Power conversion device

Abstract

To provide a power conversion device that enables multiphase resonance operation while insulating an input side and an output side by using a capacitor.SOLUTION: The power conversion device includes a voltage generation circuit that generates an N-phase (N is a positive multiple of 3) volts alternating current, a rectifier circuit, and N resonant circuits that are connected between the voltage generation circuit and the rectifier circuit and are connected in series to each other. Each resonant circuit includes a first capacitor, a second capacitor, a coupled inductor including a first core, a first winding wound around the first core and connected in series with the first capacitor, and a second winding wound around the first core and connected in series with the second capacitor, and a parallel inductor including a third winding connected between the first winding and the second winding.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a power conversion device. [Background technology]

[0002] A capacitor-isolated LLC resonant converter is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 029162 [Patent Document 2] Japanese Patent Application Publication No. 2018-152988 [Patent Document 3] Japanese Patent Publication No. 2023-007117 [Patent Document 4] Japanese Patent Publication No. 2023-049712 [Patent Document 5] Japanese Patent Publication No. 2023-070523 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of an embodiment of the present invention is to provide a power conversion device that enables multi-phase resonant operation while insulating the input side from the output side using a capacitor. [Means for solving the problem]

[0005] According to an embodiment of the present invention, a power conversion device includes a voltage generating circuit that generates an AC voltage of N phases (N is a positive multiple of 3), a rectifier circuit, and N resonant circuits connected between the voltage generating circuit and the rectifier circuit and connected in series with each other, each of the resonant circuits including a first capacitor, a second capacitor, a first core, a coupled inductor having a first winding wound around the first core and connected in series with the first capacitor, and a second winding wound around the first core and connected in series with the second capacitor, and a parallel inductor having a third winding connected between the first winding and the second winding. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a circuit diagram of a power conversion device according to an embodiment; [Figure 2] FIG. 2 is a schematic diagram of a coupled inductor according to an embodiment. [Figure 3] FIG. 2 is an equivalent circuit diagram of a coupled inductor according to an embodiment. [Figure 4] FIG. 10 is a circuit diagram of a resonant circuit of a third comparative example. [Figure 5] FIG. 2 is a circuit diagram of a resonant circuit according to an embodiment. [Figure 6] 10(a) is a waveform diagram of a resonant current in a resonant circuit of a third comparative example, and FIG. 10(b) is a waveform diagram of a resonant current in a resonant circuit of the embodiment. [Figure 7] 10(a) and 10(b) are circuit diagrams showing modified examples of the resonant circuit of the embodiment. [Figure 8] 10(a) and 10(b) are circuit diagrams showing modified examples of the resonant circuit of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Even when the same part is shown, the dimensions and ratios may be different depending on the drawing. Furthermore, identical or similar elements are given the same reference numerals.

[0008] 1 is a circuit diagram of a power conversion device 1 according to an embodiment. The power conversion device 1 according to the embodiment includes a voltage generation circuit 20 that generates an AC voltage of N phases (N is a positive multiple of 3), a rectifier circuit 30, and N resonant circuits 10 connected between the voltage generation circuit 20 and the rectifier circuit 30.

[0009] The power conversion device 1 of the embodiment is a capacitor-insulated (or electric field-coupled) LLC resonant converter in which a voltage generating circuit 20 on the input side and a rectifier circuit 30 on the output side are electrically insulated by a first capacitor Cp and a second capacitor Cn. In addition, in this embodiment, a capacitor-insulated LLC resonant converter that transmits power using three-phase AC as N-phase AC will be described.

[0010] A DC voltage Vin is input to an input terminal 40 of a voltage generating circuit 20, which outputs a three-phase AC voltage. The output of the voltage generating circuit 20 is transmitted to a rectifier circuit 30 on the output side as three-phase AC power due to the resonant operation of three resonant circuits 10. The rectifier circuit 30 rectifies the three-phase AC power and outputs a DC voltage Vout to an output terminal 50.

[0011] The voltage generating circuit 20 has three output nodes (a first output node n1, a second output node n2, and a third output node n3) that output three-phase AC voltages. The voltage generating circuit 20 is, for example, an inverter circuit, and has an input capacitor C1, a first input side semiconductor element Qp1, a second input side semiconductor element Qp2, a third input side semiconductor element Qp3, a fourth input side semiconductor element Qp4, a fifth input side semiconductor element Qp5, and a sixth input side semiconductor element Qp6.

[0012] The first input semiconductor element Qp1 and the second input semiconductor element Qp2 are connected in series. The third input semiconductor element Qp3 and the fourth input semiconductor element Qp4 are connected in series. The fifth input semiconductor element Qp5 and the sixth input semiconductor element Qp6 are connected in series. The series-connected pair of the first input semiconductor element Qp1 and the second input semiconductor element Qp2, the series-connected pair of the third input semiconductor element Qp3 and the fourth input semiconductor element Qp4, and the series-connected pair of the fifth input semiconductor element Qp5 and the sixth input semiconductor element Qp6 are connected in parallel to the input terminal 40. A first output node n1 is connected between the first input semiconductor element Qp1 and the second input semiconductor element Qp2. A second output node n2 is connected between the third input semiconductor element Qp3 and the fourth input semiconductor element Qp4. A third output node n3 is connected between the fifth input semiconductor element Qp5 and the sixth input semiconductor element Qp6.

[0013] The first input semiconductor element Qp1 and the second input semiconductor element Qp2 are alternately turned on and off to output a sinusoidal voltage to the first output node n1. The third input semiconductor element Qp3 and the fourth input semiconductor element Qp4 are alternately turned on and off to output a sinusoidal voltage to the second output node n2. The fifth input semiconductor element Qp5 and the sixth input semiconductor element Qp6 are alternately turned on and off to output a sinusoidal voltage to the third output node n3. The phases of the sinusoidal voltages output to the first output node n1, the second output node n2, and the third output node n3 are shifted by 120° each other.

[0014] A pair of input side semiconductor elements that are alternately turned on and off have a period (dead time) during which they are both off. A first input side semiconductor element Qp1 and a second input side semiconductor element Qp2 that are alternately turned on and off have a period during which they are both off. A third input side semiconductor element Qp3 and a fourth input side semiconductor element Qp4 that are alternately turned on and off have a period during which they are both off. A fifth input side semiconductor element Qp5 and a sixth input side semiconductor element Qp6 that are alternately turned on and off have a period during which they are both off.

[0015] The power conversion device 1 includes three resonant circuits 10 corresponding to the three-phase AC voltages generated by the voltage generation circuit 20. The three resonant circuits 10 are referred to as a first resonant circuit 10A, a second resonant circuit 10B, and a third resonant circuit 10C. Note that the first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C may be simply referred to as the resonant circuits 10 without being distinguished from one another.

[0016] The first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C are connected in series to each other, and in this case, the first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C are delta-connected.

[0017] Each of the first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C includes a first capacitor Cp, a second capacitor Cn, a coupled inductor Lc, and a parallel inductor (excitation inductor) Lm.

[0018] As shown in FIG. 2, the coupled inductor Lc has a first core 11, a first winding W1 wound around the first core 11, and a second winding W2 wound around the first core 11. The first winding W1 and the second winding W2 are magnetically coupled via the first core 11. The first winding W1 and the second winding W2 are not electrically connected. For example, copper wires can be used for the first winding W1 and the second winding W2. The first core 11 is a magnetic material. For example, MnZn ferrite can be used as the magnetic material of the first core 11.

[0019] 3 is an equivalent circuit diagram of the coupled inductor Lc according to the embodiment. The coupled inductor Lc has an excitation inductance L MIn addition to the above, the resonant circuit 10 has a leakage inductance Le1 generated by leakage flux on the first winding W1 side and a leakage inductance Le2 generated by leakage flux on the second winding W2 side. The main magnetic flux is linked to both the first winding W1 and the second winding W2. The leakage flux on the first winding W1 side is linked only to the first winding W1 and not to the second winding W2. The leakage flux on the second winding W2 side is linked only to the second winding W2 and not to the first winding W1. The leakage inductances Le1 and Le2 function as resonant inductors in each resonant circuit 10. This allows the resonant circuit to be made smaller than in a configuration in which a resonant inductor is provided as a component separate from the coupled inductor Lc.

[0020] 1, the coupled inductor Lc is connected between the first capacitor Cp and the parallel inductor Lm, and between the second capacitor Cn and the parallel inductor Lm. The first capacitor Cp is connected in series with the first winding W1. The second capacitor Cn is connected in series with the second winding W2.

[0021] The parallel inductor Lm has a third winding W3 connected between the first winding W1 and the second winding W2. The third winding W3 may be made of, for example, copper wire. The parallel inductor Lm may have a second core around which the third winding W3 is wound.

[0022] The first capacitor Cp and the second capacitor Cn of each resonant circuit 10 are connected to different output nodes.

[0023] The first capacitor Cp of the first resonant circuit 10A is connected between the first output node n1 of the voltage generating circuit 20 and the first winding W1 of the first resonant circuit 10A. The second capacitor Cn of the first resonant circuit 10A is connected between the second output node n2 of the voltage generating circuit 20 and the second winding W2 of the first resonant circuit 10A.

[0024] The first capacitor Cp of the second resonant circuit 10B is connected between the second output node n2 of the voltage generating circuit 20 and the first winding W1 of the second resonant circuit 10B. The second capacitor Cn of the second resonant circuit 10B is connected between the third output node n3 of the voltage generating circuit 20 and the second winding W2 of the second resonant circuit 10B.

[0025] The first capacitor Cp of the third resonant circuit 10C is connected between the third output node n3 of the voltage generating circuit 20 and the first winding W1 of the third resonant circuit 10C. The second capacitor Cn of the third resonant circuit 10C is connected between the first output node n1 of the voltage generating circuit 20 and the second winding W2 of the third resonant circuit 10C.

[0026] In each of the coupled inductors Lc of the first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C, the number of turns N1 of the first winding W1 is equal to the number of turns N2 of the second winding W2.

[0027] The rectifier circuit 30 has three input nodes (a first input node n4, a second input node n5, and a third input node n6) to which the output of the resonant circuit 10 is input. The first input node n4 is connected to the first winding W1 of the first resonant circuit 10A and the second winding W2 of the third resonant circuit 10C. The second input node n5 is connected to the second winding W2 of the first resonant circuit 10A and the first winding W1 of the second resonant circuit 10B. The third input node n6 is connected to the second winding W2 of the second resonant circuit 10B and the first winding W1 of the third resonant circuit 10C.

[0028] The rectifier circuit 30 is a three-phase rectifier circuit that uses, for example, switching semiconductor elements as rectifier elements, and has a first output semiconductor element Qs1, a second output semiconductor element Qs2, a third output semiconductor element Qs3, a fourth output semiconductor element Qs4, a fifth output semiconductor element Qs5, a sixth output semiconductor element Qs6, and a smoothing capacitor C2. Note that the rectifier circuit 30 may also be configured using diodes as rectifier elements. In the rectifier circuit 30, using switching semiconductor elements makes it easier to reduce losses.

[0029] The first output semiconductor element Qs1 and the second output semiconductor element Qs2 are connected in series. The third output semiconductor element Qs3 and the fourth output semiconductor element Qs4 are connected in series. The fifth output semiconductor element Qs5 and the sixth output semiconductor element Qs6 are connected in series. The pair of the series-connected first output semiconductor element Qs1 and the second output semiconductor element Qs2, the pair of the series-connected third output semiconductor element Qs3 and the fourth output semiconductor element Qs4, and the pair of the series-connected fifth output semiconductor element Qs5 and the sixth output semiconductor element Qs6 are connected in parallel to the output terminal 50. A first input node n4 is connected between the first output semiconductor element Qs1 and the second output semiconductor element Qs2. A second input node n5 is connected between the third output semiconductor element Qs3 and the fourth output semiconductor element Qs4. A third input node n6 is connected between the fifth output semiconductor element Qs5 and the sixth output semiconductor element Qs6.

[0030] The first output semiconductor element Qs1 and the second output semiconductor element Qs2 are alternately turned on and off to perform rectification depending on the direction of the AC voltage flowing through the first input node n4. The third output semiconductor element Qs3 and the fourth output semiconductor element Qs4 are alternately turned on and off to perform rectification depending on the direction of the AC voltage flowing through the second input node n5. The fifth output semiconductor element Qs5 and the sixth output semiconductor element Qs6 are alternately turned on and off to perform rectification depending on the direction of the AC voltage flowing through the third input node n6.

[0031] A pair of output-side semiconductor elements that are alternately turned on and off have a period (dead time) during which they are both off. A first output-side semiconductor element Qs1 and a second output-side semiconductor element Qs2 that are alternately turned on and off have a period during which they are both off. A third output-side semiconductor element Qs3 and a fourth output-side semiconductor element Qs4 that are alternately turned on and off have a period during which they are both off. A fifth output-side semiconductor element Qs5 and a sixth output-side semiconductor element Qs6 that are alternately turned on and off have a period during which they are both off.

[0032] According to this embodiment, the input side voltage generating circuit 20 and the output side rectifier circuit 30 are insulated using the first capacitor Cp and the second capacitor Cn without using a transformer, thereby making it possible to reduce the size of the power conversion device compared to a transformer-insulated type power conversion device.

[0033] Furthermore, the power conversion device 1 of this embodiment is an LLC resonant converter that transmits power using multiphase (three-phase in this example) AC, and is capable of achieving higher power density and efficiency than a single-phase LLC resonant converter.

[0034] As a first comparative example, consider a three-phase transformer-isolated LLC resonant converter. The LLC resonant converter of the first comparative example has three resonant circuits connected in series. Each resonant circuit has one capacitor, one resonant inductor, and one parallel inductor, and is magnetically coupled to the output rectifier circuit via a transformer.

[0035] The power conversion device 1 of the embodiment described above and the LLC resonant converter of the first comparative example were simply designed with the same specifications (input / output voltage of 384 V, output of 10.8 kW), and losses were compared by simulation. 3 ) and the component volume of the LLC resonant converter of the first comparative example (198 cm 3 ) are approximately equal, the loss of the LLC resonant converter of the first comparative example was 146 W, while the loss of the power conversion device 1 of the embodiment was 67 W, suggesting that the loss can be reduced by 54% compared to the first comparative example.

[0036] To increase the capacity of an LLC resonant converter, a configuration (referred to as a second comparative example) in which three single-phase LLC resonant converters are connected in parallel is considered. In this second comparative example, a voltage generation circuit must be connected to each of the three resonant circuits, which increases the number of semiconductor elements in the voltage generation circuit. Similarly, a rectification circuit must be connected to each of the three resonant circuits, which increases the number of rectification elements in the rectification circuit.

[0037] According to this embodiment, a three-phase LLC resonant converter is realized by connecting three resonant circuits 10 in series (Δ connection), and the number of semiconductor elements in the voltage generating circuit 20 and the number of rectifying elements in the rectifier circuit 30 can be reduced compared to the second comparative example. Also, the smoothing capacitor C2 in the rectifier circuit 30 can be made smaller.

[0038] The power conversion device 1 of the embodiment and the LLC resonant converter of the second comparative example were simply designed with the same specifications (input / output voltage of 384 V, output of 10.8 kW), and the component volumes were compared by simulation.

[0039] Under the design conditions in which the loss (65 W) of the power conversion device 1 of the embodiment is approximately equal to the loss (66 W) of the LLC resonant converter of the second comparative example, the component volume of the LLC resonant converter of the second comparative example is 300 cm 3 On the other hand, the component volume of the power conversion device 1 of the embodiment is 263 cm 3 As a result, it is expected that the component volume can be reduced by 12% compared to the second comparative example.

[0040] 4 is a circuit diagram of a three-phase resonant circuit in a third comparative example. In the third comparative example, three resonant circuits are connected in series (Δ connection). Each resonant circuit includes a first capacitor Cp, a first resonant inductor Lp connected in series with the first capacitor Cp, a second capacitor Cn, a second resonant inductor Ln connected in series with the second capacitor Cn, and a parallel inductor Lm connected between the first resonant inductor Lp and the second resonant inductor Ln. The resonant circuit in the third comparative example does not include a coupled inductor.

[0041] In a capacitor-isolated converter, the capacitor that provides insulation has lower impedance than a transformer. Therefore, if a resonant circuit is simply made three-phase in a capacitor-isolated converter, as in the third comparative example, a current path that interferes with the resonant circuits of other phases will be formed. Figure 6(a) is a waveform diagram obtained by simulating the resonant current flowing through one resonant circuit in the third comparative example. In the third comparative example, as shown in Figure 6(a), numerous LC resonances are observed, and LLC converter operation cannot be achieved.

[0042] In contrast, according to this embodiment, as shown in FIG. 5, a coupled inductor Lc is applied to each resonant circuit 10. In the coupled inductor Lc, V1 denotes the voltage applied to the first winding W1, i1 denotes the current flowing through the first winding W1, N1 denotes the number of turns of the first winding W1, V2 denotes the voltage applied to the second winding W2, i2 denotes the current flowing through the second winding W2, and N2 denotes the number of turns of the second winding W2. According to the law of conservation of energy, V1i1 = V2i2 = (N2 / N1)V1i2 holds. When N1 = N2, i1 = i2 holds. Therefore, according to the law of conservation of energy, the current flowing through each resonant circuit 10 is uniquely determined so that the current flowing through the first winding W1 and the first resonant inductor (in this example, leakage inductance Le1) is equal to the current flowing through the second winding W2 and the second resonant inductor (in this example, leakage inductance Le2) in each resonant circuit 10. This prevents or reduces currents that interfere with the resonant circuits 10 of other phases, allowing the resonant circuits 10 of each phase to form independent current paths.

[0043] 6(b) is a waveform diagram obtained by simulation of the resonant current flowing through one resonant circuit 10 in the embodiment. According to the embodiment, as shown in FIG. 6(b), a sinusoidal resonant current can be obtained, and a three-phase LLC converter operation can be realized.

[0044] Note that generation of currents interfering with other phases is acceptable to the extent that it does not hinder the realization of LLC converter operation. Therefore, in each of the coupled inductors Lc of the first resonant circuit 10A, the second resonant circuit 10B, and the third resonant circuit 10C, the number of turns N1 of the first winding W1 and the number of turns N2 of the second winding W2 do not necessarily have to be completely equal, and the ratio N2 / N1 of the number of turns N2 of the second winding W2 to the number of turns N1 of the first winding W1 may be 0.7 or more and 1.3 or less.

[0045] In a capacitor-insulated LLC converter, common-mode noise generated on the input side is likely to leak to the output side. According to this embodiment, by applying the coupled inductor Lc to the resonant circuit 10, the resonance point of the common-mode impedance shifts to a frequency lower than the switching frequency of the resonant circuit, and the common-mode impedance at the switching frequency increases. This makes it possible to suppress leakage of common-mode noise from the input side to the output side.

[0046] According to a first modification shown in FIG. 7(a), the resonant circuit includes a first resonant inductor Lp and a second resonant inductor Ln as components separate from the coupled inductor Lc. The first resonant inductor Lp includes a fourth winding W4 connected between the first winding W1 of the coupled inductor Lc and the third winding W3 of the parallel inductor Lm. The first resonant inductor Lp may further include a third core around which the fourth winding W4 is wound. The second resonant inductor Ln includes a fifth winding W5 connected between the second winding W2 of the coupled inductor Lc and the third winding W3 of the parallel inductor Lm. The second resonant inductor Ln may further include a fourth core around which the fifth winding W5 is wound.

[0047] As in a second modification shown in FIG. 7(b), the parallel inductor Lm may be connected between the first capacitor Cp and the first winding W1, and between the second capacitor Cn and the second winding W2.

[0048] As in the third modified example shown in Fig. 8(a), the connection order (arrangement order) of the first capacitor Cp, the first winding W1, and the parallel inductor Lm in the current path in which the first capacitor Cp and the first winding W1 are connected in series may be different from the connection order (arrangement order) of the second capacitor Cn, the second winding W2, and the parallel inductor Lm in the current path in which the second capacitor Cn and the second winding W2 are connected in series. In the example shown in Fig. 8(a), the first winding W1 is connected between the parallel inductor Lm and the first capacitor Cp, and the parallel inductor Lm is connected between the second capacitor Cn and the second winding W2.

[0049] Preferably, the connection order of the first capacitor Cp, the first winding W1, and the parallel inductor Lm between the voltage generating circuit 20 and the rectifying circuit 30 is the same as the connection order of the second capacitor Cn, the second winding W2, and the parallel inductor Lm between the voltage generating circuit 20 and the rectifying circuit 30. This facilitates designing a desired phase characteristic. It also helps to suppress noise generation.

[0050] As shown in a fourth modification example in Fig. 8(b), the resonant circuit may have a plurality of first capacitors Cp. The resonant circuit may have a plurality of second capacitors Cn. The resonant circuit may have a plurality of first resonant inductors Lp. The resonant circuit may have a plurality of second resonant inductors Ln.

[0051] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0052] REFERENCE SIGNS LIST 1...power conversion device, 10...resonant circuit, 10A...first resonant circuit, 10B...second resonant circuit, 10C...third resonant circuit, 11...first core, 20...voltage generation circuit, 30...rectifier circuit, 40...input terminal, 50...output terminal, Cp...first capacitor, Cn...second capacitor, Lc...coupled inductor, Lm...parallel inductor, Lp...first resonant inductor, Ln...second resonant inductor, W1...first winding, W2...second winding, W3...third winding, W4...fourth winding, W5...fifth winding

Claims

1. a voltage generating circuit that generates an N-phase AC voltage (N is a positive multiple of 3); A rectifier circuit; N resonant circuits connected in series to each other and connected between the voltage generating circuit and the rectifying circuit; Equipped with Each of the resonant circuits comprises: a first capacitor; a second capacitor; a coupled inductor including a first core, a first winding wound around the first core and connected in series with the first capacitor, and a second winding wound around the first core and connected in series with the second capacitor; a parallel inductor having a third winding connected between the first winding and the second winding; A power conversion device comprising:

2. The power conversion device according to claim 1 , wherein the number of turns of the first winding is equal to the number of turns of the second winding.

3. The number of turns of the first winding N １ The number of turns N of the second winding ２ Ratio of N ２ / N １ The power conversion device according to claim 1 , wherein is equal to or greater than 0.7 and equal to or less than 1.

3.

4. The resonant circuit comprises: a first resonant inductor having a fourth winding connected between the first winding and the third winding; a second resonant inductor having a fifth winding connected between the second winding and the third winding; The power conversion device according to claim 1 , further comprising:

5. the voltage generating circuit has N output nodes; 4. The power conversion device according to claim 1, wherein the first capacitor and the second capacitor in each of the N resonant circuits are connected to different output nodes among the N output nodes.

6. 4. The power conversion device according to claim 1, wherein a connection order of the first capacitor, the first winding, and the parallel inductor between the voltage generation circuit and the rectifier circuit is the same as a connection order of the second capacitor, the second winding, and the parallel inductor between the voltage generation circuit and the rectifier circuit.

7. 4. The power conversion device according to claim 1, wherein the voltage generating circuit has N pairs of input-side semiconductor elements that are alternately turned on and off.

8. The power conversion device according to claim 7 , wherein there is a period during which the pair of input side semiconductor elements that are alternately turned on and off are both turned off.

9. 4. The power conversion device according to claim 1, wherein the rectifier circuit has N pairs of output-side semiconductor elements that are alternately turned on and off.

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