Insulation transformer and power conversion device having the same.

Abstract

The insulation transformer (3) includes multiple secondary insulation transformers (11-13) connected in series. All secondary windings (14-19) have the same polarity. The configuration is such that when current (I) flows from the first main terminal (3a) through the first secondary winding (11), the phase-to-phase capacitor (C5), and the second secondary winding (17) to the third main terminal (3c), the magnetizing inductance of the first secondary winding and the magnetizing inductance of the second secondary winding have opposite polarities.

Description

Technical Field

[0001] This disclosure relates to insulated transformers and power conversion devices having the same. Background Technology

[0002] For example, International Publication No. 2018 / 016106 (Patent Document 1) discloses a power conversion device comprising: an insulated transformer including a first and a second winding; a first power converter that converts DC power supplied from a first DC power source into AC power and supplies it to the first winding; and a second power converter that converts AC power received from the second winding into DC power and supplies it to a second DC power source.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2018 / 016106 Summary of the Invention

[0006] However, in the past, power conversion devices used a large and heavy single insulated transformer, which resulted in problems such as poor assembly and heat dissipation, as well as high cost.

[0007] Therefore, the main objective of this disclosure is to provide an insulated transformer with high assemblability and heat dissipation, and a low cost, as well as a power conversion device having the same.

[0008] The insulating transformer disclosed herein includes first to Nth auxiliary insulating transformers electrically coupled to each other. N is an integer greater than or equal to 2. Each of the first to Nth auxiliary insulating transformers includes a first and a second auxiliary winding, first and second auxiliary terminals respectively connected to the first and second polarity terminals of the first auxiliary winding, and third and fourth auxiliary terminals respectively connected to the first and second polarity terminals of the second auxiliary winding. The polarities of the first and second auxiliary windings are in the same direction. Each of the first to Nth auxiliary insulating transformers is configured such that, when current flows from the first auxiliary terminal through the first auxiliary winding, the phase-to-phase capacitance between the first and second auxiliary windings, and the second auxiliary winding to the third auxiliary terminal, the magnetizing inductance of the first auxiliary winding and the magnetizing inductance of the second auxiliary winding have opposite polarities.

[0009] The insulation transformer is divided into multiple sub-insulation transformers. Therefore, it is possible to prevent an increase in volume and a concentration of weight in the insulation transformer, to achieve substrate mounting to improve assemblability, to improve heat dissipation by dispersing heat sources, and to achieve cost reduction by using readily available and versatile sub-insulation transformers.

[0010] Furthermore, when each of the first to Nth sub-transformers is configured such that current flows from the first sub-terminal through the first sub-winding, the interphase capacitance between the first and second sub-windings, and the second sub-winding to the third sub-terminal, the magnetizing inductance of the first sub-winding and the magnetizing inductance of the second sub-winding become opposite polarities. Therefore, the sum of the magnetizing inductances of the first and second windings can be reduced, suppressing resonance between the magnetizing inductances of the first and second windings and the interphase capacitance. Attached Figure Description

[0011] Figure 1 This is a circuit block diagram illustrating the structure of the bidirectional DC / DC converter according to Embodiment 1.

[0012] Figure 2 It is shown Figure 1 The circuit diagram shown illustrates the structure of an insulated transformer.

[0013] Figure 3 It is shown Figure 1 The circuit diagram shown illustrates the structure of the power converter.

[0014] Figure 4 It is used for explanation Figures 1-3 The timing diagram shown illustrates the operation of the bidirectional DC / DC converter.

[0015] Figure 5 This is a circuit diagram showing the main parts of a comparative example of Embodiment 1.

[0016] Figure 6 It shows that it has Figure 5 The circuit diagram shows the structure of the bidirectional DC / DC converter with an insulating transformer.

[0017] Figure 7 It is used to explain in Figure 6 The circuit diagram shown illustrates the resonance phenomenon that occurs in a bidirectional DC / DC converter.

[0018] Figure 8 It is used to explain in Figure 6 Other circuit diagrams showing the resonance phenomenon occurring in the bidirectional DC / DC converter.

[0019] Figure 9 This is a circuit diagram used to illustrate the effects of Implementation Method 1.

[0020] Figure 10 This is another circuit diagram used to illustrate the effects of Embodiment 1.

[0021] Figure 11 This is a circuit diagram showing the structure of the insulating transformer according to Embodiment 2.

[0022] Figure 12This is a diagram showing the insulating transformer involved in Embodiment 3.

[0023] Figure 13 This is a diagram illustrating a comparative example of Embodiment 3.

[0024] Figure 14 This is a circuit diagram showing the structure of the insulating transformer according to Embodiment 4.

[0025] (Symbol Explanation)

[0026] T1~T4: DC terminals; 1, 7: Current detectors; 2, 6: Power converters; 3, 25, 40, 50, 65, 70: Insulation transformers; 4, 5, 26, 27: Main windings; 8: Operating unit; 9: Control device; 9a: Processing device; 11~13, 31~33, 41~43, 51~53, 71: Secondary insulation transformers; 11e: Iron core; 14~19, 34~39, 44~49, 54~62, 72, 73: Secondary windings; 21, 22: DC power supply; C1, C2: Capacitors; Q1~Q8: IGBTs; D1~D8: Diodes; L1~L5: Reactors; C3, C3a, C3b, C4, C4a, C4b: Capacitors to ground; C5, C6: Interphase capacitors. Detailed Implementation

[0027] Implementation method 1.

[0028] Figure 1 This is a circuit block diagram illustrating the structure of the bidirectional DC / DC converter according to Embodiment 1. Figure 1 In this bidirectional DC / DC converter (power conversion device), the DAB (Dual Active Bridge) method is used, and it has DC terminals T1 to T4, current detectors 1 and 7, power converter 2 and 6, insulation transformer 3, operation unit 8, and control device 9.

[0029] DC terminals T1 and T2 are connected to the positive and negative terminals of DC power supply 21 (first DC power supply), respectively. DC terminals T3 and T4 are connected to the positive and negative terminals of DC power supply 22 (second DC power supply), respectively. The control device 9 detects the DC voltage VDC1 between DC terminals T1 and T2 and the DC voltage VDC2 between DC terminals T3 and T4.

[0030] For example, one of the DC power supplies 21 and 22 may be a solar cell that outputs DC power, and the other may be a battery (or capacitor) that stores DC power. Alternatively, both DC power supplies 21 and 22 may be batteries (or capacitors). Furthermore, at least one of the DC power supplies 21 and 22 may be connected in parallel to a load driven by DC power.

[0031] The insulated transformer 3 includes first and second main windings 4 and 5, and first to fourth main terminals 3a to 3d. A black ring (·) is added to the positive side of the first and second main windings 4 and 5. The positive terminal (first polarity terminal) and negative terminal (second polarity terminal) of the first main winding 4 are connected to the first and second main terminals 3a and 3b, respectively. The positive terminal and negative terminal of the second main winding 5 are connected to the third and fourth main terminals 3c and 3d, respectively.

[0032] When the direction from the negative terminal (the terminal on the negative polarity side) of the winding to the positive terminal (the terminal on the negative polarity side) of the winding is defined as the polarity direction of the winding, the polarity directions of the first and second main windings 4 and 5 are the same. Figure 1 The diagram shows the case where the polarity of both the first and second main windings 4 and 5 is upward. The first and second main windings 4 and 5 have the same number of turns.

[0033] When AC voltage VAC1 is applied between the first and second main terminals 3a and 3b, AC voltage VAC2 appears between the third and fourth main terminals 3c and 3d. Conversely, when AC voltage VAC2 is applied between the third and fourth main terminals 3c and 3d, AC voltage VAC1 appears between the first and second main terminals 3a and 3b. AC voltages VAC1 and VAC2 are of the same polarity (i.e., in phase) and have the same amplitude.

[0034] The power converter 2 (first power converter) includes DC terminals 2a and 2b connected to DC terminals T1 and T2 respectively, and AC terminals 2c and 2d connected to the first and second main terminals 3a and 3b of the insulation transformer 3 respectively, and is controlled by the control device 9.

[0035] In the first transmission mode of supplying DC power from DC power supply 21 to DC power supply 22, the power converter 2 converts the DC voltage VDC1 supplied from DC power supply 21 to DC terminals 2a and 2b into AC voltage VAC1 and outputs it to AC terminals 2c and 2d.

[0036] In the second transmission mode, when DC power is supplied from DC power supply 22 to DC power supply 21, the power converter 2 converts the AC voltage VAC1 supplied between AC terminals 2c and 2d into DC voltage VDC1 and outputs it to the DC terminals 2a and 2b.

[0037] The power converter 6 (the second power converter) includes DC terminals 6a and 6b connected to DC terminals T3 and T4 respectively, and AC terminals 6c and 6d connected to the third and fourth main terminals 3c and 3d of the insulation transformer 3 respectively, and is controlled by the control device 9.

[0038] In the first transmission mode, the power converter 6 converts the AC voltage VAC2 supplied between AC terminals 6c and 6d into a DC voltage VDC2 and outputs it between DC terminals 6a and 6b. In the second transmission mode, the power converter 6 converts the DC voltage VDC2 supplied from the DC power supply 22 to DC terminals 6a and 6b into an AC voltage VAC2 and outputs it between AC terminals 6c and 6d.

[0039] Current detector 1 detects the current I1 flowing between DC terminal T1 and DC terminal 2a of power converter 2, and outputs a signal I1f representing its detected value to control device 9. Current detector 7 detects the current I2 flowing between DC terminal T3 and DC terminal 6a of power converter 6, and outputs a signal I2f representing its detected value to control device 9.

[0040] The operation unit 8 includes multiple buttons and switches operated by the user of the bidirectional DC / DC converter, as well as an image display unit for displaying various information. By operating the operation unit 8, the user can turn the power supply of the bidirectional DC / DC converter on and off, and select either the first or second transmission mode. The operation unit 8 outputs a signal indicating the selected transmission mode to the control device 9.

[0041] The control device 9 controls the entire bidirectional DC / DC converter based on DC voltages VDC1 and VDC2, DC currents I1 and I2 represented by the output signals of current detectors 1 and 7, signals from the operation unit 8, etc.

[0042] In the first transmission mode, the control device 9 controls each of the power converters 2 and 6 in such a way that the DC current I2 becomes a predetermined reference current I2R (or in such a way that the DC voltage VDC2 becomes a predetermined reference voltage VDC2R).

[0043] In the second transmission mode, the control device 9 controls each of the power converters 2 and 6 in such a way that the DC current I1 becomes a predetermined reference current I1R (or in such a way that the DC voltage VDC1 becomes a predetermined reference voltage VDC1R).

[0044] Furthermore, the control device 9 includes a processing circuit 9a. The processing circuit 9a can be composed of digital electronic circuits such as arithmetic processing devices and storage devices, or analog electronic circuits such as comparators, operational amplifiers, and differential amplifier circuits, or both digital and analog electronic circuits.

[0045] Figure 2 This is a circuit diagram showing the structure of the insulating transformer 3. Figure 2In this context, insulation transformer 3 includes multiple secondary insulation transformers 11 to 13. Secondary insulation transformers 11 to 13 constitute the 1st to Nth secondary insulation transformers. N is an integer greater than or equal to 2. Figure 2 The example shown is the case where N=3.

[0046] The first auxiliary insulation transformer 11 includes an iron core (not shown), first and second auxiliary windings 14 and 17 wound around the iron core, and first to fourth auxiliary terminals 11a to 11d. A black ring (·) is added to the positive side of the first and second auxiliary windings 14 and 17. The positive and negative terminals of the first auxiliary winding 14 are connected to the first and second auxiliary terminals 11a and 11b, respectively. The positive and negative terminals of the second auxiliary winding 17 are connected to the third and fourth auxiliary terminals 11c and 11d, respectively.

[0047] The polarity directions of the first and second auxiliary windings 14 and 17 are the same. Figure 2 The diagram shows the case where the polarity of both the first and second auxiliary windings 14 and 17 is upward. The first and second auxiliary windings 14 and 17 have the same number of turns.

[0048] The second auxiliary transformer 12 includes an iron core (not shown), first and second auxiliary windings 15 and 18 wound around the iron core, and first to fourth auxiliary terminals 12a to 12d. A black ring (·) is added to the positive side of the first and second auxiliary windings 15 and 18. The positive and negative terminals of the first auxiliary winding 15 are connected to the first and second auxiliary terminals 12a and 12b, respectively. The positive and negative terminals of the second auxiliary winding 18 are connected to the third and fourth auxiliary terminals 12c and 12d, respectively.

[0049] The polarity directions of the first and second auxiliary windings 15 and 18 are the same. Figure 2 The diagram shows the case where the polarity of both the first and second auxiliary windings 15 and 18 is upward. The first and second auxiliary windings 15 and 18 have the same number of turns.

[0050] The third auxiliary transformer 13 includes an iron core (not shown), first and second auxiliary windings 16 and 19 wound around the iron core, and first to fourth auxiliary terminals 13a to 13d. A black ring (·) is added to the positive side of the first and second auxiliary windings 16 and 19. The positive and negative terminals of the first auxiliary winding 16 are connected to the first and second auxiliary terminals 13a and 13b, respectively. The positive and negative terminals of the second auxiliary winding 19 are connected to the third and fourth auxiliary terminals 13c and 13d, respectively.

[0051] The polarity directions of the first and second auxiliary windings 16 and 19 are the same. Figure 2The diagram shows the case where the polarity of both the first and second auxiliary windings 16 and 19 is upward. The first and second auxiliary windings 16 and 19 have the same number of turns.

[0052] The three first auxiliary windings 14-16 are oriented in the same direction. These three first auxiliary windings 14-16 are connected in series between the first and second main terminals 3a and 3b of the insulating transformer 3 to form the first main winding 4. Specifically, the first auxiliary terminal 11a of the first auxiliary insulating transformer 11 is connected to the first main terminal 3a of the insulating transformer 3. The second auxiliary terminal 11b of the first auxiliary insulating transformer 11 is connected to the first auxiliary terminal 12a of the second auxiliary insulating transformer 12. The second auxiliary terminal 12b of the second auxiliary insulating transformer 12 is connected to the first auxiliary terminal 13a of the third auxiliary insulating transformer 13. The second auxiliary terminal 13b of the third auxiliary insulating transformer 13 is connected to the second main terminal 3b of the insulating transformer 3.

[0053] The three secondary windings 17-19 are oriented in the same direction. These three secondary windings 17-19 are connected in series between the third and fourth main terminals 3c and 3d of the insulating transformer 3 to form the second main winding 5. Specifically, the third secondary terminal 11c of the first insulating transformer 11 is connected to the third main terminal 3c of the insulating transformer 3. The fourth secondary terminal 11d of the first insulating transformer 11 is connected to the third secondary terminal 12c of the second insulating transformer 12. The fourth secondary terminal 12d of the second insulating transformer 12 is connected to the third secondary terminal 13c of the third insulating transformer 13. The fourth secondary terminal 13d of the third insulating transformer 13 is connected to the fourth main terminal 3d of the insulating transformer 3.

[0054] When AC voltage VAC1 is applied between the first main terminal 3a and the second main terminal 3b, AC voltage VAC2 appears between the third main terminal 3c and the fourth main terminal 3d. When AC voltage VAC2 is applied between the third main terminal 3c and the fourth main terminal 3d, AC voltage VAC1 appears between the first main terminal 3a and the second main terminal 3b. The number of turns in the first main winding 4 is the same as the number of turns in the second main winding 5, so the amplitude of AC voltage VAC1 is the same as the amplitude of AC voltage VAC2. The polarity of the first main winding 4 is the same as the polarity of the second main winding 5, so AC voltages VAC1 and VAC2 have the same polarity, and the phase of AC voltage VAC1 is the same as the phase of AC voltage VAC2.

[0055] By connecting multiple secondary insulation transformers 11-13 in series to form a single insulation transformer 3, it is possible to prevent an increase in size and a concentration of weight, improve assemblability by enabling substrate mounting, improve heat dissipation by dispersing heat sources, and reduce costs by using readily available and versatile cores. Furthermore, aligning the polarities of the secondary windings 14-19 in the same direction suppresses resonance phenomena in the bidirectional DC / DC converter. The reasons for suppressing resonance phenomena will be explained later.

[0056] Figure 3 This is a circuit diagram showing the structure of power converters 2 and 6. Figure 3 In this circuit, the power converter 2 includes a capacitor C1, IGBTs (Insulated Gate Bipolar Transistors) Q1 to Q4, diodes D1 to D4, and reactors L1 and L2. The capacitor C1 is connected between DC terminals T1 and T2 to smooth and stabilize the DC voltage VDC1 between the DC terminals T1 and T2.

[0057] The collectors of IGBTs Q1 and Q2 are connected to the DC terminal T1, and their emitters are connected to nodes N1 and N2 (the first and second AC terminals), respectively. The collectors of IGBTs Q3 and Q4 are connected to nodes N1 and N2, respectively, and their emitters are connected to the DC terminal T2. Each of IGBTs Q1 to Q4 is switched on or off by the control device 9.

[0058] Reactor L1 is connected between node N1 and the first main terminal 3a of the insulating transformer 3. Reactor L2 is connected between node N2 and the second main terminal 3b of the insulating transformer 3. Reactors L1 and L2 each store electromagnetic energy.

[0059] The power converter 6 includes reactors L3-L5, IGBTs Q5-Q8, diodes D5-D8, and capacitor C2. Reactor L3 is connected between the third main terminal 3c of the insulating transformer 3 and node N4. Reactor L4 is connected between the fourth main terminal 3d of the insulating transformer 3 and node N3. Reactors L3 and L4 each store electromagnetic energy.

[0060] The collectors of IGBTs Q5 and Q6 are interconnected, and their emitters are connected to nodes N3 and N4, respectively. The collectors of IGBTs Q7 and Q8 are connected to nodes N3 and N4, respectively, and their emitters are all connected to the DC terminal T4. Each of IGBTs Q5 to Q8 is switched on and off via control device 9.

[0061] The capacitor C2 is connected between the collectors of the IGBTs Q5 and Q6 and the DC terminal T4. The reactor L5 is connected between the collectors of the IGBTs Q5 and Q6 and the DC terminal T3. The capacitor C2 and the reactor L5 form a low-pass filter.

[0062] In addition, instead of the IGBT, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be used. Further, a capacitor can be connected in parallel with the IGBT to form a zero-voltage switching circuit that makes the collector-emitter voltage of the IGBT approximately zero during switching.

[0063] Figure 4 is for explaining Figures 1-3 the timing diagram of the operation of the bidirectional DC / DC converter shown. In Figure 4 it shows the operation in the first transfer mode of transferring DC power from the DC power supply 21 to the DC power supply 22. The DC power supply 22 is a storage battery.

[0064] In Figure 4 (A) to (H) respectively represent the on and off operations of the IGBTs Q1, Q3, Q2, Q4, Q5, Q7, Q6, and Q8. The switching period Tsw of the IGBT Q1 is divided into 10 periods TA to TJ.

[0065] In the first transfer mode, the control device 9 makes each of the IGBTs Q1, Q3, IGBTs Q4, Q2, IGBTs Q5, Q7 conduct alternately with a short-circuit prevention time td within the switching period Tsw, and fixes the IGBTs Q6 and Q8 in the off state.

[0066] The period from when the IGBT Q2 turns off to when the IGBT Q4 turns on is set as the first phase shift amount θ1, and the period from when the IGBT Q2 turns off to when the IGBT Q7 turns on is set as the second phase shift amount θ2. The control device 9 adjusts the first phase shift amount θ1 and the second phase shift amount θ2 according to the transferred power amount.

[0067] When boosting the output voltage VDC1 of the DC power supply 21 to charge the DC power supply 22 (storage battery) (VDC2 > VDC1), the second phase shift amount θ2 is set to a value larger than the first phase shift amount θ1. When reducing the output voltage VDC1 of the DC power supply 21 to charge the DC power supply 22 (storage battery) (VDC2 < VDC1), the second phase shift amount θ2 is set to the same value as the first phase shift amount θ1.

[0068] For example, during period TB, IGBTs Q1 and Q4 are turned on, and current flows from the positive terminal of DC power supply 21 through IGBT Q1, reactor L1, the first main winding 4, reactor L2, and IGBT Q4 to the negative terminal of DC power supply 21, accumulating electromagnetic energy in reactors L1 and L2. Additionally, IGBT Q5 is turned on, and current flows from the third main terminal 3c of the insulating transformer 3 through reactor L3, diode D6, IGBT Q5, reactor L4, and the second main winding 5 to the third terminal 3c, accumulating electromagnetic energy in reactors L3 and L4.

[0069] Next, during period TC, IGBTs Q1 and Q4 are kept in the on state, and the current flows through the same path as during period TB, accumulating electromagnetic energy in reactors L1 and L2. Meanwhile, IGBT Q5 becomes off, and the current flows from terminal 3c of the insulation transformer 3 through reactor L3, diode D6, reactor L5, DC power supply 22 (battery), diode D7, reactor L4, and the second main winding 5 of the insulation transformer 3 back to terminal 3c, releasing the electromagnetic energy of reactors L3 and L4.

[0070] At this time, the voltage obtained by adding the voltage between the terminals of the second main winding 5 of the insulating transformer 3, the voltage between the terminals of reactor L3, and the voltage between the terminals of reactor L4 is applied between the terminals of the DC power supply 22 (battery). Therefore, in Figure 4 In the first transmission mode shown, the second DC power supply 22 (battery) is charged to a voltage higher than the output voltage VDC1 of the first DC power supply 21 (VDC2>VDC1).

[0071] In the second transmission mode, which transmits DC power from DC power source 22 to DC power source 21, control device 9 alternately turns on IGBTs Q6, Q8, Q7, Q5, Q2, and Q4 during the switching cycle Tsw, with each IGBT being switched on for a short-circuit prevention time td, while keeping IGBTs Q1 and Q3 in the off state. The second transmission mode performs the opposite operation to the first transmission mode, so its description will not be repeated.

[0072] In addition, as mentioned above, by connecting multiple secondary insulation transformers 11 to 13 in series to form an insulation transformer 3, it is possible to improve assemblability and heat dissipation, reduce costs, and achieve high performance in the product.

[0073] Furthermore, the inventors of this application recognized a problem that is generally not known when multiple secondary insulation transformers 11 to 13 are connected in series to form a single insulation transformer 3, and thus found a solution to this problem. This point will be explained in detail below using the accompanying drawings.

[0074] Figure 5This is a circuit showing the main part of a comparative example of Embodiment 1, which is related to... Figure 2 A comparison chart. In Figure 5 In this comparative example, an insulation transformer 25 is used. The insulation transformer 25 includes first to fourth main terminals 25a to 25d and a plurality of secondary insulation transformers 31 to 33. The plurality of secondary insulation transformers 31 to 33 are connected in series between the first and third main terminals 25a and 25c and the second and fourth main terminals 25b and 25d.

[0075] That is, the first auxiliary insulated transformer 31 includes an iron core (not shown), first and second auxiliary windings 34 and 37 wound around the iron core, and first to fourth auxiliary terminals 31a to 31d. A black ring (·) is added to the positive side of the first and second auxiliary windings 34 and 37. The positive and negative terminals of the first auxiliary winding 34 are connected to the first and second auxiliary terminals 31a and 31b, respectively. The positive and negative terminals of the second auxiliary winding 37 are connected to the fourth and third auxiliary terminals 31d and 31c, respectively.

[0076] The polarities of the first and second auxiliary windings 34 and 37 are opposite. Figure 5 The diagram shows the polarity directions of the first and second auxiliary windings 34 and 37, respectively, in the upward and downward directions. The first and second auxiliary windings 34 and 37 have the same number of turns.

[0077] The second auxiliary insulated transformer 32 includes an iron core (not shown), first and second auxiliary windings 35 and 38 wound around the iron core, and first to fourth auxiliary terminals 32a to 32d. A black ring (·) is added to the positive side of the first and second auxiliary windings 35 and 38. The positive and negative terminals of the first auxiliary winding 35 are connected to the first and second auxiliary terminals 32a and 32b, respectively. The positive and negative terminals of the second auxiliary winding 38 are connected to the fourth and third auxiliary terminals 32d and 32c, respectively.

[0078] The polarities of the first and second auxiliary windings 35 and 38 are opposite. Figure 5 The diagram shows the polarity directions of the first and second auxiliary windings 35 and 38, respectively, in the upward and downward directions. The first and second auxiliary windings 35 and 38 have the same number of turns.

[0079] The third auxiliary insulation transformer 33 includes an iron core (not shown), first and second auxiliary windings 36 and 39 wound around the iron core, and first to fourth auxiliary terminals 33a to 33d. A black ring (·) is added to the positive side of the first and second auxiliary windings 36 and 39. The positive and negative terminals of the first auxiliary winding 36 are connected to the first and second auxiliary terminals 33a and 33b, respectively. The positive and negative terminals of the second auxiliary winding 39 are connected to the fourth and third auxiliary terminals 33d and 33c, respectively.

[0080] The polarities of the first and second auxiliary windings 36 and 39 are opposite. Figure 5 The diagram shows the polarity directions of the first and second auxiliary windings 36 and 39, respectively, in the upward and downward directions. The first and second auxiliary windings 36 and 39 have the same number of turns.

[0081] The three first auxiliary windings 34-36 are polarized upwards. These three first auxiliary windings 34-36 are connected in series between the first and second main terminals 25a and 25b of the insulating transformer 25 to form the first main winding 26. Additionally, the three second auxiliary windings 37-39 are polarized downwards. These three second auxiliary windings 37-39 are connected in series between the third and fourth main terminals 25c and 25d of the insulating transformer 25 to form the second main winding 27.

[0082] When AC voltage VAC1 is applied between the first main terminal 25a and the second main terminal 25b, AC voltage VAC2 appears between the third main terminal 25c and the fourth main terminal 25d. When AC voltage VAC2 is applied between the third main terminal 25c and the fourth main terminal 25d, AC voltage VAC1 appears between the first main terminal 25a and the second main terminal 25b. The number of turns in the first main winding 26 is the same as the number of turns in the second main winding 27, so the amplitude of AC voltage VAC1 is the same as the amplitude of AC voltage VAC2. The polarity of the first main winding 26 is opposite to that of the second main winding 27, so AC voltages VAC1 and VAC2 have opposite polarities, and the phase of AC voltage VAC1 is offset by 180 degrees from the phase of AC voltage VAC2.

[0083] The secondary terminals 31b, 32a and 31d, 32c of the secondary insulation transformers 31 and 32 are high-impedance connection points that do not connect to electrical components other than the secondary insulation transformers 31 and 32. Similarly, the secondary terminals 32b, 33a and 32d, 33c of the secondary insulation transformers 32 and 33 are high-impedance connection points that do not connect to electrical components other than the secondary insulation transformers 32 and 33. Therefore, unlike the low-impedance connection points connecting low-impedance components such as voltage sources and capacitors, the phase-to-phase capacitance between the first and second secondary windings of the secondary insulation transformers 31-33 becomes significant at the connection points of the insulation transformers 31-33, resulting in resonance in the path through the first and second secondary windings and the phase-to-phase capacitance between them.

[0084] Figure 6 It shows including Figure 5 The circuit diagram shown for the structure of the bidirectional DC / DC converter of the insulation transformer 25 is related to... Figure 3 A comparison chart. In Figure 6In this circuit, the first to fourth main terminals 25a to 25d of the insulating transformer 25 are connected to one terminal of reactors L1 to L4, respectively, and the other terminals of reactors L1 to L4 are connected to nodes N1 to N4, respectively. Additionally, a ground capacitor C3 is connected between the DC terminal T2 and the line of ground voltage GND (the reference voltage line), and a ground capacitor C4 is connected between the DC terminal T4 and the line of ground voltage GND.

[0085] Furthermore, regarding the ground capacitors C3 and C4, it is envisioned that each of the DC terminals T2 and T4 is connected to the frame via a capacitor, and the frame is grounded. This represents a low-impedance coupling between the DC terminals T2 and T4 in the electrical circuit. Alternatively, each of the DC terminals T2 and T4 can be directly connected to the frame without a capacitor, and the frame can be grounded. Alternatively, each of the DC terminals T2 and T4 can be connected to a power system with a defined ground potential via an inverter circuit.

[0086] For example, when IGBT Q3 is turned on and the voltage at node N1 changes, the magnetizing inductance of the secondary windings 34 and 37 of the secondary insulation transformer 31 is energized in the current path from node N1 through reactor L1, the first secondary winding 34 of the secondary insulation transformer 31, the phase-to-phase capacitance C5 between secondary windings 34 and 37, the second secondary winding 37, reactor L3, IGBT Q7, the capacitance to ground C4, the line to ground voltage GND, the capacitance to ground C3, and diode D3 back to node N1.

[0087] The result, such as Figure 7 As shown, an interphase capacitor C5 is connected between the second and fourth terminals 31b and 31d of the secondary insulation transformer 31. The first terminal 31a is connected to the ground voltage GND via reactor L1, node N1, and ground capacitor C3. The third terminal 31c is connected to the ground voltage GND via reactor L3, node N3, and ground capacitor C4, forming a resonant circuit. Resonance occurs between the magnetizing inductance of the first winding 34, the interphase capacitor C5, and the magnetizing inductance of the second winding 37.

[0088] but, Figure 7 The equivalent circuit shown is a simplified example for the sake of simplicity. The resonant circuit is not an independent circuit in the secondary insulation transformer 31, but actually constitutes a circuit as shown in the diagram. Figure 8 The resonant circuit shown. That is, in Figure 8 In the circuit, nodes N1 to N4 are connected to the ground voltage GND via ground capacitors C3a, C3b, C4a, and C4b, respectively. An interphase capacitor C6 is connected between the second and fourth terminals 32b and 32d of the second auxiliary insulation transformer 32.

[0089] The second terminal 31b of the first auxiliary transformer 31 is connected to the ground voltage GND via auxiliary windings 35 and 36, reactor L2, and ground capacitor C3b. The fourth terminal 31d of the first auxiliary transformer 31 is connected to the ground voltage GND via auxiliary windings 38 and 39, reactor L4, and ground capacitor C4b. Resonance occurs between the magnetizing inductances of the first auxiliary windings 34-36, the phase-to-phase capacitors C5 and C6, and the magnetizing inductances of the second auxiliary windings 37-39.

[0090] In such a resonance phenomenon, the magnetizing inductance of the secondary windings 34-39 of the secondary insulation transformers 31-33 is typically several hundred times greater than the inductance of the reactors L1-L4, which have DC overlap characteristics. Therefore, even though the current flowing through the transformers due to the resonance phenomenon is relatively small compared to the main current of the circuit, it still generates a non-negligible voltage oscillation, adversely affecting the losses of the secondary insulation transformers 31-33. Figure 7 In the resonant circuit shown, the magnetizing inductance of the first secondary winding 34 and the second secondary winding 37 have the same polarity. The sum of the magnetizing inductances of the first and second secondary windings 34 and 37 becomes a large value, resulting in large voltage fluctuations. Furthermore, if we consider that the secondary windings 34 and 37 constitute a single winding, then the inductance of the winding is proportional to the square of the number of turns. Therefore, the magnetizing inductance of the secondary windings 34 and 37 is four times that of their individual windings.

[0091] Figure 9 It is shown in Figure 3 The circuit diagram shown is related to the structure of the resonant circuit that occurs in the bidirectional DC / DC converter. Figure 7 A comparison chart. In Figure 9 In the circuit, an interphase capacitor C5 is connected between the second and fourth terminals 11b and 11d of the secondary insulation transformer 11. The first terminal 11a is connected to the ground voltage GND via reactor L1, node N1, and ground capacitor C3. The third terminal 11c is connected to the ground voltage GND via reactor L3, node N3, and ground capacitor C4, thus forming a resonant circuit.

[0092] In this resonant circuit, the magnetizing inductance of the first secondary winding 14 and the magnetizing inductance of the second secondary winding 17 are opposite in polarity and cancel each other out. The sum of the magnetizing inductances of the first secondary windings 14 and 17 becomes 0, so no resonance phenomenon occurs.

[0093] Furthermore, in this embodiment 1, when the number of turns of the first secondary winding 14 and the number of turns of the second secondary winding 17 are the same, the sum of the magnetizing inductances of the first secondary windings 14 and 17 can be made zero, effectively preventing the occurrence of resonance. However, even when the number of turns of the first secondary winding 14 and the number of turns of the second secondary winding 17 are different, the sum of the magnetizing inductances of the first secondary windings 14 and 17 can be reduced, suppressing the occurrence of resonance.

[0094] Figure 10 This is a diagram showing the structure and operation of the secondary insulation transformer 11. Figure 10 In the diagram, (A) represents the normal transformer operation, and (B) represents the operation when current flows through the interphase capacitor C5.

[0095] exist Figure 10 In (A), secondary windings 14 and 17 are wound around the annular iron core 11e. Secondary windings 14 and 17 share the magnetic flux passing through the iron core 11e. When the number of turns of secondary windings 14 and 17 are set to n1 and n2 respectively, and the inter-terminal voltages of secondary windings 14 and 17 are set to V1 and V2 respectively, it becomes Where n1 = n2. V1 and V2 have the same polarity, the same phase, and the same amplitude.

[0096] exist Figure 10 In (B), when current I flows from the first secondary terminal 11a through the first secondary winding 14, the interphase capacitor C5, and the second secondary winding 17 to the third secondary terminal 11c, magnetic flux is generated in the iron core 11e through the current I flowing in the first secondary winding 14. Furthermore, magnetic flux is generated within the iron core 11e by the current I flowing through the second winding 17. Within the iron core 11e, the magnetic flux and magnetic flux It occurs in the opposite direction, magnetic flux and magnetic flux They cancel each other out.

[0097] Here, when the magnetizing inductances of the first and second auxiliary windings 14 and 17 with current I flowing through them are set to La and Lb respectively, they become become Therefore, the magnetizing inductances La and Lb of the first and second auxiliary windings 14 and 17 become opposite polarities and cancel each other out.

[0098] As described above, in this embodiment 1, multiple secondary insulation transformers 11 to 13 are connected in series to form an insulation transformer 3. Therefore, it is possible to prevent an increase in volume and a concentration of weight in the insulation transformer 3, to achieve substrate mounting to improve assemblability, to improve heat dissipation by dispersing the heat source, and to achieve cost reduction by utilizing a common secondary insulation transformer that is readily available and widely distributed.

[0099] Furthermore, since the secondary windings 14 to 19 of the secondary insulation transformers 11 to 13 have the same polarity direction, for example, when current I flows from the first main terminal 3a through the first secondary winding 14, the interphase capacitor C5, and the second secondary winding 17 to the third main terminal 3b, the sum of the magnetizing inductances La and Lb of the first and second secondary windings 14 and 17 becomes 0. Therefore, resonance can be prevented.

[0100] Furthermore, in this embodiment 1, the case where the insulation transformer 3 is provided in a bidirectional DC / DC converter in the DAB mode is described, but it is not limited to this. Of course, the same effect can be obtained when the insulation transformer 3 is provided in other high-frequency circuits.

[0101] Furthermore, in this embodiment 1, a bidirectional DC / DC converter of the DAB type is described, comprising an insulation transformer 3 with two main windings 4 and 5 and two bridge circuits (Q1-Q4 and Q5-Q8), but it is not limited to this. For example, in a DC / DC converter of the TAB (Triple Active Bridge) type, comprising an insulation transformer with three main windings, three bridge circuits connected to the three main windings respectively, and three DC terminal pairs connected to the three bridge circuits respectively, and power is transferred between each DC terminal pair and other DC terminal pairs, the insulation transformer can be divided into multiple secondary insulation transformers, and the polarity of all secondary windings can be aligned. In this case, resonance in each secondary insulation transformer can also be prevented.

[0102] Implementation method 2.

[0103] Figure 11 This is a circuit diagram illustrating the structure of the insulation transformer 40 according to Embodiment 2. Figure 11 In this embodiment, the insulation transformer 40 is a three-phase transformer with a YY connection, comprising main terminals T11-T16 (1st to 6th) and auxiliary insulation transformers 41-43 (1st to 3rd). Main terminals T11-T13 receive three-phase AC voltages Vu1, Vv1, and Vw1. Three-phase AC voltages Vu2, Vv2, and Vw2 are output to main terminals T14-T16 (4th to 6th).

[0104] The first auxiliary insulated transformer 41 includes an iron core (not shown), first and second auxiliary windings 44 and 47 wound around the iron core, and first to fourth auxiliary terminals 41a to 41d. A black ring (·) is added to the positive side of the first and second auxiliary windings 44 and 47. The positive and negative terminals of the first auxiliary winding 44 are connected to the first and second auxiliary terminals 41a and 41b, respectively. The positive and negative terminals of the second auxiliary winding 47 are connected to the third and fourth auxiliary terminals 41c and 41d, respectively.

[0105] The polarity directions of the first and second auxiliary windings 44 and 47 are the same. Figure 11 The diagram shows the case where the polarity of both the first and second auxiliary windings 44 and 47 is upward. The first and second auxiliary windings 44 and 47 have the same number of turns.

[0106] The second auxiliary transformer 42 includes an iron core (not shown), first and second auxiliary windings 45 and 48 wound around the iron core, and first to fourth auxiliary terminals 42a to 42d. A black ring (·) is added to the positive side of the first and second auxiliary windings 45 and 48. The positive and negative terminals of the first auxiliary winding 45 are connected to the first and second auxiliary terminals 42a and 42b, respectively. The positive and negative terminals of the second auxiliary winding 48 are connected to the third and fourth auxiliary terminals 42c and 42d, respectively.

[0107] The polarity directions of the first and second auxiliary windings 45 and 48 are the same. Figure 11 The diagram shows the case where the polarity of both the first and second auxiliary windings 45 and 48 is upward. The first and second auxiliary windings 45 and 48 have the same number of turns.

[0108] The third auxiliary transformer 43 includes an iron core (not shown), first and second auxiliary windings 46 and 49 wound around the iron core, and first to fourth auxiliary terminals 43a to 43d. A black ring (·) is added to the positive side of the first and second auxiliary windings 46 and 49. The positive and negative terminals of the first auxiliary winding 46 are connected to the first and second auxiliary terminals 43a and 43b, respectively. The positive and negative terminals of the second auxiliary winding 49 are connected to the third and fourth auxiliary terminals 43c and 43d, respectively.

[0109] The polarity directions of the first and second auxiliary windings 46 and 49 are the same. Figure 11 The diagram shows the case where the polarity of both the first and second auxiliary windings 46 and 49 is upward. The first and second auxiliary windings 46 and 49 have the same number of turns.

[0110] The first secondary terminals 41a, 42a, and 43a of the secondary insulation transformers 41, 42, and 43 are connected to the first to third main terminals T11 to T13, respectively. The third secondary terminals 41c, 42c, and 43c of the secondary insulation transformers 41, 42, and 43 are connected to the fourth to sixth main terminals T14 to T16, respectively. The second secondary terminals 41b, 42b, and 43b of the secondary insulation transformers 41, 42, and 43 are interconnected. The fourth secondary terminals 41d, 42d, and 43d of the secondary insulation transformers 41, 42, and 43 are interconnected.

[0111] When three-phase AC voltages Vu1, Vv1, and Vw1 are applied to the first to third main terminals T11 to T13 respectively, three-phase AC voltages Vu2, Vv2, and Vw2 appear in the fourth to sixth main terminals T14 to T16 respectively. When three-phase AC voltages Vu2, Vv2, and Vw2 are applied to the fourth to sixth main terminals T14 to T16 respectively, three-phase AC voltages Vu1, Vv1, and Vw1 appear in the first to third main terminals T11 to T13 respectively.

[0112] The number of turns in the first main winding (44, 45, 46) is the same as the number of turns in the second main winding (47, 48, 49). Therefore, the amplitudes of AC voltages Vu1, Vv1, Vw1 are the same as the amplitudes of AC voltages Vu2, Vv2, Vw2. The polarity of the first main winding (44, 45, 46) is the same as the polarity of the second main winding (47, 48, 49). Therefore, AC voltages Vu1, Vv1, Vw1 and Vu2, Vv2, Vw2 have the same polarity, and the phases of AC voltages Vu1, Vv1, Vw1 and Vu2, Vv2, Vw2 are the same.

[0113] Furthermore, even if, for some reason, current flows from the first main terminal T11 through the phase-to-phase capacitance between the first secondary winding 44, secondary windings 44 and 47, and the second secondary winding 47 to the fourth main terminal T14, such as in Figure 9 As explained, the sum of the magnetizing inductances of the secondary windings 44 and 47 becomes zero, thus suppressing resonance in the secondary insulation transformer 41. Similarly, resonance in each of the secondary insulation transformers 42 and 43 can also be suppressed.

[0114] In this second embodiment, the same effect as in the first embodiment is obtained.

[0115] Implementation method 3.

[0116] Figure 12 This is a diagram illustrating the insulation transformer 50 according to Embodiment 3. Figure 12In the diagram, (A) represents the structure of the insulation transformer 50, and (B) represents the operation of the insulation transformer 50. This insulation transformer 50 is a three-phase transformer with a Y-interleaved connection, possessing main terminals T21-T26 (1st to 6th) and auxiliary insulation transformers 51-53 (1st to 3rd). Main terminals T21-T23 (1st to 3rd) receive three-phase AC voltages Vu, Vv, and Vw. Three-phase AC voltages Va, Vb, and Vc are output to main terminals T24-T26 (4th to 6th).

[0117] The first auxiliary insulated transformer 51 includes an iron core (not shown), first to third auxiliary windings 54, 57, and 60 wound around the iron core, and first to sixth auxiliary terminals 51a to 51f. A black ring (·) is added to the positive side of the first to third auxiliary windings 54, 57, and 60. The positive and negative terminals of the first auxiliary winding 54 are connected to the first and second auxiliary terminals 51a and 51b, respectively. The positive and negative terminals of the second auxiliary winding 57 are connected to the third and fourth auxiliary terminals 51c and 51d, respectively. The positive and negative terminals of the third auxiliary winding 60 are connected to the fifth and sixth auxiliary terminals 51e and 51f, respectively.

[0118] The polarity directions of the first to third secondary windings 54, 57, and 60 are the same. Figure 12 In (A), the polarity of the first to third sub-windings 54, 57, and 60 is all in the upward direction. The ratio of the number of turns of the first to third sub-windings 54, 57, and 60 is 2:1:1.

[0119] The second auxiliary insulated transformer 52 includes an iron core (not shown), first to third auxiliary windings 55, 58, and 61 wound around the iron core, and first to sixth auxiliary terminals 52a to 52f. A black ring (·) is added to the positive side of the first to third auxiliary windings 55, 58, and 61. The positive and negative terminals of the first auxiliary winding 55 are connected to the first and second auxiliary terminals 52a and 52b, respectively. The positive and negative terminals of the second auxiliary winding 58 are connected to the third and fourth auxiliary terminals 52c and 52d, respectively. The positive and negative terminals of the third auxiliary winding 61 are connected to the fifth and sixth auxiliary terminals 52e and 52f, respectively.

[0120] The polarity directions of the first to third secondary windings 55, 58, and 61 are the same. Figure 12 In (A), the polarity of the first to third sub-windings 55, 58, and 61 is shown to be upward. The ratio of the number of turns of the first to third sub-windings 55, 58, and 61 is 2:1:1.

[0121] The third auxiliary insulated transformer 53 includes an iron core (not shown), first to third auxiliary windings 56, 59, and 62 wound around the iron core, and first to sixth auxiliary terminals 53a to 53f. A black ring (·) is added to the positive side of the first to third auxiliary windings 56, 59, and 62. The positive and negative terminals of the first auxiliary winding 56 are connected to the first and second auxiliary terminals 53a and 53b, respectively. The positive and negative terminals of the second auxiliary winding 59 are connected to the third and fourth auxiliary terminals 53c and 53d, respectively. The positive and negative terminals of the third auxiliary winding 62 are connected to the fifth and sixth auxiliary terminals 53e and 53f, respectively.

[0122] The polarity directions of the first to third secondary windings 56, 59, and 62 are the same. Figure 12 In (A), the polarity of the first to third sub-windings 56, 59, and 62 is all upward. The ratio of the number of turns of the first to third sub-windings 56, 59, and 62 is 2:1:1.

[0123] The first secondary terminals 51a, 52a, and 53a of the secondary insulation transformers 51, 52, and 53 are connected to the first to third main terminals T21 to T23, respectively. The third secondary terminals 51c, 52c, and 53c of the secondary insulation transformers 51, 52, and 53 are connected to the fourth to sixth main terminals T24 to T26, respectively. The second secondary terminals 51b, 52b, and 53b of the secondary insulation transformers 51, 52, and 53 are connected to the first neutral point M1. The fifth secondary terminals 51e, 52e, and 53e of the secondary insulation transformers 51, 52, and 53 are connected to the second neutral point M2. The sixth secondary terminals 51f, 52f, and 53f of the secondary insulation transformers 51, 52, and 53 are connected to the fourth secondary terminals 52d, 53d, and 51d of the secondary insulation transformers 52, 53, and 51, respectively.

[0124] When three-phase AC voltages Vu, Vv, and Vw are applied to the first to third main terminals T21 to T23 respectively, the inter-terminal voltages of the second auxiliary windings 57, 58, and 59 become Vu / 2, Vv / 2, and Vw / 2 respectively, and the inter-terminal voltages of the third auxiliary windings 60, 61, and 62 become Vu / 2, Vv / 2, and Vw / 2 respectively. AC voltages Va, Vb, and Vc appear in the fourth to sixth main terminals T24, T25, and T26 respectively, becoming Va = Vu / 2 - Vw / 2, Vb = Vv / 2 - Vu / 2, and Vc = Vw / 2 - Vv / 2.

[0125] like Figure 12 As shown in (B), the phases of the three-phase AC voltages Vu, Vv, and Vw are each shifted by 120 degrees, and the phases of the three-phase AC voltages Va, Vb, and Vc are also each shifted by 120 degrees. The phases of the three-phase AC voltages Va, Vb, and Vc are each 30 degrees ahead of the phases of the three-phase AC voltages Vu, Vv, and Vw.

[0126] Furthermore, even if, for some reason, current flows from the first main terminal T21 through the phase-to-phase capacitance between the first secondary winding 51, secondary windings 54, and 60, the phase-to-phase capacitance between the third secondary winding 60, secondary windings 60, and 57, and the second secondary winding 57 to the fourth main terminal T24, as in Figure 9 As explained, the sum of the magnetizing inductances of the secondary windings 51, 60, and 57 becomes zero, thus suppressing resonance in the secondary insulation transformer 51. Similarly, resonance in the secondary insulation transformers 52 and 53 can also be suppressed.

[0127] In this third embodiment, the same effect as in the first embodiment is obtained.

[0128] Figure 13 This is a diagram showing an insulation transformer 65, which is a comparative example of Embodiment 3, and is related to... Figure 12 A comparison chart. In Figure 13 In the diagram, (A) represents the structure of the insulation transformer 65, and (B) represents the operation of the insulation transformer 65.

[0129] The insulation transformer 65 and Figure 12 The difference between the insulation transformer 50 and the primary insulation transformer 51 is that the first secondary terminals 51a, 52a, and 53a of the secondary insulation transformers 51, 52, and 53 are connected to the first neutral point M1, and the second secondary terminals 51b, 52b, and 53b of the secondary insulation transformers 51, 52, and 53 are connected to the first to third main terminals T21, T22, and T23, respectively.

[0130] When three-phase AC voltages Vu, Vv, and Vw are applied to the first to third main terminals T21 to T23 respectively, the inter-terminal voltages of the second auxiliary windings 57, 58, and 59 become -Vu / 2, -Vv / 2, and -Vw / 2 respectively, and the inter-terminal voltages of the third auxiliary windings 60, 61, and 62 become -Vu / 2, -Vv / 2, and -Vw / 2 respectively. AC voltages Va, Vb, and Vc appear in the fourth to sixth main terminals T24, T25, and T26 respectively, becoming Va = -Vu / 2 + Vw / 2, Vb = -Vv / 2 + Vu / 2, and Vc = -Vw / 2 + Vv / 2.

[0131] like Figure 13 As shown in (B), the phases of the three-phase AC voltages Vw, Vv, and Vu are each shifted by 120 degrees, and the phases of the three-phase AC voltages Vc, Vb, and Va are also each shifted by 120 degrees. The phases of the three-phase AC voltages Vb, Vc, and Va are each delayed by 30 degrees compared to the phases of the three-phase AC voltages Vu, Vv, and Vw.

[0132] If, for some reason, current flows from the first main terminal T21 through the interphase capacitance between secondary windings 54 and 60, secondary winding 60, the interphase capacitance between secondary windings 60 and 57, and secondary winding 57 to the fourth main terminal T24, the magnetizing inductances of secondary windings 60 and 57 become of the same polarity, and the sum of the magnetizing inductances of secondary windings 60 and 57 becomes a large value. Therefore, resonance occurs between the interphase capacitance between secondary windings 54 and 60, the magnetizing inductance of secondary winding 60, the interphase capacitance between secondary windings 60 and 57, and the magnetizing inductance of secondary winding 57, resulting in large voltage fluctuations. Therefore, in the comparative example's insulation transformer 65, it is impossible to prevent the occurrence of resonance.

[0133] Implementation method 4.

[0134] Figure 14 This is a circuit diagram showing the structure of the insulation transformer 70 according to Embodiment 4, which is related to... Figure 2 Comparison diagram. The insulation transformer 70 and... Figure 2 The difference between the insulation transformer 3 and the insulation transformer 4 is that the first to fourth main terminals 3a to 3d are replaced with the first to fifth main terminals 70a to 70e, and a fourth auxiliary insulation transformer 71 is added.

[0135] The fourth auxiliary insulation transformer 71 includes an iron core (not shown), first and second auxiliary windings 72 and 73 wound around the iron core, and first to fourth auxiliary terminals 71a to 71d. A black ring (·) is added to the positive side of the first and second auxiliary windings 72 and 73. The positive and negative terminals of the first auxiliary winding 72 are connected to the first and second auxiliary terminals 71a and 71b, respectively. The positive and negative terminals of the second auxiliary winding 73 are connected to the third and fourth auxiliary terminals 71c and 71d, respectively.

[0136] The polarity directions of the first and second auxiliary windings 72 and 73 are the same. Figure 14 The diagram shows the case where the polarity of the first and second auxiliary windings 72 and 73 is upward. The first and second auxiliary windings 72 and 73 have the same number of turns.

[0137] The first and third terminals 71a and 71c of the fourth auxiliary transformer 71 are connected to the second and fourth terminals 13c and 13d of the third auxiliary transformer 13, respectively. The second and fourth terminals 71b and 71d of the fourth auxiliary transformer 71 are connected to the third and fifth main terminals 70c and 70e, respectively. The first and third terminals 11a and 11c of the first auxiliary transformer 11 are connected to the first and fourth main terminals 70a and 70d, respectively. The second main terminal 70b is connected to the second terminal 12b of the second auxiliary transformer 12.

[0138] The polarities of the eight secondary windings 11-13, 17-19, 72, and 73 are all oriented in the same direction. Secondary windings 11 and 12 constitute the first main winding, secondary windings 13 and 72 constitute the second main winding, and secondary windings 17-19 and 73 constitute the third main winding. The polarities of the first to third main windings are all oriented in the same direction.

[0139] When an AC voltage V1 is applied between the first and second main terminals 70a and 70b, and an AC voltage V2 is applied between the second and third main terminals 70b and 70c, an AC voltage V3 appears between the fourth and fifth main terminals 70d and 70e. When AC voltages V1 and V2 have the same polarity and the same amplitude, AC voltages V1, V2, and V3 become identical in polarity, their phases become identical, and the ratio of their amplitudes becomes 1:1:2.

[0140] Furthermore, even if, for some reason, current flows from the first main terminal 70a through the phase-to-phase capacitance between the first secondary winding 14, secondary windings 14 and 17, and the second secondary winding 17 to the fourth main terminal 70d, such as in Figure 9 As explained, the sum of the magnetizing inductances of secondary windings 14 and 17 becomes zero, thus preventing resonance in secondary insulation transformer 11. Similarly, resonance in secondary insulation transformers 12, 13, and 71 is also prevented.

[0141] In this fourth embodiment, the same effect as in the first embodiment is obtained.

[0142] Furthermore, it is of course possible to suitably combine the above-described embodiments 1 to 4. For example, even when using Figure 2 Replacement of insulation transformer 3 Figure 11 The same effect was also achieved in each of the secondary insulation transformers 41 to 43.

[0143] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The invention is not represented by the foregoing description but by the claims, and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. An insulated transformer comprising a first to an Nth electrically coupled secondary insulated transformer, where N is an integer greater than or equal to 2. Each of the first to Nth sub-insulation transformers includes: First and second auxiliary windings; The first and second auxiliary terminals are respectively connected to the first polarity terminal and the second polarity terminal of the first auxiliary winding; as well as The third and fourth terminals are respectively connected to the first polarity terminal and the second polarity terminal of the second winding. The polarity directions of the first and second auxiliary windings are the same. The first winding of each of the first to Nth sub-insulated transformers, and the second winding of each of the first to Nth sub-insulated transformers, are electrically insulated from each other. The first to Nth sub-insulation transformers are each configured such that, when current flows from the first sub-terminal through the first sub-winding, the phase-to-phase capacitance between the first and second sub-windings, and the second sub-winding to the third sub-terminal, the magnetizing inductance of the first sub-winding and the magnetizing inductance of the second sub-winding have opposite polarities.

2. The insulating transformer according to claim 1, wherein, The first and second auxiliary windings have the same number of turns.

3. The insulating transformer according to claim 1, wherein, The insulation transformer has the following features: The first and second main windings; The first and second main terminals are respectively connected to the first polarity terminal and the second polarity terminal of the first main winding; as well as The third and fourth main terminals are respectively connected to the first polarity terminal and the second polarity terminal of the second main winding. The polarities of the first and second main windings are in the same direction. The N first secondary windings included in the first to Nth sub-insulation transformers have the same polarity direction, and the N first secondary windings are connected in series between the first and second main terminals to form the first main winding. The polarity of the N second secondary windings contained in the first to Nth secondary insulation transformers is the same, and the N second secondary windings are connected in series between the third and fourth main terminals to form the second main winding.

4. The insulating transformer according to claim 3, wherein, Each of the first to Nth sub-insulated transformers includes an iron core wound with the first and second sub-windings. The cores of the first to Nth sub-insulated transformers are separated from each other.

5. The insulating transformer according to claim 1, wherein, N is 3. The insulation transformer is a three-phase transformer with a YY connection and possesses: The first to third auxiliary insulation transformers; The first to third main terminals receive three-phase AC voltage; and Terminals 4 through 6 output three-phase AC voltage. The first terminal of the first to third auxiliary insulation transformers is connected to the first to third main terminals respectively. The second terminals of the first to third auxiliary insulation transformers are interconnected. The third terminal of the first to third auxiliary insulation transformers is connected to the fourth to sixth main terminals, respectively. The fourth terminal of the first to third auxiliary insulation transformers is interconnected.

6. The insulating transformer according to claim 1, wherein, Each of the first to Nth sub-insulation transformers further includes: The third auxiliary winding; and The fifth and sixth terminals are respectively connected to the first polarity terminal and the second polarity terminal of the third winding. The polarity directions of the first to third auxiliary windings are the same. The first to Nth sub-insulation transformers are each configured such that, when current flows from the first sub-terminal through the first sub-winding, the phase-to-phase capacitance between the first and third sub-windings, the third sub-winding, the phase-to-phase capacitance between the second and third sub-windings, and the second sub-winding to the third sub-terminal, the magnetizing inductance of the first sub-winding and the magnetizing inductance of the second and third sub-windings have opposite polarities.

7. The insulating transformer according to claim 6, wherein, The number of turns in the first secondary winding is twice the number of turns in the second secondary winding. The second and third auxiliary windings have the same number of turns.

8. The insulating transformer according to claim 6, wherein, N is 3. The insulation transformer is a three-phase transformer with a Y-interleaved connection and possesses: The first to third auxiliary insulation transformers; The first to third main terminals receive three-phase AC voltage; and Terminals 4 through 6 output three-phase AC voltage. The first terminal of the first to third auxiliary insulation transformers is connected to the first to third main terminals respectively. The second terminals of the first to third auxiliary insulation transformers are interconnected. The third terminal of the first to third auxiliary insulation transformers is connected to the fourth to sixth main terminals, respectively. The fifth terminal of the first to third auxiliary insulation transformers is interconnected. The sixth terminal of the first to third auxiliary insulation transformers is connected to the fourth terminal of the second, third, and first auxiliary insulation transformers, respectively.

9. A power conversion device, comprising: The insulating transformer according to claim 1; The first power converter converts the DC power supplied from the first DC power source into AC power; and The second power converter converts the AC power supplied from the first power converter via the insulation transformer into DC power and supplies it to the second DC power source. The power conversion device is configured such that, when current flows from the first power converter through the first secondary terminal, the first secondary winding, the phase-to-phase capacitor between the first and second secondary windings, the second secondary winding, the third secondary terminal, the second power converter, and the reference voltage line to the first power converter, the magnetizing inductance of the first secondary winding and the magnetizing inductance of the second secondary winding are of opposite polarities.

10. The power conversion device according to claim 9, wherein, The first power converter includes: The first and second DC terminals accept DC voltage; The first and second AC terminals accept AC voltage; The first and second transistors are respectively connected between the first DC terminal and the first and second AC terminals; The third and fourth transistors are respectively connected between the first and second AC terminals and the second DC terminal; and Diodes 1 through 4 are connected in anti-parallel to transistors 1 through 4, respectively. The second power converter includes: The third and fourth DC terminals accept DC voltage; Terminals 3 and 4 accept AC voltage; The 5th and 6th transistors are respectively connected between the 3rd DC terminal and the 3rd and 4th AC terminals; The 7th and 8th transistors are respectively connected between the 3rd and 4th AC terminals and the 4th DC terminal; and Diodes 5 through 8 are connected in anti-parallel to transistors 5 through 8, respectively. The insulation transformer has the following features: The first and second main windings; The first and second main terminals are respectively connected to the first polarity terminal and the second polarity terminal of the first main winding; and The third and fourth main terminals are respectively connected to the first polarity terminal and the second polarity terminal of the second main winding. The polarities of the first and second main windings are in the same direction. The first and second AC terminals are respectively coupled to the first and second main terminals. The third and fourth AC terminals are coupled to the fourth and third main terminals, respectively.

11. The power conversion device according to claim 10, wherein, The first power converter also includes: A first reactor is connected between the first AC terminal and the first main terminal; and The second reactor is connected between the second AC terminal and the second main terminal. The second power converter also includes: The third reactor is connected between the third AC terminal and the fourth main terminal; and The fourth reactor is connected between the fourth AC terminal and the third main terminal. The power conversion device also includes a control device that controls the first to eighth transistors. When DC power is supplied from the first DC power source to the second DC power source, the control device alternately turns on the first and third transistors, alternately turns on the fourth and second transistors, alternately turns on the fifth and seventh transistors, and keeps the sixth and eighth transistors in the off state.

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