JP2008312285A - Dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter which can improve the accuracy in the output control at low output, while performing output control by phase adjustment. <P>SOLUTION: This DC-DC converter, which converts DC power inputted from a generator 10 into AC power by the first bridge circuit 2 and transforms the AC power by a transformer 4 and steps-down the transformed AC power by an inductor 5 and then, outputs it as DC power by the second bridge circuit 3, makes the inductance of the inductor 5 increase and decrease, thereby adjusting the output power. It can drop the output power by increasing the inductance of the inductor 5, when performing the output control, by adjusting the switching phase difference between the first bridge circuit 2 and the second bridge circuit 3. Accordingly, it can lessen the variation of output power per unit phase and perform output control accurately at low output. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a DC-DC converter that is mounted on a vehicle and performs voltage conversion.

  Conventionally, as a DC-DC converter mounted on a vehicle, for example, as described in Japanese Patent Application Laid-Open No. 2000-50402, a bridge circuit is provided on the primary side of the transformer, and a rectifier circuit is provided on the secondary side of the transformer. 2. Description of the Related Art There is known a DC-DC converter that performs voltage conversion by controlling on / off of switching elements constituting a circuit and a rectifier circuit.

Further, as shown in FIG. 4, in the DC-DC converter 101, bridge circuits 103 and 104 are provided on the primary side and the secondary side of the transformer 102, respectively, and the phase difference in switching of the switching elements of the bridge circuits 103 and 104 is provided. It is conceivable to adjust the output power of the DC-DC converter 101 by adjusting. As shown in FIG. 5, the output power of the DC-DC converter 101 has a maximum value when the phase difference is 90 degrees, and decreases as it approaches 0 degrees and 180 degrees.
JP 2000-50402 A

  The DC-DC converter 101 that performs output control by such phase adjustment has a problem that the control accuracy of power control at the time of low output decreases. That is, in FIG. 5, as the phase difference approaches 0 degrees and 180 degrees, the output change per unit phase increases, making it difficult to finely control the output power.

  Therefore, the present invention has been made to solve such problems, and provides a DC-DC converter capable of improving output control accuracy at low output while performing output control by phase adjustment. With the goal.

  That is, the DC-DC converter according to the present invention includes a first conversion circuit that converts DC power into AC power, a second conversion circuit that converts AC power into DC power, and the first conversion circuit connected to the primary side. A transformer connected to the secondary side of the second conversion circuit, an inductor disposed between the transformer and the second conversion circuit, and an output for adjusting the output power by increasing or decreasing the inductance of the inductor Power adjusting means.

  According to this invention, when the output control is performed by adjusting the switching phase difference between the first conversion circuit and the second conversion circuit by providing the output power adjustment means for adjusting the output power by increasing or decreasing the inductance of the inductor, The output power can be reduced by increasing the inductance of the inductor. At this time, since the amount of change in output power per unit phase can be reduced, output control can be performed with high accuracy at low output.

  The DC-DC converter according to the present invention preferably includes output control means for performing output control by adjusting a switching phase difference in the first conversion circuit and the second conversion circuit.

  In the DC-DC converter according to the present invention, it is preferable that the DC-DC converter further includes a transformation adjusting unit that adjusts a transformation ratio of the transformer in accordance with an amount of DC power input to the first conversion circuit.

  According to the present invention, by adjusting the transformer transformation ratio according to the input power amount, even if the input power fluctuates greatly, voltage conversion can be performed correspondingly.

  According to the present invention, it is possible to improve the accuracy of output control at low output while performing output control by phase adjustment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows a circuit schematic diagram of a DC-DC converter according to an embodiment. FIG. 2 is an explanatory diagram of output characteristics in the DC-DC converter of FIG.

  The DC-DC converter 1 according to the present embodiment is a device that performs voltage conversion, and is installed in, for example, a vehicle, and is used when voltage conversion is performed on electric power generated by the vehicle. In this case, the electric power generated by the vehicle may be electric power generated by a motor generator in a hybrid vehicle and rectified by an inverter, or may be electric power generated by an exhaust heat generator that generates electricity by heat generated from the vehicle. There may be.

  As shown in FIG. 1, the DC-DC converter 1 according to this embodiment includes a first bridge circuit 2, a second bridge circuit 3, a transformer 4, an inductor 5, switches 61 and 62, and a control unit 7. ing.

  The 1st bridge circuit 2 functions as a 1st conversion circuit which inputs the direct current power which the electric power generation part 10 outputs, and converts into alternating current power, for example, is comprised by the full bridge circuit which has the four switching elements 21-24. The As the switching elements 21 to 24, MOS FET (Field Effect Transistor) is used.

  Moreover, as the switching elements 21 to 24, it is preferable to use those in which a diode is built in the reverse direction between the drain terminal and the source terminal. Each of the switching elements 21 to 24 is connected to the control unit 7 and performs a switching operation according to a control signal output from the control unit 7.

  A transformer 4 is disposed on the output side of the first bridge circuit 2. The transformer 4 transmits the output power of the first bridge circuit 2 to the second bridge side, and includes a primary winding 41 connected to the first bridge circuit 2 side and a second coil connected to the second bridge circuit 3 side. A secondary winding 42 is provided. The secondary winding 42 includes a first winding portion 42a and a second winding portion 42b connected in series.

  An inductor 5 is disposed between the transformer 4 and the second bridge circuit 3. The inductor 5 is configured by connecting a first inductor portion 51 and a second inductor portion 52 in series. The first inductor portion 51 and the second inductor portion 52 are constituted by windings having a predetermined inductance, for example.

  In the inductor 5, a connection portion between the first inductor portion 51 and the second inductor portion 52 is connected to an end portion on the first winding portion 42 a side of the transformer 4 by a connection wiring 81. A switch 61 is disposed on the connection wiring 81. The switch 61 switches between disconnection and conduction of the connection wiring 81 by opening and closing, and is controlled to open and close by a control signal output from the control unit 7.

  In the inductor 5, the end portion on the first inductor portion side is connected to a connection portion between the first winding portion 42 a and the second winding portion 42 b of the transformer 4 by a connection wiring 82. A switch 62 is disposed on the connection wiring 82. The switch 62 switches between disconnection and conduction of the connection wiring 82 by opening and closing, and is controlled to open and close by a control signal output from the control unit 7.

  The switch 61 and the switch 62 function as output power adjusting means for adjusting the output power of the DC-DC converter 1 by increasing or decreasing the inductance of the inductor 5. That is, when the switch 61 is closed and turned on, and the switch 62 is opened and turned off, the inductance of the inductor 5 acting on the output voltage of the transformer 4 becomes only the inductance of the second inductor section 52, and the DC− The output power of the DC converter 1 can be greatly adjusted.

  On the other hand, when the switch 61 is opened and turned off, and the switch 61 is opened and turned on, the inductance of the inductor 5 acting on the output voltage of the transformer 4 is changed to the first inductor portion 51 and the second inductor portion. 52 inductance. For this reason, the output power of the DC-DC converter 1 can be adjusted small.

  Further, the switch 61 and the switch 62 also function as a transformation adjusting means for adjusting the transformation ratio by changing the turns ratio of the transformer 4. That is, when the switch 61 is closed and turned on, and the switch 62 is opened and turned off, the secondary winding acting on the transformation operation of the transformer 4 becomes the first winding portion 42a and the second winding portion. 42b. On the other hand, when the switch 61 is opened and turned off, and the switch 61 is opened and turned on, the secondary winding acting on the transformation operation of the transformer 4 is only the second winding portion 42b.

  Therefore, when the switch 61 is closed and turned on, and the switch 62 is opened and turned off, the turns ratio of the transformer 4 becomes small, and the transformation ratio can be adjusted to be small. On the other hand, when the switch 61 is opened and turned off, and the switch 61 is opened and turned on, the turn ratio of the transformer 4 is increased, and the transformation ratio can be greatly adjusted.

  In this way, by changing the turns ratio of the transformer 4 so that the transformation ratio can be adjusted, the transformation ratio can be changed without changing the switching period of the first bridge circuit 2 and the second bridge circuit 3. .

  The 2nd bridge circuit 3 functions as a 2nd conversion circuit which converts the alternating current power output from the transformer 4 into direct current power, for example, is comprised by the full bridge circuit which has the four switching elements 31-34. As the switching elements 31 to 34, MOS type FETs are used.

  Moreover, as the switching elements 31 to 34, it is preferable to use those in which a diode is built in the reverse direction between the drain terminal and the source terminal. Each switching element 31 to 34 is connected to the control unit 7 and performs a switching operation in accordance with a control signal output from the control unit 7.

  A battery 11 is connected to the output side of the second bridge circuit 3. The battery 11 is a battery that is mounted on the vehicle and stores electric power generated by the power generation unit 10.

  Next, the operation of the DC-DC converter 1 according to this embodiment will be described.

  In FIG. 1, first, DC power output from the power generation unit 10 is input to the first bridge circuit 2. The switching elements 21 to 24 of the first bridge circuit 2 are switching-controlled by the control unit 7 at a predetermined cycle.

  For example, the switching elements 21 and 24 are turned on and the switching elements 22 and 23 are turned off, and then the switching elements 21 and 24 are turned off and the switching elements 22 and 23 are turned on. Repeated in a cycle. As a result, the DC power output from the power generation unit 10 is converted into AC power by the first bridge circuit 2.

  The AC power is input to the transformer 4, transformed, and input to the second bridge circuit 3 through the inductor 5. The switching elements 31 to 34 of the second bridge circuit 3 are switching-controlled by the control unit 7 at a predetermined cycle.

  For example, the switching elements 31 and 34 are turned on and the switching elements 32 and 33 are turned off, and then the switching elements 31 and 34 are turned off and the switching elements 32 and 33 are turned on. It is repeated at the same cycle as the switching cycle of the bridge circuit 2. Thereby, the AC power input to the second bridge circuit 3 is converted into AC power by the second bridge circuit 3.

  At that time, by delaying the switching timing of the second bridge circuit 3 with respect to the switching timing of the first bridge circuit 2 by a control signal output from the control unit 7 to the switching elements 21 to 24 and the switching elements 31 to 34. The phase difference of switching between the first bridge circuit 2 and the second bridge circuit 3 can be generated. By appropriately adjusting this phase difference, the output power of the DC-DC converter 1 can be controlled.

  As shown in FIG. 2, the output power can be adjusted by increasing or decreasing the inductance of the inductor 5 in accordance with the input power from the power generation unit 10 to the DC-DC converter 1. For example, when the power generated by the power generation unit 10 is greater than a predetermined value, the control unit 7 outputs a control signal that turns on the switch 61 and turns off the switch 62. Whether or not the power generated by the power generation unit 10 is larger than a predetermined value may be determined based on the output voltage value obtained by, for example, inputting the output voltage of the power generation unit 10 to the control unit 7.

  When the switch 61 is turned on and the switch 62 is turned off, the inductance of the inductor 5 is reduced, and the output power of the DC-DC converter 1 can be largely adjusted.

  On the other hand, when the generated power of the power generation unit 10 is not greater than a predetermined value, the control unit 7 outputs a control signal for turning the switch 61 off and the switch 62 on. When the switch 61 is turned off and the switch 62 is turned on, the inductance of the inductor 5 is increased, and the output power of the DC-DC converter 1 can be adjusted to be small.

  Moreover, the transformation ratio of the transformer 4 can be adjusted by opening / closing control of the switch 61 and the switch 62. For example, when the generated power of the power generation unit 10 is larger than a predetermined value, the switch 61 is turned on and the switch 62 is turned off, so that the turns ratio of the transformer 4 can be reduced, and the transformer ratio of the transformer 4 is reduced. Can be adjusted small. On the other hand, when the power generated by the power generation unit 10 is not greater than a predetermined value, the switch 61 is turned off and the switch 62 is turned on, so that the turns ratio of the transformer 4 can be increased, and the transformer 4 The ratio can be adjusted greatly.

  Thus, by adjusting the transformation ratio according to the input power, even if the input power fluctuates and fluctuates greatly, power conversion can be made to correspond to the fluctuation.

  As described above, according to the DC-DC converter 1 according to the present embodiment, the switching phase difference between the first bridge circuit 2 and the second bridge circuit 3 is obtained by adjusting the output power by increasing / decreasing the inductance of the inductor 5. When the output is controlled by adjusting the output, the output power can be reduced by increasing the inductance of the inductor 5. At this time, since the amount of change in output power per unit phase can be reduced, output control can be performed with high accuracy at low output.

  For example, FIG. 2 shows that the output power of the DC-DC converter 1 can be switched by increasing / decreasing the inductance of the inductor 5 (high output, low output in FIG. 2). However, the amount of power change per unit phase can be reduced, and precise power control can be performed. Specifically, in the output power P, if the power change amount per unit phase at low output is ΔP1, and the power change amount per unit phase at high output is ΔP2, ΔP1 is smaller than ΔP2 in FIG. It can be seen that the output power can be finely controlled.

  In addition, according to the DC-DC converter 1 according to the present embodiment, by adjusting the transformation ratio of the transformer 4 in accordance with the input power amount, voltage conversion can be performed corresponding to the input power even if it fluctuates greatly. For this reason, even when the power generation amount of the power generation unit 10 in the vehicle greatly increases or decreases, it is possible to store appropriate power.

  In addition, embodiment mentioned above demonstrated an example of the DC-DC converter which concerns on this invention, and the DC-DC converter which concerns on this invention is not limited to what was described in this embodiment. The DC-DC converter according to the present invention may be modified from the DC-DC converter according to the embodiment or applied to other ones without changing the gist described in each claim.

  For example, although the case where the output power of the DC-DC converter 1 is adjusted in two stages has been described in the present embodiment, the output power may be adjusted in three stages or more. As shown in FIG. 3, the increase / decrease of the inductor of the inductor 5 can be switched in three stages, and the transformation adjustment of the transformer 4 can be switched in three stages.

1 is a circuit schematic diagram of a DC-DC converter according to an embodiment of the present invention. It is explanatory drawing of the output characteristic in the DC-DC converter of FIG. It is a circuit schematic diagram which shows the modification of the DC-DC converter of FIG. It is explanatory drawing of background art. It is explanatory drawing of background art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC-DC converter, 2 ... 1st bridge circuit, 3 ... 2nd bridge circuit, 4 ... Transformer, 5 ... Inductor, 7 ... Control part, 10 ... Power generation part, 11 ... Battery, 21-24 ... Switching element, 31-34 ... switching elements, 61, 62 ... switches.

Claims (3)

A first conversion circuit for converting DC power to AC power;
A second conversion circuit for converting AC power into DC power;
A transformer in which the first converter circuit is connected to the primary side and the second converter circuit is connected to the secondary side;
An inductor disposed between the transformer and the second conversion circuit;
Output power adjusting means for adjusting the output power by increasing or decreasing the inductance of the inductor;
DC-DC converter provided with.   2. The DC-DC converter according to claim 1, further comprising output control means for performing output control by adjusting a switching phase difference in the first conversion circuit and the second conversion circuit.   3. The DC-DC converter according to claim 1, further comprising: a transformation adjusting unit that adjusts a transformation ratio of the transformer in accordance with an amount of direct current power input to the first conversion circuit.

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