JP2011244656A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter capable of suppressing power loss while maintaining a transformation function during power regeneration.SOLUTION: A DC-DC converter 10 includes: a transformer 28; two secondary switching elements 30, 32 that are connected across a secondary winding of the transformer 28 and brought into conduction during power regeneration from a load 14; and an inductor 34 that is connected with a center tap 38 of the secondary winding of the transformer 28 and stores the regenerative electric power during power regeneration from the load 14, and further includes an auxiliary switching element 40 that is connected with one ends of a center tap 38 and the inductor 34 and brought into conduction during storage of regenerative electric power in the inductor 34.

Description

  The present invention relates to a DC-DC converter, and more particularly to a DC-DC converter suitable for transmitting regenerative power generated by a load through a transformer having a center tap provided in a secondary winding.

  Conventionally, a DC-DC converter that converts a direct-current voltage is known (see, for example, Patent Document 1). This DC-DC converter is a center tap type DC-DC converter in which a center tap is provided in a secondary winding of a transformer. When such a DC-DC converter is applied to a battery in which a battery is connected to the primary side of the transformer and a load is connected to the secondary side of the transformer, an inductor for storing electric power is connected to the center tap. At the same time, two switching elements that are alternately switched are connected to both ends of the secondary winding of the transformer. In such a structure, when two switchings on the transformer secondary side are alternately switched during power regeneration, the regenerative power generated in the load is accumulated in the inductor, and the regenerated power is transferred from the secondary side of the transformer to the primary side. Is transmitted to. Therefore, the regenerative power generated in the load can be transformed via the DC-DC converter and supplied to the battery.

2009-144200

  However, in the structure of the DC-DC converter described above, in order to store regenerative power in the inductor, it is necessary to switch two switching elements alternately. A relatively large current flows through the two switching elements. A switching element connected to both ends of the secondary winding of the transformer for DC voltage conversion is required to have a high withstand voltage. Since such a switching element is an element having a high on-resistance, a current flows through the switching element as described above. Power loss when flowing is high, and excessive heat generation may occur.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a DC-DC converter that suppresses power loss while maintaining a transformation function during power regeneration.

  The above-mentioned object is to connect the transformer, two secondary side switching elements connected to both ends of the secondary winding of the transformer and conducted at the time of power regeneration from the load, and the center tap of the secondary winding of the transformer. A DC-DC converter including an inductor that stores the regenerative power when the power from the load is regenerated, and is connected to the center tap and one end of the inductor and is conductive when the regenerative power is accumulated in the inductor. This is achieved by a DC-DC converter comprising an auxiliary switching element.

  In the invention of this aspect, an auxiliary switching element is connected to the center tap of the secondary winding of the transformer and one end of the inductor, and this auxiliary switching element is conducted when accumulating regenerative power in the inductor. In such a structure, when the regenerative power is accumulated in the inductor, the current flows mainly through the auxiliary switching element, while the amount of current flowing through the high-voltage secondary switching element connected to both ends of the secondary winding of the transformer is Therefore, the power loss in the switching element can be suppressed.

  In the DC-DC converter described above, the auxiliary switching element may have an on-resistance lower than the on-resistance of the two secondary side switching elements.

  In the DC-DC converter described above, the auxiliary switching element may be cut off when the regenerative power stored in the inductor is transmitted to the primary side of the transformer via the transformer.

  Furthermore, in the above-described DC-DC converter, the two secondary side switching elements are alternately conducted to transmit the regenerative power accumulated in the inductor to the primary side of the transformer via the transformer. Also good.

  According to the present invention, power loss can be suppressed while maintaining the transformation function during power regeneration.

1 is an overall configuration diagram of a system including a DC-DC converter according to an embodiment of the present invention. It is a detailed block diagram of the system provided with the DC-DC converter which is one Example of this invention. It is a flowchart of an example of the control routine performed at the time of electric power regeneration in the system provided with the DC-DC converter which is one Example of this invention. It is a figure showing the flow of the electric current at the time of charging regenerative electric power energy to an inductor at the time of electric power regeneration in the DC-DC converter which is one Example of this invention. It is a figure showing the 1st pattern of the flow of an electric current at the time of moving electric power energy from an inductor to a battery side via a transformer at the time of electric power regeneration in a DC-DC converter which is one example of the present invention. It is a figure showing the 2nd pattern of the flow of an electric current at the time of moving electric energy from a inductor to a battery side via a transformer at the time of electric power regeneration in a DC-DC converter which is one example of the present invention.

  Hereinafter, specific embodiments of a DC-DC converter according to the present invention will be described with reference to the drawings.

  FIG. 1 shows an overall configuration diagram of a system including a DC-DC converter 10 according to an embodiment of the present invention. Moreover, FIG. 2 shows the detailed block diagram of the system provided with the DC-DC converter 10 of a present Example.

  As shown in FIG. 1, the system of the present embodiment includes a battery 12, a motor 14, and a DC-DC converter 10 and an inverter 16 as a power conversion device interposed between the battery 12 and the motor 14. The system of the present embodiment is mounted on, for example, a hybrid vehicle or an electric vehicle, and is a system that exchanges power between the battery 12 and the motor 14 via a power conversion device.

  The battery 12 is, for example, a nickel metal hydride battery or a lithium ion battery, and can store electric power. The battery 12 can output a relatively high voltage (for example, 288 volts). The motor 14 is, for example, a three-phase AC drive motor provided on each wheel, and is a motor that operates by supplying power from the battery 12 and can generate regenerative power. It is.

  The DC-DC converter 10 is a bidirectional type that performs voltage conversion between a relatively high DC voltage (for example, 288 volts) for the battery 12 and a relatively low DC voltage (for example, 42 volts or 12 volts) for the motor 14. DC-DC voltage converter. The inverter 16 is a bidirectional DC-AC voltage converter that performs voltage conversion between a relatively low DC voltage and an AC voltage for the motor 14.

  The DC-DC converter 10 includes four primary side switching elements 20, 22, 24, 26 and a transformer 28. The four primary-side switching elements 20, 22, 24, and 26 constitute an H-bridge circuit in which two sets of two cascaded connections are connected in parallel. For each of the two sets of cascade-connected primary side switching elements 20, 22, 24, and 26, the connection point between the primary side switching elements 20 and 22 and the connection point between the primary side switching elements 24 and 26 are the primary of the transformer 28. It is connected to the side coil. That is, the primary side coil of the transformer 28 is interposed between the connection point between the primary side switching elements 20 and 22 and the connection point between the primary side switching elements 24 and 26.

  The DC-DC converter 10 also includes two secondary side switching elements 30 and 32, an inductor 34, and a capacitor 36. Both ends of the secondary side coil of the transformer 28 are connected to one end of the secondary side switching elements 30 and 32. The other ends of the secondary side switching elements 30 and 32 are connected to each other. A center tap 38 is provided on the secondary side coil of the transformer 28. One end of the inductor 34 is connected to the center tap 38. The capacitor 36 is interposed between the other end of the inductor 34 and the other ends of the secondary side switching elements 30 and 32.

  One end of the switching element 40 is connected to one end of the inductance 34 and the center tap 38. The other end of the switching element 40 is connected to the other ends of the secondary side switching elements 30 and 32. That is, the switching element 40 is interposed between the center tap 38 and the other ends of the secondary side switching elements 30 and 32 and is connected to both ends of the inductor 34 and the capacitor 36 connected in series. The switching element 40 has an on-resistance that is lower than the on-resistance of the secondary-side switching elements 30 and 32 described above. This is because a relatively low voltage that can be generated at the output on the inverter 16 side of the DC-DC converter 10 is only applied to both ends of the switching element 40. Hereinafter, the switching element 40 is appropriately referred to as an auxiliary switching element 40.

  The inverter 16 has six switching elements 50, 52, 54, 56, 58 and 60. The six switching elements 50, 52, 54, 56, 58, and 60 constitute a bridge circuit in which three sets of two cascaded connections are connected in parallel to each other. For each of the three sets of switching elements 50, 52, 54, 56, 58, 60 connected in cascade, the connection point between the switching elements 50 and 52, the connection point between the switching elements 54 and 56, and the switching elements 58 and 60 Is connected to each phase of the motor 14.

  The switching elements 20 to 26, 30, 32, 40, and 50 to 60 included in the DC-DC converter 10 and the inverter 16 are, for example, MOS-FETs. Each of the switching elements 20 to 26, 30, 32, 40 included in the DC-DC converter 10 is connected to a microcomputer 62 included in the DC-DC converter 10. The microcomputer 62 performs switching driving of the switching elements 20 to 26, 30, 32, and 40 as appropriate when the motor 14 is driven and when the motor 14 is regenerated. The switching elements 20 to 26, 30, 32, and 40 are respectively switched and driven by commands from the microcomputer 62 when the motor 14 is driven and when the motor is regenerated. Further, the switching elements 50 to 60 are appropriately switched and driven when the motor 14 is driven and when the motor is regenerated.

  The microcomputer 62 and the inverter 16 of the DC-DC converter 10 are connected to an electronic control unit (ECU) 64. The ECU 64 can monitor the states of the DC-DC converter 10, the battery 12, and the inverter 16 (for example, the output voltage of the DC-DC converter 10, that is, the voltage generated between both ends of the capacitor 36). The drive and regeneration of the motor 14 are controlled based on the state. The ECU 64 gives duty commands for the switching elements 20 to 26, 30, and 32 to the microcomputer 62 of the DC-DC converter 10 during driving of the motor 14 and during regeneration of the motor 14, and also switches the switching element to the inverter 16. 50-60 duty commands are performed.

  Hereinafter, with reference to FIGS. 3 to 6, the operation of the system of this embodiment will be described. FIG. 3 shows a flowchart of an example of a control routine executed by the microcomputer 62 during power regeneration in the system of this embodiment. FIG. 4 is a diagram showing a current flow when the inductor 34 is charged with regenerative power energy during power regeneration in the DC-DC converter 10 of the present embodiment. FIG. 5 is a diagram showing a first pattern of a current flow when power energy is transferred from the inductor 34 to the battery 12 side via the transformer 28 during power regeneration in the DC-DC converter 10 of the present embodiment. FIG. 6 is a diagram showing a second pattern of current flow when the power energy is transferred from the inductor 34 to the battery 12 via the transformer 28 during power regeneration in the DC-DC converter 10 of the present embodiment. Show.

  In this embodiment, first, when the motor 14 is driven, that is, when power is supplied from the battery 12 side to the motor 14 side via the DC-DC converter 10 and the inverter 16, the ECU 64 includes the microcomputer 62 of the DC-DC converter 10. On the other hand, a duty command for alternately turning on / off the primary side switching elements 20, 26 and the primary side switching elements 22, 24 is issued. When this duty command is issued, the microcomputer 62 alternately turns on / off the primary side switching elements 20, 26 and the primary side switching elements 22, 24, respectively. When the primary side switching elements 20 to 26 are switched, the DC power of the battery 12 (the voltage is, for example, a DC voltage of 288 volts) is converted into AC power. This AC power is supplied to the primary side of the transformer 28.

  The transformer 28 transforms (steps down) the supplied AC power. When the motor 14 is driven, the ECU 64 instructs the microcomputer 62 to turn on and off the secondary side switching elements 30 and 32 alternately. When this duty command is issued, the microcomputer 62 turns on / off the secondary side switching elements 30 and 32 alternately. When the secondary side switching elements 30 and 32 are switched, the AC power transformed by the transformer 28 is rectified. The rectified power is smoothed by the inductor 34 and the capacitor 36 and output from the DC-DC converter 10. The smoothed DC power (the voltage is a DC voltage of 42 volts or 12 volts, for example) is supplied to the inverter 16. Thus, the DC-DC converter 10 steps down the DC power of the battery 12 and supplies it to the inverter 16.

  The ECU 64 instructs the inverter 16 to turn on / off the switching elements 50 to 60 appropriately. When the switching of the switching elements 50 to 60 is performed, the smoothed DC power supplied from the DC-DC converter 10 is converted into AC power and supplied to the motor 14. The motor 14 is driven to rotate when AC power is supplied from the inverter 16 side. Therefore, the motor 14 can be rotationally driven by reducing the DC power of the battery 12 and supplying it to the motor 14.

  Next, during regeneration of the motor 14, that is, when power regeneration is performed from the motor 14 side to the battery 12 side via the DC-DC converter 10 and the inverter 16 (when affirmative determination is made in step 100), the ECU 64 causes the inverter 16 to On the other hand, a duty command for appropriately turning on / off the switching elements 50 to 60 is given. When the switching of the switching elements 50 to 60 is performed, AC power generated by the motor 14 is converted into DC power. This DC power (voltage is a DC voltage of 42 volts or 12 volts, for example) is first stored in the capacitor 36.

  Further, the ECU 64 instructs the microcomputer 62 of the DC-DC converter 10 to turn on the secondary side switching elements 30, 32, 40 during regeneration of the motor 14. When this command is issued, the microcomputer 62 turns on the secondary side switching elements 30, 32, and 40. When such switching elements 30, 32, and 40 are switched, current flows through the inductor 34 when DC power is obtained by switching of the switching elements 50 to 60 of the inverter 16, and therefore, the inductor 34 from the motor 14 side. Since the regenerative power is accumulated and a current flows through the secondary winding of the transformer 28, the regenerative power from the motor 14 side is transmitted to the secondary winding of the transformer 28.

  Specifically, the microcomputer 62 performs a process of turning on all of the secondary side switching elements 30 and 32 and the auxiliary switching element 40 when accumulating electric power in the inductor 34 in accordance with a command from the ECU 64. When all of the switching elements 30 and 32 and the auxiliary switching element 40 are turned on, current flows from the capacitor 36 or the inverter 16 side to the inductor 34, so that electric power is accumulated in the inductor 34. At this time, the current flowing from the capacitor 36 or the inverter 16 side to the inductor 34 does not flow so much to the secondary side switching elements 30 and 32 side, but mainly flows to the auxiliary switching element 40 side (FIG. 4).

  Further, the microcomputer 62 performs duty driving for alternately turning on / off the secondary-side switching elements 30 and 32 when transmitting power to the transformer 28. When such switching is performed, the power stored in the inductor 34 is transmitted to the secondary side of the transformer 28, and AC power is generated. The transformer 28 transforms (boosts) the generated AC power. The microcomputer 62 performs duty driving for alternately turning on / off the primary side switching elements 20 to 26 during power regeneration. When such switching is performed, the AC power transformed by the transformer 28 is rectified. This rectified electric power (voltage is a DC voltage of 288 volts, for example) is supplied to the battery 12. The DC-DC converter 10 boosts the regenerative power generated by the motor 14 and supplies it to the battery 12. The battery 12 is charged by supplying DC power from the motor 14 side. Therefore, the battery 12 can be charged by boosting the regenerative power of the motor 14 and supplying it to the battery 12.

  The microcomputer 62 turns on all of the secondary side switching elements 30 and 32 and the auxiliary switching element 40 when accumulating power in the inductor 34, and secondary side switching when performing power transmission to the transformer 28. Duty driving for alternately turning on and off the elements 30 and 32 is alternately performed.

  Specifically, first, power is stored in the inductor 34 by turning on all of the secondary side switching elements 30 and 32 and the auxiliary switching element 40 (step 102). After that, one of the secondary side switching elements 30, 32 (for example, the secondary side switching element 30) and the auxiliary switching element 40 are switched from on to off, and the other of the secondary side switching elements 30, 32 (for example, A process of maintaining the secondary side switching element 32) on is executed (step 104). When the secondary side switching element 30 and the auxiliary switching element 40 are switched from on to off while the secondary side switching element 32 is kept on, the inductor 34 passes through the center tap 38 and the secondary winding of the transformer 28. A current flows to the secondary side switching element 32 side (FIG. 5). In this case, the power accumulated in the inductor 34 is transmitted to the secondary side of the transformer 28.

  When current flows through such a path, the microcomputer 62 executes a process of turning off the primary side switching elements 20 and 26 and turning on the primary side switching elements 22 and 24. When such switching is performed, a current flows from the primary side switching element 22 side to the primary side switching element 24 side via the transformer 28, whereby electric power transmitted to the transformer 28 and transformed is supplied to the battery 12. .

  Next, the secondary side switching element 32 is turned on while the secondary side switching element 30 and the auxiliary switching element 40 are turned off to transmit the power accumulated in the inductor 34 to the transformer 28, and then again the inductor 34. When the power is stored in the secondary battery, a process of turning on all of the secondary side switching elements 30 and 32 and the auxiliary switching element 40 is executed (step 106). When all of the switching elements 30 and 32 and the auxiliary switching element 40 are turned on, current flows from the capacitor 36 or the inverter 16 side to the inductor 34, so that electric power is accumulated in the inductor 34. At this time, the current flowing from the capacitor 36 or the inverter 16 side to the inductor 34 does not flow so much to the secondary side switching elements 30 and 32 side, but mainly flows to the auxiliary switching element 40 side (FIG. 4).

  Then, after the power is stored in the inductor 34 by turning on all of the secondary side switching elements 30 and 32 and the auxiliary switching element 40, the other side of the secondary side switching elements 30 and 32 (for example, the secondary side switching elements 30 and 32). Side switching element 32) and auxiliary switching element 40 are switched from on to off, and one of the secondary side switching elements 30, 32 (for example, secondary side switching element 30) is maintained on (step 108). ). When the secondary side switching element 30 and the auxiliary switching element 40 are switched from on to off while the secondary side switching element 30 is kept on, the inductor 34 passes through the center tap 38 and the secondary winding of the transformer 28. Current flows to the secondary switching element 30 side (FIG. 6). In this case, the power accumulated in the inductor 34 is transmitted to the secondary side of the transformer 28.

  When current flows through such a path, the microcomputer 62 executes a process of turning off the primary side switching elements 22 and 24 and turning on the primary side switching elements 20 and 26. When such switching is performed, a current flows from the primary side switching element 26 side to the primary side switching element 20 side via the transformer 28, whereby electric power transmitted to the transformer 28 and transformed is supplied to the battery 12. .

  Thus, according to the present embodiment, power energy charging from the motor 14 side to the inductor 34 and power energy transmission from the inductor 34 to the transformer 28 side are alternately performed by switching of the switching elements 30, 32, and 40. Thus, it is possible to realize power regeneration that supplies power from the motor 14 side to the battery 12 side via the DC-DC converter 10.

  When power is stored in the inductor 34 during such power regeneration, since the auxiliary switching element 40 is turned on and both the secondary side switching elements 30 and 32 are turned on, a current mainly flows through the auxiliary switching element 40. On the other hand, the amount of current flowing through the secondary side switching elements 30 and 32 connected to the secondary winding of the transformer 28 decreases. As described above, the switching element 40 has an on-resistance that is lower than the on-resistance of the secondary-side switching elements 30 and 32. For this reason, when power is stored in the inductor 34 during power regeneration, the current to the secondary switching elements 30 and 32 having high on-resistance is limited, and current is mainly supplied to the auxiliary switching element 40 having low on-resistance. Since it flows, power loss in the switching element can be suppressed.

  Therefore, according to the DC-DC converter 10 of the present embodiment, it is possible to suppress power loss in the switching element during power regeneration while maintaining the transformation function (boost function) during power regeneration. Heat generation in the element can be suppressed, and the efficiency of power conversion can be increased.

  By the way, in said Example, although the battery which supplies electric power to the motor 14 and the battery in which the regenerative electric power which generate | occur | produced in the motor 14 is regenerated as charging electric power are the same batteries 12, they are different batteries. Also good.

  In the above-described embodiment, the H-bridge circuit constituted by the four primary-side switching elements 20 to 26 is used as the primary-side power circuit of the transformer 28 in the DC-DC converter 10. However, the present invention is not limited to this, and a half-bridge circuit including two primary side switching elements may be used.

DESCRIPTION OF SYMBOLS 10 DC-DC converter 12 Battery 14 Motor 16 Inverter 20-26, 30, 32, 40, 50-60 Switching element 28 Transformer 34 Inductor 36 Capacitor 38 Center tap 62 Microcomputer (microcomputer)
64 Electronic control unit (ECU)

Claims (4)

Connected to both ends of the transformer, the secondary winding of the transformer, and connected to the center tap of the secondary winding of the transformer. A DC-DC converter comprising: an inductor that stores the regenerative power during power regeneration;
A DC-DC converter, comprising: an auxiliary switching element connected to one end of the center tap and the inductor and conducted when accumulating regenerative power in the inductor.   2. The DC-DC converter according to claim 1, wherein the auxiliary switching element has an on-resistance lower than an on-resistance of the two secondary side switching elements.   3. The DC-DC converter according to claim 1, wherein the auxiliary switching element is cut off when regenerative power stored in the inductor is transmitted to a primary side of the transformer through the transformer. 4. .   4. The two secondary side switching elements are alternately conducted so as to transmit the regenerative power stored in the inductor to the primary side of the transformer via the transformer. A DC-DC converter according to claim 1.

Images