JP2016131464A - DCDC converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DCDC converter capable of reducing transformer core loss during low current flowing and reducing thermal loss during high current flowing.SOLUTION: A transformer 20 includes a conversion part 30, a rectification part 40 and a smoothing coil 50. When high current higher than a threshold is flowing, operation is performed in a continuous mode by increasing an inductance value of the smoothing coil 50. When low current lower than a threshold is flowing, operation is performed in a discontinuous mode by decreasing an inductance value of the smoothing coil 50.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a DCDC converter.

  It is known that the transformer core loss depends on the ET product in a DCDC converter having a transformer (see, for example, Patent Document 1).

JP 2010-226905 A

  In an in-vehicle DCDC converter, it is desired to reduce the loss in the low current region in order to improve the vehicle mode fuel efficiency. However, the transformer core loss is large in the low current region, and there is a problem of heat loss in the high current region.

  An object of the present invention is to provide a DCDC converter capable of reducing transformer core loss at a low current and reducing heat loss at a high current.

  In the first aspect of the present invention, a transformer having a primary winding and a secondary winding, a converter connected to the primary winding of the transformer and converting direct current to alternating current, and a secondary winding of the transformer A DCDC converter comprising a connected rectifying unit and a smoothing coil connected to the secondary winding of the transformer, wherein the inductance value of the smoothing coil is increased at a high current higher than a threshold value to increase the continuous mode. The gist is to operate in the discontinuous mode by reducing the inductance value of the smoothing coil when the current is lower than the threshold and the current is lower.

  According to the first aspect of the present invention, when the current is higher than the threshold value, the inductance value of the smoothing coil is increased to operate in the continuous mode, thereby reducing the heat loss at the time of the high current. Further, when the current is lower than the threshold value, it is possible to operate in the discontinuous mode by reducing the inductance value of the smoothing coil, thereby reducing the ET product. Therefore, the transformer core loss can be reduced at a low current, and the heat loss can be reduced at a high current.

As described in claim 2, in the DCDC converter according to claim 1, when the current is low, the duty of the switching element of the conversion unit may be reduced.
The DCDC converter according to claim 1 or 2, wherein the smoothing coil includes a first coil and a second coil, a switch that is turned on at a low current, and the second DC / DC converter. A series circuit with the coil may be connected in parallel with the first coil.

  As described in claim 4, in the DCDC converter according to any one of claims 1 to 3, it may be an in-vehicle DCDC converter for a hybrid vehicle.

  According to the present invention, the transformer core loss can be reduced at a low current, and the heat loss can be reduced at a high current.

The block diagram of the vehicle equipment in embodiment. The circuit block diagram of the DCDC converter in embodiment. It is a time chart for demonstrating the effect | action of embodiment, (a) shows the state of a main switching element, (b) shows the state of an auxiliary switching element, (c) shows the state of a switch, (d ) Shows the transition of the coil current. It is a time chart for demonstrating the effect | action of embodiment, (a) shows the state of a main switching element, (b) shows the state of an auxiliary switching element, (c) shows the state of a switch, (d ) Shows the transition of the coil current, and (e) shows the transition of the transformer applied voltage. (A) is explanatory drawing for demonstrating the relationship between the coil current in embodiment, and the inductance value of a smooth coil, (b) is explanatory drawing which shows the relationship between a coil current and efficiency. It is a time chart for demonstrating a comparative example, (a) shows the state of a main switching element, (b) shows the state of an auxiliary switching element, (c) shows transition of coil current. It is a time chart for demonstrating a comparative example, (a) shows the state of a main switching element, (b) shows the state of an auxiliary switching element, (c) shows transition of a coil current, (d) Indicates the transition of the voltage applied to the transformer.

  As shown in FIG. 1, the hybrid vehicle includes a 300V high-voltage battery 10 as a DC power source, an inverter 11, a travel motor 12, a DCDC converter 13, a plurality of auxiliary machines 14, and a 12V low-voltage battery 15. , Is installed. A traveling motor 12 is connected to the high voltage battery 10 via an inverter 11, and direct current power of the high voltage battery 10 is converted into alternating current by the inverter 11 and supplied to the traveling motor 12. The traveling motor 12 is driven by the supply of alternating current power to rotate the wheels for traveling.

  A DCDC converter 13 is connected to the high-voltage battery 10. The DCDC converter 13 inputs 300 V power of the high-voltage battery 10, steps down to 12 V, and outputs it. Each auxiliary machine 14 and a 12V low voltage battery 15 are connected to the output side of the DCDC converter 13. Each auxiliary machine 14 can be driven by supplying 12V power from the DCDC converter 13. The low voltage battery 15 is charged by supplying 12V power from the DCDC converter 13.

In the hybrid vehicle, an engine is mounted as a power source in addition to the travel motor and the battery.
FIG. 2 shows the configuration of a DCDC converter 13 that is an in-vehicle DCDC converter for a hybrid vehicle.

As shown in FIG. 2, the DCDC converter 13 is an active clamp type DCDC converter (active clamp forward converter).
The DCDC converter 13 includes a transformer 20, a converter 30, a rectifier 40, a smoothing coil 50, a capacitor 60, a current sensor 70, a switch 80, and control circuits 90 and 91. The conversion unit 30 includes a main switching element 31, a clamp capacitor 32, and an auxiliary switching element 33. The rectifying unit 40 has two diodes 41 and 42. The smoothing coil 50 has two coils (choke coils) 51 and 52, and the coil 52 is a low current coil. A smoothing circuit is configured by the smoothing coil 50 and the capacitor 60.

The transformer 20 has a primary winding 21 and a secondary winding 22.
The converter 30 is connected to the primary winding 21 of the transformer 20 and converts direct current into alternating current. The main switching element 31 in the conversion unit 30 is connected in series to the primary winding 21 of the transformer 20, and is connected in parallel to the high voltage battery 10 together with the primary winding 21. The clamp capacitor 32 is a reset capacitor. The auxiliary switching element 33 is connected in series to the clamp capacitor 32, and is connected in parallel to the primary winding 21 together with the clamp capacitor 32. An active clamp circuit is configured by a series circuit of the auxiliary switching element 33 and the clamp capacitor 32.

  The main switching element 31 and the auxiliary switching element 33 use MOSFETs. The main switching element 31 and the auxiliary switching element 33 may use IGBTs having diodes connected in parallel instead of MOSFETs.

The control circuit 90 detects the DC voltage Vout output from the smoothing circuit (coils 51 and 52, capacitor 60).
The rectifying unit 40 is connected to the secondary winding 22 of the transformer 20. The rectification unit 40 turns alternating current into direct current. The first diode 41 in the rectifying unit 40 has an anode connected to the ground on the secondary winding 22 side of the transformer 20 and a cathode connected to one end of the secondary winding 22 of the transformer 20. The second diode 42 has an anode connected to the anode of the first diode 41 and a cathode connected to the other end of the secondary winding 22 of the transformer 20.

  The smoothing coil 50 is connected to the secondary winding 22 of the transformer 20. The capacitor 60 constituting the smoothing circuit is connected in parallel to the diode 42. The first coil 51 constituting the smoothing coil 50 is provided between the secondary winding 22 of the transformer 20 and the capacitor 60. A switch 80 is connected in series to the second coil 52. This series circuit is connected in parallel to the first coil 51. The switch 80 is opened / closed, that is, turned on / off by the control circuit 91.

  The switch 80 is turned on when the current is low. As described above, the smoothing coil 50 includes the first coil 51 and the second coil 52, and the series circuit of the switch 80 and the second coil 52 that is turned on when the current is low is in parallel with the first coil 51. It is connected to the.

  Regarding the inductance value of the first coil 51 and the inductance value of the second coil 52, for example, the inductance value of the first coil 51 is large and the inductance value of the second coil 52 is small. In this case, as the second coil 52 and the switch 80, those having a small current capacity can be used.

The switch 80 may be configured with a relay or a switching element.
The current sensor 70 detects a coil current flowing through the smoothing coil 50. That is, the current i1 flowing through the first coil 51 is detected when the switch 80 is turned off, and the sum of the current i1 flowing through the first coil 51 and the current i2 flowing through the second coil 52 is detected when the switch 80 is turned on. . The detection result is sent to the control circuits 90 and 91. Therefore, the control circuit 90 and the control circuit 91 can detect the coil current flowing through the smoothing coil 50.

  The control circuit 90 controls the main switching element 31 and the auxiliary switching element 33. At this time, the control circuit 90 turns off the auxiliary switching element 33 when the main switching element 31 is turned on, and turns on the auxiliary switching element 33 when the main switching element 31 is turned off. That is, when the DCDC converter 13 is operated, the main switching element 31 and the auxiliary switching element 33 are alternately turned on / off to supply the power of the high-voltage battery 10 to the transformer 20, and both the switching elements 31, 33 are connected to the primary winding 21. Are complementarily turned on / off in synchronism with the change in the direction of the current flowing through them.

  At this time, the control circuit 90 keeps the DC voltage Vout output from the smoothing circuit (coils 51, 52, capacitor 60) constant by controlling the duty of the drive signal of the main switching element 31.

  In the active clamp type DCDC converter 13, when the main switching element 31 is turned on, an exciting current flows from the high voltage battery 10 to the primary winding 21 of the transformer 20, and a current flows through the diode 41 due to the electromotive force generated in the transformer 20. The current flowing in the diode 41 is loaded as DC power through the rectifying unit 40 including the diodes 41 and 42, the smoothing coil 50 (coils 51 and 52), and the smoothing circuit including the capacitor 60 (auxiliary machine 14 in FIG. 1). Output to the side. When the main switching element 31 is turned off, a current flows through the diode 42 by the electromotive force generated in the smoothing coil 50 (coils 51 and 52). Then, the current flowing through the diode 42 is output to the load (such as the auxiliary machine 14 in FIG. 1) as DC power through a smoothing circuit including the smoothing coil 50 (coils 51 and 52) and the capacitor 60.

As described above, the main switching element 31 is repeatedly turned on and off, whereby a constant DC voltage is output from the high voltage battery 10 via the transformer 20.
Further, in the DCDC converter 13, when the main switching element 31 is turned off from on, the exciting current flowing in the primary winding 21 of the transformer 20 flows to the clamp capacitor 32 through the parasitic diode of the auxiliary switching element (MOSFET) 33 and is clamped. The capacitor 32 is charged, and the excitation current flowing through the primary winding 21 of the transformer 20 decreases. Thereafter, when the auxiliary switching element 33 is turned on, the energy accumulated in the clamp capacitor 32 is released to the primary winding 21 of the transformer 20 and the exciting current is further reduced, and the magnetization of the transformer 20 is reset. As described above, in the active clamp type DCDC converter 13, the magnetization of the transformer 20 is reset by the active clamp circuit including the auxiliary switching element 33 and the clamp capacitor 32.

  Further, in the active clamp type DCDC converter 13, since the auxiliary switching element 33 is turned on when the main switching element 31 is turned off and the exciting current flows through the parasitic diode of the auxiliary switching element 33, the auxiliary switching element 33 is turned on. It is possible to reduce the loss that occurs during the process.

Next, the operation of the DCDC converter 13 will be described.
3A, 3B, 3C, and 3D show a high current, for example, a full power at which 100A is passed. At this time, a coil current higher than a threshold value isth (for example, 20 A) flows. When the coil current is higher than the threshold value isth, the switch 80 is in the off state. As a result, the inductance value of the smoothing coil 50 is large at the time of full power in FIG. 3 (see FIG. 5A). This operates in continuous mode.

  That is, at the time of full power, as shown in FIGS. 3A and 3B, the control circuit 90 alternately turns on and off the main switching element 31 and the auxiliary switching element 33, and the circuit shown in FIG. As shown, it operates in continuous mode. The control circuit 91 turns off the switch 80, and in the continuous mode, the current continues to flow through the coil 51 and operates without the current becoming zero.

  4 (a), (b), (c), (d), and (e) show a time when a current lower than a threshold, for example, 10 A is passed. At this time, a coil current smaller than a threshold value isth (for example, 20 A) flows. The control circuit 91 turns on the switch 80 when the coil current is smaller than the threshold value ith. Thereby, the inductance value of the smoothing coil 50 becomes a small value at the time of the low electric current of FIG. 4 (refer FIG. 5A). This operates in discontinuous mode. Further, the control circuit 90 reduces the duty by reducing the duty of the switching elements 31 and 33 when the coil current is a low current smaller than the threshold value ith. This is useful for discontinuous mode.

  At low current, as shown in FIGS. 4A and 4B, the control circuit 90 alternately turns on and off the main switching element 31 and the auxiliary switching element 33, as shown in FIG. 4D. In discontinuous mode. The control circuit 91 turns on the switch 80, and in the discontinuous mode (intermittent operation mode), a current intermittently flows through the coils 51 and 52, and a period in which the current becomes zero occurs. In this case, the ET product becomes small as shown in FIG.

  6 (a), 6 (b), and 6 (c) are comparative examples, in which one smoothing coil is provided in FIG. 2, and the inductance value of the smoothing coil is a small value. That is, the inductance value of one smoothing coil is small. FIGS. 6A, 6B, and 6C show a high current, for example, a full power that flows 100A.

  As shown in FIGS. 6A and 6B, the main switching element 31 and the auxiliary switching element 33 are alternately turned on / off to operate in a continuous mode as shown in FIG. Since the value is small, the fluctuation of the coil current is larger than that in FIG. This increases heat loss at high current. That is, the coil current largely fluctuates, and the loss proportional to the square of the current increases.

  FIG. 7 is a comparative example in which one smoothing coil is provided in FIG. 2, and the inductance value of the smoothing coil is a large value. That is, the inductance value of one smoothing coil is large. FIGS. 7A, 7B, 7C, and 7D show a time when a current is low, for example, when 10 A is passed.

  As shown in FIGS. 7A and 7B, the main switching element 31 and the auxiliary switching element 33 are alternately turned on / off to reduce the duty of the main switching element 31 as shown in FIG. 7C. However, since the inductance value is large, it operates in a continuous mode. Therefore, the ET product is larger than that in FIG. 4E, and the transformer core loss is increased.

  Compared with the comparative example described in FIGS. 6 and 7, in the present embodiment described in FIGS. 3 and 4, the inductance value of the smoothing coil 50 is increased at the time of high current higher than the threshold value, and the continuous mode is operated. When the current is lower than the threshold value, the inductance value of the smoothing coil 50 is reduced to operate in the discontinuous mode. Thereby, the transformer core loss is reduced at the time of low current, and the heat loss is reduced at the time of high current. That is, the inductance value of the smoothing coil 50 is switched between a low current and a high current. Thereby, an ET product can be made small and a transformer core loss is reduced.

As a result, as shown in FIG. 5B, the efficiency can be improved at a low current as compared with the comparative example in which the inductance value remains large.
According to the above embodiment, the following effects can be obtained.

  (1) As a configuration of the DCDC converter, when the current is higher than the threshold value, the inductance value of the smoothing coil 50 is increased to operate in a continuous mode, and when the current is lower than the threshold value, the inductance value of the smoothing coil 50 is decreased to reduce the inductance value. Operates in continuous mode. Thereby, the transformer core loss can be reduced at a low current, and the heat loss can be reduced at a high current.

explain in detail.
In an in-vehicle DCDC converter, it is desired to reduce the loss in the low current region in order to improve the vehicle mode fuel efficiency, but the transformer core loss is large in the low current region. Therefore, it is desired to reduce the transformer core loss, but the transformer core loss depends on the ET product, so that the operation is discontinuous. For this purpose, it is effective to reduce the inductance value of the output choke coil. However, if the inductance value of the choke coil is simply reduced, the loss increases at full power (for example, at 100 A output) due to the increase in ripple current as shown in FIG.

  On the other hand, in the present embodiment, when the current is higher than the threshold value, the inductance value of the smoothing coil 50 is increased to operate in the continuous mode, thereby reducing the heat loss at the time of the high current. Further, when the current is lower than the threshold value, it is possible to operate in the discontinuous mode by reducing the inductance value of the smoothing coil 50, thereby reducing the ET product. Therefore, the transformer core loss can be reduced at a low current, and the heat loss can be reduced at a high current.

(2) When the current is low, the duty of the switching elements 31 and 33 of the conversion unit 30 is reduced. Therefore, it is useful for setting the discontinuous mode.
(3) The smoothing coil 50 has a first coil 51 and a second coil 52, and a series circuit of the switch 80 and the second coil 52 that is turned on at a low current is in parallel with the first coil 51. It is connected. Thus, by providing the switch 80 on the coil 52 side where the inductance value is small and the frequency of use is small, the switch is turned on only at a low current, and the coil and the switch can be small. That is, the usage frequency of the switch 80 can be reduced at low currents where the usage frequency is low.

  (4) Since this is an in-vehicle DCDC converter for a hybrid vehicle, it is necessary to reduce the loss in the low current region when the output is low, that is, in order to improve the vehicle mode fuel efficiency in the hybrid vehicle. Vehicle mode fuel efficiency can be improved.

The embodiment is not limited to the above, and may be embodied as follows, for example.
-It is not restricted to the vehicle-mounted DCDC converter for hybrid vehicles.
The DCDC converter may be other than an active clamp type DCDC converter (active clamp forward converter). For example, a normal forward type may be used.

  The configuration for changing the inductance value of the smoothing coil may be a configuration other than connecting the series circuit of the switch 80 and the coil 52 to the coil 51 in parallel. For example, the first coil and the second coil may be connected in series, and the switch may be connected in parallel to one of the coils.

  DESCRIPTION OF SYMBOLS 13 ... DCDC converter, 20 ... Transformer, 21 ... Primary winding, 22 ... Secondary winding, 30 ... Conversion part, 40 ... Rectification part, 50 ... Smoothing coil, 51 ... 1st coil, 52 ... 2nd coil .

Claims (4)

A transformer having a primary winding and a secondary winding;
A converter that is connected to the primary winding of the transformer and converts direct current to alternating current;
A rectifier connected to the secondary winding of the transformer;
A smoothing coil connected to the secondary winding of the transformer;
A DC-DC converter comprising:
When the current is higher than a threshold value, the smoothing coil is increased in inductance value to operate in continuous mode, and when the current is lower than the threshold value, the smoothing coil is decreased in inductance value to operate in discontinuous mode. DCDC converter to do.   The DCDC converter according to claim 1, wherein the duty of the switching element of the conversion unit is reduced when the current is low. The smoothing coil has a first coil and a second coil,
3. The DCDC converter according to claim 1, wherein a series circuit of a switch that is turned on at a low current and the second coil is connected in parallel with the first coil.   The DCDC converter according to any one of claims 1 to 3, wherein the DCDC converter is a vehicle-mounted DCDC converter for a hybrid vehicle.