Nine-bridge-arm multi-frequency three-port current converter suitable for I / low frequency-direct current interaction

Abstract

The invention discloses a nine-bridge-arm multi-frequency three-port current converter suitable for power / low frequency-direct current interaction, which is connected with a power frequency system, a direct current system and a low frequency system and comprises an upper bridge arm, a lower bridge arm and a middle bridge arm, the output end of the power frequency system is connected with the positive electrode of the direct-current system through the upper bridge arm. The output end of the low-frequency system is connected with the cathode of the direct-current system through the lower bridge arm; the output end of the power frequency system is connected with the output end of the low frequency system through the intermediate bridge arm; the converter converts three-phase voltage and current of a low-frequency system into three-phase voltage and current of a power frequency system and outputs direct-current voltage on the direct-current side, and the converter can achieve power conversion of power frequency alternating current, direct current and low-frequency alternating current.

Description

Technical Field

[0001] This invention belongs to the field of converter topology for flexible AC / DC transmission systems, and relates to a nine-arm multi-frequency three-port converter suitable for industrial / low-frequency DC-DC interaction. Background Technology

[0002] In recent years, flexible low-frequency power transmission technology has become a research hotspot in the power transmission field. Without increasing the voltage level, it reduces the electrical distance of AC transmission lines by lowering the transmission frequency, alleviates the charging current problem of submarine cables, reduces transmission losses, and thus improves the capacity and efficiency of wind power transmission. It has great advantages in large-capacity, long-distance offshore wind power transmission scenarios.

[0003] Frequency converters are the core components of flexible low-frequency power transmission systems. Currently, frequency conversion is mainly achieved through power electronic devices, but this requires a large number of power electronic devices, resulting in high costs and complex control issues. With the continuous development of flexible low-frequency power transmission technology, future power grids will contain multiple frequencies, including power frequency, low frequency, and DC. However, traditional converters can only realize energy exchange between AC-AC and AC-DC electrical quantities, and there is limited research on equipment that can directly realize power frequency AC-DC-low frequency AC power conversion. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a nine-arm multi-frequency three-port converter suitable for industrial / low-frequency DC-DC interaction, which can realize power conversion from industrial frequency AC to DC to low-frequency AC.

[0005] To achieve the above objectives, the present invention discloses a nine-arm multi-frequency three-port converter suitable for industrial / low-frequency-DC interaction, which is connected to an industrial frequency system, a DC system and a low-frequency system, and includes an upper arm, a lower arm and a middle arm. The output terminal of the power frequency system is connected to the positive terminal of the DC system via the upper bridge arm; The output of the low-frequency system is connected to the negative terminal of the DC system via the lower bridge arm; The output of the power frequency system is connected to the output of the low frequency system via an intermediate bridge arm.

[0006] The converter converts the three-phase voltage and current of the low-frequency system into the three-phase voltage and current of the power frequency system, and outputs DC voltage on the DC side.

[0007] Furthermore, the intermediate bridge arm is composed of an inductor L, an equivalent resistance R, and N full-bridge sub-modules connected in series.

[0008] Furthermore, the full-bridge submodule in the intermediate bridge arm includes fully controlled insulated-gate bipolar transistors (IGBTs) VT1, VT2, VT3, and VT4, diodes VD1, VD2, VD3, and VD4, a DC capacitor C, and ports P1 and P2. The positive terminal of the DC capacitor C is connected to the collectors of both IGBTs VT1 and VT3, while the negative terminal of the DC capacitor C is connected to the emitter of IGBT VT2 and the emitter of IGBT VT3. The emitter of transistor VT4 is connected to the fully controlled insulated-gate bipolar transistor (IGBT). The emitter of fully controlled IGBT VT1 is connected to the collector and port P1 of fully controlled IGBT VT2. The emitter of fully controlled IGBT VT3 is connected to the collector and port P2 of fully controlled IGBT VT4. Diode VD1 is connected in parallel with fully controlled IGBT VT1; diode VD2 is connected in parallel with fully controlled IGBT VT2; diode VD3 is connected in parallel with fully controlled IGBT VT3; and diode VD4 is connected in parallel with fully controlled IGBT VT4.

[0009] Furthermore, during normal operation, the fully controlled insulated gate bipolar transistor VT1 and VT2 are turned on alternately, and the fully controlled insulated gate bipolar transistor VT3 and VT4 are turned on alternately.

[0010] Furthermore, when a DC system fault occurs, all fully controlled insulated-gate bipolar transistors in the intermediate bridge arm are in the off state.

[0011] Furthermore, both the upper and lower bridge arms are composed of an inductor L, an equivalent resistance R, and N / 2 simplified full-bridge twin sub-modules connected in series.

[0012] Furthermore, the simplified full-bridge twin module includes a first output terminal P1, a second output terminal P2, a first transistor VT1, a second transistor VT2, a third transistor VT3, a fourth transistor VT4, a fifth transistor VT5, a sixth transistor VT6, a first diode VD1, a second diode VD2, a third diode VD3, a fourth diode VD4, a fifth diode VD5, a sixth diode VD6, a seventh diode VD7, an eighth diode VD8, a first DC capacitor C1, and a second DC capacitor C2. The first DC capacitor C1, the first transistor VT1, the second transistor VT2, the first diode VD1, and the second diode VD2 form a first half-bridge module; the second DC capacitor C1, the third transistor VT3, the fourth transistor VT4, the third diode VD3, and the fourth diode VD4 form a second half-bridge module.

[0013] Furthermore, during normal operation, the fifth transistor VT5 and the sixth transistor VT6 are always in the on state, the first transistor VT1 and the second transistor VT2 are turned on alternately, and the third transistor VT3 and the fourth transistor VT4 are turned on alternately.

[0014] Furthermore, when the DC system fails, all transistors in the upper and lower bridge arms are in the off state.

[0015] Furthermore, the converter is used for electric drive and as a high-voltage, high-power power source, as well as for connecting new energy power sources such as low-frequency offshore wind power, low-frequency onshore wind power, and low-frequency photovoltaic power to the industrial frequency grid and for connecting to inter-frequency AC systems.

[0016] The present invention has the following beneficial effects: The nine-arm multi-frequency three-port converter of this invention, applicable to AC / low-frequency DC-DC interaction, converts the three-phase voltage and current of the low-frequency system into the three-phase voltage and current of the power frequency system during operation, and outputs a stable DC voltage on the DC side, realizing power conversion from power frequency AC to DC to low-frequency AC. It is widely applicable to high-voltage, high-power power conversion applications, providing a new path for large-capacity, long-distance offshore wind power transmission. Compared to existing technologies, this invention can realize a converter topology with three-port functionality, such as the back-to-back modular multilevel converter (BTB-MMC). Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a structural diagram of the present invention; Figure 2 This is a structural diagram of the sub-module of the middle bridge arm in this invention; Figure 3 This is a fault current path diagram for the intermediate bridge arm submodule during a DC system fault. Figure 4 This is a structural diagram of the upper bridge arm and lower bridge arm sub-modules in this invention; Figure 5 This is a fault current path diagram for the upper and lower bridge arm submodules during a DC system fault. Detailed Implementation

[0019] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0023] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0024] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0025] 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, not all, of the embodiments of the present invention. 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. Therefore, the following detailed description of the embodiments of the present 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 present invention without inventive effort are within the scope of protection of the present invention.

[0026] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0027] Example 1 refer to Figure 1 The present invention describes a nine-arm multi-frequency three-port converter suitable for industrial / low-frequency DC-DC interaction, which is connected to an industrial frequency system, a DC system, and a low-frequency system. It includes an upper arm, a lower arm, and a middle arm. The output terminal of the industrial frequency system is connected to the positive terminal of the DC system via the upper arm; the output terminal of the low-frequency system is connected to the negative terminal of the DC system via the lower arm; and the output terminal of the industrial frequency system is connected to the output terminal of the low-frequency system via the middle arm.

[0028] The intermediate bridge arm is composed of an inductor L, an equivalent resistance R, and N full-bridge sub-modules connected in series. Each full-bridge sub-module in the intermediate bridge arm includes a fully controlled insulated-gate bipolar transistor (IGBT) VT1, VT2, VT3, VT4, diodes VD1, VD2, VD3, and VD4, a DC capacitor C, and ports P1 and P2. The positive terminal of the DC capacitor C is connected to the collectors of IGBTs VT1 and VT3, and the negative terminal of the DC capacitor C is connected to the collector of IGBT VT2. The emitter of the fully controlled insulated-gate bipolar transistor (IGBT) VT4 is connected to the emitter of the fully controlled IGBT VT1, the collector of the fully controlled IGBT VT2 and port P1 are connected to the emitter of the fully controlled IGBT VT3, and the collector of the fully controlled IGBT VT4 and port P2 are connected to the emitter of the fully controlled IGBT VT4. Diode VD1 is connected in parallel with the fully controlled IGBT VT1; diode VD2 is connected in parallel with the fully controlled IGBT VT2; diode VD3 is connected in parallel with the fully controlled IGBT VT3; and diode VD4 is connected in parallel with the fully controlled IGBT VT4.

[0029] Both the upper and lower bridge arms are composed of an inductor L, an equivalent resistance R, and N / 2 simplified full-bridge twin modules connected in series. The simplified full-bridge twin module includes a first output terminal P1, a second output terminal P2, a first transistor VT1, a second transistor VT2, a third transistor VT3, a fourth transistor VT4, a fifth transistor VT5, a sixth transistor VT6, a first diode VD1, a second diode VD2, a third diode VD3, a fourth diode VD4, a fifth diode VD5, a sixth diode VD6, a seventh diode VD7, an eighth diode VD8, a first DC capacitor C1, and a second DC capacitor C2. The first DC capacitor C1, the first transistor VT1, the second transistor VT2, the first diode VD1, and the second diode VD2 form the first half-bridge module. The second DC capacitor C1, the third transistor VT3, the fourth transistor VT4, the third diode VD3, and the fourth diode VD4 form the second half-bridge module.

[0030] Example 2 refer to Figure 1The nine-arm multi-frequency three-port converter applicable to industrial / low-frequency DC-DC interaction according to the present invention includes nine arms, wherein each of the nine arms includes three upper arms, three lower arms and three middle arms. The output terminal of the industrial frequency system is connected to the positive terminal of the DC system through the upper arms, the output terminal of the low-frequency system is connected to the negative terminal of the DC system through the lower arms, and the output terminal of the industrial frequency system is connected to the output terminal of the low-frequency system through the middle arms.

[0031] The converter described in this invention converts the three-phase voltage and current of a low-frequency system into the three-phase voltage and current of a power-frequency system, and outputs a stable DC voltage on the DC side, realizing energy exchange between three different frequency systems. The low-frequency system is the input system, and the power-frequency system and DC system are the output systems. The frequency of the low-frequency system includes, but is not limited to, 20Hz, and the frequency of the power-frequency system is 50Hz.

[0032] like Figure 1 As shown, the nine bridge arms are connected sequentially in the order of pu, pv, pw, ua, vb, wc, an, bn, cn. Correspondingly, each bridge arm is named as bridge arm pu, pv, pw, ua, vb, wc, an, bn, cn.

[0033] In this embodiment, the converter of the present invention adopts modular multilevel technology and is composed of 9 bridge arms. The upper and lower bridge arms are both composed of inductor L, equivalent resistance R and N / 2 simplified full-bridge twin sub-modules connected in series. The middle bridge arm is composed of inductor L, equivalent resistance R and N full-bridge sub-modules connected in series, and has DC fault interruption capability.

[0034] In this embodiment, the number of submodules in each arm of the converter is determined by the system voltage, modulation index, and withstand voltage level of the power electronic devices on both sides of the arm.

[0035] In this embodiment, the converter outputs a power frequency voltage on the upper bridge arm, a low frequency voltage on the lower bridge arm, and a mixed power and low frequency voltage on the middle bridge arm. The power frequency and low frequency components of the middle bridge arm voltage are opposite to those of the upper and lower bridge arm voltages, respectively. Thus, the voltage components of different frequencies can cancel each other out, thereby outputting a stable DC voltage on the DC side and realizing energy conversion between three different frequency systems.

[0036] In this embodiment, as Figure 2As shown, the full-bridge submodule in the middle bridge arm includes fully controlled insulated-gate bipolar transistors (IGBTs) VT1, VT2, VT3, and VT4, diodes VD1, VD2, VD3, and VD4, and a DC capacitor C. Ports P1 and P2 are the input and output ports of this submodule. The positive terminal of the DC capacitor C is connected to the collector of both IGBTs VT1 and VT3, and the negative terminal of the DC capacitor C is connected to the emitter of IGBT VT2 and the full-bridge submodule. The emitter of the fully controlled insulated-gate bipolar transistor VT4 is connected to the collector of the fully controlled insulated-gate bipolar transistor VT1 and the collector of the fully controlled insulated-gate bipolar transistor VT2 and port P1 are connected to the collector of the fully controlled insulated-gate bipolar transistor VT3 and the collector of the fully controlled insulated-gate bipolar transistor VT4 and port P2. Diode VD1 is connected in parallel with the fully controlled insulated-gate bipolar transistor VT1; diode VD2 is connected in parallel with the fully controlled insulated-gate bipolar transistor VT2; diode VD3 is connected in parallel with the fully controlled insulated-gate bipolar transistor VT3; diode VD4 is connected in parallel with the fully controlled insulated-gate bipolar transistor VT4. Furthermore, in other embodiments, the transistors can also be metal-oxide-semiconductor field-effect transistors or bipolar transistors, etc., as needed.

[0037] In this embodiment, the full-bridge submodule used in the middle bridge arm operates with fully controlled insulated-gate bipolar transistors VT1 and VT2 conducting alternately, and fully controlled insulated-gate bipolar transistors VT3 and VT4 conducting alternately. This can be divided into three operating states: positive input, negative input, and bypass state. Assuming the forward voltage of the capacitor is... Then, the submodule outputs a positive voltage when it is in the active state. When in negative input state, the output voltage is negative. The output voltage is 0 in bypass mode.

[0038] like Figure 3 As shown, when the DC system fails, all fully controlled insulated gate bipolar transistors of the intermediate bridge arm neutron module are in the off state. Regardless of whether the fault current is forward or reverse, the DC capacitor C is in the fault circuit, providing blocking voltage to suppress the fault current.

[0039] like Figure 4As shown, the upper and lower bridge arms adopt a simplified full-bridge twin-module structure, which includes a first output terminal P1, a second output terminal P2, a first transistor VT1, a second transistor VT2, a third transistor VT3, a fourth transistor VT4, a fifth transistor VT5, a sixth transistor VT6, a first diode VD1, a second diode VD2, a third diode VD3, a fourth diode VD4, a fifth diode VD5, a sixth diode VD6, a seventh diode VD7, an eighth diode VD8, a first DC capacitor C1, and a second DC capacitor C2. The first DC capacitor C1, the first transistor VT1, the second transistor VT2, the first diode VD1, and the second diode VD2 form the first half-bridge module; the second DC capacitor C1, the third transistor VT3, the fourth transistor VT4, the third diode VD3, and the fourth diode VD4 form the second half-bridge module. The specific combination of each component is as follows: Figure 4 As shown.

[0040] The upper and lower bridge arms use a simplified full-bridge twin-submodule. During normal operation, the fifth transistor VT5 and the sixth transistor VT6 are always on, while the first transistor VT1 and the second transistor VT2 are on alternately, and the third transistor VT3 and the fourth transistor VT4 are on alternately. Assuming the capacitor voltage is... When a forward current flows through a submodule and a reverse current flows through it, the two half-bridge submodules each have four operating states and can output three different voltages. , And 0.

[0041] like Figure 5 As shown, when the DC system fails, the transistors of the submodules in the upper and lower bridge arms are in the off state. Regardless of whether the fault current is in the forward or reverse direction, DC capacitors C1 and C2 are in the fault circuit, providing twice the blocking voltage to suppress the fault current.

[0042] It should be noted that the application scenarios of this invention may include: 1) electric transmission and acting as a high-voltage, high-power power source; 2) access of low-frequency offshore wind power, low-frequency onshore wind power, and low-frequency photovoltaic and other new energy power sources to the industrial frequency power grid; 3) networking of different frequency AC systems, etc.

[0043] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0044] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0045] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction, characterized in that, The converter is connected with a power frequency system, a direct current system and a low frequency system, and includes an upper bridge arm, a lower bridge arm and a middle bridge arm; An output end of the power frequency system is connected with a positive pole of the direct current system through the upper bridge arm; An output end of the low frequency system is connected with a negative pole of the direct current system through the lower bridge arm; An output end of the power frequency system is connected with an output end of the low frequency system through the middle bridge arm; The converter converts three-phase voltage and current of the low frequency system into three-phase voltage and current of the power frequency system, and outputs a direct current voltage on a direct current side.

2. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 1, characterized in that, The middle bridge arm is composed of an inductor L, an equivalent resistor R and N full-bridge sub-modules connected in series.

3. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 2, characterized in that, The full-bridge sub-module in the middle bridge arm includes a full-controlled insulated gate bipolar transistor VT1, a full-controlled insulated gate bipolar transistor VT2, a full-controlled insulated gate bipolar transistor VT3, a full-controlled insulated gate bipolar transistor VT4, a diode VD1, a diode VD2, a diode VD3, a diode VD4, a direct current capacitor C, a port P1 and a port P2, wherein a positive pole of the direct current capacitor C is connected with a collector of the full-controlled insulated gate bipolar transistor VT1 and a collector of the full-controlled insulated gate bipolar transistor VT3, a negative pole of the direct current capacitor C is connected with an emitter of the full-controlled insulated gate bipolar transistor VT2 and an emitter of the full-controlled insulated gate bipolar transistor VT4, an emitter of the full-controlled insulated gate bipolar transistor VT1 is connected with a collector of the full-controlled insulated gate bipolar transistor VT2 and the port P1, an emitter of the full-controlled insulated gate bipolar transistor VT3 is connected with a collector of the full-controlled insulated gate bipolar transistor VT4 and the port P2, the diode VD1 is connected in parallel with the full-controlled insulated gate bipolar transistor VT1, the diode VD2 is connected in parallel with the full-controlled insulated gate bipolar transistor VT2, the diode VD3 is connected in parallel with the full-controlled insulated gate bipolar transistor VT3, and the diode VD4 is connected in parallel with the full-controlled insulated gate bipolar transistor VT4.

4. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 3, characterized in that, In normal operation, the full-controlled insulated gate bipolar transistor VT1 and the full-controlled insulated gate bipolar transistor VT2 are turned on alternately, and the full-controlled insulated gate bipolar transistor VT3 and the full-controlled insulated gate bipolar transistor VT4 are turned on alternately.

5. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 3, characterized in that, When the direct current system fails, all the full-controlled insulated gate bipolar transistors in the middle bridge arm are in an off state.

6. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 1, characterized in that, The upper bridge arm and the lower bridge arm are each composed of an inductor L, an equivalent resistor R and N / 2 simplified full-bridge double sub-modules connected in series.

7. The nine-bride multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 6, characterized in that, The simplified full-bridge twin module comprises a first output end P1, a second output end P2, a first transistor VT1, a second transistor VT2, a third transistor VT3, a fourth transistor VT4, a fifth transistor VT5, a sixth transistor VT6, a first diode VD1, a second diode VD2, a third diode VD3, a fourth diode VD4, a fifth diode VD5, a sixth diode VD6, a seventh diode VD7, an eighth diode VD8, a first direct-current capacitor C1 and a second direct-current capacitor C2, wherein the first direct-current capacitor C1, the first transistor VT1, the second transistor VT2, the first diode VD1 and the second diode VD2 constitute a first half-bridge submodule; and the second direct-current capacitor C1, the third transistor VT3, the fourth transistor VT4, the third diode VD3 and the fourth diode VD4 constitute a second half-bridge submodule.

8. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 7, characterized in that, In normal operation, the fifth transistor VT5 and the sixth transistor VT6 are always in the on state, the first transistor VT1 and the second transistor VT2 are turned on alternately, and the third transistor VT3 and the fourth transistor VT4 are turned on alternately.

9. The nine-bride multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 7, characterized in that, When the direct-current system fails, each transistor in the upper bridge arm and the lower bridge arm is in the off state.

10. The nine-bridge-arm multi-frequency three-port converter suitable for industrial / low frequency-dc interaction according to claim 1, characterized in that, The converter is used for power transmission and serves as a high-voltage high-power power supply, low-frequency offshore wind power, low-frequency onshore wind power and low-frequency photovoltaic new energy power supply access to a power frequency power grid and a low-frequency alternating current system networking.

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