DC-DC converter

Abstract

To provide a DC-DC converter that prevents damage to elements when transferring power.SOLUTION: A DC-DC converter (1) includes: a first AC-DC conversion circuit group (G1) including a plurality of AC-DC conversion circuits (P1 to 4), each consisting of a smoothing circuit (SM1 to 4), a bridge circuit (BR1 to 4), and an AC terminal pair that outputs AC power; a second AC-DC conversion circuit group (G2) including at least one of the above; first windings (Tr1, 2) connected to the first AC-DC conversion circuit group; second windings (Tr3, 4) connected to the second AC-DC conversion circuit group; and a core (CORE0), in which a transformer (Tr) is configured with a common core to which the first windings and the second windings are wound.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses, as a conventional technique, a DC-DC converter including a first AC-DC conversion circuit group in which a plurality of AC-DC conversion circuits are connected in series, a second AC-DC conversion circuit group in which a plurality of AC-DC conversion circuits are connected in series and paired with the first AC-DC conversion circuit group, and a plurality of different transformers connecting the respective AC-DC conversion circuits of the first AC-DC conversion circuit group and the second AC-DC conversion circuit group.

[0003] By connecting a plurality of AC-DC conversion circuits in series, the voltage applied from the connected DC voltage source can be shared, and the voltage borne by each AC-DC conversion circuit can be reduced. Therefore, there is an advantage that inexpensive components (elements) can be used as components of the DC-DC converter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above-described conventional technology, if there are unintentional variations in the circuit constants or control parameters of each AC-DC conversion circuit, the voltage borne will be biased to a specific AC-DC conversion circuit, which may lead to damage to the elements in the AC-DC conversion circuit. Therefore, it is necessary to perform complex control according to the operating conditions of the DC-DC converter in order to balance the borne voltage. In addition, when the transferred power is zero, it is necessary to intentionally increase the loss of a specific DC-DC converter module, resulting in a decrease in efficiency.

[0006] One aspect of the present invention aims to realize a DC-DC converter that can handle various operating conditions and distributes the transferred power among a plurality of AC-DC conversion circuits.

Means for Solving the Problems

[0007] To solve the above problems, a DC-DC converter according to the present invention includes a first terminal pair for connecting to a first DC voltage source and a second terminal pair for connecting to a second DC voltage source, and is a DC-DC converter that controls the transfer of power between the first DC voltage source and the second DC voltage source. Each of them includes a smoothing circuit and a bi A cative bridge circuit connected in series from the side of the first terminal pair, and ji A an AC terminal pair for inputting and outputting AC power connected to the cative bridge circuit, and is composed of a first group of AC-DC conversion circuits composed of a plurality of AC-DC conversion circuits, a first winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the first group of AC-DC conversion circuits, each of which includes a smoothing circuit and a bi A cative bridge circuit connected in series from the side of the second terminal pair, and ji A an AC terminal pair for inputting and outputting AC power connected to the cative bridge circuit, and is composed of a second group of AC-DC conversion circuits composed of at least one AC-DC conversion circuit, a second winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the second group of AC-DC conversion circuits, a core, and a control unit for controlling the switching elements included in the first group of AC-DC conversion circuits and the second group of AC-DC conversion circuits. A transformer is configured in which the first winding and the second winding are commonly wound around the core.

Advantages of the Invention

[0008] According to one aspect of the present invention, it is possible to realize a DC-DC converter that can handle various operating conditions and distributes the transferred power among a plurality of AC-DC conversion circuits.

Brief Description of the Drawings

[0009]

Figure 1

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Mode for Carrying Out the Invention

[0010] 〔Embodiment 1〕 Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0011] (Configuration of DC-DC Converter 1) FIG. 1 is a circuit diagram of a DC-DC converter 1 according to Embodiment 1. The DC-DC converter 1 includes a first AC-DC conversion circuit group G1, a second AC-DC conversion circuit group G2, a conversion unit 30, and a control unit 40.

[0012] The first AC-DC conversion circuit group G1 is composed of a plurality of AC-DC conversion circuits. In this embodiment, the number of AC-DC conversion circuits in the first AC-DC conversion circuit group G1 is two, which are the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2. The first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in series. The first AC-DC conversion circuit group G1 is connected to a first terminal pair T1. Note that a first DC voltage source may be connected to the first terminal pair T1.

[0013] The first AC-DC conversion circuit P1 is an AC-DC conversion circuit connected to a terminal pair composed of a terminal T1a and a terminal T1b. The first AC-DC conversion circuit P1 is sequentially connected in cascade with a smoothing circuit SM1 and 、 A a bridge circuit BR1, which is a full-bridge circuit, and includes switching elements S11 to S14.

[0014] The second AC-DC conversion circuit P2 is an AC-DC conversion circuit connected to a terminal pair composed of a terminal T1c and a terminal T1d. The second AC-DC conversion circuit P2 is sequentially connected in cascade with a smoothing circuit SM2 and 、 A a bridge circuit BR2, which is a full-bridge circuit, and includes switching elements S21 to S24.

[0015] The first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 include a smoothing circuit connected in series from the side of the first terminal pair T1 and bi A a positive bridge circuit 、 A and an AC terminal pair for inputting and outputting AC power connected to the positive bridge circuit.

[0016] The second AC-DC conversion circuit group G2 is composed of a plurality of AC-DC conversion circuits. In this embodiment, there are two AC-DC conversion circuits in the second AC-DC conversion circuit group G2, which are the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4. The third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in series. The second AC-DC conversion circuit group G2 is connected to the second terminal pair T2. Note that a second DC voltage source may be connected to the second terminal pair T2.

[0017] The third AC-DC conversion circuit P3 is an AC-DC conversion circuit connected to a terminal pair composed of a terminal T2a and a terminal T2b. The third AC-DC conversion circuit P3 sequentially includes a smoothing circuit SM3 and 、 A a bridge circuit BR3 which is a positive bridge circuit and is connected in series. The bridge circuit BR3 includes switching elements S31 to S34.

[0018] The fourth AC-DC conversion circuit P4 is an AC-DC conversion circuit connected to a terminal pair composed of a terminal T2c and a terminal T2d. The fourth AC-DC conversion circuit P4 sequentially includes a smoothing circuit SM4 and 、 A a bridge circuit BR4 which is a positive bridge circuit and is connected in series. The bridge circuit BR4 includes switching elements S41 to S44.

[0019] The third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 include a smoothing circuit connected in series from the side of the second terminal pair T2 and bi A a positive bridge circuit 、 A and an AC terminal pair for inputting and outputting AC power connected to the positive bridge circuit.

[0020] The smoothing circuits SM1, SM2, SM3, and SM4 may each be a circuit that smooths the voltage between terminal pairs, for example, a circuit having a capacitor between terminal pairs. Specifically, the smoothing circuit SM1 includes a capacitor C1, the smoothing circuit SM2 includes a capacitor C2, the smoothing circuit SM3 includes a capacitor C3, and the smoothing circuit SM4 includes a capacitor C4.

[0021] The conversion unit 30 has a transformer Tr. FIG. 2 is a perspective view showing an overview of the transformer Tr. The transformer Tr is a transformer having four windings, a winding Tr1 (first winding) connected to the AC terminal pair of the first AC-DC conversion circuit P1, a winding Tr2 (first winding) connected to the AC terminal pair of the second AC-DC conversion circuit P2, a winding Tr3 (second winding) connected to the AC terminal pair of the third AC-DC conversion circuit P3, and a winding Tr4 (second winding) connected to the AC terminal pair of the fourth AC-DC conversion circuit P4. The windings Tr1, Tr2, Tr3, and Tr4 are all wound around a common core CORE0.

[0022] That is, the transformer Tr includes a winding (first winding) respectively connected to the AC terminal pairs of each AC-DC conversion circuit constituting the first AC-DC conversion circuit group G1, a winding (second winding) respectively connected to the AC terminal pairs of each AC-DC conversion circuit constituting the second AC-DC conversion circuit group G2, and a core CORE0 around which these windings are commonly wound. That is, although there are four windings wound around the core CORE0, three or more windings may be sufficient as will be described later.

[0023] Between the connection point of the switching elements S11 and S12 and the connection point of the switching elements S13 and S14 in the first AC-DC conversion circuit P1, the winding Tr1 and the reactor L1 are connected in series. Note that the reactor L1 may represent an inductance component not included in the winding Tr1 in the first AC-DC conversion circuit P1.

[0024] Between the connection point of the switching element S21 and the switching element S22 and the connection point of the switching element S23 and the switching element S24 in the second AC-DC conversion circuit P2, a winding Tr2 and a reactor L2 are connected in series. Note that the reactor L2 may represent an inductance component not included in the winding Tr2 in the second AC-DC conversion circuit P2.

[0025] Between the connection point of the switching element S31 and the switching element S32 and the connection point of the switching element S33 and the switching element S34 in the third AC-DC conversion circuit P3, a winding Tr3 and a reactor L3 are connected in series. Note that the reactor L3 may represent an inductance component not included in the winding Tr3 in the third AC-DC conversion circuit P3.

[0026] Between the connection point of the switching element S41 and the switching element S42 and the connection point of the switching element S43 and the switching element S44 in the fourth AC-DC conversion circuit P4, a winding Tr4 and a reactor L4 are connected in series. Note that the reactor L4 may represent an inductance component not included in the winding Tr4 in the fourth AC-DC conversion circuit P4.

[0027] Note that the reactors L1 to L4 are included in the conversion unit 30.

[0028] The control unit 40 controls the switching elements S11 to S14 in the first AC-DC conversion circuit P1, the switching elements S21 to S24 in the second AC-DC conversion circuit P2, the switching elements S31 to S34 in the third AC-DC conversion circuit P3, and the switching elements S41 to S44 in the fourth AC-DC conversion circuit P4. That is, the control unit 40 controls the switching elements included in the first AC-DC conversion circuit group G1 and the second AC-DC conversion circuit group G2.

[0029] Since the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in series on the side of the first DC voltage source, the terminal T1b and the terminal T1c are connected and have the same potential. The terminal T1a and the terminal T1d constitute a first terminal pair T1 for connecting the first DC voltage source. Since the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in series on the side of the second DC voltage source, the terminal T2b and the terminal T2c are connected and have the same potential. The terminal T2a and the terminal T2d constitute a second terminal pair T2 for connecting the second DC voltage source.

[0030] (Voltage and current of each part in the DC-DC converter 1) Between the first terminal pair T1 for connecting the first DC voltage source in the first AC-DC conversion circuit group G1, that is, from the terminal T1d to the terminal T1a, the voltage Vin is applied from the first DC voltage source. In the first AC-DC conversion circuit group G1, the current Iin flows from the terminal T1a to the first AC-DC conversion circuit group G1.

[0031] Between the second terminal pair T2 for connecting the second DC voltage source in the second AC-DC conversion circuit group G2, that is, from the terminal T2d to the terminal T2a, the voltage Vout is applied from the second DC voltage source. In the second AC-DC conversion circuit group G2, the current Iout flows from the second AC-DC conversion circuit group G2 to the terminal T2a.

[0032] Note that the suffix "in" for the first AC-DC conversion circuit group G1 and the suffix "out" for the second AC-DC conversion circuit group G2 are for convenience and are not limited to the power transfer operation from the first AC-DC conversion circuit group G1 to the second AC-DC conversion circuit group G2. That is, a regeneration operation for transferring power from the second AC-DC conversion circuit group G2 to the first AC-DC conversion circuit group G1 may be performed.

[0033] In this way, a voltage Vdc1 is applied across the terminal pair consisting of terminals T1b and T1a of the first AC-DC conversion circuit P1, sharing a part of the voltage Vin. The current flowing into the first AC-DC conversion circuit P1 from terminal T1a is Idc1, which is equal to the current Iin. A voltage Vac1 is applied from the connection point of the switching elements S13 and S14 to the connection point of the switching elements S11 and S12. A current Iac1 flows from the connection point of the switching elements S11 and S12 to the winding Tr1.

[0034] A voltage Vdc2 is applied across the terminal pair consisting of terminals T1d and T1c of the second AC-DC conversion circuit P2, sharing a part of the voltage Vin. The current flowing into the second AC-DC conversion circuit P2 from terminal T1c is Idc2, which is equal to the current Iin. A voltage Vac2 is applied from the connection point of the switching elements S23 and S24 to the connection point of the switching elements S21 and S22. A current Iac2 flows from the connection point of the switching elements S21 and S22 to the winding Tr2.

[0035] A voltage Vdc3 is applied across the terminal pair consisting of terminals T2b and T2a of the third AC-DC conversion circuit P3, sharing a part of the voltage Vout. The current flowing out from the third AC-DC conversion circuit P3 to terminal T2a is Idc3, which is equal to the current Iout. A voltage Vac3 is applied from the connection point of the switching elements S33 and S34 to the connection point of the switching elements S31 and S32. A current Iac3 flows from the winding Tr3 to the connection point of the switching elements S31 and S32.

[0036] A voltage Vdc4 is applied across a terminal pair consisting of terminal T2d and terminal T2c of the fourth AC-DC conversion circuit P4, and it shares a part of the voltage Vout. The current flowing out from the fourth AC-DC conversion circuit P4 to terminal T2c is Idc4, which is equal to the current Iout. A voltage Vac4 is applied from the connection point of the switching elements S43 and S44 to the connection point of the switching elements S41 and S42. A current Iac4 flows from the winding Tr4 to the connection point of the switching elements S41 and S42.

[0037] (Block diagram) FIG. 3 is a block diagram showing the processing in the control unit 40 of the DC-DC converter 1 according to Embodiment 1. The control unit 40 performs control divided into several blocks. In Embodiment 1, the control unit 40 controls the switching so as to make the output current Iout the target current Iout * .

[0038] In block 41, by PI-controlling the deviation of the output current Iout with respect to the target current Iout * , the inter-group phase difference φG, which is the phase difference between the third AC-DC conversion circuit P3 and the first AC-DC conversion circuit P1, is determined.

[0039] Note that the inter-group phase difference φG is not limited to the phase difference between the third AC-DC conversion circuit P3 and the first AC-DC conversion circuit P1, and may be the phase difference between the fourth AC-DC conversion circuit P4 and the first AC-DC conversion circuit P1, or the phase difference between the third AC-DC conversion circuit P3 and the second AC-DC conversion circuit P2, or the phase difference between the fourth AC-DC conversion circuit P4 and the second AC-DC conversion circuit P2. That is, the phase difference between the second AC-DC conversion circuit group G2 and the first AC-DC conversion circuit group G1 is the inter-group phase difference φG.

[0040] Here, the first AC-DC conversion circuit P1 is also referred to as the first specific AC-DC conversion circuit, and the third AC-DC conversion circuit P3 is also referred to as the second specific AC-DC conversion circuit. That is, the first specific AC-DC conversion circuit and the second specific AC-DC conversion circuit are the AC-DC conversion circuits that are the targets of the inter-group phase difference φG. Therefore, the control unit 40 determines the inter-group phase difference φG, which is the phase difference of switching between the first specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group G1, and the second specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the second AC-DC conversion circuit group G2.

[0041] Thereafter, the control unit 40 calculates the inter-circuit phase difference, which is the phase difference between the AC-DC conversion circuits with respect to the first specific AC-DC conversion circuit in the first AC-DC conversion circuit group G1, and calculates the inter-circuit phase difference, which is the phase difference between the AC-DC conversion circuits with respect to the second specific AC-DC conversion circuit in the second AC-DC conversion circuit group G2.

[0042] Note that in block 41, the control is performed by referring to the current flowing in and out of the second terminal pair T2, but it is not limited to this. For example, the control may be performed by referring to the current flowing in and out of the first terminal pair T1, which is synonymous with this, or the control may be performed by referring to the power transferred between the first DC voltage source and the second DC voltage source.

[0043] In block 42, the inter-circuit phase difference in the first AC-DC conversion circuit group G1 is determined. By performing PI control on the deviation of the voltage Vdc2 in the second AC-DC conversion circuit P2 with respect to the voltage Vdc1 in the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), the first inter-circuit phase difference φ12, which is the phase difference of switching of the second AC-DC conversion circuit P2 with respect to the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), is determined.

[0044] That is, based on the difference between the voltage applied to the smoothing circuit SM2 of the second AC-DC conversion circuit P2 and the voltage applied to the smoothing circuit SM1 of the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), the first inter-circuit phase difference φ12, which is the phase difference of switching of the second AC-DC conversion circuit P2 with respect to the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), is determined.

[0045] Due to such a phase difference φ12 between the first circuits, power transfer occurs between the winding Tr1 and the winding Tr2 wound around the common core CORE0. As a result, it becomes possible to perform feedback so that the voltage Vdc2 applied to the smoothing circuit SM2 of the second AC-DC conversion circuit P2 and the voltage Vdc1 applied to the smoothing circuit SM1 of the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit) are balanced.

[0046] In block 43, the phase difference between the circuits in the second AC-DC conversion circuit group G2 is determined. By PI controlling the deviation of the voltage Vdc4 in the fourth AC-DC conversion circuit P4 with respect to the voltage Vdc3 in the third AC-DC conversion circuit P3 (the second specific AC-DC conversion circuit), the second inter-circuit phase difference φ34, which is the phase difference of the switching of the fourth AC-DC conversion circuit P4 with respect to the third AC-DC conversion circuit P3, is determined.

[0047] That is, based on the difference between the voltage applied to the smoothing circuit SM4 of the fourth AC-DC conversion circuit P4 and the voltage applied to the smoothing circuit SM3 of the third AC-DC conversion circuit P3 (the second specific AC-DC conversion circuit), the second inter-circuit phase difference φ34, which is the phase difference of the switching of the fourth AC-DC conversion circuit P4 with respect to the third AC-DC conversion circuit P3, is determined.

[0048] Due to such a second inter-circuit phase difference φ34, power transfer occurs between the winding Tr3 and the winding Tr4 wound around the common core CORE0. As a result, it becomes possible to perform feedback so that the voltage Vdc4 applied to the smoothing circuit SM4 of the fourth AC-DC conversion circuit P4 and the voltage Vdc3 applied to the smoothing circuit SM3 of the third AC-DC conversion circuit P3 (the first specific AC-DC conversion circuit) are balanced.

[0049] (Circuit diagram of the comparative example) Here, a comparative example for Embodiment 1 will be described. FIG. 4 is a circuit diagram of a DC-DC converter 100 according to the comparative example. In Embodiment 1, the winding Tr1, the winding Tr2, the winding Tr3, and the winding Tr4 were wound around a single core CORE0. In contrast, in the comparative example, the winding Tr1 and the winding Tr3 are wound around the same core CORE1, and the winding Tr2 and the winding Tr4 are wound around the same core CORE2 different from the previous core.

[0050] That is, in the conversion unit 31 of the DC-DC converter 100, the first AC-DC conversion circuit P1 and the third AC-DC conversion circuit P3 are connected via the same transformer, and the second AC-DC conversion circuit P2 and the fourth AC-DC conversion circuit P4 are connected via a transformer different from the said transformer. Therefore, in the comparative example, the magnetic flux cannot be shared by the windings Tr1 to Tr4 connected to the four AC-DC conversion circuits P1 to P4.

[0051] The DC-DC converter 100 of the comparative example is composed of two general DC-DC converter modules. The first DC-DC converter module includes a conversion unit composed of the winding Tr1, the core CORE1, the winding Tr3, etc., the first AC-DC conversion circuit P1, and the third AC-DC conversion circuit P3.

[0052] The other second DC-DC converter module is composed of a conversion unit composed of the winding Tr2, the core CORE2, the winding Tr4, etc., the second AC-DC conversion circuit P2, and the fourth AC-DC conversion circuit P4. The control unit 40 of the DC-DC converter 100 of the comparative example controls the phase difference between the bridges in each DC-DC converter module so that the current Iout follows the target current Iout * and performs power transfer.

[0053] (Control result of the comparative example) FIG. 5 shows the voltages of the smoothing circuits SM1 to 4 in each part of the DC-DC converter 100 when the control unit 40 controls the phase difference between the bridges in the comparative example. The target current Iout * is set to zero.

[0054] As shown in FIG. 5, in the DC-DC converter 100 of the comparative example, regardless of whether or not the blocks 42 and 43 of the control unit 40 perform control, it can be seen that the voltages of the smoothing circuits SM1 to 4 in the same AC-DC conversion circuit group gradually deviate due to the control of the comparative example. As a result, the voltage burden on the components constituting a specific AC-DC conversion circuit increases, leading to heating or component damage.

[0055] For example, the case where the voltage Vdc1 in the first AC-DC conversion circuit P1 is larger than the voltage Vdc2 in the second AC-DC conversion circuit P2 is shown. This voltage difference occurs because the circuit constants or parameters of the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are different, and the losses are different. Also, the circuit constants or parameters of the transformers are different between the DC-DC converter modules, and the losses are different. Such losses of the transformer include copper loss or iron loss.

[0056] Assume that the loss of the first DC-DC converter module is relatively small. Then, the power transferred by the first DC-DC converter module becomes relatively small. Therefore, the power sent to the bridge circuit BR1 by the capacitor C1 of the smoothing circuit SM1 with respect to the power received from the first terminal pair T1 side becomes small, and the surplus is charged to the capacitor C1. As a result, the voltage Vdc1, which is the voltage of the capacitor C1, increases. Since the loss increases due to the increase in the voltage Vdc1, the rising slope gradually becomes gentle, and eventually, the power transfer by the capacitor C1 becomes the same value and stabilizes.

[0057] Conversely, in the second DC-DC converter module, the loss is relatively large. Therefore, the power sent to the bridge circuit BR2 by the capacitor C2 of the smoothing circuit SM2 with respect to the power received from the first terminal pair T1 side becomes large, and the shortage is discharged from the capacitor C2. As a result, the voltage Vdc2, which is the voltage of the capacitor C2, decreases. Since the loss decreases due to the decrease in the voltage Vdc2, the decreasing slope gradually becomes gentle, and eventually, the power transfer by the capacitor C2 becomes the same value and stabilizes.

[0058] On the other hand, for the voltage Vdc3 of the smoothing circuit SM3 and the voltage Vdc4 of the smoothing circuit SM4, the smoothing circuit that receives relatively more power from the bridge circuit has its voltage increased, and the smoothing circuit that receives less power from the bridge circuit has its voltage decreased. The magnitude of the received power varies depending on the difference in losses and the difference in the power sent from the smoothing circuit to the bridge circuit. When the voltage of the smoothing circuit increases, the power sent to the second terminal pair T2 side increases, so that the slope of the voltage increase gradually becomes gentle and eventually stabilizes. When the voltage of the smoothing circuit decreases, the power sent to the second terminal pair T2 side decreases, so that the slope of the voltage decrease gradually becomes gentle and stabilizes.

[0059] The greater the transfer power of the DC-DC converter 100, the greater the difference in load losses such as the conduction loss of the switching element and the copper loss of the transformer. However, since the ratio of the loss to the transfer power is small, the difference in the power exchanged by the smoothing circuits is small, and the voltage deviation width is also small. On the other hand, the smaller the transfer power of the DC-DC converter 100, the relatively greater the difference in the power exchanged by the smoothing circuits due to the variation in no-load losses such as the loss due to capacitor leakage current and the iron loss of the transformer.

[0060] Therefore, when the target current Iout * is controlled to zero, the voltage deviation width becomes the largest. Therefore, in the comparative example, when the target current Iout * is small, there is a high possibility of causing component damage due to overvoltage.

[0061] (Control Results of Embodiment 1) FIG. 6 is a graph regarding the AC voltage in each AC-DC conversion circuit according to Embodiment 1. As shown in FIG. 6, it can be said that the group-to-group phase difference φG, the first circuit-to-circuit phase difference φ12, and the second circuit-to-circuit phase difference φ34 are involved in determining the AC voltage in each AC-DC conversion circuit. That is, it can be said that the on-off timing of each switching element in each AC-DC conversion circuit is determined by the group-to-group phase difference φG, the first circuit-to-circuit phase difference φ12, and the second circuit-to-circuit phase difference φ34.

[0062] Note that the duty of each switching element is 50%. Therefore, each switching element turns on and off in a half cycle.

[0063] FIG. 7 shows the voltages of the smoothing circuits SM1 to 4 in each part of the DC-DC converter 1 according to Embodiment 1. From the time indicated as control start in FIG. 7, by starting the control for applying the first inter-circuit phase difference φ12 and the second inter-circuit phase difference φ34, it can be seen that the voltages applied to each smoothing circuit balance to the same voltage for each AC-DC conversion circuit group.

[0064] As a result, even when it is necessary to apply a high voltage in the first AC-DC conversion circuit group G1 and the second AC-DC conversion circuit group G2, a plurality of AC-DC conversion circuits will share the voltage of the first terminal pair T1 or the second terminal pair T2 by dividing it. Therefore, the voltage borne by each AC-DC conversion circuit becomes sufficiently small, making it difficult for an overload to occur in each AC-DC conversion circuit, and the possibility of the AC-DC conversion circuit being damaged can be reduced.

[0065] Further, regardless of whether the operation executed by the DC-DC converter 1 is a step-up operation, a rated voltage operation, a step-down operation, whether it is power running or regeneration, and further regardless of the magnitude of the transferred power, the control unit 40 can achieve voltage balance by performing the above-described control process. Therefore, unlike Patent Document 1, since there is no need to switch between a plurality of control processes, the process is simple. Also, unlike Patent Document 1, when the transferred power is zero, there is no need to intentionally increase the loss of a specific DC-DC converter module, and it is highly efficient.

[0066] Furthermore, by appropriately setting the phase difference between legs by the switching elements connected in series within each AC-DC conversion circuit, the switching loss within each AC-DC conversion circuit can be reduced, and high efficiency can be achieved. Note that various existing methods can be used as the method for setting the phase difference between legs at this time.

[0067] (Parentheses) As shown in FIG. 1, in the first AC-DC conversion circuit group G1, the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in series. In the second AC-DC conversion circuit group G2, the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in series. That is, terminal T1b and terminal T1c are connected, and terminal T2b and terminal T2c are connected.

[0068] According to the block diagram shown in FIG. 3, when the control unit 40 controls each switching element, the voltages of the AC-DC conversion circuits in the first AC-DC conversion circuit group G1 are balanced, and the voltages of the AC-DC conversion circuits in the second AC-DC conversion circuit group G2 are balanced. As a result, the possibility of each AC-DC conversion circuit being damaged can be reduced.

[0069] In addition, the DC-DC converter 1 according to Embodiment 1 is preferable when connecting the high voltage on the operator side to the first AC-DC conversion circuit group G1 and connecting the high voltage on the operator side to the second AC-DC conversion circuit group G2. For example, it is the case when an operator sells the generated power to another operator.

[0070] 〔Embodiment 2〕 Another embodiment of the present invention will be described below. For the sake of convenience of explanation, members having the same functions as those described in the above embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.

[0071] In Embodiment 1, the DC-DC converter 1 adopting two AC-DC conversion circuits connected in series to the first AC-DC conversion circuit group G1 and two AC-DC conversion circuits connected in series to the second AC-DC conversion circuit group G2 was shown. In contrast, in Embodiment 2, the connection of each AC-DC conversion circuit in the first AC-DC conversion circuit group G1 and the second AC-DC conversion circuit group G2 is not limited to series.

[0072] That is, in Embodiment 2, in at least any of the AC-DC conversion circuit groups, the connections of the AC-DC conversion circuits are in parallel. In Embodiment 1, by connecting the AC-DC conversion circuits in series, the voltage applied to each AC-DC conversion circuit is dispersed to prevent damage to the components of the AC-DC conversion circuit. In contrast, in Embodiment 2, by connecting the AC-DC conversion circuits in parallel, the current flowing through each AC-DC conversion circuit is dispersed to prevent damage to the components of the AC-DC conversion circuit.

[0073] (The first AC-DC conversion circuit group G1a is in series, and the second AC-DC conversion circuit group G2a is in parallel) FIG. 8 is a circuit diagram of a certain DC-DC converter 1a according to Embodiment 2. As shown in FIG. 8, in the first AC-DC conversion circuit group G1a, the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in series, and in the second AC-DC conversion circuit group G2a, the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in parallel. That is, the terminal T1b and the terminal T1c are connected, the terminal T2a and the terminal T2c are connected, and the terminal T2b and the terminal T2d are connected.

[0074] Therefore, the voltage Vdc1 of the first AC-DC conversion circuit P1 shares a part of the voltage Vin, and the current Idc1 is equal to the current Iin. The voltage Vdc2 of the second AC-DC conversion circuit P2 shares a part of the voltage Vin, and the current Idc2 is equal to the current Iin. The voltage Vdc3 of the third AC-DC conversion circuit P3 is equal to the voltage Vout, and the current Idc3 shares a part of the current Iout. The voltage Vdc4 of the fourth AC-DC conversion circuit P4 is equal to the voltage Vout, and the current Idc4 shares a part of the current Iout.

[0075] FIG. 9 is a block diagram showing the processing in the control unit 40a of a certain DC-DC converter 1a according to Embodiment 2. The control unit 40a is divided into several blocks for control, and the blocks 41 and 42 are common to Embodiment 1.

[0076] On the contrary, block 44 is included instead of block 43. In block 44, the phase difference φ34 between the second circuits in the second AC-DC conversion circuit group G2a is determined. The phase difference φ34 between the second circuits, which is the phase difference of the switching of the fourth AC-DC conversion circuit P4 with respect to the third AC-DC conversion circuit P3 (the second specific AC-DC conversion circuit), is determined by PI controlling the deviation of the current Idc4 flowing through the fourth AC-DC conversion circuit P4 with respect to the current Idc3 flowing through the third AC-DC conversion circuit P3 (the second specific AC-DC conversion circuit).

[0077] Even in this case, on the first AC-DC conversion circuit group G1a side, the voltages borne by the respective AC-DC conversion circuits can be balanced, and on the second AC-DC conversion circuit group G2a side, the currents borne by the respective AC-DC conversion circuits can be balanced.

[0078] Therefore, it is suitable for cases such as connecting the high voltage on the operator side to the first AC-DC conversion circuit group G1a and the low voltage on the user side to the second AC-DC conversion circuit group G2a, and for cases of taking out a low voltage and large current from a high voltage and small current. For example, it is the case when a power company sells the generated power to each household.

[0079] (The first AC-DC conversion circuit group G1b is in parallel, and the second AC-DC conversion circuit group G2b is in series) FIG. 10 is a circuit diagram of another DC-DC converter 1b according to Embodiment 2. As shown in FIG. 10, in the first AC-DC conversion circuit group G1b, the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in parallel, and in the second AC-DC conversion circuit group G2b, the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in series. That is, the terminal T1a and the terminal T1c are connected, the terminal T1b and the terminal T1d are connected, and the terminal T2b and the terminal T2c are connected.

[0080] Therefore, the voltage Vdc1 of the first AC-DC conversion circuit P1 is equal to the voltage Vin, and the current Idc1 shares a part of the current Iin. The voltage Vdc2 of the second AC-DC conversion circuit P2 is equal to the voltage Vin, and the current Idc2 shares a part of the current Iin. The voltage Vdc3 of the third AC-DC conversion circuit P3 shares a part of the voltage Vout, and the current Idc3 is equal to the current Iout. The voltage Vdc4 of the fourth AC-DC conversion circuit P4 shares a part of the voltage Vout, and the current Idc4 is equal to the current Iout.

[0081] FIG. 11 is a block diagram showing the processing in the control unit 40b of another DC-DC converter 1b according to Embodiment 2. The control unit 40b performs control divided into several blocks, and blocks 41 and 43 are common to Embodiment 1.

[0082] On the other hand, block 45 is included instead of block 42. In block 45, the first inter-circuit phase difference φ12 in the first AC-DC conversion circuit group G1b is determined. By PI controlling the deviation of the current Idc2 flowing through the second AC-DC conversion circuit P2 with respect to the current Idc1 flowing through the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), the first inter-circuit phase difference φ12, which is the phase difference of the switching of the second AC-DC conversion circuit P2 with respect to the first AC-DC conversion circuit P1 (the first specific AC-DC conversion circuit), is determined.

[0083] Even in this case, on the first AC-DC conversion circuit group G1b side, the currents borne by each AC-DC conversion circuit can be balanced, and on the second AC-DC conversion circuit group G2b side, the voltages borne by each AC-DC conversion circuit can be balanced.

[0084] Therefore, it is suitable for cases where the low voltage on the user side is connected to the first AC-DC conversion circuit group G1b and the high voltage on the operator side is connected to the second AC-DC conversion circuit group G2b, and is suitable for cases where a high voltage with a small current is taken out from a low voltage with a large current. For example, it is the case when selling the power generated in each household to the operator.

[0085] (The first AC-DC conversion circuit group G1c is in parallel, and the second AC-DC conversion circuit group G2c is in parallel) FIG. 12 is a circuit diagram of yet another DC-DC converter 1c according to Embodiment 2. As shown in FIG. 12, in the first AC-DC conversion circuit group G1c, the first AC-DC conversion circuit P1 and the second AC-DC conversion circuit P2 are connected in parallel, and in the second AC-DC conversion circuit group G2c, the third AC-DC conversion circuit P3 and the fourth AC-DC conversion circuit P4 are connected in parallel. That is, terminal T1a and terminal T1c are connected, terminal T1b and terminal T1d are connected, terminal T2a and terminal T2c are connected, and terminal T2b and terminal T2d are connected.

[0086] Therefore, the voltage Vdc1 of the first AC-DC conversion circuit P1 is equal to the voltage Vin, and the current Idc1 shares a part of the current Iin. The voltage Vdc2 of the second AC-DC conversion circuit P2 is equal to the voltage Vin, and the current Idc2 shares a part of the current Iin. The voltage Vdc3 of the third AC-DC conversion circuit P3 is equal to the voltage Vout, and the current Idc3 shares a part of the current Iout. The voltage Vdc4 of the fourth AC-DC conversion circuit P4 is equal to the voltage Vout, and the current Idc4 shares a part of the current Iout.

[0087] FIG. 13 is a block diagram showing the processing in the control unit 40c of yet another DC-DC converter 1c according to Embodiment 2. The control unit 40c is divided into several blocks for control, and block 41 is common to Embodiment 1. Block 44 is the same as the control unit 40a, and block 45 is the same as the control unit 40b.

[0088] Even in this case, on the side of the first AC-DC conversion circuit group G1c, the currents borne by the respective AC-DC conversion circuits can be balanced, and in the second AC-DC conversion circuit group G2c, the currents borne by the respective AC-DC conversion circuits can be balanced.

[0089] Therefore, it is suitable for cases where a low voltage on the user side is connected to the first AC-DC conversion circuit group G1c and a low voltage on the user side is connected to the second AC-DC conversion circuit group G2c, and is suitable for power transmission from a low voltage and large current to a low voltage and large current. For example, it is the case of transmitting the power generated in each household to other households.

[0090] 〔Embodiment 3〕 Other embodiments of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions will not be repeated.

[0091] In Embodiments 1 and 2, the first AC-DC conversion circuit groups G1, G1a, G1b, and G1c and the second AC-DC conversion circuit groups G2, G2a, G2b, and G2c are each assumed to have two connected AC-DC conversion circuits, but the number of AC-DC conversion circuits is not limited.

[0092] Specifically, the first AC-DC conversion circuit group G1 may be composed of a plurality of AC-DC conversion circuits connected to the first terminal pair T1. The second AC-DC conversion circuit group G2 may be composed of at least one AC-DC conversion circuit connected to the second terminal pair T2. That is, as a DC-DC converter, at least three AC-DC conversion circuits may be included in total for the first AC-DC conversion circuit group G1 and the second AC-DC conversion circuit group G2.

[0093] Note that the DC-DC converter can perform a regeneration operation that is a power transfer from the second AC-DC conversion circuit group G2 to the first AC-DC conversion circuit group G1 in addition to a power running operation that is a power transfer from the first AC-DC conversion circuit group G1 to the second AC-DC conversion circuit group G2. That is, since forward and reverse operations are possible, the first AC-DC conversion circuit group G1 and the second AC-DC conversion circuit group G2 are substantially equivalent.

[0094] Therefore, the first AC-DC conversion circuit group G1 requires at least two AC-DC conversion circuits, and the second AC-DC conversion circuit group G2 requires one AC-DC conversion circuit. However, this limitation may also apply when the second AC-DC conversion circuit group G2 requires at least two AC-DC conversion circuits and the first AC-DC conversion circuit group G1 includes one AC-DC conversion circuit.

[0095] 〔Embodiment 4〕 Other embodiments of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions will not be repeated.

[0096] In Embodiment 4, reference is made to the equivalent circuit of the transformer Tr in Embodiment 1.

[0097] FIG. 14 is an example of an equivalent circuit corresponding to the transformer Tr according to Embodiment 4. In the equivalent circuit shown in FIG. 14, a plurality of general one-core two-winding transformers are used to construct the equivalent circuit of the transformer Tr according to Embodiment 1.

[0098] The equivalent circuit shown in FIG. 14 forms reactors L12, L13, L24, and L34 on a bridge circuit, and connects a one-core two-winding transformer to the connection points between the reactors. Two of the transformers are transformers with a turns ratio of 1:1, and the remaining two are transformers with a turns ratio of N:1.

[0099] FIG. 15 is an example of another equivalent circuit corresponding to the transformer Tr according to Embodiment 4. In the equivalent circuit shown in FIG. 15, a plurality of general one-core two-winding transformers are used to construct the equivalent circuit of the transformer Tr according to Embodiment 1.

[0100] The equivalent circuit shown in FIG. 15 connects two transformers with a turns ratio of 1:1 and two transformers with a turns ratio of N:1 in series via reactor L3, and connects two transformers with a turns ratio of 1:1 and two transformers with a turns ratio of N:1 in series via reactor L4. A bypass connection line is connected from the loop in the windings of one pair of two transformers to the loop in the windings of the other pair of two transformers. Note that reactor L1 is connected to the primary side of one of the transformers with a turns ratio of 1:1, and reactor L2 is connected to the primary side of the other transformer with a turns ratio of 1:1.

[0101] FIG. 16 is an example of yet another equivalent circuit corresponding to the transformer Tr according to Embodiment 4. In the equivalent circuit shown in FIG. 16, a plurality of general one-core two-winding transformers are used to construct the equivalent circuit of the transformer Tr according to Embodiment 1.

[0102] The equivalent circuit shown in FIG. 16 includes a transformer with a turns ratio of N:1 having a reactor L13 connected to the primary side, and a transformer with a turns ratio of N:1 having a reactor L24 connected to the primary side. The primary sides of these transformers are each bypassed by a circuit in which a transformer with a turns ratio of 1:1 and a reactor L12 are connected in series.

[0103] Note that the example of the equivalent circuit of the transformer Tr is not limited to FIGS. 14 to 16, and any equivalent circuit may be used.

[0104] 〔Summary〕 The DC-DC converter according to Embodiment 1 of the present invention includes a first terminal pair for connecting a first DC voltage source and a second terminal pair for connecting a second DC voltage source, and is a DC-DC converter that controls power transfer between the first DC voltage source and the second DC voltage source. Each of them includes a smoothing circuit and a bi A cutive bridge circuit connected in cascade from the side of the first terminal pair, and a ji A first AC-DC conversion circuit group composed of a plurality of AC-DC conversion circuits including an AC terminal pair for inputting and outputting AC power connected to the cutive bridge circuit, a first winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the first AC-DC conversion circuit group, each of which includes a smoothing circuit and a bi A cutive bridge circuit connected in cascade from the side of the second terminal pair, and a ji A second AC-DC conversion circuit group composed of at least one AC-DC conversion circuit including an AC terminal pair for inputting and outputting AC power connected to the cutive bridge circuit, a second winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the second AC-DC conversion circuit group, a core, and a control unit that controls switching elements included in the first AC-DC conversion circuit group and the second AC-DC conversion circuit group. A transformer is configured in which the first winding and the second winding are commonly wound around the core.

[0105] According to the above configuration, power can be transferred between a plurality of AC-DC conversion circuits without damaging each element in the smoothing circuit and the bridge circuit.

[0106] In the DC-DC converter according to Embodiment 2 of the present invention, in the above Embodiment 1, the control unit is based on any one of the power to be transferred, the current flowing in and out of the first terminal pair, or the current flowing in and out of the second terminal pair. A group phase difference, which is a phase difference of switching between a first specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, and a second specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the second AC-DC conversion circuit group, may be determined, and the switching of each switching element may be controlled.

[0107] According to the above configuration, the power or current to be transferred can be controlled between a plurality of AC-DC conversion circuits.

[0108] In the DC-DC converter according to Embodiment 3 of the present invention, in the above Embodiment 2, the control unit is based on the difference between the voltage applied to the smoothing circuit of the AC-DC conversion circuit connected in series with the first specific AC-DC conversion circuit and the voltage applied to the smoothing circuit of the first specific AC-DC conversion circuit between the first terminal pairs. A first inter-circuit phase difference, which is a phase difference of switching with respect to the first specific AC-DC conversion circuit, may be determined.

[0109] According to the above configuration, a high voltage can be input.

[0110] In the DC-DC converter according to Embodiment 4 of the present invention, in the above Embodiment 2 or 3, the second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, and the control unit is based on the difference between the voltage applied to the smoothing circuit of the AC-DC conversion circuit connected in series with the second specific AC-DC conversion circuit and the voltage applied to the smoothing circuit of the second specific AC-DC conversion circuit between the second terminal pairs. A second inter-circuit phase difference, which is a phase difference of switching with respect to the second specific AC-DC conversion circuit, may be determined.

[0111] According to the above configuration, high voltage can be output.

[0112] In the DC-DC converter according to Embodiment 5 of the present invention, in the above Embodiment 2, the control unit is configured to determine, for the AC-DC conversion circuit connected in parallel to the first specific AC-DC conversion circuit at the first terminal pair, a first inter-circuit phase difference that is the phase difference of switching with respect to the first specific AC-DC conversion circuit based on the difference between the current flowing in and out of the AC-DC conversion circuit from the first terminal pair and the current flowing in and out of the first specific AC-DC conversion circuit from the first terminal pair.

[0113] According to the above configuration, a large current can be input.

[0114] In the DC-DC converter according to Embodiment 6 of the present invention, in any one of the above Embodiments 2, 3, and 5, the second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, and the control unit is configured to determine, for the AC-DC conversion circuit connected in parallel to the second specific AC-DC conversion circuit at the second terminal pair, a second inter-circuit phase difference that is the phase difference of switching with respect to the second specific AC-DC conversion circuit based on the difference between the current flowing in and out of the AC-DC conversion circuit from the second terminal pair and the current flowing in and out of the second specific AC-DC conversion circuit from the second terminal pair.

[0115] According to the above configuration, a large current can be output.

[0116] 〔Supplementary Notes〕 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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 Reference Numerals

[0117] 1, 1a, 1b, 1c, 100 DC-DC converter 30, 31 Conversion unit Control units 40, 40a, 40b, 40c Cores CORE0, CORE1, CORE2 Capacitors C1 to 4 First AC-DC conversion circuit groups G1, G1a, G1b, G1c Second AC-DC conversion circuit groups G2, G2a, G2b, G2c Bridge circuits BR1 to 4 AC-DC conversion circuits P1 to 4 Switching elements S11 to 14, S21 to 24, S31 to 34, S41 to 44 Smoothing circuits SM1 to 4 Transformer Tr Windings (first winding) Tr1, Tr2 Windings (second winding) Tr3, Tr4 First terminal pair T1 Second terminal pair T2

Claims

1. A DC-DC converter comprising a first terminal pair for connecting a first DC voltage source and a second terminal pair for connecting a second DC voltage source, and controlling power transfer between the first DC voltage source and the second DC voltage source, A first AC-DC conversion circuit group composed of a plurality of AC-DC conversion circuits, each of which comprises a smoothing circuit and a dual active bridge circuit connected in series from the side of the first terminal pair, and an AC terminal pair for inputting and outputting AC power connected to the dual active bridge circuit, A first winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the first AC-DC conversion circuit group, A second AC-DC conversion circuit group composed of at least one AC-DC conversion circuit, each of which comprises a smoothing circuit and a dual active bridge circuit connected in series from the side of the second terminal pair, and an AC terminal pair for inputting and outputting AC power connected to the dual active bridge circuit, A second winding respectively connected to the AC terminal pairs of the respective AC-DC conversion circuits constituting the second AC-DC conversion circuit group, A core, And a control unit for controlling switching elements included in the first AC-DC conversion circuit group and the second AC-DC conversion circuit group, A DC-DC converter in which the first winding and the second winding are commonly wound around the core to form a transformer.

2. The control unit, Based on any one of the power to be transferred, the current flowing in and out of the first terminal pair, or the current flowing in and out of the second terminal pair, determines a group phase difference, which is the phase difference of switching between a first specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, and a second specific AC-DC conversion circuit, which is one of the AC-DC conversion circuits constituting the second AC-DC conversion circuit group, The DC-DC converter according to claim 1, wherein the switching of each switching element is controlled.

3. The control unit, Regarding the AC-DC conversion circuit connected in series to the first specific AC-DC conversion circuit between the first terminal pairs, Based on the difference between the voltage applied to the smoothing circuit of the AC-DC conversion circuit and the voltage applied to the smoothing circuit of the first specific AC-DC conversion circuit, determines a first circuit phase difference, which is the phase difference of switching for the first specific AC-DC conversion circuit. The DC-DC converter according to claim 2.

4. The second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, the control unit, for the AC-DC conversion circuit connected in series to the second specific AC-DC conversion circuit between the second terminal pairs, based on the difference between the voltage applied to the smoothing circuit of the AC-DC conversion circuit and the voltage applied to the smoothing circuit of the second specific AC-DC conversion circuit, determines a second inter-circuit phase difference that is the phase difference of switching with respect to the second specific AC-DC conversion circuit. The DC-DC converter according to claim 3

5. the control unit, for the AC-DC conversion circuit connected in parallel to the first specific AC-DC conversion circuit at the first terminal pair, based on the difference between the current flowing in and out of the AC-DC conversion circuit from the first terminal pair and the current flowing in and out of the first specific AC-DC conversion circuit from the first terminal pair, determines a first inter-circuit phase difference that is the phase difference of switching with respect to the first specific AC-DC conversion circuit. The DC-DC converter according to claim 2.

6. The second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, the control unit, for the AC-DC conversion circuit connected in parallel to the second specific AC-DC conversion circuit at the second terminal pair, based on the difference between the current flowing in and out of the AC-DC conversion circuit from the second terminal pair and the current flowing in and out of the second specific AC-DC conversion circuit from the second terminal pair, determines a second inter-circuit phase difference that is the phase difference of switching with respect to the second specific AC-DC conversion circuit. The DC-DC converter according to claim 3 or 5.

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