Solid-state transformer based on alternating current-alternating current direct conversion and current conversion method thereof

Abstract

The invention discloses a solid-state transformer based on alternating current-alternating current direct conversion and a conversion method of the solid-state transformer. The solid-state transformer based on alternating current-alternating current direct conversion comprises three common-mode transformers and six primary side waveform generators, and each common-mode transformer comprises a first winding, a second winding and a first input inductor which are arranged on the primary side of the common-mode transformer; one end of the first input inductor is connected to the first midpoint, and the other end of the first input inductor is a third input end and is used for being connected with three-phase primary side alternating current; the voltage between the first input end and the second input end of each common-mode transformer is differential-mode voltage, and the voltage of the third input end of each common-mode transformer is common-mode voltage; every two primary side waveform generators are connected to the first input end and the second input end of one common-mode transformer respectively and are configured to control primary side differential mode high-frequency alternating voltage and primary side common mode power frequency alternating voltage of the common-mode transformer.

Description

Technical Field

[0001] The present application relates to the technical field of solid-state transformers, and in particular to a solid-state transformer based on AC-AC direct conversion and a current conversion method thereof. Background Art

[0002] Solid-state transformers (SSTs), as energy conversion devices that combine power electronics and high-frequency transformers, have shown tremendous potential for application in modern power systems. Using power electronics, SSTs convert three-phase industrial-frequency alternating current (AC) into high-frequency AC. This is then isolated and converted using a high-frequency transformer. Finally, power electronics are used to convert this energy into various desired forms, such as DC, industrial-frequency single-phase, or three-phase AC. All conversions are bidirectional, meaning that energy flows in both directions.

[0003] Compared with traditional transformers, solid-state transformers have the following advantages: the primary and secondary sides of the solid-state transformer can be electrically isolated, so that common three-phase power grid disadvantages such as high-order harmonics, reactive components and three-phase imbalance will not be transmitted through the primary and secondary sides of the solid-state transformer; due to the increase in operating frequency, the volume and weight of the solid-state transformer are greatly reduced; due to the reduction in the volume of the solid-state transformer core, the excitation power required by the solid-state transformer will also be proportionally reduced, thereby greatly reducing the standby power consumption of the solid-state transformer; the output form of the secondary side of the solid-state transformer is not limited to three-phase industrial frequency AC, but can be any required form of electrical energy, thereby improving the flexibility and overall cost-effectiveness of the entire system.

[0004] With the continuous promotion and extensive use of new energy power equipment, the application scope of solid-state transformers will continue to expand. For example, they have good application prospects in wind power, photovoltaics, energy storage, and high-speed rail.

[0005] However, despite the many advantages of solid-state transformers, current mainstream solid-state transformer technology generally adopts a relatively complex conversion path when achieving power conversion. Specifically, existing solutions usually first rectify and convert three-phase industrial frequency AC power into DC power. The DC power is then converted into high-frequency AC power through an inverter and fed into a high-frequency transformer. The secondary side of the high-frequency transformer then undergoes a series of reverse conversion processes, such as rectification and inversion, to finally output the required form of electrical energy. This "AC-DC-AC" conversion architecture results in numerous voltage transformation links and high design and control complexity, which significantly increases the overall manufacturing cost and operation and maintenance expenses of solid-state transformers, and to some extent limits their wider application.

[0006] In view of the above-mentioned deficiencies in the existing technologies, the industry urgently needs a more efficient and simple power conversion solution. Summary of the Invention

[0007] One advantage of the present application is that it provides a solid-state transformer based on AC-AC direct conversion and a current conversion method thereof, wherein the current conversion method of the solid-state transformer based on AC-AC direct conversion is relatively simplified, the structure of the solid-state transformer is also simplified, and the cost is relatively reduced.

[0008] According to one aspect of the present application, there is provided a solid-state transformer based on AC-AC direct conversion, comprising:

[0009] A solid-state transformer based on AC-AC direct conversion, characterized by comprising:

[0010] Three common-mode transformers, each comprising a first winding, a second winding, and a first input inductor disposed on its primary side, wherein the opposite-name end of the first winding serves as the first input terminal of the common-mode transformer, and the same-name end is connected to the opposite-name end of the second winding; the same-name end of the second winding serves as the second input terminal of the common-mode transformer; a first midpoint is defined between the first winding and the second winding; one end of the first input inductor is connected to the first midpoint, and the other end serves as a third input terminal for connection to three-phase primary alternating current;

[0011] Six primary waveform generators, wherein every two of the primary waveform generators are respectively connected to the first input terminal and the second input terminal of a common-mode transformer, and are configured to control the primary differential-mode high-frequency AC voltage between the first input terminal and the second input terminal of the common-mode transformer and the primary common-mode power-frequency AC voltage at the first midpoint of the common-mode transformer.

[0012] In one embodiment of the solid-state transformer based on AC-AC direct conversion according to the present application, the phase angles of the primary common-mode power-frequency AC voltages of the three common-mode transformers are different.

[0013] In one embodiment of the solid-state transformer based on AC-AC direct conversion according to the present application, the phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers are different.

[0014] In one embodiment of the solid-state transformer based on AC-AC direct conversion described in the present application, the secondary sides of the three common-mode transformers are shared; the phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers are equal, so that the secondary sides of the three common-mode transformers output single-phase high-frequency voltages.

[0015] In one embodiment of the solid-state transformer based on AC-AC direct conversion described in the present application, each common-mode transformer also includes a third winding, a fourth winding and a second input inductor arranged on its secondary side, wherein the opposite-name end of the third winding is the fourth input end of the common-mode transformer, and the same-name end is connected to the opposite-name end of the fourth winding; the same-name end of the fourth winding is the fifth input end of the common-mode transformer; there is a second midpoint between the third winding and the fourth winding; one end of the second input inductor is connected to the second midpoint, and the other end is the sixth input end, which is used to connect the secondary AC three-phase power; the solid-state transformer based on AC-AC direct transformation also includes six secondary waveform generators, wherein every two of the secondary waveform generators are respectively connected to the fourth input end and the fifth input end of a common-mode transformer, and are configured to control the secondary differential-mode AC voltage between the fourth input end and the fifth input end of the common-mode transformer and the secondary common-mode industrial frequency AC voltage at the second midpoint of the common-mode transformer.

[0016] In one embodiment of the solid-state transformer based on AC-AC direct conversion according to the present application, the three common-mode transformers form a three-phase three-column structure.

[0017] According to another aspect of the present application, the present application proposes a current conversion method for a solid-state transformer, comprising:

[0018] Connect three-phase primary AC power;

[0019] A primary differential-mode high-frequency AC voltage and a primary common-mode power-frequency AC voltage are generated based on the voltage of the three-phase primary AC power, so that the solid-state transformer directly converts the power-frequency AC voltage into a high-frequency AC voltage without DC conversion.

[0020] In one embodiment of the current conversion method for a solid-state transformer described in the present application, a primary differential-mode high-frequency AC voltage and a primary common-mode industrial frequency AC voltage are generated based on the voltage of the three-phase primary AC power, including: generating a primary differential-mode high-frequency AC voltage with different three-phase phase angles based on the voltage of the three-phase primary AC power; generating a primary common-mode industrial frequency AC voltage with different three-phase phase angles based on the voltage of the three-phase primary AC power.

[0021] In one embodiment of the current conversion method for a solid-state transformer described in the present application, a primary differential-mode high-frequency AC voltage and a primary common-mode industrial frequency AC voltage are generated based on the voltage of the three-phase primary AC power, including: generating a primary differential-mode high-frequency AC voltage with the same three-phase phase angle based on the voltage of the three-phase primary AC power; generating a primary common-mode industrial frequency AC voltage with different three-phase phase angles based on the voltage of the three-phase primary AC power.

[0022] In one embodiment of the current conversion method for a solid-state transformer according to the present application, the current conversion method for a solid-state transformer also includes: connecting a three-phase secondary AC power; generating a secondary differential-mode AC voltage and a secondary common-mode industrial frequency AC voltage based on the voltage of the three-phase secondary AC power.

[0023] Further objectives and advantages of the present application will be fully reflected through understanding of the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other purposes, features, and advantages of the present application will become more apparent through a more detailed description of the embodiments of the present application in conjunction with the accompanying drawings. The accompanying drawings are intended to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the drawings, the same reference numerals generally represent the same components or steps.

[0025] Figure 1 The figure shows a schematic diagram of the basic primary side topology structure of a solid-state transformer based on AC-AC direct conversion according to an embodiment of the present application.

[0026] Figure 2 The diagram illustrates a topological structure diagram of an implementation of a solid-state transformer based on AC-AC direct conversion according to an embodiment of the present application.

[0027] Figure 3 The diagram illustrates a topological structure diagram of another implementation of a solid-state transformer based on AC-AC direct conversion according to an embodiment of the present application.

[0028] Figure 4 The figure shows a topological structure diagram of another implementation of a solid-state transformer based on AC-AC direct conversion according to an embodiment of the present application.

[0029] Figure 5 The figure illustrates a flow chart of a current conversion method for a solid-state transformer according to an embodiment of the present application. DETAILED DESCRIPTION

[0030] Below, the exemplary embodiments according to the present application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application, and it should be understood that the present application is not limited to the exemplary embodiments described herein.

[0031] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "a" should not be understood as limiting the number. "Multiple" means greater than or equal to two.

[0032] Although ordinal numbers such as "first," "second," and the like will be used to describe various components, these are not intended to limit those components. The terms are used solely to distinguish one component from another. For example, a first component could be referred to as a second component, and similarly, a second component could be referred to as a first component without departing from the teachings of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0033] The terms used herein are for the purpose of describing various embodiments only and are not intended to be limiting. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It will also be understood that the terms "including" and / or "having" when used in this specification specify the presence of a stated feature, number, operation, component, element, or combination thereof, and do not preclude the presence or addition of one or more other features, numbers, operations, components, elements, or combinations thereof.

[0034] As mentioned above, current mainstream solid-state transformer technology generally adopts a relatively complex conversion path when achieving power conversion. Specifically, existing solutions usually first rectify and convert three-phase industrial frequency AC power into DC power. Then, the DC power is converted into high-frequency AC power through an inverter and fed into a high-frequency transformer. Subsequently, the secondary side of the high-frequency transformer undergoes a series of reverse conversion processes, such as rectification and inversion, to finally output the required power form. This "AC-DC-AC" conversion architecture leads to numerous transformation steps and high design and control complexity, which significantly increases the overall manufacturing cost and operation and maintenance expenses of solid-state transformers, and to some extent limits their wider application.

[0035] In view of the above-mentioned deficiencies in the existing technologies, the industry urgently needs a more efficient and simple power conversion solution.

[0036] Based on this, this application proposes a novel voltage conversion solution for solid-state transformers. Specifically, it adopts an AC-AC direct conversion solution, which does not require the traditional rectification link to convert AC power to DC power, but instead directly completes the frequency and voltage conversion in the AC domain.

[0037] Specifically, at the hardware level, a common-mode transformer and controller are introduced. At the algorithm level, a control strategy for the controller is designed. This controller controls the common-mode power-frequency AC voltage and differential-mode high-frequency AC voltage on the primary side of the common-mode transformer, thereby inducing a corresponding high-frequency voltage on the secondary side of the common-mode transformer. Further conversion can also achieve an AC output with the desired frequency and phase. This direct AC-to-AC conversion method can effectively simplify the structure of solid-state transformers, reduce unnecessary intermediate conversion steps, significantly reduce the complexity and cost of solid-state transformers, and improve overall energy conversion efficiency, opening up new avenues for the promotion and application of solid-state transformers.

[0038] Furthermore, common-mode inductors are widely used in signal isolation and anti-interference. Their characteristics are that they allow DC and low-frequency signals to pass through, while high-frequency interference will be blocked. Inspired by this, the applicant transformed the common-mode inductor into a transformer form, allowing the industrial frequency current to pass through unimpeded, while the high-frequency current will be coupled to the secondary side through the magnetic core. This modified transformer is a common-mode transformer.

[0039] A waveform generator is a device that can output a specified waveform. This application also controls the waveform generator via an external signal, thereby controlling the input and output voltages of the common-mode transformer. The waveform generator connected to the primary side of the common-mode transformer is called a primary waveform generator, and the waveform generator connected to the secondary side of the common-mode transformer is called a secondary waveform generator.

[0040] Accordingly, if Figures 1 to 4 As shown, a solid-state transformer based on AC-AC direct conversion according to an embodiment of the present application is illustrated. The solid-state transformer based on AC-AC direct conversion includes three common-mode transformers 10 and six primary waveform generators 20, wherein the three common-mode transformers 10 include a first common-mode transformer T1, a second common-mode transformer T2, and a third common-mode transformer T3; the six primary waveform generators 20 include a first primary waveform generator S1, a second primary waveform generator S2, a third primary waveform generator S3, a fourth primary waveform generator S4, a fifth primary waveform generator S5, and a sixth primary waveform generator S6.

[0041] like Figure 1As shown, each common-mode transformer 10 includes a first winding 11, a second winding 12, and a first input inductor 13 disposed on its primary side. The first winding 11 and the second winding 12 are two mutually inducted coils. Like-name and opposite-name terminals are used to distinguish the phase of the current or electromotive force between the mutually inducted coils. When current flows through the two mutually inducted coils and the generated magnetic flux is in the same direction, the current-inflow terminals of the two coils are called like-name terminals. When the magnetic flux is in opposite directions, the current-inflow terminals of the two coils are called opposite-name terminals. Accordingly, the opposite-name terminal of the first winding 11 is the terminal into which current flows when the magnetic flux directions of the first winding 11 and the second winding 12 are opposite; the like-name terminal of the first winding 11 is the terminal into which current flows when the magnetic flux directions of the first winding 11 and the second winding 12 are the same. The opposite-name terminal of the second winding 12 is the terminal into which current flows when the magnetic flux directions of the first winding 11 and the second winding 12 are opposite. The same-name end of the second winding 12 is the end into which the current of the second winding 12 flows when the magnetic flux directions of the first winding 11 and the second winding 12 are the same.

[0042] The opposite-name end of the first winding 11 is the first input end 101 of the common-mode transformer 10, and the same-name end is connected to the opposite-name end of the second winding 12; the same-name end of the second winding 12 is the second input end 102 of the common-mode transformer 10; there is a first midpoint 107 between the first winding 11 and the second winding 12; one end of the first input inductor 13 is connected to the first midpoint 107, and the other end is the third input end 103, which is used to connect the three-phase primary alternating current. For example, one end of the first input inductor I1 of the first common-mode transformer T1 is used to connect the first-phase primary alternating current (phase A primary alternating current); one end of the first input inductor I2 of the second common-mode transformer T2 is used to connect the second-phase primary alternating current (phase B primary alternating current); one end of the first input inductor I3 of the third common-mode transformer T3 is used to connect the third-phase primary alternating current (phase C primary alternating current).

[0043] Each two primary waveform generators 20 are respectively connected to the first input terminal 101 and the second input terminal 102 of a common-mode transformer 10. For example, the first primary waveform generator S1 is connected to the first input terminal A1 of the first common-mode transformer T1; the second primary waveform generator S2 is connected to the second input terminal A2 of the first common-mode transformer T1; the third primary waveform generator S3 is connected to the first input terminal B1 of the second common-mode transformer T2; the fourth primary waveform generator S4 is connected to the second input terminal B2 of the second common-mode transformer T2; the fifth primary waveform generator S5 is connected to the first input terminal C1 of the third common-mode transformer T3; and the sixth primary waveform generator S6 is connected to the second input terminal C2 of the third common-mode transformer T3.

[0044] Each of the two primary waveform generators 20 is configured to control the primary differential-mode high-frequency AC voltage between the first input terminal 101 and the second input terminal 102 of the common-mode transformer 10 and the primary common-mode power-frequency AC voltage at the first midpoint 107 of the common-mode transformer 10. For example, the first primary waveform generator S1 and the second primary waveform generator S2 are configured to control the primary differential-mode high-frequency AC voltage between the first input terminal A1 and the second input terminal A2 of the first common-mode transformer T1 and the primary common-mode power-frequency AC voltage at the first midpoint A0 of the first common-mode transformer T1. The third primary waveform generator S3 and the fourth primary waveform generator S4 are configured to control the primary differential mode high frequency AC voltage between the first input terminal B1 and the second input terminal B2 of the second common mode transformer T2 and the primary common mode industrial frequency AC voltage at the first midpoint B0 of the second common mode transformer T2; the fifth primary waveform generator S5 and the sixth primary waveform generator S6 are configured to control the primary differential mode high frequency AC voltage between the first input terminal C1 and the second input terminal C2 of the third common mode transformer T3 and the primary common mode industrial frequency AC voltage at the first midpoint C0 of the third common mode transformer T3.

[0045] Specifically, each common-mode transformer 10 further includes an iron core, and the first winding 11 and the second winding 12 are connected in series and wound around the iron core. The common-mode transformer 10 further includes a secondary winding 17 arranged on the secondary side, wherein the secondary winding 17 is wound around the iron core. In one embodiment of the present application, the first winding 11 and the second winding 12 are identical. The midpoint of the first winding 11 and the second winding 12, i.e., the first midpoint 107, is connected to a first input inductor 13; one end of the first input inductor 13 is connected to a three-phase input, i.e., a three-phase primary alternating current.

[0046] Common-mode voltage describes the average potential of the voltages at two points; differential-mode voltage describes the relative potential difference between the voltages at two points. As can be seen from the structure of common-mode transformer 10, when external three-phase primary AC power is applied to first midpoint 107 via first input inductor 13, since first winding 11 and second winding 12 are identical, the common-mode voltage is equal to half the sum of the voltages at first input terminal 101 and second input terminal 102; and the differential-mode voltage is equal to the difference between the voltages at second input terminal 102 and first input terminal 101.

[0047] Accordingly, the primary common-mode power frequency AC voltage at the first midpoint A0 of the first common-mode transformer T1 is equal to half the sum of the voltage at the first input terminal A1 and the voltage at the second input terminal A2 of the first common-mode transformer T1, that is, V A0 =(V A1 +V A2 ) / 2, where V A0 V represents the primary common-mode power frequency AC voltage at the first midpoint A0 of the first common-mode transformer T1;A1 represents the voltage at the first input terminal A1 of the first common-mode transformer T1; V A2 represents the voltage at the second input terminal A2 of the first common-mode transformer T1; the primary differential mode voltage between the first input terminal A1 and the second input terminal A2 of the first common-mode transformer T1 is equal to the difference between the voltage at the second input terminal A2 and the voltage at the first input terminal A1 of the first common-mode transformer T1, that is, V A21 =V A2 -V A1 , where V A21 represents the primary differential mode voltage between the first input terminal A1 and the second input terminal A2 of the first common mode transformer T1.

[0048] The primary common-mode power frequency AC voltage at the first midpoint B0 of the second common-mode transformer T2 is equal to half the sum of the voltage at the first input terminal B1 and the voltage at the second input terminal B2 of the second common-mode transformer T2, that is, V B0 =(V B1 +V B2 ) / 2, where V B0 V represents the primary common-mode power frequency AC voltage at the first midpoint B0 of the second common-mode transformer T2; B1 represents the voltage at the first input terminal B1 of the second common-mode transformer T2; V B2 represents the voltage at the second input terminal B2 of the second common-mode transformer T2; the primary differential mode voltage between the first input terminal B1 and the second input terminal B2 of the second common-mode transformer T2 is equal to the difference between the voltage at the second input terminal B2 and the voltage at the first input terminal B1 of the second common-mode transformer T2, that is, V B21 =V B2 -V B1 , where V B21 represents the primary differential mode voltage between the first input terminal B1 and the second input terminal B2 of the second common mode transformer T2.

[0049] The primary common-mode power frequency AC voltage at the first midpoint C0 of the third common-mode transformer T3 is equal to half the sum of the voltage at the first input terminal C1 and the voltage at the second input terminal C2 of the third common-mode transformer T3, that is, V C0 =(V C1 +V C2 ) / 2, where V C0 V represents the primary common-mode power frequency AC voltage at the first midpoint C0 of the third common-mode transformer T3; C1represents the voltage at the first input terminal C1 of the third common-mode transformer T3; v2 represents the voltage at the second input terminal C2 of the third common-mode transformer T3; the primary differential mode voltage between the first input terminal C1 and the second input terminal C2 of the third common-mode transformer T3 is equal to the difference between the voltage at the second input terminal C2 and the voltage at the first input terminal C1 of the third common-mode transformer T3, that is, V C21 =V C2 -V C1 , where V C21 represents the primary differential mode voltage between the first input terminal C1 and the second input terminal C2 of the third common mode transformer T3.

[0050] In one embodiment of the present application, the primary waveform generator 20 is capable of controlling its output voltage and generating a voltage waveform with steps through a control signal. Its output current is bidirectional, that is, when the external voltage is higher than the output voltage of the primary waveform generator 20, the current flows into the primary waveform generator 20, and when the external voltage is lower than the output voltage of the primary waveform generator 20, the current flows out of the primary waveform generator 20.

[0051] Each primary waveform generator 20 has the following control terminals: V+: increases the output voltage by one level, up to +Vmax; V-: decreases the output voltage by one level, up to -Vmax; EPO: emergency shutdown signal, which makes the primary waveform generator 20 high-impedance, capable of withstanding voltages from -Vmax to +Vmax. If the external voltage exceeds this range, the primary waveform generator 20 can absorb the external voltage and simultaneously increase the Vmax value.

[0052] At startup, the voltage of each of the six primary waveform generators 20 is zero, and they are in a high-impedance state. By applying external three-phase AC power (i.e., three-phase primary AC power) to the primary waveform generators 20 and charging them, the Vmax values ​​of each of the six primary waveform generators 20 rise to a level higher than the peak value of the three-phase AC voltage and eventually stabilize.

[0053] Continuously sending signals to the six primary waveform generators 20 so that the first primary waveform generator S1 and the second primary waveform generator S2 control the primary common-mode power frequency AC voltage to meet the following conditions:

[0054] V A0 =(V A1 +V A2 ) / 2=V A sin(ω1t)+V I1

[0055] Among them, V Arepresents the amplitude of the voltage of the first-phase primary AC power (phase A primary AC power); the frequencies of the three-phase primary AC power are consistent, ω1 represents the angular frequency of the three-phase primary AC power, and is equal to the frequency of the primary common-mode power frequency AC voltage; t represents time; ω1t is the phase angle of the primary common-mode power frequency AC voltage output by the first primary waveform generator S1 and the second primary waveform generator S2, that is, the phase angle of the primary common-mode power frequency AC voltage of the first common-mode transformer T1; V I1 Represents the voltage across the first input inductor I1.

[0056] The third primary waveform generator S3 and the fourth primary waveform generator S4 control the primary common-mode power frequency AC voltage to meet the following requirements:

[0057] V B0 =(V B1 +V B2 ) / 2=V B sin(ω1t-120°)+V I2

[0058] Among them, V B represents the voltage amplitude of the second-phase primary AC power (phase B primary AC power); (ω1t-120°) is the phase angle of the primary common-mode power-frequency AC voltage output by the third primary waveform generator S3 and the fourth primary waveform generator S4, that is, the phase angle of the primary common-mode power-frequency AC voltage of the second common-mode transformer T2; V I2 Represents the voltage across the second input inductor I2.

[0059] The fifth primary waveform generator S5 and the sixth primary waveform generator S6 control the primary common-mode power frequency AC voltage to satisfy:

[0060] V C0 =(V C1 +V C2 ) / 2=V C sin(ω1t+120°)+V I3

[0061] Among them, V C represents the amplitude of the third-phase primary AC power (C-phase primary AC power); (ω1t+120°) is the phase angle of the primary common-mode power-frequency AC voltage output by the fifth primary waveform generator S5 and the sixth primary waveform generator S6, that is, the phase angle of the primary common-mode power-frequency AC voltage of the third common-mode transformer T3; V I3 represents the voltage across the third input inductor I3.

[0062] Accordingly, the phase angles of the primary common-mode power-frequency AC voltages of the three common-mode transformers 10 are different. For example, the phase angles of the primary common-mode power-frequency AC voltages of two common-mode transformers 10 (the second common-mode transformer T2 and the third common-mode transformer T3) are different and differ by 120° from the phase angle of the primary common-mode power-frequency AC voltage of the other common-mode transformer 10 (the first common-mode transformer T1). It should be understood that in other embodiments, the phase angles of the primary common-mode power-frequency AC voltages of the two common-mode transformers 10 are different, and the difference between the phase angles of the primary common-mode power-frequency AC voltages of the two common-mode transformers 10 and the phase angle of the primary common-mode power-frequency AC voltage of the other common-mode transformer 10 can be other values.

[0063] In one embodiment of the present application, the amplitude of each phase primary AC signal in the three-phase primary AC signal is consistent, V C =V B =V A =V1.

[0064] The first primary waveform generator S1 and the second primary waveform generator S2 control the primary differential mode power frequency AC voltage to meet the following requirements:

[0065] v A21 =V A2 -V A1 =V2sin(ω2t)

[0066] Among them, the voltages output by the six primary waveform generators 20 under the drive of the three-phase primary AC signal are consistent, V2 represents the amplitude of the voltage output by the primary waveform generator 20 under the drive of the three-phase primary AC signal, and is equal to the amplitude of the primary differential mode power frequency AC voltage; ω2 represents the angular frequency of the voltage output by the primary waveform generator 20 under the drive of the three-phase primary AC signal; ω2t is the phase angle of the primary differential mode voltage output by the first primary waveform generator S1 and the second primary waveform generator S2, that is, the phase angle of the primary differential mode voltage of the first common-mode transformer T1.

[0067] The third primary waveform generator S3 and the fourth primary waveform generator S4 control the primary differential mode power frequency AC voltage to meet the following requirements:

[0068] V B21 =V B2 -V B1 =V2sin(ω2t-120°)

[0069] Wherein, (ω2t-120°) is the phase angle of the primary differential mode voltage output by the third primary waveform generator S3 and the fourth primary waveform generator S4, that is, the phase angle of the primary differential mode voltage of the second common mode transformer T2.

[0070] The fifth primary waveform generator S5 and the sixth primary waveform generator S6 control the primary differential mode power frequency AC voltage to satisfy:

[0071] V C21 =V C2 -V C1 =V2sin(ω2t+120°)

[0072] Wherein, (ω2t+120°) is the phase angle of the primary differential mode voltage output by the fifth primary waveform generator S5 and the sixth primary waveform generator S6, that is, the phase angle of the primary differential mode voltage of the third common mode transformer T3.

[0073] Accordingly, the phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers 10 are different. For example, the phase angles of the primary differential-mode high-frequency AC voltages of two common-mode transformers 10 (the second common-mode transformer T2 and the third common-mode transformer T3) are different and differ by 120° from the phase angle of the primary differential-mode high-frequency AC voltage of the other common-mode transformer 10 (the first common-mode transformer T1). Figure 1 As shown, in one embodiment of the present application, the secondary sides of the three common-mode transformers 10 are independent of each other. It should be understood that in other embodiments, the phase angles of the primary differential-mode power-frequency AC voltages of two common-mode transformers 10 are different, and the difference between the phase angles of the primary differential-mode power-frequency AC voltage of another common-mode transformer 10 and the primary differential-mode power-frequency AC voltage can be other values.

[0074] In this way, a high-frequency AC voltage, i.e., a primary differential-mode high-frequency AC voltage, can be generated across the primary winding of the common-mode transformer 10 (i.e., the first input terminal 101 and the second input terminal 102). Simultaneously, the same high-frequency AC voltage is induced on the secondary side of the common-mode transformer 10. The midpoint voltage of the common-mode transformer 10 is an industrial frequency AC voltage, thereby completing AC-AC conversion without DC. The input three-phase primary AC power is three-phase industrial frequency AC power, and the output is high-frequency AC power.

[0075] It is worth mentioning that when the differential-mode voltage exists (i.e., is not zero), current flows through the two series windings on the primary side, i.e., the first winding 11 and the second winding 12. According to Faraday's law of electromagnetic induction, the AC current flowing through the first winding 11 and the second winding 12 generates a changing magnetic field (magnetic flux), which in turn induces a voltage on the secondary side of the common-mode transformer 10 that is the same as the primary differential-mode high-frequency AC voltage through mutual inductance. This application utilizes the control of the differential-mode voltage and the common-mode voltage to achieve AC-AC conversion without a DC link.

[0076] Specifically, the frequency of the three-phase primary AC signal is relatively low, for example, a 50Hz industrial frequency AC voltage. If a 50Hz industrial frequency AC voltage is applied to a high-frequency solid-state transformer operating at 10kHz or 100kHz, and the three-phase input signal is directly transmitted to the high-frequency solid-state transformer, severe magnetic saturation will immediately occur due to the low rate of change of magnetic flux (too low frequency), causing the core to malfunction or even burn out.

[0077] The present application provides a mechanism that enables a high-frequency solid-state transformer to only withstand high-frequency voltage and effectively separate the lower-frequency power frequency voltage.

[0078] The present application uses a common-mode transformer 10 and a primary waveform generator 20, and actively controls the primary waveform generator 20, thereby achieving voltage decomposition through the common-mode voltage and differential-mode voltage of the common-mode transformer 10. The common-mode voltage is designed to carry an industrial frequency (e.g., 50 Hz) AC voltage and is connected to an external industrial frequency AC grid through a first input inductor 13; this industrial frequency AC voltage does not directly drive the common-mode transformer 10 to generate the high-frequency magnetic flux required for effective power transmission. The differential-mode voltage is accurately synthesized or generated as a high-frequency AC voltage. The industrial frequency AC current under the common-mode voltage is mainly shunted into the first winding 11 and the second winding 12 through the first midpoint 107 of the common-mode transformer 10, replenishing the energy of the primary waveform generator 20. The generated industrial frequency magnetic fluxes will cancel each other out, thereby preventing the establishment of significant industrial frequency magnetic flux that may cause saturation. In other words, the solid-state transformer hardly responds to changes in the magnetic flux of the industrial frequency part. At the same time, the differential-mode voltage drives a high-frequency current through the two series windings, effectively establishing a high-frequency magnetic flux. This high-frequency flux is the actual carrier for transferring energy from the primary to the secondary. This mechanism separates the absorption of power-frequency voltage and current from the transmission of high-frequency energy. The power-frequency portion is primarily responsible for matching the voltage and current of the external grid and processing the power-frequency power. The high-frequency portion focuses on efficient energy transmission and voltage conversion, enabling power transmission using a small solid-state transformer without the need for a bulky power-frequency filter or complex AC-DC rectification prior to the high-frequency transformer to process the low-frequency input. This significantly simplifies the structure of the solid-state transformer, reduces costs, improves efficiency, and provides more flexible control capabilities. This represents a key technological breakthrough in achieving direct AC-AC conversion.

[0079] As mentioned above, a high-frequency AC voltage, i.e., a primary differential-mode high-frequency AC voltage, can be generated at both ends of the primary winding of the common-mode transformer 10 (i.e., the first input terminal 101 and the second input terminal 102). At the same time, the same high-frequency AC voltage can also be induced on the secondary side of the common-mode transformer 10. If the secondary side output of the common-mode transformer 10 is also required to be at the industrial frequency or other low frequency, the secondary side of the common-mode transformer 10 needs to be processed in the same way as the primary side, such as Figure 2 shown.

[0080] Accordingly, in one embodiment of the present application, each common-mode transformer 10 further includes a third winding 14, a fourth winding 15, and a second input inductor 16 disposed on its secondary side. The third winding 14 and the fourth winding 15 are two mutually inducted coils. The opposite-name end of the third winding 14 is the end into which current flows when the magnetic flux directions of the third winding 14 and the fourth winding 15 are opposite; the same-name end of the third winding 14 is the end into which current flows when the magnetic flux directions of the third winding 14 and the fourth winding 15 are the same. The opposite-name end of the fourth winding 15 is the end into which current flows when the magnetic flux directions of the third winding 14 and the fourth winding 15 are opposite. The same-name end of the fourth winding 15 is the end into which current flows when the magnetic flux directions of the third winding 14 and the fourth winding 15 are the same.

[0081] The opposite-name end of the third winding 14 is the fourth input end 104 of the common-mode transformer 10, and the same-name end is connected to the opposite-name end of the fourth winding 15; the same-name end of the fourth winding 15 is the fifth input end 105 of the common-mode transformer 10; there is a second midpoint 108 between the third winding 14 and the fourth winding 15; one end of the second input inductor 16 is connected to the second midpoint 108, and the other end is the sixth input end 106, which is used to connect the secondary three-phase AC power. For example, one end of the second input inductor I4 of the first common-mode transformer T1 is used to connect the first-phase secondary AC power (AA-phase secondary AC power); one end of the second input inductor I5 of the second common-mode transformer T2 is used to connect the second-phase secondary AC power (BB-phase secondary AC power); one end of the second input inductor I6 of the third common-mode transformer T3 is used to connect the third-phase secondary AC power (CC-phase secondary AC power).

[0082] The solid-state transformer based on AC-AC direct transformation further includes six secondary waveform generators 30. The six secondary waveform generators 30 include a first secondary waveform generator SS1, a second secondary waveform generator SS2, a third secondary waveform generator SS3, a fourth secondary waveform generator SS4, a fifth secondary waveform generator SS5, and a sixth secondary waveform generator SS6.

[0083] Wherein, every two of the secondary waveform generators 30 are respectively connected to the fourth input terminal 104 and the fifth input terminal 105 of a common-mode transformer 10. For example, the first secondary waveform generator SS1 is connected to the fourth input terminal AA1 of the first common-mode transformer T1; the second secondary waveform generator SS2 is connected to the fifth input terminal AA2 of the first common-mode transformer T1; the third secondary waveform generator SS3 is connected to the fourth input terminal BB1 of the second common-mode transformer T2; the fourth secondary waveform generator SS4 is connected to the fifth input terminal BB2 of the second common-mode transformer T2; the fifth secondary waveform generator SS5 is connected to the fourth input terminal CC1 of the third common-mode transformer T3; and the sixth secondary waveform generator SS6 is connected to the fifth input terminal CC2 of the third common-mode transformer T3.

[0084] Each of the two secondary waveform generators 30 is configured to control the secondary differential mode AC voltage between the fourth input terminal 104 and the fifth input terminal 105 of the common mode transformer 10 and the secondary common mode power frequency AC voltage at the second midpoint 108 of the common mode transformer 10. For example, the first secondary waveform generator SS1 and the second secondary waveform generator SS2 are configured to control the secondary differential mode AC voltage between the fourth input terminal AA1 and the fifth input terminal AA2 of the first common mode transformer T1 and the secondary common mode power frequency AC voltage at the second midpoint AA0 of the first common mode transformer T1; the third secondary waveform generator SS1 and the second secondary waveform generator SS2 are configured to control the secondary differential mode AC voltage between the fourth input terminal AA1 and the fifth input terminal AA2 of the first common mode transformer T1 and the secondary common mode power frequency AC voltage at the second midpoint AA0 of the first common mode transformer T1; The fourth secondary waveform generator SS3 and the fourth secondary waveform generator SS4 are configured to control the secondary differential mode AC voltage between the fourth input terminal BB1 and the fifth input terminal BB2 of the second common mode transformer T2 and the secondary common mode power frequency AC voltage of the second mid point BB0 of the second common mode transformer T2; the fifth secondary waveform generator SS5 and the sixth secondary waveform generator SS6 are configured to control the secondary differential mode AC voltage between the fourth input terminal CC1 and the fifth input terminal CC2 of the third common mode transformer T3 and the secondary common mode power frequency AC voltage of the second mid point CC0 of the third common mode transformer T3.

[0085] Specifically, the third winding 14 and the fourth winding 15 are connected in series and wound around the iron core. In one embodiment of the present application, the third winding 14 and the fourth winding 15 are identical. The midpoint between the third winding 14 and the fourth winding 15, i.e., the second midpoint 106, is connected to a second input inductor 16; one end of the second input inductor 16 is connected to the three-phase secondary AC power supply.

[0086] The secondary common-mode power frequency AC voltage at the second midpoint AA0 of the first common-mode transformer T1 is equal to half the sum of the voltage at the fourth input terminal AA1 and the voltage at the fifth input terminal AA2 of the first common-mode transformer T1, that is, V AA0 =(V AA1 +V AA2 ) / 2, where V AA0V represents the secondary common-mode power frequency AC voltage at the second midpoint AA0 of the first common-mode transformer T1; AA1 represents the voltage at the fourth input terminal AA1 of the first common-mode transformer T1; V AA2 represents the fifth input terminal AA2 of the first common-mode transformer T1; the secondary differential mode voltage between the fourth input terminal AA1 and the fifth input terminal AA2 of the first common-mode transformer T1 is equal to the difference between the voltage at the fifth input terminal AA2 and the voltage at the fourth input terminal AA1 of the first common-mode transformer T1, that is, V AA21 =V AA2 -V AA1 , where V AA21 represents the secondary differential mode voltage between the fourth input terminal AA1 and the fifth input terminal AA2 of the first common mode transformer T1.

[0087] The secondary common-mode power frequency AC voltage at the second midpoint BB0 of the second common-mode transformer T2 is equal to half the sum of the voltage at the fourth input terminal BB1 and the voltage at the fifth input terminal BB2 of the second common-mode transformer T2, that is, V BB0 =(V BB1 +V BB2 ) / 2, where V BB0 V represents the secondary common-mode power frequency AC voltage at the second midpoint BB0 of the second common-mode transformer T2; BB1 represents the voltage at the fourth input terminal BB1 of the second common-mode transformer T2; V BB2 represents the fifth input terminal BB2 of the second common-mode transformer T2; the secondary differential mode voltage between the fourth input terminal BB1 and the fifth input terminal BB2 of the second common-mode transformer T2 is equal to the difference between the voltage at the fifth input terminal BB2 and the voltage at the fourth input terminal BB1 of the second common-mode transformer T2, that is, V BB21 =V BB2 -V BB1 , where V BB21 represents the secondary differential mode voltage between the fourth input terminal BB1 and the fifth input terminal BB2 of the second common mode transformer T2.

[0088] The secondary common-mode power frequency AC voltage at the second midpoint CC0 of the third common-mode transformer T3 is equal to half the sum of the voltage at the fourth input terminal CC1 and the voltage at the fifth input terminal CC2 of the third common-mode transformer T3, that is, V CC0 =(V CC1 +V CC2 ) / 2, where V CC0 V represents the secondary common-mode power frequency AC voltage at the second midpoint CC0 of the third common-mode transformer T3; CC1 represents the voltage at the fourth input terminal CC1 of the third common-mode transformer T3; V CC2represents the fifth input terminal CC2 of the third common-mode transformer T3; the secondary differential mode voltage between the fourth input terminal CC1 and the fifth input terminal CC2 of the third common-mode transformer T3 is equal to the difference between the voltage at the fifth input terminal CC2 and the voltage at the fourth input terminal CC1 of the third common-mode transformer T3, that is, V CC21 =V CC2 -V CC1 , where V CC21 represents the secondary differential mode voltage between the fourth input terminal CC1 and the fifth input terminal CC2 of the third common mode transformer T3.

[0089] In one embodiment of the present application, the secondary waveform generator 30 is capable of controlling its output voltage and generating a voltage waveform with steps through a control signal. Its output current is bidirectional, that is, when the external voltage is higher than the output voltage of the secondary waveform generator 30, the current flows into the secondary waveform generator 30, and when the external voltage is lower than the output voltage of the secondary waveform generator 30, the current flows out of the secondary waveform generator 30.

[0090] Each secondary waveform generator 30 has the following control terminals: V+: increases the output voltage by one grid, up to +Vmax; V-: decreases the output voltage by one grid, up to -Vmax; EPO: emergency shutdown signal, which makes the secondary waveform generator 30 high-impedance, capable of withstanding voltages from -Vmax to +Vmax. If the external voltage exceeds this range, the secondary waveform generator 30 can absorb the external voltage and simultaneously increase the Vmax value.

[0091] At startup, the voltage of each of the six secondary waveform generators 30 is zero, and they are in a high-impedance state. By inputting and charging the secondary waveform generators 30 with high-frequency AC power induced from the primary side or external three-phase AC power (i.e., three-phase secondary AC voltage), the Vmax values ​​of each of the six secondary waveform generators 30 rise to a level higher than the peak value of the high-frequency AC voltage or the three-phase AC voltage, and eventually stabilize.

[0092] Continuously sending signals to the six waveform generators 30 so that the first secondary waveform generator SS1 and the second secondary waveform generator SS2 control the secondary common-mode power frequency AC voltage to meet the following conditions:

[0093] V AA0 =(V AA1 +V AA2 ) / 2=V AA sin(ω3t)+V I4

[0094] Among them, V AArepresents the amplitude of the first-phase secondary AC (AA-phase secondary AC) signal; the frequencies of the three-phase secondary AC signals are consistent, ω3 represents the angular frequency of the three-phase secondary AC signals, and is equal to the frequency of the secondary common-mode power frequency AC voltage, which may be different from the frequency of the three-phase primary AC signal; t represents time; ω3t is the phase angle of the secondary common-mode power frequency AC voltage output by the first secondary waveform generator SS1 and the second secondary waveform generator SS2, that is, the phase angle of the secondary common-mode power frequency AC voltage of the first common-mode transformer T1; V I4 represents the voltage across the second input inductor I4.

[0095] The third secondary waveform generator SS3 and the fourth secondary waveform generator SS4 control the secondary common-mode power frequency AC voltage to meet the following requirements:

[0096]

[0097] Among them, V BB Indicates the amplitude of the B second-phase secondary AC current (BB phase secondary AC current) signal; V is the phase angle of the secondary common-mode power-frequency AC voltage output by the third secondary waveform generator SS3 and the fourth secondary waveform generator SS4, that is, the phase angle of the secondary common-mode power-frequency AC voltage of the second common-mode transformer T2; I5 represents the voltage across the second input inductor I5.

[0098] The fifth secondary side waveform generator SS5 and the sixth secondary side waveform generator SS6 control the secondary side common mode power frequency AC voltage to meet the following requirements:

[0099]

[0100] Among them, V CC Indicates the amplitude of the C third phase secondary AC (CC phase secondary AC) signal; V is the phase angle of the secondary common-mode power-frequency AC voltage output by the fifth secondary waveform generator SS5 and the sixth secondary waveform generator SS6, that is, the phase angle of the secondary common-mode power-frequency AC voltage of the third common-mode transformer T3; I6 represents the voltage across the third input inductor I6.

[0101] In one embodiment of the present application, the amplitude of each phase of the three-phase secondary AC signal is consistent, V CC =V BB =V AA =V3.

[0102] The first secondary side waveform generator SS1 and the second secondary side waveform generator SS2 control the secondary side differential mode voltage to meet the following requirements:

[0103] V AA21 =VAA2 -V AA1 =V4sin(ω2t)

[0104] Among them, the voltages output by the six secondary waveform generators 30 under the drive of the three-phase secondary AC voltage are consistent, V4 represents the amplitude of the high-frequency voltage output by the secondary waveform generator 30 under the drive of the three-phase secondary AC voltage, and is equal to the amplitude of the secondary differential-mode high-frequency AC voltage; the frequency of the voltage output under the drive of the three-phase secondary AC voltage is equal to the frequency of the voltage output under the drive of the three-phase secondary AC power, and is equal to the frequency of the secondary differential-mode high-frequency AC voltage; ω2t is the phase angle of the secondary differential-mode high-frequency AC voltage output by the first secondary waveform generator SS1 and the second secondary waveform generator SS2, that is, the phase angle of the secondary differential-mode high-frequency AC voltage of the first common-mode transformer T1. According to the transformer principle, this phase angle is the same as the phase angle of the primary side of the common-mode transformer 10.

[0105] The third secondary waveform generator SS3 and the fourth secondary waveform generator SS4 control the secondary differential mode voltage to meet the following requirements:

[0106] V BB21 =V BB2 -V BB1 =V4sin(ω2t-120°)

[0107] Among them, (ω2t-120°) is the phase angle of the secondary differential-mode high-frequency AC voltage output by the third secondary waveform generator SS3 and the fourth secondary waveform generator SS4, that is, the phase angle of the secondary differential-mode high-frequency AC voltage of the second common-mode transformer T2. This phase angle is the same as the phase angle of the primary side of the common-mode transformer 10.

[0108] The voltages of the fifth secondary waveform generator SS5 and the sixth secondary waveform generator SS6 satisfy:

[0109] V CC21 =V CC2 -V CC1 =V4sin(ω2t+120°)

[0110] Among them, (ω2t+120°) is the phase angle of the secondary differential-mode high-frequency AC voltage output by the fifth secondary waveform generator SS5 and the sixth secondary waveform generator SS6, that is, the phase angle of the secondary differential-mode high-frequency AC voltage of the third common-mode transformer T3. This phase angle is the same as the phase angle of the primary side of the common-mode transformer 10.

[0111] If the phase angles of the secondary common-mode power frequency AC voltages of the three common-mode transformers 10 (the first common-mode transformer T1, the second common-mode transformer T2, and the third common-mode transformer T3) are the same, that is, The common-mode transformer 10 outputs a single-phase voltage. Therefore, in addition to the voltage conversion function of traditional transformers, solid-state transformers can also perform a variety of new conversions, such as multi-phase to single-phase, single-phase to multi-phase, power frequency to high frequency, power frequency to power frequency, and power frequency to low frequency. These conversions are applicable to a variety of fields, including high-speed rail, high-frequency heat transfer, and medium-frequency smelting, which are not listed here.

[0112] It is worth mentioning that if the secondary sides of three common-mode transformers 10 are required to output single-phase secondary AC power, the three common-mode transformers 10 can be integrated into one common-mode transformer 10, wherein the secondary sides of the three common-mode transformers 10 are shared, such as Figure 3 As shown. The secondary sides of the three common-mode transformers 10 are not provided with the third winding 14, the fourth winding 15, and the second input inductor 16. The solid-state transformer based on AC-AC direct conversion is not provided with six secondary waveform generators 30. The phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers 10 are equal, that is, V AA2 -V AA1 =V BB2 -V BB1 =V CC2 -V CC1 .

[0113] If three common mode transformers 10 are required to output three-phase AC power from their secondary sides, Figure 2 The cores of the three common-mode transformers 10 in the solid-state transformer are connected, and the three common-mode transformers 10 form a three-phase three-column structure, as shown in FIG. Figure 4 As shown, the calculation method of the primary differential mode high frequency AC voltage, the primary common mode power frequency AC voltage, the secondary differential mode AC voltage and the secondary common mode power frequency AC voltage is the same as Figure 2 The calculation method of the primary differential-mode high-frequency AC voltage, the primary common-mode power-frequency AC voltage, the secondary differential-mode high-frequency AC voltage, and the secondary common-mode power-frequency AC voltage of the solid-state transformer shown is the same.

[0114] Based on the working mode of the solid-state transformer of AC-AC direct conversion, this application proposes a current conversion method for solid-state transformer. Figure 5 As shown, a current conversion method for a solid-state transformer is described. The current conversion method for a solid-state transformer includes the following steps: S110, connecting a three-phase primary AC power source; S120, generating a primary differential-mode high-frequency AC voltage and a primary common-mode power-frequency AC voltage based on the voltage of the three-phase primary AC power source, so that the solid-state transformer directly converts the power-frequency AC voltage into a high-frequency AC voltage without undergoing DC conversion.

[0115] In one embodiment of the present application, in step S110, three-phase primary AC power is connected. Specifically, the three-phase primary AC power comes from a power grid.

[0116] In one embodiment of the present application, step S120 includes: generating a primary differential-mode high-frequency AC voltage with three-phase different phase angles based on the voltage of the three-phase primary AC power; generating a primary common-mode industrial frequency AC voltage with three-phase different phase angles based on the voltage of the three-phase primary AC power.

[0117] In another embodiment of the present application, step S120 includes: generating a primary differential-mode high-frequency AC voltage with the same three-phase phase angle based on the voltage of the three-phase primary AC power; and generating a primary common-mode industrial frequency AC voltage with different three-phase phase angles based on the voltage of the three-phase primary AC power.

[0118] In one embodiment of the present application, a voltage equal to the primary differential-mode high-frequency AC voltage is induced on the secondary side of the common-mode transformer by mutual inductance. The current conversion method for a solid-state transformer further includes the step of: inducing a voltage equal to the primary differential-mode high-frequency AC voltage on the secondary side of the common-mode transformer by mutual inductance.

[0119] In another embodiment of the present application, a voltage is output on the secondary side of the common-mode transformer by other means. Specifically, the current conversion method for a solid-state transformer further includes the steps of: connecting a three-phase secondary AC power supply; and generating a secondary differential-mode AC voltage and a secondary common-mode power-frequency AC voltage based on the voltage of the three-phase secondary AC power supply.

[0120] In summary, the solid-state transformer based on direct AC-AC conversion and its power conversion method have been described. The solid-state transformer based on direct AC-AC conversion controls the primary differential-mode high-frequency AC voltage and the primary common-mode power-frequency AC voltage of the common-mode transformer 10 via the primary waveform generator 20, directly converting AC power into AC power. This simplifies the power conversion method, simplifies the structure of the solid-state transformer, and reduces costs.

[0121] The above description of the present application and its embodiments is non-limiting. The drawings show only one embodiment of the present application, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the inventive purpose of this application, designs a structure and embodiment similar to this technical solution without creatively designing, they shall fall within the scope of protection of this application.

Claims

1. A solid-state transformer based on AC-AC direct conversion, characterized in that: include: Three common-mode transformers, each comprising a first winding, a second winding, and a first input inductor disposed on its primary side, wherein the opposite-name end of the first winding serves as the first input terminal of the common-mode transformer, and the same-name end is connected to the opposite-name end of the second winding; the same-name end of the second winding serves as the second input terminal of the common-mode transformer; a first midpoint is defined between the first winding and the second winding; one end of the first input inductor is connected to the first midpoint, and the other end serves as a third input terminal for connection to three-phase primary alternating current; Six primary waveform generators, wherein every two of the primary waveform generators are respectively connected to the first input terminal and the second input terminal of a common-mode transformer, and are configured to control the primary differential-mode high-frequency AC voltage between the first input terminal and the second input terminal of the common-mode transformer and the primary common-mode power-frequency AC voltage at the first midpoint of the common-mode transformer.

2. The solid-state transformer based on AC-AC direct conversion according to claim 1, characterized in that: The phase angles of the primary common-mode power-frequency AC voltages of the three common-mode transformers are different.

3. The solid-state transformer based on AC-AC direct conversion according to claim 1, characterized in that: The phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers are different.

4. The solid-state transformer based on AC-AC direct conversion according to claim 2, characterized in that: The secondary sides of the three common-mode transformers are shared; the phase angles of the primary differential-mode high-frequency AC voltages of the three common-mode transformers are equal, so that the secondary sides of the three common-mode transformers output single-phase high-frequency voltages.

5. The solid-state transformer based on AC-AC direct conversion according to claim 3, characterized in that: Each common-mode transformer also includes a third winding, a fourth winding and a second input inductor arranged on its secondary side, wherein the opposite-name end of the third winding is the fourth input terminal of the common-mode transformer, and the same-name end is connected to the opposite-name end of the fourth winding; the same-name end of the fourth winding is the fifth input terminal of the common-mode transformer; there is a second midpoint between the third winding and the fourth winding; one end of the second input inductor is connected to the second midpoint, and the other end is the sixth input terminal, which is used to connect the secondary AC three-phase power; the solid-state transformer based on AC-AC direct transformation also includes six secondary waveform generators, wherein every two of the secondary waveform generators are respectively connected to the fourth input terminal and the fifth input terminal of a common-mode transformer, and are configured to control the secondary differential-mode AC voltage between the fourth input terminal and the fifth input terminal of the common-mode transformer and the secondary common-mode industrial frequency AC voltage at the second midpoint of the common-mode transformer.

6. The solid-state transformer based on AC-AC direct conversion according to claim 5, characterized in that: The three common-mode transformers form a three-phase three-column structure.

7. A current conversion method for a solid-state transformer, characterized in that: include: Connect three-phase primary AC power; A primary differential-mode high-frequency AC voltage and a primary common-mode power-frequency AC voltage are generated based on the voltage of the three-phase primary AC power, so that the solid-state transformer directly converts the power-frequency AC voltage into a high-frequency AC voltage without DC conversion.

8. The current conversion method for a solid-state transformer according to claim 7, characterized in that: The primary differential-mode high-frequency AC voltage and the primary common-mode power-frequency AC voltage are generated based on the voltage of the three-phase primary AC power, including: Generate primary differential-mode high-frequency AC voltages with three-phase different phase angles based on the voltage of the three-phase primary AC power; Based on the voltage of the three-phase primary AC power, three-phase primary common-mode power frequency AC voltages with different phase angles are generated.

9. The current conversion method for a solid-state transformer according to claim 7, characterized in that: The primary differential-mode high-frequency AC voltage and the primary common-mode power-frequency AC voltage are generated based on the voltage of the three-phase primary AC power, including: Generate primary differential-mode high-frequency AC voltages with the same three-phase phase angles based on the voltage of the three-phase primary AC power; Based on the voltage of the three-phase primary AC power, three-phase primary common-mode power frequency AC voltages with different phase angles are generated.

10. The current conversion method for a solid-state transformer according to claim 7, characterized in that: Current conversion methods for solid-state transformers also include: Connect the three-phase secondary AC power; A secondary side differential mode AC voltage and a secondary side common mode power frequency AC voltage are generated based on the voltage of the three-phase secondary side AC power.

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