DC / DC converter

Abstract

To provide a DC / DC converter which is capable of making an input / output voltage higher than a breakdown voltage of a switch element without using the switch element of high ON resistance and the high breakdown voltage and eliminates the need of precise switching control.SOLUTION: A DC / DC converter is a DAB type. A full-bridge switching circuit consisting of four switch devices (Sx:x=1 to 4) is connected to one side of a transformer 11, and a full-bridge switching circuit consisting of four switches (Sy:y=5 to 8) is connected to the other side. In each of legs (12 and 13) of the switching circuit on the one side, upper and lower arms are connected by flying capacitors (FC1 and FC2). In each of switches, two switch elements (Qxa and Qxb) are connected in series, and the flying capacitors (FC1 and FC2) connect connection points of the switch elements (Qxa and Qxb) with each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a DC / DC converter capable of bidirectional input and output. [Background technology]

[0002] Converters and bidirectional converters that can accommodate a wide range of input and output voltages and currents and have reduced switching losses are known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-075943 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-075944 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-124050 Summary of the Invention [Problem to be solved by the invention]

[0004] In the DC / DC converters described in Patent Documents 1 and 2, an input voltage is applied to a switch element on the primary side of a transformer, and an output voltage is applied to a switch element on the secondary side. Therefore, when inputting or outputting a high voltage (for example, 1000 to 1500 V or higher), a high-voltage switch element must be used. However, high-voltage switch elements have a high on-resistance, and configuring a DC / DC converter using high-voltage switch elements poses the problem of large losses during operation. In addition, there is a limit to the withstand voltage of switch elements currently available on the market, making it difficult to design a DC / DC converter that can handle higher input and output voltages.

[0005] To address the above issue, it is possible to connect switch elements in series to share the applied voltage. However, if there is a discrepancy in the switching timing, a voltage exceeding the breakdown voltage may be applied to the switch element, which could cause it to malfunction. In other words, connecting switch elements in series to divide the voltage creates the issue of difficulty in controlling the switching.

[0006] As described above, the DC / DC converters disclosed in Patent Documents 1 and 2 have the problem that it is difficult to input and output high voltages. Therefore, in order to solve the above problems, an object of the present invention is to provide a DC / DC converter that can make input / output voltages higher than the withstand voltage of a switch element without using a switch element with a large on-resistance and a high withstand voltage, and that does not require precise switching control. [Means for solving the problem]

[0007] In order to achieve the above object, the DC / DC converter according to the present invention divides the input / output voltage by connecting switch elements in series on the primary side or secondary side of a transformer having a high input / output voltage, and employs a flying capacitor design.

[0008] Specifically, the DC / DC converter according to the present invention comprises: a transformer (11) having a primary winding (11a) and a secondary winding (11b); two switching circuits (1&2) connected to the primary winding (11a) side of the transformer and the secondary winding (11b) side of the transformer, respectively; an inductance means (L) arranged between the transformer and the switching circuit (1 / 2) on the primary winding (11a) side or the secondary winding (11b) side of the transformer; a control circuit (3) for controlling the switching of the switching circuits (1 & 2); Equipped with One of the switching circuits (1) is The power supply includes a first leg (12) and a second leg (13) in which four switch devices (Sdx: x=1-4) are connected in parallel between two terminals (Ter1 & Ter2) as upper and lower arms, and flying capacitors (FC1, FC2) that connect the upper and lower arms in each of the first leg (12) and the second leg (13), Each of the switch devices (Sdx) has switch elements (Qxa, Qxb) connected in series to anti-parallel diodes (Dxa, Dxb) and parallel capacitors (Cxa, Cxb), respectively, and an additional capacitor (Cxp) is connected in parallel to the switch elements (Qxa / Qxb) on one side (Ter1 / Ter2) of the two terminals; the flying capacitors (FC1, FC2) connect the connection points of the switch elements (Qxa, Qxb) together; The other switching circuit (2) is a third leg (24) and a fourth leg (25) each having four switches (Sy) as upper and lower arms, each having a switch element (Qy) with an anti-parallel diode (Dy: y=5-8) and a parallel capacitor (Cy) connected in parallel, connected in parallel between the other two terminals (Ter3 & Ter4); a first capacitor (Ca) connected in parallel to one of the switches (Sy) in the upper or lower arm of the third leg or fourth leg (24 / 25) or one of the switches (Sy) in the upper or lower arm of the third leg and fourth leg (24 & 25); and a second capacitor (Cb) connected in parallel to the other of the switches (Sy) in the upper or lower arm of the third leg or fourth leg (24 / 25) or the other of the switches (Sy) in the upper or lower arm of the third leg and fourth leg (24 & 25); The inductance means (L) connects the connection points of the upper and lower arms of the first leg (12) and the connection points of the upper and lower arms of the second leg (13) together with the primary winding (11a) connected in series, or connects the connection points of the upper and lower arms of the third leg (24) and the connection points of the upper and lower arms of the fourth leg (25) together with the secondary winding (11b) connected in series. It is characterized by:

[0009] The DC / DC converter according to the present invention replaces each switch element in one of the switching circuits of the DC / DC converters described in Patent Documents 1 and 2 with a switch device in which two switch elements are connected in series, and employs a flying capacitor architecture. As a result, this DC / DC converter can suppress the voltage applied to each switch element to approximately half the input voltage or approximately half the output voltage, and can handle input / output voltages higher than the withstand voltage of the switch elements without using switch elements with high on-resistance and high withstand voltage.

[0010] Furthermore, the operation of this DC / DC converter is basically the same as that of the DC / DC converters described in Patent Documents 1 and 2, so it is sufficient to perform switching control equivalent to that of the DC / DC converters described in Patent Documents 1 and 2.

[0011] Therefore, the present invention can provide a DC / DC converter that can make the input / output voltage higher than the withstand voltage of a switch element without using a switch element with a large on-resistance and a high withstand voltage, and that does not require precise switching control. Furthermore, the operation of this DC / DC converter is basically the same as that of the DC / DC converters described in Patent Documents 1 and 2, making ZVS possible over a wide range of input and output voltages and currents, and achieving highly efficient bidirectional operation with reduced switching losses. [Effects of the Invention]

[0012] The present invention can provide a DC / DC converter that can make the input / output voltage higher than the withstand voltage of a switch element without using a switch element with a large on-resistance and a high withstand voltage, and that does not require precise switching control. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a DC / DC converter according to the present invention. [Figure 2]FIG. 3 is a diagram illustrating the switching timing in the DC / DC converter according to the present invention. [Figure 3] 3 is a diagram illustrating the relationship between the switching timing and the current flowing through the inductance means in the DC / DC converter according to the present invention. FIG. [Figure 4] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 5] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 6] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 7] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 8] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 9] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 10] FIG. 3 is a diagram illustrating the switching timing in the DC / DC converter according to the present invention. [Figure 11] 3 is a diagram illustrating the relationship between the switching timing and the current flowing through the inductance means in the DC / DC converter according to the present invention. FIG. [Figure 12] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 13] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 14] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 15] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 16] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 17]FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 18] FIG. 3 is a diagram illustrating the switching timing in the DC / DC converter according to the present invention. [Figure 19] 3 is a diagram illustrating the relationship between the switching timing and the current flowing through the inductance means in the DC / DC converter according to the present invention. FIG. [Figure 20] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 21] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 22] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 23] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 24] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 25] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 26] FIG. 3 is a diagram illustrating the switching timing in the DC / DC converter according to the present invention. [Figure 27] 3 is a diagram illustrating the relationship between the switching timing and the current flowing through the inductance means in the DC / DC converter according to the present invention. FIG. [Figure 28] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 29] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 30] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 31] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 32]FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. [Figure 33] FIG. 2 is a diagram illustrating a current flow in the DC / DC converter according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0015] (Embodiment 1) FIG. 1 is a diagram illustrating the configuration of a DC / DC converter according to this embodiment. This DC / DC converter is a DAB type, a transformer (11) having a primary winding (11a) and a secondary winding (11b); two switching circuits (1&2) connected to the primary winding (11a) side of the transformer and the secondary winding (11b) side of the transformer, respectively; an inductance means (L) arranged between the transformer and the switching circuit (1 / 2) on the primary winding (11a) side or the secondary winding (11b) side of the transformer; a control circuit (3) for controlling the switching of the switching circuits (1 & 2); Equipped with One of the switching circuits (1) is The power supply includes a first leg (12) and a second leg (13) in which four switch devices (Sdx: x=1-4) are connected in parallel between two terminals (Ter1 & Ter2) as upper and lower arms, and flying capacitors (FC1, FC2) that connect the upper and lower arms in each of the first leg (12) and the second leg (13), Each of the switch devices (Sdx) has switch elements (Qxa, Qxb) connected in series to anti-parallel diodes (Dxa, Dxb) and parallel capacitors (Cxa, Cxb), respectively, and an additional capacitor (Cxp) is connected in parallel to the switch elements (Qxa / Qxb) on one side (Ter1 / Ter2) of the two terminals; the flying capacitors (FC1, FC2) connect the connection points of the switch elements (Qxa, Qxb) together; The other switching circuit (2) is a third leg (24) and a fourth leg (25) each having four switches (Sy) as upper and lower arms, each having a switch element (Qy) with an anti-parallel diode (Dy: y=5-8) and a parallel capacitor (Cy) connected in parallel, connected in parallel between the other two terminals (Ter3 & Ter4); a first capacitor (Ca) connected in parallel to one of the switches (Sy) in the upper or lower arm of the third leg or fourth leg (24 / 25) or one of the switches (Sy) in the upper or lower arm of the third leg and fourth leg (24 & 25); and a second capacitor (Cb) connected in parallel to the other of the switches (Sy) in the upper or lower arm of the third leg or fourth leg (24 / 25) or the other of the switches (Sy) in the upper or lower arm of the third leg and fourth leg (24 & 25); The inductance means (L) connects the connection points of the upper and lower arms of the first leg (12) and the connection points of the upper and lower arms of the second leg (13) together with the primary winding (11a) connected in series, or connects the connection points of the upper and lower arms of the third leg (24) and the connection points of the upper and lower arms of the fourth leg (25) together with the secondary winding (11b) connected in series. It is characterized by:

[0016] Each switch element (Qxa, Qxb: x=1 to 4, Qy: y=5 to 8) is connected in parallel with an anti-parallel diode (Dxa, Dxb, Dy) and a parallel capacitor (Cxa, Cxb, Cy). It is assumed here that there is no variation in the constants of each switch element, each diode, each capacitor, or the pulse width of the signal that drives each switch element.

[0017] In the present invention, the anti-parallel diodes (Dxa, Dxb, Dy) connected in parallel to the switch elements (Qxa, Qxb, Qy) may be built-in diodes of the switch elements, external diodes separate from the switch elements, or a combination of these. Similarly, the parallel capacitors (Cxa, Cxb, Cy) connected in parallel to the switch elements (Qxa, Qxb, Qy) may be parasitic capacitances of the switch elements, external capacitors separate from the switch elements, or a combination of these.

[0018] A configuration in which switch elements Qxa and Qxb, each having an anti-parallel diode (Dxa, Dxb) and a parallel capacitor (Cxa, Cxb) connected in parallel, are connected in series is referred to as switch device Sdx. Note that the series switch elements included in switch Sdx will be described with the switch element Qxa on the terminal Ter1 side and the switch element Qxb on the terminal Ter2 side. Also, a configuration in which switch element Qy is connected in parallel with an anti-parallel diode Dy and a parallel capacitor Cy is referred to as switch Sy.

[0019] The flying capacitor connects the connection point of two switch elements (Qxa, Qxb) that make up one switch device Sdx to the connection point of two switch elements (Qxa, Qxb) that make up another switch device Sdx in the same leg. The capacitance of the flying capacitors (FC1, FC2) is set to a value large enough that the voltage can be considered constant between switching periods. Here, the voltage of the flying capacitors (FC1, FC2) of switching circuit 1 is assumed to be half the voltage between terminals Ter1 and Ter2 (input voltage Vin or output voltage Vo).

[0020] The control circuit 3 synchronizes the operation of switch elements Q1b and Q4b, switch elements Q2b and Q3b, switch elements Q1a and Q4a, and switch elements Q2a and Q3a. For this reason, in the following description, switch elements Q1b and Q4b will be referred to as pair switch PS1, switch elements Q2b and Q3b as pair switch PS2, switch elements Q2a and Q3a as pair switch PS3, and switch elements Q1a and Q4a as pair switch PS4. The control circuit 3 also controls the operation of the switch element Qy, as will be described later.

[0021] This DC / DC converter includes a transformer 11, a switching circuit 1 connected to a primary winding 11a of the transformer 11, a switching circuit 2 connected to a secondary winding 11b of the transformer 11, inductance means L, and a control circuit 3. The DC / DC converter of this embodiment converts DC input from the first terminal Ter1 and the second terminal Ter2 into AC and outputs it from the switching circuit 1, and converts the AC into DC in the switching circuit 2 via the transformer 11 and supplies power to the third terminal Ter3 and fourth terminal Ter4 on the output side. In other words, the DC / DC converter of this embodiment transitions power in the X direction.

[0022] The switching circuit 1 has a first leg (12) and a second leg (13) connected in parallel between two terminals (Ter1 & Ter2) with the switch device Sdx as the upper and lower arms, respectively, and an additional capacitor Cxp connected in parallel to each of the switch elements Qxa or each of the switch elements Qxb.

[0023] Power is input from an external power supply to the first terminal Ter1 and the second terminal Ter2. A capacitor 16 is connected between the first terminal Ter1 and the second terminal Ter2 to generate a DC voltage (the DC voltage is input between the first terminal Ter1 and the second terminal Ter2). Furthermore, a switching circuit 1 is connected between the first terminal Ter1 and the second terminal Ter2, and the switching circuit 1 is a full-bridge circuit in which the upper and lower arms of the first leg 12 and the second leg 13 are configured with switch devices Sdx. Furthermore, a detection means 19 detects the voltage between the first terminal Ter1 and the second terminal Ter2, or the current or power input / output to / from the switching circuit 1 via the first terminal Ter1 and the second terminal Ter2.

[0024] In the bridge connection circuit of the switching circuit 1, a primary winding 11a of a transformer 11 is connected to the connection points of the switches of each leg (the connection point of the switch devices Sd1 and Sd2, and the connection point of the switch devices Sd3 and Sd4).

[0025] In the following description, the object to be detected is voltage, but the present invention is not limited to voltage, and the same operation and effect can be obtained even when detecting current or power.

[0026] 1 of this embodiment, the first leg 12 and the second leg 13 are connected in parallel between the first terminal and the second terminal. The first leg 12 has switch devices (Sd1, Sd2) as upper and lower arms, and the second leg 13 has switch devices (Sd3, Sd4) as upper and lower arms. The switch device Sdx is formed by connecting switch elements Q1a and Q1b, Q2a and Q2b, Q3a and Q3b, and Q4a and Q4b in series, respectively. Flying capacitor FC1 connects the connection point between switch elements Q1a and Q1b and the connection point between switch elements Q2a and Q2b, and flying capacitor FC2 connects the connection point between switch elements Q3a and Q3b and the connection point between switch elements Q4a and Q4b.

[0027] The additional capacitor Cxp is connected in parallel to the switch element of the pair of switches PS1 and PS4 or PS2 and PS3 that are to be turned off first in the group of switching circuits 1. In Fig. 1, the additional capacitor Cxp is connected in parallel to each switch element Qxa of the pair of switches (PS3, PS4) that are to be turned off first.

[0028] A capacitor 17 is connected between the third terminal Ter3 and the fourth terminal Ter4 of the switching circuit 2, which generates a DC voltage (the DC voltage is output between the third terminal Ter3 and the fourth terminal Ter4). Furthermore, the switching circuit 2 is connected between the third terminal Ter3 and the fourth terminal Ter4, and the switching circuit 2 is a full-bridge circuit in which the upper and lower arms of the first leg 25 and the second leg 24 are configured with switches Sy. Furthermore, detection means 18 detects the voltage between the third terminal Ter3 and the fourth terminal Ter4, or the current or power input / output to / from the switching circuit 2 via the third terminal Ter3 and the fourth terminal Ter4.

[0029] The first capacitor Ca and the second capacitor Cb are connected in parallel to the switching elements Q7 and Q6 or Q8 and Q5, which are to be turned off first, as will be described later. In Fig. 1, the first capacitor Ca and the second capacitor Cb are connected in parallel to the switching elements Q5 and Q6, which are to be turned off first, in the upper and lower arms of the third leg 24.

[0030] In the bridge connection circuit of the switching circuit 2, the secondary winding 11b of the transformer 11 is connected to the connection points of the switches of each leg (the connection point of the switches S5 and S6, and the connection point of the switches S7 and S8).

[0031] The inductance means L is connected to the connection point between the upper and lower arms of the first leg 12 and the connection point between the upper and lower arms of the second leg 13 via the primary winding 11a of the transformer 11. This inductance means L may be connected to the switching circuit 2 via the secondary winding 11b of the transformer 11. Also, in FIG. 1, one end of the inductance means L is connected to the connection point between the upper and lower arms of the first leg 12 and the other end is connected to the primary winding 11a of the transformer 11, but one end of the inductance means L may be connected to the connection point between the upper and lower arms of the second leg 13 and the other end is connected to the primary winding 11a of the transformer 11. The same applies when the inductance means L is connected via the secondary winding 11b.

[0032] In this embodiment, control of power transition in the X direction in FIG. 1 will be described. The control circuit 3 controls the on / off of each switch by supplying a drive signal to each of the switch Sx of the switching circuit 1 and the switch Sy of the switching circuit 2. First, the zero voltage switching (ZVS) control will be described. The control circuit (3) On / off control is performed on the switching circuit (1) that converts the direct current input from the two terminals (Ter1 & Ter2) into alternating current and outputs the converted alternating current to the transformer (11), by alternately turning on and off a pair of a switch device (Sd1 / 3) on the upper arm of the first or second leg and a switch device (Sd4 / 2) on the lower arm of the second or first leg; and When performing the on / off control, in each of the groups, Synchronizing the on / off operations of the switch elements (Qxa) connected in parallel with the additional capacitor (Cxp) and synchronizing the on / off operations of the switch elements (Qxb) connected in parallel with the additional capacitor (Cxp); The switch element (Qxa) connected in parallel to the additional capacitor (Cxp) is turned off first; and The switch element (Qxb) to which the additional capacitor (Cxp) included in one of the pairs is not connected in parallel is turned off, and after a fixed time (Td) has elapsed, the switch element (Qxa) to which the additional capacitor (Cxp) included in the other pair is connected in parallel is turned on. It is characterized by:

[0033] 1, a pair of switches PS1 or PS3 and a pair of switches PS4 or PS2 are alternately turned on and off in pairs. Of the pair of switches (PS1, PS4) in a switching circuit 1 that make up a pair, the pair of switches PS4 or PS1 is turned off first, and then the pair of switches PS1 or PS4 is turned off later. Similarly, of the pair of switches (PS2, PS3) in the other switching circuit 1 that make up a pair, the pair of switches PS3 or PS2 is turned off first, and then the pair of switches PS2 or PS3 is turned off later.

[0034] The AC obtained by converting the DC input from the first terminal Ter1 and the second terminal Ter2 by the switching circuit 1 is input to the switching circuit 2 via the transformer 11. The switching circuit 2 rectifies this AC into DC and outputs it to the third terminal Ter3 and the fourth terminal Ter4. In other words, the control circuit (3) performs a rectification operation on the switching circuit (2) that converts the AC input from the transformer (11) side into DC and outputs it from the other two terminals (Ter3 & Ter4) by alternately turning on and off the pair of the switch element (Q5) to which the first capacitor (Ca) is parallel and the switch element (Q6) to which the second capacitor (Cb) is parallel.

[0035] The control that operates the switching circuits (1, 2) so that the DC input from the first terminal Ter1 and the second terminal Ter2 is converted into AC and output from the switching circuit 1, and the AC is converted into DC in the switching circuit 2 via the transformer 11 and then power is supplied to the third terminal Ter3 and the fourth terminal Ter4 on the output side is called "energy transition switching control."

[0036] This energy transition switching control will be explained below. Energy transition switching control is performed by shifting the phase of the timing for turning on and off the pair of switches (PS5, PS6). The control circuit (3) By performing phase shift control to shift the phase of the on / off operation of the switching circuit (1) on the side that converts the DC input from the two terminals (Ter1 & Ter2) side into AC and outputs it to the transformer (11) and the phase of the rectification operation of the switching circuit (2) on the side that converts the AC input from the transformer (11) side into DC and outputs it from the other two terminals (Ter3 & Ter4), The detection value of the voltage, current or power output from between the other two terminals (Ter3 & Ter4) or the detection value of the voltage, current or power input from between the two terminals (Ter1 & Ter2) is brought closer to a target value.

[0037] The detection means 18 of the switching circuit 2 shown in FIG. 1 detects the output voltage of the switching circuit 2, which is output between the third terminal Ter3 and the fourth terminal Ter4. This detected output voltage value is input to the control circuit 3. The control circuit 3 controls the output voltage of the switching circuit 2 by turning on and off the pair of switches (PS1 to PS4) of the switching circuit 1 and the switches (S5, S6) of the switching circuit 2 based on the detected output voltage value. For example, the control circuit 3 performs pulse control to modulate the pulse width, frequency, etc. of the pair of switches (PS1 to PS4) of the switching circuit 1 and the switches (S5, S6) of the switching circuit 2 so that the detected output voltage value approaches a target voltage value according to the load conditions. The detection means 18 of the switching circuit 2 detects the voltage applied to a resistor connected to the output side, for example.

[0038] When the control circuit 3 performs an operation (boost operation) to make the output voltage output between the third terminal Ter3 and the fourth terminal Ter4 higher than the input voltage input between the first terminal Ter1 and the second terminal Ter2, the control circuit 3 controls the amount of energy stored in the inductance means L from the first terminal Ter1 and the second terminal Ter2 side by pulse control of the drive signal provided to the switch S5 or S6 of the switching circuit 2. In this case, while the pair of switches PS1 and PS4 or the pair of switches PS2 and PS3 of the switching circuit 1 are both on, the switch S6 or S5 of the switching circuit 2 is turned on to short-circuit the secondary winding 11b side of the transformer 11 (the states of periods a to e in FIGS. 12 to 16). As a result, the energy input from the first terminal Ter1 and the second terminal Ter2 side is stored in the inductance means L. Next, while the pair of switches PS1 and PS4 or the pair of switches PS2 and PS3 of the switching circuit 1 are both in the on state, the switch S6 or S5 of the switching circuit 2 is turned off, so that the energy stored in the inductance means L is supplied to the third terminal Ter3 and the fourth terminal Ter4 (the state of period f in FIG. 17).

[0039] Furthermore, in the case of an operation (step-down operation) in which the output voltage output between the third terminal Ter3 and the fourth terminal Ter4 is made lower than the input voltage input between the first terminal Ter1 and the second terminal Ter2, the control circuit 3 pulse-controls the switch device Sdx of the switching circuit 1 and operates the switches (S5, S6) of the switching circuit 2 so as not to conduct in the forward direction. Specifically, during a period in which the paired switches PS1 and PS4 or the paired switches PS2 and PS3 of the switching circuit 1 that make up a group are in the on state, the control circuit 3 pulse-controls the switches of the switching circuit 1 so as to supply energy input from the first terminal Ter1 and the second terminal Ter2 to the third terminal Ter3 and the fourth terminal Ter4 via the inductance means L, and operates the switches (S5, S6) of the switching circuit 2 so as not to conduct in the forward direction. In this operation, the control circuit 3 does not cause the switches S5 and S6 of the switching circuit 2 to conduct in the forward direction, so that the bridge-connected circuit of the switching circuit 2 functions as a full-bridge rectifier circuit in which the anti-parallel diodes (Dy: y=5 to 8) are conductive.

[0040] The operation of the drive signals will be explained below assuming that the drive signal for turning on the switches of switching circuit 1 and switching circuit 2 is an on signal, and the drive signal for turning them off is an off signal. Voltage, current, etc. are used as the drive signals. Furthermore, the on and off signals are not particularly limited and may be signals that are given throughout the on and off periods, or may be signals that are given for a short time as a trigger.

[0041] Next, an example of the operation (ZVS control and energy transition switching control) of this DC / DC converter will be described. In this embodiment, the switches (S7, S8) of the switching circuit 2 are always off.

[0042] (X-direction step-down operation) First, the voltage step-down operation will be described. The voltage step-down operation is an operation for making the voltage Vo output between the third terminal Ter3 and the fourth terminal Ter4 lower than the voltage Vin input between the first terminal Ter1 and the second terminal Ter2. FIG. 2 is a waveform diagram showing an example of drive signals for the pair of switches (PS1 to PS4) of switching circuit 1 and the switches (S5 to S8) of switching circuit 2 during step-down operation. The on-time of the pair of switches (PS3, PS4) is T1, and the on-time of the switches (S5, S6) is T2. During step-down operation, the phase shift amount of the switches (S5, S6) is kept to a minimum. Note that the minimum phase shift amount refers to when the phase is shifted all the way to the left, which in the case of FIG. 2 refers to a phase state in which switch S5 is turned on immediately after switch PS4 is turned on.

[0043] The minimum phase shift amount is In the switching circuit (1) on the side that converts the DC input from the two terminals (Ter1 & Ter2) into AC and outputs the AC to the transformer (11), when the switch element (Qxa: x=1, 4 / 3, 2) to which the additional capacitor (Cxp) included in the switch device (Sd1 / 3) of the upper arm of the first or second leg and the switch device (Sd4 / 2) of the lower arm of the second or first leg is connected in parallel is turned on, This is the phase in which the switching circuit (2) on the side that converts AC input from the transformer (11) side into DC and outputs it from the other two terminals (Ter3 & Ter4) turns on the switch element (Q5) to which the first capacitor (Ca) is parallel or the switch element (Q6) to which the second capacitor (Cb) is parallel.

[0044] Fig. 3 is an example of a waveform diagram showing the relationship between the on / off timing (drive signal) of each pair of switches in the switching circuit (1, 2) and the excitation current of the transformer 11 for one cycle (Tt). Figs. 4 to 9 are circuit diagrams showing the current flowing in each period of one half cycle.

[0045] [Period a] See Figure 4. The current flow is indicated by arrows. In the switching circuit 1, after the pair of switches PS3 (switch elements Q2a and Q3a) is turned off, the current of the inductance means L flows through the anti-parallel diodes of the switch elements (Q1b and Q4b), the flying capacitors (FC1 and FC2), and the pair of switches PS2 (switch elements Q2b and Q3b) in the ON state. At this time, the voltage of the flying capacitor FC1 (half of Vin) is applied to the switch element Q2a, and the difference between the voltages Vin and FC1 (half of Vin) is applied to the switch element Q1a. Similarly, a voltage of half Vin is applied to the switch elements (Q4a and Q3a). In addition, current flows through the path shown in the figure in the switching circuit 2. That is, the secondary current of the transformer 11 passes through the anti-parallel diode D7 of the switching element Q7 and the switching element Q6, and is output from the third terminal Ter3 and the fourth terminal Ter4.

[0046] [Period b] See Figure 5. The current flow is indicated by arrows. In the switching circuit 2, when the current flowing through the anti-parallel diode D7 of the switch element Q7 and the switch element Q6 drops to zero or less and the anti-parallel diode cuts off, the excitation current of the transformer 11 flows through the path shown in FIG.

[0047] [Period c] See Figure 6. The current flow is indicated by arrows. In the switching circuit 2, after the switch S6 (switch element Q6) is turned off, the current in the inductance means L increases due to resonance between the parallel capacitors (C5, C6) of the switch elements (Q5, Q6) and the first and second capacitors (Ca, Cb) and the inductance means L, and therefore, in the switching circuit 1, it becomes easier to ensure the excitation current required for ZVS of the switch elements (Q1a, Q4a) (see Patent Document 3).

[0048] [Periods d and e] See Figures 7 and 8. The current flow is indicated by arrows. When the pair switch PS2 (switch elements Q2b, Q3b) is turned off, current flows as shown in Figure 7, charging the parallel capacitors of the switch elements (Q2b, Q3b) and increasing the voltage. At the same time, the parallel capacitors of the switch elements (Q1a, Q4a) and the additional capacitors (C1p, C4p) are discharged, and the voltage of the switch elements (Q1a, Q4a) decreases. If a sufficient current (current through the inductance means L) is ensured at the end of period c, the voltage reaches zero and the anti-parallel diodes of the switch elements (Q1a, Q4a) become conductive (see Figure 8). The voltage of the switch elements (Q2b, Q3b) also becomes half of Vin. It is necessary to provide a period Td during which the pair of switches (PS2 and PS4, or PS1 and PS3) are turned off so that the parallel capacitors of the switch elements (Q1a, Q4a) and the additional capacitors (C1p, C4p) are discharged by the current of the inductance means L and the voltage of the switch elements (Q1a, Q4a) becomes zero. In other words, the period Td is the period from when the pair of switch PS2 is turned off until the pair of switch PS4 is turned on, and the period from when the pair of switch PS1 is turned off until the pair of switch PS3 is turned on. ZVS is achieved by turning on the pair switch PS1 (switch elements Q1b, Q4b) during periods (a to e) when the anti-parallel diodes of the switch elements (Q1b, Q4b) are conducting.

[0049] [Period f] See Figure 9. The current flow is indicated by arrows. In switching circuit 1, ZVS is achieved by turning on pair switch PS4 (switch elements Q1a, Q4a) when the anti-parallel diodes of switch elements (Q1a, Q4a) are conducting. In switching circuit 2, ZVS is achieved by turning on switch S5 (switch element Q5) while the anti-parallel diodes (D5, D8) of switch elements (Q5, Q8) are conducting (as shown in Figure 3, switch S5 is turned on in the middle of period f). Although the current value increases when the pair switch PS4 (switch elements Q1a, Q4a) is turned off, the voltage rise after turning off is gradual due to the addition of additional capacitors (C1p, C4p), and switching loss is reduced.

[0050] The same applies to the currents that flow in each period of the other half cycles.

[0051] In this way, all switch elements can be turned on with ZVS. Furthermore, the voltage applied to all switch elements in switching circuit 1 is half the input voltage Vin. Therefore, even if the voltage Vin is high, the withstand voltage required of the switch elements can be reduced. Furthermore, if there is a difference in the switching timing of each switch element, the voltage applied to the switch element will exceed half the input / output voltage, but normally the difference in timing is slight, and the difference in voltage applied to the switch elements is also slight, so the withstand voltage of the switch element will not be exceeded.

[0052] (X-direction boost operation) Next, the voltage step-up operation will be described. The voltage step-down operation is an operation in which the voltage Vo output between the third terminal Ter3 and the fourth terminal Ter4 is made higher than the voltage Vin input between the first terminal Ter1 and the second terminal Ter2. 10 is a waveform diagram showing an example of drive signals for the pair of switches (PS1 to PS4) of switching circuit 1 and the switches (S5 to S8) of switching circuit 2 in boost operation. The on-time of the pair of switches (PS3, PS4) is T1, and the on-time of the switches (S5, S6) is T2. In boost operation, the overlap time Tp of the pair of switches (PS3 and PS5, PS4 and PS6) is adjusted by adjusting the phase shift amount and on-time T2 of the switches (S5, S6).

[0053] The control circuit (3) is characterized in that it adjusts the time during which both (1) and (2), and both (3) and (4) are on by the phase shift control so as to bring the detected value closer to the target value. (1) The switching circuit (1) on the side that converts DC input from the two terminals (Ter1 & Ter2) into AC and outputs the AC to the transformer (11), the switching device (Sd1) of the upper arm of the first leg and the switching device (Sd4) of the lower arm of the second leg, the switching element (Qxa: x=1, 4) to which the additional capacitor (Cxp) is connected in parallel; (2) the switch element (Q6) connected in parallel with the second capacitor (Cb) of the switching circuit (2) on the side that converts AC input from the transformer (11) side into DC and outputs it from the other two terminals (Ter3 & Ter4); (3) the switch element (Qxa: x=2, 3) to which the additional capacitor (Cxp) included in the switch device (Sd2) of the lower arm of the first leg and the switch device (Sd3) of the upper arm of the second leg of the switching circuit (1) on the side that converts the direct current input from the two terminals (Ter1 & Ter2) side into alternating current and outputs the alternating current to the transformer (11) is connected in parallel; (4) The switch element (Q5) in the switching circuit (2) that converts AC input from the transformer (11) side into DC and outputs it from the other two terminals (Ter3 & Ter4) is connected in parallel with the first capacitor (Ca).

[0054] A more specific explanation will be given. The control circuit 3 monitors the input voltage to the two terminals (Ter1 and Ter2) detected by the detection means 19 of the switching circuit 1, and performs energy transition switching control to adjust the energy transition period Tp during which the pair of switches (PS1 and PS4 / PS3 and PS2) and the switch (S6 / S5) are in the on state.

[0055] For example, the control circuit (3) When the voltage Vo output from between the two terminals (Ter3, Ter4) is made higher than the voltage Vin input from between the two terminals (Ter1, Ter2), the energy transition switching control is as follows: To lengthen the energy transition period Tp, phase control is performed to shift the phase of the on / off cycle of the switches (S6 / S5), and time control is performed to adjust the time T2 during which the switches (S6 / S5) are on.

[0056] Specifically, the control circuit 3 performs phase control to delay (shift to the right in the drawing) the phase of the switches (S5, S6) and lengthen the time Tp during which the pair of switches (PS1, PS4) and switch S6 are simultaneously on and the pair of switches (PS2, PS3) and switch S5 are simultaneously on. Here, the phase control of the switches (S5, S6) can be delayed until the pair of switches (PS2, PS3 or PS1, PS4) are turned on.

[0057] If it is detected that the output voltage Vo, etc. is still insufficient to the target value after the phase of the switches (S5, S6) has been delayed to the maximum extent, the control circuit 3 extends the time T2 for which the switches (S5, S6) are turned on, and performs time control to lengthen the time Tp.

[0058] In this way, in the energy transition switching control, the time Tp is lengthened by phase control or time control to increase the energy stored in the inductance means L, causing a transition from switching circuit 1 to switching circuit 2, and making the output voltage Vo higher than the input voltage Vin.

[0059] Fig. 11 is an example of a waveform diagram showing the relationship, for one cycle (Tt), between the on / off timing (drive signal) of each pair of switches in the switching circuit (1, 2) and the excitation current of the transformer 11. Figs. 12 to 17 are circuit diagrams showing the current flowing in each period of one half cycle.

[0060] [Period a] See Figure 12. The current flow is indicated by arrows. The current flow is the same as in the period a of the voltage step-down operation. [Period b] See Figure 13. The current flow is indicated by arrows. The current flow is the same as in the step-down operation period b. [Periods c and d] See Figures 14 and 15. The current flow is indicated by arrows. The current flow in switching circuit 1 is the same as in periods d and e of the step-down operation. In switching circuit 2, because switch element Q6 is on, the current flows through switch element Q6 without passing through parallel capacitor C6a and second capacitor Cb.

[0061] [Period e] See Figure 16. The current flow is indicated by arrows. The current flow in switching circuit 1 is the same as during period f of step-down operation. ZVS is achieved by turning on the switching elements (Q1a, Q4a) when the parallel diodes (D1a, D4a) of the switching elements (Q1a, Q4a) are conducting. In switching circuit 2, because switching element Q6a is on, current flows through switching element Q6 without passing through parallel capacitor C6 and second capacitor Cb. Furthermore, although the current value increases when the switching element Q6 is turned off, the voltage rise after the switching element Q6 is turned off becomes gradual because the second capacitor Cb is connected in parallel, and switching loss decreases. [Period f] See Figure 17. The current flow is indicated by arrows. The current flow in the switching circuit 1 is the same as during the step-down operation period f. The presence of the additional capacitors (C1p, C4p) also reduces switching loss when the switch elements (Q1a, Q4a) are turned off. The current flow in the switching circuit 2 is the same as that in the period f during the step-down operation. Furthermore, ZVS is achieved by turning on the switch S5 (switch element Q5) while the anti-parallel diode D5 of the switch element Q5 is conducting (as shown in FIG. 11, the switch S5 is turned on in the middle of the period f).

[0062] The same applies to the currents that flow in each period of the other half cycles.

[0063] In step-up operation, as in step-down operation, all switch elements can be turned on by ZVS. In addition, the voltage applied to all switch elements in switching circuit 1 is half the input voltage Vin, so even if the voltage Vin is high, the withstand voltage required for the switch elements can be reduced.

[0064] (Embodiment 2) The circuit of the DC / DC converter of this embodiment is the same as the circuit described in Fig. 1. However, the DC / DC converter of this embodiment converts direct current input from the third terminal Ter3 and fourth terminal Ter4 side into alternating current and outputs it from switching circuit 2, and converts the alternating current into direct current in switching circuit 1 via transformer 11 and supplies power to the first terminal Ter1 and second terminal Ter2 side on the output side. In other words, the DC / DC converter of this embodiment transitions power in the Y direction.

[0065] The control circuit 3 controls the on / off of each switch by supplying a drive signal to each switch Sx of each switching circuit (1, 2). First, the zero voltage switching (ZVS) control will be described. The control circuit (3) On / off control is performed on the switching circuit (2) that converts the DC input from the other two terminals (Ter3 & Ter4) into AC and outputs the AC to the transformer (11) by alternately turning on and off the switch (S7 / 5) of the upper arm of the fourth or third leg and the switch (S6 / 8) of the lower arm of the third or fourth leg in pairs; and When performing the on / off control, in each of the groups, The switch element (Q5, 6) to which the first and second capacitors (Ca, Cb) are connected in parallel is turned off first; and After the switch element (Q7 / 8) in one of the pairs, in which the first and second capacitors (Ca, Cb) are not connected in parallel, is turned off and a fixed time (Td) has elapsed, the switch element (Q8 / 7) in the other pair, in which the first and second capacitors (Ca, Cb) are not connected in parallel, is turned on. It is characterized by:

[0066] 1, the switch element Q7 or Q5 on the upper arm of the fourth leg 25 or the third leg 24 and the switch element Q6 or Q8 on the lower arm of the third leg 24 or the fourth leg 25 form a pair and are alternately turned on and off. Of the switch elements Q7 and Q6 of the switching circuit 2 that form the pair, the switch element Q7 or Q6 is turned off first, and then the switch element Q6 or Q7 is turned off later. Similarly, of the switch elements Q8 and Q5 of the switching circuit 2 that form the other pair, the switch element Q8 or Q5 is turned off first, and then the switch element Q5 or Q8 is turned off later.

[0067] The AC obtained by converting the DC input from the third terminal Ter3 and the fourth terminal Ter4 by the switching circuit 2 is input to the switching circuit 1 via the transformer 11. The switching circuit 1 rectifies this AC to DC and outputs it to the first terminal Ter1 and the second terminal Ter2. That is, the control circuit (3) performs a rectification operation for the switching circuit (1) that converts the AC input from the transformer (11) side to DC and outputs it from the two terminals (Ter1 & Ter2) by alternately turning on and off the switch element (Qxa) to which the additional capacitor (Cxp) included in the switch device (Sd1,3) of the upper arm of the first or second leg is paralleled and the switch element (Qxa) to which the additional capacitor (Cxp) included in the switch device (Sd4,2) of the lower arm of the second or first leg is paralleled, as a pair.

[0068] The control that operates the switching circuits (1, 2) so that the DC input from the third terminal Ter3 and the fourth terminal Ter4 is converted into AC and output from the switching circuit 2, and the AC is converted into DC in the switching circuit 1 via the transformer 11 and then power is supplied to the first terminal Ter1 and the second terminal Ter2 on the output side is called "energy transition switching control."

[0069] This energy transition switching control will be explained below. Energy transition switching control is performed by shifting the phase of the timing for turning on and off the pair of switches (PS3, PS4). The control circuit (3) By performing phase shift control to shift the phase of the on / off operation of the switching circuit (2) on the side that converts the DC input from the other two terminals (Ter3 & Ter4) side into AC and outputs it to the transformer (11) and the phase of the rectification operation of the switching circuit (1) on the side that converts the AC input from the transformer (11) side into DC and outputs it from the two terminals (Ter1 & Ter2), The device is characterized by bringing the detected value of voltage, current or power output from between the two terminals (Ter1 & Ter2) or the detected value of voltage, current or power input from between the other two terminals (Ter3 & Ter4) closer to a target value.

[0070] The detection means 19 of the switching circuit 1 shown in FIG. 1 detects the output voltage of the switching circuit 1, which is output between the first terminal Ter1 and the second terminal Ter2. This detected output voltage value is input to the control circuit 3. The control circuit 3 controls the output voltage of the switching circuit 1 by turning on and off the switches (S5 to S8) of the switching circuit 2 and the pair of switches (PS3, PS4) of the switching circuit 1 based on the detected output voltage value. For example, the control circuit 3 performs pulse control to modulate the pulse width, frequency, etc. of the switches (S5 to S8) of the switching circuit 2 and the pair of switches (PS3, PS4) of the switching circuit 1 so that the detected output voltage value approaches a target voltage value according to the load conditions. The detection means 19 of the switching circuit 1 detects the voltage applied to a resistor connected to the output side, for example.

[0071] When the control circuit 3 performs an operation (boost operation) to make the output voltage between the first terminal Ter1 and the second terminal Ter2 higher than the input voltage input between the third terminal Ter3 and the fourth terminal Ter4, the control circuit 3 controls the amount of energy stored in the inductance means L from the third terminal Ter3 and the fourth terminal Ter4 side by pulse control of the drive signal provided to the pair of switches PS3 or PS4 of the switching circuit 1. In this case, the pair of switches PS3 or PS4 of the switching circuit 1 is turned on while the pair of switches S7 and S6 of the switching circuit 2 or the pair of switches S8 and S5 of the switching circuit 2 are both on, thereby shorting the secondary winding 11b side of the transformer 11 (the state of periods a to e in Figures 28 to 32). As a result, the energy input from the third terminal Ter3 and the fourth terminal Ter4 side is stored in the inductance means L. Next, while the switches S7 and S6 or the switches S8 and S5 of the paired switching circuit 2 are both on, the paired switch PS4 or PS3 of the switching circuit 1 is turned off, thereby supplying the energy stored in the inductance means L to the first terminal Ter1 and the second terminal Ter2 (the state of period f in FIG. 33).

[0072] Furthermore, in the case of an operation (step-down operation) in which the output voltage output between the first terminal Ter1 and the second terminal Ter2 is made lower than the input voltage input between the third terminal Ter3 and the fourth terminal Ter4, the control circuit 3 pulse-controls the switches of the switching circuit 2 and operates to prevent forward conduction of the pair of switches (PS3, PS4) of the switching circuit 1. Specifically, during a period in which the switches S7 and S6 or the switches S8 and S5 of the pair of switching circuit 2 are on, the control circuit 3 pulse-controls the switches of the switching circuit 2 so that energy input from the third terminal Ter3 and the fourth terminal Ter4 side is supplied to the first terminal Ter1 and the second terminal Ter2 side via the inductance means L, and operates to prevent forward conduction of the pair of switches (PS3, PS4) of the switching circuit 1. In this operation, the control circuit 3 does not cause the pair of switches PS3 and PS4 of the switching circuit 1 to conduct in the forward direction, so that the bridge connection circuit of the switching circuit 1 functions as a full-bridge rectifier circuit (a full-bridge rectifier circuit in which the set of Dxa and Dxb forms one diode) in which the anti-parallel diodes (Dxa, Dxb: x=1 to 4) are conductive.

[0073] The operation of the drive signals will be explained below assuming that the drive signal for turning on the switches of switching circuit 1 and switching circuit 2 is an on signal, and the drive signal for turning them off is an off signal. Voltage, current, etc. are used as the drive signals. Furthermore, the on and off signals are not particularly limited and may be signals that are given throughout the on and off periods, or may be signals that are given for a short time as a trigger.

[0074] Next, an example of the operation (ZVS control and energy transition switching control) of this DC / DC converter will be described. In this embodiment, the pair of switches (PS1, PS2) of the switching circuit 1 are always off.

[0075] (Y-direction step-down operation) First, the voltage step-down operation will be described. The voltage step-down operation is an operation for making the voltage Vo output between the first terminal Ter1 and the second terminal Ter2 lower than the voltage Vin input between the third terminal Ter3 and the fourth terminal Ter4. FIG. 18 is a waveform diagram showing an example of drive signals for the pair of switches (PS1 to PS4) of switching circuit 1 and the switches (S5 to S8) of switching circuit 2 in step-down operation. The on-time of the switches (S5, S6) is T1, and the on-time of the pair of switches (PS3, PS4) is T2. In step-down operation, the amount of phase shift for the pair of switches (PS3, PS4) is kept at a minimum. Note that the minimum phase shift amount refers to when the phase is shifted all the way to the left, and in the case of FIG. 18, this refers to a phase state in which the pair of switch PS4 is turned on immediately after switch S5 is turned on.

[0076] The minimum phase shift amount is In the switching circuit (2) on the side that converts the DC input from the other two terminals (Ter3 & Ter4) into AC and outputs the AC to the transformer (11), when the switch element (Qxa: x=7, 6 / 8, 5) to which the additional capacitor (Cxp) included in the switch (S7 / 5) of the upper arm of the fourth or third leg and the switch (S6 / 8) of the lower arm of the third or fourth leg is connected in parallel is turned on, This is the phase in which the switching circuit (1) on the side that converts AC input from the transformer (11) side into DC and outputs the DC from the two terminals (Ter1 & Ter2) turns on the switch element (Q3a / Q1a) to which the additional capacitor (Cxp) included in the switch device (Sd3 / Sd1) of the upper arm of the second or first leg is connected in parallel, and the switch element (Q2a / Q4a) to which the additional capacitor (Cxp) included in the switch device (Sd2 / Sd4) of the lower arm of the first or second leg is connected in parallel.

[0077] Fig. 19 is an example of a waveform diagram showing the relationship, for one cycle (Tt), between the on / off timing (drive signal) of each switch element of the switching circuit (1, 2) and the excitation current of the transformer 11. Figs. 20 to 25 are circuit diagrams showing the current flowing in each period of one half cycle.

[0078] [Period a] See Figure 20. The current flow is indicated by arrows. In the switching circuit 2, after the switch S6 is turned off, the secondary current of the transformer 11 flows through the anti-parallel diode D6 of the switch element Q6 and the switch S8 in the on state. In addition, current flows through the path shown in the figure in switching circuit 1. The voltage (1 / 2 of Vo) of flying capacitor FC1 is applied to switch element Q2a, and the difference between the voltages Vo and FC1 (1 / 2 of Vo) is applied to switch element Q1a. Similarly, a voltage of 1 / 2 of Vo is applied to switch elements (Q4a, Q3a).

[0079] [Period b] See Figure 21. The current flow is indicated by arrows. In the switching circuit 1, when the current flowing through the anti-parallel diode of the switch element (Q4b, Q1b) drops below zero and the anti-parallel diode is cut off, the excitation current of the transformer 11 flows through the path shown in Fig. 21. At this time, the voltage of the switch element (Q4b, Q1b) becomes 1 / 2 of Vo.

[0080] [Period c] See Figure 22. The current flow is indicated by arrows. In the switching circuit 2, after the switch S6 (switch element Q6) is turned off, the current in the inductance means L increases due to resonance between the parallel capacitor C6 and second capacitor Cb of the switch element Q6a and the inductance means L, making it easier to ensure the excitation current required for ZVS of the switch elements (Q7, Q8) in the switching circuit 2 (see Patent Document 3).

[0081] [Periods d and e] See Figures 23 and 24. The current flow is indicated by arrows. When switch S8 (switch element Q8) is turned off, current flows as shown in Fig. 23, parallel capacitor C8 of switch element Q8 is charged and the voltage rises, and at the same time, parallel capacitor C7 of switch element Q7 is discharged and the voltage of switch element Q7 drops. Here, if a sufficient amount of current (current through inductance means L) is ensured at the end of period c, the voltage reaches zero and anti-parallel diode D7 of switch element Q7 becomes conductive (see Fig. 24). It is necessary to provide a period Td during which the switches (S7 and S8) are turned off so that the parallel capacitor C7 of the switch element Q7 is discharged by the current of the inductance means L and the voltage of the switch element Q7 becomes zero. In other words, the period Td is the period from when the switch S7 is turned off until when the switch S8 is turned on, and the period from when the switch S8 is turned off until when the switch S7 is turned on. ZVS is achieved by turning on the switch S7 (switch element Q7) during the period e in which the anti-parallel diode D7 of the switch element Q7 is conducting.

[0082] [Period f] See Figure 25. The current flow is indicated by arrows. In the switching circuit 2, ZVS is achieved by turning on the switch S6 (switch element Q6) when the anti-parallel diode D6 of the switch element Q6 is conducting. Also, in the switching circuit 1, ZVS is achieved by turning on the switch elements (Q3a, Q2a) while the anti-parallel diodes (D3a, D2a) of the switch elements (Q3a, Q2a) are conducting (as shown in FIG. 19, the pair switch PS3 is turned on in the middle of period f). Although the current value increases when the switch S6 (switch element Q6) is turned off, the voltage rise after the switch S6 is turned off becomes gradual due to the addition of the second capacitor Cb, and switching loss decreases.

[0083] The same applies to the currents that flow in each period of the other half cycles.

[0084] In this way, all switch elements can be turned on with ZVS. Also, the voltage applied to all switch elements in switching circuit 1 is half the output voltage Vo. Therefore, even if the voltage Vo is high, the withstand voltage required of the switch elements can be reduced. Furthermore, if there is a difference in the switching timing of each switch element, the voltage applied to the switch element will exceed half the input / output voltage, but usually the difference in timing is slight, and the difference in voltage applied to the switch element is also slight, so the withstand voltage of the switch element will not be exceeded.

[0085] (Y direction voltage boost operation) Next, the boost operation will be described. The boost operation is an operation for making the voltage Vo output between the first terminal Ter1 and the second terminal Ter2 higher than the voltage Vin input between the third terminal Ter3 and the fourth terminal Ter4. 26 is a waveform diagram showing an example of drive signals for the pair of switches (PS1 to PS4) of switching circuit 1 and the switches (S5 to S8) of switching circuit 2 in boost operation. The on-time of the switches (S5, S6) is T1, and the on-time of the pair of switches (PS3, PS4) is T2. In boost operation, the overlap time Tp between the switches (S5, S6) and the pair of switches (PS4, PS3) is adjusted by adjusting the phase shift amount of the pair of switches (PS3, PS4) and the on-time T2.

[0086] The control circuit (3) is characterized in that it adjusts the time during which both (1) and (2), and both (3) and (4) are on by the phase shift control so as to bring the detected value closer to the target value. (1) the switch element (Q6) connected in parallel with the second capacitor (Cb) of the switching circuit (2) on the side that converts DC input from the other two terminals (Ter3 & Ter4) into AC and outputs the AC to the transformer (11); (2) the switching circuit (1) on the side that converts AC input from the transformer (11) side into DC and outputs the DC from the two terminals (Ter1 & Ter2), the switch element (Q1a) to which the additional capacitor (C1p) included in the switch device (Sd1) of the upper arm of the first leg is paralleled, and the switch element (Q4a) to which the additional capacitor (C4p) included in the switch device (Sd4) of the lower arm of the second leg is paralleled; (3) the switch element (Q5) connected in parallel with the first capacitor (Ca) of the switching circuit (2) on the side that converts DC input from the other two terminals (Ter3 & Ter4) into AC and outputs the AC to the transformer (11); (4) The switching circuit (1) on the side that converts AC input from the transformer (11) side into DC and outputs the DC from the two terminals (Ter1 & Ter2) includes the switch element (Q2a) to which the additional capacitor (C2p) included in the switch device (Sd2) of the lower arm of the first leg is paralleled, and the switch element (Q3a) to which the additional capacitor (C3p) included in the switch device (Sd3) of the upper arm of the second leg is paralleled.

[0087] A more specific explanation will be given. The control circuit 3 monitors the input voltages of the two terminals (Ter3 and Ter4) detected by the detection means 18 and the output voltages of the two terminals (Ter1 and Ter2) detected by the detection means 19, and performs energy transition switching control to adjust the energy transition period Tp during which the pair of switches (PS3 / PS4) and the switches (S5 / S6) are in the on state.

[0088] For example, the control circuit (3) When the voltage Vo output from between the two terminals (Ter1, Ter2) is made higher than the voltage Vin input from between the two terminals (Ter3, Ter4), the energy transition switching control is as follows: To lengthen the energy transition period Tp, phase control is performed to shift the phase of the on / off cycle of the pair switch (PS3 / PS4), and time control is also performed to adjust the time T2 during which the pair switch (PS3 / PS4) is on.

[0089] Specifically, the control circuit 3 performs phase control to delay (shift to the right in the drawing) the phase of the pair of switches (PS3, PS4) and lengthen the time Tp during which the switches (S7, S6) and the pair of switch PS4 are simultaneously on and the switches (S8, S5) and the pair of switch PS3 are simultaneously on. Here, the phase control of the pair of switches (PS3, PS4) can be delayed until the switches (S8, S5 or S7, S6) are turned on.

[0090] If it is detected that the output voltage Vo, etc. is still insufficient to the target value after the phase of the pair switches (PS3, PS4) has been delayed to the maximum extent, the control circuit 3 extends the time T2 for turning on the pair switches (PS3, PS4) and performs time control to lengthen the time Tp.

[0091] In this way, in the energy transition switching control, the time Tp is lengthened by phase control or time control to increase the energy stored in the inductance means L, causing a transition from switching circuit 2 to switching circuit 1, and making the output voltage Vo higher than the input voltage Vin.

[0092] Fig. 27 is an example of a waveform diagram showing the relationship, for one cycle (Tt), between the on / off timing (drive signal) of each switch element of the switching circuit (1, 2) and the excitation current of the transformer 11. Figs. 28 to 33 are circuit diagrams showing the current flowing in each period of one half cycle.

[0093] [Period a] See Figure 28. The current flow is indicated by arrows. The current flow is the same as in the period a of the voltage step-down operation. [Period b] See Figure 29. The current flow is indicated by arrows. The current flow is the same as in the step-down operation period b. [Periods c and d] See Figures 30 and 31. The current flow is indicated by arrows. The current flow in switching circuit 2 is the same as during periods d and e of the step-down operation. In switching circuit 1, the switch elements (Q1a, Q4a) are on, so the current flows through the switch elements (Q1a, Q4a) without passing through the parallel capacitors (C1a, C4a) and additional capacitors (C1p, C4p).

[0094] [Period e] See Figure 32. The current flow is indicated by arrows. The current flow in switching circuit 2 is the same as during period f of step-down operation. ZVS is achieved by turning on switching element Q6 when its parallel diode D6 is conducting. In switching circuit 1, because the switching elements (Q1a, Q4a) are on, the current flows through the switching elements (Q1a, Q4a) without passing through the parallel capacitors (C1a, C4a) and additional capacitors (C1p, C4p). During this period as well, the voltage applied to each switch in switching circuit 1 is 1 / 2 of Vo. Furthermore, although the current value increases when the switching element Q6 is turned off, the voltage rise after the switching element Q6 is turned off becomes gradual because the second capacitor Cb is connected in parallel, and switching loss decreases. [Period f] See Figure 33. The current flow is indicated by arrows. The current flow in the switching circuit 2 is the same as during the step-down operation period f. When the switch element Q6 is turned off, the presence of the second capacitor Cb also reduces the switching loss. The current flow in the switching circuit 1 is the same as that in the period f during the step-down operation. Furthermore, ZVS is achieved by turning on the pair switch PS3 (switch elements Q3a, Q2a) while the anti-parallel diodes (D3a, D2a) of the switch elements (Q3a, Q2a) are conducting (as shown in FIG. 27, the pair switch PS3 is turned on in the middle of the period f).

[0095] The same applies to the currents that flow in each period of the other half cycles.

[0096] In step-up operation, as in step-down operation, all switch elements can be turned on by ZVS. In addition, the voltage applied to all switch elements in switching circuit 1 is half the output voltage Vo. Therefore, even if the voltage Vo is high, the withstand voltage required for the switch elements can be reduced.

[0097] In the present invention, in the above description, the excitation inductance of the transformer also includes an inductance component connected in parallel to the primary winding or secondary winding of the transformer 11 in order to adjust the excitation current to an appropriate magnitude. Also, in the above description, the current flowing due to a combined inductance formed by the excitation inductance of the transformer 11 and an inductance component connected in parallel thereto is also included in the excitation current. The excitation inductance of the transformer can be adjusted by, for example, the gap width of the core, the number of turns of the winding, the material of the core, etc. in the transformer structure.

[0098] (Addendum) In the above embodiment, the control circuit 3 makes the voltage values ​​detected by the detection means 18 of the switching circuit 2 and the detection means 19 of the switching circuit 1 approach the target values, but the detected values ​​used may be the output current value, the output power, or a combination of these. Similarly, the detected values ​​of the input voltage, current, or power may be made to approach the target values. Generally, the detected power value is a calculated value obtained by multiplying the detected voltage and current. The above-mentioned detected values ​​of the output voltage, current, or power or the detected values ​​of the input voltage, current, or power also include values ​​obtained by performing calculations such as multiplying or dividing these values ​​by a certain coefficient, or adding or subtracting a certain value.

[0099] The present invention uses inductance means connected to the primary or secondary winding of a transformer to realize an operation of turning on and off the pair of switches of the output-side switching circuit 2 or switching circuit 1 and an operation of making the output-side switching circuit 2 or switching circuit 1 function as a rectifier circuit, thereby enabling compatibility with a wide range of input / output voltages and currents. Furthermore, it is possible to reduce switching loss that occurs when a pair of switches is turned off while current is flowing, and to reduce switching loss that occurs when one of the pair of switches of the paired switching circuit 1 is subsequently turned off. Furthermore, by realizing ZVS, it is possible to reduce switching loss.

[0100] In this embodiment, "step-down operation" has been described as an operation that makes the output voltage lower than the input voltage, and "step-up operation" as an operation that makes the output voltage higher than the input voltage, but this applies when the turns ratio between the primary and secondary sides of the transformer is 1:1. If the turns ratio between the primary and secondary sides of the transformer is not 1:1, "step-up operation" may be performed even when the output voltage is lower than the input voltage, and "step-down operation" may be performed even when the output voltage is higher than the input voltage. Furthermore, a switching circuit that employs a flying capacitor is intended to keep the voltage applied to the switch element low, and does not exclude cases where the input and output voltages are low. Furthermore, power efficiency improves when the transformer is operated near the boundary between step-down and step-up operation, so the transformer turns ratio and other factors are sometimes adjusted to achieve this operation; step-up operation in the X direction and step-down operation in the Y direction also exist.

[0101] (Other embodiments) In the electric circuits of the present invention, a connection point refers to a location that is electrically connected and at the same potential, and does not refer to a location where a physical connection is made. Furthermore, the configuration, structure, number, arrangement, shape, material, etc. of each part of the DC / DC converter and bidirectional DC / DC converter of the present invention are not limited to the specific examples described above, and any suitable selections made by a person skilled in the art are also included within the scope of the present invention as long as they include the gist of the present invention.

[0102] More specifically, for example, semiconductor elements exemplified by symbols are not limited to these specific electrical elements, but can be configured as a single electrical element or an electrical circuit including multiple electrical elements having the same function or action, and all such variations are encompassed within the scope of the present invention. Similarly, the number and layout of circuit elements, including diodes, capacitors, and switches, as appropriately modified by a person skilled in the art are encompassed within the scope of the present invention.

[0103] (effect) This DC / DC converter can use switching elements with low on-resistance and low withstand voltage relative to the input and output voltages, reducing conduction losses. Furthermore, this DC / DC converter can turn on all switching elements using ZVS over a wide range of input and output conditions, reducing switching losses. Thus, the present invention provides a highly efficient bidirectional DC / DC converter, even at high input and output voltages. Furthermore, if there is a difference in the switching timing of each switching element, the voltage applied to the switching element will exceed half the input and output voltage. However, since the difference in timing is usually slight and the difference in voltage applied to the switching elements is also slight, the withstand voltage of the switching element will not be exceeded. [Explanation of symbols]

[0104] Ter1: Terminal 1 Ter2: Terminal 2 Ter3: Third terminal Ter4: 4th terminal 1: Switching circuit 2: Switching circuit 3: Control circuit 11: Trance 11a: Primary winding 11b: Secondary winding 12: First leg 13: Second leg 24: Third leg 25: 4th leg 16, 17: Capacitor 18, 19: Detection means Sx (x=1~4): Switch device Sy(y=5~8): Switch Qxa, Qxb (x=1 to 4): Switch elements Qy (y=5~8): Switch element PSx (x=1~4): Pair switch Dxa, Dxb (x=1~4): Anti-parallel diodes Cxa, Cxb (x=1 to 4): parallel capacitors Dy (y=5~8): Anti-parallel diode Cy (y=5~8): parallel capacitor Cxp(x=1~4): Additional capacitor Ca: First capacitor Cb: Second capacitor FC1~FC2: Flying Capacitor L: inductance means

Claims

1. a transformer having a primary winding and a secondary winding; two switching circuits connected to the primary winding side of the transformer and the secondary winding side of the transformer, respectively; an inductance means disposed between the transformer and the switching circuit on the primary winding side or the secondary winding side of the transformer; a control circuit that controls the switching of the switching circuit; Equipped with One of the switching circuits is a first leg and a second leg in which four switch devices are connected in parallel between two terminals as upper and lower arms, and a flying capacitor connecting the upper and lower arms in each of the first leg and the second leg; Each of the switch devices has switch elements connected in series to which an anti-parallel diode and a parallel capacitor are respectively connected in parallel, and an additional capacitor is connected in parallel to the switch element on one side of the two terminals; the flying capacitor connects the connection points of the switch elements together; The other of the switching circuits is a third leg and a fourth leg, each of which has four switches as upper and lower arms connected in parallel between the other two terminals, each of which has a switch element with an anti-parallel diode and a parallel capacitor connected in parallel; a first capacitor connected in parallel to one of the switches in the upper or lower arm of the third leg or the fourth leg or one of the switches in the upper arm or the lower arm of the third leg and the fourth leg; and a second capacitor connected in parallel to the other of the switches in the upper or lower arm of the third leg or the fourth leg or the other of the switches in the upper arm or the lower arm of the third leg and the fourth leg, The inductance means connects the connection points of the upper and lower arms of the first leg and the upper and lower arms of the second leg together with the primary winding connected in series, or connects the connection points of the upper and lower arms of the third leg and the connection points of the upper and lower arms of the fourth leg together with the secondary winding connected in series. A DC / DC converter comprising:

2. The control circuit performing on / off control for the switching circuit that converts the direct current input from the two terminals into alternating current and outputs the converted alternating current to the transformer, by alternately turning on and off a pair of a switch device of an upper arm of the first or second leg and a switch device of a lower arm of the second or first leg; and When performing the on / off control, in each of the groups, Synchronizing the on / off operations of the switch elements connected in parallel with the additional capacitor, and synchronizing the on / off operations of the switch elements not connected in parallel with the additional capacitor; The switch element connected in parallel to the additional capacitor is turned off first; and the switch element in one of the sets to which the additional capacitor is not connected in parallel is turned off, and after a fixed time has elapsed, the switch element in the other set to which the additional capacitor is connected in parallel is turned on; 2. The DC / DC converter according to claim 1,

3. The control circuit a rectification operation for alternately turning on and off the switching element to which the first capacitor is connected in parallel and the switching element to which the second capacitor is connected in parallel in the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the other two terminals; 3. The DC / DC converter according to claim 2, wherein:

4. The control circuit By performing phase shift control to shift the phase of the on / off operation of the switching circuit on the side that converts the DC input from the two terminals into AC and outputs it to the transformer, and the phase of the rectification operation of the switching circuit on the side that converts the AC input from the transformer side into DC and outputs it from the other two terminals, 4. The DC / DC converter according to claim 3, wherein a detected value of a voltage, current, or power output from the other two terminals or a detected value of a voltage, current, or power input from the two terminals is made to approach a target value.

5. The minimum shift amount of the phase shift control is In the switching circuit that converts DC input from the two terminals into AC and outputs the AC to the transformer, when the switch element to which the additional capacitor is connected in parallel, which is included in the switch device of the upper arm of the first or second leg and the switch device of the lower arm of the second or first leg, is turned on, The phase is when the switch element to which the first capacitor is parallel or the switch element to which the second capacitor is parallel of the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the other two terminals is turned on.

5. The DC / DC converter according to claim 4, wherein:

6. 5. The DC / DC converter according to claim 4, wherein the control circuit adjusts the time during which both (1) and (2), and both (3) and (4) are on by the phase shift control so as to bring the detected value closer to the target value. (1) The switch element, to which the additional capacitor is connected in parallel, is included in the switch device of the upper arm of the first leg and the switch device of the lower arm of the second leg of the switching circuit that converts direct current input from the two terminal sides into alternating current and outputs the alternating current to the transformer; (2) the switch element, to which the second capacitor is connected in parallel, of the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the other two terminals; (3) the switch element, to which the additional capacitor is connected in parallel, is included in the switch device of the lower arm of the first leg and the switch device of the upper arm of the second leg of the switching circuit that converts the direct current input from the two terminal sides into alternating current and outputs the alternating current to the transformer; (4) The switch element, to which the first capacitor is connected in parallel, of the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the other two terminals.

7. The control circuit performing on / off control for the switching circuit that converts the direct current input from the other two terminals into alternating current and outputs the converted alternating current to the transformer, by alternately turning on and off a pair of a switch of an upper arm of the fourth or third leg and a switch of a lower arm of the third or fourth leg; and When performing the on / off control, in each of the groups, The switch element to which the first and second capacitors are connected in parallel is turned off first; and the switch element in one of the sets, in which the first and second capacitors are not connected in parallel, is turned off, and after a fixed time has elapsed, the switch element in the other set, in which the first and second capacitors are not connected in parallel, is turned on.

2. The DC / DC converter according to claim 1,

8. The control circuit a rectification operation for alternately turning on and off a pair of the switch element to which the additional capacitor included in the switch device of the upper arm of the first or second leg is paralleled and a pair of the switch element to which the additional capacitor included in the switch device of the lower arm of the second or first leg is paralleled, for the switching circuit that converts AC input from the transformer side into DC and outputs the DC from the two terminals; 8. The DC / DC converter according to claim 7,

9. The control circuit By performing phase shift control to shift the phase of the on / off operation of the switching circuit on the side that converts the DC input from the other two terminals into AC and outputs it to the transformer, and the phase of the rectification operation of the switching circuit on the side that converts the AC input from the transformer side into DC and outputs it from the two terminals, 9. The DC / DC converter according to claim 8, wherein a detected value of a voltage, current, or power output from between the two terminals or a detected value of a voltage, current, or power input from between the other two terminals is made to approach a target value.

10. The minimum shift amount of the phase shift control is In the switching circuit that converts the DC input from the other two terminals into AC and outputs the AC to the transformer, when the switch element to which the additional capacitor is connected in parallel, which is included in the switch of the upper arm of the fourth or third leg and the switch of the lower arm of the third or fourth leg, is turned on, the phase in which the switch element to which the additional capacitor included in the switch device of the upper arm of the second or first leg is paralleled and the switch element to which the additional capacitor included in the switch device of the lower arm of the first or second leg is paralleled are turned on in the switching circuit on the side that converts AC input from the transformer side to DC and outputs the DC from the two terminals; 10. The DC / DC converter according to claim 9,

11. 10. The DC / DC converter according to claim 9, wherein the control circuit adjusts the time during which both (1) and (2), and both (3) and (4) are on by the phase shift control so as to bring the detected value closer to the target value. (1) the switch element, to which the second capacitor is connected in parallel, of the switching circuit on the side that converts direct current input from the other two terminals into alternating current and outputs the converted alternating current to the transformer; (2) the switch element with which the additional capacitor is paralleled, which is included in a switch device of an upper arm of the first leg, and the switch element with which the additional capacitor is paralleled, which is included in a switch device of a lower arm of the second leg, of the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the two terminals; (3) the switch element to which the first capacitor (Ca) is connected in parallel of the switching circuit on the side that converts DC input from the other two terminals into AC and outputs the AC to the transformer; (4) The switch element to which the additional capacitor included in the switch device of the lower arm of the first leg is paralleled and the switch element to which the additional capacitor included in the switch device of the upper arm of the second leg is paralleled, of the switching circuit on the side that converts AC input from the transformer side into DC and outputs the DC from the two terminals.

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