Harmonic suppression method and system for bipolar AC-AC frequency converter

Abstract

The invention relates to the technical field of power electronic equipment control, in particular to a bipolar AC-AC frequency converter harmonic suppression method and system, and the method comprises the steps: measuring low-frequency-side and power-frequency-side three-phase currents; respectively carrying out Park coordinate transformation on the low-frequency-side three-phase current harmonic component and the power-frequency-side three-phase current harmonic component to obtain d and q components of the low-frequency-side harmonic and the power-frequency-side harmonic; d and q components of the low-frequency-side harmonic waves and the power-frequency-side harmonic waves are input into a proportional-integral (PI) controller, a control target is set to be 0, and output of the low-frequency-side PI controller and output of the power-frequency-side PI controller are obtained; park inversion is carried out on the output of the low-frequency-side PI controller and the output of the power-frequency-side PI controller to obtain low-frequency-side three-phase modulation wave components and power-frequency-side three-phase modulation wave components; and superposing the low-frequency-side and power-frequency-side three-phase modulation wave components to form modulation waves of upper and lower bridge arms of each phase, and driving corresponding sub-modules according to the modulation waves so as to generate positive-sequence differential-mode voltages and / or negative-sequence common-mode voltages for offsetting harmonic waves on each phase and suppress the harmonic waves.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic device control, and particularly relates to a method and system for suppressing harmonics of a bipolar AC-AC frequency converter. BACKGROUND

[0002] In a bipolar AC-AC frequency converter, low-frequency side harmonics and power-frequency side harmonics will cause voltage and current waveform distortion of a power system. The line loss and transformer heat are increased, the device operation efficiency and service life are reduced, the stable operation of the power grid is threatened, and then the power transmission efficiency, device stability and power quality are affected. Therefore, an efficient suppression strategy specifically for this problem is urgently needed to offset the harmonics and protect the power quality of the output of the bipolar AC-AC frequency converter.

[0003] The information disclosed in this BACKGROUND section is only for the purpose of enhancing the understanding of the background of the present application and should not be treated as admitting that the information forms prior art with respect to the present application. SUMMARY

[0004] The present application provides a method and system for suppressing harmonics of a bipolar AC-AC frequency converter, thereby effectively solving the problems in the background.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a method for suppressing harmonics of a bipolar AC-AC frequency converter, comprising the following steps:

[0006] measuring three-phase currents on a low-frequency side and three-phase currents on a power-frequency side of the bipolar AC-AC frequency converter;

[0007] performing Park coordinate transformation on harmonic components mainly at 80 Hz in the three-phase currents on the low-frequency side and harmonic components mainly at 10 Hz in the three-phase currents on the power-frequency side, respectively, to obtain d and q components of the low-frequency side harmonics and the power-frequency side harmonics;

[0008] inputting the d and q components of the low-frequency side harmonics and the power-frequency side harmonics into proportional integral (PI) controllers, respectively, and setting a control target as 0 to obtain outputs of the low-frequency side and power-frequency side PI controllers;

[0009] performing Park inverse transformation on the outputs of the low-frequency side and power-frequency side PI controllers, respectively, to obtain three-phase modulation wave components on the low-frequency side and the power-frequency side;

[0010] superimposing the three-phase modulation wave components on the low-frequency side and the power-frequency side to form modulation waves of upper and lower bridge arms of each phase, and driving corresponding sub-modules according to the modulation waves to generate positive sequence differential mode voltages and / or negative sequence common mode voltages for offsetting harmonics in each phase, so as to suppress the harmonics.

[0011] Further, the double pole AC-AC converter comprises two secondary winding W2u and W2l, the secondary winding W2u adopts Y0 connection, the secondary winding W2l adopts Y6 connection, and the neutral point o' of W2u is connected with the neutral point o" of W2l.

[0012] Further, the three-phase port X, Y and Z of W2u are connected to the upper end of the upper bridge arm of the double pole AC-AC converter A, B and C respectively, and the three-phase port x, y and z of W2l are connected to the lower end of the lower bridge arm of the double pole AC-AC converter A, B and C respectively.

[0013] Further, each phase of the double pole AC-AC converter comprises N full-bridge sub-modules and bridge inductance in series, the full-bridge sub-module comprises first to fourth IGBT and an electrolytic capacitor, and each IGBT is connected with a reverse diode in parallel.

[0014] Further, the Park coordinate transformation is performed on the harmonic component mainly at 80Hz in the low-frequency three-phase current, including:

[0015] ;

[0016] In the formula, i ld_80Hz and i lq_80Hz respectively represent the d and q components of the 80Hz harmonic component in the low-frequency side; i k respectively represent the k-phase current of the low-frequency AC power grid, wherein k = u, v, w;

[0017] The Park coordinate transformation is performed on the harmonic component mainly at 10Hz in the power-frequency three-phase current, including:

[0018] ;

[0019] In the formula, i gd_10Hz and i gq_10Hz respectively represent the d and q components of the 10Hz harmonic component in the power-frequency side; i j respectively represent the j-phase current of the low-frequency AC power grid, wherein j = a, b, c.

[0020] Further, the d and q components of the low-frequency harmonic are input into a proportional integral PI controller, the control target is set to 0, and the output u ld_80Hz and u lq_80Hz of the proportional integral PI controller are obtained, including:

[0021] ;

[0022] The d and q components of the power-frequency harmonic are input into a proportional integral PI controller, the control target is set to 0, and the output ugd_10Hz and u gq_10Hz ,include:

[0023] ;

[0024] In the formula, K p and K i These represent the proportional gain and integral gain of the controller, respectively.

[0025] Further, the step of performing Park inversion on the outputs of the low-frequency side and the power frequency side PI controllers respectively to obtain the three-phase modulated wave components on the low-frequency side and the power frequency side includes:

[0026] The output u of the low-frequency side proportional-integral controller ld_80Hz and u lq_80Hz Performing the inverse Park transform yields the three-phase upper and lower arm modulation waves u. lj_80Hz :

[0027] ;

[0028] The output u of the proportional-integral controller on the power frequency side gd_10Hz and u gq_10Hz Performing the inverse Park transform yields the three-phase upper and lower arm modulation waves u. gj_10Hz :

[0029] .

[0030] Furthermore, the step of superimposing the three-phase modulation wave components of the low-frequency side and the power frequency side to form the modulation wave of each phase's upper and lower bridge arms, and driving the corresponding sub-modules according to the modulation wave, includes:

[0031] The modulation wave y of the upper bridge arm of phase j of the bipolar AC-AC inverter ju and lower bridge arm modulated wave y jl The expressions are as follows:

[0032] ;

[0033] In the formula, y j_l For low-frequency modulated wave components; y j_g It is a power frequency modulated wave component;

[0034] j-phase low-frequency modulation wave y j_l and power frequency modulation wave y j_g The expressions are as follows:

[0035] ;

[0036] In the formula, m g For power frequency modulation; m l For low-frequency modulation; ω gω is the power frequency angular frequency; l θ is the low-frequency angular frequency. jg θ is the phase shift angle of phase j at power frequency; jl The phase shift angle for phase j at low frequency;

[0037] The voltage u of the upper bridge arm of phase j au and lower bridge arm voltage u al The expressions are as follows:

[0038] .

[0039] The present invention also includes a bipolar AC-AC inverter harmonic suppression system using the method described above, the system comprising:

[0040] The measurement unit is used to measure the three-phase current on the low-frequency side and the three-phase current on the power frequency side of a bipolar AC-AC inverter.

[0041] The Park transformation unit is used to perform Park coordinate transformation on the harmonic components of the low-frequency side three-phase current dominated by 80Hz and the harmonic components of the power frequency side three-phase current dominated by 10Hz, respectively, to obtain the d and q components of the low-frequency side harmonics and the power frequency side harmonics.

[0042] The PI control unit is used to input the d and q components of the low-frequency side harmonics and the power frequency side harmonics into the proportional-integral PI controller, set the control target to 0, and obtain the outputs of the low-frequency side and the power frequency side PI controller.

[0043] Park inverter unit is used to perform Park inverter on the output of the low-frequency side and the power frequency side PI controller respectively to obtain the three-phase modulated wave components on the low-frequency side and the power frequency side.

[0044] The harmonic suppression unit is used to superimpose the three-phase modulation wave components of the low-frequency side and the power frequency side to form the modulation wave of the upper and lower bridge arms of each phase, and drive the corresponding sub-module according to the modulation wave to generate positive sequence differential mode voltage and / or negative sequence common mode voltage on each phase to suppress harmonics.

[0045] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0046] The beneficial effects of this invention are as follows: The positive sequence differential voltage u is obtained by performing Park transformation, proportional-integral control, and inverse Park transformation on the harmonic currents of the AC-AC inverter's high-frequency and low-frequency sides, respectively. gj_10Hz Negative sequence common-mode voltage u lj_80HzThis is applied to the three-phase bridge arm modulation wave to achieve precise capacitor voltage balance, ensuring the stable operation of the bipolar AC-AC inverter and improving power quality. It effectively cancels harmonics, ensures the stability of capacitor voltage between the three-phase bridge arm sub-modules, and improves the stability of power transmission between the mains frequency and low-frequency power grids, thus possessing high industrial value. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart of the method in Example 1;

[0049] Figure 2 This is a schematic diagram of the system structure in Example 1;

[0050] Figure 3 This is a flowchart of the method in Example 2;

[0051] Figure 4 This is a schematic diagram of the structure of the computer device of the present invention. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0053] Example 1:

[0054] like Figure 1 As shown: A harmonic suppression method for a bipolar AC-AC frequency converter includes the following steps:

[0055] Measure the three-phase current on the low-frequency side and the three-phase current on the power frequency side of the bipolar AC-AC inverter;

[0056] Park coordinate transformations were performed on the harmonic components of the low-frequency side three-phase current dominated by 80Hz and the harmonic components of the power frequency side three-phase current dominated by 10Hz, respectively, to obtain the d and q components of the low-frequency side harmonics and the power frequency side harmonics.

[0057] The d and q components of the low-frequency harmonics and the power frequency harmonics are input into the proportional-integral (PI) controller, respectively. The control target is set to 0, and the outputs of the low-frequency and power frequency PI controllers are obtained.

[0058] Park inverters are executed on the outputs of the PI controllers on the low-frequency side and the power frequency side respectively to obtain the three-phase modulated wave components on the low-frequency side and the power frequency side.

[0059] The three-phase modulation wave components on the low-frequency side and the power frequency side are superimposed to form the modulation waves of the upper and lower arms of each phase. The corresponding sub-modules are driven according to the modulation waves to generate positive sequence differential mode voltage and / or negative sequence common mode voltage on each phase to suppress harmonics.

[0060] The positive-sequence differential voltage u is obtained by performing Park transform, proportional-integral control, and inverse Park transform on the harmonic currents of the AC-AC inverter's high-frequency and low-frequency sides, respectively. gj_10Hz Negative sequence common-mode voltage u lj_80Hz This is applied to the three-phase bridge arm modulation wave to achieve precise capacitor voltage balance, ensuring the stable operation of the bipolar AC-AC inverter and improving power quality. It effectively cancels harmonics, ensures the stability of capacitor voltage between the three-phase bridge arm sub-modules, and improves the stability of power transmission between the mains frequency and low-frequency power grids, thus possessing high industrial value.

[0061] In this embodiment, the bipolar AC-AC inverter includes two secondary windings W2u and W2l. The secondary winding W2u adopts a Y0 connection, and the secondary winding W2l adopts a Y6 connection. The neutral point o' of W2u and the neutral point o'' of W2l are connected to each other.

[0062] Among them, the three-phase ports X, Y, and Z of W2u are connected to the upper end of the upper bridge arm of phases A, B, and C of the bipolar AC-AC inverter, respectively, and the three-phase ports x, y, and z of W2l are connected to the lower end of the lower bridge arm of phases A, B, and C of the bipolar AC-AC inverter, respectively.

[0063] Each phase of the bipolar AC-AC inverter contains N full-bridge sub-modules connected in series and a bridge arm inductor in each upper and lower bridge arm. The full-bridge sub-module contains the first to fourth IGBTs and an electrolytic capacitor, and each IGBT is connected in parallel with a reverse diode.

[0064] As a preferred embodiment of the above, Park coordinate transformation is performed on the harmonic components, which are predominantly 80Hz, in the low-frequency three-phase current, including:

[0065] ;

[0066] In the formula, i ld_80Hz and i lq_80Hz These represent the d and q components of the 80Hz harmonic component on the low-frequency side, respectively; i k Let u, v, w represent the k-th phase current of the low-frequency AC power grid, respectively.

[0067] Park coordinate transformation is performed on the harmonic components, predominantly 10Hz, in the three-phase current on the power frequency side, including:

[0068] ;

[0069] In the formula, i gd_10Hz and i gq_10Hz These represent the d and q components of the main harmonic components at 10Hz on the power frequency side, respectively; i j Let a, b, and c represent the j-th phase current of the low-frequency AC power grid, respectively.

[0070] The d and q components of the low-frequency harmonics are input into a proportional-integral (PI) controller, the control target is set to 0, and the output u of the PI controller is obtained. ld_80Hz and u lq_80Hz ,include:

[0071] ;

[0072] The d and q components of the power frequency harmonics are input into a proportional-integral (PI) controller, and the control target is set to 0. The output u of the PI controller is then obtained. gd_10Hz and u gq_10Hz ,include:

[0073] ;

[0074] In the formula, K p and K i These represent the proportional gain and integral gain of the controller, respectively.

[0075] In this embodiment, Park inverters are performed on the outputs of the PI controllers on the low-frequency side and the power frequency side, respectively, to obtain the three-phase modulated wave components on the low-frequency side and the power frequency side, including:

[0076] The output u of the low-frequency side proportional-integral controller ld_80Hz and u lq_80Hz Performing the inverse Park transform yields the three-phase upper and lower arm modulation waves u. lj_80Hz :

[0077] ;

[0078] The output u of the proportional-integral controller on the power frequency side gd_10Hz and u gq_10Hz Performing the inverse Park transform yields the three-phase upper and lower arm modulation waves u. gj_10Hz :

[0079] .

[0080] Specifically, the three-phase modulation wave components from the low-frequency side and the power frequency side are superimposed to form the modulation waves of the upper and lower arms of each phase, and the corresponding sub-modules are driven according to the modulation waves, including:

[0081] Bipolar AC-AC inverter j-phase upper bridge arm modulation wave y ju and lower bridge arm modulated wave y jl The expressions are as follows:

[0082] ;

[0083] In the formula, y j_l For low-frequency modulated wave components; y j_g It is a power frequency modulated wave component;

[0084] j-phase low-frequency modulation wave y j_l and power frequency modulation wave y j_g The expressions are as follows:

[0085] ;

[0086] In the formula, m g For power frequency modulation; m l For low-frequency modulation; ω g ω is the power frequency angular frequency; l θ is the low-frequency angular frequency. jg θ is the phase shift angle of phase j at power frequency; jl The phase shift angle for phase j at low frequency;

[0087] The voltage u of the upper bridge arm of phase j au and lower bridge arm voltage u al The expressions are as follows:

[0088] .

[0089] like Figure 2 As shown, this embodiment also includes a bipolar AC-AC inverter harmonic suppression system, using the method described above. The system includes:

[0090] The measurement unit is used to measure the three-phase current on the low-frequency side and the three-phase current on the power frequency side of a bipolar AC-AC inverter.

[0091] The Park transformation unit is used to perform Park coordinate transformation on the harmonic components of the low-frequency side three-phase current dominated by 80Hz and the harmonic components of the power frequency side three-phase current dominated by 10Hz, respectively, to obtain the d and q components of the low-frequency side harmonics and the power frequency side harmonics.

[0092] The PI control unit is used to input the d and q components of the low-frequency side harmonics and the power frequency side harmonics into the proportional-integral PI controller, set the control target to 0, and obtain the outputs of the low-frequency side and the power frequency side PI controller.

[0093] The Park inverter unit is used to perform Park inverter on the output of the PI controller on the low-frequency side and the power frequency side respectively to obtain the three-phase modulated wave components on the low-frequency side and the power frequency side.

[0094] The harmonic suppression unit is used to superimpose the three-phase modulation wave components of the low-frequency side and the power frequency side to form the modulation wave of the upper and lower bridge arms of each phase, and drive the corresponding sub-module according to the modulation wave to generate positive sequence differential mode voltage and / or negative sequence common mode voltage on each phase to suppress harmonics.

[0095] Example 2:

[0096] like Figure 3 As shown, the control method implementation system in this embodiment consists of two main parts: the first part is a bipolar AC-AC inverter 1, which has an ABC three-phase structure, with each phase containing identical upper and lower bridge arms. Each upper and lower bridge arm contains N full-bridge submodules 1-1 connected in series and one bridge arm inductor 1-2. The second part is a bipolar transformer 2, with the secondary winding W2u having three-phase ports X, Y, and Z, and the secondary winding W2l having three-phase ports x, y, and z. In the proposed bipolar AC-AC inverter, the power frequency side of the inverter is connected to the power frequency AC grid, and the low-frequency side is connected to the low-frequency AC grid via the bipolar transformer.

[0097] The connection method between the bipolar transformer and the frequency converter is as follows: the secondary winding W2u port X is connected to the upper end of the upper bridge arm of phase A of the bipolar AC-AC frequency converter, port Y is connected to the upper end of the upper bridge arm of phase B of the bipolar AC-AC frequency converter, and port Z is connected to the upper end of the upper bridge arm of phase C of the bipolar AC-AC frequency converter; the secondary winding W2l port x is connected to the lower end of the lower bridge arm of phase A of the bipolar AC-AC frequency converter, port y is connected to the lower end of the lower bridge arm of phase B of the bipolar AC-AC frequency converter, and port z is connected to the lower end of the lower bridge arm of phase C of the bipolar AC-AC frequency converter.

[0098] The full-bridge submodule includes a first to a fourth IGBT and a first electrolytic capacitor. The emitter of the first IGBT is connected to the collector of the second IGBT, and this connection point serves as the positive terminal of the full-bridge submodule. The emitter of the third IGBT is connected to the collector of the fourth IGBT, and this connection point serves as the negative terminal of the full-bridge submodule. The collectors of the first and third IGBTs are connected to the positive terminal of the first electrolytic capacitor. The emitters of the second and fourth IGBTs are connected to the negative terminal of the first electrolytic capacitor. Each of the first to fourth IGBTs is connected to an anti-parallel diode.

[0099] The neutral points o' and o'' of the secondary winding W2u and W2l of the bipolar transformer are interconnected. The voltage relationships between the transformer ports W2u and W2l are as follows: the voltages at ports X and x are 180° out of phase, the voltages at ports Y and y are 180° out of phase, and the voltages at ports Z and z are 180° out of phase.

[0100] In a bipolar AC-AC inverter, power can flow from the power frequency side to the low frequency side, or from the low frequency side to the power frequency side.

[0101] The bipolar AC-AC inverter has a modulation waveform y on the upper bridge arm of phase j. ju and lower bridge arm modulated wave y jl The expressions are as follows:

[0102] ;

[0103] In the formula, y j_l For low-frequency modulated wave components, y j_g For the power frequency modulated wave component, their expressions are as follows:

[0104] ;

[0105] In the formula, m g For power frequency modulation; m l For low-frequency modulation; ω g ω is the power frequency angular frequency; l θ is the low-frequency angular frequency. jg θ is the phase shift angle of phase j at power frequency; jl The phase shift angle for phase j is the low-frequency phase shift angle.

[0106] The voltage u of the upper bridge arm of phase j ju and lower bridge arm voltage u jl The expressions are as follows:

[0107] .

[0108] Please see Figure 4 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410, and when the computer program is executed by the processor 410, it performs the method described above.

[0109] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0110] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0111] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0112] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0113] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0114] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0115] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0116] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0117] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it includes one or a combination of the steps of the method embodiments.

[0118] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A harmonic suppression method for a bipolar AC-AC frequency converter, characterized in that, The method comprises the following steps: measuring three-phase currents on the low-frequency side and three-phase currents on the power-frequency side of a double-pole AC / AC frequency converter; performing Park coordinate transformation on harmonic components mainly at 80 Hz in the three-phase currents on the low-frequency side and on harmonic components mainly at 10 Hz in the three-phase currents on the power-frequency side, respectively, to obtain d and q components of the low-frequency side and the power-frequency side; inputting the d and q components of the low-frequency side and the power-frequency side into proportional integral (PI) controllers, respectively, and setting a control target as 0 to obtain outputs of the low-frequency side and the power-frequency side PI controllers; performing Park inverse transformation on the outputs of the low-frequency side and the power-frequency side PI controllers, respectively, to obtain three-phase modulation wave components on the low-frequency side and the power-frequency side; superimposing the three-phase modulation wave components on the low-frequency side and the power-frequency side to form modulation waves of upper and lower bridge arms of each phase, and driving corresponding sub-modules according to the modulation waves to generate positive sequence differential mode voltage and / or negative sequence common mode voltage for offsetting harmonics in each phase, thereby suppressing the harmonics.

2. The method of claim 1, wherein the method is applied to a double- line-to-line frequency converter. The double-pole AC / AC frequency converter comprises two secondary winding W2u and W2l, the secondary winding W2u adopts Y0 connection, the secondary winding W2l adopts Y6 connection, and the neutral point o' of W2u and the neutral point o'' of W2l are connected to each other.

3. The harmonic suppression method for a bipolar AC-AC frequency converter according to claim 2, characterized in that, The three-phase ports X, Y and Z of W2u are connected to upper ends of upper bridge arms of phases A, B and C of the double-pole AC / AC frequency converter, respectively, and the three-phase ports x, y and z of W2l are connected to lower ends of lower bridge arms of phases A, B and C of the double-pole AC / AC frequency converter, respectively.

4. The method of claim 1, wherein the method is a method of harmonic suppression for a double-fed induction generator (DFIG). Each of the upper and lower bridge arms of each phase of the double-pole AC / AC frequency converter comprises N full-bridge sub-modules and a bridge inductor connected in series, each full-bridge sub-module comprises first to fourth IGBTs and an electrolytic capacitor, and each IGBT is connected in parallel with a reverse diode.

5. The method of claim 1, wherein the method is a method of harmonic suppression for a double-fed induction generator (DFIG). The Park coordinate transformation on the harmonic components mainly at 80 Hz in the three-phase currents on the low-frequency side comprises: ； where i ld_80Hz and i lq_80Hz represent the d, q components of the 80 Hz harmonic component of the low frequency side; i k represent the k-th phase current of the low frequency AC grid, where k = u, v, w; The Park coordinate transformation on the harmonic components mainly at 10 Hz in the three-phase currents on the power-frequency side comprises: ； where i gd_10Hz and i gq_10Hz represent the d, q components of the fundamental 10 Hz harmonic component of the power frequency; i j represent the jth phase current of the low frequency AC grid, where j = a, b, c.

6. The harmonic suppression method for a bipolar AC-AC frequency converter according to claim 5, characterized in that, The d, q components of the low-frequency side harmonic are input into a proportional integral PI controller, the control target is set to 0, and the output u of the proportional integral PI controller is obtained ld_80Hz and u lq_80Hz , The method comprises: ； The d, q components of the power frequency side harmonic are input into a proportional integral PI controller, a control target is set as 0, and an output u of the proportional integral PI controller is obtained gd_10Hz and u gq_10Hz , comprising: ； In the formula, K p and K i respectively represent the controller proportional gain and integral gain.

7. The harmonic suppression method for a bipolar AC-AC frequency converter according to claim 5, characterized in that, The Park inverse transformation on the outputs of the low-frequency side and the power-frequency side PI controllers comprises: The low-frequency side proportional-integral controller outputs u ld_80Hz and u lq_80Hz The park inverse transformation is performed to obtain three-phase upper and lower bridge arm modulation waves u lj_80Hz : ； The output u of the power frequency side proportional-integral controller gd_10Hz and u gq_10Hz The park inverse transformation is performed to obtain three-phase upper and lower bridge arm modulation waves u gj_10Hz : 。 8. The method of claim 5, wherein the harmonic suppression is performed by a filter. The superimposition of the three-phase modulation wave components on the low-frequency side and the power-frequency side to form modulation waves of upper and lower bridge arms of each phase, and the driving of corresponding sub-modules according to the modulation waves comprises: The expression of the bipolar AC-AC frequency converter j-phase upper bridge arm modulation wave y ju and lower bridge arm modulation wave y jl is respectively: ； wherein y j_l is a low frequency modulated wave component; y j_g is a power frequency modulated wave component; j phase low frequency modulation wave y j_l and power frequency modulation wave y j_g The expressions are respectively: ； where m g is the power frequency modulation; m l is the low frequency modulation; ω g is the power frequency angular frequency; ω l is the low frequency angular frequency; θ jg is the j-phase power frequency phase shift angle; θ jl is the j-phase low frequency phase shift angle; j the upper bridge leg voltage u au and the lower bridge leg voltage u al The expressions are respectively: 。 9. A system for harmonic suppression in a double-fed induction generator, comprising: The system comprises: a measurement unit for measuring three-phase currents on the low-frequency side and three-phase currents on the power-frequency side of a double-pole AC / AC frequency converter; a Park transformation unit for performing Park coordinate transformation on harmonic components mainly at 80 Hz in the three-phase currents on the low-frequency side and on harmonic components mainly at 10 Hz in the three-phase currents on the power-frequency side, respectively, to obtain d and q components of the low-frequency side and the power-frequency side; a PI control unit for inputting the d and q components of the low-frequency side and the power-frequency side into proportional integral (PI) controllers, respectively, and setting a control target as 0 to obtain outputs of the low-frequency side and the power-frequency side PI controllers; a Park inverse transformation unit for performing Park inverse transformation on the outputs of the low-frequency side and the power-frequency side PI controllers, respectively, to obtain three-phase modulation wave components on the low-frequency side and the power-frequency side; and a superimposition unit for superimposing the three-phase modulation wave components on the low-frequency side and the power-frequency side to form modulation waves of upper and lower bridge arms of each phase, and driving corresponding sub-modules according to the modulation waves to generate positive sequence differential mode voltage and / or negative sequence common mode voltage for offsetting harmonics in each phase, thereby suppressing the harmonics. A harmonic suppression unit is configured to superimpose low-frequency side and power-frequency side three-phase modulation wave components to form modulation waves of upper and lower bridge arms of each phase, and drive corresponding sub-modules according to the modulation waves to generate positive sequence differential mode voltage and / or negative sequence common mode voltage for canceling harmonics in each phase, thereby suppressing harmonics.

10. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor, when executing the computer program, implements the method of any one of claims 1-8.

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