Power converter

Abstract

To provide a power conversion device with a magnetic link capable of reducing the overall volume and cost while having strong coupling at the magnetic link.SOLUTION: A power conversion device comprises an AC-DC bidirectional power converter cell that performs a two-stage power conversion from AC to DC and from DC to DC at each of three phases. One power electronics converter of the AC-DC bidirectional power converter cell converts AC to DC. Two power electronics converters of the AC-DC bidirectional power converter cell that are insulated by a two-winding high-frequency isolation transformer convert DC to DC. At the DC-DC conversion stage of the two-stage power conversion, a coupling inductor is connected in series between a first power electronics converter of the AC-DC bidirectional power converter cell and the two-winding high-frequency isolation transformer, where the coupling inductor magnetically connects each of the three phases.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the configuration of a power conversion device. More specifically, the present invention relates to the configuration of a solid-state transformer (SST) having magnetic coupling through a coupled inductor.

Background Art

[0002] As is known in this technical field, in power electronics, there is a classification of circuits called power converter circuits (or more simply "power converters"). A power converter converts electrical energy from one form to another. For example, a power converter converts between AC power and DC power and changes the voltage, frequency, or a combination thereof of a signal.

[0003] Also, as is known, conventionally, power converters having a high-frequency transformer-based insulation structure have been widely used.

[0004] Also, as is known, conventionally, power converters having a coupled inductor have been widely used. A coupled inductor is an inductor having two or more windings on the same core.

[0005] Also, as is known, a high-power AC-DC converter connected to a three-phase AC power supply converts AC to DC (mainly low voltage) using two stages in each phase. The first stage is for converting AC to DC (mainly high voltage), and the second stage is for converting DC (mainly high voltage) to DC (mainly low voltage) using galvanic insulation through a high-frequency transformer.

[0006] Between the two conversion stages, a DC link capacitor is used to absorb the double grid frequency ripple current in each phase.

[0007] The size of the DC link capacitor can be reduced by transmitting the dual grid frequency ripple current from the DC link capacitor to the high-frequency AC magnetic link formed in each phase. Due to the three-phase symmetry, the magnetic flux generated by the dual grid frequency ripple current in each phase cancels each other out in the magnetic link.

[0008] As background technology to this field, for example, there is technology such as that described in Patent Document 1. Patent Document 1 relates to the structure of a magnetic link created by adding a two-winding transformer in series between the power electronics converter and the high-frequency isolation transformer in each leg of a DC-DC resonant converter, and magnetically coupling the two-winding transformer. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 9819275B2 [Overview of the project] [Problems that the invention aims to solve]

[0010] Figure 6 shows a prior art configuration illustrating a magnetic link

[0607] connecting three converter cells

[0601] of a resonant DC-DC power electronics converter

[0600] . The magnetic link

[0607] is formed via a two-winding coupled transformer

[0603] positioned between the power electronics converter [103b] and the high-frequency isolation transformer

[0105] , corresponding to Patent Document 1. The converter is powered by a DC power supply

[0602] and has one DC output port

[0608] .

[0011] The magnetic link

[0607] created by the two-winding coupled transformer configuration within the resonant DC-DC power electronics converter

[0600] has the following problems:

[0012] The first problem is that each two-winding coupled transformer

[0603] in the magnetic link

[0607] has one core

[0606] and two windings [604, 605], which increases the volume of the resonant DC-DC power electronics converter

[0600] . Overall, for the three number of two-winding coupled transformers

[0603] in the magnetic link

[0607] , there are three cores

[0606] and six windings [604, 605], which significantly increases the volume of the resonant DC-DC power electronics converter

[0600] .

[0013] The second problem is the increased cost of the resonant DC-DC power electronics converter

[0600] , which is directly related to the volume of the resonant DC-DC power electronics converter

[0600] . Overall, the magnetic link

[0607] of the resonant DC-DC power electronics converter

[0600] incurs the additional cost of three cores

[0606] and six windings [604,605].

[0014] The third problem is that the primary windings

[0604] of the three two-winding coupled transformers

[0603] of the magnetic link

[0607] are weakly coupled due to the leakage inductance between the primary winding

[0604] and the secondary winding

[0605] of each two-winding coupled transformer

[0603] .

[0015] Therefore, the object of the present invention is to provide a power conversion device having a magnetic link that can reduce the overall volume and cost while having a strong coupling in the magnetic link. [Means for solving the problem]

[0016] To solve the above problems, the present invention provides a power conversion device including an AC-DC bidirectional power converter cell that performs two-stage power conversion from AC to DC and from DC to DC in each of three phases. One power electronics converter of the AC-DC bidirectional power converter cell converts AC to DC, and two power electronics converters insulated by a two-winding high-frequency isolation transformer of the AC-DC bidirectional power converter cell convert DC to DC. In the DC-DC conversion stage of the two-stage power conversion, a coupling inductor is connected in series between the first power electronics converter of the AC-DC bidirectional power converter cell and the two-winding high-frequency isolation transformer. The coupling inductor magnetically connects each of the three phases.

Advantages of the Invention

[0017] According to the present invention, it is possible to realize a power conversion device having a magnetic link that can reduce the overall volume and cost while having a strong coupling in the magnetic link.

[0018] Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing a schematic configuration of a power conversion device according to Example 1. [Figure 2] It is a diagram showing an example of one converter unit (having three converter cells) of the power electronics converter in FIG. 1. [Figure 3] It is a diagram showing an example of the bidirectional power electronics converters 103a, 103b, and 103c in FIG. 1. [Figure 4] It is a diagram showing an example of the bidirectional power electronics converters 103a, 103b, and 103c in FIG. 1. [Figure 5] It is a diagram showing a schematic configuration of a power conversion device according to Example 2. [Figure 6]It is a diagram showing a schematic configuration of a resonant DC-DC power conversion device having a two-winding coupled transformer in a magnetic link as shown in Patent Document 1 which is a prior art document.

Mode for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and detailed description of overlapping parts will be omitted.

Embodiment

[0021] Referring to FIGS. 1 to 4, a power conversion device according to Embodiment 1 of the present invention will be described.

[0022] FIG. 1 is a diagram showing a schematic configuration of a power electronics converter

[0109] having a multi-port DC output according to Embodiment 1.

[0023] Power is supplied to the power electronics converter

[0109] from a three-phase (UVW) four-wire AC power supply

[0100] , and a plurality (n) of converter cells

[0102] in each phase convert AC power into DC power. Instead of the three-phase four-wire AC power supply

[0100] , a three-phase three-wire AC power supply can also be used, and in such a case, the fourth (neutral) wire

[0110] does not exist. The three-phase lines are composed of a U-phase line

[0111] , a V-phase line

[0112] , and a W-phase line

[0113] .

[0024] Each converter cell

[0102] includes an AC-DC bidirectional power electronics converter [103a] for converting single-phase AC power into DC power, followed by a DC-AC bidirectional power electronics converter [103b] for converting the DC power back into single-phase high-frequency AC power, and finally, an AC-DC bidirectional power electronics converter [103c] for converting the high-frequency AC power into DC power.

[0025] In each converter cell

[0102] , the output terminal of the AC-DC bidirectional power electronics converter [103a] is connected to the input terminal of the DC-AC bidirectional power electronics converter [103b] via a DC link capacitor

[0104] arranged in parallel between the two converters.

[0026] Each converter cell

[0102] has a two-winding high-frequency isolation transformer

[0105] that electrically isolates the DC-AC bidirectional power electronics converter [103b] and the AC-DC bidirectional power electronics converter [103c].

[0027] In each phase, multiple (n) converter cells

[0102] are connected in series with each other on the input side. One end [111, 112, 113] of the AC input terminals is connected to one phase of a three-phase four-wire AC power supply

[0100] , and the other end

[0110] is connected to the neutral point of the three-phase four-wire AC power supply

[0100] via a neutral wire

[0110] . As mentioned above, in a three-phase three-wire AC power supply, there is no neutral wire

[0110] .

[0028] In each phase, n converter cells

[0102] are collectively called a "phase cluster"

[0101] . Since there are three phases, there are three phase clusters

[0101] .

[0029] In this embodiment, as shown in Figure 1, the magnetic link

[0106] is established by a plurality of (n) coupling inductors

[0106] arranged in series between a plurality of (n) DC-AC bidirectional power electronics converters [103b] and a plurality of (n) two-winding high-frequency isolation transformers

[0105] within each converter cell

[0102] .

[0030] Each coupled inductor

[0106] has three coils wound on a single core. Each coil of the coupled inductor

[0106] comes from each converter cell

[0102] , and the three converter cells

[0102] corresponding to the three coils come from three different phase clusters

[0101] .

[0031] Therefore, since there are "n" converter cells

[0102] within each phase cluster

[0101] , there are "n" coupling inductors

[0106] .

[0032] This magnetic link

[0106] , formed by multiple coupling inductors

[0106] , magnetically couples three converter cells

[0102] from three phase clusters

[0101] .

[0033] The core of the coupling inductor

[0106] that connects the three converter cells

[0102] is located in one of the three converter cells

[0102] , preferably the central converter cell

[0102] (for example, the V-phase).

[0034] Each DC output port

[0108] of the power electronics converter

[0109] is formed by combining the individual outputs of three converter cells

[0102] in parallel, and the three converter cells come from three phase clusters

[0101] .

[0035] Therefore, since there are n converter cells in each phase cluster

[0101] , there are n DC output ports

[0108] . Each DC output capacitor

[0107] is placed in each pair of DC output ports

[0108] to smooth the DC power.

[0036] Figure 2 shows an example of one converter unit (having three converter cells) of the power electronics converter

[0109] in Figure 1. In Figure 2, the number of "n" in each phase cluster

[0101] is "1" for each phase.

[0037] The DC outputs of the three converter cells

[0102] are combined in parallel to form a DC output port

[0108] . These three converter cells

[0102] are from three different phase clusters (corresponding to U, V, and W), and as shown in Figure 2, these three converter cells

[0102] together form a single converter unit

[0200] .

[0038] Generally, the number of converter units

[0200] is equal to the number of converter cells

[0102] , i.e., "n". Furthermore, since each DC output port

[0108] is supplied by one converter unit

[0200] , the number of DC output ports

[0108] is also equal to "n".

[0039] However, in some cases, one DC output port

[0108] may be connected to two or more converter units

[0200] . In such cases, the number of DC output ports

[0108] is less than the number of converter units

[0200] . An example of this is shown in Figure 5 and explained in the following Embodiment 2.

[0040] Inside the converter cell

[0102] , all bidirectional power electronics converters [103a, 103b, 103c] have a pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] at one end and a pair of DC ports [203a and 204a, 203b and 204b, 203c and 204c] at the other end. The bidirectional power electronics converters [103a, 103b, 103c] can operate as bidirectional power conversion circuits having a power flow from the pair of DC ports [203a and 204a, 203b and 204b, 203c and 204c] to the pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] or vice versa.

[0041] The coupled inductor

[0106] has three coils [205u, 205v, 205w], and the current

[0206] in these coils is i for the three phases U, V, and W, respectively. U iV , and i W These currents are shifted by 120° in time, and due to the symmetry of the three phases, i U i V and i W The magnetic fluxes generated by these processes cancel each other out.

[0042] Figure 3 shows an example of the bidirectional power electronics converters 103a, 103b, and 103c shown in Figure 1.

[0043] As shown in Figure 3, the bidirectional power electronics converters [103a, 103b, 103c] are equipped with single-phase full-bridge circuits using semiconductor devices such as MOSFETs and IGBTs

[0300] (in Figure 3, the IGBTs and diodes are connected in antiparallel to each other). A DC link capacitor

[0104] is connected in parallel to the single-phase full-bridge circuits [103a, 103b, 103c]. The connection points at the midpoints of each half-bridge form AC ports [201a, 202a, 201b, 202b, 201c, 202c]. In the converter cell

[0102] , a pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] are connected to either a three-phase four-wire AC power supply

[0100] or a two-winding high-frequency isolation transformer

[0105] .

[0044] The parallel connection point of the two half-bridge circuits forms the DC ports [203a, 204a, 203b, 204b, 203c, 204c].

[0045] The bidirectional power electronics converters [103a, 103b, 103c] can operate as bidirectional power conversion circuits having a power flow from a pair of DC ports [203a and 204a, 203b and 204b, 203c and 204c] to a pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] or vice versa.

[0046] Figure 4 shows an example of the bidirectional power electronics converters 103a, 103b, and 103c shown in Figure 1.

[0047] As shown in Figure 4, the bidirectional power electronics converter [103a, 103b, 103c] includes a parallel connection of half-bridge circuits using semiconductor devices such as MOSFETs and IGBTs

[0300] (in Figure 4, the IGBT and diode are connected in antiparallel to each other).

[0048] The half-bridge DC link capacitors [401, 402] are connected in series and together they are equivalent to the single DC link capacitor

[0104] shown in Figures 1 to 3.

[0049] The connection points at the midpoints of the half-bridges [103a, 103b, 103c] and the midpoints of the half-bridge DC link capacitors [401, 402] form AC ports [201a, 202a, 201b, 202b, 201c, 202c]. In the converter cell

[0102] , the pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] are connected to either a three-phase four-wire AC power supply

[0100] or a two-winding high-frequency isolation transformer

[0105] .

[0050] The parallel connection points of the half-bridge circuit and the half-bridge DC link capacitors [401, 402] form DC ports [203a, 204a, 203b, 204b, 203c, 204c].

[0051] The bidirectional power electronics converters [103a, 103b, 103c] can operate as bidirectional power conversion circuits having a power flow from a pair of DC ports [203a and 204a, 203b and 204b, 203c and 204c] to a pair of AC ports [201a and 202a, 201b and 202b, 201c and 202c] or vice versa. [Examples]

[0052] Referring to Figure 5, a power conversion device according to Embodiment 2 of the present invention will be described.

[0053] Figure 5 shows a schematic configuration of a power electronics converter

[0500] having a single port DC output according to Example 2.

[0054] There is only one difference between Example 2 (Figure 5) and Example 1 (Figure 1). The difference lies in the configuration style of the DC output port

[0108] .

[0055] As shown in Figure 5, the individual outputs of all converter cells

[0102] are connected in parallel to form a single DC output port

[0108] . The other configurations are the same as in Example 1 (Figure 1) and will not be described.

[0056] Figure 6 shows a schematic configuration of a resonant DC-DC power electronics converter

[0600] equipped with a magnetic link

[0607] and a two-winding coupled transformer

[0603] , as shown in the prior art document Patent Document 1.

[0057] In Figure 6, the magnetic link

[0607] is generated by a magnetically coupled two-winding coupled transformer

[0603] positioned between the DC-AC bidirectional power electronics converter [103b] and the two-winding high-frequency isolation transformer

[0105] within each DC-DC converter cell

[0601] .

[0058] The resonant DC-DC power electronics converter

[0600] is powered by a DC power supply

[0602] and has a single DC output port

[0608] .

[0059] Each two-winding coupled transformer

[0603] within the magnetic link

[0607] has one core

[0606] and two windings [604,605], which increases the volume and cost of the resonant DC-DC power electronics converter

[0600] . Overall, for three two-winding coupled transformers

[0603] within the magnetic link

[0607] , there are three cores

[0606] and six windings [604,605]. Furthermore, the magnetic coupling in the magnetic link

[0607] is weaker compared to the coupled inductor due to the leakage inductance between the primary winding

[0604] and secondary winding

[0605] of each two-winding coupled transformer

[0603] .

[0060] According to the present invention, the first effect is that a power conversion device with a smaller overall volume of magnetic links can be realized. This is because, compared to the three cores and six windings required in the two-winding configuration shown in Figure 6, only one core and three coils are required to form the magnetic link between the three cells shown in Figure 2.

[0061] The second benefit is that the overall cost can be reduced because only one core and three coils are needed to form the magnetic link between the three cells.

[0062] The third effect is that strong magnetic coupling is achieved because the three coils of the coupled inductor are wound on the same core.

[0063] As a result, it is possible to reduce the size of the DC link capacitor while minimizing the overall increase in volume and cost of the power converter.

[0064] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0065] 100: Three-phase four-wire AC power supply 101: Phase cluster containing "n" converter cells 102: Converter cell for two-stage AC-DC conversion with high-frequency transformer isolation 103a, 103b, 103c: AC-DC / DC-AC bidirectional power electronics converters 104: DC Link Capacitor 105:2 winding high-frequency isolation transformer 106: Magnetic link (3-winding coupled inductor) 107: DC output capacitor 108: DC output port 109: Power Electronics Converter with Multi-Port DC Output 110: Neutral line 111: U-phase AC input line 112: AC input line for V phase 113: AC input line for W phase 200: Converter unit with 3 converter cells 201a, 202a, 201b, 202b, 201c, 202c: AC port 203a, 204a, 203b, 204b, 203c, 204c: DC port 205u, 205v, 205w: Coils of coupled inductors 206: Three-phase 120° displacement coil current 300: Semiconductor Equipment 401, 402: Half-bridge DC link capacitors 500: Power Electronics Converter with Single Port DC Output 600: Resonant DC-DC Power Electronics Converter 601: Converter cell for single-stage DC-DC conversion with high-frequency transformer isolation 602: DC power supply 603:2-winding coupled transformer 604: Primary winding of a two-winding coupled transformer 605: Secondary winding of a two-winding coupled transformer 606: Core of a 2-winding coupled transformer 607: Magnetic Link 608: DC output port

Claims

1. Each of the three phases is equipped with an AC-DC bidirectional power converter cell that performs two-stage power conversion from AC to DC and from DC to DC. One power electronics converter in the AC-DC bidirectional power converter cell converts AC to DC, and two power electronics converters isolated by a two-winding high-frequency isolation transformer in the AC-DC bidirectional power converter cell convert DC to DC. In the DC-DC conversion stage of the two-stage power conversion described above, a coupling inductor is connected in series between the first power electronics converter of the AC-DC bidirectional power converter cell and the two-winding high-frequency isolation transformer. The aforementioned coupling inductor is a power conversion device characterized by magnetically connecting each of the three phases.

2. A power conversion device according to claim 1, The coupled inductor has three coils, Each of the three coils is from one of three different converter cells of the power converter, A power converter characterized in that each of the three converter cells is from one of three different phases of the power converter.

3. A power conversion device according to claim 2, A power conversion device characterized by three converter cells sharing the same coupling inductor being magnetically coupled.

4. A power conversion device according to claim 1, The power conversion device has a plurality of converter units that input AC power and output DC power, The power electronics converters on the input side of the aforementioned plurality of converter units are connected in series and powered by an AC power supply. The outputs of each of the three power electronics converters of the converter unit are connected in parallel to form a single DC output port. A power conversion device characterized in that the outputs of the plurality of converter units form a plurality of DC output ports.

5. A power conversion device according to claim 4, The total number of coupling inductors is equal to the total number of converter units. A power conversion device characterized in that the total number of DC output ports is equal to the total number of converter units.

6. A power conversion device according to claim 1, The power conversion device has a plurality of converter units that input AC power and output DC power, The power electronics converters on the input side of the aforementioned plurality of converter units are connected in series and powered by an AC power supply. A power conversion device characterized in that the outputs of the plurality of converter units are connected in parallel to form a single DC output port.

7. A power conversion device according to claim 6, The total number of coupling inductors is equal to the total number of converter units. A power conversion device characterized in that the total number of DC output ports is only one.

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