JP2022042414A - DC-DC converter - Google Patents

Abstract

To achieve a high-efficiency operation without complicating switching control.SOLUTION: A controller (40) of a DC-DC converter (1) sets a phase difference between legs of a primary side bridge circuit (10) to zero and sets a phase difference between legs of a secondary side bridge circuit (20) to a constant value. The controller (40) controls a phase difference between the primary side bridge circuit (10) and the secondary side bridge circuit (20) depending on a power to be transported from the primary side to the secondary side or vice versa.SELECTED DRAWING: Figure 1

Description

The present invention relates to a DC-DC converter.

As an isolated DC-DC converter, a DAB (Dual Active Bridge) type DC-DC converter is known. The DAB DC-DC converter switches the primary side switching element on and off in the primary side bridge circuit connected to the primary winding of the transformer, and the secondary winding connected to the secondary winding of the transformer. Power can be transmitted from the primary side to the secondary side of the transformer due to the phase difference between the on / off switching of the secondary side switching element in the side bridge circuit.

Japanese Unexamined Patent Publication No. 2016-152687

The conventional DC-DC converter of Patent Document 1 monitors the instantaneous value of the current flowing through the circuit, and controls the on / off timing of each switching element based on the monitoring result. Further, in the present conventional technique, power transmission is controlled by simultaneously controlling the phase difference between bridges and the phase difference between legs. Therefore, the process of controlling power transmission is complicated.

One aspect of the present invention is to realize a DC-DC converter that can operate with high efficiency without complicating the switching control of each switching element.

In order to solve the above problems, the DC-DC converter according to one aspect of the present invention includes a plurality of primary side switching elements and a plurality of capacitor elements connected in parallel to each of the primary side switching elements. , A secondary side bridge circuit having a plurality of secondary side switching elements, and a transformer, connected between the primary side bridge circuit and the secondary side bridge circuit. A conversion unit and a control unit that controls switching between the primary side switching element and the secondary side switching element are provided, and the control unit sets the phase difference between the legs of the primary side bridge circuit to 0. With the phase difference between the legs of the secondary side bridge circuit as a constant value, with the primary side bridge circuit according to the power transported from the primary side to the secondary side or from the secondary side to the primary side. It is characterized in that the phase difference with the secondary side bridge circuit is controlled.

According to one aspect of the present invention, it is possible to realize a DC-DC converter that can operate with high efficiency without complicating the switching control of each switching element.

It is a circuit diagram of the DC-DC converter which concerns on Embodiment 1. FIG. 6 is a timing chart showing a case where power transmission is not performed between the primary side bridge circuit and the secondary side bridge circuit of the DC-DC converter according to the first embodiment. It is a timing chart which shows the case where the power transmission is performed in the 1st mode between the primary side bridge circuit and the secondary side bridge circuit of the DC-DC converter which concerns on Embodiment 1. FIG. 6 is a timing chart showing a case where power is transmitted from the primary side bridge circuit to the secondary side bridge circuit in the second mode of the DC-DC converter according to the first embodiment. It is a timing chart which shows the case where the power is transmitted from the secondary side bridge circuit to the primary side bridge circuit in the 3rd mode of the DC-DC converter which concerns on Embodiment 1. FIG. It is a graph which shows the phase difference φ _B between bridges, and the output characteristic of a DC-DC converter of the DC-DC converter which concerns on Embodiment 1. FIG. It is a circuit diagram of the DC-DC converter which concerns on Embodiment 2. FIG. It is a block diagram which shows the structure of the control part in Embodiment 3. FIG.

[Embodiment 1]
Hereinafter, the DC-DC converter of the first embodiment will be described. For convenience of explanation, the members having the same functions as those described in the first embodiment are designated by the same reference numerals in the following embodiments, and the description thereof will not be repeated. Further, for the sake of brevity, the description of the same matters as those of the publicly known technology will be omitted as appropriate.

(Overall configuration of DC-DC converter)
FIG. 1 is a circuit diagram of a DC-DC converter 1. The DC-DC converter 1 includes a primary side bridge circuit 10, a secondary side bridge circuit 20, a conversion unit 30, and a control unit 40. A DC power supply E10 is connected between the input terminal pairs of the primary bridge circuit 10, which is also the input terminal pair of the DC-DC converter 1. A DC power supply E20 is connected between the output terminal pairs of the secondary bridge circuit 10, which is also the output terminal pair of the DC-DC converter 1. At least one of the DC power source E10 and the DC power source E20 may be a secondary battery.

Here, the "input" and "output" are expressions assuming that electric power is transmitted from the DC power supply E10 side to the DC power supply E20 side, that is, from the primary side to the secondary side. However, this is an expression for convenience, and the same applies to the following. The DC-DC converter 1 of the first embodiment is a bidirectional DC-DC converter, and can also transmit electric power from the secondary side to the primary side.

(Structure of conversion part)
The primary side bridge circuit 10 is connected to the primary side of the conversion unit 30. That is, the output terminal of the primary bridge circuit 10 is connected to the input terminal of the conversion unit 30. The secondary side bridge circuit 20 is connected to the secondary side of the conversion unit 30. That is, the output terminal of the conversion unit 30 (the terminal on the secondary side of the conversion unit) is connected to the input terminal of the secondary bridge circuit 20.

The conversion unit 30 includes a transformer Tr, a reactor L11, and a reactor L12. The reactor L11 and the reactor L12 in the circuit diagram of FIG. 1 equivalently represent the inductance components in the conversion unit 30. The inductance component represented by the reactor L11 and the reactor L12 includes the leakage inductance of the transformer Tr.

Further, the inductance component represented by the reactor L11 and the reactor L12 may include an inductance component due to the reactor as an actual circuit element connected to at least one of the primary winding or the secondary winding of the transformer Tr. good. In the circuit diagram of FIG. 1, the reactor L11, the primary winding of the transformer Tr, and the reactor L12 are shown as being connected in series in this order.

(Configuration of primary bridge circuit)
The primary side bridge circuit 10 includes capacitors C10, primary side switching elements S1 to S4, and snubber capacitors C1 to C4 (capacitor elements). The primary side switching elements S1 to S4 include return diodes D1 to D4, respectively. Snubber capacitors C1 to C4 are connected in parallel to the primary switching elements S1 to S4, respectively. That is, both terminals of the snubber capacitors C1 to C4 are connected to the drain and the source of the primary switching elements S1 to S4, respectively.

A capacitor C10, a first leg on the primary side, and a second leg on the primary side are connected in parallel between the input terminals of the primary side bridge circuit 10. As the primary side first leg, the primary side switching element S1 and the primary side switching element S2 are connected in series in order from the input terminal on the high potential side. Further, as the second leg on the primary side, the primary side switching element S3 and the primary side switching element S4 are connected in series in order from the input terminal on the high potential side.

The intermediate point of the first leg on the primary side, that is, the connection point between the primary side switching element S1 and the primary side switching element S2 is one output terminal of the primary side bridge circuit 10. The intermediate point of the second leg on the primary side, that is, the connection point between the primary side switching element S3 and the primary side switching element S4 is the other output terminal of the primary side bridge circuit 10. That is, the reactor L11 of the conversion unit 30 is connected to the connection point between the primary side switching element S1 and the primary side switching element S2, and the reactor L12 is connected to the primary side switching element S3 and the primary side switching element S4. It is connected to the connection point of.

(Configuration of secondary bridge circuit)
The secondary side bridge circuit 20 includes capacitors C20, secondary side switching elements S5 to S8, and snubber capacitors C5 to C8 (capacitor elements). The secondary side switching elements S5 to S8 include return diodes D5 to D8, respectively. Snubber capacitors C5 to C8 are connected in parallel to the secondary switching elements S5 to S8, respectively. That is, both terminals of the snubber capacitors C5 to C8 are connected to the drain and the source of the secondary switching elements S5 to S8, respectively.

A capacitor C20, a first leg on the secondary side, and a second leg on the secondary side are connected in parallel between the output terminals of the secondary side bridge circuit 20. As the first leg on the secondary side, the secondary side switching element S5 and the secondary side switching element S6 are connected in series in order from the input terminal on the high potential side. Further, as the secondary side second leg, the secondary side switching element S7 and the secondary side switching element S8 are connected in series in order from the input terminal on the high potential side.

The intermediate point of the first leg on the secondary side, that is, the connection point between the secondary side switching element S5 and the secondary side switching element S6 is one input terminal of the secondary side bridge circuit 20. The intermediate point of the secondary side second leg, that is, the connection point between the secondary side switching element S7 and the secondary side switching element S8 becomes the other input terminal of the secondary side bridge circuit 20. That is, the secondary winding of the transformer Tr of the conversion unit 30 is the connection point between the secondary side switching element S5 and the secondary side switching element S6, and the connection between the secondary side switching element S7 and the secondary side switching element S8. Connected to a point.

(Control unit)
The control unit 40 refers to the primary side voltage V1 which is the input voltage to the primary side bridge circuit 10 and the primary side current I1 which is the input current to the primary side bridge circuit 10 for primary side switching. It controls the switching of the elements S1 to S4 and the secondary side switching elements S5 to S8.

Alternatively, the control unit 40 refers to the secondary side voltage V2 which is the output voltage of the secondary side bridge circuit 20 and the secondary side current I2 which is the output current of the secondary side bridge circuit 20 and refers to the primary side switching element. It controls the switching of S1 to S4 and the secondary side switching elements S5 to S8.

Here, each of the primary side voltage V1, the primary side current I1, the secondary side voltage V2, and the secondary side current I2 represents a time average value.

(DC-DC converter operation: basic operation)
The operation of the DC-DC converter 1 according to the first embodiment will be described with reference to FIGS. 2 to 5. FIG. 2 is a timing chart showing a case where power transmission is not performed between the primary side bridge circuit 10 and the secondary side bridge circuit 20. FIG. 3 is a timing chart showing a case where power is transmitted in the first mode between the primary side bridge circuit and the secondary side bridge circuit. FIG. 4 is a timing chart showing a case where power is transmitted from the primary side bridge circuit to the secondary side bridge circuit in the second mode. FIG. 5 is a timing chart showing a case where power is transmitted to the primary bridge circuit in the third mode.

As is generally known, in order to prevent a through current that flows when two switching elements are simultaneously conducted in each leg, a gate signal that turns off both of these two switching elements is used when switching on and off. It is necessary to set a dead time to emit. However, in the following description and FIGS. 2 to 5, the dead time is ignored for the sake of clarity. However, in reality, a dead time is appropriately provided.

First, the operation of the DC-DC converter 1 of the present embodiment will be described with reference to FIG. The duty of the primary side switching elements S1 to S4 in the primary side bridge circuit 10 is a fixed value of 50% ignoring the dead time. Further, the switching timings of the primary side switching elements S1 and S4 match, and the switching timings of the primary side switching elements S2 and S3 match. That is, the phase difference between the legs of the primary side bridge circuit 10 is 0.

Further, the duty of the secondary side switching elements S5 to S8 in the secondary side bridge circuit 20 is a fixed value of 50% ignoring the dead time. Further, a phase difference φ _L between legs is provided at the switching timing of the secondary side switching elements S5 and S8, and a phase difference φ _L between legs is also provided at the switching timing of the secondary side switching elements S6 and S7. Here, it is assumed that the switching timing of the secondary side switching element S8 is delayed from that of the secondary side switching element S5.

Further, a phase difference φ _B between the bridges between the secondary side bridge circuit 20 and the primary side bridge circuit 10 is provided. Here, when the switching timing of the secondary side switching element S5 is delayed from that of the primary side switching element S1, the inter-bridge phase difference φ _B is positive, and when it is advanced, the inter-bridge phase difference φ _B is negative. do. FIG. 2 shows the case of φ _B = −φ _L / 2.

Here, the conversion unit primary voltage v _tr1 shown in FIG. 2 is the potential of the source of the primary switching element S1 with respect to the drain of the primary switching element S4, and is the output voltage of the primary bridge circuit 10. Is. The conversion unit secondary side voltage v _tr2 is the potential of the source of the secondary side switching element S5 with respect to the drain of the secondary side switching element S8, and is the input voltage of the secondary side bridge circuit 20. The conversion unit primary side current _itr1 is a current flowing through the primary winding of the transformer Tr. The conversion unit secondary side current _itr2 is a current flowing through the secondary side winding of the transformer Tr.

The conversion unit primary voltage v _tr1 generates a voltage waveform in which + V1 and −V1 appear alternately by the on / off operation of the primary switching elements S1 to S4 described above. On the other hand, the conversion unit secondary side voltage v _tr2 generates an AC waveform in which + V2, 0, and −V2 appear in sequence by the operation of the above-mentioned secondary side switching elements S5 to S8.

The conversion unit secondary side voltage v _tr2 becomes 0 during the period in which the switching of the secondary side second leg is delayed with respect to the secondary side first leg. At this time, the secondary side switching element S6 and the secondary side switching element S8 are turned on at the same time. Therefore, the output terminal pair of the conversion unit 30 is short-circuited through the secondary side switching element S6 and the secondary side switching element S8. Alternatively, at this time, the secondary side switching element S5 and the secondary side switching element S7 are turned on at the same time.

Of the AC waveform generated in the conversion unit secondary voltage v _tr2 , the section where the voltage is not 0 is defined as the pulse width τ of the interbridge voltage. As is clear from FIG. 2, the inter-leg phase difference φ _L and the inter-bridge voltage pulse width τ have the following relational expressions.

During the period of the pulse width τ, the voltage (+ V1) of the DC power supply E10 is applied to the conversion unit primary side voltage v _tr1 and the voltage (+ V2) of the DC power supply E20 is applied to the conversion unit secondary side voltage v _tr2 . And these voltages are balanced. Next, when switching is performed in the first leg of the secondary side and the period shifts to the period in which the conversion unit secondary side voltage v _tr2 is 0, the conversion unit primary side current _itr1 and the conversion unit secondary side current _itr2 are in the positive direction. It gradually increases and energy is stored in the reactor L11 and the reactor L12.

The conversion unit primary _side voltage v _tr1 is inverted to −V1 when the phase difference between the bridges φB has elapsed after the transition to the period in which the conversion unit secondary side voltage v _tr2 is 0. The magnitude of the conversion unit primary side current _itr1 and the conversion unit secondary side current _itr2 peaks at this time and then gradually decreases. Then, the energy stored in the reactor L11 and the reactor L12 is reduced. After shifting to the period when the conversion unit secondary voltage v _tr2 is 0, when the phase difference between legs φ _L has elapsed, -V1 is used as the conversion unit primary voltage v _tr1 and the conversion unit secondary voltage. -V2 is applied to the conversion unit 30 as v _tr2 , and these voltages are balanced.

If the inter-bridge phase difference φ _B is exactly half of the inter-leg phase difference φ _L , the period in which the magnitude of the conversion unit primary side current _itr1 increases and the period in which it decreases are equal. In this case, during the period of the pulse width τ, the conversion unit primary side current _itr1 and the conversion unit secondary side current _itr2 are 0. Further, in the section of the pulse width τ of the bridge-to-bridge voltage, since the conversion unit secondary voltage v _tr2 is 0, the power transmission is always 0. Therefore, power transmission between the primary side bridge circuit 10 and the secondary side bridge circuit 20 is not performed.

The maximum value of the magnitude of the conversion unit primary side current _itr1 that peaks at the timing when the primary side switching elements S1 to S4 are switched is the inductor current maximum value _iLpeak of the following equation.

Here, in order to realize zero voltage switching (ZVS) when the primary side switching elements S1 to S4 turn off in the primary side bridge circuit 10, the primary side (reactor) of the conversion unit 30 at the time of switching is realized. It is necessary that sufficient current is flowing through L11 and the reactor L12). Such a ZVS minimum possible current I _{min_ZVS} is expressed by the following equation.

Therefore, zero volt switching (ZVS) in the primary side bridge circuit 10 is realized under the condition that the maximum inductor current value i _Lpeak is larger than the minimum ZVS possible current _{Imin_ZVS} and the following equation is satisfied.

However, if the inductor current maximum value _iLpeak is larger than necessary for the ZVS possible minimum current _{Imin_ZVS} , a current loss due to charging and discharging of the snubber capacitor occurs. Therefore, it is advisable to determine the inter-leg phase difference φ _L so that the maximum inductor current value i _Lpeak is as small as possible within the range that satisfies the inequality.

(Operation of DC-DC converter: 1st mode)
When the following equation is satisfied, it operates as a first mode in which relatively little power transmission can be performed between the primary side and the secondary side. In the first mode, zero volt switching (ZVS) is possible in the primary side bridge circuit 10 by defining the phase difference φ _L between the legs as described above.

FIG. 3 shows a case where the phase on the secondary side is advanced within the range of the above equation (when φ _B is reduced) from the case of FIG. 2 (φ _B = −φ _L / 2). In this case, the switching of the primary side switching elements S1 to S4 is performed in the section of the leg-to-leg phase difference φ _L where the conversion unit secondary side voltage v _tr2 is 0. The current flowing through the reactor L11 and the reactor L12 at the timing when the primary side switching elements S1 to S4 are switched is the above-mentioned maximum inductor current value i _Lpeak .

Further, in the section of the phase difference between legs φ _L , the conversion unit secondary side voltage v _tr2 is 0, but in the section of the pulse width τ of the bridge-to-bridge voltage, the conversion unit secondary side current _itr2 is not 0. Power transmission occurs between the primary side bridge circuit 10 and the secondary side bridge circuit 20. That is, power can be transmitted by fixing the phase difference φ _L between the legs and changing only the phase difference φ _B between the bridges.

The transmission power P _OUT in the first mode can be expressed by the following equation. In the first mode, the control unit 40 determines the inter _- bridge phase difference φB according to the transmission power P _OUT according to the following equation, and executes switching of each switching element.

Further, depending on the value of the phase difference φ _B between the bridges, the transfer of power transmission between the primary side bridge circuit 10 and the secondary side bridge circuit 20 changes, and in φ _B > −φ _L / 2, from the primary side bridge circuit 10. Power can be transmitted to the secondary side bridge circuit 20, and if φ _B <−φ _L / 2, power can be transmitted from the secondary side bridge circuit 20 to the primary side bridge circuit 10. That is, the direction of power transmission can be selected by the phase difference between the bridges.

(Operation of DC-DC converter: 2nd mode)
As shown in FIG. 4, when the phase difference between bridges φ _B is further increased (advanced in the positive direction) from the range of the first mode, that is, in the range of the following equation, from the primary side to the secondary side. It operates as a second mode in which a larger amount of power is transmitted than in the case of the first mode.

In this case, the switching of the primary side switching elements S1 to S4 is performed not in the section of the leg-to-leg phase difference _φL where the conversion unit secondary side voltage v _tr2 is 0, but in the section of the pulse width τ of the bridge-to-bridge voltage. .. The conversion unit primary side current _itr1 in the interval of the pulse width τ is larger than the inductor current maximum value _iLpeak . Therefore, zero volt switching (ZVS) is realized in the primary side bridge circuit.

Further, since the conversion unit secondary side voltage v _tr2 and the conversion unit secondary side current _itr2 are generated in the section of the pulse width τ of the inter-bridge voltage and the section of the inter _- bridge phase difference φB, the second In the mode, power transfer is performed. The amount of power transmission in the second mode can be expressed by the following equation. In the second mode, the control unit 40 determines the inter _- bridge phase difference φB according to the following equation according to the amount of power transmission, and executes switching of each switching element.

(Operation of DC-DC converter: 3rd mode)
As shown in FIG. 5, when the phase difference between bridges φ _B is further reduced (advanced in the negative direction) from the range of the first mode, that is, in the range of the following equation, from the secondary side to the primary side, It operates as a third mode in which a larger amount of power is transmitted than in the case of the first mode.

In the third mode as well as in the second mode, zero volt switching (ZVS) is realized in the primary side bridge circuit. The amount of power transmission in the third mode can be expressed by the following equation. In the third mode, the control unit 40 determines the inter _- bridge phase difference φB according to the following equation according to the amount of power transmission, and executes switching of each switching element.

(Output characteristics)
FIG. 6 is a graph showing the phase difference between bridges φB and the output characteristics of the DC _- DC converter 1. The horizontal axis of FIG. 6 is the phase difference φ _B between bridges. The first vertical axis of FIG. 6 is the transmission power between the primary side and the secondary side, where the case of transmission from the primary side to the secondary side is positive. The second vertical axis shows the inductor current (time average value) which is the current flowing on the primary side of the conversion unit 30. In FIG. 6, the transmission power is represented by a solid line, and the inductor current is represented by a alternate long and short dash line.

As shown in FIG. 6, in the DC-DC converter 1 according to the first embodiment, when the operation mode is switched, it is possible to perform output control that makes a smooth change without losing the continuity of the transmission power and the maximum value of the inductor current. Therefore, control with good controllability is possible even in the output region where the operation mode is switched.

(Action effect)
In the DC-DC converter 1 according to the first embodiment, in the output control, not both the inter-bridge phase difference φ _B and the inter-leg phase difference φ _L are controlled, but only the inter-bridge phase difference φ _B is controlled. Further, it is not necessary to determine the switching timing based on the instantaneous value of the output voltage or the output current. Therefore, the calculation load of the control unit is small and simple control is possible. In addition, seamless transmission power and inductor current can be adjusted when changing the operation mode in the first mode, the second mode, and the third mode.

Further, in a DC-DC converter in which a snubber capacitor is arranged in a switching element, the current normally flowing in the conversion unit is small at the time of low power transmission, and it is difficult to realize zero volt switching (ZVS) at the time of turning on the switching element. However, in the DC-DC converter 1 according to the first embodiment, a sufficient inductor current is secured to extract the charge of the snubber capacitor when the primary side switching element is turned on in the low power transmission (first mode). .. Therefore, even in the range of the operation mode 1 at the time of low power transmission, it is possible to perform control with little loss of power transmission.

[Modification 1]
In the first embodiment, the phase difference between the legs of the primary side bridge circuit 10 is set to 0, the phase difference φ _L between the legs of the secondary side bridge circuit is fixed, and the primary side bridge circuit is zero-volt switched (ZVS). Although the main operation is described, the operation of the primary side bridge circuit 10 and the secondary side bridge circuit 20 may be interchanged. This is because the DC-DC converter 1 of the first embodiment is a bidirectional DC-DC converter, and the names of the primary side and the secondary side are for convenience.

That is, the phase difference between the legs of the secondary side bridge circuit 20 may be set to 0, and the phase difference φ _L between the legs of the primary side bridge circuit 10 may be fixed. In this case, in the section of the operation mode 1, the secondary side bridge circuit 20 can perform zero volt switching (ZVS). Further, when φ _B <φ _L / 2, power can be transmitted from the secondary side bridge circuit 20 to the primary side bridge circuit 10, and when φ _B > φ _L / 2, power can be transmitted from the primary side bridge circuit 10 to the secondary side bridge circuit. Power can be transmitted to 20.

[Modification 2]
When the ratio of the primary side voltage V1 and the secondary side voltage V2 is different from the turns ratio n of the primary winding and the secondary winding of the transformer Tr, the primary side and the secondary side of the conversion unit 30 are The balancing condition is different from that of the first embodiment. In this case, although the condition that power transmission is not performed shifts between the primary side and the secondary side, control may be performed in the same manner as in the first embodiment.

[Modification 3]
The primary side bridge circuit, the secondary side bridge circuit, and the conversion unit may be a three-phase circuit instead of the single-phase circuit as shown in FIG.

[Embodiment 2]
Embodiment 2 of the present invention will be described below with reference to FIG. 7. FIG. 7 is a circuit diagram of the DC-DC converter 2 according to the second embodiment. The DC-DC converter 2 according to the second embodiment includes a primary side bridge circuit 11, a secondary side bridge circuit 20, a conversion unit 30, and a control unit 41.

The primary side bridge circuit 11 is a half bridge circuit provided with a capacitor Cp and a capacitor Cn instead of the primary side switching element S1 and the primary side switching element S2 of the primary side bridge circuit 10 in the DC-DC converter 1. be. Further, the control unit 41 is not a full bridge circuit but a control unit 41 that controls a half bridge circuit. As described above, the present invention can be applied even if one of the primary side bridge circuit and the secondary side bridge circuit is used as a half bridge circuit. In that case, the phase difference between the legs φ _L may be provided on the side of the full bridge circuit.

By switching the primary side switching element S3 or the primary side switching element S4, the control unit 41 causes the conversion unit primary side current i _HB to flow, and the conversion unit secondary side current i _tr2 is generated. Assuming that the voltage on the primary side of the conversion unit at this time is v _HB , v _HB shows a value that is half that of V1.

In the present embodiment, there is an advantage that the control of the primary side bridge circuit 11 becomes easier by using the half bridge circuit as compared with the first embodiment using the full bridge circuit.

[Embodiment 3]
Embodiment 3 of the present invention will be described below with reference to FIG. In the third embodiment, the internal configuration of the control unit is shown more concretely. FIG. 8 is a block diagram showing the configuration of the control unit 50 in the third embodiment.

The control unit 50 includes a power calculation unit 51, a deviation calculation unit 52, a phase calculation unit 53, and a switching pulse generation unit 54.

The power calculation unit 51 calculates the output power P2 based on the secondary side voltage V2 and the secondary side current I2. The power calculation unit 51 outputs the output power P2 to the deviation calculation unit 52.

The deviation calculation unit 52 calculates the deviation ΔP _out from the output power P2 and the target output power P _out ^* . The deviation calculation unit 52 outputs the deviation ΔP _out to the phase calculation unit 53.

The phase calculation unit 53 determines the inter-leg phase difference φ _L and the inter-bridge phase difference φ _B based on the input deviation ΔP _out , and the relational expression between the transmission power P _OUT and the inter-bridge phase difference φ _B described in the first embodiment. Derived based on. In the calculation, the primary side voltage V1, the secondary side voltage V2, the inductance L in the equivalent circuit based on the primary side, the frequency f of the current applied to the transformer, and the snubber capacitors C1 to C8, respectively. Capacitance C _snub and is also used. The calculated inter-leg phase difference φ _L and inter-bridge phase difference φ _B are output to the switching pulse generation unit.

The switching pulse generation unit 54 uses the calculated inter-leg phase difference φ _L and inter-bridge phase difference φ _B to generate a signal for controlling the on / off of each of the switching elements S1 to S8.

The control unit 50 has a function of feeding back to a predetermined target output power P _out ^* based on the power of the secondary bridge circuit currently being output. The items to be fed back are not limited to electric power, but may be voltage and current.

〔summary〕
The DC-DC converter according to the first aspect of the present invention is a primary side bridge circuit having a plurality of primary side switching elements and a plurality of capacitor elements connected in parallel to each of the primary side switching elements. , A secondary side bridge circuit having a plurality of secondary side switching elements, a conversion unit having a transformer and connected between the primary side bridge circuit and the secondary side bridge circuit, and the primary side switching. A control unit that controls switching between the element and the secondary side switching element is provided, and the control unit sets the phase difference between the legs of the primary side bridge circuit to 0 and sets the phase difference between the legs of the secondary side bridge circuit to 0. The primary side _bridge circuit and the said It is characterized in that the phase difference between the secondary side bridge circuit and the bridge circuit (phase difference between bridges φ _B ) is controlled.

In the DC-DC converter according to the second aspect of the present invention, in the first aspect, when the power of the control unit is equal to or less than a predetermined value, the secondary side terminals of the conversion unit are connected to each other. It is characterized by executing a first mode for controlling the primary side switching element to turn on or off during a short circuit period via the side switching element.

In the DC-DC converter according to the third aspect of the present invention, in the second aspect, when the electric power exceeds the predetermined value, the control unit has the second terminal between the terminals on the secondary side of the conversion unit. It is characterized in that a second mode for controlling the primary side switching element to turn on or off is executed outside the period of short-circuiting via the secondary side switching element.

In the DC-DC converter according to the fourth aspect of the present invention, in the second or third aspect, the constant value is set at the timing when the primary side switching element is turned on or off at the time of executing the first mode. The current flowing from the primary side bridge circuit to the conversion unit (inductor current maximum value _iLpeak ) is defined to be a value that enables zero volt switching of the primary side switching element.

The DC-DC converter according to the fifth aspect of the present invention is characterized in that, in any one of aspects 1 to 4, the primary side bridge circuit is a full bridge or a half bridge.

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

1, 2 DC-DC converter 10, 11 Primary side bridge circuit 20 Secondary side bridge circuit 30 Conversion unit 40, 41, 50 Control unit C1 to C8 Snubber capacitor (capacitor element)
S1 to S4 Primary side switching element S5 to S8 Secondary side switching element Tr Transformer

Claims (6)

A primary side bridge circuit having a plurality of primary side switching elements and a plurality of capacitor elements connected in parallel to each of the primary side switching elements.
A secondary bridge circuit with multiple secondary switching elements,
A conversion unit having a transformer and connected between the primary side bridge circuit and the secondary side bridge circuit,
A control unit for controlling switching between the primary side switching element and the secondary side switching element is provided.
The control unit
The phase difference between the legs of the primary bridge circuit is set to 0.
The phase difference between the legs of the secondary bridge circuit is set to a constant value.
Controlling the phase difference between the primary side bridge circuit and the secondary side bridge circuit according to the power transported from the primary side to the secondary side or from the secondary side to the primary side. A featured DC-DC converter. The control unit
When the power is less than or equal to a predetermined value,
Executing the first mode for controlling the primary side switching element to turn on or off during the period in which the terminals on the secondary side of the conversion unit are short-circuited via the secondary side switching element. The DC-DC converter according to claim 1. The control unit
When the electric power exceeds the predetermined value,
A second mode for controlling the primary side switching element to turn on or off is executed outside the period in which the terminals on the secondary side of the conversion unit are short-circuited via the secondary side switching element. 2. The DC-DC converter according to claim 2. The constant value means that the current flowing from the primary side bridge circuit to the conversion unit at the timing when the primary side switching element is turned on or off during the execution of the first mode is the primary side switching element. The DC-DC converter according to claim 2 or 3, wherein the DC-DC converter is defined to have a value that enables zero-volt switching. The DC-DC converter according to any one of claims 1 to 4, wherein the primary bridge circuit is a full bridge. The DC-DC converter according to any one of claims 1 to 4, wherein the primary bridge circuit is a half bridge.

Images