A method and system for harmonic current suppression of a cascaded sub-module tied diode bridge controllable rectifier

Abstract

This invention discloses a method and system for suppressing harmonic currents in a cascaded submodule-connected diode bridge controllable rectifier, relating to the field of harmonic suppression technology for power electronic converters. The controllable rectifier comprises cascaded submodule units, a transformer, and a diode rectifier unit. This invention obtains the amplitude and phase angle of harmonic current components in the AC line through Fourier decomposition. The amplitude of the harmonic current components is used for negative feedback PI control to generate a compensated harmonic voltage amplitude. The phase angle of the harmonic current components is increased by 90 degrees to obtain the compensated harmonic voltage phase angle. The compensated harmonic voltage component is subtracted from the modulation wave of the cascaded submodules to generate a corresponding harmonic current component that cancels out the original harmonic current components in the AC line. This invention achieves harmonic current filtering without requiring additional filtering equipment for the diode rectifier unit, has a simple control strategy, and effectively filters out harmonic current components in the AC line.

Description

Technical Field

[0001] This invention relates to the field of harmonic suppression in power electronic equipment, and more particularly to a method for suppressing AC side harmonic currents in a cascaded submodule-connected diode bridge controllable rectifier. Background Technology

[0002] With the continuous increase in the utilization of renewable energy, high-voltage direct current (HVDC) transmission has developed rapidly. Submodule-connected diode bridge controlled rectifiers, with their lightweight and flexible characteristics, can be applied to such systems. However, due to the use of 12-pulse diode bridge rectifiers, the AC side lines contain a large amount of 11th and 13th harmonic currents. Currently, most solutions address this issue using additional filtering equipment, but this increases system costs. Therefore, there is an urgent need for a simple and effective harmonic current suppression strategy that does not require additional filtering equipment. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a harmonic current suppression strategy for a cascaded submodule-connected diode bridge controllable rectifier, so as to effectively suppress the AC side harmonic current of the cascaded submodule-connected diode bridge controllable rectifier.

[0004] To solve the above technical problems, the present invention is achieved by adopting the following technical solution:

[0005] This invention proposes a harmonic current suppression strategy for a cascaded submodule-connected diode bridge controllable rectifier. This cascaded submodule-connected diode bridge controllable rectifier mainly consists of a three-phase Y-connected cascaded submodule, a transformer, and a diode rectifier unit.

[0006] The aforementioned three-phase Y-connected cascaded submodule is characterized in that each phase is composed of N full-bridge submodules cascaded together. Each full-bridge submodule consists of a capacitor C and four anti-parallel diodes of IGBTs (Insulated-Gate Bipolar Transistors) T1~T4. The emitter of T1 is connected to the collector of T2, and this point serves as the positive output of the full-bridge submodule. The emitter of T3 is connected to the collector of T4, and this point serves as the negative output of the full-bridge submodule. The collectors of T1 and T3 are connected to the positive terminal of capacitor C, and the emitters of T2 and T4 are connected to the negative terminal of capacitor C.

[0007] The transformer has a Y-type connection on the main side and an I-type connection on the secondary side. The left side of the secondary side is connected to the cascaded submodule, and the right side of the secondary side is connected to the AC side of the diode rectifier unit.

[0008] The diode rectifier unit consists of two sets of 6-pulse diode rectifier bridges connected in series. The main side of the transformers at the ports of the two sets of diode rectifier bridges is Y-connected, and the secondary side is Δ-connected and Y-connected respectively. This results in a 30° phase shift, and the two sets of 6-pulse diode bridges form a 12-pulse DC voltage output. At this time, the AC side current mainly contains the 11th and 13th harmonics.

[0009] The AC side harmonic current of the cascaded submodule-connected diode bridge controllable rectifier mainly refers to the 11th and 13th harmonic currents.

[0010] Therefore, this invention proposes a method for suppressing harmonic currents in a cascaded submodule-connected diode bridge controllable rectifier, specifically including the following steps:

[0011] S1. When the system is running stably, the amplitudes M of the 11th and 13th harmonics of the AC side current are obtained by Fourier decomposition. a11 M a13 and phase angle P a11 P a13 ;

[0012] S2, the amplitude M of the 11th harmonic current a11 Subtracting from 0 and passing through a PI control loop yields the compensated amplitude of the 11th harmonic voltage, and the phase angle P of the 11th harmonic current is then calculated. a11 Adding 90° will yield the compensated 11th harmonic voltage phase angle;

[0013] S3, the amplitude M of the 13th harmonic current a13 Subtracting from 0 and passing through a PI control circuit yields the amplitude of the compensated 13th harmonic voltage, and the phase angle P of the 13th harmonic current is then calculated. a13 Adding 90° will yield the compensated 13th harmonic voltage phase angle;

[0014] S4. Subtracting the 11th and 13th harmonic voltages compensated above from the modulation wave of the original cascaded submodule will achieve the filtering of AC side harmonic current.

[0015] Furthermore, the total harmonic distortion (THD) of the current is calculated using the amplitude of the harmonic current components. i ) Calculation verification:

[0016] ,

[0017] Where I1 is the effective value of the fundamental current, I n The effective value of the nth harmonic current (n≥2).

[0018] Secondly, this invention proposes a harmonic current suppression system for a cascaded submodule-connected diode bridge controllable rectifier, comprising:

[0019] The harmonic voltage component calculation module is used to obtain the amplitude and phase angle of the harmonic current component in the AC side line through Fourier decomposition. The amplitude of the harmonic current component can be used for negative feedback PI control to generate the compensated harmonic voltage amplitude. The compensated harmonic voltage phase angle is obtained by adding 90° to the phase angle of the harmonic current.

[0020] The harmonic current filtering module is used to subtract the compensated harmonic voltage component from the modulation wave of the original cascaded submodule, thereby filtering out the harmonic current in the AC side line.

[0021] Thirdly, the present invention provides an electronic system including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described method.

[0022] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described method.

[0023] Finally, the present invention also proposes a computer program product, including a computer program / instructions, wherein when the computer program / instructions are executed by a processor, the steps of the method proposed in the present invention are employed.

[0024] By adopting the above technical solution, compared with the prior art, the present invention has the following technical effects:

[0025] 1. The harmonic current suppression strategy of the cascaded submodule-connected diode bridge controllable rectifier proposed in this invention obtains the amplitude and phase angle of the corresponding harmonic current through Fourier decomposition, and obtains the harmonic voltage on the modulation wave of the cascaded submodule through closed-loop PI control. Since this invention uses PI control, there is no steady-state error, and harmonics can always be effectively suppressed.

[0026] 2. The harmonic current suppression strategy of the cascaded sub-module connected diode bridge controllable rectifier proposed in this invention does not require a precise mathematical model or additional filtering equipment. The algorithm is simple and efficient and can effectively suppress AC side harmonic current. Attached Figure Description

[0027] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the topology of a cascaded submodule-connected diode bridge controllable rectifier according to an embodiment of the present invention.

[0029] Figure 2 This is a harmonic current suppression strategy according to an embodiment of the present invention.

[0030] Figure 3 The three-phase AC currents and their total harmonic distortion (THD) before harmonic current suppression according to an embodiment of the present invention are shown. i ).

[0031] Figure 4 The three-phase AC side currents and their total harmonic distortion (THD) after harmonic current suppression according to embodiments of the present invention are... i ). Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0033] like Figure 1 As shown, this cascaded submodule-connected diode bridge controlled rectifier mainly consists of three-phase Y-connected cascaded submodules, a transformer, and a diode rectifier unit. Figure 1 in u mj (j=a, b, c) represents the three-phase voltage output of the cascaded submodule, u Lj (j=a, b, c) represents the three-phase leakage inductance voltage on the secondary side of the transformer, u sj (j=a, b, c) represents the three-phase output voltage of the transformer secondary side, u dj (j=a, b, c) represents the three-phase input voltage on the AC side of the diode rectifier unit, i sj (j=a, b, c) represents the three-phase current on the AC side, I dc V is the DC-side output current. dc This is the DC-side output voltage.

[0034] The aforementioned three-phase Y-connected cascaded submodules are composed of N full-bridge submodules cascaded in each phase. Each full-bridge submodule consists of an IGBT with one capacitor C and four anti-parallel diodes, namely T1 to T4. The emitter of T1 is connected to the collector of T2, and this point serves as the positive output of the full-bridge submodule. The emitter of T3 is connected to the collector of T4, and this point serves as the negative output of the full-bridge submodule. The collectors of T1 and T3 are connected to the positive terminal of capacitor C, and the emitters of T2 and T4 are connected to the negative terminal of capacitor C.

[0035] The transformer has a Y-type connection on the main side and an I-type connection on the secondary side. The left side of the secondary side is connected to the cascaded submodule, and the right side of the secondary side is connected to the AC side of the diode rectifier unit.

[0036] The diode rectifier unit consists of two sets of 6-pulse diode rectifier bridges connected in series. The main side of the transformers at the ports of the two sets of diode rectifier bridges is Y-connected, and the secondary side is Δ-connected and Y-connected respectively. This results in a 30° phase shift, and the two sets of 6-pulse diode bridges form a 12-pulse DC voltage output. At this time, the AC side current mainly contains the 11th and 13th harmonics.

[0037] Figure 2 This is the harmonic current suppression strategy used in this invention, M in the figure. a11 M a13 These are the amplitudes of the 11th and 13th harmonic currents of phase A, respectively, P a11 P a13 The phase angles of the 11th and 13th harmonic currents of phase A are f, respectively. 11 f 13 These are the 11th and 13th harmonic compensation voltage frequencies of phase A, respectively, u ma11 u ma13 These are the 11th and 13th harmonic compensation voltages of phase A, u mas For the total harmonic compensation voltage of phase A, u maref For the modulated wave of the A-phase cascaded submodule, u maref 'This is the modulation waveform of the A-phase cascaded submodule after subtracting the compensation harmonic voltage. When the system is running stably, the amplitude M of the 11th harmonic current of phase A is...' a11 The amplitude of the 11th harmonic voltage of phase A is obtained by subtracting it from 0 and then passing it through a PI control loop. The phase angle P of the 11th harmonic current of phase A is then calculated. a11 Adding 90° yields the phase angle of the compensated 11th harmonic voltage in phase A. Similarly, the amplitude and phase angle of the compensated 13th harmonic voltage in phase A can be obtained. Finally, subtracting the above-mentioned 11th and 13th harmonic voltages from the modulation wave of the original cascaded submodules effectively suppresses the harmonic current on the AC side of phase A. Similarly, the harmonic currents in phases B and C can be suppressed.

[0038] In this embodiment of the invention, the amplitude of the harmonic current components is used to calculate the total harmonic distortion (THD) of the current. i Calculate the inhibition effect:

[0039] ,

[0040] Where I1 is the effective value of the fundamental current, I n The effective value of the nth harmonic current (n≥2).

[0041] like Figure 3 As shown, this represents the three-phase AC currents before harmonic current suppression and their total harmonic distortion (THD). i );like Figure 4As shown, this represents the three-phase AC current after harmonic current suppression and its total harmonic distortion (THD). i After employing the harmonic suppression method of the present invention, the total harmonic distortion (THD) of the current is reduced. i The percentage decreased from 7.1% to 2.9%, indicating a good inhibitory effect.

[0042] Example 1: This example proposes a method for suppressing harmonic currents in a cascaded submodule-connected diode bridge controllable rectifier, including:

[0043] The amplitude and phase angle of the harmonic current were extracted by Fourier decomposition.

[0044] Furthermore, the amplitude of the harmonic current is subtracted from 0 and then passed through a PI control loop to obtain the amplitude of the compensated harmonic voltage. The phase angle of the compensated harmonic voltage is obtained by adding 90° to the phase angle of the harmonic current.

[0045] Furthermore, the compensated harmonic voltage is subtracted from the original cascaded submodule modulation wave.

[0046] Furthermore, as the amplitude of the harmonic current continuously decreases to 0, the PI control process tends to stabilize.

[0047] Furthermore, through the total harmonic distortion (THD) of the current... i The changes in the harmonic current suppression strategy are used to verify its effectiveness.

[0048] Example 2: This example proposes a harmonic current suppression system for a cascaded submodule-connected diode bridge controllable rectifier, comprising:

[0049] The harmonic voltage component calculation module is used to obtain the amplitude and phase angle of the harmonic current component in the AC side line through Fourier decomposition, use the amplitude of the harmonic current component for negative feedback PI control to generate the compensated harmonic voltage amplitude, and add 90° to the phase angle of the harmonic current to obtain the compensated harmonic voltage phase angle.

[0050] The harmonic current filtering module is used to subtract the compensated harmonic voltage component from the modulation wave of the original cascaded submodule, thereby filtering out the harmonic current in the AC side line.

[0051] Example 3: This example provides an electronic system including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the method proposed in the above example.

[0052] Example 4: This example provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method proposed in the above examples.

[0053] It should be noted that the electronic system can use terminal devices such as desktop computers, laptops, or cloud servers. Furthermore, terminal devices include, but are not limited to, processors and memory. For example, terminal devices can also include input / output devices, network access devices, and buses.

[0054] Furthermore, the processor can be a central processing unit (CPU). Of course, depending on the actual use, other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. can also be used. The general-purpose processor can be a microprocessor or any conventional processor, etc., and this application does not limit it in this regard.

[0055] Furthermore, the memory can be an internal storage unit of the terminal device, such as the hard disk or RAM of the terminal device, or an external storage device of the terminal device, such as a plug-in hard disk, smart memory card (SMC), secure digital card (SD), or flash memory card (FC) equipped on the terminal device. In addition, the memory can also be a combination of the internal storage unit and the external storage device of the terminal device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory can also be used to temporarily store data that has been output or will be output. This application does not limit this.

[0056] Furthermore, through this electronic system, any one of the methods in the above embodiments can be stored in the memory of the electronic system and loaded and executed on the processor of the terminal device for convenient use.

[0057] Example 5: This example also discloses a computer program product, including a computer program / instruction, wherein when the computer program / instruction is executed by a processor, it employs the steps of any of the methods in the above examples.

[0058] The computer program can be stored in a computer-readable medium. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or certain middleware. The computer-readable medium includes any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the computer-readable medium includes, but is not limited to, the above-mentioned components.

[0059] It should be further noted that the detection methods in the above embodiments are stored in the computer-readable storage medium and loaded and executed on the processor through this computer-readable storage medium, so as to facilitate the storage and application of the above methods. In the description of this specification, the descriptions of terms such as "an embodiment," "example," "specific example," etc., mean that the specific feature, structure, material, or characteristic described in connection with the 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.

[0060] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for suppressing harmonic currents in a cascaded submodule-connected diode bridge controllable rectifier, characterized in that, The method includes: The amplitude and phase angle of the harmonic current components in the AC side line are obtained by Fourier decomposition. The amplitude of the harmonic current components is used for negative feedback PI control to generate the compensated harmonic voltage amplitude. The phase angle of the harmonic current components is increased by 90° to obtain the compensated harmonic voltage phase angle. The compensated harmonic voltage components are composed of the compensated harmonic voltage amplitude and phase angle. By subtracting the aforementioned compensated harmonic voltage component from the modulation wave of the original cascaded submodule, harmonic current in the AC side line is filtered out.

2. The method according to claim 1, characterized in that, The controllable rectifier consists of a three-phase Y-connected cascaded submodule, a transformer, and a diode rectifier unit. The three-phase Y-connected cascaded submodules are composed of N full-bridge submodules cascaded in each phase. Each full-bridge submodule consists of an IGBT (T1-T4) with a capacitor and four anti-parallel diodes. The emitter of the first IGBT (T1) is connected to the collector of the second IGBT (T2), and this point is used as the positive output of the full-bridge submodule. The emitter of the third IGBT (T3) and the collector of the fourth IGBT (T4) are connected, and this point is used as the negative output of the full-bridge submodule. The collectors of the first IGBT (T1) and the third IGBT (T3) are connected to the positive terminal of the capacitor, and the emitters of the second IGBT (T2) and the fourth IGBT (T4) are connected to the negative terminal of the capacitor. The transformer's main side adopts a Y-type connection, and the secondary side adopts an I-type connection. The left side of the secondary side is connected to the cascaded sub-module, and the right side of the secondary side is connected to the AC side of the diode rectifier unit. The diode rectifier unit consists of two sets of 6-pulse diode rectifier bridges connected in series. The main side of the transformers at the ports of the two sets of diode rectifier bridges is Y-connected, and the secondary side is Δ-connected and Y-connected respectively. This results in a 30° phase shift, and the two sets of 6-pulse diode rectifier bridges form a 12-pulse DC voltage output. At this time, the AC side current contains the 11th and 13th harmonics.

3. The method according to claim 2, characterized in that, The amplitudes of the 11th and 13th harmonic components of the AC current are used for negative feedback PI control to obtain the compensated amplitudes of the 11th and 13th harmonic voltages. The phase angles of the 11th and 13th harmonic components of the AC current are obtained by adding 90° to them. The above harmonic voltage amplitudes and phase angles are then subtracted from the modulation wave of the original cascaded submodule to achieve AC side harmonic current filtering.

4. The method according to any one of claims 1-3, characterized in that, This also includes the total harmonic distortion (THD) of the current. i The changes verify the effectiveness of the harmonic current suppression method.

5. The method according to claim 4, characterized in that, The total harmonic distortion (THD) of the current is calculated using the amplitude of the harmonic current components. i calculate: ， Where I1 is the effective value of the fundamental current, I n Let be the effective value of the nth harmonic current, where n ≥ 2.

6. A harmonic current suppression system for a cascaded submodule-connected diode bridge controllable rectifier, characterized in that, include: The harmonic voltage component calculation module is used to obtain the amplitude and phase angle of the harmonic current component in the AC side line through Fourier decomposition. The amplitude of the harmonic current component is used for negative feedback PI control to generate the compensated harmonic voltage amplitude. The phase angle of the harmonic current component is added by 90° to obtain the compensated harmonic voltage phase angle. The compensated harmonic voltage component is composed of the compensated harmonic voltage amplitude and phase angle. The harmonic current filtering module is used to subtract the compensated harmonic voltage component from the modulation wave of the original cascaded submodule, thereby filtering out the harmonic current in the AC side line.

7. The system according to claim 6, characterized in that, It also includes a verification module for calculating the total harmonic distortion (THD) of the current. i The changes verify the effectiveness of the harmonic current suppression method.

8. A computer program product comprising a computer program / instructions, characterized in that, When a computer program / instruction is executed by a processor, the steps of the method described in any one of claims 1 to 5 are employed.

9. An electronic system comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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