JP2023166914A - DC-DC converter - Google Patents

Abstract

To provide a DC-DC converter that can reduce switching loss, even at the time of high output.SOLUTION: A DC-DC converter (1) comprises a primary side bridge circuit (10) including a first leg (11) and a second leg (12), a secondary side bridge circuit (20) including a third leg (21) and a fourth leg (22), and a conversion part (30), and further includes a first virtual leg (Q1) and a second virtual leg (Q2) as well as a third virtual leg (Q3) and a fourth virtual leg (Q4) having phase differences from each other which are switched at each half cycle, which switches the virtual legs for controlling the legs respectively.SELECTED DRAWING: Figure 13

Description

The present invention relates to a DC-DC converter.

A dual active bridge type DC-DC converter is known.

Patent Document 1 discloses a method that can reduce switching loss in boost operation using a primary-side full-bridge circuit using four switches and a secondary-side full-bridge circuit using two switches and two diodes. .

Japanese Patent Application Publication No. 2014-75943

In the DC-DC converter of Patent Document 1, when the output is low, switching can be performed during a period when no current is flowing through the switching element, so switching loss can be reduced. However, it has been found that it is not possible to prevent current from flowing in each switching element at the timing of switching even at high outputs, and switching loss occurs at high outputs.

One aspect of the present invention aims to realize a DC-DC converter that can reduce switching loss even at high output.

In order to solve the above problems, a DC-DC converter according to one aspect of the present invention includes a plurality of primary side switching elements and a free wheel diode connected in parallel to each of the primary side switching elements. a primary side bridge circuit having a first leg and a second leg, a plurality of secondary side switching elements, and a freewheeling diode connected in parallel to each of the secondary side switching elements, a secondary bridge circuit having a third leg and a fourth leg; a conversion section having a transformer and connected between the primary bridge circuit and the secondary bridge circuit; a control section that controls the side switching element and the secondary side switching element, the control section controlling the first leg as a first virtual leg, the second leg as a second virtual leg, and the third leg as a first virtual leg; a first operation of regarding a third virtual leg and the fourth leg as a fourth virtual leg; a first operation of regarding the second leg as a first virtual leg; a second virtual leg as the first leg; , a second operation in which the third leg is regarded as a fourth virtual leg are alternately executed, and through the first operation and the second operation, the first virtual leg, the second virtual leg, and the third virtual leg are In the fourth virtual leg, each switching element is switched every half cycle, a first inter-leg phase difference is provided between the virtual first leg and the virtual second leg, and a first inter-leg phase difference is provided between the virtual third leg and the virtual third leg. A second inter-leg phase difference is provided between the virtual fourth leg, and the ratio of the first inter-leg phase difference to the second leg phase difference is determined based on the input voltage of the primary bridge circuit and the secondary leg. Each of the primary side switching elements and each of the secondary side switching elements is controlled by setting a value according to the ratio of the output voltages of the side bridge circuits.

According to one aspect of the present invention, switching loss can be reduced even at high output.

1 is a circuit diagram showing a DC-DC converter according to Embodiment 1. FIG. 5 is a timing chart of control signals in a step-up operation of a DC-DC converter according to a reference operation example. 3 shows voltage and current waveforms of each switching element in a DC-DC converter according to a reference operation example. 3 shows voltage and current waveforms of each switching element at maximum output in a DC-DC converter according to a reference operation example. 3 is a timing chart of a plurality of cycles in a DC-DC converter according to a reference operation example. 12 is a timing chart of control signals when dead time in boosting operation of a DC-DC converter according to a reference operation example is taken into account. These are voltage and current waveforms of each switching element when dead time in a DC-DC converter according to a reference operation example is taken into consideration. 8 is an enlarged view of before and after turning off the switching element S5 in FIG. 7. FIG. 12 is a timing chart of control signals when power loss is reduced in consideration of dead time in boosting operation of a DC-DC converter according to a reference operation example. These are voltage and current waveforms of each switching element when dead time in the DC-DC converter according to the reference operation example is considered and power loss is reduced. 11 is an enlarged view of before and after turning off the switching element S5 in FIG. 10. FIG. 5 is a timing chart for multiple cycles in the DC-DC converter according to the first embodiment. The timing charts of the reference operation example and the first embodiment are compared. 3 shows a block diagram of a control section in the DC-DC converter according to Embodiment 1. FIG. It is an example of the timing chart which controls the 1st leg and the 2nd leg by the 1st virtual leg, the 2nd virtual leg, and the switching signal SEL.

[Reference operation example]
Prior to describing the first embodiment, reference operation examples of the present invention will first be described in detail using FIGS. 1 to 11.

(Configuration of DC-DC converter 1)
FIG. 1 is a circuit diagram showing a DC-DC converter 1 according to the first embodiment. The DC-DC converter 1 includes a primary bridge circuit 10, a secondary bridge circuit 20, a converter 30, and a controller 40.

The primary side bridge circuit 10 is connected to a DC power source with a primary side voltage E1. The secondary bridge circuit 20 is connected to a DC power source with a secondary voltage E2. Here, the primary side voltage E1 and the secondary side voltage E2 are time average values acquired by the control unit 40, and are used for control described later.

The primary side bridge circuit 10 is a full bridge circuit provided with four primary side switching elements S1 to S4. The primary bridge circuit 10 includes a first leg 11, a second leg 12, and a capacitor element C1. In the first leg 11, a primary switching element S1 and a primary switching element S2 are connected in series. In the second leg 12, a primary switching element S3 and a primary switching element S4 are connected in series.

The secondary bridge circuit 20 is a full bridge circuit provided with four secondary switching elements S5 to S8. The secondary bridge circuit 20 includes a third leg 21, a fourth leg 22, and a capacitor element C2. In the third leg 21, a secondary switching element S5 and a secondary switching element S6 are connected in series. In the fourth leg 22, a secondary switching element S7 and a secondary switching element S8 are connected in series.

The primary side switching elements S1 to S4 and the secondary side switching elements S5 to S8 (hereinafter collectively referred to as switching elements S1 to S8) are MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or other FETs (Field Effect Transistors). Transistor). Alternatively, the switching elements S1 to S8 may be composed of IGBTs (Insulated Gate Bipolar Transistors) or other transistors. The following description assumes that the switching elements S1 to S8 are MOSFETs.

Freewheeling diodes D1 to D8 are connected in parallel to the switching elements S1 to S8, respectively.

The converter 30 includes at least a transformer Tr having a winding ratio n (=number of turns of the primary winding/number of turns of the secondary winding). In the circuit diagram of FIG. 1, the inductance component of the converter 30 is equivalently represented as a reactor L1 provided on the primary side and a reactor L2 provided on the secondary side. In the equivalent circuit of FIG. 1, the reactor L1 is connected to the connection point between the primary switching element S1 and the primary switching element S2, and to the primary winding of the transformer Tr. The reactor L2 is connected to a connection point between the secondary switching element S5 and the secondary switching element S6 and to the secondary winding of the transformer Tr.

When the converter 30 is provided with a reactor element as an actual element, the reactor element may be placed on the primary side, the secondary side, or both of the transformer Tr. good.

The voltage on the primary side of the converter 30, that is, from the connection point between the primary switching element S3 and the primary switching element S4 to the connection point between the primary switching element S1 and the primary switching element S2. The voltage is assumed to be primary side AC voltage Vac1. Further, the current on the primary side of the converting section 30, that is, the current flowing between the converting section 30 and the primary side bridge circuit 10, is defined as a primary side alternating current Iac1.

The voltage on the secondary side of the converter 30, that is, from the connection point between the secondary switching element S7 and the secondary switching element S8 to the connection point between the secondary switching element S5 and the secondary switching element S6. The voltage is assumed to be secondary AC voltage Vac2. Further, the current on the secondary side of the converting section 30, that is, the current flowing between the converting section 30 and the secondary side bridge circuit 20 is defined as a secondary side AC current Iac2.

The control unit 40 controls switching of the switching elements S1 to S8 with reference to the primary voltage E1 and the secondary voltage E2.

Here, it is assumed that the configuration of the DC-DC converter 1 is such that power is transmitted from the primary side to the secondary side. Therefore, the primary side voltage is also called an input voltage, and the secondary side voltage is also called an output voltage. Further, the output voltage of the secondary side bridge circuit is set to be higher than the input voltage of the primary side bridge circuit, taking into consideration the winding ratio n. That is, the primary side converted output voltage of the secondary side bridge circuit is set to be higher than the input voltage of the primary side bridge circuit. That is, it is assumed that the DC-DC converter 1 operates in a step-up operation.

The DC-DC converter 1 of the reference operation example is a bidirectional dual active bridge type DC-DC converter. The expressions "primary" and "secondary" in the names of each part are for convenience, and merely represent the input side as primary and the output side as secondary, depending on the direction of power transmission.

(Step-up operation of DC-DC converter 1)
FIG. 2 is a timing chart of control signals in the step-up operation of the DC-DC converter 1 according to the reference operation example. The timing chart shows changes in the control signals of the switching elements S1 to S8 and changes in the primary side/secondary side AC voltage and current. Each control signal indicates closed when on (High) and open when off (Low).

As shown in FIG. 2, each switching element performs switching every half cycle. That is, the duty ratio of each switching element is 50%.

The switching element S3 of the second leg 12 is turned on and off by a control signal delayed by the first leg phase difference φL1 with respect to the switching element S1 of the first leg 11. The switching element S7 of the fourth leg 22 is turned on and off by a control signal delayed by the second inter-leg phase difference φL2 with respect to the switching element S5 of the third leg 21. No phase difference is provided between the primary bridge circuit 10 and the secondary bridge circuit 20. Switching elements S2, 4, 6, and 8 switch with a phase shift of 180 degrees with respect to switching elements S1, 3, 5, and 7, respectively. That is, a first inter-leg phase difference φL1 is provided between the first leg and the second leg, and a second inter-leg phase difference φL2 is provided between the third leg and the fourth leg.

参考動作例では、この関係性を満たしさえすれば、リアクトルＬ１、Ｌ２の値およびスイッチング周波数等には関係なく、ＤＣ－ＤＣコンバータ１を制御することができる。 The ratio of the phase difference φL1 between the first legs and the phase difference φL2 between the second legs is calculated by calculating the ratio between the input voltage of the primary bridge circuit (primary voltage E1) and the output voltage of the secondary bridge circuit (secondary voltage E2). ) is determined so that the following relationship holds true.

In the reference operation example, as long as this relationship is satisfied, the DC-DC converter 1 can be controlled regardless of the values of reactors L1 and L2, the switching frequency, etc.

FIG. 3 shows voltage and current waveforms of each switching element in the DC-DC converter 1 according to a reference operation example. Although FIG. 3 shows the switching elements S1, 3, 5, and 7, the waveforms for the switching elements S2, 4, 6, and 8 are waveforms whose phases are shifted by 180 degrees (waveforms with opposite phases).

Although FIG. 2 shows the control signals of the switching elements S1 to S8, FIG. 3 shows the voltage and current waveforms of the switching elements S1, 3, 5, and 7. Here, the current is a current flowing from the drain to the source in each switching element, and the voltage is the potential difference between the drain and the source in each switching element.

Therefore, when comparing the voltage waveforms in Figures 2 and 3, the voltage waveform becomes 0 in the section where each switching element is on, and the voltage waveform becomes 0 in the section where each switching element is off. Please note that this will be a value other than 0. Further, when the current has a positive value, the current is flowing through each switching element, and when the current has a negative value, the current is flowing through the free wheel diode connected in parallel to each switching element.

As shown in FIG. 3, regarding the switching elements S1, 3, and 5, the current flowing through the switching elements S1, 3, and 5 is zero during turn-on and turn-off. Therefore, power loss associated with turn-on and turn-off does not occur.

On the other hand, regarding the switching element S7, the current flowing through the switching element S7 is not zero during both turn-on and turn-off. Therefore, power loss occurs due to turn-on and turn-off.

S2, 4, 6, 8 operate symmetrically to S1, 3, 5, 7. That is, when power is transmitted from the input side of the primary side bridge circuit 10 to the output side of the secondary side bridge circuit 20, the primary side switching elements S1 to S4 and the secondary side switching elements of the third leg Elements S5 to S6 switch when the current flowing through each is zero. Therefore, switching loss does not occur in the switching elements S1 to S6, and switching loss can be reduced.

In this way, by controlling the ratio of the first inter-leg phase difference φL1 and the second inter-leg phase difference φL2 to satisfy the above formula, each leg except one leg (fourth leg 22) on the secondary side The current flowing through the switching element of the leg becomes 0 when it is turned on and when it is turned off.

This is due to the following two points.

(i) (a) A period in which the secondary AC voltage Vac2 is 0 and only the primary AC voltage Vac1 is applied to the converter 30, and (b) from the secondary AC voltage Vac2 to the primary AC voltage Vac1. The time integral value of the voltage in the section where the voltage obtained by subtracting the voltage is applied to the conversion unit 30 becomes 0. That is, the time integral value of the interval (a) has the same absolute value as the time integral value of the interval (b), and has an opposite sign.

Furthermore, (ii) at the timing when the second leg switches, that is, at the timing when the primary side AC voltage Vac1 is no longer 0, the primary side AC current Iac1 is 0.

(Voltage/current waveform at maximum output)
The power to be transmitted is determined by the value of the first inter-leg phase difference φL1, and the larger the first inter-leg phase difference φL1, the greater the transmitted power. Therefore, the maximum output is achieved when the first inter-leg phase difference φL1 is 180°.

FIG. 4 shows voltage and current waveforms of each switching element at maximum output in the DC-DC converter 1 according to the reference operation example. Although FIG. 4 shows the switching elements S1, 3, 5, and 7, the waveforms for the switching elements S2, 4, 6, and 8 are waveforms whose phases are shifted by 180 degrees.

As shown in FIG. 4, even at maximum output, the current flowing through each switching element S1 to S6 at turn-on and turn-off is 0, so No power loss occurs. Therefore, in the boost operation according to the reference operation example, switching loss can be reduced regardless of the output power.

Further, FIG. 5 is a timing chart for a plurality of cycles in the DC-DC converter 1 according to a reference operation example.

In FIG. 5, control signals S1 to S4 are signals that turn on and off the respective switching elements S1 to S4. Here, the control signals S1 to S4 do not take dead time into consideration. The consideration of dead time will be described later.

In addition, "S1 voltage" is the potential difference between the drain and the source in switching element S1, and "S1 current" is the current flowing from the drain to the source in switching element S1 when positive, and when negative, it is the current flowing from the drain to the source in switching element S1. This is the current flowing from the anode to the cathode in D1. "S3", "S5", and "S7" are also similar to "S1". Furthermore, the switching elements S2, S4, S6, and S8 have waveforms whose phases are delayed by half a period relative to the switching elements S1, S3, S5, and S7, respectively.

(dead time)
In the reference operation example described above, dead time was not taken into consideration for the sake of simplicity. Here, dead time is considered in order to correspond to actual operation.

Here, the dead time is a time for preventing a through current from flowing due to two switching elements connected in series of each leg being turned on at the same time.

(Loss caused by dead time)
FIG. 6 is a timing chart of control signals in consideration of dead time in the boost operation of the DC-DC converter 1 according to the reference operation example. FIG. 7 shows voltage and current waveforms of each switching element in consideration of dead time in the DC-DC converter 1 according to the reference operation example.

Comparing FIG. 6 with FIG. 2, there is a period in which each switching element is turned off at the same time in each leg. This period is dead time.

FIG. 8 is an enlarged view of the state before and after turning off the switching element S5 in FIG. The upper diagram in FIG. 8 is an enlarged diagram of the waveforms of the collector-emitter voltage and collector current before and after turning off the switching element S5. The lower diagram of FIG. 8 is an enlarged view of the waveforms of the gate-source voltages of the switching elements S5 and 6 before and after turning off the switching element S5.

As shown in the upper diagram of FIG. 8, at the timing when switching element S5 (or switching element S6) turns off (the timing at which the voltage between the collector and emitter rises), a collector current flows, which causes power loss. . This power loss also occurs in switching element S1 (or switching element S2).

Further, in the lower diagram of FIG. 8, the dead time is the interval from when the gate-source voltage of the switching element S5 starts to fall until the gate-source voltage of the switching element S6 starts to rise.

(Reduction of losses due to dead time)
Therefore, the DC-DC converter 1 according to the reference operation example further performs control to reduce loss due to dead time. The dead time is taken into account and the current is controlled to become 0 before the dead time. FIG. 9 is a timing chart of control signals in the case where dead time in the step-up operation of the DC-DC converter 1 according to the reference operation example is taken into account and power loss is reduced. FIG. 10 shows voltage and current waveforms of each switching element when dead time in the DC-DC converter 1 according to the reference operation example is considered and power loss is reduced.

In FIG. 9, as in FIG. 6, there is a period in which each switching element is turned off at the same time in each leg, and it can be seen that dead time is taken into consideration. Moreover, when FIG. 6 and FIG. 9 are compared, it can be seen that an inter-bridge phase difference φB is provided between the primary side bridge circuit 10 and the secondary side bridge circuit 20. The length of the inter-bridge phase difference φB is determined to be equal to the length of dead time in each leg from the first leg to the fourth leg.

FIG. 11 is an enlarged view of the state before and after turning off the switching element S5 in FIG. The upper diagram in FIG. 11 is an enlarged diagram of the waveforms of the collector-emitter voltage and collector current before and after turning off the switching element S5. The lower diagram of FIG. 11 is an enlarged diagram of the waveforms of the gate-source voltages of the switching elements S5 and 6 before and after turning off the switching element S5.

Comparing FIG. 11 and FIG. 8, at the timing when switching element S5 (or switching element S6) is turned off (timing when the collector-emitter voltage rises), the flowing collector current is smaller in FIG. 11 than in FIG. 8. ing. Therefore, it can be seen that power loss is reduced by providing the inter-bridge phase difference φB. This tendency is the same for switching element S1 (or switching element S2).

Further, in FIG. 11 as well, the collector current flowing through the switching element is not completely zero. This is because a typical switching element has characteristics different from theoretical calculations using an ideal element and includes parasitic components. In order to eliminate this power loss, it is necessary to finely adjust the inter-bridge phase difference φB so as to take into account the parasitic components of the semiconductor that constitutes the switching element.

However, if the switching element has no parasitic components and complies with ideal theoretical calculations, the switching loss can be reduced to 0 by setting the length of the inter-bridge phase difference φB equal to the length of the dead time. It can be done.

(Brief Summary)
Therefore, by providing a first inter-leg phase difference φL1 and a second inter-leg phase difference φL2 that satisfy the relationship of Equation 1, and providing an inter-bridge phase difference φB that is equal to the dead time, ZCS ( Zero Current Switching) is possible, and losses can be reduced.

However, in the reference operation example, switching elements S7 and S8 cannot perform ZCS. Therefore, heat is generated in the switching elements S7 and S8, and the heat generated by the DC-DC converter 1 is localized to the switching elements S7 and S8, so that heat radiation becomes inefficient.

[Embodiment 1]
Next, the leveled rectifier operation in the DC-DC converter 1 according to the first embodiment will be explained. The DC-DC converter 1 according to the first embodiment has the same circuit as the DC-DC converter 1 according to the reference operation example.

First, an overview of the first embodiment will be explained. In Embodiment 1, in the secondary side bridge circuit 20 of the reference operation example, the switching loss is increased only in the switching elements S7 and S8, whereas the switching loss in the switching elements S5 to S8 is equalized. make it work as it should. To achieve this, the operation of each leg in the reference operation example is exchanged between the first leg 11 and the second leg 12 and between the third leg 21 and the fourth leg 22 for each switching cycle to equalize the heat generation of each leg. , improve heat dissipation efficiency.

Specifically, in the first embodiment, a first virtual leg Q1, a second virtual leg Q2, a third virtual leg Q3, and a fourth virtual leg Q4 are defined, and the control unit defines the first virtual leg Q1, the second virtual leg Q2, and the fourth virtual leg Q4. It is assumed that the leg Q2, the third virtual leg Q3, and the fourth virtual leg Q4 are controlled similarly to the first leg 11, the second leg 12, the third leg 21, and the fourth leg 22 in the reference operation example, respectively. Furthermore, the first leg 11 is the first virtual leg Q1, the second leg 12 is the second virtual leg Q2, the third leg 21 is the third virtual leg Q3, and the fourth leg 22 is the fourth virtual leg Q4. The second leg 12 is the first virtual leg Q1, the first leg 11 is the second virtual leg Q2, the fourth leg 22 is the third virtual leg Q3, and the third leg 21 is the fourth virtual leg. Each switching element is controlled to alternately perform the second operation, which is regarded as Q4, every switching period.

FIG. 12 is a timing chart for multiple cycles in the DC-DC converter 1 according to the first embodiment. Further, FIG. 13 compares the timing charts of the reference operation example and the first embodiment.

In FIG. 13, when comparing the timing charts according to the reference operation example and Embodiment 1, it is found that the primary side current I1 and the secondary side current I2 are the same, but the primary side AC voltage Vac1 and the secondary side AC Voltage Vac2 and primary side AC current Iac1 are different.

In the reference operation example, the primary side AC voltage Vac1, the secondary side AC voltage Vac2, and the primary side AC current Iac1 each have an oscillating waveform whose sign is reversed every half cycle.

On the other hand, in the first embodiment, the primary side AC voltage Vac1, the secondary side AC voltage Vac2, and the primary side AC current Iac1 each have an oscillating waveform in which the sign is reversed every cycle. However, the vibration waveform oscillates in a range in which the positive and negative values are not reversed every half period, and as a result, in one cycle, it oscillates twice in a range in which the positive and negative values are not reversed.

(1st virtual leg Q1 to 4th virtual leg Q4)
Inside the control unit 40, a first virtual leg Q1 (not shown), a second virtual leg Q2 (not shown), a third virtual leg Q3 (not shown), and a fourth virtual leg Q4 (not shown) are controlled. A signal corresponding to the signal may be included. In this case, the control unit 40 controls the first leg 11, the second leg 12, the third leg 21, and controls the fourth leg 22.

実施形態１では、この関係性を満たしさえすれば、リアクトルＬ１、Ｌ２の値およびスイッチング周波数等には関係なく、ＤＣ－ＤＣコンバータ１を制御することができる。 The first virtual leg Q1, the second virtual leg Q2, the third virtual leg Q3, and the fourth virtual leg Q4 each switch their duty at 50%, that is, every half cycle. A first inter-leg phase difference φL1 is provided between the first virtual leg Q1 and the second virtual leg Q2, and a second inter-leg phase difference φL2 is provided between the third virtual leg Q3 and the fourth virtual leg Q4. The ratio of the phase difference φL1 between the first legs and the phase difference φL2 between the second legs is calculated by calculating the ratio between the input voltage of the primary bridge circuit (primary voltage E1) and the output voltage of the secondary bridge circuit (secondary voltage E2). ) is determined so that the following relationship holds true.

In the first embodiment, as long as this relationship is satisfied, the DC-DC converter 1 can be controlled regardless of the values of the reactors L1 and L2, the switching frequency, etc.

(Switching signal SEL)
A specific method for generating control signals for the switching elements S1 to S8 in the control section 40 will be described below. The control unit 40 includes a switching signal SEL (not shown). The control unit 40 has two operating modes. In the first operation, the first virtual leg Q1 controls the first leg 11, the second virtual leg Q2 controls the second leg 12, the third virtual leg Q3 controls the third leg 21, and the fourth virtual leg Q2 controls the second leg 12. The fourth leg 22 is controlled by leg Q4. On the other hand, in the second operation, the first virtual leg Q1 controls the second leg 12, the second virtual leg Q2 controls the first leg 11, the third virtual leg Q3 controls the fourth leg 22, The third leg 21 is controlled by the fourth virtual leg Q4. A signal for selecting which of the first operation and the second operation to perform is the switching signal SEL. Here, in the first operation, the same operation as the reference operation example is performed.

By switching between the first operation and the second operation using the switching signal SEL, the positive and negative values of the primary side AC voltage Vac1, the secondary side AC voltage Vac2, and the primary side AC current Iac1 in the reference operation example in FIG. 13 can be changed. Partially inverted (reversing the sign of the arrow in the reference operation example in FIG. 11), the primary side AC voltage Vac1, the secondary side AC voltage Vac2, and the primary side AC current Iac1 in Embodiment 1 in FIG. The waveform is created.

The first leg 11 and the second leg 12 are actually controlled as shown in FIG. 12 in consideration of the switching signal SEL. In contrast to FIG. 5, in FIG. 12, the intervals between the control signals S1 to S8 are not every half period. This is because, for example, what controls the first leg 11 changes from the first virtual leg Q1 to the second virtual leg Q2, and what controls the third leg 21 changes from the third virtual leg Q3 to the switching signal SEL. This is because it has changed to the fourth virtual leg Q4.

Also, when comparing "S5 current" and "S7 current", it is found that the switching element is off when current is flowing, and the switching element is off when current is 0. You can see that there is. Therefore, the switching elements that are not ZCS are alternated, and heat loss is dispersed. Therefore, heat distribution is improved and heat dissipation efficiency is improved.

(Block diagram of control unit 40)
FIG. 14 shows a block diagram of the control section 40 in the DC-DC converter 1 according to the first embodiment. As shown in FIG. 14, the output power Pout is calculated from the secondary voltage E2 and the secondary current I2. A power deviation ΔPout is derived from the output power Pout and the target power Pout*.

The value obtained by multiplying the power deviation ΔPout by the gain Kp and the second inter-leg phase difference φL2 are added together to obtain the control second inter-leg phase difference φL2*. From the relationship of Equation 2, the phase difference between the first control legs φL1 is derived using the phase difference between the second control legs φL2*.

A first virtual leg Q1, a second virtual leg Q2, a third virtual leg Q3, and a fourth virtual leg Q4 are generated from a PWM (Pulse Width Modulation) signal. Here, the second virtual leg Q2 is a signal whose phase is delayed by the first inter-leg phase difference φL1 with respect to the first virtual leg Q1, and the fourth virtual leg Q4 is a signal whose phase is delayed with respect to the third virtual leg Q3. This is a signal whose phase is delayed by the phase difference φL2 between the second legs.

Further, as shown in FIG. 14, by performing a logical operation on the first virtual leg Q1, the second virtual leg Q2, and the switching signal SEL, the on/off state of the switching elements S1 to S4 is determined. By performing a logical operation on the third virtual leg Q3, the fourth virtual leg Q4, and the switching signal SEL, on/off of the switching elements S5 to S8 is determined.

FIG. 15 is an example of a timing chart for controlling the first leg 11 and the second leg 12 using the first virtual leg Q1, the second virtual leg Q2, and the switching signal SEL. The control signal S1 and the control signal S3 in FIG. 12 are similar to the control signal S1 and the control signal S3 in FIG. 15, according to the block diagram shown in FIG. It is derived from

Further, in FIG. 15, a timing chart for controlling the third leg 21 and the fourth leg 22 by the third virtual leg Q3, the fourth virtual leg Q4, and the switching signal SEL is shown in FIG. Q3, the second virtual leg Q2 is replaced with the fourth virtual leg Q4, the control signal S1 is replaced with the control signal S5, and the control signal S3 is replaced with the control signal S7. Note that the control signals S2, S4, S6, and S8 have the opposite logic of the control signals S1, S3, S5, and S7, respectively.

(Brief Summary)
Therefore, when transmitting power in the DC-DC converter 1, the switching elements that perform ZCS are replaced regularly to equalize the power and reduce the heat generated by the switching elements S1 to S8 while maintaining the output of the DC-DC converter 1. It can be leveled. Therefore, the heat dissipation efficiency of the switching elements S1 to S8 forming the DC-DC converter 1 is improved.

(Modified example)
In the first embodiment, the switching signal SEL is turned on and off every cycle, but the present invention is not limited to this. That is, the switching signal SEL only needs to be turned on and off during a period that is N times the period (N is a natural number of 1 or more).

〔summary〕
In order to solve the above problems, the DC-DC converter according to aspect 1 of the present invention includes a plurality of primary side switching elements and a free wheel diode connected in parallel to each of the primary side switching elements. a primary side bridge circuit having a first leg and a second leg, a plurality of secondary side switching elements, and a freewheeling diode connected in parallel to each of the secondary side switching elements, a secondary bridge circuit having a third leg and a fourth leg; a conversion section having a transformer and connected between the primary bridge circuit and the secondary bridge circuit; a control section that controls the side switching element and the secondary side switching element, the control section controlling the first leg as a first virtual leg, the second leg as a second virtual leg, and the third leg as a first virtual leg; a first operation of regarding a third virtual leg and the fourth leg as a fourth virtual leg; a first operation of regarding the second leg as a first virtual leg; a second virtual leg as the first leg; , a second operation in which the third leg is regarded as a fourth virtual leg are alternately executed, and through the first operation and the second operation, the first virtual leg, the second virtual leg, and the third virtual leg are In the fourth virtual leg, each switching element is switched every half cycle, a first inter-leg phase difference is provided between the virtual first leg and the virtual second leg, and a first inter-leg phase difference is provided between the virtual third leg and the virtual third leg. A second inter-leg phase difference is provided between the virtual fourth leg, and the ratio of the first inter-leg phase difference to the second leg phase difference is determined based on the input voltage of the primary bridge circuit and the secondary leg. Each of the primary side switching elements and each of the secondary side switching elements is controlled by setting a value according to the ratio of the output voltages of the side bridge circuits.

According to the above configuration, by switching between the case where the third leg and the fourth leg perform ZCS and the case where they do not perform ZCS, heat generation in the switching element can be dispersed, and heat radiation efficiency is good.

In the DC-DC converter according to the second aspect of the present invention, in the first aspect, the first operation and the second operation may be switched every cycle.

According to the above configuration, the leg to be subjected to ZCS can be switched every cycle. Therefore, heat generation can be made uniform between the third leg and the fourth leg.

In the DC-DC converter according to aspect 3 of the present invention, in aspect 1, the first operation and the second operation may be switched every N times the period (N is a natural number of 1 or more). .

According to the above configuration, the legs for ZCS can be switched in a period that is N times the period. Therefore, heat generation can be made uniform between the third leg and the fourth leg.

In the DC-DC converter according to aspect 4 of the present invention, in any one of aspects 1 to 3 above, the control section further controls an inter-bridge phase difference between the virtual first leg and the virtual third leg. The length of the inter-bridge phase difference may be set to be equal to the length of dead time in each leg from the first leg to the fourth leg.

According to the above configuration, switching loss occurring during dead time can be reduced.

In the DC-DC converter according to aspect 5 of the present invention, in any one of aspects 1 to 4 above, power is transmitted from the input side of the primary side bridge circuit to the output side of the secondary side bridge circuit. In this case, in the first operation, each of the primary side switching elements and each of the secondary side switching elements of the third leg switches when the current flowing through each is 0, and in the second operation, Each of the primary side switching elements and each of the secondary side switching elements of the fourth leg may be switched when the current flowing therein is zero.

According to the above configuration, in the first operation, switching is performed in the first leg, second leg, and third leg, and in the second operation, switching is performed in the first leg, second leg, and fourth leg. Loss can be reduced to 0.

In the DC-DC converter according to aspect 6 of the present invention, in any one of aspects 1 to 5 above, the primary side converted output voltage of the secondary side bridge circuit is higher than the input voltage of the primary side bridge circuit. It may be.

According to the above configuration, the voltage of the secondary bridge circuit can be made higher than that of the primary bridge circuit. That is, the DC-DC converter can be operated to boost the voltage.

In the DC-DC converter according to aspect 7 of the present invention, in any one of aspects 1 to 6, the first leg-to-leg phase difference is φL1, the second leg-to-leg phase difference is φL2, and the primary side bridge circuit is When the input voltage is E1, the output voltage of the secondary bridge circuit is E2, and the turns ratio of the primary side to the secondary side of the transformer of the converting section is n, even if the following relationship holds true: good.

上記の構成によれば、第１レグ間位相差と第２レグ間位相差とを一意に定めることができる。

According to the above configuration, the first inter-leg phase difference and the second inter-leg phase difference can be uniquely determined.

[Example of implementation using software]
The function of the DC-DC converter 1 (hereinafter referred to as "device") is a program for making a computer function as the device, and the function of the DC-DC converter 1 (hereinafter referred to as "device") is a program for making a computer function as the device. This can be realized by a program to make it function.

In this case, the device includes a computer having at least one control device (for example, a processor) and at least one storage device (for example, a memory) as hardware for executing the program. By executing the above program using this control device and storage device, each function described in each of the above embodiments is realized.

The above program may be recorded on one or more computer-readable recording media instead of temporary. This recording medium may or may not be included in the above device. In the latter case, the program may be supplied to the device via any transmission medium, wired or wireless.

Further, part or all of the functions of each of the control blocks described above can also be realized by a logic circuit. For example, an integrated circuit in which a logic circuit functioning as each of the control blocks described above is formed is also included in the scope of the present invention. In addition to this, it is also possible to realize the functions of each of the control blocks described above using, for example, a quantum computer.

[Additional notes]
The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

1 DC-DC converter 10 Primary side bridge circuit 11 1st leg 12 2nd leg 20 Secondary side bridge circuit 21 3rd leg 22 4th leg 30 Conversion section 40 Control section D1 to D8 Free wheel diode Q1 1st virtual leg Q2 2nd virtual leg Q3 3rd virtual leg Q4 4th virtual leg SEL switching signal S1~S4 Primary side switching element S5~S8 Secondary side switching element Tr Transformer

Claims (7)

A primary side bridge circuit including a plurality of primary side switching elements and free wheel diodes connected in parallel to each of the primary side switching elements, and having a first leg and a second leg;
A secondary side bridge circuit including a plurality of secondary side switching elements and a free wheel diode connected in parallel to each of the secondary side switching elements, and having a third leg and a fourth leg;
a conversion unit including a transformer and connected between the primary side bridge circuit and the secondary side bridge circuit;
A control unit that controls the primary side switching element and the secondary side switching element,
The control unit includes:
a first operation of regarding the first leg as a first virtual leg, the second leg as a second virtual leg, the third leg as a third virtual leg, and the fourth leg as a fourth virtual leg;
A second operation in which the second leg is regarded as a first virtual leg, the first leg as a second virtual leg, the fourth leg as a third virtual leg, and the third leg as a fourth virtual leg is alternately performed. At the same time,
Through the first operation and the second operation, each switching element is switched every half cycle in the first virtual leg, second virtual leg, third virtual leg, and fourth virtual leg,
providing a first inter-leg phase difference between the virtual first leg and the virtual second leg;
providing a second inter-leg phase difference between the virtual third leg and the virtual fourth leg,
setting the ratio of the first inter-leg phase difference to the second inter-leg phase difference to a value corresponding to the ratio of the input voltage of the primary side bridge circuit and the output voltage of the secondary side bridge circuit,
A DC-DC converter, characterized in that it controls each of the primary side switching elements and each of the secondary side switching elements. The DC-DC converter according to claim 1, wherein the first operation and the second operation are switched every cycle. 2. The DC-DC converter according to claim 1, wherein the first operation and the second operation are switched every N times the period (N is a natural number of 1 or more). The control unit further includes:
providing an inter-bridge phase difference between the virtual first leg and the virtual third leg;
4. The method according to claim 1, wherein the length of the inter-bridge phase difference is set to be equal to the length of dead time in each leg from the first leg to the fourth leg. The DC-DC converter described. When power is transmitted from the input side of the primary side bridge circuit to the output side of the secondary side bridge circuit,
In the first operation, each of the primary side switching elements and each of the secondary side switching elements of the third leg switches when the current flowing therein is 0, and in the second operation, each of the secondary side switching elements of the third leg switches when the current flowing therein is 0. 4. The primary side switching element and each of the secondary side switching elements of the fourth leg switch when the current flowing through each of them is 0. The DC-DC converter described. The DC-DC converter according to any one of claims 1 to 3, wherein the primary-side converted output voltage of the secondary-side bridge circuit is higher than the input voltage of the primary-side bridge circuit. DC converter. The phase difference between the first legs is φL1, the phase difference between the second legs is φL2, the input voltage of the primary side bridge circuit is E1, the output voltage of the secondary side bridge circuit is E2, the transformer of the conversion section The DC-DC converter according to any one of claims 1 to 3, characterized in that, when n is the turns ratio of the primary side to the secondary side of the converter, the following relationship holds true.

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