JP2009213223A - Voltage converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage converter to be used together with a battery, which can suppress variation in operation of an auxiliary machine for supplying power supply voltage at low. <P>SOLUTION: A controller 30 restricts output of a DC/DC converter 16 to protect the DC/DC converter 16. The output is restricted based on output characteristics having a plurality of regions for reducing an output voltage in response to an increase in an output current value. The gradient of a decrease in voltage for an increase amount of current of the first region, of the plurality of regions, is more gradual than the gradient of a decrease in voltage for an increase amount of current in the second region having a current value larger than that of the first region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a voltage converter, and more particularly to a voltage converter that is connected to an output and used together with the battery to supply a power supply voltage to an auxiliary load.

  In recent years, electric vehicles and hybrid vehicles in which a high-voltage battery exceeding 100 volts is mounted as a power storage device and a motor is mounted for driving have appeared. In such an automobile, as in the conventional vehicle, many loads driven by a 12-volt battery are used, and charging from the high voltage battery to the low voltage battery is performed using a DC / DC converter.

Japanese Patent Laying-Open No. 2007-168477 (Patent Document 1) discloses a power supply device for a vehicle that can quickly detect an abnormality of a cooling device that cools a voltage conversion device, and a vehicle including the same. This vehicle power supply device is connected between a main high voltage battery and an auxiliary battery having different output voltages, and a DC / DC converter that performs voltage conversion when charging the auxiliary battery from the high voltage battery; A cooling device that cools the DC / DC converter, a temperature sensor that detects the temperature of the DC / DC converter, an output restriction on the DC / DC converter according to the output of the temperature sensor, and a malfunction of the cooling device And a control device that makes a determination based on the determination condition.
JP 2007-168477 A JP-A-6-149396 Japanese Utility Model Publication No. 3-101180 JP 2006-271136 A

  In the technology disclosed in Japanese Patent Application Laid-Open No. 2007-168477, the DC / DC converter output is limited when the temperature rises. However, if an overcurrent state occurs when the output is limited, the output voltage of the converter rapidly decreases, Since the power supply voltage is suddenly reduced, the operation of the auxiliary machine fluctuates. For example, the brightness of the headlight may fluctuate, causing the driver to feel uncomfortable.

FIG. 19 is a simplified diagram of a conventional vehicle power supply system.
Referring to FIG. 19, a normal automobile equipped with an engine is equipped with a lead battery of about 12 V, and power supply voltage is supplied from the lead battery to auxiliary loads such as a headlight and audio. In the case of a normal automobile, the lead battery is charged with a voltage of about 14 V from an alternator driven by an engine. Further, while the engine is in operation, a power supply voltage is supplied from the alternator to the auxiliary load.

  In a hybrid vehicle and an electric vehicle which have been attracting attention in recent years due to environmental problems, a high voltage of about 200 V from a high voltage battery is stepped down to 14 V by a DC / DC converter, as shown in FIG. The stepped down 14V is used as a charging voltage for a lead storage battery or a power supply voltage to an auxiliary machine load.

  FIG. 20 is a diagram showing output characteristics of the DC / DC converter used in FIG.

  Referring to FIG. 20, the DC / DC converter outputs an output voltage of 14 V until the output current reaches a predetermined maximum current. When the output current exceeds the maximum current, the current limiter works and the output voltage decreases rapidly. A DC / DC converter usually has such output characteristics and protects an internal circuit from an overcurrent. The maximum current for operating the current limiter is set to a value smaller than the allowable current of the fuse so that the fuse of the auxiliary circuit is not blown by the total current of the auxiliary load.

  FIG. 21 is a diagram showing current-voltage characteristics when the DC / DC converter having the characteristics shown in FIG. 20 is used in combination with a storage battery to supply voltage to the auxiliary load.

  As shown in FIG. 21, when the output current of the DC / DC converter exceeds the maximum current, the current limiter works as shown by Y1, and a voltage drop occurs. However, since the lead battery is connected to the auxiliary machine load as shown in FIG. 19, when the voltage drops to 12 V, current is supplied from the lead battery to the auxiliary machine load, so that no further voltage drop occurs. Here, if the sum of the currents of the auxiliary load fluctuates near the maximum current, the power supply voltage of the auxiliary load frequently switches between 14V and 12V.

FIG. 22 is a diagram showing how the power supply voltage fluctuates.
In FIG. 22, if the total current of the auxiliary load is near the maximum current, the current limiter operates as shown by Y2, and the output voltage drops to the lead battery voltage of 12V. Then, since a current is also supplied from the lead battery, the current output from the DC / DC converter decreases. Also, the total load current is slightly reduced due to the voltage drop. Then, the DC / DC converter again raises the output voltage to the normal 14V. And since the burden of auxiliary machine load current concentrates on a DC / DC converter again, a current limiter operates. Such a voltage change may appear as a change in the operation of an auxiliary device such as a flickering of a headlight, which may cause discomfort to the passenger.

  An object of the present invention is to provide a voltage converter that is used in combination with a battery and can suppress a change in the operation of an auxiliary machine that supplies a power supply voltage to a small extent.

  In summary, the present invention is a voltage converter, a current sensor for detecting an output current, a voltage sensor for detecting an output voltage, and a voltage conversion for stepping down a voltage of a high voltage battery and supplying the voltage to a low voltage battery and an auxiliary load. And a control device that controls the voltage conversion unit according to outputs of the current sensor and the voltage sensor. The control device limits the output to the voltage conversion unit to protect the voltage conversion unit. The output restriction is performed based on output characteristics having a plurality of regions in which the output voltage is lowered as the output current value increases. Among the plurality of regions, the slope of the voltage decrease with respect to the current increase amount in the first region is gentler than the slope of the voltage decrease with respect to the current increase amount in the second region having a current value larger than that of the first region.

  Preferably, the output characteristic in the first region is a characteristic that gradually decreases from a steady output voltage value sufficient to charge the low voltage battery to a voltage value of the low voltage battery as the output current value increases.

  More preferably, the control device acquires the voltage value of the low-voltage battery when the vehicle is started, and determines the output characteristics based on the acquired voltage value.

  More preferably, the control device acquires the voltage value of the low-voltage battery by capturing the output of the voltage sensor in a state where the operation of the voltage conversion unit is stopped when the vehicle is started and the driving of the auxiliary load is limited.

  Preferably, the output characteristic in the first region is a characteristic in which the voltage is decreased with respect to an increase in current so that the power passing through the voltage conversion unit is constant.

  Preferably, the output characteristic in the third region of the plurality of regions located between the first region and the second region is such that the output voltage of the low-voltage battery is the same even if the current increases or decreases in the third region. It is a characteristic that becomes a voltage value.

  Preferably, a temperature sensor for detecting the temperature of the voltage conversion unit is further provided, and a plurality of types of output characteristics for output restriction are determined, and the control device performs output restriction from among the plurality of types of output characteristics according to the output of the temperature sensor. Select output characteristics to apply to.

  According to the present invention, in the voltage converter used in combination with the battery, when the current is limited, the voltage is gradually reduced in the vicinity of the battery voltage, so that the operation change of the auxiliary device that supplies the power supply voltage can be reduced.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Overall configuration of vehicle]
FIG. 1 is a block diagram showing a configuration of a vehicle 100 to which the present invention is applied. Vehicle 100 may be an electric vehicle, a hybrid vehicle, a fuel cell vehicle, or the like as long as it uses a main battery and an auxiliary battery.

  Referring to FIG. 1, vehicle 100 includes a high voltage battery 10, system main relays SMRB and SMRG, a boost converter 12, an inverter 14, and a motor M1.

  The high voltage battery 10 is a main battery of the motor M1 for driving the vehicle. For example, a nickel hydride battery, a lithium ion battery, or a large capacity capacitor for electric storage such as an electric double layer capacitor can be used.

  System main relay SMRB is provided between the positive electrode of high voltage battery 10 and power supply line PL1. System main relay SMRG is provided between the negative electrode of high voltage battery 10 and ground line SL.

  Boost converter 12 boosts the voltage between power supply line PL1 and ground line SL and outputs the boosted voltage between power supply line PL2 and ground line SL. Inverter 14 receives the DC voltage between power supply line PL2 and ground line SL as a power supply voltage, and is controlled to generate a three-phase AC current. Then, the motor M1 is driven by the inverter 14, and a differential gear and wheels (not shown) are rotated by the motor M1.

  The vehicle 100 further includes a 12V auxiliary battery 18, a voltage sensor 19 that monitors the inter-terminal voltage VB of the auxiliary battery 18, auxiliary loads 31 to 33 driven by the auxiliary battery 18, and a power line PL1. And a DC / DC converter 16 that steps down the voltage between the ground line SL and supplies it to the auxiliary battery 18.

  The auxiliary loads 31 to 33 include, for example, electric power steering, hydraulic pumps for brakes, headlamps, air conditioner fan motors, power sources for various ECUs (Electric Control Units), power sources for driving system main relays, etc. However, FIG. 1 illustrates an ECU, a headlight, and audio.

  Particularly important as the role of the auxiliary battery 18 is the supply of the power supply voltage to the ECU at the time of starting the vehicle. When the vehicle is started and the DC / DC converter 16 starts to operate, the auxiliary loads 31 to 33 are mainly supplied with power from the DC / DC converter 16.

  Vehicle 100 further includes a temperature sensor 22 that measures temperature T of DC / DC converter 16, a current sensor 23 that measures output current I output from DC / DC converter 16, and control device 30.

  Control device 30 performs switching control of system main relays SMRB and SMRG, boosting control of boost converter 12 and switching control of inverter 14, and receives a temperature T from temperature sensor and a current I from current sensor 23 to receive DC / Limit the output of the DC converter. And according to the setting of the input device 24, on / off control of the switches SW1 to SW3 for operating the auxiliary machine loads 31 to 33 is performed.

  The control device 30 includes a plurality of ECUs such as an engine control ECU, a hybrid control ECU, a control unit in the IPM (intelligent power module) of the inverter 14 and the boost converter 12, and a battery control ECU. It may be realized by communication.

[Embodiment 1]
FIG. 2 is a diagram showing a simplified current supply path from the high voltage battery 10 of the vehicle 100 of FIG. 1 to the auxiliary machine load.

  Referring to FIG. 2, the voltage (for example, 200 V) of high voltage battery 10 is stepped down to a voltage (for example, 14 V) that can charge auxiliary battery 18 by DC / DC converter 16. With the output voltage of the DC / DC converter 16, the power supply voltage is supplied to the auxiliary loads 31 to 33 and the charging voltage is supplied to the auxiliary battery 18. For example, a 12V lead acid battery is used as the auxiliary battery 18.

  That is, there are two roles for the DC / DC converter 16. One is the supply of power supply voltage to the auxiliary machine load. The other is charging of the auxiliary battery 18. Here, even if the auxiliary battery 18 is not charged, if the current is supplied to the auxiliary load and no current is taken out from the auxiliary battery 18, the auxiliary battery 18 is not discharged and the vehicle is not discharged. There is no hindrance to driving. That is, even if the output voltage of the DC / DC converter 16 is lowered to a voltage approximately equal to the voltage of the auxiliary battery 18, there is no problem in running the vehicle.

  Therefore, even when the overcurrent output is limited to the DC / DC converter 16, it is preferable to reduce the voltage to such an extent that the voltage of the auxiliary battery 18 can be output. Further, the performance of the DC / DC converter 16 may be such that it can output power determined by the product of the auxiliary battery voltage and the maximum current.

  In the conventional example shown in FIG. 20, the maximum power performance that can be output from the DC / DC converter 16 is determined by a charging voltage (14V) higher than the auxiliary battery voltage and a maximum current (current determined by a fuse or the like). However, it was supposed to have excessive capacity. In this embodiment, since it is determined by the output voltage of the auxiliary battery and the maximum current (current determined by a fuse or the like), it is possible to reduce the size of the components of the DC / DC converter 16 and reduce the cost. .

  FIG. 3 is a flowchart for explaining control of the DC / DC converter 16 executed by the control device 30 of FIG.

  Referring to FIG. 3, when the vehicle is activated by the driver's operation, activation signal IGON is activated, and accordingly, in step S1, switch SW1 for supplying the power source current to the ECU is set to the on state. Switches SW2 to SWn for supplying a power supply current to the auxiliary load are set to an off state. Since the ECU consumes less power than other loads, almost no current flows from the auxiliary battery 18, and even if the voltage is measured by the voltage sensor 19, the voltage drop due to the internal resistance can be ignored and the open circuit voltage can be obtained. A close voltage can be measured.

  In this state, DC / DC converter 16 is turned off in step S2, voltage VB of auxiliary battery 18 is measured using voltage sensor 19 in step S3, and this measured value is stored as auxiliary battery voltage V0.

In step S4, the voltage V1 for determining the power limit value is calculated by the following equation.
V1 = V0 + Vt + Vch
Here, V0 indicates the voltage of the auxiliary battery 18 at the time of startup, Vt indicates a temperature correction value, and Vch indicates a detection error value.

Next, in step S5, the power limit value P is determined by the following equation.
P = V1 × I0
Here, I0 indicates a maximum current value determined mainly based on the fusing current of the fuse in the current supply path to the auxiliary machine. Further, in step S6, the DC / DC converter 16 is set to an on state. At this time, the DC / DC converter 16 is controlled so that the output characteristic to which the power limit value P is applied is obtained. In step S7, on / off of the switches SW2 to SWn for supplying the power supply voltage to the auxiliary load is permitted.

  FIG. 4 is a diagram showing output characteristics of the DC / DC converter 16 to which the power limit value P is applied.

  As shown in FIG. 4, while the output current I is small, a voltage of 14V necessary for charging the auxiliary battery is output, but when the output current increases and the output power reaches the power limit value P, the output Control is performed so that the output voltage gradually decreases so that the electric power does not exceed the limit value P. Control is performed so that the voltage drops sharply when the current exceeds the maximum current value I0.

  FIG. 5 is a diagram showing current-voltage characteristics when the DC / DC converter 16 controlled to have the characteristics shown in FIG. 4 is used together with the auxiliary battery 18 to supply voltage to the auxiliary load. is there.

  Referring to FIG. 5, when the output power of DC / DC converter 16 exceeds limit value P, the output voltage of DC / DC converter 16 decreases as indicated by Y3, so the voltage supplied to the auxiliary machine also decreases. However, even if the maximum current I0 is exceeded, a steep voltage drop as shown in FIG. 4 does not occur. This is because current is supplied from the auxiliary battery 18 to the auxiliary load.

  Compared with FIG. 21, it can be seen that the slope of the decrease in voltage near the maximum current I0 is gentler in FIG. Therefore, it is possible to prevent the occupant from feeling much a change in the behavior of the auxiliary machine when the fluctuation of the auxiliary machine load current occurs in the range indicated by ΔI.

FIG. 6 is a diagram showing how the fluctuation of the power supply voltage is improved.
In FIG. 6, even if the auxiliary load current fluctuates within a range of ΔI around the maximum current I0, the control of the DC / DC converter 16 is performed so as to fluctuate the voltage. Is significantly smaller than that of FIG. Thereby, for example, fluctuations in headlight brightness are reduced.

  As described above, in the first embodiment, the output characteristics of the DC / DC converter 16 are not reduced suddenly even when the output current increases, but the voltage is reduced so as to limit the power to a constant value. Let The target value to be lowered is the voltage of the auxiliary battery 18. When the DC / DC converter 16 is operating so as to output the voltage of the auxiliary battery 18, the auxiliary battery 18 cannot be charged, but the current of the auxiliary battery 18 is not continuously consumed. I can say that. Therefore, the auxiliary battery 18 can be prevented from being over-discharged even if the vehicle continues to travel, so that no problem occurs when the vehicle is traveling.

  By introducing the control for limiting the power to a constant value in this way, it is possible to prevent a sudden voltage change. Therefore, it is possible to make it difficult for the driver to feel a change in the behavior of the load such as flickering of the headlight, and to reduce discomfort.

  In the first embodiment, the power limit value P is obtained based on the voltage at the time of maximum current output. However, the output limit using the power limit value P is not limited thereto. For example, the Y portion in FIG. 5 may be a straight line instead of a curve. If the slope for dropping the voltage is gentler than that in the region where the maximum current value is exceeded, the flickering of the headlight is improved as compared with the case of FIG.

[Embodiment 2]
In the first embodiment, the introduction of the power limit value P to the control of the DC / DC converter 16 has been described. In the second embodiment, a description will be given of further limiting and protecting the current according to the temperature of the DC / DC converter 16.

FIG. 7 is a diagram showing a comparative example in the case of performing simple control.
Referring to FIG. 7, while DC / DC converter 16 is not overheated, output is limited at maximum current Imax1, but when DC / DC converter 16 is overheated, the current at which output limitation starts is limited to the current limit. It is conceivable to lower it to Imax2. However, when such control is performed, the usable current range is narrowed at a stretch. Even when the DC / DC converter 16 is overheated, it is preferable that the usable current be as large as possible.

  FIG. 8 is a diagram showing the output limit range of the DC / DC converter 16 applied in the second embodiment.

  Referring to FIG. 8, line L1 is a line where output voltage V = 14V. Line L2 is a line where the output power (output voltage V × output voltage I) is P = V1 × I0. The line L3 is a line indicating that the voltage is quickly reduced when the output current I exceeds the maximum current value I0. The line L4 is a line whose output power is P = V1 × I1. The line L5 is a line where the output voltage V = V1. The line L6 is a line indicating that the voltage is quickly reduced when the output current I exceeds the maximum current value I1.

  The combination of these lines L1 to L6 represents the output characteristics of the DC / DC converter 16 of the second embodiment. The output characteristics are determined by selecting one to be applied from the lines L1 to L6 according to the temperature of the DC / DC converter 16.

  FIG. 9 is a first flowchart of the control executed in the second embodiment. According to the control shown in this flowchart, the voltage V1 required to limit the output is determined.

  Referring to FIG. 1 and FIG. 9, when the vehicle is started by the driver's operation, activation signal IGON is activated, and accordingly, in step S11, switch SW1 for supplying the power source current to ECU is set to the on state. The switches SW2 to SWn for supplying the power supply current to the other auxiliary loads are set to the off state. Since the ECU consumes less power than other loads, almost no current flows from the auxiliary battery 18, and even if the voltage is measured by the voltage sensor 19, the voltage drop due to the internal resistance can be ignored and the open circuit voltage can be obtained. A close voltage can be measured.

  In this state, the DC / DC converter 16 is turned off in step S12, the voltage VB of the auxiliary battery 18 is measured using the voltage sensor 19 in step S13, and this measured value is stored as the auxiliary battery voltage V0.

In step S14, a voltage V1 for determining the power limit value is calculated by the following equation.
V1 = V0 + Vt + Vch
Here, V0 indicates the voltage of the auxiliary battery 18 at the time of startup, Vt indicates a temperature correction value, and Vch indicates a detection error value.

  Further, in step S15, the DC / DC converter 16 is set to an on state. At this time, the DC / DC converter 16 is controlled so that the power limit value P has an output characteristic to which the same value as in the first embodiment is applied.

  In step S16, on / off of the switches SW2 to SWn for supplying the power supply voltage to the auxiliary load is permitted. Thereafter, the setting of the output characteristics of the DC / DC converter 16 in step S17 is periodically executed until IGOFF is detected in step S18. In step S17, the output characteristics are set in consideration of the temperature of the DC / DC converter 16 as will be described later with reference to FIG.

  In step S18, when the activation signal IGOFF is deactivated by the driver's operation, the process proceeds to step S19 and the control is finished.

  FIG. 10 is a flowchart showing details of the output characteristic setting process executed in step S17 of FIG. 9 in the second embodiment.

  Referring to FIGS. 1 and 10, the temperature of DC / DC converter 16 is detected using temperature sensor 22 in step S21. If the temperature is low, there is no problem, but if the temperature indicates overheating, it is necessary to limit the output to prevent the temperature from rising.

  It is determined whether or not the temperature T detected in step S22 is lower than T1. If T <T1 is satisfied in step S22, the process proceeds to step S23. In step S23, output restriction A is executed.

  FIG. 11 is a diagram illustrating output characteristics of the DC / DC converter 16 when the output restriction A is executed.

  A line A in FIG. 11 indicates an output characteristic constituted by the lines L1, L2, and L3 described in FIG. As described above, by introducing the power limit partially indicated by the line L2, the same effect as in the first embodiment can be obtained.

  If T <T1 is not satisfied in step S22, the process proceeds to step S24. In step S24, it is determined whether T1 ≦ T <T2 is satisfied. T2 is a predetermined temperature higher than T1.

  If T1 ≦ T <T2 is satisfied in step S24, the process proceeds to step S25. In step S25, output restriction B is executed.

  FIG. 12 is a diagram illustrating output characteristics of the DC / DC converter 16 when the output restriction B is executed.

  A line B shown in FIG. 12 indicates an output characteristic constituted by the lines L1, L4, L5, and L3 described with reference to FIG. In particular, when the DC / DC converter 16 is operating on the line L5, the auxiliary battery 18 cannot be charged, but it can be said that the current of the auxiliary battery 18 is not continuously consumed. Therefore, the auxiliary battery 18 can be prevented from being over-discharged even if the vehicle continues to travel, so that no problem occurs when the vehicle is traveling. Even when the temperature rises above T1, the operation is performed on the line L5 when the output current is between I1 and I0, and the power is reduced by reducing the voltage to an output voltage that does not interfere with vehicle travel. Can be avoided.

  Referring to FIG. 10 again, if T1 ≦ T <T2 is not satisfied in step S24, the process proceeds to step S26. In step S26, it is determined whether T2 ≦ T <T3 is satisfied. T3 is a predetermined temperature higher than T2.

  If T2 ≦ T <T3 is satisfied in step S26, the process proceeds to step S27. In step S27, output restriction C is executed.

  FIG. 13 is a diagram illustrating output characteristics of the DC / DC converter 16 when the output restriction C is executed.

  A line C in FIG. 13 shows an output characteristic constituted by the lines L1, L4, and L6 described in FIG. As described above, when the temperature of the DC / DC converter 16 becomes equal to or higher than T2, the maximum current value is reduced from I0 to I1 to prevent the temperature from rising compared to the case of the output limit B shown in FIG.

  Referring to FIG. 10 again, if T2 ≦ T <T3 is not satisfied in step S26, the process proceeds to step S28. In this case, the temperature T of the DC / DC converter 16 has risen to T3 or higher. Therefore, in order to prevent the DC / DC converter 16 from being damaged by heat, the output is immediately stopped. That is, output = 0 is set as the output limit.

  When the output restriction characteristic is determined in any of steps S23, S25, S27, and S28, the process proceeds to step S29, and the output restriction value of the DC / DC converter 16 is updated. In step S30, control is transferred to the flowchart in FIG. 9, and the process in step S18 is executed.

  As described above, in the second embodiment, the output limit of the DC / DC converter 16 is changed stepwise as the temperature rises. Each output characteristic is set so as not to cause a sudden voltage change by introducing a power limit even if the output current increases. In this way, it is possible to control the load of the DC / DC converter unit and perform temperature management.

[Embodiment 3]
In the third embodiment, similarly to the second embodiment, the output characteristics are changed stepwise as the temperature of the DC / DC converter 16 rises, and control is performed so as to avoid a sudden voltage drop as much as possible.

  In the third embodiment, the setting of the output characteristics in step S17 in FIG. 9 is different from that in the second embodiment. Since other parts are the same as those in the second embodiment, description thereof will not be repeated.

  FIG. 14 is a flowchart showing details of output characteristic setting processing executed in step S17 of FIG. 9 in the third embodiment.

  Referring to FIGS. 1 and 14, the temperature of DC / DC converter 16 is detected using temperature sensor 22 in step S41. If the temperature is low, there is no problem, but if the temperature indicates overheating, it is necessary to limit the output to prevent the temperature from rising.

  It is determined whether or not the temperature T detected in step S42 is lower than T1. If T <T1 is satisfied in step S42, the process proceeds to step S43. In step S43, output restriction D is executed.

  FIG. 15 is a diagram showing the output characteristics of the DC / DC converter 16 when the output restriction D is executed.

  A line D shown in FIG. 15 indicates an output characteristic constituted by the lines L1, L2, and L3 described in FIG. As described above, by introducing the power limit partially indicated by the line L2, the same effect as in the first embodiment can be obtained.

  If T <T1 is not satisfied in step S42, the process proceeds to step S44. In step S44, it is determined whether or not T1 ≦ T <T2. T2 is a predetermined temperature higher than T1.

  If T1 ≦ T <T2 is satisfied in step S44, the process proceeds to step S45. In step S45, output restriction E is executed.

  FIG. 16 is a diagram illustrating output characteristics of the DC / DC converter 16 when the output restriction E is executed.

  A line E in FIG. 16 indicates an output characteristic constituted by the lines L5 and L3 described in FIG. In particular, when the DC / DC converter 16 is operating on the line L5, the auxiliary battery 18 cannot be charged, but it can be said that the current of the auxiliary battery 18 is not continuously consumed. Therefore, the auxiliary battery 18 can be prevented from being over-discharged even if the vehicle continues to travel, so that no problem occurs when the vehicle is traveling. Even when the temperature rises above T1, the operation is performed on the line L5 when the output current is between I1 and I0, and the power is reduced by reducing the voltage to an output voltage that does not interfere with vehicle travel. Can be avoided. If the output voltage is lowered to reduce the heat generation of the DC / DC converter 16, the temperature may also be lowered.

  Referring to FIG. 14 again, if T1 ≦ T <T2 is not satisfied in step S44, the process proceeds to step S46. In step S46, it is determined whether T2 ≦ T <T3 is satisfied. T3 is a predetermined temperature higher than T2.

  If T2 ≦ T <T3 is satisfied in step S46, the process proceeds to step S47. In step S47, output restriction F is executed.

  FIG. 17 is a diagram illustrating output characteristics of the DC / DC converter 16 when the output restriction F is executed.

  A line F in FIG. 17 indicates an output characteristic constituted by the lines L5 and L6 described in FIG. As described above, when the temperature of the DC / DC converter 16 becomes equal to or higher than T2, the maximum current value is reduced from I0 to I1 to prevent the temperature from rising compared to the case of the output limit E shown in FIG.

  Referring to FIG. 14 again, if T2 ≦ T <T3 is not satisfied in step S46, the process proceeds to step S48. In this case, the temperature T of the DC / DC converter 16 has risen to T3 or higher. Therefore, in order to prevent the DC / DC converter 16 from being damaged by heat, the output is immediately stopped. That is, output = 0 is set as the output limit.

  When the output limit characteristic is determined in any of steps S43, S45, S47, and S48, the process proceeds to step S49, and the output limit value of the DC / DC converter 16 is updated. Then, the control is moved to the flowchart of FIG. 9, and the process of step S18 is executed.

  As described above, in the third embodiment, as the temperature rises, the output limit of the DC / DC converter 16 is changed stepwise by a method slightly different from the second embodiment. In this way, the output characteristics of the DC / DC converter unit may be controlled.

FIG. 18 is a diagram showing the relationship between temperature and current that can be output.
Referring to FIG. 18, in the comparative example in which the control as shown in FIG. 7 is performed, when the temperature rises above T1, control is performed to reduce the current from I0 to I1. Compared to this, in the control executed in the second and third embodiments, the voltage can be decreased but the current can be passed through I0 between temperatures T1 and T2. Therefore, a large current can be output for a long time by performing the voltage limiting mode while the temperature is between T1 and T2, and the burden on the auxiliary battery 18 can be reduced. That is, it is not necessary to discharge the auxiliary battery 18.

  Finally, referring to FIG. 1 and others again, the present embodiment will be generally described. The voltage converter according to the present embodiment includes a current sensor 23 that detects an output current, a voltage sensor 19 that detects an output voltage, a low voltage battery (auxiliary battery 18), and an auxiliary load by stepping down the voltage of the high voltage battery 10. The voltage conversion part (DC / DC converter 16) supplied to 31-33 and the control apparatus 30 which controls a voltage conversion part according to the output of the current sensor 23 and the voltage sensor 19 are provided. The control device 30 performs output limitation on the voltage conversion unit to protect the voltage conversion unit. The output restriction is performed based on output characteristics having a plurality of regions in which the output voltage is lowered as the output current value increases. As shown in FIG. 4, the slope of the voltage drop with respect to the amount of current increase in the first region (L2) among the plurality of regions has a current increase in the second region (L3) having a larger current value than the first region. It is gentler than the slope of the voltage drop with respect to the quantity.

  Preferably, the output characteristic in the first region is from a steady output voltage value (eg, 14V) sufficient to charge the low voltage battery as the output current value increases to a voltage value (eg, 12V) of the low voltage battery. It is a characteristic that gradually decreases.

  More preferably, the control device acquires the voltage value of the low-voltage battery when the vehicle is started (step S3 in FIG. 3), and determines the output characteristics based on the acquired voltage value (steps S4 and S5).

  More preferably, the control device stops the operation of the voltage conversion unit when the vehicle is started (step S2) and restricts the driving of the auxiliary load (step S1). Get the voltage value.

  Preferably, the output characteristic in the first region (L2 in FIG. 4) is a characteristic that decreases the voltage with respect to an increase in current so that the power passing through the voltage conversion unit is constant.

  Preferably, as shown in FIG. 12, the output characteristics in the third region (L5) among the plurality of regions located between the first region (L4) and the second region (L3) This is a characteristic in which the output voltage becomes the voltage value (V1) of the low-voltage battery even if the current increases or decreases in the region.

  Preferably, a temperature sensor 22 for detecting the temperature of the voltage conversion unit is further provided, and a plurality of types of output characteristics of the output restriction are determined (L1 to L6) as shown in FIG. An output characteristic to be applied to output restriction is selected from a plurality of types of output characteristics according to the output.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a block diagram showing a configuration of a vehicle 100 to which the present invention is applied. FIG. 2 is a diagram showing a simplified current supply path from a high voltage battery 10 to an auxiliary load of the vehicle 100 of FIG. 1. 2 is a flowchart for explaining control of a DC / DC converter 16 executed by a control device 30 of FIG. It is the figure which showed the output characteristic of the DC / DC converter 16 to which the electric power limit value P was applied. FIG. 5 is a diagram showing current-voltage characteristics when a DC / DC converter 16 controlled to have the characteristics shown in FIG. 4 is used together with an auxiliary battery 18 to supply voltage to an auxiliary load. It is the figure which showed a mode that the fluctuation | variation of the power supply voltage was improved. It is the figure which showed the comparative example in the case of performing simple control. It is the figure which showed the range of the output restriction | limiting of the DC / DC converter 16 applied in Embodiment 2. FIG. 6 is a first flowchart of control executed in the second embodiment. 10 is a flowchart showing details of output characteristic setting processing executed in step S17 of FIG. 9 in the second embodiment. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction | limiting A is performed. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction | limiting B is performed. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction C is performed. 10 is a flowchart showing details of output characteristic setting processing executed in step S17 of FIG. 9 in the third embodiment. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction | limiting D is performed. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction E is performed. It is the figure which showed the output characteristic of the DC / DC converter 16 in case the output restriction | limiting F is performed. It is the figure which showed the relationship between temperature and the electric current which can be output. It is the figure which simplified and showed the conventional vehicle power supply system. It is the figure which showed the output characteristic of the DC / DC converter used in FIG. It is the figure which showed the electric current-voltage characteristic at the time of supplying a voltage to auxiliary machine load using the DC / DC converter which has the characteristic shown in FIG. 20 together with a storage battery. It is the figure which showed the mode of the fluctuation | variation of a power supply voltage.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 High voltage battery, 12 Boost converter, 14 Inverter, 16 DC / DC converter, 18 Auxiliary battery, 19 Voltage sensor, 22 Temperature sensor, 23 Current sensor, 24 Input device, 30 Control apparatus, 31 Auxiliary load, 100 Vehicle, M1 motor, PL1, PL2 power line, SMRB, SMRG system main relay, SW1, SW2 switch.

Claims (7)

A current sensor for detecting the output current;
A voltage sensor for detecting the output voltage;
A voltage converter that steps down the voltage of the high voltage battery and supplies it to the low voltage battery and the auxiliary load;
A control device that controls the voltage conversion unit according to the output of the current sensor and the voltage sensor;
The control device performs output limitation on the voltage conversion unit to protect the voltage conversion unit,
The output limitation is performed based on an output characteristic having a plurality of regions in which the output voltage is decreased as the output current value increases.
The slope of the voltage decrease with respect to the current increase amount in the first region among the plurality of regions is gentler than the slope of the voltage decrease with respect to the current increase amount in the second region having a larger current value than the first region. , Voltage converter.   The output characteristic in the first region is a characteristic that gradually decreases from a steady output voltage value sufficient to charge the low-voltage battery to a voltage value of the low-voltage battery as the output current value increases. Item 2. The voltage converter according to Item 1.   The voltage converter according to claim 2, wherein the control device acquires a voltage value of the low-voltage battery when the vehicle is started and determines the output characteristic based on the acquired voltage value.   The control device acquires the voltage value of the low-voltage battery by capturing the output of the voltage sensor in a state where the operation of the voltage conversion unit is stopped at the time of starting the vehicle and the driving of the auxiliary load is limited. Item 4. The voltage converter according to item 3.   2. The voltage converter according to claim 1, wherein the output characteristic in the first region is a characteristic in which a voltage is decreased with respect to an increase in current so that electric power passing through the voltage conversion unit is constant.   The output characteristics in the third region of the plurality of regions located between the first region and the second region are such that the output voltage is the low voltage even if the current increases or decreases in the third region. The voltage converter according to claim 1, wherein the voltage converter has a characteristic that is a voltage value of the battery. A temperature sensor for detecting the temperature of the voltage converter;
A plurality of types of output characteristics of the output restriction are determined,
The voltage converter according to claim 1, wherein the control device selects an output characteristic to be applied to output restriction from the plurality of types of output characteristics according to an output of the temperature sensor.

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