JP2006149127A - Dc-dc converter device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter device for a vehicle that can achieve with a simple circuit structure a voltage drop of a low-voltage battery by reverse direction step-up power transmission of two-way DC-DC converter of two power supply systems for a vehicle. <P>SOLUTION: This two-way DC-DC converter for a vehicle, arranged between a high-voltage power supply system including a high-voltage battery and a high-voltage electrical load and another high-voltage power supply system including a low-voltage battery and a low-voltage electrical load, controls transmission electric power at the time of its reverse direction step-up power transmission. The transmission electric power at the time of the reverse direction step-up transmission is regulated (S104) so that a voltage VL of an auxiliary battery 5 does not become lower than a threshold value voltage VLth corresponding to its permissible lowest voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicular DC-DC converter device used in a vehicular dual power supply system.

  2. Description of the Related Art A vehicle dual power supply system having two batteries with different voltages has been put to practical use or proposed in a technical field such as a hybrid vehicle. In this two power supply system for a vehicle, the high voltage power supply system is configured by a high voltage battery and an electric load that consumes a large amount of power, and the low voltage power supply system is configured by a low voltage battery and a low voltage load that are the same as the conventional one. Usually, the power generation device preferentially feeds the generated power to the high voltage power supply system, and the low voltage power supply system is usually fed from the high voltage power supply system through a step-down DC-DC converter.

  In this type of vehicle dual power supply system, the DC-DC converter is a bidirectional DC-DC converter, so that reverse boost transmission is performed from the low voltage power supply system to the high voltage power supply system when the power of the high voltage power supply system is insufficient. It has been proposed. Further, prior to the start of forward step-down power transmission of the DC-DC converter, the DC-DC converter is reversely stepped up to transmit the input smoothing capacitor of the DC-DC converter in advance, and the input smoothing capacitor from the high voltage power supply system to this input smoothing capacitor Techniques for reducing inrush current have also been proposed.

Although various types of bidirectional DC-DC converters are known, it is common to employ a PWM control system for output control for controlling transmission power (transmission current). More specifically, the PWM duty ratio of the switching element of the DC-DC converter is feedback controlled so that the output voltage of the DC-DC converter converges to the target value. However, in this type of DC-DC converter, even if the PWM duty ratio of the switching element is constant, the output current varies if the input voltage varies. For this reason, the following Patent Document 1 adds a correction voltage indicating a function value of the duty ratio of the switching element to the current of the switching element, in other words, by correcting the current of the switching element with the correction voltage, It is proposed to regard it as the output current of a DC-DC converter.
JP 2003-274648 A

  However, when performing reverse step-up power transmission in a vehicle two power supply system using the above-described PWM feedback type bidirectional DC-DC converter, the output current of the DC-DC converter becomes excessive and the voltage of the low-voltage battery decreases. It has been found that there is a possibility that the power supply voltage of the control device or electronic device connected to the low voltage battery is lowered. This is because the capacity of the low voltage battery is not so large from the beginning, and if the output current of the DC-DC converter increases during reverse boost transmission, the voltage drop of the low voltage battery increases due to the increase in the discharge current of the low voltage battery. This is because the terminal voltage of the low voltage battery decreases. Such a decrease in the terminal voltage of the low-voltage battery causes a malfunction or a decrease in operational reliability of the control device or the electronic device.

  Various solutions can be considered to solve this problem. For example, an increase in capacity of a low-voltage battery is one of them, but there is a problem in that it increases the physique, weight, and manufacturing cost of on-vehicle weight.

  Although it is possible to monitor the output current of the DC-DC converter during reverse step-up power transmission and regulate the duty ratio of the switching element of the DC-DC converter so that it does not exceed a predetermined value, current detection is troublesome. In addition, it is usually necessary to match the voltage of the high voltage power supply system having a different reference voltage level with the voltage of the control circuit, which further complicates the circuit configuration.

  The present invention has been made in view of the above-described problems, and is a vehicle DC that can realize a voltage drop of a low-voltage battery due to reverse step-up power transmission of a bidirectional DC-DC converter for a two-power supply system for a vehicle with a simple circuit configuration. The object is to provide a DC converter device.

  The vehicle DC-DC converter device of the present invention is disposed between a high-voltage power supply system including a high-voltage battery and a high-voltage electric load and a low-voltage power supply system including a low-voltage battery and a low-voltage electric load. A bidirectional DC-DC converter for a vehicle that performs power transmission between the two systems by switching of a built-in switching element; a forward step-down power transmission mode that is a power transmission operation from the high-voltage power supply system to the low-voltage power supply system; The power transmission direction of the DC-DC converter is selected according to an operation mode selected from the low voltage power supply system and the reverse step-up power transmission mode which is a power transmission mode to the high voltage power supply system, and the low voltage during forward step-down power transmission. A vehicle that performs feedback control for adjusting the PWM duty ratio of the switching element so as to converge the battery voltage to a predetermined target level. In the DC-DC converter device, the control circuit regulates the transmission power during the reverse boost transmission based on the voltage of the low voltage power supply system when the reverse boost transmission mode is executed, so that the low voltage The voltage drop of the power supply system is maintained within a predetermined allowable range. The PWM duty ratio here refers to the duty ratio of a control pulse signal applied to a switching element that is PWM controlled.

  In other words, the bidirectional DC-DC converter is controlled to perform the reverse step-up power transmission in a range where the voltage drop of the low-voltage battery falls within an allowable range. In this way, since power transmission control is performed based on the voltage of the low voltage battery, the output current at the time of reverse step-up power transmission of the DC-DC converter is limited to a predetermined range with a much simpler circuit configuration. The voltage drop of the low voltage battery can be prevented. In addition, since the voltage of the low voltage battery is directly monitored, the voltage drop of the low voltage battery can be limited with high accuracy. Furthermore, this bidirectional DC-DC converter performs feedback control that adjusts the PWM duty ratio of the switching element so as to converge the voltage of the low-voltage battery to a predetermined target level for output control during forward step-down power transmission. In other words, according to the present invention, the control circuit system is greatly increased because the voltage of the low voltage battery is monitored and the PWM duty ratio of the switching element is controlled during forward step-down power transmission and reverse step-up power transmission. The circuit configuration can be further simplified.

  In addition, as a bidirectional | two-way DC-DC converter used for this invention, various DC-DC converters, such as a flyback system other than a forward system, are employable.

  In a preferred aspect, the control circuit determines whether or not the voltage of the low-voltage power supply system has fallen below a predetermined threshold when the reverse step-up power transmission mode is executed, and if it falls, the PWM duty ratio of the switching element The transmission power is regulated to a predetermined value or less by restricting. In this way, when the voltage of the low-voltage battery is sufficiently higher than the allowable power supply voltage of the electric load of the low-voltage power supply system, the reverse boost transmission can be performed strongly because the transmission power is not regulated. Furthermore, if the voltage of the low-voltage battery approaches the lowest level of the allowable power supply voltage of the electric load of the low-voltage power supply system, the transmission power can be regulated to suppress the voltage drop of the low-voltage power supply system.

  In a preferred embodiment, the control circuit is configured such that the PWM duty ratio of the switching element or the maximum value thereof depends on a deviation between the voltage of the low voltage power supply system and a predetermined threshold value when the reverse boost power transmission mode is executed. The transmission power is regulated by determining In this way, in a situation where the deviation is large and the voltage of the low-voltage power supply system is sufficiently high, the limitation of the PWM duty ratio of the switching element can be relaxed to realize high power transmission, and as the voltage of the low-voltage power supply system decreases. Since transmission power can be reduced, soft transmission regulation can be realized.

  In a preferred aspect, the control circuit performs the switching based on a comparison result between a voltage of the low-voltage power supply system and a predetermined threshold value so as to restrict transmission power to a predetermined value or less when the reverse boost transmission mode is executed. A first means for determining a PWM duty ratio of the element as a first duty ratio; a voltage of the high-voltage power supply system and a predetermined threshold value for restricting transmission power to a predetermined value or less when executing the reverse boost transmission mode; And a second means for determining the PWM duty ratio of the switching element as a second duty ratio based on the comparison result, and the DC-DC converter to restrict the transmission power to a predetermined value or less when executing the reverse boost transmission mode. The PWM duty ratio of the switching element is set as a third duty ratio based on a comparison result between the current of the current and a predetermined threshold value. And selecting a minimum duty ratio out of at least one of the second duty ratio and the third duty ratio and the first duty ratio, or a duty ratio of the switching element or the third duty ratio thereof. The maximum value is set to the minimum duty ratio or a smaller value.

  That is, in this aspect, the PWM duty ratio of the switching element based on the voltage of the low-voltage power supply system is smaller than the PWM duty ratio of the switching element when the output current or output voltage during reverse boost transmission is adjusted to a predetermined level. In order to regulate the PWM duty ratio of the switching element based on the voltage of the low-voltage power supply system only in such a case, the smooth reverse boost transmission is executed by reducing the transmission restriction at the stage where the voltage drop of the low-voltage power supply is small as much as possible. In addition, if the voltage drop of the low-voltage power supply system becomes serious, the transmission power can be regulated preferentially, so that an undesired drop in the power supply voltage supplied to the electric load of the low-voltage power supply system can be ensured. Can be prevented.

  In a preferred aspect, the transmission power is regulated based on the voltage of the low-voltage power supply system only immediately after the reverse boost transmission mode is started. Normally, the problem that a large current flows through the DC-DC converter during reverse boost transmission and the terminal voltage of the low voltage battery greatly decreases occurs immediately after the start of reverse boost transmission. By stopping the transmission power limitation based on the voltage drop of the low voltage power supply system, it is possible to realize a smooth inference of reverse boost transmission.

  A preferred embodiment of a vehicle power supply system using the vehicle DC-DC converter device of the present invention will be described below with reference to the drawings. However, the bidirectional DC-DC converter used in the DC-DC converter device for vehicles according to the present invention is not limited to the bidirectional DC-DC converter used in the following embodiment, and various known ones can be used. Of course, it can be adopted.

(Circuit configuration)
1, 1 is a high voltage main battery, 2 is a primary side orthogonal transform unit, 3 is a transformer, 4 is a secondary side orthogonal transform unit, and 5 is a low voltage auxiliary battery (rated voltage). About 12V). The main battery 1 is a high voltage battery as referred to in the present invention. The primary side orthogonal transform unit 2, the transformer 3, and the secondary side orthogonal transform unit 4 constitute a bidirectional DC-DC converter referred to in the present invention.

  The primary side orthogonal transform unit 2 includes a single-phase inverter circuit 21 connected in a full bridge and a primary side smoothing circuit 22 arranged on the input side thereof.

  The single-phase inverter circuit 21 has four transistors 211 to 214, and each of the transistors 211 to 214 has a known parasitic diode that functions as a flywheel diode. Separate flywheel diodes may be connected in parallel to the transistors 211 to 214, respectively. The single-phase inverter circuit 21 has a pair of DC terminals connected to the output end of the primary side smoothing circuit 22 and a pair of AC terminals connected to both ends of the primary coil of the transformer 3. Since the configuration and operation of the single-phase inverter circuit 21 are well known and not the gist of the present invention, further explanation is omitted. The primary side smoothing circuit 22 includes capacitors 221 to 223 and a choke coil 224, and is connected to both ends of the main battery 1 through first DC terminals 6 and 7. Since the configuration and operation of the primary side smoothing circuit 22 are well known and are not the gist of the present invention, further explanation is omitted.

  The transformer 3 is a step-down transformer having a pair of secondary coils wound in the same direction and having one end grounded through the second DC terminal 8.

  The secondary side orthogonal transform unit 4 includes a switching / rectifying unit 41 and a secondary side smoothing circuit 42 disposed on the output side thereof. The switching / rectifying unit 41 includes a pair of transistors 411 and 412 whose one ends are individually connected to the output ends of the pair of secondary coils of the transformer 3. D is a parasitic diode of the transistors 411 and 412, but a diode may be positively added. The secondary smoothing circuit 42 includes a choke coil 421 that connects the other ends of the pair of transistors 411 and 412 and the second DC terminal 9, and a smoothing capacitor 422 that is connected between the pair of second DC terminals 8 and 9. have.

  The auxiliary battery 5 is connected between the second DC terminals 8 and 9. The auxiliary battery 5 constituting a low voltage battery referred to in the present invention supplies power to various on-vehicle electric loads (not shown).

  A controller 10 controls the bidirectional DC-DC converter, and constitutes a control circuit referred to in the present invention. The function performed by the controller 10 is preferably constituted by a hardware circuit, but software processing by a microcomputer can also be performed. The control portion that characterizes this embodiment will be described by software processing for easy understanding.

(DC step-down operation)
The step-down power supply from the main battery 1 to the auxiliary battery 5 is performed as follows. A pair of transistors 211 and 214 and a pair of transistors 412 and 413 of the single-phase inverter circuit 21 are alternately turned on at a predetermined cycle to generate a single-phase rectangular wave AC voltage, which is stepped down by the transformer 3 and switched. A single-phase full-wave rectification is performed by the rectification unit 41, and the secondary-side smoothing circuit 42 smoothes and applies to the auxiliary battery 5. Further, the controller 10 turns on one of the transistors 411 and 412 connected to one of the pair of secondary coils only during a period in which one output voltage of the pair of secondary coils is higher than the terminal voltage of the auxiliary battery 5. During the period when the other output voltage of the pair of secondary coils is higher than the terminal voltage of the auxiliary battery 5, the other of the transistors 411 and 412 connected to the other of the pair of secondary coils is turned on to perform synchronous rectification. . Instead of performing the synchronous rectification, the transistors 411 and 412 may be turned off during the step-down power supply and diode rectification by the parasitic diode D may be performed.

(DC boost operation)
The step-up power supply from the auxiliary battery 5 to the main battery 1 will be described below with reference to the timing chart of FIG. First, both the transistors 411 and 412 of the switching / rectifying unit 41 are turned on. At this time, since the transistors 411 and 412 energize a pair of secondary coils having the same winding direction and the same number of turns in the reverse direction, the magnetic flux of the transformer core is substantially 0 and no voltage is induced in the secondary coil. . With this energization, magnetic energy is accumulated in the choke coil 421. Next, the transistor 411 is turned off. Thereby, the current of the secondary coil on the transistor 411 side becomes zero. As a result, the magnetic energy stored in the choke coil 421 tries to maintain the current state before the transistor 411 is turned off, so that a current twice as large as that in the secondary coil on the transistor 412 side temporarily passes through the transistor 412. Flowing. After all, this is because the same magnetic flux change is applied to the core of the transformer 3 as the current of the secondary coil on the transistor 411 side is temporarily reversed, and the AC voltage component (half wave) proportional to the magnetic flux change is applied to the primary coil of the transformer 3. ). This AC voltage component is full-wave rectified by the flywheel diode D of the single-phase inverter circuit 21 and smoothed by the primary side smoothing circuit 22 to charge the main battery 1. Next, the transistor 411 is turned on. As a result, the magnetic flux flowing through the core of the transformer 3 becomes substantially 0 as in the beginning, and no voltage is induced in the primary coil of the transformer 3. Next, the transistor 412 is turned off. As a result, the current of the secondary coil on the transistor 412 side becomes zero. As a result, the magnetic energy accumulated in the choke coil 421 tries to maintain the current state before the transistor 412 is turned off, so that a current twice as large as that in the secondary coil on the transistor 411 side temporarily passes through the transistor 411. Flowing. After all, this is because the same magnetic flux change is applied to the core of the transformer 3 as the current of the secondary coil on the transistor 412 side is temporarily reversed, and the AC voltage component (half wave) proportional to the magnetic flux change is applied to the primary coil of the transformer 3. ). This AC voltage component is full-wave rectified by the flywheel diode D of the single-phase inverter circuit 21 and smoothed by the primary side smoothing circuit 22 to charge the main battery 1. Hereinafter, if the transistors 411 and 412 are sequentially turned on and off, high voltage transmission (DC boost transmission) energized by the magnetic energy of the choke coil 421 can be continuously performed from the auxiliary battery 5 to the main battery 1. it can.

  That is, when the transistor 411 is turned off, a situation is temporarily generated from a situation where no current flows through the pair of secondary coils to a situation where a current twice the normal current flows through the other of the pair of secondary coils. A magnetic flux change equal to the current change of the secondary coil is generated in the core of the transformer 3, and a voltage proportional to the magnetic flux change is induced in the primary coil. This is equivalent to temporarily boosting up the voltage of the auxiliary battery 5, so that a large DC voltage can be generated between the first DC terminals 6 and 7.

(Modification)
It is obvious that the switching / rectifying unit 41 in FIG. 1 may be a single-phase inverter circuit having the same configuration as the single-phase inverter circuit 21. In a bidirectional DC-DC converter, it is essential to set the step-up ratio to be significantly larger than the step-down ratio due to the internal voltage loss and the difference between the voltage at the time of discharging and charging the battery. Since the magnetic energy of the choke coil that performs current smoothing during forward power transmission can be used for boosting up, the circuit configuration can be simplified.

(Modification)
The direction of the transistors 411 and 412 of the switching / rectifying unit 41 in FIG. 1 may be reversed, and the middle point (connection point) of the secondary coil of the transformer 3 may be connected to the choke coil 421. In this way, since the source electrodes of the transistors 411 and 412 can be grounded, the on-resistance of the transistors 411 and 412 can be reduced even at a low control voltage, which is practically advantageous.

(Explanation of control)
The control operation of the DC-DC converter performed by the controller 10 will be described below.

(Basic control routine)
FIG. 3 shows a basic control routine. First, a command relating to DC-DC converter operation is read from an electronic control device (not shown) for vehicle control (S100), and it is determined whether forward step-down power transmission is commanded (S102). A subroutine described later corresponding to the directional step-down power transmission mode is executed (S104). If not instructed, it is determined whether or not reverse step-up power transmission is instructed (S106). A corresponding subroutine described later is executed (S108), and the process returns to step S100.

(Forward step-down power transmission control)
FIG. 4 shows a forward step-down power transmission control subroutine employed in this embodiment. This forward step-down power transmission control subroutine is performed during engine operation. First, the voltage VL of the auxiliary battery 5 is read (S200), the difference ΔV between the threshold voltage VLth at which the voltage VL of the auxiliary battery 5 should converge and the voltage VL of the auxiliary battery 5 is calculated, and this difference ΔV is further calculated. The PWM duty ratio Dr of the DC-DC converter corresponding to is obtained from a map or the like (S202). Next, the switching element of the DC-DC converter is PWM controlled by the determined PWM duty ratio Dr. The PWM duty ratio Dr is set so that the forward step-down transmission power increases as the difference ΔV increases.

  As a result, the voltage VL of the auxiliary battery 5 becomes the threshold voltage VLth, which is a suitable voltage. Since the storage capacity of the auxiliary battery 5 is much smaller than that of the main battery 1 that is charged from a generator (not shown), the charging current of the auxiliary battery 5 by this forward step-down power transmission is almost connected in parallel with the auxiliary battery 5. Thus, the current consumption of the low voltage electric load constituting the low voltage power supply system together with the auxiliary battery 5 becomes equal.

(Reverse direction boost transmission control)
FIG. 5 shows a reverse boost power transmission control subroutine employed in this embodiment. The reverse step-up power transmission control subroutine is executed when the main battery 1 has a small storage capacity at the time of starting the engine by power supply from the main battery 1 or when the high voltage side smoothing is performed before the forward step-down step-down power transmission of the DC-DC converter is started. This is done for precharging the capacitor 221 and other DC-LINK capacitors of devices connected to the high voltage power supply system.

  First, the voltage VL of the auxiliary battery 5 is read (S300), and it is determined whether it is lower than the threshold voltage VLth (S302). The threshold voltage VLth is set to the allowable minimum power supply voltage of the low voltage electric load to which the auxiliary battery 5 is connected or a value slightly higher than that. If the voltage VL of the auxiliary battery 5 is lower than the threshold voltage VLth, it is determined that further reverse boost transmission is impossible, and the operation of the DC-DC converter is stopped (S304). As a result, it is possible to prevent an operation error or the like of the low-voltage electric load that is sensitive to the power supply voltage drop, such as an electronic device, from occurring due to a decrease in the power supply voltage of the low-voltage electric load.

  Next, if the voltage VL of the auxiliary battery 5 is higher than the threshold voltage VLth, a difference ΔV between the voltage VL of the auxiliary battery 5 and the threshold voltage VLth is calculated, and DC-DC corresponding to this difference ΔV is calculated. The PWM duty ratio Dr of the converter is obtained from a map or the like (S306). Next, the switching element of the DC-DC converter is subjected to PWM control with the determined PWM duty ratio Dr (S308). The PWM duty ratio Dr is set such that the reverse boosted transmission power increases as the difference ΔV increases.

  As a result, the reverse boosted transmission power can be reduced as the voltage VL of the auxiliary battery 5 approaches the threshold voltage VLth, which is the lowest voltage. The direction boosted transmission power can be sufficiently secured, and in the state where the storage capacity of the auxiliary battery 5 is small, the reverse direction boosted transmission power can be reduced to suppress the power supply voltage drop of the low voltage electric load.

  In this embodiment, the reverse boosted transmission power is continuously reduced as the voltage VL of the auxiliary battery 5 decreases, but it goes without saying that it may be reduced step by step.

  The reverse step-up power transmission control of another embodiment will be described below with reference to FIG.

  First, the voltage VL of the auxiliary battery 5 and the voltage VH of the main battery 1 are read (S400), and it is determined whether the voltage VL of the auxiliary battery 5 is lower than the threshold voltage VLth (S402). The threshold voltage VLth is set to the allowable minimum power supply voltage of the low voltage electric load to which the auxiliary battery 5 is connected or a value slightly higher than that. If the voltage VL of the auxiliary battery 5 is equal to or lower than the threshold voltage VLth, it is determined that further reverse boost transmission is impossible and the operation of the DC-DC converter is stopped (S404). As a result, it is possible to prevent an operation error or the like of the low-voltage electric load that is sensitive to the power supply voltage drop, such as an electronic device, from occurring due to a decrease in the power supply voltage of the low-voltage electric load.

  If the voltage VL of the auxiliary battery 5 is higher than the threshold voltage VLth, the difference ΔV between the threshold voltage VHth that is the target voltage of the voltage VH of the main battery 1 and the voltage VH of the main battery 1 is calculated. The PWM duty ratio Dr of the DC-DC converter corresponding to the difference ΔV is obtained from a map or the like (S406). Next, the switching element of the DC-DC converter is subjected to PWM control with the determined PWM duty ratio Dr (S408). The PWM duty ratio Dr is set such that the reverse boosted transmission power increases as the difference ΔV increases.

  Thereby, the voltage VH of the main battery 1 converges to the threshold voltage VHth, which is a suitable voltage. If the voltage VL of the auxiliary battery 5 drops below the threshold voltage VLth during the reverse boost transmission, the transmission is stopped immediately. Therefore, the low voltage power supply system is connected together with the auxiliary battery 5 and connected to the auxiliary battery 5 in parallel. It is possible to prevent the power supply voltage of the low-voltage electric load to be configured from dropping to an undesirable level.

  According to this embodiment, the lower the voltage VH of the main battery 1 within the range where the power supply voltage of the low voltage electric load can be reduced, in other words, the higher the power requirement of the main battery 1, the higher the reverse power is transmitted in the reverse direction. be able to.

  The reverse step-up power transmission control according to another embodiment will be described below with reference to FIG.

  First, the voltage VL of the auxiliary battery 5, the voltage VH of the main battery 1, and the current I of the DC-DC converter are read (S500), and three PWM duty ratios Dr1, Dr2, and Dr3 are calculated based on these detected values. (S502). The PWM duty ratio Dr1 is a PWM duty ratio Dr of the DC-DC converter corresponding to the difference ΔV = VL−VLth between the voltage VL of the auxiliary battery 5 and the threshold voltage VLth, and is obtained from a map or the like. The PWM duty ratio Dr1 is set such that the reverse boosted transmission power increases as the difference ΔV increases.

  The PWM duty ratio Dr2 is the PWM duty ratio Dr of the DC-DC converter corresponding to the difference ΔV between the threshold voltage VHth, which is the target voltage of the voltage VH of the main battery 1, and the voltage VH of the main battery 1, and is a map or the like. It is requested from. The PWM duty ratio Dr2 is set such that the reverse boosted transmission power increases as the difference ΔV = VHth−VH increases.

  The PWM duty ratio Dr3 is the PWM duty ratio Dr of the DC-DC converter corresponding to the difference ΔV = Ith-I between the target value Ith of the DC-DC converter and the detected current I of the DC-DC converter. Desired. The PWM duty ratio Dr3 is set such that the reverse boosted transmission power increases as the difference ΔV = Ith−I increases. Next, the minimum value among the PWM duty ratios Dr1 to Dr3 is selected (S504), and the switching element of the DC-DC converter is subjected to PWM control based on the selected PWM duty ratio (S506).

  As a result, if the voltage VL of the auxiliary battery 5 falls below the threshold voltage VLth which is the allowable minimum value, the PWM duty ratio Dr becomes 0, so the operation of the DC-DC converter is stopped and the low voltage Further reduction of the power supply voltage of the electric load can be prevented, and when the voltage VL of the auxiliary battery 5 is in a range larger than the threshold voltage VLth and the voltage VL of the auxiliary battery 5 is sufficiently large, Feedback control based on the voltage VH or the current I of the DC-DC converter can be performed, and the voltage VH of the main battery 1 or the current I of the DC-DC converter can be suitably controlled.

  As the current I of the DC-DC converter, it is preferable to employ the output current of the DC-DC converter, but the input current of the DC-DC converter or its internal current may be employed.

(Modification)
Instead of the voltage VL of the auxiliary battery 5 employed in each of the above embodiments, the low-voltage terminal voltage of the DC-DC converter or the power supply voltage of the low-voltage electric load may be employed. In the latter case, it is preferable to employ the power supply voltage of the electric load where the power supply voltage drop is most undesirable.

(Modification)
Note that power transmission restriction or power transmission stop in the above-described reverse boost transmission control may be performed only immediately after the start of reverse boost transmission. This is because reverse boost transmission with a large current corresponding to a large voltage drop in the voltage VL of the auxiliary battery 5 usually occurs only immediately after the start of reverse boost transmission. Alternatively, it may be carried out only immediately before the start of forward step-down power transmission, and only the high-voltage side smoothing capacitor may be charged, or this reverse step-up power transmission may be performed only when the engine is started.

1 is a circuit diagram showing a dual power supply system for a hybrid vehicle used in Example 1. FIG. 2 is a timing chart showing the operation of the bidirectional DC-DC converter of FIG. 1. 3 is a flowchart illustrating a basic part of power transmission control of the bidirectional DC-DC converter according to the first embodiment. 3 is a flowchart illustrating details of forward step-down power transmission control of the bidirectional DC-DC converter according to the first embodiment. 3 is a flowchart illustrating reverse step-up power transmission control of the bidirectional DC-DC converter according to the first embodiment. 6 is a flowchart illustrating reverse step-up power transmission control of a bidirectional DC-DC converter according to a second embodiment. 6 is a flowchart illustrating reverse step-up power transmission control of a bidirectional DC-DC converter according to a third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main battery 2 Primary side orthogonal transformation part 3 Transformer 4 Secondary side orthogonal transformation part 5 Auxiliary battery 10 Controller (control circuit)
DESCRIPTION OF SYMBOLS 21 Single phase inverter circuit 22 Primary side smoothing circuit 41 Rectifier 42 Secondary side smoothing circuit 211-214 Transistor 221-223 Smoothing capacitor 224 Choke coil 411, 412 Transistor 421 Choke coil 422 Smoothing capacitor

Claims (5)

A high voltage power supply system including a high voltage battery and a high voltage electric load and a low voltage power supply system including a low voltage battery and a low voltage electric load are interposed between the two systems by switching of a built-in switching element. A bidirectional DC-DC converter for a vehicle that performs power transmission of
Selected from a forward step-down power transmission mode that is a power transmission operation from the high-voltage power system to the low-voltage power system, and a reverse step-up power transmission mode that is a power transmission mode to the low-voltage power system and the high-voltage power system The power transmission direction of the DC-DC converter is selected according to the operation mode, and feedback control is performed to adjust the PWM duty ratio of the switching element to converge the voltage of the low voltage battery to a predetermined target level during forward step-down power transmission. In a vehicle DC-DC converter device,
The control circuit includes:
Maintaining the voltage drop of the low-voltage power supply system within a predetermined allowable range by regulating the transmission power during the reverse-boosted power transmission based on the voltage of the low-voltage power supply system when executing the reverse boost transmission mode. The DC-DC converter device for vehicles characterized by these. The vehicle DC-DC converter device according to claim 1,
The control circuit includes:
When executing the reverse step-up power transmission mode, it is determined whether or not the voltage of the low-voltage power supply system has fallen below a predetermined threshold, and if lower, the transmission power is set to a predetermined value by limiting the PWM duty ratio of the switching element. A DC-DC converter device for a vehicle, characterized in that it is regulated as follows. The vehicle DC-DC converter device according to claim 1,
The control circuit includes:
The transmission power is regulated by determining the PWM duty ratio of the switching element or the maximum value thereof according to the deviation between the voltage of the low-voltage power supply system and a predetermined threshold when executing the reverse boost transmission mode. A DC-DC converter device for a vehicle that is characterized. The DC-DC converter device for a vehicle according to any one of claims 1 to 3,
The control circuit includes:
The PWM duty ratio of the switching element is set to a first duty ratio based on a comparison result between the voltage of the low-voltage power supply system and a predetermined threshold value so as to restrict the transmission power to a predetermined value or less when executing the reverse boost transmission mode. A first means to determine:
The PWM duty ratio of the switching element is set to a second duty ratio based on a comparison result between the voltage of the high-voltage power supply system and a predetermined threshold value so as to restrict the transmission power to a predetermined value or less when the reverse boost transmission mode is executed. A second means to determine:
The PWM duty ratio of the switching element is set to a third duty ratio based on the comparison result between the current of the DC-DC converter and a predetermined threshold value so as to restrict the transmission power to a predetermined value or less when the reverse boost transmission mode is executed. A third means to determine:
Have
A minimum duty ratio is selected from at least one of the second duty ratio and the third duty ratio and the first duty ratio, and the duty ratio of the switching element or its maximum value is set to the minimum duty ratio or the same. A vehicular DC-DC converter device characterized by being set to a smaller value. The DC-DC converter device for a vehicle according to any one of claims 1 to 4,
The control circuit includes:
The DC-DC converter device for a vehicle is characterized in that the transmission power is regulated based on the voltage of the low-voltage power supply system only immediately after the reverse boost transmission mode is started.

Images