DC-DC converter

Abstract

To reduce switching loss in a DC-DC converter.SOLUTION: A DC-DC converter (1) comprises: a primary bridge circuit (10) having a first leg (11) and a second leg (12); and a secondary bridge circuit (20) having a third leg (21) and a fourth leg (22). The DC-DC converter determines a phase difference between the primary bridge circuit and the secondary bridge circuit in accordance with a voltage difference between a voltage applied to the primary bridge circuit and a primary conversion voltage of a voltage applied to the secondary bridge circuit. The DC-DC converter controls a phase difference between the first leg and the second leg, and a phase difference between the third leg and the fourth leg in accordance with electric power to be carried.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a DC-DC converter. [Background Art]

[0002] Patent Document 1 discloses a method for bidirectional power transmission and step-up / step-down by controlling the phase difference between bridges, the phase difference between legs, and the duty ratio in a dual active bridge type DC-DC converter. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2021-048702 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the conventional technology as described above requires simultaneous control of the aforementioned individual control parameters, which makes control complicated.

[0005] One aspect of the present invention aims to reduce switching loss through simple control in a DC-DC converter. [Means for Solving the Problem]

[0006] To solve the above problems, a DC-DC converter according to one aspect of the present invention comprises: a primary bridge circuit including a plurality of primary switching elements and having a first leg and a second leg; a secondary bridge circuit including a plurality of secondary switching elements and having a third leg and a fourth leg; a conversion unit having a transformer and connected between the primary bridge circuit and the secondary bridge circuit; and a control unit that controls the switching of the primary and secondary switching elements. The control unit determines the phase difference between the primary bridge circuit and the secondary bridge circuit according to the voltage difference between a first voltage, which is a voltage applied to the primary bridge circuit from outside the DC-DC converter, and a second voltage, which is the primary-side converted voltage of the voltage applied to the secondary bridge circuit from outside the DC-DC converter, and controls the phase difference between the first leg and the second leg and the phase difference between the third leg and the fourth leg according to the power transported from the primary side to the secondary side or from the secondary side to the primary side. [Effects of the Invention]

[0007] According to one aspect of the present invention, switching losses in a DC-DC converter can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This document shows the circuit diagram and block diagram of the DC-DC converter 1 according to this embodiment. [Figure 2] This timing chart shows an example of operation in the low-power region at rated voltage (motoring) when variable a = 1. [Figure 3] This timing chart shows an example of operation (powering) in the low-power region at rated voltage when variable a > a > 0. [Figure 4] This timing chart shows an example of operation in the high-power region at rated voltage (motoring) when variable a = 1. [Figure 5]This timing chart shows an example of operation (motoring) in the high-power region at rated voltage when variable a > a > 0. [Figure 6] This graph shows the relationship between the phase difference φL1 between the first legs and the power Pout. [Figure 7] This timing chart shows an example of operation (regeneration) in the low-power region at rated voltage when a=1 for variable a. [Figure 8] This timing chart shows an example of operation in the high-power region under rated voltage (regeneration) when a=1 for variable a. [Figure 9] This is a timing chart showing an example of operation during voltage boosting. [Figure 10] This is a timing chart showing an example of operation during step-down voltage conversion. [Modes for carrying out the invention]

[0009] [Embodiment] One embodiment of the present invention will be described in detail below. Figure 1 is a circuit diagram and block diagram of the DC-DC converter 1 according to this embodiment. The DC-DC converter 1 comprises a primary bridge circuit 10, a secondary bridge circuit 20, a conversion unit 30, and a control unit 40.

[0010] (Configuration of DC-DC converter 1) The primary bridge circuit 10 is connected to a DC power supply at its input terminals. The secondary bridge circuit 20 is connected to a DC power supply at its output terminals. The voltage between the input terminals of the primary bridge circuit 10, that is, the voltage applied to the primary bridge circuit 10 from outside the DC-DC converter 1, is the primary voltage E1, and the current flowing through the input terminals of the primary bridge circuit 10 is the primary current I1. The voltage between the output terminals of the secondary bridge circuit 20, that is, the voltage applied to the secondary bridge circuit 20 from outside the DC-DC converter 1, is the secondary voltage E2, and the current flowing through the output terminals of the secondary bridge circuit 20 is the secondary current I2. Here, the primary voltage E1, primary current I1, secondary voltage E2, and secondary current I2 are time-averaged values ​​acquired by the control unit 40 and are used for control described later.

[0011] Here, "input" and "output" are expressions that assume power is transmitted from the primary bridge circuit 10 to the secondary bridge circuit 20. However, this is a convenient expression, and the same applies below. The DC-DC converter 1 of Embodiment 1 is a bidirectional dual active bridge type DC-DC converter, and is also capable of transmitting power from the secondary side to the primary side. Furthermore, in this specification, the transmission of power Pout from the primary side to the secondary side is referred to as power transmission (Pout>0), and the transmission of power Pout from the secondary side to the primary side is referred to as regeneration (Pout<0).

[0012] The primary bridge circuit 10 is a circuit in which a capacitor element C1 is connected in parallel to a full bridge circuit provided with four primary switching elements S1 to S4. The primary bridge circuit 10 consists of a first leg 11, a second leg 12, and a capacitor element C1. The first leg 11 is composed of primary switching elements S1 and S2 connected in series. The second leg 12 is composed of primary switching elements S3 and S4 connected in series.

[0013] The secondary-side bridge circuit 20 is a circuit in which a capacitor element C2 is connected in parallel to a full-bridge circuit provided with four secondary-side switching elements S5 to S8. The secondary-side bridge circuit 20 includes a third leg 21, a fourth leg 22, and the capacitor element C2. The third leg 21 is configured by connecting the secondary-side switching element S5 and the secondary-side switching element S6 in series. The fourth leg 22 is configured by connecting the secondary-side switching element S7 and the secondary-side switching element S8 in series.

[0014] Primary-side switching elements S1 to S4 and secondary-side switching elements S5 to S8 (hereinafter collectively referred to as switching elements S1 to S8) can each be formed of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or another FET (Field Effect Transistor). Alternatively, the switching elements S1 to S8 may be formed of an IGBT (Insulated Gate Bipolar Transistor) or other transistors.

[0015] The conversion unit 30 includes a transformer Tr with a turns ratio n and a reactor L, and is connected between the primary-side bridge circuit 10 and the secondary-side bridge circuit 20. In the circuit diagram of FIG. 1, an inductance component of the conversion unit 30 is equivalently represented as the reactor L provided on the primary side. Here, the reactor L is represented as being connected to a connection point between the primary-side switching element S1 and the primary-side switching element S2, and to one end of a primary winding of the transformer Tr. Further, the other end of the primary winding of the transformer Tr is represented as being connected to a connection point between the primary-side switching element S3 and the primary-side switching element S4.

[0016] Herein, although the description is given such that reactor L is connected to the primary winding of transformer Tr, the present invention is not limited thereto. In addition, reactor L is described to represent a configuration including an inductance that is not included in transformer L; that is, an actual reactor element does not need to be present on the circuit. In a case where conversion unit 30 is provided with a reactor element as an actual element, the reactor element may be disposed on the primary side of transformer Tr, may be disposed on the secondary side thereof, or may be disposed on both the primary side and the secondary side thereof.

[0017] Reactor L may include a leakage inductance of transformer Tr. In the circuit diagram of FIG. 1, the secondary winding of transformer Tr is illustrated as being connected to the connection point between secondary-side switching element S5 and secondary-side switching element S6 and the connection point between secondary-side switching element S7 and secondary-side switching element S8.

[0018] A voltage on the primary side of conversion unit 30, that is, a voltage from the connection point between primary-side switching element S3 and primary-side switching element S4 to the connection point between primary-side switching element S1 and primary-side switching element S2 is defined as primary-side AC voltage Vac1. In addition, a current on the primary side of conversion unit 30, that is, a current flowing between conversion unit 30 and primary-side bridge circuit 10 is defined as primary-side AC current Iac1.

[0019] A voltage on the secondary side of conversion unit 30, that is, a voltage from the connection point between secondary-side switching element S7 and secondary-side switching element S8 to the connection point between secondary-side switching element S5 and secondary-side switching element S6 is defined as secondary-side AC voltage Vac2. In addition, a current on the secondary side of conversion unit 30, that is, a current flowing between conversion unit 30 and secondary-side bridge circuit 20 is defined as secondary-side AC current Iac2.

[0020] Here, primary-side voltage E1 is also referred to as a first voltage (=E1), and a voltage obtained by multiplying secondary-side voltage E2 by winding ratio n is also referred to as a second voltage (=nE2). That is, the second voltage is a primary-side converted voltage of secondary-side voltage E2.

[0021] (Reference Operation Example) In the invention described in Patent Document 1, power transmission and voltage boosting / bucking are performed by simultaneously controlling each of the above-mentioned control parameters. Furthermore, each switching element reduces losses by setting its voltage or current to zero during switching. However, since the switching element whose losses are reduced in this way changes depending on the control mode, it is necessary to implement the same level of thermal countermeasures for all switching elements.

[0022] Furthermore, when the primary and secondary voltages are in voltage balance, or when the secondary voltage is greater than the primary voltage (boost operation: Figures 12 and 16 of Patent Document 1), a large output can be obtained, but it also has the disadvantage of high losses. In the case of voltage balance, Patent Document 1 achieves a reduction in switching losses by ZCS in one leg. Also, when the secondary voltage is smaller than the primary voltage (buck operation: Figures 6 and 15 of Patent Document 1), it has the disadvantage that the output cannot be increased if the voltage difference is small. The buck operation in Patent Document 1 utilizes the fact that energy is stored when the potential difference between the power supplies on both sides is applied to the inductor.

[0023] (Setting of winding ratio n) The winding ratio n of a transformer Tr can be expressed as follows, using the number of turns n1 of the primary winding and the number of turns n2 of the secondary winding.

number

[0024] The control unit 40 controls the switching of the switching elements S1 to S8 by appropriately referring to the secondary voltage E2 and secondary current I2.

[0025] The winding ratio n of the transformer Tr is set such that the following relationship is satisfied by the maximum value E1max within the range of the primary voltage E1 to which the DC-DC converter 1 of this embodiment is applied and the minimum value E2min within the range of the secondary voltage E2.

number

[0026] However, the DC-DC converter 1 of this embodiment is applicable only when the winding ratio n is greater than 1.

[0027] As mentioned above, the DC-DC converter 1 is a bidirectional dual active bridge type DC-DC converter, so the terms primary and secondary are merely for convenience. If the relationship between the maximum value E2max of the secondary voltage E2 and the minimum value E1min of the primary voltage E1 satisfies E2max > E1min, then the secondary bridge circuit can be read as the primary bridge circuit, and the primary bridge circuit as the secondary bridge circuit, and the DC-DC converter 1 of this embodiment can be applied accordingly.

[0028] (Block diagram) The control unit 40 controls each switching element S1 to S8 according to the block diagram shown in Figure 1. The block diagram determines the phase difference between each switching element. The block diagram shown in Figure 1 is broadly divided into block diagram 41, block diagram 42, and block diagram 43. The duty cycle of each switching element S1 to S8 is fixed, for example, to 0.5. Therefore, since there is no need to control the duty cycle, control is easy.

[0029] (Determination of the phase difference φL1 between the first leg and the phase difference φL2 between the second leg) Next, we will explain the details of each block diagram. First, we will explain block diagrams 41 and 42.

[0030] Block diagram 41 shows that the control unit 40 determines the phase difference between legs (first leg phase difference φL1) in the primary bridge circuit 10 according to the power Pout of the DC-DC converter 1. The first leg phase difference φL1 is the phase difference between the first leg 11 and the second leg 12, and the sign of this value changes depending on the control mode.

[0031] The control unit 40 determines the power Pout of the DC-DC converter 1 from the secondary voltage E2 and secondary current I2, and feeds back the deviation between the power Pout and the target power Pref_n using PI control. The control unit 40 determines the phase difference φL1 between the first legs through a limiter that restricts the absolute value of the controlled quantity determined by PI control to an appropriate value that does not saturate.

[0032] Block diagram 42 shows that the control unit 40 determines the phase difference between legs in the secondary bridge circuit 20 (second leg phase difference φL2) according to the first leg phase difference φL1 and the primary voltage E1 and secondary voltage E2. The second leg phase difference φL2 is the phase difference between the third leg 21 and the fourth leg 22, and the sign of this value changes depending on the control mode.

[0033] The control unit 40 multiplies the phase difference φL1 between the first legs by the ratio of the second voltage to the first voltage (=E1 / nE2) to obtain the phase difference φL2 between the second legs.

[0034] Therefore, depending on the power being transported from the primary bridge circuit 10 to the secondary bridge circuit 20, or from the secondary bridge circuit 20 to the primary bridge circuit 10, the phase difference between the first legs, φL1 (the phase difference between the first leg 11 and the second leg 12), is determined, and the phase difference between the second legs, φL2 (the phase difference between the third leg 21 and the fourth leg 22), is determined and controlled.

[0035] (Phase difference between bridges φB) Block diagram 43 shows that the control unit 40 determines the phase difference (inter-bridge phase difference φB) between the primary bridge circuit 10 and the secondary bridge circuit 20 according to the primary voltage E1 and the secondary voltage E2. The inter-bridge phase difference φB is positive when the primary bridge circuit 10 leads the secondary bridge circuit 20.

[0036] The control unit 40 determines the variable a by the following equation.

number

[0037] Subsequently, the control unit 40 checks whether variable a is less than or equal to 0, and if it is, it performs a limit process to set variable a to 0. In other words, if variable a is less than or equal to 0, the inter-bridge phase difference is set to 0. Also, if variable a is greater than 1, it performs a limit process to set variable a to 1. Furthermore, the control unit 40 determines the inter-bridge phase difference φB by multiplying variable a by the maximum value of the inter-bridge phase difference φB_max, which is a constant specific to the DC-DC converter 1.

[0038] In other words, the inter-bridge phase difference φB is the phase difference between the primary bridge circuit 10 and the secondary bridge circuit 20, determined according to the voltage difference between the first voltage and the second voltage. The inter-bridge phase difference φB does not depend on the output power. Note that when variable a is 1, the first voltage and the second voltage are equal.

[0039] (Control mode) The DC-DC converter 1 according to this embodiment operates in three control modes: rated voltage operation, boost operation, and buck operation. Of these, boost operation and buck operation are operating modes when the relationship between the primary voltage E1 and the secondary voltage E2 deviates significantly from the balanced state determined by the winding ratio n of the transformer Tr. In this case, the operation of the DC-DC converter 1 according to this embodiment is restricted so that the power in boost operation becomes powering and the power in buck operation becomes regenerative.

[0040] In contrast, rated voltage operation is an operating mode in which the relationship between the primary voltage E1 and the secondary voltage E2 is matched to the winding ratio n of the transformer Tr, and the power can be used for both traction and regeneration. Rated voltage operation is a state in which the primary voltage E1 and the secondary voltage E2 are in voltage balance.

[0041] (Operates at rated voltage) Rated voltage operation occurs when variable a is positive. That is, when the voltage difference between the first voltage (=E1) and the second voltage (=nE2) is less than the reference voltage Diff. In rated voltage operation, the phase difference φL1 between the first legs is positive when the second leg 12 leads the first leg 11, and the phase difference φL2 between the second legs is positive when the fourth leg 22 leads the third leg 21. Furthermore, rated voltage operation is broadly divided into low-power region and high-power region.

[0042] Figure 2 is a timing chart showing an example of operation in the low-power region at rated voltage (motoring) when variable a = 1 (when the first voltage (= E1) and the second voltage (= nE2) are equal). Figure 3 is a timing chart showing an example of operation in the low-power region at rated voltage (motoring) when variable a > a > 0. As shown in Figures 2 and 3, in the low-power region at rated voltage operation, the currents in the second leg 12 and the third leg 21 become 0 when the second leg 12 and the third leg 21 switch. Therefore, there is no power loss associated with the switching of the second leg 12 and the third leg 21, and ZCS (Zero Current Switching) is possible.

[0043] The low-output region occurs when the voltage difference between the first voltage (E1) and the second voltage (nE2) is less than the reference voltage Diff (variable a > 0), and when the phase difference between bridges φB > phase difference between the first leg φL1 or the phase difference between bridges φB > phase difference between the second leg φL2 is true.

[0044] The output power in the low-power region can be expressed by the following equation.

number

[0045] Figure 4 is a timing chart showing an example of operation in the high-power region at rated voltage (motoring) when a=1 for variable a. Figure 5 is a timing chart showing an example of operation in the high-power region at rated voltage (motoring) when 1>a>0 for variable a. As shown in Figures 4 and 5, in the high-power region at rated voltage, the second leg 12 and the third leg 21 are ZCS (Zero-Critical Speed ​​Control).

[0046] Note that in Figures 4 and 5, only the odd-numbered switching elements (upper arms) are shown as representatives from each leg. However, the state of the even-numbered switching elements (lower arms) is 180° out of phase with the state of the odd-numbered switching elements within the same leg. This relationship is the same in other drawings as well.

[0047] The high-output region occurs when the voltage difference between the first voltage (=E1) and the second voltage (=nE2) is less than the reference voltage Diff (variable a>0), and when the phase difference between bridges φB < phase difference between the first leg φL1 or the phase difference between bridges φB < phase difference between the second leg φL2 is satisfied.

[0048] The output power in the high-power range can be expressed by the following equation.

number

[0049] Figure 6 is a graph showing the relationship between the phase difference φL1 between the first legs and the power Pout. As shown in Figure 6, in the case of rated voltage operation, the low-power region and the high-power region are continuous, and seamless mode switching is possible.

[0050] In both the low-power and high-power regions, the above procedure determines the phase difference between the bridges φB, the phase difference between the first legs φL1, and the phase difference between the second legs φL2. Therefore, the changes in the phase difference between the bridges φB, the phase difference between the first legs φL1, and the phase difference between the second legs φL2 are continuous, and their values ​​do not fluctuate discontinuously. As a result, the change in power is also continuous.

[0051] Furthermore, the above-mentioned examples of rated voltage operation relate to powering (Pout>0), but similar trends can be obtained even in regeneration (Pout<0). Figure 7 is a timing chart showing an example of operation in the low-power region rated voltage operation (regeneration) with variable a = 1. Figure 8 is a timing chart showing an example of operation in the high-power region rated voltage operation (regeneration) with variable a = 1. Note that in regeneration, the phase difference between the first leg φL1 and the phase difference between the second leg φL2 are negative numbers.

[0052] As shown in Figures 7 and 8, ZCS is possible in the second leg 12 and the third leg 21 not only during powering but also during regeneration. In other words, during rated voltage operation (voltage balance), switching loss reduction is achieved by ZCS in both legs, resulting in a higher switching loss reduction effect than the method described in Patent Document 1.

[0053] (Boost operation) Boost operation occurs when variable a is negative; that is, when the voltage difference between the first voltage (E1) and the second voltage (nE2) is greater than or equal to the reference voltage Diff. In boost operation, the phase difference φL1 between the first legs is positive when the second leg 12 leads the first leg 11, and the phase difference φL2 between the second legs is positive when the fourth leg 22 leads the third leg 21.

[0054] Figure 9 is a timing chart showing an example of operation during boost operation. In boost operation, variable a becomes 0 due to limit processing, so the phase difference φB between bridges also becomes 0. Therefore, in boost operation, power, voltage, and current are controlled by the phase difference φL1 between the first legs and the phase difference φL2 between the second legs.

[0055] In the boost operation, the process involves first determining the phase difference φL1 between the first legs, and then using that value to determine the phase difference φL2 between the second legs. This ensures that the time product of the AC voltages applied to the transformer Tr of the conversion unit 30 is equal. By making the time product of the AC voltages on the primary and secondary sides equal, the effect of preventing reactive current from flowing in the circuit is achieved.

[0056] As shown in Figure 9, in boost operation, the current generated when the switching elements in the first leg 11, second leg 12, and third leg 21 switch is zero, making ZCS (Zero Switching System) possible. In other words, in boost operation, switching losses occur only in the fourth leg 22. Therefore, power can be driven with low loss, and the cooling mechanism can be reduced.

[0057] The output power Pout in this case can be expressed by the following equation.

number

[0058] (Step-down operation) Step-down operation occurs when variable a is negative. That is, when the voltage difference between the first voltage (=E1) and the second voltage (=nE2) is greater than or equal to the reference voltage Diff. In step-down operation, the phase difference φL1 between the first legs is positive when the first leg 11 leads the second leg 12, and the phase difference φL2 between the second legs is positive when the third leg 21 leads the fourth leg 22.

[0059] Figure 10 is a timing chart showing an example of operation in buck-down mode. In buck-down mode, variable a becomes 0 due to limit processing, so the phase difference φB between bridges also becomes 0. Therefore, in buck-down mode, power, voltage, and current are controlled by the phase difference φL1 between the first legs and the phase difference φL2 between the second legs.

[0060] Furthermore, just like in boost operation, measures are taken to prevent reactive current from flowing through the circuit during step-down operation.

[0061] As shown in Figure 10, in step-down operation, the current generated when the switching elements in the first leg 11, second leg 12, and third leg 21 switch is zero, making zero-switching (ZCS) possible. In other words, in step-down operation, switching losses occur only in the fourth leg 22. Therefore, power can be regenerated with low loss, and the cooling mechanism can be reduced.

[0062] Furthermore, the output power Pout in this case is the same as that in equation (6). Therefore, when transitioning between rated voltage operation and step-down operation, there is no need to discontinuously change each phase difference, and seamless control can be achieved.

[0063] (summary) The control modes for rated voltage operation, boost operation, and buck operation can be seamlessly switched. In this case, significant heat loss occurs because ZCS cannot be performed for some of the switching elements S1 to S8, so only the cooling of those switching elements needs to be enhanced. Therefore, sufficient heat dissipation is only required for some of the switching elements S1 to S8, which simplifies thermal design and reduces costs. In addition, because each control parameter is continuous, the transformer does not become magnetized.

[0064] Furthermore, regardless of the type of operation (boost or buck), a large output can be obtained even when the voltage difference between the first voltage and the second voltage is small. In addition, losses can be reduced compared to the control method described in Patent Document 1.

[0065] [Variation] In this embodiment, the phase difference between the first leg φL1 and the phase difference between the second leg φL2 were determined by feedback control, but the control unit 40 can determine the phase difference between the second leg φL2, which is the phase difference between the third leg 21 and the fourth leg 22, by multiplying the phase difference between the first leg φL1, which is the phase difference between the first leg 11 and the second leg 12, by the ratio of the second voltage to the first voltage.

[0066] 〔summary〕 To solve the above problems, a DC-DC converter according to one aspect of the present invention comprises: a primary bridge circuit including a plurality of primary switching elements and having a first leg and a second leg; a secondary bridge circuit including a plurality of secondary switching elements and having a third leg and a fourth leg; a conversion unit having a transformer and connected between the primary bridge circuit and the secondary bridge circuit; and a control unit that controls the switching of the primary and secondary switching elements. The control unit determines the phase difference between the primary bridge circuit and the secondary bridge circuit according to the voltage difference between a first voltage, which is a voltage applied to the primary bridge circuit from outside the DC-DC converter, and a second voltage, which is the primary-side converted voltage of the voltage applied to the secondary bridge circuit from outside the DC-DC converter, and controls the phase difference between the first leg and the second leg and the phase difference between the third leg and the fourth leg according to the power transported from the primary side to the secondary side or from the secondary side to the primary side.

[0067] With the above configuration, the legs in which switching losses occur are fixed to specific legs, while ZCS (Zero-Simulation Cooling) becomes possible in other legs. Therefore, switching losses in the DC-DC converter can be reduced with simple control. In addition, because switching losses are concentrated in specific legs, it is not necessary to cool all switching elements, simplifying thermal design.

[0068] The control unit may obtain a variable by dividing the value obtained by subtracting the voltage difference from the reference voltage by the reference voltage, and determine the phase difference between the primary bridge circuit and the secondary bridge circuit according to the variable.

[0069] With the above configuration, it is possible to appropriately select and control rated voltage operation, boost operation, and buck operation, respectively, during rated voltage operation.

[0070] The control unit may set the phase difference between the primary bridge circuit and the secondary bridge circuit to 0 if the variable is 0 or less.

[0071] With the above configuration, when transitioning from rated voltage operation to boost or buck operation, or vice versa, seamless and continuous control of each control parameter, namely the phase difference, can be achieved. Therefore, because each control parameter is continuous, the transformer does not become magnetized.

[0072] The control unit may, when the variable is positive, multiply the variable by a predetermined maximum phase difference to determine the phase difference between the primary bridge circuit and the secondary bridge circuit.

[0073] With the above configuration, the phase difference between bridges can be kept within a range controllable by the DC-DC converter, enabling stable control.

[0074] The control unit may determine the phase difference between the second and third legs, which is the phase difference between the third and fourth legs, by multiplying the phase difference between the first and second legs, which is the phase difference between the first and second legs, by the ratio of the second voltage to the first voltage.

[0075] With the above configuration, seamless and continuous control of the phase difference, which is a control parameter, can be achieved with respect to the output power during rated voltage operation, boost operation, and buck operation. Therefore, because each control parameter is continuous, the transformer does not become magnetized.

[0076] The winding ratio of the transformer may be the ratio of the maximum value within the voltage range of the primary bridge circuit to the minimum value within the voltage range of the secondary bridge circuit.

[0077] The maximum value within the first voltage range and the minimum value within the second voltage range may be equal.

[0078] With the above configuration, even when the first voltage and the second voltage are different, seamless and continuous control of the phase difference between the bridges can be achieved.

[0079] The duty cycle of the primary and secondary switching elements may be 0.5.

[0080] With the above configuration, there is no need to control the duty cycle, making it easy to control the DC-DC converter.

[0081] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0082] 1 DC-DC converter 10 Primary bridge circuit 11 Leg 1 12 Leg 2 20 Secondary bridge circuit 21 Third Leg 22 Leg 4 30 Conversion section 40 Control Unit S1~4 Primary switching elements S5~8 Secondary switching elements

Claims

1. A primary side bridge circuit comprising multiple primary side switching elements and having a first leg and a second leg, A secondary bridge circuit comprising multiple secondary switching elements and having a third leg and a fourth leg, A conversion unit having a transformer and connected between the primary bridge circuit and the secondary bridge circuit, A DC-DC converter comprising a control unit for controlling the switching of the primary switching element and the secondary switching element, The control unit determines the phase difference between the primary bridge circuit and the secondary bridge circuit according to the voltage difference between a first voltage, which is a voltage applied to the primary bridge circuit from outside the DC-DC converter, and a second voltage, which is the primary-side converted voltage of a voltage applied to the secondary bridge circuit from outside the DC-DC converter, and controls the phase difference between the first leg and the second leg and the phase difference between the third leg and the fourth leg according to the power transported from the primary side to the secondary side or from the secondary side to the primary side, in a DC-DC converter.

2. The control unit obtains a variable by dividing the value obtained by subtracting the voltage difference from the reference voltage by the reference voltage, The DC-DC converter according to claim 1, wherein the phase difference between the primary bridge circuit and the secondary bridge circuit is determined according to the aforementioned variable.

3. The DC-DC converter according to claim 2, wherein the control unit sets the phase difference between the primary bridge circuit and the secondary bridge circuit to 0 when the variable is 0 or less.

4. The DC-DC converter according to claim 2, wherein the control unit determines the phase difference between the primary bridge circuit and the secondary bridge circuit by multiplying the variable by a predetermined maximum phase difference when the variable is positive.

5. The DC-DC converter according to claim 1, wherein the control unit determines the phase difference between the third leg and the fourth leg, which is the phase difference between the third leg and the fourth leg, by multiplying the phase difference between the first leg, which is the phase difference between the first leg and the second leg, by the ratio of the second voltage to the first voltage.

6. The DC-DC converter according to any one of claims 1 to 5, wherein the winding ratio of the transformer is the ratio of the maximum value in the voltage range of the primary bridge circuit to the minimum value in the voltage range of the secondary bridge circuit.

7. The DC-DC converter according to any one of claims 1 to 5, wherein the maximum value in the first voltage range is equal to the minimum value in the second voltage range.

8. The DC-DC converter according to any one of claims 1 to 5, wherein the duty cycle of the primary switching element and the secondary switching element is 0.5.

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