JP2021083185A - Insulation type dc-dc converter - Google Patents

Abstract

To provide an insulation type DC-DC converter capable of easily stabilizing an output even if a dead time is changed.SOLUTION: An insulation type DC-DC converter 100 includes: a transformer 10; a full-bridge type switching circuit 20; a control unit 40; an inductor 13; and an output circuit 30. The control unit 40 adjusts a dead time that is a time between an ON period of a first switch element 20A and an ON period of a second switch element 20B and a time between an ON period of a third switch element 20C and an ON period of a fourth switch element 20D. The larger the dead time becomes, the larger a phase difference between a first arm A1 and a second arm A2 is increased. The smaller the dead time becomes, the smaller the phase difference is decreased.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an isolated DCDC converter.

Patent Document 1 discloses a phase-shift type full-bridge type DCDC converter. This type of DCDC converter aims to reduce switching loss by performing ZVS (Zero Voltage Switching) control. Further, the DCDC converter disclosed in Patent Document 1 dynamically changes the dead time in order to suppress a decrease in power conversion efficiency due to a change in the resonance waveform based on a change in input / output.

Japanese Unexamined Patent Publication No. 2016-11805

In the phase shift type full bridge type DCDC converter, when the dead time is dynamically changed as in Patent Document 1, the magnitude of the output current can be changed according to the change in the dead time. However, if the dead time is changed while keeping the phase difference between the two arms constituting the full bridge constant, the length of the transmission period will change, which will increase the magnitude of the output voltage on the secondary side. It may fluctuate.

Therefore, the present disclosure provides a technique for easily stabilizing the output even if the dead time is changed, with respect to the phase shift type isolated DCDC converter capable of changing the dead time.

The isolated DCDC converter of the present disclosure is
A transformer with a primary coil and a secondary coil,
A full-bridge type switching circuit including a first switch element, a second switch element, a third switch element, and a fourth switch element, and
A control unit that controls the operation of the switching circuit,
With an inductor
The output circuit connected to the secondary coil and
With
The first switch element and the second switch element are connected in series between the first conductive path and the second conductive path to form a first arm.
The third switch element and the fourth switch element are connected in series between the first conductive path and the second conductive path to form a second arm.
One end of the inductor is electrically connected to a first connection point between the first switch element and the second switch element.
The other end of the inductor is electrically connected to one end of the primary coil.
The other end of the primary coil is a phase-shift type isolated DCDC converter electrically connected to a second connection point between the third switch element and the fourth switch element.
In the control unit, the time between the on period of the first switch element and the on period of the second switch element and the time between the on period of the third switch element and the on period of the fourth switch element. The dead time is adjusted so that the larger the dead time is, the larger the phase difference between the first arm and the second arm is, and the smaller the dead time is, the smaller the phase difference is.

According to the present disclosure, it is possible to realize an isolated DCDC converter that can easily stabilize the output even if the dead time is changed.

FIG. 1 is a circuit diagram showing an isolated DCDC converter according to the first embodiment. FIG. 2 is a timing chart showing the timing of switching each of the first switch element, the second switch element, the third switch element, and the fourth switch element on and off in the isolated DCDC converter of the first embodiment. .. FIG. 3 is a circuit diagram showing a path of current flowing to the primary side and the secondary side of the transformer when the second switch element and the third switch element are in the ON state in the isolated DCDC converter of the first embodiment. FIG. 4 shows the primary side of the transformer in the isolated DCDC converter of the first embodiment when the second switch element is in the on state and the first switch element, the third switch element, and the fourth switch element are in the off state. It is a circuit diagram which shows the path of the flowing current. FIG. 5 is a circuit diagram showing a path of current flowing to the primary side and the secondary side of the transformer when the first switch element and the fourth switch element are in the ON state in the isolated DCDC converter of the first embodiment. FIG. 6 shows the primary side of the transformer in the isolated DCDC converter of the first embodiment when the first switch element is in the on state and the second switch element, the third switch element, and the fourth switch element are in the off state. It is a circuit diagram which shows the path of the flowing current. FIG. 7 shows an enlarged view of the timing chart between time T1 and time T2 in FIG. 2 on the upper side, and is applied between the drain and the source of the fourth switch element between time T1 and time T2. The graph showing the change in voltage is shown at the bottom. FIG. 8 is a flowchart showing the control in which the control unit calculates the dead time and the phase difference in the isolated DCDC converter of the first embodiment. FIG. 9 is an example of a data table in which a dead time is associated with a voltage value detected by the first voltage detection unit and a current value detected by the second current detection unit.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.
(1) The isolated DCDC converter of the present disclosure includes a transformer, a full-bridge type switching circuit, a control unit, an inductor, and an output circuit. The transformer has a primary coil and a secondary coil. The full bridge type switching circuit includes a first switch element, a second switch element, a third switch element, and a fourth switch element. The control unit controls the operation of the switching circuit. The output circuit is connected to the secondary coil. The first switch element and the second switch element are connected in series between the first conductive path and the second conductive path to form the first arm. A third switch element and a fourth switch element are connected in series between the first conductive path and the second conductive path to form a second arm. One end of the inductor is electrically connected to the first connection point between the first switch element and the second switch element. The other end of the inductor is electrically connected to one end of the primary coil. The other end of the primary coil is electrically connected to a second connection point between the third switch element and the fourth switch element. The control unit sets a dead time, which is the time between the on period of the first switch element and the on period of the second switch element, and the time between the on period of the third switch element and the on period of the fourth switch element. adjust. The control unit increases the phase difference between the first arm and the second arm as the dead time increases. The control unit reduces the phase difference as the dead time decreases.

Therefore, this isolated DCDC converter can change the phase difference according to the change in the dead time, thereby suppressing the change in the transmission period and suppressing the fluctuation of the output voltage.

In the present disclosure, "electrically connected" is preferably configured to be connected in a state of being electrically connected to each other (a state in which a current can flow) so that both potentials of the connection target are equal. However, the configuration is not limited to this. For example, "electrically connected" may be a configuration in which both connection targets are connected in a state in which both connection targets can be electrically connected while electrical components are interposed between the two connection targets.

(2) The isolated DCDC converter of the first disclosure includes at least one of a voltage detection unit and a current detection unit. The voltage detection unit detects at least one of the input voltage applied between the first conductive path and the second conductive path or the output voltage output from the output circuit. The current detector detects at least one of the input current flowing through the switching circuit and the output current flowing through the output circuit. The control unit may determine the dead time based on at least one of the voltage value and the current value.
According to this configuration, the dead time can be determined according to the operation status of the switching circuit.

(3) The control unit of the isolated DCDC converter of the second disclosure is a first calculation unit that calculates a first value that is a candidate for a dead time based on at least one of a voltage value and a current value, and a first calculation unit. A second calculation unit that calculates a second value that is a candidate for a phase difference based on the first value calculated by the unit may be provided. The control unit determines the dead time based on the first value when the second value calculated by the second calculation unit is less than the threshold value, and when the second value is equal to or more than the threshold value, the first calculation unit determines the dead time. The first value can be calculated again.
According to this configuration, the change in the transmission period can be suppressed and the fluctuation of the output voltage can be suppressed by recalculating the dead time and changing the dead time.

(4) The control unit of the isolated DCDC converter of the second disclosure is a first calculation unit that calculates a first value that is a candidate for a dead time based on at least one of a voltage value and a current value, and a first calculation unit. A second calculation unit that calculates a second value that is a candidate for a phase difference based on the first value calculated by the unit may be provided. When the second value calculated by the second calculation unit is less than the threshold value, the dead time is determined based on the first value, and when the second value is equal to or more than the threshold value, the dead time is set to a predetermined fixed value. Can be.
According to this configuration, the dead time is not recalculated, so that the control in the control unit can be simplified.

(5) The control unit of the third or fourth disclosed insulated DCDC converter performs on / off operation of each of the first switch element, the second switch element, the third switch element, and the fourth switch element at a predetermined cycle. The threshold can be half the time of the cycle.
According to this configuration, it is possible to suppress a change in the transmission period while maintaining the operation of the switching circuit as either a step-up operation or a step-down operation.
[Details of Embodiments of the present disclosure]

<Embodiment 1>
[Overview of isolated DCDC converter]

The isolated DCDC converter 100 of the first embodiment (hereinafter, also simply referred to as a converter 100) generates electric power for driving an electric drive device (motor or the like) in a vehicle such as a hybrid vehicle or an electric vehicle (EV (Electric Vehicle)). It is used as an output power source. The converter 100 transforms the input voltage Vin given between the first conductive path 1 and the second conductive path 2 to generate an output voltage Vout, which is between the third conductive path 3 and the fourth conductive path 4. Apply to. As shown in FIG. 1, the converter 100 includes a transformer 10, a switching circuit 20 provided between the first conductive path 1 and the transformer 10, and an output circuit connected between the transformer 10 and the third conductive path 3. 30 and a control unit 40 for controlling the operation of the switching circuit 20 are provided. In actual use, a DC power supply (not shown) is connected between the first conductive path 1 and the second conductive path 2, and a load is applied between the third conductive path 3 and the fourth conductive path 4. 6 is connected. Further, an input capacitor 7 for stabilizing the input voltage Vin is connected between the first conductive path 1 and the second conductive path 2.

The transformer 10 includes a primary coil 11 and secondary coils 12A and 12B. The number of turns of the primary coil 11 is N1. The number of turns of the secondary coil 12A and 12B is N2. The secondary coils 12A and 12B are electrically connected in series with each other at the third connection point P3. The turns ratio N of the transformer 10 is represented by N2 / N1. An exciting inductance is formed in the transformer 10 in parallel with the primary coil 11 (not shown). The exciting inductance is a parasitic component of the transformer 10.

The switching circuit 20 converts the input voltage Vin, which is a DC voltage given to the first conductive path 1 and the second conductive path 2, into alternating current and supplies it to the primary coil 11 of the transformer 10. The switching circuit 20 has a configuration in which the first switch element 20A, the second switch element 20B, the third switch element 20C, and the fourth switch element 20D (hereinafter, also referred to as switch elements 20A, 20B, 20C, 20D) are fully bridge-connected. Has.

The switching circuit 20 includes switch elements 20A, 20B, 20C, 20D, and an inductor 13. Although various switch elements can be used for the switch elements 20A, 20B, 20C, and 20D, it is preferable to use a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

Each of the switch elements 20A, 20B, 20C, and 20D is provided with parasitic diodes 20G, 20H, 20J, and 20K, which are parasitic components. Specifically, in each of the switch elements 20A, 20B, 20C, and 20D, the cathodes of the parasitic diodes 20G, 20H, 20J, and 20K are electrically connected to the drain side, and the anode is electrically connected to the source side. .. In addition to the parasitic diodes 20G, 20H, 20J, and 20K, a diode may be added as a separate element.

Parasitic capacitors, which are parasitic components, are electrically connected in parallel to each of the switch elements 20A, 20B, 20C, and 20D (not shown). Specifically, one terminal of each parasitic capacitor is electrically connected to the drain of each of the switch elements 20A, 20B, 20C, and 20D, and the other terminal of each parasitic capacitor is electrically connected to the source. .. In addition to the parasitic capacitor, a capacitor may be added as a separate element.

The first switch element 20A and the second switch element 20B are connected in series between the first conductive path 1 and the second conductive path 2 that input an input voltage to the switching circuit 20, and are connected to each other at the first connection point P1. It is electrically connected. The third switch element 20C and the fourth switch element 20D are connected in series between the first conductive path 1 and the second conductive path 2, and are electrically connected to each other at the second connection point P2. In the switching circuit 20, the first arm A1 is composed of the first switch element 20A and the second switch element 20B, and the second arm A2 is composed of the third switch element 20C and the fourth switch element 20D.

One end of the inductor 13 is electrically connected to the first connection point P1. The other end of the inductor 13 is electrically connected to one end of the primary coil 11 of the transformer 10. The second connection point P2 is electrically connected to the other end of the primary coil 11. The inductor 13 is provided for the purpose of LC resonance with a parasitic capacitor in order to reduce the switching loss generated in the switching circuit 20.

The output circuit 30 rectifies and smoothes the AC voltage appearing in the secondary coils 12A and 12B of the transformer 10 to generate an output voltage Vout which is a DC voltage, and uses this output voltage Vout as the third conductive path 3 and the fourth conductive path 3. It is applied between the road 4 and the road 4. The output circuit 30 includes a fifth switch element 30A, a sixth switch element 30B, a rectified output path 30C, a choke coil 33, and an output capacitor 34. The fifth switch element 30A is connected between one end of the secondary coil 12A of the transformer 10 and the ground path G. The sixth switch element 30B is connected between one end of the secondary coil 12B of the transformer 10 and the ground path G.

One end of the rectified output path 30C is electrically connected to a third connection point P3 where the other end of the secondary coil 12A and the other end of the secondary coil 12B are electrically connected. One end of the choke coil 33 is electrically connected to the other end of the rectified output path 30C. The other end of the choke coil 33 (that is, the end on the side away from the third connection point P3 side) is electrically connected to the third conductive path 3 and electrically connected to the fourth conductive path 4 via the output capacitor 34. Is connected. That is, the choke coil 33 is interposed between the third connection point P3 and the third conductive path 3. The output capacitor 34 is electrically connected between the third conductive path 3 and the fourth conductive path 4. The fourth conductive path 4 is electrically connected to the ground path G.

Although various switch elements can be used for the fifth switch element 30A and the sixth switch element 30B, it is preferable to use MOSFETs. The drain of the fifth switch element 30A is electrically connected to one end of the secondary coil 12A, and the source is electrically connected to the ground path G. The drain of the sixth switch element 30B is electrically connected to one end of the secondary coil 12B, and the source is electrically connected to the ground path G. Each of the fifth switch element 30A and the sixth switch element 30B is provided with a parasitic diode which is a parasitic component. Specifically, in each of the fifth switch element 30A and the sixth switch element 30B, the cathode of the parasitic diode is electrically connected to the drain side and the anode is electrically connected to the source side.

Among the output circuits 30 having such a configuration, the fifth switch element 30A and the sixth switch element 30B form a rectifier circuit that rectifies the AC voltage appearing in the secondary coil 12A and 12B of the transformer 10. The choke coil 33 and the output capacitor 34 smooth the rectified output appearing in the rectified output path 30C.

The control unit 40 is mainly composed of, for example, a microcomputer, a computing device such as a CPU (Central Processing Unit), a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and an A / D converter. Etc. The control unit 40 has a configuration in which the potential difference between the first conductive path 1 and the second conductive path 2 can be grasped as a voltage value by the first voltage detecting unit 40A. The control unit 40 is configured so that the second voltage detection unit 40B can grasp the potential difference between the third conductive path 3 and the fourth conductive path 4 as a voltage value. The second voltage detection unit 40B detects the voltage value of the output voltage output from the output circuit 30. The first voltage detection unit 40A and the second voltage detection unit 40B constitute a voltage detection unit 40G. That is, the voltage detection unit 40G detects the voltage value of the input voltage applied between the first conductive path 1 and the second conductive path 2 and the output voltage output from the output circuit 30. The first voltage detection unit 40A and the second voltage detection unit 40B are configured as a voltage detection circuit.

The control unit 40 is configured so that the first current detection unit 40C can grasp the current value flowing through the first conductive path 1. That is, the first current detection unit 40C detects the current value of the input current flowing through the switching circuit 20. The control unit 40 is configured so that the second current detection unit 40D can grasp the current value flowing through the third conductive path 3. The second current detection unit 40D detects the current value of the output current flowing through the output circuit 30. The first current detection unit 40C and the second current detection unit 40D constitute the current detection unit 40H. The current detection unit 40H detects the current values of the input current flowing through the switching circuit 20 and the output current flowing through the output circuit 30. The first current detection unit 40C and the second current detection unit 40D are configured as a current detection circuit using, for example, a current transformer or a shunt resistor.

The control unit 40 uses a phase shift method based on the values input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D, and the switch elements 20A and 20B. , 20C, 20D, and output a PWM signal toward each gate. The control unit 40 causes each of the switch elements 20A, 20B, 20C, and 20D to perform on / off operations at a predetermined cycle. As a result, the switch elements 20A, 20B, 20C, and 20D perform switching operations by the phase shift method. The control unit 40 is the fifth switch element 30A and the sixth switch based on the values input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D. A switching signal at a predetermined timing can be output toward each gate of the element 30B.

The control unit 40 has a first calculation unit 40E and a second calculation unit 40F. The first calculation unit 40E is dead based on at least one of the voltage value and the current value input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D. The first value that is a candidate for time can be calculated. The dead time is the time between the on period of the first switch element 20A and the on period of the second switch element 20B, and the time between the on period of the third switch element 20C and the on period of the fourth switch element 20D. is there. That is, the control unit 40 determines the dead time based on at least one of the voltage value and the current value.

The second calculation unit 40F is a candidate for a phase difference (hereinafter, also simply referred to as a phase difference) between the first arm A1 and the second arm A2 based on the first value calculated by the first calculation unit 40E. Two values can be calculated. The phase difference in the first embodiment is the time between the turn-on time of the first switch element 20A and the turn-on time of the third switch element 20C. The control unit 40 can set the dead time and the phase difference based on the calculated first value and the second value, and the first calculation unit 40E can calculate the first value again.

[Operation of isolated DCDC converter]
Next, the operation of the converter 100 will be described with reference to FIGS. 2 to 6 and the like. In a vehicle equipped with the converter 100, for example, the ignition switch is switched from an off state to an on state. Then, the control unit 40 outputs a PWM signal to each of the switch elements 20A, 20B, 20C, and 20D, and outputs a switching signal at a predetermined timing to each of the fifth switch element 30A and the sixth switch element 30B.

The converter 100 performs a switching operation by a phase shift method in which the first arm A1 and the second arm A2 operate in a phase shift system in which the turn-on and turn-off timings of the switch elements constituting the first arm A1 and the second arm A2 are shifted by a predetermined phase from each other. In the phase shift method, the switch element of one of the first arm A1 and the second arm A2 turns on and off first, and the other arm turns on after a predetermined time (phase difference) delay with respect to this arm. And turn off.

Specifically, the converter 100 is used between the first switch element 20A and the third switch element 20C, between the second switch element 20B and the fourth switch element 20D, and between the switch elements 20A, 20B, 20C, and 20D. The on / off operation timings are staggered between each other. In FIG. 2, the time between the time T4 and the time T6 is the phase difference between the first arm A1 and the second arm A2.

By turning on and off the switch elements 20A, 20B, 20C, and 20D at the timing shown in FIG. 2, ZVS is realized when the switch elements 20A, 20B, 20C, and 20D turn on, and the converter 100 operates with higher efficiency. Can be made to. In FIG. 2, either the high level or the low level of the PWM signal corresponds to the on state of the switch elements 20A, 20B, 20C, 20D, and the PWM signal corresponds to the off state of the switch elements 20A, 20B, 20C, 20D. Either the high level or the low level of the above corresponds.

In FIG. 2, the second switch element 20B and the third switch element 20C are in the ON state between the time T0 and the time T1. At this time, a current flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C1 (see FIG. 3). The path indicated by the arrow C1 is the path of the first conductive path 1 → the third switch element 20C → the primary coil 11 → the inductor 13 → the second switch element 20B → the second conductive path 2. A current flows in the path indicated by the arrow C2 on the output circuit 30 side (secondary side of the transformer 10) corresponding to the current flowing in the path indicated by the arrow C1 (see FIG. 3). The path indicated by the arrow C2 is the path of the fourth conductive path 4 → the fifth switch element 30A → the secondary coil 12A → the rectified output path 30C → the choke coil 33 → the third conductive path 3. The period from time T0 to time T1 is a transmission period for transmitting electric power from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T1 and the time T2, there is a dead time provided for the third switch element 20C to switch from the on state to the off state and the fourth switch element 20D to switch from the off state to the on state. From time T1 to time T2, the third switch element 20C and the fourth switch element 20D are in the off state. At this time, the second switch element 20B is in the on state, and the first switch element 20A is in the off state. At this time, a current flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C3 (see FIG. 4). The path indicated by the arrow C3 is the path of the inductor 13 → the second switch element 20B → the second conductive path 2 → the fourth switch element 20D → the primary coil 11. At this time, although the fourth switch element 20D is in the off state, a current flows through the parasitic diode 20K. The period from time T1 to time T2 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T2 and the time T3, the second switch element 20B and the fourth switch element 20D are in the on state, and the first switch element 20A and the third switch element 20C are in the off state. At this time, a current continuously flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C3 (see FIG. 4). The period from time T2 to time T3 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T3 and the time T4, there is a dead time provided for the second switch element 20B to switch from the on state to the off state and the first switch element 20A to switch from the off state to the on state. From time T3 to time T4, the first switch element 20A and the second switch element 20B are in the off state. At this time, the fourth switch element 20D is in the on state, and the third switch element 20C is in the off state. The period from time T3 to time T4 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T4 and the time T5, the first switch element 20A and the fourth switch element 20D are in the on state, and the second switch element 20B and the third switch element 20C are in the off state. At this time, a current flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C4 (see FIG. 5). The path indicated by the arrow C4 is the path of the first conductive path 1 → the first switch element 20A → the inductor 13 → the primary coil 11 → the fourth switch element 20D → the second conductive path 2. A current flows in the path indicated by the arrow C5 on the output circuit 30 side (secondary side of the transformer 10) corresponding to the current flowing in the path indicated by the arrow C4 (see FIG. 5). The path indicated by the arrow C5 is the path of the fourth conductive path 4 → the sixth switch element 30B → the secondary coil 12B → the rectified output path 30C → the choke coil 33 → the third conductive path 3. The period from time T4 to time T5 is a transmission period for transmitting electric power from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T5 and the time T6, there is a dead time provided for the fourth switch element 20D to switch from the on state to the off state and the third switch element 20C to switch from the off state to the on state. From time T5 to time T6, the third switch element 20C and the fourth switch element 20D are in the off state. At this time, the first switch element 20A is in the on state, and the second switch element 20B is in the off state. At this time, a current flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C6 (see FIG. 6). The path indicated by the arrow C6 is the inductor 13 → the primary coil 11 → the third switch element 20C →. This is the path from the first conductive path 1 to the first switch element 20A. At this time, although the third switch element 20C is in the off state, a current flows through the parasitic diode 20J. The period from time T5 to time T6 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T6 and the time T7, the first switch element 20A and the third switch element 20C are in the on state, and the second switch element 20B and the fourth switch element 20D are in the off state. At this time, a current continuously flows through the switching circuit 20 side (primary side of the transformer 10) along the path indicated by the arrow C6 (see FIG. 6). The period from time T6 to time T7 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10.

In FIG. 2, between the time T7 and the time T8, there is a dead time provided for the first switch element 20A to switch from the on state to the off state and the second switch element 20B to switch from the off state to the on state. From time T7 to time T8, the first switch element 20A and the second switch element 20B are in the off state. At this time, the third switch element 20C is in the on state, and the fourth switch element 20D is in the off state. The period from time T7 to time T8 is a non-transmission period in which power is not transmitted from the primary side to the secondary side of the transformer 10. For example, when the ignition switch is on and the dead time and the phase do not fluctuate, the control unit 40 causes each of the switch elements 20A, 20B, 20C, and 20D to repeat the operation from time T0 to time T8.

[Operation of ZVS]
Next, focusing on the dead time between the times T1 and T2, the case where the fourth switch element 20D is switched from off to on will be described with reference to FIG. 7 and the like. As shown in FIG. 7, before the time T2S (that is, the third switch element 20C is on), a DC input voltage Vin is applied between the drain and the source of the fourth switch element 20D. (See the bottom of FIG. 7). At this time, the DC input voltage Vin is also applied to the parasitic capacitor of the fourth switch element 20D.

Then, at time T2S, when the third switch element 20C is switched from on to off, no current flows through the third switch element 20C. At this time, LC resonance starts between the parasitic capacitor of the 4th switch element 20D and the inductor 13, and the voltage between the drain and the source of the 4th switch element 20D becomes half the magnitude of the DC input voltage Vin. Get closer. The voltage between the drain and the source of the fourth switch element 20D is closest to 0V at the time T2E when the LC resonance starts and the voltage first drops (see the lower side of FIG. 7). Therefore, by setting the time for switching the fourth switch element 20D from off to on as T2E, ZVS at the turn-on of the fourth switch element 20D can be realized. The operation of this ZVS is the same for the other dead times in FIG. The operation of ZVS shows that the smaller the output current, the slower the change in voltage between time T2S and T2E, and the larger the output current, the slower the change in voltage between time T2S and time T2E. It tends to be steep. Further, in the operation of ZVS, the larger the input voltage, the more gradual the change in the voltage between the time T2S and the time T2E tends to be, and the smaller the input voltage, the more the voltage between the time T2S and the time T2E tends to change. The change tends to be steep. Therefore, when ZVS is realized, the dead time increases as the voltage value detected by the first voltage detection unit 40A increases, and the dead time decreases as the current value detected by the second current detection unit 40D increases. Determine the dead time.

[Operation of control unit]
The operation of the control unit 40 will be described with reference to FIGS. 8 and 9. The control unit 40 is based on the voltage value detected by the first voltage detection unit 40A or the second voltage detection unit 40B, the current value detected by the second current detection unit 40D, and a predetermined target voltage value. The feedback calculation for calculating the duty so that the output voltage approaches the target voltage value is periodically repeated by a feedback calculation method such as a PI calculation method or a PID calculation method. The control unit 40 is configured to output a new duty PWM each time the duty is calculated.

First, as shown in FIG. 8, the control unit 40 acquires the voltage value detected by the first voltage detection unit 40A and the current value detected by the second current detection unit 40D (step S1).

Next, the control unit 40 calculates the dead time based on the voltage value and the current value acquired in step S1 (step S2). The dead time calculation in the control unit 40 is performed for each on / off operation cycle of the first switch element 20A, the second switch element 20B, the third switch element 20C, and the fourth switch element 20D. It may be configured to be executed every predetermined time longer than that.

For example, the data table shown in FIG. 9 is stored in the ROM or the like in the control unit 40. In this data table, the voltage value detected by the first voltage detection unit 40A and the current value detected by the second current detection unit 40D are associated with the first value which is a candidate for the dead time. For example, the first value is determined so that the larger the voltage value detected by the first voltage detection unit 40A, the larger the first value, and the larger the current value detected by the second current detection unit 40D, the smaller the first value. In step S2, the first calculation unit 40E of the control unit 40 calculates the first value as a candidate for the dead time based on this data table. For example, when the voltage value detected by the first voltage detection unit 40A is XXX and the current value detected by the second current detection unit 40D is YYYY, the first calculation unit 40E corresponds to these voltage values and current values. The dead time Dt34 to be used is calculated as the first value which is a candidate for the dead time.

Next, the control unit 40 shifts to step S3 and calculates the phase difference between the first arm A1 and the second arm A2. For example, the control unit 40 calculates the time of the current transmission period by subtracting the current dead time from the current phase difference. Then, the second calculation unit 40F of the control unit 40 adds the first value calculated in step S2 to the time of the transmission period calculated in this way. In this way, the second calculation unit 40F of the control unit 40 calculates the second value as a candidate for a new phase difference. The second value is the total value of the time of the transmission period and the first value. The second value becomes a larger value as the first value, which is a candidate for the dead time, becomes larger, and becomes a smaller value as the first value becomes smaller.

Next, the control unit 40 proceeds to step S4 and compares the second value with the threshold value stored in its own ROM or the like. The threshold value is, for example, half the time of the cycle in which each of the first switch element 20A, the second switch element 20B, the third switch element 20C, and the fourth switch element 20D operates on and off (that is, 1/2 of one cycle). It is a value corresponding to. When the control unit 40 determines that the second value is equal to or higher than the threshold value (that is, 1/2 or more of one cycle) (No in step S4), the control unit 40 shifts to step S5 and the first calculation unit 40E performs the first step. Calculate the value again.

For example, in step S5, the time within the range of the difference between the threshold value and the transmission period is recalculated as the first value. When the second value (the total value of the time of the transmission period and the first value) becomes larger than the threshold value, the relationship between the phase advance and the slow phase of the first arm A1 and the second arm A2 is reversed. .. Therefore, if the second value crosses the threshold value, the operation of the converter 100 that has been performing the step-up operation may be switched to the step-down operation, or the operation of the converter 100 that has been performing the step-down operation may be switched to the step-up operation. Not preferable. Therefore, by calculating the first value again, the total value (second value) of the time of the transmission period and the first value is maintained at a value less than the threshold value.

When the control unit 40 determines in step S4 that the second value is equal to or greater than the threshold value, a predetermined fixed value may be adopted as the first value which is a candidate for the dead time. In this case, it is conceivable that the fixed value is stored in, for example, the ROM of the control unit 40. The fixed value may be, for example, the shortest time that can function as a dead time.

When it is determined in step S4 that the second value calculated by the second calculation unit 40F is less than the threshold value (Yes in step S4), the process proceeds to step S6 and the control unit 40 shifts to each switch element 20A, 20B, 20C, 20D. Outputs a signal toward. Specifically, the control unit 40 sets the first value calculated in step S2 as the dead time for the PWM signals output toward the switch elements 20A, 20B, 20C, and 20D, and calculates in step S3. The second value is set as the phase difference. That is, the control unit 40 sets the dead time based on the first value.

The control unit 40 outputs the PWM signals in which the first value and the second value are set toward the gates of the switch elements 20A, 20B, 20C, and 20D. The second value is the total value of the time of the transmission period and the first value. The second value becomes a larger value as the first value, which is a candidate for the dead time, becomes larger, and becomes a smaller value as the first value becomes smaller. That is, the control unit 40 increases the phase difference (that is, the second value) between the first arm A1 and the second arm A2 as the dead time (that is, the first value) increases, and the dead time (that is, the first value) increases. ) Is smaller, the phase difference (that is, the second value) is controlled to be smaller.

An example of reflecting the first value and the second value in the PWM signal will be described with reference to FIG. As shown in FIG. 2, before the time C, the time between the time T0 and the time T1 which is the transmission period, the time between the time T4 and the time T5, and the time between the time T8 and the time T9. Are both time A. Before time C, the time between time T1 and time T2, which is the dead time, the time between time T3 and time T4, the time between time T5 and time T6, and the time between time T7 and time T8. The time between and the time between time T9 and time T10 are the same.

After the time C, the control unit 40 sets the time between the time T11 and the time T12 as the first value. Then, the control unit 40 sets the time between the time T12 and the time T14 (that is, the phase difference between the first arm A1 and the second arm A2) as the second value. The second value is the total value of the time A and the first value of the transmission period before the time C. Therefore, between the time T12 and the time T14, the time between the time T12 and the time T13, which is the transmission period, becomes the same time A as the length of the transmission period before the time C, and the time T13 and the time T14 The time between them is the first value. That is, the control unit 40 changes the dead time without changing the length of the transmission period by setting the phase difference between the first arm A1 and the second arm A2 to the second value.

Further, the control unit 40 sets the time between the time T15 and the time T17 as the second value. Between time T15 and time T17, the time between time T15 and time T16 becomes the first value, and the time between time T16 and time T17, which is the transmission period, is the transmission period before time C. It will be the same time A as the length. Then, the control unit 40 sets the time between the time T17 and the time T18 as the first value. In this way, the control unit 40 changes the dead time after the time C while maintaining the length of the transmission period before the time C. When the ignition switch is on after time T18 and the voltage value detected by the first voltage detection unit 40A and the current value detected by the second current detection unit 40D do not fluctuate, each switch element is operated by the control unit 40. 20A, 20B, 20C, 20D repeat the operation from the time T11 to the time T18.

Next, the effect of this configuration will be illustrated.
The isolated DCDC converter 100 of the present disclosure includes a transformer 10, a full-bridge type switching circuit 20, a control unit 40, an inductor 13, and an output circuit 30. The transformer 10 has a primary coil 11 and secondary coils 12A and 12B. The full bridge type switching circuit 20 includes a first switch element 20A, a second switch element 20B, a third switch element 20C, and a fourth switch element 20D.

The control unit 40 controls the operation of the switching circuit 20. The output circuit 30 is connected to the secondary coils 12A and 12B. The first switch element 20A and the second switch element 20B are connected in series between the first conductive path 1 and the second conductive path 2 to form the first arm A1. The third switch element 20C and the fourth switch element 20D are connected in series between the first conductive path 1 and the second conductive path 2 to form the second arm A2. One end of the inductor 13 is electrically connected to the first connection point P1 between the first switch element 20A and the second switch element 20B. The other end of the inductor 13 is electrically connected to one end of the primary coil 11. The other end of the primary coil 11 is electrically connected to the second connection point P2 between the third switch element 20C and the fourth switch element 20D.

The control unit 40 determines the time between the on period of the first switch element 20A and the on period of the second switch element 20B and the time between the on period of the third switch element 20C and the on period of the fourth switch element 20D. Adjust the dead time that is. The control unit 40 increases the phase difference between the first arm A1 and the second arm A2 as the dead time increases. The control unit 40 reduces the phase difference as the dead time becomes smaller.

Therefore, the isolated DCDC converter 100 can change the phase difference according to the change in the dead time, whereby the change in the transmission period can be suppressed and the fluctuation of the output voltage can be suppressed.

The insulated DCDC converter 100 of the present disclosure includes a first voltage detection unit 40A for detecting a voltage value of an input voltage applied between the first conductive path 1 and the second conductive path 2, and an output flowing through an output circuit 30. A second current detection unit 40D for detecting the current value of the current is provided. The control unit 40 determines the dead time based on the voltage value and the current value.
According to this configuration, the dead time can be determined according to the operation status of the switching circuit 20.

The control unit 40 of the isolated DCDC converter 100 of the present disclosure includes a first calculation unit 40E and a second calculation unit 40F. The first calculation unit 40E calculates the first value as a candidate for the dead time based on the voltage value and the current value. The second calculation unit 40F calculates a second value as a candidate for the phase difference based on the first value calculated by the first calculation unit 40E. The control unit 40 determines the dead time based on the first value when the second value calculated by the second calculation unit 40F is less than the threshold value, and when the second value is equal to or more than the threshold value, the first calculation is performed. The first value is calculated again by the unit 40E.
According to this configuration, the change in the transmission period can be suppressed and the fluctuation of the output voltage can be suppressed by recalculating the dead time and changing the dead time.

The control unit 40 of the isolated DCDC converter 100 of the present disclosure includes a first calculation unit 40E and a second calculation unit 40F. The first calculation unit 40E calculates the first value as a candidate for the dead time based on the voltage value and the current value. The second calculation unit 40F calculates a second value as a candidate for the phase difference based on the first value calculated by the first calculation unit 40E. The control unit 40 determines the dead time based on the first value when the second value calculated by the second calculation unit 40F is less than the threshold value, and sets the dead time when the second value is equal to or more than the threshold value. Set to a predetermined fixed value.
According to this configuration, the dead time is not recalculated, so that the control in the control unit 40 can be simplified.

The control unit 40 of the isolated DCDC converter 100 of the present disclosure causes each of the first switch element 20A, the second switch element 20B, the third switch element 20C, and the fourth switch element 20D to perform on / off operations at a predetermined cycle. The threshold is half the time of the cycle.
According to this configuration, it is possible to suppress a change in the transmission period while maintaining the operation of the switching circuit 20 as either a step-up operation or a step-down operation.

<Other Embodiments>
The present configuration is not limited to the embodiments described in the above description and drawings, and for example, the following embodiments are also included in the technical scope of the present invention.

In the first embodiment, a change point of the dead time is provided at the time C between the time T10 and the time T11. Not limited to this, the change point of the dead time may be performed at another timing.

In the first embodiment, the phase difference is the time between the turn-on time of the first switch element and the turn-on time of the third switch element. Not limited to this, the phase difference is between the turn-off time of the first switch element and the turn-off time of the third switch element, and the turn-on time of the second switch element and the turn-on time of the fourth switch element. It may be the time, or the time between the turn-off time of the second switch element and the turn-off time of the fourth switch element.

In the first embodiment, the MOSFET is used for the fifth switch element 30A and the sixth switch element 30B, but a diode may be used.

In the first embodiment, the control unit 40 is mainly composed of a microcomputer, but it may be realized by a plurality of hardware circuits other than the microcomputer.

In the first embodiment, the dead time is calculated based on the voltage value detected by the first voltage detection unit 40A and the current value detected by the second current detection unit 40D. Not limited to this, the dead time may be calculated based on either the voltage value detected by the first voltage detection unit or the current value detected by the second current detection unit. Further, the dead time may be calculated based on the voltage value detected by the second voltage detection unit and the current value detected by the first current detection unit.

In the first embodiment, the first value that is a candidate for the dead time is calculated based on the data table. Not limited to this, a predetermined calculation formula (for example, a linear formula such as a proportional formula, a quadratic formula, etc.) based on the voltage value detected by the first voltage detection unit and the current value detected by the second current detection unit, etc. ) May be used to calculate the first value.

Not limited to the control of the first embodiment, the dead time may be changed while maintaining the transmission period by accelerating the turn-off timing of each switch element of the first arm. The dead time may be changed while maintaining the transmission period by delaying the turn-on timing of each switch element of the second arm. Moreover, you may use these controls together.

In the first embodiment, the second value is calculated by adding up the phase difference calculated by the feedback control and the first value. Not limited to this, the second value corresponding to the first value may be calculated based on the data table, and a predetermined arithmetic expression using the first value (for example, a linear expression such as a proportional expression or a quadratic expression, etc.) may be calculated. ) May be used to calculate the second value.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed here, but may be indicated by the claims and include all modifications within the meaning and scope equivalent to the claims. Intended.

1 ... 1st conductive path 2 ... 2nd conductive path 3 ... 3rd conductive path 4 ... 4th conductive path 6 ... Load 7 ... Input capacitor 10 ... Transformer 11 ... Primary side coil 12A, 12B ... Secondary side coil 13 ... Inductor 20 ... Switching circuit 20A ... 1st switch element 20B ... 2nd switch element 20C ... 3rd switch element 20D ... 4th switch element 20G, 20H, 20J, 20K ... Parasitic diode 30 ... Output circuit 30A ... 5th switch element 30B ... 6th switch element 30C ... Rectification output path 33 ... Chalk coil 34 ... Output capacitor 40 ... Control unit 40A ... 1st voltage detection unit (voltage detection unit)
40B ... Second voltage detection unit (voltage detection unit)
40C ... First current detection unit (current detection unit)
40D ... Second current detection unit (current detection unit)
40E ... 1st calculation unit 40F ... 2nd calculation unit 40G ... Voltage detection unit 40H ... Current detection unit 100 ... Insulated DCDC converter A1 ... 1st arm A2 ... 2nd arm C1, C2, C3, C4, C5, C6 ... Arrow G ... Ground path P1 ... First connection point P2 ... Second connection point P3 ... Third connection point Vin ... Input voltage Vout ... Output voltage

Claims (5)

A transformer with a primary coil and a secondary coil,
A full-bridge type switching circuit including a first switch element, a second switch element, a third switch element, and a fourth switch element, and
A control unit that controls the operation of the switching circuit,
With an inductor
The output circuit connected to the secondary coil and
With
The first switch element and the second switch element are connected in series between the first conductive path and the second conductive path to form a first arm.
The third switch element and the fourth switch element are connected in series between the first conductive path and the second conductive path to form a second arm.
One end of the inductor is electrically connected to a first connection point between the first switch element and the second switch element.
The other end of the inductor is electrically connected to one end of the primary coil.
The other end of the primary coil is a phase-shift type isolated DCDC converter electrically connected to a second connection point between the third switch element and the fourth switch element.
In the control unit, the time between the on period of the first switch element and the on period of the second switch element and the time between the on period of the third switch element and the on period of the fourth switch element. An isolated DCDC converter that adjusts the dead time, increases the phase difference between the first arm and the second arm as the dead time increases, and decreases the phase difference as the dead time decreases. It flows through a voltage detection unit that detects at least one of an input voltage applied between the first conductive path and the second conductive path or an output voltage output from the output circuit, and the switching circuit. It includes at least one of a current detectors for detecting at least one of an input current and an output current flowing through the output circuit.
The isolated DCDC converter according to claim 1, wherein the control unit determines the dead time based on at least one of the voltage value and the current value. The control unit includes a first calculation unit that calculates a first value that is a candidate for the dead time based on at least one of the voltage value and the current value.
A second calculation unit that calculates a second value that is a candidate for the phase difference based on the first value calculated by the first calculation unit.
With
When the second value calculated by the second calculation unit is less than the threshold value, the dead time is determined based on the first value, and when the second value is equal to or more than the threshold value, the first value is determined. The isolated DCDC converter according to claim 2, wherein the calculation unit calculates the first value again. The control unit includes a first calculation unit that calculates a first value that is a candidate for the dead time based on at least one of the voltage value and the current value.
A second calculation unit that calculates a second value that is a candidate for the phase difference based on the first value calculated by the first calculation unit.
With
When the second value calculated by the second calculation unit is less than the threshold value, the dead time is determined based on the first value, and when the second value is equal to or more than the threshold value, the dead time is determined. The isolated DCDC converter according to claim 2, wherein the value is set to a predetermined fixed value. The control unit causes the first switch element, the second switch element, the third switch element, and the fourth switch element to perform on / off operations at predetermined cycles.
The isolated DCDC converter according to claim 3 or 4, wherein the threshold value is half the time of the cycle.

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