Power factor adjustable 12-pulse fundamental frequency modulation converter and control method

Abstract

The present application belongs to the field of modulation converter, and particularly relates to a 12-pulse base frequency modulation converter with adjustable power factor and a control method, aiming to solve the problems of the existing DC power transmission converter, such as commutation failure risk, active power and reactive power coupling, large volume, heavy weight, high cost and the like of the modular multilevel converter (MMC). The present application comprises a 6-pulse thyristor converter, an active commutation converter based on self-turn-off power semiconductor devices, DC reactors Ldc1 and Ldc2, and transformers T1 and T2. The switching frequency of the 6-pulse thyristor converter and the active commutation converter is the frequency of the AC side power grid, the AC side current of the 6-pulse thyristor converter lags behind the voltage, and the AC side current of the active commutation converter can either lag behind the AC voltage or lead the AC voltage. The 12-pulse base frequency modulation converter of the present application has an adjustable power factor, and is simple in structure, light in weight and simple in control method.

Description

Technical Field

[0001] This invention belongs to the field of modulation converters, specifically relating to a 12-pulse fundamental frequency modulation converter with adjustable power factor and a control method thereof. Background Technology

[0002] Line commutated converters (LCCs) based on semi-controlled power semiconductor devices (thyristors) have a simple structure, low cost, and relatively simple control, making them suitable for building large-capacity, long-distance high-voltage direct current transmission systems. However, LCCs are subject to the risk of commutation failure, and the active and reactive power of LCCs are coupled, requiring a large number of additional reactive power compensation devices.

[0003] Modular multilevel converters (MMCs) based on modular power modules have advantages such as modular structure, a large number of output voltage levels, high reliability, and high efficiency. Modular multilevel converters can solve the problems of dynamic and static voltage equalization difficulties in the use of semiconductor power devices directly connected in series in high-voltage applications of two-level or three-level voltage source converters [1]. However, as the number of power sub-modules used in modular multilevel converters (MMCs) increases, the size and weight of the converter become larger, the control system becomes very complex, and the manufacturing cost of the converter becomes high.

[0004] By connecting the modular multilevel converter (MMC) in series with the DC side of the grid voltage commutation converter (LCC) and in parallel with the AC side, the number of semiconductor power devices used can be reduced. Furthermore, the MMC can provide reactive power to the LCC and reduce the probability of commutation failure in the LCC [2]. However, due to the use of the MMC, it has disadvantages such as large size and weight, complex control, and high manufacturing cost.

[0005] The following documents are technical background information related to this invention:

[0006] [1] Yuan Zhaoxiang, Hu Jinsong, Qi Lizhong, et al., A modular multi-level flexible DC transmission system for offshore wind power, CN201520107377.7

[0007] [2] Guo Gaopeng, Song Qiang, Liu Wenhua, A hybrid grid-connected converter station for series-connected DC offshore wind power, CN201710016539.X Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, namely the risks of commutation failure, active and reactive power coupling, and the large size, heavy weight, and high cost of modular multilevel converters (MMCs), this invention provides a 12-pulse baseband modulation converter with adjustable power factor. The 12-pulse baseband modulation converter with adjustable power factor includes a 6-pulse thyristor converter, an active commutation converter based on self-turn-off power semiconductor devices, DC reactors Ldc1 and Ldc2, and transformers T1 and T2.

[0009] The positive DC terminal of the 6-pulse thyristor converter serves as the positive DC terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the positive terminal of the high voltage DC side through the DC reactor Ldc1.

[0010] The DC negative terminal of the 6-pulse thyristor converter is connected to the positive terminal of the active commutation converter based on the self-turn-off power semiconductor device;

[0011] The negative terminal of the active commutation converter based on self-turn-off power semiconductor device serves as the DC negative terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the negative terminal of the high voltage DC side through the DC reactor Ldc2.

[0012] The AC terminals of the power factor adjustable 12-pulse baseband modulation converter are connected to the three-phase AC power grid via transformers T1 and T2, respectively.

[0013] In some preferred embodiments, the 6-pulse thyristor converter includes bridge arm S1, bridge arm S2, bridge arm S3, bridge arm S4, bridge arm S5 and bridge arm S6.

[0014] The cathodes of bridge arm S1, bridge arm S3 and bridge arm S5 are connected together as the DC positive terminal LCC+ of the 6-pulse thyristor converter;

[0015] The anodes of bridge arm S2, bridge arm S4 and bridge arm S6 are connected together as the DC negative terminal LCC- of the 6-pulse thyristor converter;

[0016] The anode of bridge arm S1 and the cathode of bridge arm S4 are connected together as the AC side terminal u1 of the 6-pulse thyristor converter;

[0017] The anode of bridge arm S3 and the cathode of bridge arm S6 are connected together as the AC side terminal v1 of the 6-pulse thyristor converter;

[0018] The anode of bridge arm S5 and the cathode of bridge arm S2 are connected together as the AC side terminal w1 of the 6-pulse thyristor converter.

[0019] In some preferred embodiments, the AC side terminals u1, v1 and w1 of the 6-pulse thyristor converter are respectively connected to the secondary side terminals a1, b1 and c1 of the transformer T1.

[0020] In some preferred embodiments, the active commutation converter based on self-turn-off power semiconductor devices includes bridge arms G1, G2, G3, G4, G5 and G6.

[0021] The cathodes of bridge arm G1, bridge arm G3 and bridge arm G5 are connected together as the DC positive terminal ACC+ of the active commutator based on self-turn-off power semiconductor device.

[0022] The anodes of bridge arm G2, bridge arm G4 and bridge arm G6 are connected together as the DC negative terminal ACC- of the active commutator based on self-turn-off power semiconductor device;

[0023] The anode of the bridge arm G1 and the cathode of the bridge arm G4 are connected together as the AC side terminal u2 of the active commutator based on the self-turn-off power semiconductor device.

[0024] The anode of the bridge arm G3 and the cathode of the bridge arm G6 are connected together as the AC side terminal v2 of the active commutator based on the self-turn-off power semiconductor device.

[0025] The anode of bridge arm G5 and the cathode of bridge arm G2 are connected together as the AC side terminal w2 of the active commutator based on self-turn-off power semiconductor device.

[0026] In some preferred embodiments, the AC side terminals u2, v2 and w2 of the active commutation converter based on self-turn-off power semiconductor devices are respectively connected to the secondary side terminals a2, b2 and c2 of the transformer T2.

[0027] In some preferred embodiments, the primary terminal A1 of the transformer T1 is connected to the primary terminal A2 of the transformer T2, serving as the AC terminal A of the power factor adjustable 12-pulse fundamental frequency modulation converter;

[0028] The primary terminal B1 of the transformer T1 is connected to the primary terminal B2 of the transformer T2, serving as the AC terminal B of the power factor adjustable 12-pulse fundamental frequency modulation converter.

[0029] The primary terminal C1 of the transformer T1 is connected to the primary terminal C2 of the transformer T2, serving as the AC terminal C of the power factor adjustable 12-pulse fundamental frequency modulation converter.

[0030] In some preferred embodiments, the transformer T1 has a primary winding and a secondary winding connected in a Y / Y configuration, and the turns ratio of the primary winding to the secondary winding is 1:n, where n is a positive integer.

[0031] In some preferred embodiments, the transformer T2 has a primary winding and a secondary winding connected in a Y / Δ configuration, and the turns ratio of the primary winding to the secondary winding is 1.732:n, where n is a positive integer.

[0032] In another aspect, the present invention proposes a control method for a 12-pulse fundamental frequency modulation converter with adjustable power factor, wherein the control method is as follows:

[0033] The bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter and the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutation converter based on self-turn-off power semiconductor devices all operate once within one fundamental cycle of the three-phase AC power grid, and the switching frequency is the fundamental frequency of the AC power grid.

[0034] Let T be the period of the three-phase AC power grid, and U be the AC line voltage. AC The zero-crossing point from negative to positive is recorded as the starting time t0, the time when the bridge arm S1 of the 6-pulse thyristor converter is actively turned on is recorded as t1, and the time when the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices is actively turned on is recorded as t2.

[0035] The conduction sequence of the bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter is S1→S2→S3→S4→S5→S6→S1:

[0036] The bridge arm S1 is turned on at time t1 and turned off at time t1+T / 3;

[0037] The bridge arm S2 is turned on at t1+T / 6 and turned off at t1+T / 2;

[0038] The opening time of bridge arm S3 is t1+T / 3, and the closing time is t1+2T / 3;

[0039] The opening time of bridge arm S4 is t1+T / 2, and the closing time is t1+5T / 6;

[0040] The opening time of bridge arm S5 is t1+2T / 3, and the closing time is t1+T;

[0041] The opening time of bridge arm S6 is t1+5T / 6, and the closing time is t1+7T / 6;

[0042] The conduction sequence of the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutator based on self-turn-off power semiconductor devices is G1→G2→G3→G4→G5→G6→G1.

[0043] The bridge arm G1 is turned on at time t2 and turned off at time t2+T / 3;

[0044] The opening time of bridge arm G2 is t2+T / 6, and the closing time is t2+T / 2;

[0045] The opening time of bridge arm G3 is t2+T / 3, and the closing time is t2+2T / 3;

[0046] The opening time of bridge arm G4 is t2+T / 2, and the closing time is t2+5T / 6;

[0047] The opening time of bridge arm G5 is t2+2T / 3, and the closing time is t2+T;

[0048] The bridge arm G6 is turned on at t2+5T / 6 and turned off at t2+7T / 6.

[0049] In some preferred embodiments, while maintaining a constant output active power, the power factor-adjustable 12-pulse fundamental frequency modulation converter can output different amounts of reactive power:

[0050] The turn-on time t1 of the bridge arm S1 of the 6-pulse thyristor converter, the turn-on time t2 of the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices, and the AC side line voltage U AC The relationship between the zero-crossing time t0 when the result changes from negative to positive satisfies:

[0051] The turn-on time t1 of bridge arm S1 lags behind the AC side line voltage U. AC At the zero-crossing time t0 when the current changes from negative to positive, the AC side current of the 6-pulse thyristor converter always lags behind the AC side grid voltage.

[0052] The turn-on time of bridge arm G1 is t2, which lags behind the AC side line voltage U. AC At the zero-crossing time t0 when the voltage changes from negative to positive, the AC side current of the active commutator based on the self-turn-off power semiconductor device lags behind the AC side voltage.

[0053] The turn-on time of bridge arm G1 is t2, which is ahead of the AC side line voltage U. AC At the zero-crossing time t0 when the voltage changes from negative to positive, the AC side current of the active commutator based on the self-turn-off power semiconductor device leads the AC side voltage.

[0054] The beneficial effects of this invention are:

[0055] (1) The 12-pulse baseband modulation converter with adjustable power factor of the present invention has a simple structure and light weight. When the active power remains constant, it can output different amounts of reactive power and the control method is simple.

[0056] (2) The switching frequencies of the 12-pulse baseband modulation converter, the 6-pulse thyristor converter, and the active commutation converter of the present invention are all AC grid frequencies. The AC current of the 6-pulse thyristor converter lags behind the voltage, and the AC current of the active commutation converter can both lag behind the AC voltage and lead the AC voltage. The 12-pulse baseband modulation converter has an actively adjustable power factor. Attached Figure Description

[0057] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0058] Figure 1 This is the circuit diagram of the 12-pulse baseband modulation converter with adjustable power factor of the present invention. Detailed Implementation

[0059] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0060] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0061] The present invention provides a 12-pulse baseband modulation converter with adjustable power factor, the 12-pulse baseband modulation converter with adjustable power factor includes a 6-pulse thyristor converter, an active commutation converter based on self-turn-off power semiconductor devices, DC reactors Ldc1 and Ldc2, and transformers T1 and T2.

[0062] The positive DC terminal of the 6-pulse thyristor converter serves as the positive DC terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the positive terminal of the high voltage DC side through the DC reactor Ldc1.

[0063] The DC negative terminal of the 6-pulse thyristor converter is connected to the positive terminal of the active commutation converter based on the self-turn-off power semiconductor device;

[0064] The negative terminal of the active commutation converter based on self-turn-off power semiconductor device serves as the DC negative terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the negative terminal of the high voltage DC side through the DC reactor Ldc2.

[0065] The AC terminals of the power factor adjustable 12-pulse baseband modulation converter are connected to the three-phase AC power grid via transformers T1 and T2, respectively.

[0066] To more clearly explain the 12-pulse fundamental frequency modulation converter with adjustable power factor of the present invention, the following description is in conjunction with... Figure 1 The modules in the embodiments of the present invention will be described in detail below.

[0067] The first embodiment of the present invention provides a 12-pulse fundamental frequency modulation converter with adjustable power factor, comprising a 6-pulse thyristor converter, an active commutation converter based on self-turn-off power semiconductor devices, DC reactors Ldc1 and Ldc2, and transformers T1 and T2. Detailed descriptions of each module are as follows:

[0068] The DC positive terminal of the 6-pulse thyristor converter serves as the DC positive terminal of the 12-pulse fundamental frequency modulation converter with adjustable power factor, and is connected to the positive terminal of the high voltage DC side through the DC reactor Ldc1. The DC negative terminal of the 6-pulse thyristor converter is connected to the positive terminal of the active commutation converter based on self-turn-off power semiconductor devices.

[0069] The 6-pulse thyristor converter includes bridge arms S1, S2, S3, S4, S5, and S6:

[0070] The cathodes of bridge arms S1, S3 and S5 are connected together as the DC positive terminal LCC+ of the 6-pulse thyristor converter, and the anodes of bridge arms S2, S4 and S6 are connected together as the DC negative terminal LCC- of the 6-pulse thyristor converter.

[0071] The anode of bridge arm S1 and the cathode of bridge arm S4 are connected together as the AC side terminal u1 of the 6-pulse thyristor converter; the anode of bridge arm S3 and the cathode of bridge arm S6 are connected together as the AC side terminal v1 of the 6-pulse thyristor converter; and the anode of bridge arm S5 and the cathode of bridge arm S2 are connected together as the AC side terminal w1 of the 6-pulse thyristor converter.

[0072] The bridge arms of a 6-pulse thyristor converter can be thyristors.

[0073] The negative terminal of the active commutator based on self-turn-off power semiconductor devices serves as the DC negative terminal of a 12-pulse fundamental frequency modulation converter with adjustable power factor, and is connected to the negative terminal of the high-voltage DC side through a DC reactor Ldc2.

[0074] The active commutator based on self-turn-off power semiconductor devices includes bridge arms G1, G2, G3, G4, G5, and G6:

[0075] The cathodes of bridge arms G1, G3 and G5 are connected together as the DC positive terminal ACC+ of the active commutator based on self-turn-off power semiconductor devices, and the anodes of bridge arms G2, G4 and G6 are connected together as the DC negative terminal ACC- of the active commutator based on self-turn-off power semiconductor devices.

[0076] The anode of arm G1 and the cathode of arm G4 are connected together as the AC side terminal u2 of the active commutator based on self-turn-off power semiconductor devices; the anode of arm G3 and the cathode of arm G6 are connected together as the AC side terminal v2 of the active commutator based on self-turn-off power semiconductor devices; and the anode of arm G5 and the cathode of arm G2 are connected together as the AC side terminal w2 of the active commutator based on self-turn-off power semiconductor devices.

[0077] The bridge arms of an active commutator based on self-turn-off power semiconductor devices can be self-turn-off power semiconductor devices.

[0078] The AC terminals of the 12-pulse fundamental frequency modulation converter with adjustable power factor are connected to the three-phase AC power grid through transformers T1 and T2, respectively.

[0079] The AC side terminals u1, v1, and w1 of the 6-pulse thyristor converter are connected to the secondary side terminals a1, b1, and c1 of transformer T1, respectively. The AC side terminals u2, v2, and w2 of the active commutation converter based on self-turn-off power semiconductor devices are connected to the secondary side terminals a2, b2, and c2 of transformer T2, respectively.

[0080] The primary terminal A1 of transformer T1 is connected to the primary terminal A2 of transformer T2, serving as the AC terminal A of the 12-pulse fundamental frequency modulation converter with adjustable power factor. The primary terminal B1 of transformer T1 is connected to the primary terminal B2 of transformer T2, serving as the AC terminal B of the 12-pulse fundamental frequency modulation converter with adjustable power factor. The primary terminal C1 of transformer T1 is connected to the primary terminal C2 of transformer T2, serving as the AC terminal C of the 12-pulse fundamental frequency modulation converter with adjustable power factor.

[0081] Transformer T1 has a primary winding and a secondary winding connected in a Y / Y configuration, with a turns ratio of 1:n. Transformer T2 has a primary winding and a secondary winding connected in a Y / Δ configuration, with a turns ratio of 1.732:n, where n is a positive integer.

[0082] The control method of the 12-pulse fundamental frequency modulation converter with adjustable power factor according to the second embodiment of the present invention is as follows:

[0083] The bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter and the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutation converter based on self-turn-off power semiconductor devices all operate once within one fundamental cycle of the three-phase AC power grid, and the switching frequency is the fundamental frequency of the AC power grid.

[0084] Let T be the period of the three-phase AC power grid, and U be the AC line voltage. AC The zero-crossing point from negative to positive is recorded as the starting time t0, the time when the bridge arm S1 of the 6-pulse thyristor converter is actively turned on is recorded as t1, and the time when the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices is actively turned on is recorded as t2.

[0085] The conduction sequence of the bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter is S1→S2→S3→S4→S5→S6→S1:

[0086] The bridge arm S1 is turned on at time t1 and turned off at time t1+T / 3;

[0087] The bridge arm S2 is turned on at t1+T / 6 and turned off at t1+T / 2;

[0088] The opening time of bridge arm S3 is t1+T / 3, and the closing time is t1+2T / 3;

[0089] The opening time of bridge arm S4 is t1+T / 2, and the closing time is t1+5T / 6;

[0090] The opening time of bridge arm S5 is t1+2T / 3, and the closing time is t1+T;

[0091] The opening time of bridge arm S6 is t1+5T / 6, and the closing time is t1+7T / 6;

[0092] The conduction sequence of the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutator based on self-turn-off power semiconductor devices is G1→G2→G3→G4→G5→G6→G1.

[0093] The bridge arm G1 is turned on at time t2 and turned off at time t2+T / 3;

[0094] The opening time of bridge arm G2 is t2+T / 6, and the closing time is t2+T / 2;

[0095] The turn-on time of bridge arm G3 is t2+T / 3, and the turn-off time is t2+2T / 3;

[0096] The turn-on time of bridge arm G4 is t2+T / 2, and the turn-off time is t2+5T / 6;

[0097] The turn-on time of bridge arm G5 is t2+2T / 3, and the turn-off time is t2+T;

[0098] The turn-on time of bridge arm G6 is t2+5T / 6, and the turn-off time is t2+7T / 6.

[0099] When the 12-pulse fundamental frequency modulation converter with adjustable power factor keeps the output active power unchanged, it can output reactive power of different magnitudes:

[0100] The turn-on time t1 of the bridge arm S1 of the 6-pulse thyristor converter, and the turn-on time t2 of the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices and the AC side line voltage U AC The relationship between the zero-crossing time t0 when the voltage changes from negative to positive satisfies:

[0101] The turn-on time t1 of bridge arm S1 lags behind the AC side line voltage U AC The zero-crossing time t0 when the voltage changes from negative to positive, that is, t1>t0, and the AC side current of the 6-pulse thyristor converter always lags behind the AC side grid voltage;

[0102] The turn-on time t2 of bridge arm G1 lags behind the AC side line voltage U AC The zero-crossing time t0 when the voltage changes from negative to positive, that is, t2>t0, and the AC side current of the active commutation converter based on self-turn-off power semiconductor devices lags behind the AC side voltage;

[0103] The turn-on time t2 of bridge arm G1 leads the AC side line voltage U AC The zero-crossing time t0 when the voltage changes from negative to positive, that is, t2<t0, and the AC side current of the active commutation converter based on self-turn-off power semiconductor devices leads the AC side voltage.

[0104] The 12-pulse fundamental frequency modulation converter has an actively adjustable power factor.

[0105] Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working process and related description of the method described above can refer to the corresponding processes in the foregoing system embodiments, and will not be repeated here.

[0106] It should be noted that the power factor adjustable 12-pulse baseband modulation converter and method provided in the above embodiments are only illustrative examples of the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be merged into one module, or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the various modules or steps and are not considered as an improper limitation of the present invention.

[0107] A device according to a third embodiment of the present invention includes:

[0108] At least one processor; and

[0109] A memory communicatively connected to at least one of the processors; wherein,

[0110] The memory stores instructions that can be executed by the processor to implement the control method of the power factor adjustable 12-pulse baseband modulation converter described above.

[0111] A computer-readable storage medium according to a fourth embodiment of the present invention stores computer instructions, which are executed by the computer to implement the above-described control method for a power factor adjustable 12-pulse baseband modulation converter.

[0112] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process and related descriptions of the storage device and processing device described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0113] Those skilled in the art will recognize that the modules and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. The programs corresponding to the software modules and method steps can be placed in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the art. To clearly illustrate the interchangeability of electronic hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the invention.

[0114] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0115] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0116] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A 12-pulse fundamental frequency modulation converter with adjustable power factor, characterized in that, The power factor adjustable 12-pulse fundamental frequency modulation converter includes a 6-pulse thyristor converter, an active commutation converter based on self-turn-off power semiconductor devices, DC reactors Ldc1 and Ldc2, and transformers T1 and T2. The positive DC terminal of the 6-pulse thyristor converter serves as the positive DC terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the positive terminal of the high voltage DC side through the DC reactor Ldc1. The DC negative terminal of the 6-pulse thyristor converter is connected to the positive terminal of the active commutation converter based on the self-turn-off power semiconductor device; The negative terminal of the active commutation converter based on self-turn-off power semiconductor device serves as the DC negative terminal of the power factor adjustable 12-pulse fundamental frequency modulation converter, and is connected to the negative terminal of the high voltage DC side through the DC reactor Ldc2. The AC terminals of the power factor adjustable 12-pulse fundamental frequency modulation converter are connected to the three-phase AC power grid through transformers T1 and T2, respectively. Specifically, when the power factor adjustable 12-pulse fundamental frequency modulation converter maintains a constant output active power, it can output different amounts of reactive power: The turn-on time t1 of the bridge arm S1 of the 6-pulse thyristor converter, the turn-on time t2 of the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices, and the AC side line voltage U AC The relationship between the zero-crossing time t0 when the result changes from negative to positive satisfies: The turn-on time t1 of bridge arm S1 lags behind the AC side line voltage U. AC At the zero-crossing time t0 when the current changes from negative to positive, the AC side current of the 6-pulse thyristor converter always lags behind the AC side grid voltage. The turn-on time of bridge arm G1 is t2, which lags behind the AC side line voltage U. AC At the zero-crossing time t0 when the voltage changes from negative to positive, the AC side current of the active commutator based on the self-turn-off power semiconductor device lags behind the AC side voltage. The turn-on time of bridge arm G1 is t2, which is ahead of the AC side line voltage U. AC At the zero-crossing time t0 when the voltage changes from negative to positive, the AC side current of the active commutator based on the self-turn-off power semiconductor device leads the AC side voltage. The 6-pulse thyristor converter includes bridge arm S1, bridge arm S2, bridge arm S3, bridge arm S4, bridge arm S5 and bridge arm S6. The cathodes of bridge arm S1, bridge arm S3 and bridge arm S5 are connected together as the DC positive terminal LCC+ of the 6-pulse thyristor converter; The anodes of bridge arm S2, bridge arm S4 and bridge arm S6 are connected together as the DC negative terminal LCC- of the 6-pulse thyristor converter; The anode of bridge arm S1 and the cathode of bridge arm S4 are connected together as the AC side terminal u1 of the 6-pulse thyristor converter; The anode of bridge arm S3 and the cathode of bridge arm S6 are connected together as the AC side terminal v1 of the 6-pulse thyristor converter; The anode of bridge arm S5 and the cathode of bridge arm S2 are connected together as the AC side terminal w1 of the 6-pulse thyristor converter; The active commutation converter based on self-turn-off power semiconductor devices includes bridge arm G1, bridge arm G2, bridge arm G3, bridge arm G4, bridge arm G5 and bridge arm G6. The cathodes of bridge arm G1, bridge arm G3 and bridge arm G5 are connected together as the DC positive terminal ACC+ of the active commutator based on self-turn-off power semiconductor device. The anodes of bridge arm G2, bridge arm G4 and bridge arm G6 are connected together as the DC negative terminal ACC- of the active commutator based on self-turn-off power semiconductor device; The anode of the bridge arm G1 and the cathode of the bridge arm G4 are connected together as the AC side terminal u2 of the active commutator based on the self-turn-off power semiconductor device. The anode of the bridge arm G3 and the cathode of the bridge arm G6 are connected together as the AC side terminal v2 of the active commutator based on the self-turn-off power semiconductor device. The anode of bridge arm G5 and the cathode of bridge arm G2 are connected together as the AC side terminal w2 of the active commutator based on self-turn-off power semiconductor device.

2. The 12-pulse fundamental frequency modulation converter with adjustable power factor according to claim 1, characterized in that, The AC side terminals u1, v1, and w1 of the 6-pulse thyristor converter are respectively connected to the secondary side terminals a1, b1, and c1 of the transformer T1.

3. The 12-pulse fundamental frequency modulation converter with adjustable power factor according to claim 1, characterized in that, The AC side terminals u2, v2, and w2 of the active commutation converter based on self-turn-off power semiconductor devices are respectively connected to the secondary side terminals a2, b2, and c2 of the transformer T2.

4. The 12-pulse fundamental frequency modulation converter with adjustable power factor according to claim 1, characterized in that, The primary terminal A1 of the transformer T1 is connected to the primary terminal A2 of the transformer T2, serving as the AC terminal A of the power factor adjustable 12-pulse fundamental frequency modulation converter; The primary terminal B1 of the transformer T1 is connected to the primary terminal B2 of the transformer T2, serving as the AC terminal B of the power factor adjustable 12-pulse fundamental frequency modulation converter. The primary terminal C1 of the transformer T1 is connected to the primary terminal C2 of the transformer T2, serving as the AC terminal C of the power factor adjustable 12-pulse fundamental frequency modulation converter.

5. The 12-pulse fundamental frequency modulation converter with adjustable power factor according to claim 1, characterized in that, The transformer T1 has a primary winding and a secondary winding connected in a Y / Y configuration, and the turns ratio of the primary winding to the secondary winding is 1:n, where n is a positive integer.

6. The 12-pulse fundamental frequency modulation converter with adjustable power factor according to claim 1, characterized in that, The transformer T2 has a primary winding and a secondary winding connected in a Y / Δ configuration, and the turns ratio of the primary winding to the secondary winding is 1.732:n, where n is a positive integer.

7. A control method for a 12-pulse fundamental frequency modulation converter with adjustable power factor, used to control the 12-pulse fundamental frequency modulation converter with adjustable power factor as described in any one of claims 1-6, characterized in that, The control method is as follows: The bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter and the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutation converter based on self-turn-off power semiconductor devices all operate once within one fundamental cycle of the three-phase AC power grid, and the switching frequency is the fundamental frequency of the AC power grid. Let T be the period of the three-phase AC power grid, and U be the AC line voltage. AC The zero-crossing point from negative to positive is recorded as the starting time t0, the time when the bridge arm S1 of the 6-pulse thyristor converter is actively turned on is recorded as t1, and the time when the bridge arm G1 of the active commutation converter based on self-turn-off power semiconductor devices is actively turned on is recorded as t2. The conduction sequence of the bridge arms S1, S2, S3, S4, S5, and S6 of the 6-pulse thyristor converter is S1→S2→S3→S4→S5→S6→S1: The bridge arm S1 is turned on at time t1 and turned off at time t1+T / 3; The bridge arm S2 is turned on at t1+T / 6 and turned off at t1+T / 2; The opening time of bridge arm S3 is t1+T / 3, and the closing time is t1+2T / 3; The opening time of bridge arm S4 is t1+T / 2, and the closing time is t1+5T / 6; The opening time of bridge arm S5 is t1+2T / 3, and the closing time is t1+T; The opening time of bridge arm S6 is t1+5T / 6, and the closing time is t1+7T / 6; The conduction sequence of the bridge arms G1, G2, G3, G4, G5, and G6 of the active commutator based on self-turn-off power semiconductor devices is G1→G2→G3→G4→G5→G6→G1. The bridge arm G1 is turned on at time t2 and turned off at time t2+T / 3; The opening time of bridge arm G2 is t2+T / 6, and the closing time is t2+T / 2; The opening time of bridge arm G3 is t2+T / 3, and the closing time is t2+2T / 3; The opening time of bridge arm G4 is t2+T / 2, and the closing time is t2+5T / 6; The opening time of bridge arm G5 is t2+2T / 3, and the closing time is t2+T; The bridge arm G6 is turned on at t2+5T / 6 and turned off at t2+7T / 6.

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