High-frequency resonance suppression method and device for flexible direct-current power transmission system

Abstract

The invention discloses a high-frequency resonance suppression method and device for a flexible direct-current power transmission system. The method comprises the following steps: firstly, obtaining the harmonic content of grid-side alternating-current voltage or alternating-current current; then, when the harmonic content exceeds a threshold value, a phase compensator is put into an inner loop current control link of the flexible direct current power transmission system; wherein the parameters of the phase compensator are determined by a transfer function, and the transfer function is obtained according to the harmonic frequency with the highest content exceeding the threshold value. The method is easy to implement, the positive resistance interval range of the flexible direct current system can be expanded on the basis that the steady state and dynamic performance of an original control strategy of the flexible direct current system is not reduced, the high-frequency oscillation risk generated by the flexible direct current system and an external alternating current power grid or a new energy island system is greatly reduced, and the operation stability of the flexible direct current system is improved.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission and distribution, and specifically relates to a method and device for suppressing high-frequency resonance in a flexible DC power transmission system. Background Technology

[0002] With the continuous increase in installed capacity of new energy sources such as wind power and photovoltaics, and the vigorous development of offshore wind power, large-scale transmission of new energy via flexible DC is gradually becoming one of the important technical means for grid connection of new energy. High-frequency oscillations have repeatedly occurred in flexible DC projects that have been built and put into operation both domestically and internationally. Analysis of the system's AC impedance reveals that the negative resistance of the flexible DC converter in the high-frequency band is the root cause of the system oscillations, while the control link delay t... d This is a significant factor causing negative resistance in flexible DC converters. While the impact of voltage feedforward delay has been addressed in engineering practice, converters employing current closed-loop control still exhibit this effect. The system still exhibits negative impedance characteristics within the specified frequency range. Several studies have investigated methods to suppress high-frequency oscillations. For example, flexible DC systems employ weak feedback control algorithms to alter their impedance characteristics, but this leads to difficulties in suppressing fault through-current. Flexible DC systems can also correct the impedance at the resonant point by configuring adaptive harmonic converters, but this requires real-time monitoring of each harmonic frequency and simultaneously affects the impedance characteristics of other frequency bands. Other studies have proposed altering the grid impedance, such as by adding impedance adapters, but this poses operational risks during equipment maintenance. Further research is needed to find a simple and effective way to improve the AC equivalent impedance characteristics of flexible DC systems without affecting their existing performance. Summary of the Invention

[0003] The purpose of this invention is to provide a method and apparatus for suppressing high-frequency resonance in a flexible DC transmission system, thereby increasing the positive impedance range of the AC equivalent impedance of the flexible DC system and reducing the risk of high-frequency oscillation in the system.

[0004] To achieve the above objectives, the solution of the present invention is:

[0005] A method for suppressing high-frequency resonance in a flexible DC transmission system includes,

[0006] Obtain the harmonic content of the grid-side AC voltage or AC current;

[0007] When the harmonic content exceeds a threshold value, a phase compensator is activated in the inner loop current control stage of the flexible DC transmission system; wherein, the parameters of the phase compensator are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

[0008] The transfer function of the phase compensator is: Wherein, τ1 and τ2 are compensator parameters, m is the sign bit, and s is the Laplace operator; wherein, the phase compensator parameters τ1 and τ2 are designed according to the positive impedance range of improving the equivalent AC impedance of flexible DC, and m is used to set the adjustment direction.

[0009] In the flexible DC transmission system, the phase compensator is installed in the inner loop current control link. This includes the current control link adopting proportional-integral control, with the phase compensator set in the proportional control link of the proportional-integral control. The output of the proportional controller is then summed with the output of the integral controller after passing through the phase compensator.

[0010] In this process, a phase compensator is installed in the inner loop current control stage of the flexible DC transmission system. This includes setting the phase compensator in the current feedback stage of the current control stage, and then subtracting the measured current value from the current reference value after passing through the phase compensator. The difference is used as the input of the current control stage.

[0011] The process of installing a phase compensator in the inner loop current control stage of the flexible DC transmission system includes setting the phase compensator in the output stage of the current control stage. The current control stage adopts proportional-integral control, and the output of the proportional-integral control is obtained after passing through the phase compensator to obtain the output of the current control stage.

[0012] Among these, obtaining the harmonic content of the grid-side AC voltage or AC current includes,

[0013] Obtain the AC voltage or AC current from the grid side;

[0014] Real-time FFT analysis is performed on the grid-side AC voltage or AC current to obtain the amplitude of each harmonic and its percentage relative to the fundamental amplitude.

[0015] A high-frequency resonance suppression device for a flexible DC transmission system includes,

[0016] The harmonic detection unit is configured to acquire the harmonic content of the grid-side AC voltage or AC current;

[0017] The current control unit is configured as the inner loop current control element of the flexible DC transmission system.

[0018] A phase compensation unit is configured to connect to the current control unit for phase compensation when the harmonic content exceeds a threshold value, thereby improving the positive impedance range of the flexible DC equivalent AC impedance; and,

[0019] A parameter adjustment unit is configured to adjust the parameters of the phase compensation unit; wherein the parameters of the phase compensation unit are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

[0020] The transfer function of the phase compensator is: Wherein, τ1 and τ2 are compensator parameters, m is the sign bit, and s is the Laplace operator; wherein, the phase compensator parameters τ1 and τ2 are designed according to the positive impedance range of improving the equivalent AC impedance of flexible DC, and m is used to set the adjustment direction.

[0021] The current control unit adopts proportional-integral control. The input of the phase compensation unit is connected to the output of the proportional controller. The output of the proportional controller is then summed with the output of the integral controller after passing through the phase compensation unit.

[0022] The phase compensation unit is connected to the current feedback loop of the current control unit. The measured current value is passed through the phase compensator and then the difference is calculated with the current reference value. The difference is used as the input of the current control unit.

[0023] The phase compensation unit is connected to the output stage of the current control unit. The current control unit adopts proportional-integral control, and the output of the proportional-integral control is used as the output of the current control unit after passing through the phase compensation unit.

[0024] The harmonic detection unit acquires the harmonic content of the grid-side AC voltage or AC current, including:

[0025] Obtain the AC voltage or AC current from the grid side;

[0026] Real-time FFT analysis is performed on the grid-side AC voltage or AC current to obtain the amplitude of each harmonic and its percentage relative to the fundamental amplitude.

[0027] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor; the processor executes the computer program to implement the steps of the high-frequency resonance suppression method for a flexible DC transmission system as described above.

[0028] A computer-readable storage medium storing a computer program; when executed by a processor, the computer program implements the steps of the high-frequency resonance suppression method for the flexible DC transmission system as described above.

[0029] By adopting the above scheme, this invention improves the positive impedance range of the flexible DC-AC equivalent impedance through a phase compensator, thereby reducing the risk of high-frequency oscillation in the system. The phase compensator employs a first-order lead-lag controller. In the low-frequency range, the gain and phase angle remain constant; in the high-frequency range, the gain is fixed and the phase angle remains constant; in the mid-frequency range, the gain gradually changes to a fixed value, and the phase angle gradually changes to a certain value before returning to its original value. By rationally designing the parameters of the phase compensator, the frequency range of the flexible DC negative resistance circuit can be changed. The phase angle characteristics allow the upper limit of the positive resistance frequency of the flexible DC converter to be determined by... Maximum upgrade to The improvement is as high as 100%. Taking a control link delay of 120µs in a certain project as an example, after adopting this solution, the lowest frequency at which the flexible DC converter exhibits negative resistance can be increased from 2000Hz to 4000Hz, significantly reducing the risk of high-frequency resonance with the system. Flexible DC systems mainly operate at the power frequency, and high-frequency harmonics can be ignored when resonance does not occur. Therefore, this invention has almost no impact on the steady-state and dynamic performance of the flexible DC system. Considering that the flexible DC system does not resonate under most operating conditions, the input and output of the phase compensator are equal when τ1 = τ2. Therefore, the initial parameters of the phase compensator can be set to τ1 = τ2. By monitoring the harmonic content in the compensation interval, τ1 or τ2 can be automatically adjusted to achieve dynamic adjustment of the positive resistance interval, further reducing operational impact. This invention is simple to implement. Without reducing the steady-state and dynamic performance of the original control strategy of the flexible DC system, it can expand the range of the positive resistance interval of the flexible DC system, significantly reducing the risk of high-frequency oscillations between the flexible DC system and the external AC grid or renewable energy islanding system, and improving the operational stability of the flexible DC system. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the first embodiment of the suppression method of the present invention;

[0031] Figure 2 This is a schematic diagram of a second embodiment of the suppression method of the present invention;

[0032] Figure 3 This is a schematic diagram of the third embodiment of the suppression method of the present invention;

[0033] Figure 4 This is a schematic diagram of the fourth embodiment of the suppression method of the present invention;

[0034] Figure 5 This is a schematic diagram of an embodiment of the suppression device of the present invention. Detailed Implementation

[0035] The technical solution and beneficial effects of the present invention will be described in detail below with reference to specific embodiments.

[0036] This invention provides a method for suppressing high-frequency resonance in a flexible DC transmission system, comprising:

[0037] Obtain the harmonic content of the grid-side AC voltage or AC current;

[0038] When the harmonic content exceeds a threshold value, a phase compensator is activated in the inner loop current control stage of the flexible DC transmission system; wherein, the parameters of the phase compensator are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

[0039] This invention provides a high-frequency resonance suppression method for a flexible DC transmission system. A phase compensator is set in the inner loop current control loop. When the harmonic content of the grid-side AC voltage or AC current exceeds a threshold value, the phase compensator is activated. The harmonic frequency with the highest content exceeding the threshold value is sent to the phase compensator. The phase compensator transfer function is output according to the harmonic frequency to determine the compensator parameters.

[0040] The transfer function of the phase compensator is: Where τ1 and τ2 are the compensator parameters, m is the sign bit (0 or 1), and s is the Laplace operator; the phase compensator parameters τ1 and τ2 are designed according to the positive impedance range for improving the equivalent AC impedance of flexible DC. According to theoretical calculations, the phase compensator does not function when τ1 = τ2, and the upper limit of the positive impedance frequency is... (t d To control link delay; when τ1 > τ2, the phase compensator increases the positive impedance range, and can increase the upper frequency limit of the positive impedance by up to twice 2f. d Considering that the amplitude of the phase compensator at high frequencies is greater when τ1 > τ2. It amplifies the signal, but the transfer function is also affected by the discretization task cycle. In practical applications, the upper limit of the positive impedance frequency can be appropriately reduced to decrease the amplification effect on high-frequency harmonics; the sign bit m is used to set the adjustment direction.

[0041] like Figure 1 The figure shows an embodiment of the high-frequency resonance suppression method of the present invention. The phase compensator is set in the proportional-integral controller stage of the current control. The output of the proportional controller is summed with the output of the integral controller after passing through the phase compensator.

[0042] like Figure 2 The figure shows another embodiment of the high-frequency resonance suppression method of the present invention. The phase compensator is set in the current feedback loop of the current control. The current feedback value is then compared with the current reference value after passing through the phase compensator.

[0043] like Figure 3 The figure shows a third embodiment of the high-frequency resonance suppression method of the present invention. The phase compensator is set in the output stage of the current control, and the output of the proportional-integral controller is generated into a modulation wave after passing through the phase compensator.

[0044] Once the position of the phase compensator is determined, the value of its sign bit m can be determined.

[0045] like Figure 4The above is a fourth embodiment of the high-frequency resonance suppression method of the present invention. The harmonic content of the grid current in a set frequency band is monitored in real time. When the harmonic content is higher than the harmonic threshold, the parameters of the phase compensator are automatically adjusted so that the flexible DC system presents positive impedance in that frequency band.

[0046] In a preferred embodiment, the harmonic content of the grid voltage within a set frequency band is monitored in real time. When the harmonic content is higher than the harmonic threshold, the parameters of the phase compensator are automatically adjusted so that the flexible DC system presents positive impedance in that frequency band.

[0047] In a preferred embodiment of the present invention, the harmonic content of the grid-side voltage or current of the converter is monitored in real time, and the grid-side AC voltage or current is subjected to real-time FFT analysis to obtain the amplitude of each harmonic and its percentage relative to the fundamental amplitude; wherein, in a preferred embodiment, the frequency interval of the FFT analysis is 50Hz, and the detection range is 500 to 4000Hz.

[0048] In a preferred embodiment of the present invention, the threshold value is a harmonic content threshold value, and the threshold value ranges from 5% to 10%.

[0049] The reference adjustment of the phase compensator can be dynamically adjusted using segmented parameters. Taking a method where τ2 is constant and τ1 is variable as an example, τ1 can be set to τ... 11 τ 12 The two segmented parameters correspond to the upper limit of the positive resistance f. 11 f 12 Initially, τ1 = τ2, the phase compensator has no effect, and the output is equal to the input; when (f) is detected... d f 12 When the AC harmonic content in the frequency band is higher than the harmonic threshold, if at the same time (f d f 11 If the AC harmonic content within the frequency band is also higher than the harmonic threshold, then τ1 = τ 11 Otherwise τ1=τ 12 When the phase difference between the output and input of the phase compensator is less than the exit threshold, τ1 is pressed again by τ. 12 τ 11 τ2 is gradually restored to its value.

[0050] The present invention also provides a high-frequency resonance suppression device for a flexible DC transmission system, comprising,

[0051] The harmonic detection unit is configured to acquire the harmonic content of the grid-side AC voltage or AC current;

[0052] The current control unit is configured as the inner loop current control element of the flexible DC transmission system.

[0053] A phase compensation unit is configured to connect to the current control unit for phase compensation when the harmonic content exceeds a threshold value, thereby improving the positive impedance range of the flexible DC equivalent AC impedance; and,

[0054] A parameter adjustment unit is configured to adjust the parameters of the phase compensation unit; wherein the parameters of the phase compensation unit are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

[0055] This invention also provides a high-frequency resonance suppression device for a flexible DC transmission system, whose input includes system AC voltage and AC current, and whose output includes a converter valve modulation wave, such as... Figure 5 The diagram illustrates an embodiment of the apparatus of the present invention, the apparatus comprising:

[0056] Current control unit: The closed-loop control link for alternating current, which achieves precise control through a proportional-integral controller;

[0057] Phase compensation unit: Improves the positive impedance range of the flexible DC equivalent AC impedance through the phase compensator;

[0058] Harmonic detection unit: Real-time monitoring of the harmonic content of AC voltage / AC current within a set frequency band;

[0059] Parameter adjustment unit: Automatically adjusts the parameters of the phase compensator according to the harmonics.

[0060] In a preferred embodiment, the phase compensation unit is connected in series with the proportional controller of the current control unit, and its input is connected to the output of the proportional controller, and its output is summed with the output of the integral controller.

[0061] In a preferred embodiment, the phase compensation unit is connected in series with the current control unit, and its input is AC current, while its output is connected to the input of the current control unit.

[0062] like Figure 5 As shown, the phase compensation unit is connected in series with the current control unit, and its input is connected to the output of the current control unit. The output is a converter valve modulation wave.

[0063] In a preferred embodiment, when the harmonic content of the set frequency band output by the harmonic detection unit is higher than the harmonic threshold, the parameter adjustment unit automatically adjusts the parameters of the phase compensator so that the flexible DC system presents positive impedance in that frequency band.

[0064] In a preferred embodiment, the harmonic detection unit outputs the frequency point where the harmonic content exceeds the set value and transmits the frequency to the parameter adjustment unit.

[0065] In a preferred embodiment, the parameter adjustment unit receives the harmonic frequency points output by the harmonic detection unit, automatically calculates the phase compensation parameters, and outputs them to the phase compensation unit.

[0066] In a preferred embodiment, the phase compensation unit acts on the inner loop current control loop to improve the impedance characteristics of the flexible DC near the frequency point.

[0067] This invention also provides another computer device, including a processor and a memory configured to store a computer program capable of running on the processor; wherein, when the processor is configured to run the computer program, it performs the method steps described in the foregoing embodiments.

[0068] In practical applications, the aforementioned processor includes a Field-Programmable Gate Array (FPGA), and the processor can be a Central Processing Unit (CPU) or a Digital Signal Processor (DSP). It is understood that for different devices, the electronic devices used to implement the functions of the aforementioned processor can also be other types, and this embodiment of the invention does not impose specific limitations.

[0069] The aforementioned memory can be volatile memory, such as random-access memory (RAM); or non-volatile memory, such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid-state drive (SSD); or a combination of the above types of memory, and provides instructions and data to the processor.

[0070] In an exemplary embodiment, the present invention also provides a computer-readable storage medium for storing a computer program.

[0071] Optionally, the computer-readable storage medium can be applied to any of the methods in the embodiments of the present invention, and the computer program causes the computer to execute the corresponding processes implemented by the processor in the various methods of the embodiments of the present invention. For the sake of brevity, these will not be described in detail here.

[0072] In the several embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0073] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0074] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0075] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0076] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for suppressing high-frequency resonance in a flexible DC transmission system, characterized in that: include, Obtain the harmonic content of the grid-side AC voltage or AC current; When the harmonic content exceeds a threshold value, a phase compensator is activated in the inner loop current control stage of the flexible DC transmission system; wherein, the parameters of the phase compensator are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

2. The method as described in claim 1, characterized in that: The transfer function of the phase compensator is: Wherein, τ1 and τ2 are compensator parameters, m is the sign bit, and s is the Laplace operator; wherein, the phase compensator parameters τ1 and τ2 are designed according to the positive impedance range of improving the equivalent AC impedance of flexible DC, and m is used to set the adjustment direction.

3. The method as described in claim 1, characterized in that: In the flexible DC transmission system, a phase compensator is installed in the inner loop current control link. The current control link adopts proportional-integral control, and the phase compensator is set in the proportional control link of the proportional-integral control. The output of the proportional controller is passed through the phase compensator and then summed with the output of the integral controller.

4. The method as described in claim 1, characterized in that: In the inner loop current control stage of the flexible DC transmission system, a phase compensator is installed. This includes setting the phase compensator in the current feedback stage of the current control stage, and then subtracting the measured current value from the current reference value after passing through the phase compensator. The difference is used as the input of the current control stage.

5. The method as described in claim 1, characterized in that: The phase compensator is installed in the inner loop current control link of the flexible DC transmission system. This includes setting the phase compensator in the output link of the current control link. The current control link adopts proportional-integral control. The output of the proportional-integral control is obtained after passing through the phase compensator to obtain the output of the current control link.

6. The method as described in claim 1, characterized in that: Obtain the harmonic content of the grid-side AC voltage or AC current, including, Obtain the AC voltage or AC current from the grid side; Real-time FFT analysis is performed on the grid-side AC voltage or AC current to obtain the amplitude of each harmonic and its percentage relative to the fundamental amplitude.

7. A high-frequency resonance suppression device for a flexible DC transmission system, characterized in that: include, The harmonic detection unit is configured to acquire the harmonic content of the grid-side AC voltage or AC current; The current control unit is configured as the inner loop current control element of the flexible DC transmission system. The phase compensation unit is configured to connect to the current control unit to perform phase compensation when the harmonic content exceeds a threshold value, so as to improve the positive impedance range of the flexible DC equivalent AC impedance. as well as, A parameter adjustment unit is configured to adjust the parameters of the phase compensation unit; wherein the parameters of the phase compensation unit are determined by a transfer function, which is obtained based on the harmonic frequency with the highest content exceeding the threshold value.

8. The apparatus as claimed in claim 7, characterized in that: The transfer function of the phase compensator is: Wherein, τ1 and τ2 are compensator parameters, m is the sign bit, and s is the Laplace operator; wherein, the phase compensator parameters τ1 and τ2 are designed according to the positive impedance range of improving the equivalent AC impedance of flexible DC, and m is used to set the adjustment direction.

9. The apparatus as claimed in claim 7, characterized in that: The current control unit adopts proportional-integral control. The input of the phase compensation unit is connected to the output of the proportional controller. The output of the proportional controller is then summed with the output of the integral controller after passing through the phase compensation unit.

10. The apparatus as claimed in claim 7, characterized in that: The phase compensation unit is connected to the current feedback loop of the current control unit. The measured current value is passed through the phase compensator and then the difference is calculated with the current reference value. The difference is used as the input of the current control unit.

11. The apparatus as claimed in claim 7, characterized in that: The phase compensation unit is connected to the output stage of the current control unit. The current control unit adopts proportional-integral control, and the output of the proportional-integral control is used as the output of the current control unit after passing through the phase compensation unit.

12. The apparatus as claimed in claim 7, characterized in that: The harmonic detection unit acquires the harmonic content of the grid-side AC voltage or AC current, including, Obtain the AC voltage or AC current from the grid side; Real-time FFT analysis is performed on the grid-side AC voltage or AC current to obtain the amplitude of each harmonic and its percentage relative to the fundamental amplitude.

13. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, it implements the steps of the high-frequency resonance suppression method for the flexible DC transmission system as described in any one of claims 1 to 6.

14. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it implements the steps of the high-frequency resonance suppression method for the flexible DC transmission system as described in any one of claims 1 to 6.

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