motor may be used as the motor 14. In this case, a DC / DC converter may be used as the power conversion device instead of the inverter.

  The low voltage battery 20 is connected to the power lines 24 and 26 via a DC / DC converter 34. The DC / DC converter 34 and the low-voltage battery are connected by two low-voltage power lines 36 and 38. A voltage sensor 40 for detecting a voltage between terminals of the low voltage battery 20 is provided between the power lines 36 and 38, and a current sensor 42 for detecting a current flowing into and out of the low voltage battery 20 is provided on the power line 36. ing. The detection values by the sensors 40 and 42 are transmitted to the control device 22. The two low-voltage power lines 36 and 38 are connected to in-vehicle auxiliary equipment (indicated as ACC in the figure) 44 such as an air conditioner, audio equipment, and lighting.

  The low-voltage battery 20 is used to supply low-voltage power for driving the in-vehicle auxiliary machinery 44, and is preferably configured by a secondary battery such as a nickel metal hydride battery, a nickel cadmium battery, or a lead storage battery. Further, the low voltage battery 20 is charged by reducing the high voltage DC voltage supplied from the high voltage battery 18 or the charging device 16 to a low voltage DC voltage suitable for charging by the DC / DC converter 34. .

  The DC / DC converter 34 has a plurality of switching elements such as transistors, for example, and operates when the switching elements are controlled to be turned on / off in response to a command from the control device 22. The high-voltage power supplied from 26 can be converted into low-voltage power suitable for charging the low-voltage battery 20. Further, the low-voltage power converted by the DC / DC converter 34 can be directly supplied to the in-vehicle auxiliary equipment 44 and used as drive power.

  The charging device 16 includes a power supply port or receptacle 46 provided in the vehicle body, and a charger 48 that converts AC power supplied from the power supply port 46 side to DC power and supplies power to the high-voltage power lines 24 and 26. . The AC / DC conversion function of the charger 48 is realized by the on / off control of a switching element included therein according to a command from the control device 22.

  In addition, the charger 48 includes a relay that interrupts the power path through which the power supplied from the power supply port 46 flows to the power lines 24 and 26. When this relay is turned on in response to a command from the control device 22, a charging plug 54 connected to an external power supply 50 which is a household AC power supply or a commercial AC power supply via a power cable 52 is attached to the power supply port 46. The battery charging is started when the relay is turned on, and the battery charging is ended when the relay is turned off.

  The control device 22 is preferably configured by a microcomputer centering on a CPU that executes a control program, a ROM that stores a control program in advance, a RAM that temporarily stores a control program and various detection data, a voltage sensor 28, 40, an input port that receives detection signals from the current sensors 30, 42, and an output port that outputs control signals to the DC / DC converter 34 and the charger 48.

  The control device 22 has a function of monitoring and controlling each state of charge or SOC of the high voltage battery 18 and the low voltage battery 20. Specifically, the control device 22 controls the state of charge of each of the batteries 18 and 22 so that the SOC is maintained in a range of 30 to 90%, for example, centering on 60%. Here, the SOC of each of the batteries 18 and 20 can be calculated by integrating the current values input from the current sensors 30 and 42 in the control device 22, respectively.

  In the above description, it is assumed that the SOC control ranges of the batteries 18 and 20 are the same. However, the present invention is not limited to this, and the charge / discharge characteristics, lifespan, etc. of the batteries 18 and 20 are taken into consideration. The SOC control range may be different between the high voltage battery 18 and the low voltage battery 20.

  Next, the operation of the electric vehicle 100 having the above configuration will be described.

  When the charging plug 54 is attached to the power supply port 46 in a state where the electric vehicle 100 is parked, the control device 22 activates the charger 48 and starts charging the batteries 18 and 20. When the SOC of each of the batteries 18 and 20 reaches the upper limit value of the control range, for example, 90%, the operation of the charger 48 is stopped and the charging operation is terminated.

  In this charging operation, first, the high voltage battery 18 is preferentially charged, and when the SOC of the high voltage battery 18 reaches the upper limit value, the DC / DC converter 34 is subsequently operated to charge the low voltage battery 20. Alternatively, the high voltage battery 18 may be charged after the low voltage battery 20 is preferentially charged, or the high voltage battery 18 and the low voltage battery 20 may be charged in parallel.

  When the battery charging is completed and the vehicle 100 travels, high-voltage DC power supplied from the high-voltage battery 18 is AC-converted by the inverter 12 and applied to the motor 14. As a result, the motor 14 is driven to output driving power.

  On the other hand, the low voltage battery 20 is supplied with low voltage DC power for driving in-vehicle auxiliary equipment such as an air conditioner and audio equipment. Then, when the SOC of the low-voltage battery 20 decreases due to the power supply to the auxiliary machinery and reaches the lower limit value of the control range, for example, 30%, a low-voltage battery charging request is generated in the control device 22. Upon receiving this charge request, the control device 22 operates the DC / DC converter 34 to step down the high-voltage power from the high-voltage battery 18 and charge the low-voltage battery 20.

  Thus, when the low voltage battery 20 is charged with the electric power from the high voltage battery 18, if it is always charged to a certain SOC (for example, 90%), the amount of electric power taken out from the high voltage battery 18 is increased once. The cruising range that can be driven by EV at full charge becomes shorter. Further, the SOC of the high voltage battery 18 is reduced to near the lower limit of the control range by discharging the electric power for traveling, but the SOC of the low voltage battery 20 is maintained at a high level depending on the usage condition of the in-vehicle auxiliary equipment 44. The energy balance between the high voltage battery 18 and the low voltage battery 20 may be poor. Therefore, in the battery charging system 10 of the present embodiment, the control device 22 performs the following control.

  FIG. 2 shows a processing procedure of a battery charging control routine executed in the control device 22, and FIG. 3 shows a change in SOC of each of the batteries 18 and 20 when this processing is executed. The battery charge control routine of FIG. 2 is repeatedly executed at predetermined time intervals in the CPU when the electric vehicle 100 is activated and is running or is in a runnable state.

  Referring to FIG. 2, the control device 22 first acquires the SOC1 of the high voltage battery 18 in step S10. As the SOC 1, an integrated value of detection values obtained by the current sensor 30 can be used.

  Next, the control apparatus 22 determines whether there exists a charge request | requirement of the low voltage battery 20 by step S12. In this determination, that is, when it is determined that there is no charge request for the low-voltage battery 20, the processing is ended as it is. On the other hand, when it is determined that there is a request for charging the low voltage battery 20, the charging target value SOC2 * of the low voltage battery 20 is set to the same value as the SOC1 of the high voltage battery 18 in the subsequent step S14.

  In subsequent step S16, the low-voltage battery 20 is charged to the charge target value SOC2 * using the electric power from the high-voltage battery 18. At this time, the control device 22 monitors the SOC of the low-voltage battery 20 from the integrated value of the current value detected by the current sensor 42, and when it reaches SOC2 *, stops the operation of the DC / DC converter 34 and ends the charging operation. .

  FIG. 3 shows a change in the SOC of each of the batteries 18 and 20 due to the execution of this charging control routine. In this figure, the horizontal axis represents time, the vertical axis represents SOC, SOC1 of the high-voltage battery 18 is indicated by a solid line, and SOC2 of the low-voltage battery 20 is indicated by an alternate long and short dash line. The upper broken line indicates the SOC upper limit value (for example, 90%), and the lower broken line indicates the SOC lower limit value (for example, 30%).

  As shown in FIG. 3, the SOC 1 of the high-voltage battery 18 gradually decreases as the traveling power is discharged. Here, in order to facilitate understanding, the SOC1 is illustrated as linearly decreasing, but of course not limited thereto. For example, depending on the running state of the vehicle, etc., the curve may be undulating and may decrease to the right, or the regenerative power generated by the motor 14 when traveling on a long downhill is charged, so that the SOC1 There may be a slight increase. Further, in FIG. 3, the SOC2 of the low voltage battery 20 is drawn so as to be always equal to or lower than the SOC1 of the high voltage battery 18, but this is also for easy understanding, and the power consumption of the in-vehicle auxiliary equipment 44 is small. Note that in some cases, SOC2 may be greater than SOC1 due to a small decrease in SOC2.

  On the other hand, since the low voltage battery 20 has a relatively small capacity, the SOC 2 greatly decreases depending on the use of the in-vehicle auxiliary equipment 44. When SOC2 reaches the lower limit value, a request for charging the low voltage battery 20 is generated, and the SOC2 is recovered by being charged by the electric power from the high voltage battery 18 in response to this. However, since the charging target value SOC2 * of the low-voltage battery 20 is set to coincide with the SOC1 of the high-voltage battery 18 as described above, if the SOC1 at that time is, for example, 70%, the SOC2 becomes 70%. By the way, the charging operation of the low voltage battery 20 is stopped. This charging stop point is indicated by reference numeral 56 in the figure.

  Thereafter, whenever the SOC2 of the low voltage battery 20 is lowered to the lower limit value, the charging by the electric power from the high voltage battery 18 is repeatedly performed. Each time, the charging target value SOC2 * is set to the SOC1 of the high voltage battery 18 at that time. Therefore, as SOC1 of high-voltage battery 18 decreases, charging target value SOC2 * of low-voltage battery 20 is also set low. This is indicated by reference numerals 58, 60, and 62 in FIG.

  As described above, according to the battery charging system 10 of the present embodiment, when the SOC of the high voltage battery 18 that supplies the traveling power is high, the low voltage that supplies the driving power for the in-vehicle auxiliary machinery 44 is lower. Since the charging state target value SOC2 * at the time of charging the battery 20 is set low, the amount of electric power taken out from the high voltage battery 18 to charge the low voltage battery 20 can be suppressed, and as a result, the travel distance per charge Can be stretched.

  In addition, when the low voltage battery 20 is charged by the electric power from the high voltage battery 18, the charge state target value SOC2 * of the low voltage battery 20 is in accordance with the current charge state value SOC1 of the high voltage battery 18. The energy balance between the batteries 18 and 20 can be optimized.

  Further, as described above, when the SOC of the low voltage battery 20 reaches the lower limit value of the control range, the low voltage battery 20 is charged, so that the frequency of charging the low voltage battery 20 by the electric power from the high voltage battery 18 can be suppressed. The power loss in the DC / DC converter 34 that occurs during charging is also suppressed. Thereby, the electric power charged in the high-voltage battery 18 can be used more effectively as electric power for traveling, which can contribute to extending the traveling distance per charge.

  Next, another battery charge control executed by the control device 22 will be described with reference to FIGS. FIG. 4 shows a processing procedure of another battery charging control routine executed in the control device 22, and FIG. 5 schematically shows the state of this control. Here, the same description is not repeated by giving the same step number to the process already described above.

  Referring to FIG. 4, steps S10 to S16 are the same as described above. The difference here is that when it is determined in step S12 that there is a charge request for the low voltage battery 20, it is determined in step S20 whether SOC1 of the high voltage battery 18 is equal to or lower than the first threshold value. The first threshold value can be stored in advance as an appropriate value (for example, 50%) obtained from experience, experiment, simulation, or the like.

  If it is determined in this determination that SOC1 is equal to or lower than the first threshold value, the charging target value SOC2 * of the low-voltage battery 20 is set to a value lower than the current SOC1 in the subsequent step S22. The state of this control is shown in FIG. The charging target value SOC2 * of the low-voltage battery 20 indicated by reference numerals 56 and 58 matches SOC1 as in the case of FIG. 3, but is set to a value lower than SOC1 at reference numerals 60a and 62a.

  In this way, when the remaining capacity of the high-voltage battery 18 is reduced, the amount of electric power taken out for charging the low-voltage battery 20 can be reduced, and can be preserved as traveling electric power. It is more advantageous to extend the travel distance at.

  Next, another battery charge control routine will be described with reference to FIGS. FIG. 6 shows a processing procedure of still another battery charging control routine executed in the control device 22, and FIG. 7 schematically shows the state of this control. Here, the same description is not repeated by giving the same step number to the process already described above.

  Referring to FIG. 6, steps S10 to S16 are the same as described above. The difference here is that when it is determined in step S12 that there is a charge request for the low voltage battery 20, it is determined in step S24 whether or not the SOC1 of the high voltage battery 18 is equal to or lower than the second threshold value. This second threshold value can be stored in advance as an appropriate value obtained from experience, experiment, simulation, or the like. The second threshold value is preferably smaller than the first threshold value (for example, 40%).

  If it is determined in this determination that SOC1 is equal to or lower than the second threshold value, charging of the low voltage battery 20 is prohibited in the subsequent step S26. In combination with this prohibition process, a process for limiting the discharge from the low-voltage battery 20 may be executed. For example, in-vehicle accessories that do not affect the EV running itself, such as air conditioners and audio devices, are disabled or forcibly stopped.

  The state of this control is shown in FIG. The charging target value SOC2 * of the low-voltage battery 20 indicated by reference numerals 56, 58 and 60 is identical to the SOC1 as in the case of FIG. 3, but the SOC2 of the low-voltage battery 20 after the SOC1 falls below the second threshold value. The use of the in-vehicle auxiliary equipments 44 is restricted so as to moderate the decrease in the vehicle.

  By doing in this way, when the remaining capacity of the high-voltage battery 18 is reduced to near the lower limit, the amount of electric power taken out for charging the low-voltage battery 20 is set to zero and the vehicle is used for traveling until the next charging place is reached. It is possible to secure as much power as possible, and to further extend the travel distance per charge.

  The battery charging system and the battery charging method for an electric vehicle according to the present invention are not limited to those of the above-described embodiment, and various changes and improvements can be made.

  For example, in the above description, the charging target value SOC2 * of the low voltage battery 20 is set to be equal to or lower than the SOC1 of the high voltage battery 18. However, the present invention is not limited to this. As long as the condition that SOC2 * is set lower is satisfied, SOC2 * may be set to a value larger than SOC1.

  Further, the processing in steps S24 and S26 described above with reference to FIG. 6 may be executed in combination with the control routine described with reference to FIG.

  Furthermore, the control device stores a history of power consumption of in-vehicle accessories during EV traveling per charge, and by referring to this history, the high voltage battery and the low voltage battery are almost at the same timing. You may make it set the charging target value of a low voltage battery optimally so that it may become the lower limit of a control range.

  DESCRIPTION OF SYMBOLS 10 Battery charging system, 12 Inverter, 14 Motor, 16 Charging device, 18 High voltage battery (1st battery), 20 Low voltage battery, 22 Control apparatus, 24, 26 High voltage power line, 28, 40 Voltage sensor, 30, 42 Current Sensor, 32 Smoothing capacitor, 34 DC / DC converter, 36, 38 Low-voltage power line, 44 In-vehicle accessories, 46 Power supply port, 48 Charger, 50 External power supply, 52 Power cable, 54 Charging plug, 100 Electric vehicle.

Claims (6)

A chargeable / dischargeable first battery that supplies electric power for traveling, a second battery that is charged by electric power from the first battery and supplies driving power to in-vehicle accessories, and the first battery and the second battery A battery charging system for an electric vehicle comprising a control device that controls each of the charging states of
The control device sets the charge state target value at the time of charging the second battery lower when the charge state value of the first battery is higher than when the charge state value of the first battery is high.
Battery charging system for electric vehicles. The battery charging system for an electric vehicle according to claim 1,
The said control apparatus performs charge to the said 2nd battery from the said 1st battery after the charge condition of the said 2nd battery reaches a charge condition lower limit, The battery charging system of the electric vehicle characterized by the above-mentioned. The battery charging system for an electric vehicle according to claim 1 or 2,
The said control apparatus is made to correspond with the charge condition value of a said 1st battery, and reduces the charge condition target value of a said 2nd battery, The battery charge system of the electric vehicle characterized by the above-mentioned. A battery charging system for an electric vehicle according to any one of claims 1 to 3,
The control device sets a charge state target value at the time of charging of the second battery to a value lower than the charge state value of the first battery when the charge state value of the first battery drops below a first threshold value. A battery charging system for an electric vehicle. In the battery charging system according to any one of claims 1 to 4,
The control device prohibits charging from the first battery to the second battery when a charge state value of the first battery drops below a second threshold value. . A chargeable / dischargeable first battery that supplies electric power for traveling, a second battery that is charged by electric power from the first battery and supplies driving power to in-vehicle accessories, and the first battery and the second battery A battery charging method for an electric vehicle comprising: a control device that controls each of the charging states of:
The battery charging method for an electric vehicle, wherein the charging state target value when charging the second battery is set lower when the charging state value of the first battery is lower than when the charging state value of the first battery is high.

Images