JP2008079374A - Power unit for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power unit for a vehicle, which can suppress voltage variation on an input side, even if the current on the output side of a voltage converting means suddenly changes. <P>SOLUTION: The power unit for a vehicle is equipped with a DC-DC converter 30 for voltage converting the input side power to supply it to an output side on-vehicle load 24, a current detector 54 for detecting the output side current of the DC-DC converter 30, and a current limiting circuit 50 and a PWM control circuit 38 which can suppress the variation on the input side voltage by varying the output side current below the specified variation speed, when the current value on the output side current detected by the current detector 54 reaches a specified current threshold value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicle power supply device that converts input-side power into a voltage and supplies it to an in-vehicle load on the output side.

Conventionally, a power supply device in which a DC-DC voltage converter (DC-DC converter) is provided between a high voltage system having a high voltage battery and a low voltage system having a low voltage battery is known (see, for example, Patent Document 1). ). This power supply device drives a DC-DC converter and transmits power from one voltage system battery to the other voltage system battery, thereby reducing voltage fluctuation when the other voltage system battery uses a large current. ing.
JP 2002-176704 A

  However, in the conventional technology as described above, when the load current of the in-vehicle load on the output side of the converter changes suddenly, the output side current of the converter changes suddenly. As a result, the applied voltage to the electric load connected to the input side of the converter becomes unstable. As a result, for example, if the electric load on the input side is a lamp, the lamp may blink.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a vehicle power supply device that can suppress voltage fluctuation on the input side even when the current on the output side of the voltage conversion means changes suddenly.

In order to achieve the above object, a vehicle power supply device according to the present invention includes:
Voltage conversion means for converting the power on the input side to supply to the vehicle load on the output side; and
Current detection means for detecting an output side current of the voltage conversion means;
Current limiting means for changing the output side current at a predetermined change rate or less when the current value of the output side current detected by the current detection means reaches a predetermined current threshold value.

  As a result, even if the output side current of the voltage conversion means changes suddenly due to a sudden increase in the load current of the on-vehicle load on the output side, if the output side current reaches a predetermined current threshold, the output side current that flows thereafter is predetermined. Can be kept below the rate of change. Therefore, by suppressing the change rate of the output side current after the voltage conversion by the voltage conversion unit, the fluctuation of the input side current before the voltage conversion by the voltage conversion unit is also suppressed, and the input of the voltage conversion unit Side voltage fluctuation can be suppressed.

  The current limiting means limits the current value of the output-side current to the predetermined current threshold, and the output is achieved by changing the predetermined current threshold at the predetermined change speed or less. It is preferable to change the side current at the predetermined change speed or less. As a result, the current value of the output-side current is limited to the predetermined current threshold that changes below the predetermined change speed while the change speed of the output-side current is linked to the change speed of the predetermined current threshold. can do.

  For example, the current limiting unit may change the output side current to a predetermined increase rate when the current value of the output side current detected by the current detection unit reaches a predetermined current upper limit value. Alternatively, when the current value of the output-side current detected by the current detection means reaches a predetermined current lower limit value, the output-side current may be changed with a predetermined decrease rate as a limit.

  The predetermined current threshold is detected by the current detection unit when a current value of the output-side current detected by the current detection unit is separated from the predetermined current threshold by a predetermined value or more. It is preferable to set the current value obtained by adding or subtracting a predetermined amount to the current value of the output side current. As a result, even if the current value deviates from the predetermined current threshold value due to a change in the output-side current, the predetermined current threshold value is more than the current value of the output-side current by a predetermined amount if the current value is separated by a predetermined value or more. It is set to a current value obtained by adding or subtracting only. Therefore, since the difference between the actual current value of the output side current and the predetermined current threshold value can be prevented from increasing, the amount of change can be suppressed even if the current value of the output side current changes. The current value can be suppressed up to the predetermined current threshold.

  Moreover, it is preferable that the said current limiting means stops the change of the said output side electric current on the limit of the allowable electric current value of the said output side electric current. As a result, even if the output-side current changes, the current value can be limited to the allowable current value as a limit, so that it is possible to prevent an excessive current from flowing.

  The current limiting means can limit the rate of change of the output-side current by voltage conversion of the voltage conversion means.

In order to achieve the above object, the vehicle power supply device of the present invention includes:
Voltage conversion means for converting the power on the input side to supply to the vehicle load on the output side; and
Current detecting means for detecting an input side current of the voltage converting means;
Current limiting means for changing the input-side current at a predetermined change speed or less when the current value of the input-side current detected by the current detection means reaches a predetermined current threshold value.

  As a result, even if the output side current of the voltage conversion means changes suddenly due to a sudden increase in the load current of the on-vehicle load on the output side, if the input side current that fluctuates due to the sudden change reaches a predetermined current threshold, The input-side current flowing through can be suppressed to a predetermined change speed or less. Therefore, voltage fluctuation on the input side of the voltage conversion means can be suppressed.

  Further, the current limiting means limits the current value of the input-side current to the predetermined current threshold, and the input by changing the predetermined current threshold at the predetermined change speed or less. It is preferable to change the side current at the predetermined change speed or less. As a result, the current value of the input-side current is limited to the predetermined current threshold that changes below the predetermined change speed while the change speed of the input-side current is linked to the change speed of the predetermined current threshold. can do.

  For example, the current limiting unit may change the input side current to a predetermined increase rate when the current value of the input side current detected by the current detection unit reaches a predetermined current upper limit value. Alternatively, when the current value of the input-side current detected by the current detection means reaches a predetermined current lower limit value, the input-side current may be changed with a predetermined decrease rate as a limit.

  The predetermined current threshold is detected by the current detection unit when a current value of the input-side current detected by the current detection unit is separated from the predetermined current threshold by a predetermined value or more. It is preferable to set the current value obtained by adding or subtracting a predetermined amount to the current value of the input side current. As a result, even if the current value deviates from the predetermined current threshold due to the change in the input-side current, the predetermined current threshold becomes a predetermined amount greater than the current value of the input-side current if the current value is separated by a predetermined value or more. It is set to a current value obtained by adding or subtracting only. Therefore, since the difference between the actual current value of the input side current and the predetermined current threshold value can be prevented from increasing, the amount of change can be suppressed even if the current value of the input side current changes. The current value can be suppressed up to the predetermined current threshold.

  Moreover, it is preferable that the said current limiting means stops the change of the said input side electric current on the limit of the allowable electric current value of the said input side electric current. As a result, even if the input-side current changes, the current value can be limited to the allowable current value as a limit, so that it is possible to prevent an excessive current from flowing.

  According to the present invention, even if the current on the output side of the voltage conversion means changes suddenly, voltage fluctuation on the input side can be suppressed.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a vehicle power supply device according to the present invention. The vehicle power supply device of this embodiment is mounted on a vehicle, and is a step-up / step-down DC-DC voltage converter (DC-) capable of boosting the power supply voltage of the low voltage system 10 or stepping down the power supply voltage of the high voltage system 12. DC converter) 30 is provided.

  As shown in FIG. 1, the vehicle power supply device of the present embodiment includes two systems, a low voltage system 10 and a high voltage system 12. The low voltage system 10 includes a secondary battery 14 and a generator 16. The secondary battery 14 is a power storage device such as a lead battery having an output voltage of about 12V. The generator 16 is a generator that generates electric power by the rotation of a vehicle engine, which is one of vehicle regenerative brakes and vehicle power. Further, the high voltage system 12 has a secondary battery 18. The secondary battery 18 is a power storage device such as a nickel metal hydride battery or a lithium ion battery having an output voltage of about 36V. Note that the secondary battery 14 and the secondary battery 18 may be a lead battery, a lithium ion battery, a nickel metal hydride battery, an electric double layer capacitor, or the like, or a combination of them. Hereinafter, the secondary battery 14 is referred to as a low-voltage battery 14, and the secondary battery 18 is referred to as a high-voltage battery 18.

  The low voltage system 10 includes an electric load 20 such as a headlamp and a light (lamp) such as a meter, an air conditioner such as a blower motor, a compressor and an electric heater, and an emergency notification device (Mayday). The low-voltage battery 14 and the generator 16 mainly discharge and supply the stored electric power or the generated electric power to the electric load 20. The electric load 20 becomes operable when supplied with electric power stored in the low-voltage battery 14 or electric power generated by the generator 16.

  The high voltage system 12 also has an electric load 24 such as a motor for electric power steering (EPS) and an electric stabilizer and a drive motor that is one of vehicle power. The high-voltage battery 18 mainly discharges and supplies the stored electric power to the electric load 24. The electric load 24 becomes operable when the electric power stored in the high-voltage battery 18 is supplied.

  The DC-DC converter 30 is interposed between the low voltage system 10 and the high voltage system 12. The DC-DC converter 30 performs step-up conversion of input power from the low voltage system 10 side and supplies and outputs it to the high voltage system 12 side, while stepping down conversion of input power from the high voltage system 12 side. Supply to 10 side. The DC-DC converter 30 includes a step-up / step-down circuit that performs a step-up or step-down operation using an inductor 32, a pair of switching elements 40, 42, a low-voltage capacitor 34, a high-voltage capacitor 36, a PWM (pulse width modulation) control circuit 38, and the like. have.

  The inductor 32 is connected in series on a line connecting the low voltage system 10 side and the high voltage system 12 side of the DC-DC converter 30.

  Each of the switching elements 40 and 42 is a switching element made of a semiconductor such as an IGBT, MOSFET, or bipolar transistor. The switching element 40 has one end connected to the terminal on the high voltage system 12 side of the inductor 32 and the other end grounded. The switching element 42 has one end connected to the terminal on the high voltage system 12 side of the inductor 32 and the other end connected to the high voltage system 12 side of the DC-DC converter 30.

  The low-voltage capacitor 34 is connected between the terminal on the low voltage system 10 side of the inductor 32 and the ground terminal. The high-voltage capacitor 36 is connected between the collector (drain) terminal and the ground terminal of the switching element 42 connected to the high-voltage system 12 side terminal of the inductor 32. The low-voltage capacitor 34 and the high-voltage capacitor 36 can store and discharge power supplied from the low-voltage battery 14 and the generator 16 or power supplied from the high-voltage battery 18. The low voltage system capacitor 34 and the high voltage system capacitor 36 can smooth the voltage of the low voltage system 10 and the voltage of the high voltage system 12 when the DC-DC converter 30 is operated.

  The PWM control circuit 38 includes a microcomputer having a central processing unit, is connected to the gate of the switching element 40 via a driver 44 such as a transistor, and is connected to the gate of the switching element 42 via a driver 46 such as a transistor. The switching elements 40 and 42 are respectively driven to be switched. The PWM control circuit 38 inverts the switching element 40 and the switching element 42 to realize step-up conversion from the low voltage system 10 to the high voltage system 12 or step-down conversion from the high voltage system 12 to the low voltage system 10. Let Each of the switching elements 40 and 42 performs a switching operation in accordance with a command signal from the PWM control circuit 38.

  Here, the step-up conversion operation and the step-down conversion operation of the DC-DC converter 30 will be described. The PWM control circuit 38 of the DC-DC converter 30 is connected to the power supply state of the low voltage system 10 (for example, the voltage value of the low voltage system 10 (low voltage battery 14) or the remaining capacity of the low voltage battery 14) and the high voltage system 12. The boost conversion from the low voltage system 10 to the high voltage system 12 is performed based on the relationship with the power supply state (for example, the voltage value of the high voltage system 12 (high voltage battery 18) and the remaining capacity of the high voltage battery 18). It is determined whether or not the DC-DC converter 30 should be started by determining whether or not step-down conversion from the high voltage system 12 to the low voltage system 10 is necessary. Is determined. When the DC-DC converter 30 is to be activated, the PWM control circuit 38 determines a target voltage on the high voltage system 12 side or the low voltage system 10 side, and outputs the voltage on the output side of the DC-DC converter 30 (i.e., The drive duty ratio of the pair of switching elements 40 and 42 is set so that the actual voltage on the high voltage system 12 side or the low voltage system 10 side) becomes the target voltage.

  The PWM control circuit 38 performs voltage feedback control based on the output value ea of the error amplifier 52, and sets the pair of switching elements 40, 42 to a predetermined duty ratio so that the output side voltage of the DC-DC converter 30 becomes the target voltage. PWM drive. The error amplifier 52 amplifies the deviation between the actual voltage on the high voltage system 12 side (the output side voltage of the DC-DC converter 30) and the target voltage and outputs the amplified voltage (ie, “output value ea = K X (target voltage-actual voltage on the high voltage system 12 side) "(K is an amplification factor)). That is, the PWM control circuit 38 has a duty ratio that causes the actual voltage on the high voltage system 12 side to converge to the target voltage based on the output value of the error amplifier 52 even if the load current on the high voltage system 12 side fluctuates. Thus, each of the switching elements 40 and 42 can be driven.

  When the step-up conversion is to be performed by the DC-DC converter 30, the PWM control circuit 38 first turns on the switching element 40 and turns off the switching element 42 in accordance with the set duty ratio. When the switching element 40 is turned on and the switching element 42 is turned off, a current flows through the inductor 32 from the low voltage system 10 toward the high voltage system 12, so that electric power is accumulated in the inductor 32. The PWM control circuit 38 then turns off the switching element 40 and turns on the switching element 42 in accordance with the set duty ratio in a state where power is stored in the inductor 32. When the switching element 40 is turned off and the switching element 42 is turned on, the power stored in the inductance 32 is stored in the high-voltage capacitor 36 through the switching element 42. As a result, a voltage higher than the voltage on the low voltage system 10 side is output to the high voltage system 12 in a smoothed state.

  When the DC-DC converter 30 should perform step-down conversion, the PWM control circuit 38 first turns off the switching element 40 and turns on the switching element 42 according to the set duty ratio. When the switching element 40 is turned off and the switching element 42 is turned on, a current flows through the inductor 32 from the high voltage system 12 toward the low voltage system 10, whereby electric power is stored in the inductor 32 and a low voltage system capacitor. Charge is accumulated in 34. The PWM control circuit 38 then turns on the switching element 40 and turns off the switching element 42 in accordance with the set duty ratio in a state where power is stored in the inductor 32. When the switching element 40 is turned on and the switching element 42 is turned off, the energization of the inductor 32 is continued through the switching element 40 and stored in the low-voltage capacitor 34. As a result, a voltage lower than the voltage on the high voltage system 12 side is output to the low voltage system 10 in a smoothed state.

  Further, when the PWM control circuit 38 increases the voltage increase rate on the high voltage system 12 side during the boost conversion, the set duty ratio is varied in a direction in which the switching element 40 is turned on for a long time. When the voltage increase rate on the voltage system 12 side is slowed, the set duty ratio is varied in a direction that shortens the time during which the switching element 40 is turned on.

  Further, when the PWM control circuit 38 increases the voltage decrease rate on the high voltage system 12 side during the step-down conversion, the set duty ratio is varied in a direction in which the switching element 42 is turned on for a long time. When the rate of voltage decrease on the voltage system 12 side is slowed, the set duty ratio is varied in a direction that shortens the time during which the switching element 42 is turned on.

  Therefore, according to the vehicle power supply device of the present embodiment, the DC-DC converter 30 is operated by repeating the on / off drive at a predetermined duty ratio while the pair of switching elements 40 and 42 are operated in reverse with each other. The voltage conversion between the low voltage system 10 and the high voltage system 12 can be performed by synchronous rectification, and the voltage of the low voltage system 10 is boosted as desired by the switching control of the DC-DC converter 30, or the high voltage system 12 It is possible to supply the power of the low voltage system 10 or the high voltage system 12 to the high voltage system 12 or the low voltage system 10 while stepping down the voltage as desired.

  By the way, generally, a power supply device has a current limiting function as a protection function. When the load requires an excessive load current exceeding a predetermined current limit value, the power supply device performs control to make the output current constant at the current limit value. On the other hand, by the voltage feedback control described above, the output current to the high voltage system 12 side of the DC-DC converter 30 decreases as the actual voltage of the high voltage system 12 approaches the target voltage. Therefore, when the actual voltage of the high voltage system 12 is close to the target voltage and the output current to the high voltage system 12 is small, the difference between the output current and the current limit value is large. Therefore, if the load current on the high voltage system 12 side suddenly increases in this state, the output value of the error amplifier 52 changes suddenly in the conventional vehicle power supply device as shown in FIG. The output current to is also controlled so as to increase rapidly with a certain current limit value as a limit (see FIG. 14). As a result, the DC-DC converter 30 abruptly draws current from the low voltage system 10 side in order to cope with the sudden increase in output current to the high voltage system 12 side (rapid increase in input current). The voltage drops rapidly, and there is a risk of malfunction or reset of the electric load 20 on the low voltage system 10 side due to the drop. For example, if the electric load 20 is a meter or a lamp, there is a risk of blinking (the fluctuation speed of the power supply voltage at which the lamp load begins to blink is about 0.5 V / 100 ms). In FIG. 1 showing an embodiment of a vehicle power supply device according to the present invention and FIG. 13 showing a conventional vehicle power supply device, the same components are denoted by the same reference numerals.

  When a motor is present as the electric load 24 on the high voltage system 12 side, the voltage on the high voltage system 12 side may increase due to regeneration of the motor. In this case, since the output value of the error amplifier 52 changes in the synchronous rectification type DC-DC converter, the actual voltage on the high voltage system 12 side increased by the regeneration of the motor by the voltage feedback control described above is the high voltage system 12. The output current to the high voltage system 12 side is decreased so as to converge to the target voltage on the side, and consequently, the current is controlled to be sucked from the high voltage system 12 side. In this case, in the conventional vehicle power supply device as shown in FIG. 13, the output current to the high voltage system 12 side has a constant current limit value (-) corresponding to the limit value in the decreasing direction of the output current. It will be limited to the limit (see FIG. 15). Therefore, when the output current to the high voltage system 12 side is suddenly reduced (when the sink current from the high voltage system 12 side is suddenly increased), the DC-DC converter 30 responds to the sudden change. Since the current is controlled to be suddenly discharged to the low voltage system 10 side in the direction from the side to the low voltage system 10 side, the voltage on the low voltage system 10 side suddenly rises, and the low voltage system 10 due to the rise There is a risk of malfunction or reset of the electrical load 20 on the side. Similar to the above, for example, if the electrical load 20 is a meter, a lamp, or the like, there is a risk of blinking.

  Therefore, in order to suppress the voltage fluctuation on the low voltage system 10 side due to the current fluctuation on the high voltage system 12 side, the vehicle power supply device of the present embodiment has a current detector 54 and a current limiting circuit as shown in FIG. 50 is used.

  The current detector 54 outputs a voltage signal corresponding to the current Io flowing through the high voltage system 12 side of the DC-DC converter 30 using a current sensor or a shunt resistor. An output signal of the current detector 54 is input to the current limiting circuit 50. For example, the output voltage of the current detector 54 increases as the discharge current Io from the DC-DC converter 30 flowing in the direction from the low voltage system 10 side to the high voltage system 12 side increases and decreases from the high voltage system 12 side. It decreases as the suction current Io to the DC-DC converter 30 flowing in the direction toward the voltage system 10 increases.

  The current limiting circuit 50 includes a current limiting circuit 50a that limits a change in the increasing direction of the output current toward the high voltage system 12 and a current limiting circuit 50b that limits a change in the decreasing direction of the output current toward the high voltage system 12 side. And have. In accordance with the output value Im of the current limiting circuit 50, the PWM control circuit 38 performs the above-described step-up conversion or step-down conversion.

  FIG. 2 is a block diagram of a current limiting circuit 50a that limits a change in the increasing direction of the output current to the high voltage system 12 side. The control circuit 101a in the current limit circuit 50a compares the output value ea of the error amplifier 52 described above with a current limit value Is + described later, and outputs the smaller one to the PWM control circuit 38 as the output value Im of the current limit circuit 50a. To do.

  FIG. 3 is a waveform for explaining the operation of the vehicular power supply apparatus according to the present invention when the output current to the high voltage system 12 side suddenly increases due to a sudden increase in the load current on the high voltage system 12 side. In the period t1 when the output voltage on the high voltage system 12 side converges to the target voltage, the switch 105a of the current limiting circuit 50a shown in FIG. 2 is connected to the level shift circuit 104a side. The level shift circuit 104a is a circuit that adds a predetermined voltage value a to a detected voltage value corresponding to the current output current Io detected by the current detector 54 and outputs the result. When the switch 105a is connected to the level shift circuit 104a side, the current limit value Is + corresponding to the limit value in the increasing direction of the output current to the high voltage system 12 side is changed to the current output current Io by the level shift circuit 104a. It is equal to a voltage value obtained by adding a predetermined voltage a (a is a positive value) to the corresponding detected voltage value. On the other hand, during the period t1 when the output voltage on the high voltage system 12 side converges to the target voltage, the output current Io is almost zero and the output value ea of the error amplifier is almost zero because voltage feedback control is performed. is there. Therefore, since the output value ea is smaller than the current limit value Is + during the period t1, the output value Im of the current limit circuit 50a becomes ea by the control circuit 101a. Therefore, the PWM control circuit 38 performs voltage feedback control for causing the output voltage on the high voltage system 12 side to follow the target voltage in accordance with the output value ea of the error amplifier 52 during the period t1.

  Thereafter, when the load current on the high voltage system 12 side suddenly increases, the output value ea of the error amplifier 52 rapidly increases, so that the output value ea reaches the current limit value Is +. When the output value ea becomes equal to or greater than the current limit value Is +, the control circuit 101a switches the output value Im of the current limit circuit 50a from ea to Is +. In this case, the period t2 in FIG. 3 is entered.

  When the output value Im is switched from ea to Is +, the control circuit 101a transmits a switching signal to the switch 105a. The switch 105a that has received the switching signal switches the connection destination of the capacitor 106a from the level shift circuit 104a to the constant current source 103a. When the constant current source 103a and the capacitor 106a are connected, the voltage of the capacitor 106a increases at a speed determined by the current of the constant current source 103a. That is, when the switch 105a is connected to the constant current source 103a side, the current limit value Is + is equal to the voltage value of the capacitor 106a and increases at a rising speed determined by the current of the constant current source 103a. Therefore, the PWM control circuit 38 performs current feedback control for limiting the increase in the output current to the high voltage system 12 side at the rising speed of the current limit value Is + in accordance with the current limit value Is + during the period t2. As a result, even if the current Io flowing through the high voltage system 12 increases in the direction from the low voltage system 10 to the high voltage system 12, the current value of the current Io is limited by the current limit value and the current Io The increase rate of can be suppressed to the increase rate of the current limit value. As a result, it is possible to prevent malfunction of the electric load such as blinking of the lamp connected to the low voltage 10 side.

  The rising voltage of the capacitor 106a has the maximum value of the Zener voltage of the Zener diode 102a. In this case, the period of t3 in FIG. 3 is entered. This corresponds to the current limit value Is + becoming the maximum current value indicating the maximum value of the allowable output current. Therefore, the PWM control circuit 38 performs current feedback control for limiting the output current to the high voltage system 12 side to the maximum value in accordance with the maximum current value of the current limit value Is + during the period t3. As a result, the current value of the current Io increased at the rising speed of the current limit value can be limited by the upper limit value of the current limit value.

  Thereafter, when the load current on the high voltage system 12 side decreases, the output voltage on the high voltage system 12 side approaches the target voltage and the output value ea of the error amplifier 52 also decreases. Therefore, the output value ea is more than the current limit value Is + at some point. Get smaller. When the output value ea becomes smaller than the current limit value Is +, the control circuit 101a switches the output value Im of the current limit circuit 50a from Is + to ea. This corresponds to the period t4 in FIG.

  When the output value Im is switched from Is + to ea, the control circuit 101a transmits a switching signal to the switch 105a. The connection destination of the switch 105a that has received the switching signal is switched from the constant current source 103a to the level shift circuit 104a. By being connected to the level shift circuit 104a side, the current limit value Is + is equal to a voltage value obtained by adding the predetermined voltage a to the detection voltage value corresponding to the current output current Io by the level shift circuit 104a. Therefore, the PWM control circuit 38 performs voltage feedback control for converging the output voltage on the high voltage system 12 side to the target voltage in accordance with the output value ea of the error amplifier 52 during the period t4. As a result, even if the load current on the high voltage system 12 side increases again during the period t4 when the current output current Io decreases and converges to the target voltage, the sudden increase of the output current to the high voltage system 12 side is limited to the current limit. It is possible to suppress the current value corresponding to the value Is + (that is, a current value higher than the current output current Io by a current value corresponding to the predetermined voltage a).

  Note that the current limiting circuit 50a can similarly limit the rate of increase of the output current to the high voltage system 12 regardless of the current value of the output current Io.

  On the other hand, FIG. 4 is a block diagram of a current limiting circuit 50b that limits the change in the decreasing direction of the output current to the high voltage system 12 side. The control circuit 101b in the current limit circuit 50b compares the output value ea of the error amplifier 52 described above with a current limit value Is− described later, and the larger one is output to the PWM control circuit 38 as the output value Im of the current limit circuit 50b. Output.

  FIG. 5 is a waveform for explaining the operation of the vehicle power supply device according to the present invention when the output current to the high voltage system 12 side suddenly decreases due to a sudden increase in the voltage on the high voltage system 12 side. In this waveform, the DC-DC converter 30 is sucking current from the high voltage system. In the period t5 when the output voltage on the high voltage system 12 side converges to the target voltage, the switch 105b of the current limiting circuit 50b shown in FIG. 4 is connected to the level shift circuit 104b side. The level shift circuit 104b is a circuit that subtracts a predetermined voltage value a from the detected voltage value corresponding to the current output current Io detected by the current detector 54 and outputs the result. When the switch 105b is connected to the level shift circuit 104b side, the current limit value Is− corresponding to the limit value in the decreasing direction of the output current to the high voltage system 12 side is obtained by the level shift circuit 104b by the current output current Io. Is equal to a voltage value obtained by subtracting a predetermined voltage a (a is a positive value) from the detected voltage value corresponding to. On the other hand, during the period t5 when the output voltage on the high voltage system 12 side converges to the target voltage, the output current Io is almost zero and the output value ea of the error amplifier is almost zero because voltage feedback control is performed. is there. Therefore, in the period t5, the output value ea is larger than the current limit value Is−, and therefore the output value Im of the current limit circuit 50b becomes ea by the control circuit 101b. Therefore, the PWM control circuit 38 performs voltage feedback control for keeping the output voltage on the high voltage system 12 side constant in accordance with the output value ea of the error amplifier 52 during the period t5.

  Thereafter, when the output current to the high voltage system 12 side suddenly decreases due to a voltage increase due to motor regeneration, the output value ea of the error amplifier 52 rapidly increases in the negative direction, so that the output value ea reaches the current limit value Is−. . When the output value ea becomes equal to or less than the current limit value Is−, the control circuit 101b switches the output value Im of the current limit circuit 50b from ea to Is−. In this case, the period of t6 in FIG. 5 is entered.

  When the output value Im is switched from ea to Is−, the control circuit 101b transmits a switching signal to the switch 105b. The switch 105b that has received the switching signal switches the connection destination of the capacitor 106b from the level shift circuit 104b to the constant current source 103b. When the constant current source 103b and the capacitor 106b are connected, the voltage of the capacitor 106b decreases at a speed determined by the current of the constant current source 103b. That is, when the switch 105b is connected to the constant current source 103b side, the current limit value Is− is equal to the voltage value of the capacitor 106b and decreases at a decreasing rate determined by the current of the constant current source 103b. Therefore, the PWM control circuit 38 performs current feedback control for limiting the decrease in the output current to the high voltage system 12 side at the rate of decrease of the current limit value Is− according to the current limit value Is− during the period t6. As a result, even if the current Io flowing through the high voltage system 12 decreases in the direction from the low voltage system 10 to the high voltage system 12, the current value of the current Io is limited by the current limit value and the current Io The rate of decrease can be suppressed to the rate of decrease of the current limit value. As a result, it is possible to prevent malfunction of the electric load such as blinking of the lamp connected to the low voltage 10 side.

  The voltage of the capacitor 106b that decreases is a minimum value obtained by subtracting the voltage drop of the diode 107b from the voltage of the power source 108b by the diode 107b. This corresponds to the current limit value Is− becoming the minimum current value indicating the minimum allowable output current. Therefore, the PWM control circuit 38 performs current feedback control for limiting the output current to the minimum value according to the current minimum value of the current limit value Is−. As a result, the current value of the current Io reduced at the rate of decrease of the current limit value can be limited by the lower limit value of the current limit value.

  After that, the output value ea of the error amplifier 52 that has changed in the negative direction as the output voltage on the high voltage system 12 side approaches the target voltage again converges to zero, so that the output value ea is larger than the current limit value Is− at a certain point. Become. When the output value ea becomes larger than the current limit value Is−, the control circuit 101b switches the output value Im of the current limit circuit 50b from Is− to ea. This corresponds to the period t7 in FIG.

  When the output value Im is switched from Is− to ea, the control circuit 101b transmits a switching signal to the switch 105b. The connection destination of the switch 105b that has received the switching signal is switched from the constant current source 103b to the level shift circuit 104b. By being connected to the level shift circuit 104b side, the current limit value Is− is equal to the voltage value obtained by subtracting the predetermined voltage a from the detection voltage value corresponding to the current output current Io by the level shift circuit 104b. Therefore, the PWM control circuit 38 performs voltage feedback control for converging the output voltage on the high voltage system 12 side to the target voltage in accordance with the output value ea of the error amplifier 52 during the period t7. Thereby, even if the output current to the high voltage system 12 side decreases again during the period t7 when the target voltage is converged, the sudden decrease in the output current to the high voltage system 12 side corresponds to the current limit value Is−. The current value (that is, a current value lower than the current output current Io by a current value corresponding to the predetermined voltage a) can be suppressed.

  Note that the current limiting circuit 50b can similarly limit the rate of decrease of the output current to the high voltage system 12 side no matter what the current value of the output current Io suddenly decreases.

  “To limit the change in the increase direction of the discharge current (output current to the high voltage system 12 side) from the DC-DC converter 30 flowing in the direction from the low voltage system 10 side to the high voltage system 12 side” This is equivalent to “restricting the change in the decreasing direction of the suction current flowing into the DC-DC converter 30 flowing in the direction from the high voltage system 12 side to the low voltage system 10 side”, so both changes are the current limiting circuit 50a. Can be limited by. This is because the current limit circuit 50a can set the current limit value to a current value higher than the current output current Io flowing on the high voltage system 12 side by a current value corresponding to the predetermined voltage a.

  For example, when the regeneration of the motor ends, the output voltage of the DC-DC converter 30 (the output voltage on the motor connection side) decreases, but a power storage device having a large capacity such as a battery is connected to the output side. As the output voltage approaches the target voltage, the reduction rate of the sink current becomes slower. On the other hand, when a power storage device having a capacity smaller than that of a battery, such as a capacitor, is connected to the output side, the output voltage decreases rapidly, and the sink current decreases rapidly faster than the rate of decrease when the battery is connected. . As the sink current on the output side suddenly decreases, the voltage on the input side also drops rapidly. In other words, if the reduction of the sink current is moderated, fluctuations in the voltage on the input side can be suppressed. That is, if the current limit circuit 50a limits the sudden decrease in the sink current, it is possible to prevent malfunction of the electrical load connected to the input side.

  Further, “to restrict the change in the increase direction of the suction current to the DC-DC converter 30 flowing in the direction from the high voltage system 12 side to the low voltage system 10 side” and “from the low voltage system 10 side to the high voltage system 12. This is equivalent to “limiting the change in the decreasing direction of the discharge current (output current to the high voltage system 12) flowing from the DC-DC converter 30 flowing in the direction toward the side”, so both changes are the current limiting circuit 50b. Can be limited by. This is because the current limit circuit 50b can set the current limit value to a current value lower than the current output current Io flowing on the high voltage system 12 side by a current value corresponding to the predetermined voltage a.

  For example, when a large-capacity power storage device such as a battery is connected to the output side of the DC-DC converter 30, the rate of decrease in the output current (discharge current) decreases as the output voltage approaches the target voltage. On the other hand, when a power storage device having a capacity smaller than that of a battery such as a capacitor is connected to the output side, the output side actual voltage quickly reaches the target voltage when the output side load current rapidly decreases. For this reason, the output current rapidly decreases faster than the rate of decrease when the battery is connected. As the output current decreases rapidly, the voltage on the input side increases rapidly. That is, if the decrease in the output current is moderated, fluctuations in the voltage on the input side can be suppressed. That is, by limiting the sudden decrease in the output current by the current limiting circuit 50b, it is possible to prevent malfunction of the electrical load connected to the input side.

  FIG. 6 is a diagram showing a simulation circuit of the vehicle power supply device of the present embodiment. 7 to 10 are diagrams showing the simulation results. The circuit shown in FIG. 6 is configured to realize the above-described contents regarding FIGS. In each part of FIG. 6, the same reference numerals are given to the parts corresponding to those of FIGS. In FIG. 6, the logic circuit and the synchronous rectifier circuit correspond to the PWM control circuit 38, and the outputs G <b> 1 and G <b> 2 of the synchronous rectifier circuit are input to the switching elements 40 and 41, respectively.

  FIG. 7 shows changes in the voltage on the input side when the load current on the output side of the DC-DC converter 30 suddenly increases. FIG. 8 shows the load current on the output side of the DC-DC converter 30. It shows the change transition of the voltage on the input side when the output side current at the time of sudden increase is limited by the current limit value. As shown in the simulation results of FIGS. 7 and 8, even when the load current on the output side suddenly increases, the voltage fluctuation on the input side is suppressed to a constant change rate.

  FIG. 9 shows the relationship of the fluctuation transition between the output value Im of the current limiting circuit 50 and the current limiting values Is + and Is−. FIG. 10 shows the output value Im and the limit value of the current limiting circuit 50. It shows the relationship of fluctuation transition with the current limit values Is + and Is−. As shown in the simulation results of FIG. 9, the output value Im is constant during the period in which the voltage on the output side of the DC-DC converter 30 converges to the target voltage, and the current limit values Is +, Is− are above and below it. Is provided. Then, the current to the output side increases, and the increase of the output side current that has reached the current limit value Is + is limited to the rising speed of the current limit value Is +. Then, the current to the output side decreases, and the decrease in the output side current that reaches the current limit value Is− is limited to the rate of decrease of the current limit value Is−. FIG. 10 is the same as FIG. 9 except that the output side current is limited to the upper limit value of the current limit value Is +.

  Therefore, according to the vehicle power supply device of this embodiment, even if the current on the output side of the DC-DC converter 30 changes suddenly, the voltage fluctuation on the input side can be suppressed.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, as shown in FIG. 11, a current controller 56 may be provided on the high voltage system 12 side of the DC-DC converter 30. The current controller 56 limits the current flowing through the high voltage system 12 side of the DC-DC converter 30 and is, for example, a series regulator. The current controller 56 is inserted into a power supply line between the input / output terminal on the high voltage system 12 side of the DC-DC converter 30 and the electric load 24 of the high voltage system 12. In the case of FIG. 11, the PWM control circuit 38 performs voltage feedback control only according to the output value ea of the error amplifier 52, and sets the pair of switching elements 40 and 42 so that the output side voltage of the DC-DC converter 30 becomes the target voltage. PWM drive with a duty ratio of

  On the other hand, according to only the output value Io of the current detector 54, the current limit circuit 50 of FIG. 11 increases or decreases the current flowing through the high voltage system 12 side of the DC-DC converter 30 at the changing speed of the current limit values Is + and Is−. The switching element of the current controller 56 is operated via the drive circuit so as to be limited. The current limiting circuit 50 in FIG. 11 also has a current limiting circuit 50a similar to that in FIG. 2 for limiting the change in the increase direction of the output current toward the high voltage system 12, and the decrease in the output current to the high voltage system 12 side. A current limiting circuit 50b similar to that shown in FIG. 4 is provided for limiting the change.

  When the current Io detected by the current detector 54 reaches the current limit value Is +, the current limit circuit 50a of FIG. 11 has a current limit value at a rising speed determined by the capacitor 106a and the constant current source 103a, as described above. Increase Is +. Further, when the current Io and the current limit value Is + are separated by a predetermined value or more, the current limit circuit 50a in FIG. 11 sets the current limit value Is + to a current value obtained by adding a predetermined amount to the current current value Io. . 11 sets the upper limit value of the current limit value Is + determined by the Zener diode 102a, as described above.

  When the current Io detected by the current detector 54 reaches the current limit value Is−, the current limit circuit 50b in FIG. 11 limits the current at a decreasing rate determined by the capacitor 106b and the constant current source 103b as described above. Decrease the value Is-. Further, when the current Io and the current limit value Is− are separated by a predetermined value or more, the current limit circuit 50b of FIG. 11 sets the current limit value Is− to a current value obtained by subtracting a predetermined amount from the current current value Io. Set. In addition, the current limiting circuit 50b in FIG. 11 sets the lower limit value of the current limiting value Is− determined by the diode 107b in the same manner as described above.

  In other words, in the case of the embodiment of FIG. 11, the current controller 56 does not limit the change rate of the current flowing through the high voltage system 12 side by the step-up or step-down conversion by the PWM control circuit 38. ing. That is, the current controller 56 limits the rate of change of the current flowing through the high voltage system 12 side of the DC-DC converter 30 that has performed voltage feedback by the error amplifier 52. Therefore, even with the vehicular power supply apparatus of the embodiment of FIG. 11, even if the current on the output side of the DC-DC converter 30 changes suddenly, the voltage fluctuation on the input side can be suppressed.

  For example, as shown in FIG. 12, a current controller 56 may be provided on the low voltage system 10 side of the DC-DC converter 30. The current controller 56 limits the current flowing through the low voltage system 10 side of the DC-DC converter 30 and is, for example, a series regulator. The current controller 56 is inserted into a power supply line between the input / output terminal on the low voltage system 10 side of the DC-DC converter 30 and the electric load 20 of the low voltage system 10. In the case of FIG. 12, the PWM control circuit 38 performs voltage feedback control only in accordance with the output value ea of the error amplifier 52, and sets the pair of switching elements 40 and 42 so that the output side voltage of the DC-DC converter 30 becomes the target voltage. PWM drive with a duty ratio of

  On the other hand, according to only the output value Io of the current detector 54, the current limit circuit 50 in FIG. 12 increases or decreases the current flowing through the low voltage system 10 side of the DC-DC converter 30 at the rate of change of the current limit values Is + and Is−. The switching element of the current controller 56 is operated via the drive circuit so as to be limited. The current limiting circuit 50 in FIG. 12 is also similar to the current limiting circuit in FIG. 2 that limits the change in the increase direction of the suction current from the low voltage system 10 side (change in the decrease direction of the discharge current to the low voltage system 10 side). 50a and a current limiting circuit 50b similar to FIG. 4 for limiting the change in the decreasing direction of the suction current from the low voltage system 10 side (change in the increasing direction of the discharge current to the low voltage system 10 side).

  When the current Io detected by the current detector 54 reaches the current limit value Is +, the current limit circuit 50a of FIG. 12 has a current limit value at a rising speed determined by the capacitor 106a and the constant current source 103a as described above. Increase Is +. 12 sets the current limit value Is + to the current value obtained by adding a predetermined amount to the current current value Io when the current Io and the current limit value Is + are separated by a predetermined value or more. . 12 sets an upper limit value of the current limit value Is + determined by the Zener diode 102a, as described above.

  When the current Io detected by the current detector 54 reaches the current limit value Is−, the current limit circuit 50b of FIG. 12 limits the current at a decreasing rate determined by the capacitor 106b and the constant current source 103b as described above. Decrease the value Is-. Further, when the current Io and the current limit value Is− are separated by a predetermined value or more, the current limit circuit 50b of FIG. 12 sets the current limit value Is− to a current value obtained by subtracting a predetermined amount from the current current value Io. Set. Also, the current limiting circuit 50b of FIG. 12 sets the lower limit value of the current limiting value Is− determined by the diode 107b, as described above.

  That is, in the case of the embodiment of FIG. 12, the current controller 56 does not limit the change rate of the current flowing through the low voltage system 10 side by the step-up or step-down conversion by the PWM control circuit 38. ing. That is, the current controller 56 limits the rate of change of the current flowing through the low voltage system 10 side of the DC-DC converter 30. Therefore, even with the vehicular power supply apparatus of the embodiment of FIG. 12, even if the current on the output side of the DC-DC converter 30 changes suddenly, the voltage fluctuation on the input side can be suppressed.

It is the figure which showed one Embodiment of the power supply device for vehicles which concerns on this invention. It is a block diagram of a current limiting circuit 50a that limits the change in the increasing direction of the output current to the high voltage system 12 side. It is a waveform for demonstrating operation | movement of the vehicle power supply device which concerns on this invention when the output current to the high voltage system 12 side increases rapidly. It is a block diagram of the current limiting circuit 50b which limits the change of the decreasing direction of the output current to the high voltage system 12 side. It is a waveform for demonstrating operation | movement of the vehicle power supply device which concerns on this invention when the output current to the high voltage system 12 side falls rapidly. It is a figure which shows the simulation circuit of the power supply device for vehicles of this embodiment. It is the figure which showed the fluctuation transition of the voltage of the input side when the load current of the output side of the DC-DC converter 30 increases rapidly. It is the figure which showed the change transition of the voltage of the input side when the output side current when the load current of the output side of the DC-DC converter 30 increases rapidly by the current limit value. It is the figure which showed the relationship of the change transition of the output value Im of the current limiting circuit 50, and current limiting value Is +, Is-. It is the figure which showed the relationship of the fluctuation transition of the output value Im of the current limiting circuit 50, and the current limiting value Is + and Is- in which the limit value was provided. This is another embodiment according to the present invention in which a current controller 56 is provided on the high voltage system 12 side. It is other embodiment which concerns on this invention provided with the current controller 56 in the low voltage system 10 side. It is the figure which showed the conventional power supply device for vehicles. It is a waveform for demonstrating operation | movement of the conventional vehicle power supply device when the output current to the high voltage system 12 side increases rapidly. It is a waveform for demonstrating operation | movement of the conventional vehicle power supply device when the output current to the high voltage system 12 side falls rapidly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Low voltage system 12 High voltage system 14 Low voltage system battery 16 Generator 18 High voltage system battery 20 Low voltage system electric load 24 High voltage system electric load 30 DC-DC converter 32 Inductor 34 Low voltage system capacitor 36 High voltage system capacitor 38 PWM control circuit 40, 42 switching element 50 current limiting circuit 52 error amplifier circuit 54 current detector 56 current controller 104a, 104b level shift circuit

Claims (9)

Voltage conversion means for converting the power on the input side to supply to the vehicle load on the output side; and
Current detection means for detecting an output side current of the voltage conversion means;
A vehicle power supply apparatus comprising: a current limiting unit configured to change the output side current at a predetermined change speed or less when a current value of the output side current detected by the current detection unit reaches a predetermined current threshold value.   The current limiting means limits the current value of the output-side current to the predetermined current threshold, and the output-side current is changed by changing the predetermined current threshold at the predetermined change speed or less. The vehicle power supply device according to claim 1, wherein the power is changed at a speed equal to or less than the predetermined change speed.   The predetermined current threshold is the output side detected by the current detection unit when the current value of the output side current detected by the current detection unit is separated from the predetermined current threshold by a predetermined value or more. The vehicular power supply device according to claim 1, wherein the current value is set to a current value obtained by adding or subtracting a predetermined amount to a current value of the current.   4. The vehicle power supply device according to claim 1, wherein the current limiting unit stops a change in the output-side current with an allowable current value of the output-side current as a limit. 5.   5. The vehicle power supply device according to claim 1, wherein the current limiting unit limits a change speed of the output-side current by voltage conversion of the voltage conversion unit. Voltage conversion means for converting the power on the input side to supply to the vehicle load on the output side; and
Current detecting means for detecting an input side current of the voltage converting means;
A vehicle power supply device comprising: current limiting means for changing the input side current at a predetermined change speed or less when a current value of the input side current detected by the current detection means reaches a predetermined current threshold value.   The current limiting means limits the current value of the input-side current to the predetermined current threshold, and the input-side current is changed by changing the predetermined current threshold at the predetermined change speed or less. The vehicle power supply device according to claim 7, wherein the power is changed at a speed equal to or less than the predetermined change speed.   The predetermined current threshold is the input side detected by the current detection means when the current value of the input side current detected by the current detection means is separated from the predetermined current threshold by a predetermined value or more. The vehicle power supply device according to claim 6 or 7, wherein the current value is set to a current value obtained by adding or subtracting a predetermined amount to a current value of the current.   The vehicle power supply device according to any one of claims 6 to 8, wherein the current limiting means stops the change of the input side current with an allowable current value of the input side current as a limit.

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