A three-phase static ferromagnetic transformer-frequency converter for power transmission

Abstract

This invention discloses a three-phase static ferromagnetic transformer-frequency converter for power transmission, comprising a core section with three cores forming a non-closed delta circuit. Three-phase input windings are arranged inside the core section, two of which include phase-shifting portions. Three-phase output windings are arranged outside the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected. This device has three-phase symmetrical input and output, and possesses the capability to transform and convert power from 50 / 3Hz to 50Hz. It does not require separate power electronic equipment support, nor does it require rotation for magnetic field modulation. The device exhibits low input and output current harmonics, offering superior economy and reliability compared to power electronic frequency converters. It is suitable for frequency division transmission systems and other frequency doubling scenarios requiring high power quality.

Description

Technical Field

[0001] This invention belongs to the technical field of frequency converters for power transmission, specifically a three-phase static ferromagnetic transformer frequency converter for power transmission. Background Technology

[0002] With the vigorous development of large-scale wind and solar power generation, the geographical distribution characteristics of power sources and loads mean that a large amount of onshore renewable energy cannot be consumed locally, thus facing the practical problem of long-distance, efficient transmission. Meanwhile, for large-scale offshore wind power along the coast, especially deep-sea, large-capacity offshore wind power, the initial investment and operation and maintenance costs of offshore converter stations remain high when using flexible direct current transmission, severely impacting the economic viability of the transmission method. Therefore, an efficient and economical deep-sea wind power transmission method is urgently needed. Furthermore, with the continuous advancement of the "dual carbon" target, the construction of new power systems also presents new demands for new power transmission methods.

[0003] In 1994, Academician Wang Xifan of Xi'an Jiaotong University first proposed a novel power transmission method—Fractional Frequency Transmission System (FFTS). FFTS reduces line reactance, allowing its transmission capacity to be multiplied. For example, when the transmission line frequency is reduced to 50 / 3Hz, the theoretical maximum transmission power increases to three times its original value, essentially reaching the thermal limit of the transmission line. Various technical indicators of the line, such as end-of-line voltage, compensation capacity, and voltage fluctuation, are significantly improved. Furthermore, the increased maximum transmission power can drastically reduce the number of line loops, saving transmission corridor space. FFTS offers good operational performance and numerous advantages, making it a promising power transmission method. The core factor restricting its development is the limitation of frequency converters. High-power frequency converters based on power electronic devices have complex structures, large control systems, low overall reliability, and high investment and maintenance costs, making them difficult to apply in harsh environments such as offshore wind power. Ferromagnetic frequency converters based on motors rely on rotor rotation and magnetic field modulation, resulting in high mechanical losses and operating noise, and still have significant room for improvement in long-term operating costs and reliability. Therefore, further research on static ferromagnetic transformer frequency converters is urgently needed for the further application of frequency division transmission systems.

[0004] In the research of rotary ferromagnetic power conversion devices, GE in the United States began developing variable frequency transformers in the 1990s and successfully applied them to the power grid in the early 21st century. The core technology involves rotary transformers with three-phase windings on both the stator and rotor sides. A DC motor drive system ensures the synchronization of the equivalent rotor magnetic field with the stator magnetic field in the rotational space, thereby adjusting the phase difference between the rotor magnetic field and the stator magnetic field, thus changing the direction and magnitude of the active power transmitted by the variable frequency transformer. However, its efficiency is relatively low. In the research of static ferromagnetic power conversion devices, researchers at the University of Toronto in Australia have manufactured a static ferromagnetic triple-frequency transformer for metal smelting, but it only has single-phase output capability, low output efficiency, and high harmonics, making it difficult to apply in the power transmission field. Summary of the Invention

[0005] This invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, which solves the problems of low output efficiency, large harmonics, and difficulty in applying existing frequency converters to the power transmission field.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A three-phase static ferromagnetic transformer frequency converter for power transmission includes a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is disposed on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is disposed on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0008] Preferably, the input winding does not contain any third-order or multiple-order harmonic paths.

[0009] Preferably, the output winding contains only third-order and multiples of harmonic current.

[0010] Preferably, the non-closed triangular circuit composed of the three iron cores contains a third harmonic magnetic flux path.

[0011] Preferably, the iron core consists of a saturated core column and an unsaturated magnetic yoke.

[0012] Preferably, the three-phase output windings are delta connected.

[0013] Preferably, each input winding of the three-phase input winding comprises three sets of windings.

[0014] Preferably, each output winding of the three-phase output winding comprises three sets of windings.

[0015] Preferably, the output frequency of the output winding is three times that of the input winding.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a three-phase static ferromagnetic transformer-frequency converter for power transmission, including an iron core part, wherein the iron core part includes three iron cores, the three iron cores forming a non-closed delta circuit, and a three-phase input winding is provided on the inner side of the iron core part, wherein two phase input windings include a phase-shifting part, and a three-phase output winding is provided on the outer side of the iron core part corresponding to the three-phase input windings, the three-phase output windings being interconnected. This device has three-phase symmetrical input and output, and has the capability of transformer-frequency conversion of 50 / 3Hz to 50Hz power. It does not require separate power electronic equipment support, does not require rotation for magnetic field modulation, and the input and output current harmonics of the device are both low. Compared with power electronic frequency converters, it has better economy and reliability, and is suitable for frequency division transmission systems and other frequency doubling scenarios requiring high power quality.

[0017] Furthermore, the device contains no rotating parts, avoiding mechanical loss and equipment wear. In addition to lower operating noise, it also has better economy and reliability.

[0018] Furthermore, the proposed three-phase static ferromagnetic transformer-frequency converter has three-phase symmetrical output capability, which can meet the requirements of different voltage level conversion in the frequency division transmission system, meet the frequency conversion performance requirements, have fewer output harmonics, and do not pollute the power grid, thus stably and reliably realizing the frequency and voltage level conversion function. Attached Figure Description

[0019] Figure 1 This invention provides a typical structure for a three-phase static ferromagnetic transformer-frequency converter for power transmission.

[0020] Figure 2 The result of the voltage frequency conversion simulation is shown in the figure.

[0021] Figure 3 The figure shows the simulation results of voltage frequency conversion based on actual experimental measurements. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0027] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] like Figure 1 As shown, the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0030] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0031] The input winding does not contain any third-order or multiple-order harmonic paths.

[0032] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0033] The output winding contains only third-order and multiples of harmonic current.

[0034] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0035] The non-closed triangular circuit composed of the three iron cores contains a third harmonic magnetic flux path.

[0036] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0037] The iron core consists of a saturated core column and an unsaturated magnetic yoke.

[0038] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0039] The three-phase output windings are connected in a delta configuration.

[0040] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0041] Each input winding of the three-phase input winding comprises three sets of windings.

[0042] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0043] Each of the three-phase output windings comprises three sets of windings.

[0044] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two phase input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

[0045] The output frequency of the output winding is three times that of the input winding.

[0046] Another embodiment of the present invention provides a three-phase static ferromagnetic transformer frequency converter for power transmission, including an input winding, an output winding and an iron core. Figure 1 Based on the typical topology of a three-phase static ferromagnetic transformer-frequency converter for power transmission, the input windings include an A-phase winding composed of windings A1, A2, and A3; a B-phase winding composed of windings B1, B2, and B3 (including phase-shifting components); and a C-phase winding composed of windings C1, C2, and C3 (including phase-shifting components). The output windings include an a-phase winding composed of windings a1, a2, and a3; a b-phase winding composed of windings b1, b2, and b3; and a c-phase winding composed of windings c1, c2, and c3. In the diagram, terminals A, B, and C are the three-phase voltage input terminals with a frequency of f, and terminals a, b, and c are the three-phase voltage output terminals with a frequency of 3f.

[0047] The A-phase, B-phase, and C-phase windings of the input side windings do not contain any third-order or multiple-order harmonic paths, meaning that the current flowing through each phase winding does not contain third-order or multiple-order harmonic currents. The a-phase, b-phase, and c-phase windings of the output side windings contain only third-order or multiple-order harmonic paths, meaning that the current flowing through each phase winding contains only third-order or multiple-order harmonic currents.

[0048] Research process:

[0049] This invention is based on the nonlinear constitutive relation of ferromagnetic materials and the law of electromagnetic induction:

[0050] B(t)=μ(H(t))H(t)

[0051]

[0052] Where B(t) is the magnetic induction intensity, H(t) is the magnetic field strength, μ is the magnetic permeability, which is nonlinearly related to the magnetic field strength, ε(t) is the induced electromotive force on the winding, and S is the cross section of the saturated iron core; by removing the third harmonic path and multiples thereof in the input winding and the nonlinear constitutive relationship of the ferromagnetic material, the third harmonic magnetic flux is generated in the iron core, and only the third harmonic path and multiples thereof are retained in the output winding to realize the function of power frequency conversion.

[0053] Without loss of generality, neglecting higher harmonics, we assume that the cardiac column magnetic flux consists only of the fundamental flux and the third flux, and denote the ratio of the third flux to the fundamental flux as x, i.e., φ3 = xφ1. Therefore, the cardiac column magnetic flux can be written as:

[0054]

[0055] Where ω1 is the fundamental angular frequency, Assuming the initial phase of the magnetic flux, taking phase a as an example, and neglecting the voltage drop across the winding resistance, the output voltage can be written as:

[0056]

[0057] After simplification, we get:

[0058]

[0059] Where N1 and N2 are the number of winding turns on the input side and the output side, respectively.

[0060] Furthermore, the magnitudes of the space vectors after the input and output three-phase voltages are combined can be written as follows:

[0061] U1≈ω1N1φ1

[0062] U2=9ω1N2φ3

[0063] In the formula, U1 and U2 are the magnitudes of the combined space vectors of the three-phase voltages on the input and output sides, respectively. From the above formula, we can obtain:

[0064]

[0065] The above formula enables the transformation function.

[0066] Therefore, based on the above principle, the basic functions of the proposed three-phase static ferromagnetic transformer frequency converter for power transmission are realized.

[0067] Implementation results:

[0068] Using finite element simulation software, a three-phase static ferromagnetic transformer-frequency converter was applied to a frequency-division power transmission system, where the equipment input frequency was 50 / 3Hz. Figure 2 The simulation results of the voltage frequency conversion are shown in the figure. When the input voltage frequency is 50 / 3Hz, the output voltage frequency becomes 50Hz after passing through the three-phase static ferromagnetic transformer frequency converter, thus realizing the frequency conversion function.

[0069] Using the proposed principle, a three-phase static ferromagnetic transformer-frequency converter was fabricated as a prototype for use in a frequency-division transmission system. The transformer-frequency conversion performance of the prototype was verified through dynamic simulation tests of the power system. Figure 3 The experimental voltage-frequency conversion simulation results shown in the figure indicate that when the input voltage frequency is 50 / 3Hz, after passing through the three-phase static ferromagnetic transformer-frequency converter, the output voltage frequency becomes 50Hz. The output voltage has high three-phase symmetry and low harmonic content, which proves the good voltage-frequency conversion performance of the proposed device.

[0070] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art, guided by the specification, can make many other modifications without departing from the scope of the claims of the present invention, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A three-phase static ferromagnetic transformer-frequency converter for power transmission, characterized in that, The system includes a core section comprising three cores forming a non-closed delta circuit. A three-phase input winding is provided on the inner side of the core section, wherein two of the input windings include a phase-shifting portion. A three-phase output winding is provided on the outer side of the core section corresponding to the three-phase input windings, and the three-phase output windings are interconnected.

2. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The input winding does not contain any third-order or multiple-order harmonic paths.

3. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The output winding contains only third-order and multiples of harmonic current.

4. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The non-closed triangular circuit composed of the three iron cores contains a third harmonic magnetic flux path.

5. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The iron core consists of a saturated core column and an unsaturated magnetic yoke.

6. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The three-phase output windings are connected in a delta configuration.

7. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, Each input winding of the three-phase input winding comprises three sets of windings.

8. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, Each of the three-phase output windings comprises three sets of windings.

9. A three-phase static ferromagnetic transformer-frequency converter for power transmission according to claim 1, characterized in that, The output frequency of the output winding is three times that of the input winding.

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