DC / DC converter

Abstract

To provide a DC / DC converter that can increase power capacity without causing a decrease in efficiency and size increase.SOLUTION: A DC / DC converter 301 according to the present invention includes: a single multi-leg transformer 100 having a primary winding Pn and a secondary winding Sn per n phase (n is an integer of two or more); n inverter circuits 12-n connected to each of the primary windings Pn of the multi-leg transformer 100 and configured to convert between direct current and alternate current; and n rectifier circuits 13-n connected to each of the secondary windings Sn of the multi-leg transformer 100. The multi-leg transformer 100 uses a leakage inductance produced in an interval between the primary winding Pn and the secondary winding Sn per middle leg 20#n, as a resonance reactor 32.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a DC / DC converter that uses a transformer with a magnetic flux cancellation system. [Background technology]

[0002] Patent Document 1 discloses a DAB (Dual Active Bridge) DC / DC converter capable of transferring power in both directions. This DAB DC / DC converter includes a transformer, a switching circuit composed of a main switching element on the primary side and secondary side of the transformer, a reactor connecting the primary side or secondary side switching circuit and the transformer, and an input / output smoothing unit. In a DAB DC / DC converter, the transformer and the reactor are generally configured as separate components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-075944 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the power to be transferred exceeds the power capacity of a single DAB DC / DC converter, multiple DAB DC / DC converters are connected in parallel and driven in the same phase in parallel operation to keep the power handled by each DAB DC / DC converter below its power capacity. Alternatively, as shown in the circuit diagram of Figure 1, the components (switching element 31, resonant reactor 32, transformer 33) in one DAB DC / DC converter can be connected in parallel to distribute the current flowing through each component and expand the power capacity, making single-phase operation possible.

[0005] Here, when trying to increase power capacity using single-phase operation, the following two problems arise. (Issue 1) As mentioned above, each component is connected in parallel to distribute the current, so the number of components increases and the mounting area becomes larger. Therefore, if an attempt is made to increase the power capacity with single-phase operation, the circuits and devices become larger, making it difficult to miniaturize the DC / DC converter. (Issue 2) By increasing the operating frequency of the main switching element, each component can be made smaller. However, this increases the high-frequency loss of the transformer and the loss of the main switching element, and each component generates heat. For this reason, if an attempt is made to increase the power capacity by using single-phase operation, the increase in frequency increases the loss in each component, making it difficult to prevent a decrease in efficiency.

[0006] Therefore, in order to solve the above problems, an object of the present invention is to provide a DC / DC converter that can increase the power capacity without decreasing efficiency or increasing in size. [Means for solving the problem]

[0007] In order to achieve the above object, a DC / DC converter according to the present invention is provided with a multi-leg transformer that includes the functions of a plurality of conventional transformers and a plurality of resonant reactors, and operates in n phases.

[0008] Specifically, the DC / DC converter according to the present invention comprises: A multi-legged transformer having a primary winding and a secondary winding for each of n phases (n is an integer of 2 or more); n primary side circuits connected to the respective primary windings of the multi-legged transformer; n secondary side circuits connected to the secondary windings of the multi-leg transformer, respectively; Equipped with The primary side circuit functions as an inverter that converts between direct current and alternating current, The secondary circuit functions as a rectifier; The multi-legged transformer has a magnetic core including outer legs that are rectangular frames, and n center legs that are arranged in a unidirectional lattice pattern within the frame of the outer legs and around which the primary winding and the secondary winding for each phase are wound, The middle leg has a gap in the longitudinal direction at a position where the primary winding and the secondary winding are not wound.

[0009] This DC / DC converter integrates n-phase transformers and resonant reactors into a single multi-leg transformer, realizing n-phase operation and expanding power capacity while avoiding the need to increase the size of the device. In addition, the multi-leg transformer has a winding section separated from the gap section of the center leg, which significantly reduces high-frequency loss due to leakage flux. In other words, it is possible to prevent a decrease in efficiency even when the frequency is increased to achieve compact size. Therefore, the present invention can provide a DC / DC converter that can increase the power capacity without decreasing efficiency or increasing size. Effect of the Invention

[0010] The present invention can provide a DC / DC converter that can increase the power capacity without decreasing efficiency or increasing size. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a DAB DC / DC converter with increased power capacity. [Diagram 2] FIG. 1 is a diagram illustrating a DC / DC converter according to the present invention. [Diagram 3] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. [Figure 4] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. [Diagram 5] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. [Figure 6] FIG. 1 is a diagram illustrating a DC / DC converter according to the present invention. [Figure 7] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. [Figure 8] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. [Figure 9] 1 is a diagram illustrating a multi-leg transformer of a DC / DC converter according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0013] (Embodiment 1) FIG. 2 is a diagram illustrating a DC / DC converter 301 according to the present embodiment. The DC / DC converter 301 includes: A multi-legged transformer 100 having a primary winding Pn and a secondary winding Sn for each of n phases (n is an integer of 2 or more); n primary side circuits 12-n connected to the primary windings Pn of the multi-leg transformer 100, n secondary circuits 13-n connected to the secondary windings Sn of the multi-leg transformer 100, Equipped with. In this embodiment, the primary circuit 12-n functions as an inverter that converts between direct current and alternating current, and the secondary circuit 13-n functions as a rectifier. In addition, n is a phase number, and in the case of three phases, n = 1, 2, 3. In this embodiment, the case where n = 3 will be described, but n is not limited to 3.

[0014] The multi-leg transformer 100 is characterized in that the leakage inductance generated in the gap between the primary winding Pn and the secondary winding Sn for each middle leg 20#n is used as a resonant reactor 32. Moreover, the inverter of the primary side circuit 12-n is characterized in that the phases of the drive signals are shifted by 360° / n, and thus the inverter operates in an n-phase interleaved manner.

[0015] FIG. 3 is a diagram illustrating the multi-leg transformer 100. As shown in FIG. The multi-leg transformer 100 is An outer leg 10 which is a rectangular frame; n center legs 20#n are arranged in a lattice pattern in one direction (Y direction in the case of FIG. 3) within the frame of the outer legs 10, and a primary winding Pn and a secondary winding Sn for each phase n are wound around the center legs 20#n; The magnetic core is made of The middle leg has a gap GP in the longitudinal direction (Y direction in the case of FIG. 3) at a position where the primary winding Pn and the secondary winding Sn are not wound.

[0016] The magnetic material of the outer frame 10 and the center leg 20 is, for example, a silicon steel plate or ferrite. Both may be made of the same type of magnetic material, or may be made of different magnetic materials. The gap GP may be a space, or a gap material such as an insulating sheet may be fitted in. The presence of the gap material improves the strength of the core. Furthermore, in this embodiment, the center leg 20 is disposed so that the longitudinal direction is the Y direction, but the center leg 20 may be disposed so that the longitudinal direction is the X direction. Also, since it is three phases, there are three center legs, 20#1, 20#2, and 20#3, three primary windings, P1, P2, and P3, and three secondary windings, S1, S2, and S3.

[0017] The position of the gap GP may be a position shown in Fig. 4 or Fig. 5 (Fig. 4 shows an example in which the gap GP is at the upper end of the center leg 20 (where it contacts the outer leg)). That is, as shown in Fig. 3 or Fig. 4, the primary winding Pn and the secondary winding Sn may both be wound around the center leg 20 on one side with respect to the gap GP (in Figs. 3 and 4, the gap GP is on the primary winding Pn side, but the gap GP may be on the secondary winding Sn side), or as shown in Fig. 5, the primary winding Pn and the secondary winding Sn may be wound around the center leg 20 on both sides of the gap GP (in Fig. 5, the gap GP is between the primary winding Pn and the secondary winding Sn).

[0018] In other words, the multi-leg transformer 100 has the following features. (1) It is composed of a plurality of middle legs 20#n (n=3 in this embodiment) having gaps GP and outer legs 10 having no gaps. (2) The primary winding Pn and the secondary winding Sn are wound at a position other than the gap GP on the center leg 20#n. This reduces the amount of leakage flux at the gap GP that links with the primary winding Pn and the secondary winding Sn, thereby reducing winding loss. (3) Since the magnetic resistance of the gap GP is large, the magnetic fluxes generated in the center legs 20#n do not interfere with each other and pass through the outer legs 10, which have a low magnetic resistance. (4) This structure allows one multi-legged transformer 100 to function in the same way as n transformers. (5) By operating the currents flowing through the respective windings with a phase shift of 360° / n, the magnetic fluxes in the outer legs 10 are offset, enabling iron loss to be reduced. (6) The multi-leg transformer 100 can reduce the core volume by making the outer legs 10 common to each phase, and can be made smaller than a transformer having multiple (n) transformers.

[0019] <Supplementary Information> When a large current flows through the winding, the number of turns is increased to avoid saturation, but the inductance value becomes large. For this reason, a gap is provided in the core to reduce the inductance value. The inductance value can be adjusted by adjusting the gap distance of the core. Specifically, in the multi-leg transformer 100, widening the gap GP reduces the excitation inductance. On the other hand, providing a gap in the core generates leakage flux, which interlinks with the windings and causes losses. Therefore, in the multi-legged transformer 100, the position of the gap GP and the position of the windings (Pn, Sn) are shifted as shown in Figures 3 to 5 to reduce the effects of leakage flux. <End of supplement>

[0020] In the case of a DC / DC converter as shown in Fig. 1, for example, doubling the power capacity doubles the number of each component. In particular, the resonant reactor 32 and the transformer 33 are independent components, and are the main cause of the increase in size of the DC / DC converter. In order to miniaturize the circuit, it is common to increase the switching frequency, but increasing the frequency increases the high-frequency loss of the resonant reactor 32 and the transformer 33, making it necessary to design for heat dissipation.

[0021] On the other hand, DC / DC converter 301 has a circuit configuration for three-phase operation (n=3), and the functions of the leakage inductance (resonant reactor 32) and excitation inductance on the primary and secondary sides of each phase are integrated into one multi-legged transformer 100. Therefore, even if the power capacity of DC / DC converter 301 increases, it is possible to avoid the DC / DC converter 301 becoming larger in size as in the DC / DC converter shown in Fig. 1. Furthermore, because the size does not increase, there is no need to increase the frequency, and no need to design for heat dissipation.

[0022] In addition, the phase of the drive signal for the primary circuit 12-n of each phase, which is an inverter, is shifted by 120° (=360° / 3) and an interleaved operation is performed, thereby realizing a flux cancellation method that cancels the excitation magnetic flux of three phases in the multi-leg transformer 100. As described in (5) above, the iron loss can be reduced.

[0023] (Embodiment 2) 6 is a diagram illustrating a DC / DC converter 302 according to this embodiment. DC / DC converter 302 differs from DC / DC converter 301 in FIG. (a) The secondary circuit 13-n also functions as an inverter that converts between DC and AC. (b) By making the primary circuit 12-n of the multi-legged transformer 100 function as an inverter and the secondary circuit 13-n function as a rectifier, or by making the secondary circuit 13-n of the multi-legged transformer 100 function as an inverter and the primary circuit 12-n function as a rectifier, power can be transferred in both directions. In other words, the DC / DC converter 302 is a DAB type DC / DC converter.

[0024] The multi-legged transformer 100 of the DC / DC converter 302 preferably has the structure described in FIG. 5, but more preferably has the following structure. (c) In the multi-leg transformer 100, each middle leg 20#n has a gap GP on both outer sides of the section in which the primary winding Pn and the secondary winding Sn are wound in the longitudinal direction. FIG. 7 is a diagram illustrating a multi-leg transformer 100 having a more preferable structure. The multi-leg transformer 100 has the following features: An outer leg 10 which is a rectangular frame made of a magnetic material; A plurality of center legs 20#n, which are made of a magnetic material and are arranged in a lattice pattern in one direction (Y direction in the case of FIG. 5) within the frame of the outer leg 10; A primary winding Pn and a secondary winding Sn are wound around each of the center legs 20#n, Equipped with Each of the middle legs 20#n is characterized by having a gap GP on both outer sides of the section in which the primary winding Pn and the secondary winding Sn are wound in the longitudinal direction (Y direction in the case of FIG. 7).

[0025] To equalize the inductance seen from both sides of the transformer (primary side and secondary side), a structure in which the gap GP is provided in the center of the middle leg 20#n (between the primary winding Pn and secondary winding Sn) as in the multi-legged transformer 100 in FIG. 5 is preferable. As explained in the "Supplementary Note" above, the excitation inductance can be adjusted by the gap GP. However, with this structure, if the gap GP is widened to reduce the excitation inductance, loss due to leakage flux generated near the gap GP increases. In other words, with this structure, there is a problem in that it is difficult to adjust the excitation inductance while avoiding loss due to the gap GP.

[0026] Therefore, to achieve a structure that can equalize the inductance seen from both sides of the transformer and easily adjust the excitation inductance while avoiding loss due to the gap GP, we decided to provide a gap GP at both ends of the center leg 20#n, as in the multi-leg transformer 100. Since the gap GP can be widened to both ends of the center leg 20#n by widening the outer legs 10, the gap GP can be widened (the excitation inductance can be reduced) without causing leakage magnetic flux generated near the gap GP to interfere with the primary winding Pn or secondary winding Sn (without increasing loss).

[0027] Here, in order to facilitate adjustment of the gap GP, it is preferable that the outer leg 10 of the multi-leg transformer 100 is divided as shown in Fig. 8. Specifically, the outer leg 10 is composed of a plurality of parts (outer leg parts 10-1 to 10-8). Therefore, the distance between the gaps GP can be adjusted by moving the part (10-1, 10-2, 10-3, 10-5, 10-6, 10-7) on which the center leg 20 is installed in the longitudinal direction (Y direction) of the center leg 20.

[0028] The transformer 100 is characterized in that the outer leg 10 is configured by interlacing the above-mentioned multiple parts. Interlacing is an assembly method as shown in Fig. 9(A). Specifically, one end of the outer leg parts (10-1, 10-2, 10-3) is installed on the side of the outer leg part 10-4, one end of the outer leg part 10-4 is installed on the side of the outer leg part (10-5, 10-6, 10-7), one end of the outer leg parts (10-5, 10-6, 10-7) is installed on the side of the outer leg part 10-8, and one end of the outer leg part 10-8 is installed on the side of the outer leg parts (10-1, 10-2, 10-3). 9(B) shows an explanation of the "one end" and "side" of part 10-n. "One end" means one bottom surface of prismatic part 10-n, and "side" means one side surface of prismatic part 10-n (the side surface that faces inward when assembled). Furthermore, if the assembly of parts 10-n as shown in FIG. 9(A) is a "clockwise swastika group," the outer leg 10 may be a "counterclockwise swastika group."

[0029] In other words, because the core of the transformer 100 is composed of multiple parts, the gap length of the gap GP can be adjusted for each center leg, which has the effect of absorbing deviations in gap length due to manufacturing errors in the core and the effect of adjusting the excitation inductance to a desired value.

[0030] By adjusting each gap GP of the multi-leg transformer 100 using multiple parts of the outer leg 10 and equalizing the excitation inductance and leakage inductance as viewed from the primary and secondary sides of each phase, it becomes possible to use the same inverter circuit for the primary circuit 12-n and secondary circuit 13-n of each phase. However, it is difficult to match the characteristics (circuit constants) of each inverter circuit due to differences between parts and manufacturing errors. Therefore, by adjusting each gap GP of the multi-leg transformer 100 with multiple parts of the outer leg 10, the excitation inductance and leakage inductance seen from the primary and secondary sides of each phase can be adjusted, and the characteristic differences between the inverter circuits can be absorbed.

[0031] When power is transferred from the primary side to the secondary side (from left to right in FIG. 6), a drive signal for driving a switching element is input to the primary side circuit 12-n, and each switching element of the secondary side circuit 13-n is opened to function as a rectifier. On the other hand, when power is transferred from the secondary side to the primary side (from right to left in FIG. 6), a drive signal for driving a switching element is input to the secondary side circuit 13-n, and each switching element of the primary side circuit 12-n is opened to function as a rectifier.

[0032] In other words, even DC / DC converter 302 of the circuit in FIG. 6 can function as DC / DC converter 301 described in FIG. 2 by stopping the switching operation of the primary side circuit or the secondary side circuit (open state). In the second embodiment, the multi-legged transformer 100 having the structure shown in Fig. 7 or 8 has been described as a preferred embodiment of the DC / DC converter 302, but the DC / DC converter 302 may also be the multi-legged transformer 100 having the structure shown in Fig. 5. In this case, the swastika described in Fig. 9 may be applied to the structure of the multi-legged transformer 100 in Fig. 5.

[0033] (Other embodiments) In the multi-legged transformer 100 described in the first and second embodiments, the gap GP may be a space, or a gap material such as an insulating sheet may be fitted into the gap GP. By fitting the gap material into the gap GP, the center leg 20#n can be fixed to the outer leg 10. In the case of the multi-legged transformer 100 of embodiment 2, the gap material 15 may be an integrated structure in which it is commonly fitted into the gaps GP at one end side and the other end side of the middle leg 20#n, or may be a divided structure for each middle leg 20#n.

[0034] (effect) By using a multi-legged transformer with a magnetic flux cancellation system, the present invention can significantly reduce the number of resonant reactors and transformers compared to conventional systems, thereby achieving a compact DC / DC converter. The present invention uses a magnetic flux cancellation method that makes it possible to reduce the volume of the transformer windings without increasing the switching frequency compared to conventional methods, and can reduce the size of the circuit without increasing the high-frequency loss in the windings or the switching loss of the main switching elements. According to the present invention, the peak of the ripple current of each phase is shifted by n-phase interleaving operation, so that the effective value of the ripple current flowing through the input / output smoothing capacitors can be reduced, and the capacitors can be made smaller. [Explanation of symbols]

[0035] 10: Outer leg 10-1, 10-2, ..., 10-8, 10-i: Outer leg parts (i is the part number) 12, 12-1, 12-2, ..., 12-n: Primary circuit 13, 13-1, 13-2, . . ., 13-n: Secondary circuit 20, 20#1, 20#2,..., 20#n: middle leg 31: Switching element 32: Resonant reactor 33: Trance 100: Multi-leg transformer 301, 302: DC / DC converter P1, P2, ..., Pn: Primary windings S1, S2, ..., Sn: Secondary windings GP: Gap

Claims

1. 1. A DC / DC converter comprising: A multi-legged transformer having a primary winding and a secondary winding for each of n phases (n is an integer of 2 or more); n primary side circuits connected to the primary windings of the multi-legged transformer, n secondary side circuits connected to the secondary windings of the multi-leg transformer, respectively; Equipped with The primary side circuit functions as an inverter that converts between direct current and alternating current, The secondary circuit functions as a rectifier, The multi-legged transformer has a magnetic core including outer legs that are rectangular frames, and n center legs that are arranged in a unidirectional lattice pattern within the frame of the outer legs and around which the primary winding and the secondary winding for each phase are wound, The DC / DC converter according to claim 1, wherein the middle leg has a gap in a longitudinal direction at a position where the primary winding and the secondary winding are not wound.

2. 2. The DC / DC converter according to claim 1, wherein the multi-legged transformer has the primary winding and the secondary winding both wound around the center leg on one side of the gap.

3. 2. The DC / DC converter according to claim 1, wherein the multi-legged transformer has the primary winding and the secondary winding wound around the center leg on one side and the center leg on the other side of the gap, respectively.

4. 2. The DC / DC converter according to claim 1, wherein each of the middle legs of the multi-legged transformer has the gap on both outer sides of a section in a longitudinal direction in which the primary winding and the secondary winding are wound.

5. The multi-legged transformer is The outer leg is composed of a plurality of parts of the magnetic material, and the distance between the gaps can be adjusted by moving the part on which the middle leg is installed in the longitudinal direction of the middle leg.

4. The DC / DC converter according to claim 3 .

6. The multi-legged transformer is The outer leg is composed of a plurality of parts of the magnetic material, and the distance between the gaps can be adjusted by moving the part on which the middle leg is installed in the longitudinal direction of the middle leg.

5. The DC / DC converter according to claim 4 .

7. 6. The DC / DC converter according to claim 5, wherein the outer leg is formed by assembling a plurality of parts of the magnetic material.

8. 7. The DC / DC converter according to claim 6, wherein the outer leg is formed by assembling a plurality of parts of the magnetic material.

9. 2. The DC / DC converter according to claim 1, wherein a leakage inductance generated in a gap between the primary winding and the secondary winding for each of the middle legs of the multi-leg transformer serves as a resonant reactor.

10. The secondary circuit also functions as an inverter that converts DC and AC.

10. A DC / DC converter as described in any one of claims 3 to 9, characterized in that the primary side circuit functions as an inverter and the secondary side circuit functions as a rectifier, or the secondary side circuit functions as an inverter and the primary side circuit functions as a rectifier, thereby enabling power to move in both directions.

11. 10. The DC / DC converter according to claim 1, wherein the inverter performs n-phase interleaved operation with the phases of the drive signals shifted by 360[deg.] / n.

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