Power grid resonance suppression method, system and device based on MMC virtual damping and medium

Abstract

The present application belongs to the technical field of power grid resonance suppression, and discloses a power grid resonance suppression method, system, device and medium based on MMC virtual damping, to solve the problem that in the existing virtual impedance control, the high-frequency damping instruction is attenuated in gain and lagged in phase when passing through the PI current inner loop, resulting in the damping effect being weakened. The method of the present application is applied to an LCC-MMC hybrid multi-infeed receiving end power grid, and comprises: establishing a positive sequence s-domain node admittance model and calculating resonance modes to obtain the resonance frequency and damping ratio of each mode; identifying high-risk resonance modes according to the double criteria of frequency deviation and damping ratio; determining the MMC virtual damping access node according to the node voltage mode and setting the target resonance angular frequency; extracting the target frequency harmonic voltage component, generating the damping current instruction after phase compensation, and converting it into a damping voltage instruction; and bypassing the damping voltage instruction in the stationary coordinate system to superimpose it on the MMC modulation wave instruction, so that the MMC is equivalent to a parallel virtual resistor at the target frequency.

Description

Technical Field

[0001] This invention belongs to the field of power grid resonance suppression technology, specifically relating to a power grid resonance suppression method, system, device, and medium based on MMC virtual damping. Background Technology

[0002] With the continuous increase in the scale of high-voltage direct current (HVDC) transmission projects, a hybrid multi-feed operation pattern has emerged in the receiving-end AC grid, where both grid-commutated converters (LCCs) and modular multilevel converters (MMCs) are fed into the system. Under twelve-pulse operation, the LCC injects characteristic harmonic currents into the connected AC system, with the 11th, 13th, 23rd, and 25th harmonic components being the most significant. Simultaneously, the equivalent impedance of the MMC AC side, the receiving-end AC line impedance, filter branches, and grid loads together constitute a complex frequency-dependent network. When this network exhibits a resonant mode with a damping ratio below the engineering safety threshold at a specific frequency, the characteristic harmonic current injected by the LCC will be significantly amplified at adjacent resonant frequencies, leading to over-limit voltage harmonics at the transmitting end and broadband power oscillations, threatening the safe and stable operation of the receiving-end grid.

[0003] To address the aforementioned resonance problem, existing technologies primarily employ three suppression methods: passive filters, active filters, and converter-based additional control based on virtual impedance. Passive filters utilize resistors, inductors, and capacitors with fixed parameters to form the filtering channel, and their resonant suppression frequency is predetermined by these parameters. However, as the power grid's operating mode changes, the resonant frequency may shift. Filters with fixed parameters cannot adjust the damping frequency online according to the dynamic changes in the resonant mode, thus reducing their suppression effectiveness. Active filters inject compensation current into the grid using independent power electronic devices, enabling more flexible harmonic suppression. However, this approach requires additional primary equipment capacity, a dedicated control system, and connection switching equipment, resulting in significant investment and a large land area, making implementation difficult in retrofitting projects at existing sites.

[0004] Converter-addition control based on virtual impedance utilizes the converter's own control link to simulate resistance characteristics, eliminating the need for additional main circuit hardware and offering significant advantages in terms of economy and ease of engineering implementation. However, in existing schemes, high-frequency damping current commands are typically superimposed onto the PI current inner loop of the MMC's dq coordinate system. Since the gain of the PI controller's integral element decreases significantly with increasing frequency at high frequencies, the closed-loop bandwidth of the current inner loop cannot effectively track the command at the target resonant frequency. This results in the actual injected current deviating from the in-phase current relationship required by the parallel virtual resistor in both amplitude and phase, significantly weakening the damping effect.

[0005] Therefore, how to construct parallel virtual damping at the target frequency using the existing MMC modulation link, and how to make the high-frequency damping channel bypass the PI integral path to maintain the resistive phase relationship between the harmonic voltage and the damping current, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a grid resonance suppression method, system, device, and medium based on MMC virtual damping that meets one or more of the aforementioned requirements, so as to achieve the purpose of constructing a parallel virtual resistor at the target resonant frequency using the existing MMC modulation link without increasing the main circuit hardware, so as to absorb the characteristic harmonic energy of LCC and suppress grid resonance.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a grid resonance suppression method based on MMC virtual damping, applicable to LCC-MMC hybrid multi-infeed receiving-end grids, the method comprising the following steps: Obtain the topology parameters of the hybrid multi-feed receiving-end power grid and establish a positive-sequence s-domain node admittance model based on them; The resonant modes of the power grid are calculated based on the positive-sequence s-domain nodal admittance model, and the resonant frequency and damping ratio of each resonant mode are obtained. Based on the frequency deviation between the resonant frequency of each resonant mode and the characteristic harmonic frequency of the LCC, and the damping ratio of each resonant mode, high-risk resonant modes are identified. The high-risk resonant modes are those in which both the frequency deviation and the damping ratio are not greater than the corresponding preset values. Based on the node voltage mode corresponding to the high-risk resonant mode, determine the MMC virtual damping access node, and set the angular frequency of the high-risk resonant mode as the target resonant angular frequency; The three-phase voltage is obtained at the AC side common connection point of the MMC, and the stationary coordinate system voltage is obtained by Clarke transformation. The target frequency harmonic voltage component is extracted by passing it through a bandpass filter with the target resonant angular frequency as the center angular frequency. Digital control delay phase compensation is performed on the target frequency harmonic voltage component, a damping current command is generated based on the parallel virtual resistor, and the damping current command is converted into a damping voltage command; The damping voltage command is bypassed and superimposed onto the modulation wave command of the MMC in the stationary coordinate system, so that the MMC is equivalent to a parallel virtual resistor at the target resonant frequency.

[0008] In a second aspect, the present invention provides a grid resonance suppression system based on MMC virtual damping, for implementing the method described in the first aspect.

[0009] Thirdly, the present invention provides an electronic device, the electronic device including a memory, a processor and a computer program, wherein the computer program, when executed by the processor, implements the method described in the first aspect.

[0010] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in the first aspect.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention identifies high-risk resonant modes based on two conditions: the frequency deviation between the resonant frequency and the characteristic harmonic frequency of the LCC (not greater than a corresponding preset value), and the damping ratio of the resonant mode (not greater than a corresponding preset value). The frequency deviation criterion ensures that the suppressed mode has an electrical correlation with the LCC characteristic harmonic excitation source, avoiding ineffective control of modes unrelated to LCC harmonics; the damping ratio criterion ensures that only dangerous modes with damping levels below the engineering safety threshold are suppressed. The synergistic effect of these two criteria prevents both malfunctions and missed controls, improving the targeting and reliability of resonant suppression.

[0012] 2. This invention directly superimposes the damping voltage command onto the MMC modulation wave command in the stationary coordinate system. This channel is completely independent of the fundamental PI current inner loop in the dq coordinate system. Since the high-frequency damping command does not pass through the integrator of the PI controller, it avoids the amplitude attenuation and phase lag problems caused by the gain reduction of the integrator in the high-frequency band. This allows the actual injected current to accurately track the command, maintaining the in-phase resistance relationship between the harmonic voltage and the damping current at the target resonant frequency, significantly improving the high-frequency resonance suppression effect.

[0013] 3. This invention selects virtual damping access nodes based on the normalized voltage mode components of each node in the node voltage mode vector of the high-risk resonant mode, and optimizes them from the controllable MMC access node set, so that the virtual resistance access point is located at the voltage antinode of the resonant mode, thereby obtaining the maximum resonant energy dissipation effect with the minimum control cost.

[0014] 4. This invention addresses the inherent calculation delay and PWM update delay of the MMC digital control system by determining the phase compensation angle based on the MMC control cycle and the target resonant angular frequency. In the stationary coordinate system, it performs phase lead compensation on the target frequency harmonic voltage component, eliminating the influence of digital control delay on the phase of high-frequency signals, ensuring the accurate realization of the parallel virtual resistance characteristics, and further guaranteeing the in-phase relationship between the damping current and the harmonic voltage.

[0015] 5. When multiple high-risk resonant modes exist, this invention sets up multiple bandpass filter channels for the target resonant angular frequency of each high-risk resonant mode. Each channel independently extracts the harmonic voltage of the corresponding frequency and independently generates the damping voltage command. Finally, the damping voltage commands are linearly superimposed and then bypassed and superimposed onto the MMC modulation wave command, so that a single MMC can absorb the resonant energy of multiple frequencies at the same time, which is suitable for the engineering practice of multiple modes of resonance coexisting in complex power grids.

[0016] 6. This invention is based entirely on the existing control and modulation links of MMC. It achieves resonance suppression through improvements at the software algorithm level without increasing the capacity of primary equipment, control system, or connecting switchgear. It is suitable for the renovation and upgrading of existing sites and has good economic benefits and engineering promotion value.

[0017] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0018] 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 of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the LCC-MMC hybrid multi-feed receiving-end power grid described in this invention.

[0020] Figure 2 This is a schematic diagram of the MMC virtual damped modulated wave bypass injection control described in Embodiment 1 of the present invention.

[0021] Figure 3 This is a structural diagram of the electronic device described in Embodiment 3 of the present invention.

[0022] Figure 4 This is a waveform comparison of node harmonic voltages before applying virtual damping as described in Embodiment 1 of the present invention.

[0023] Figure 5 This is a waveform comparison of node harmonic voltages after applying virtual damping as described in Embodiment 1 of the present invention.

[0024] Icon labels: 300. Electronic devices; 301. Processor; 302. Communication bus; 303. User interface; 304. Network interface; 305. Memory. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] In the following description, several embodiments of the present invention are provided. Different embodiments can be substituted or combined. Therefore, the present invention can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then the present invention should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0027] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of the invention. Various processes or components may be appropriately omitted, substituted, or added to the various examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0028] To facilitate a better understanding of the embodiments of the present invention, its application scenarios will be explained before providing a detailed explanation of the specific implementation methods.

[0029] The grid resonance suppression method described in this specification is applied to LCC-MMC hybrid multi-infeed receiving-end grids. In these scenarios, the LCC converter injects characteristic harmonic currents into the AC side under twelve-pulse operation. The equivalent impedance of the MMC AC side, the AC line impedance of the receiving end, the filter branch, and the grid load together constitute a frequency-dependent network. When the network has a resonant mode with a damping ratio lower than the engineering threshold at a specific frequency, the LCC characteristic harmonic current will be amplified at adjacent resonant frequencies. The application of the grid resonance suppression method aims to construct parallel virtual damping at the target frequency through MMC modulation wave bypass injection to absorb harmonic energy and suppress resonance.

[0030] The following is a brief explanation of the LCC-MMC hybrid multi-infeed receiving-end grid, LCC, MMC, positive-sequence s-domain node admittance model, grid resonant mode, frequency deviation, damping ratio, bandpass filter, digital control delay phase compensation, stationary coordinate system, and current inner-loop PI controller involved in several embodiments of this specification: LCC-MMC hybrid multi-feed receiving-end power grid refers to a receiving-end power system in an AC power grid that simultaneously connects a line commutated converter (LCC) and a modular multilevel converter (MMC). The LCC and MMC are connected to the AC bus through their respective converter transformers.

[0031] LCC, or grid-commutated converter, uses thyristors as switching devices and relies on the AC grid voltage to achieve commutation. Under the twelve-pulse operation mode, it injects characteristic harmonic current into the AC side.

[0032] MMC stands for Modular Multilevel Converter, which consists of multiple cascaded sub-modules. The switching state of each sub-module is controlled by a modulation strategy to output the desired AC voltage.

[0033] Positive-sequence s-domain node admittance model: A mathematical model established in the Laplace domain to describe the relationship between the injected current and the node voltage at each node of the power grid, considering only the positive-sequence component.

[0034] The resonant mode of a power grid refers to the characteristic mode corresponding to the singular or near-singular state of the admittance matrix of a power grid node at a specific frequency. Each mode corresponds to a resonant frequency and a characteristic root.

[0035] Frequency deviation refers to the absolute value of the difference between the resonant frequency of the power grid resonant mode and the characteristic harmonic frequency of the LCC.

[0036] The damping ratio is a dimensionless parameter used to characterize the decay characteristics of resonant modes. The smaller the value, the more difficult it is for the resonance to decay on its own.

[0037] Bandpass filter: A filter that allows only signals within a specific frequency range to pass through. It filters the input signal with the target resonant angular frequency as the center angular frequency to extract the target frequency component.

[0038] Digital control delay phase compensation: To address the inherent calculation delay and PWM update delay of the MMC digital control system, the target frequency signal is phase-advanced in the control algorithm to compensate for the phase lag caused by the delay.

[0039] Stationary coordinate system: dq coordinate system, which uses Clarke transformation to convert electrical quantities in the three-phase stationary coordinate system to a two-phase orthogonal stationary coordinate system.

[0040] Inner-loop PI controller: The current closed-loop regulator in the MMC control system, consisting of proportional (P) and integral (I) elements, is used to achieve zero steady-state error tracking of current commands.

[0041] Example 1: This embodiment provides a grid resonance suppression method based on MMC virtual damping, applied to an LCC-MMC hybrid multi-infeed receiving-end grid. The structure of the LCC-MMC hybrid multi-infeed receiving-end grid is as follows: Figure 1 As shown, LCC is a twelve-pulse converter, and MMC is a half-bridge modular multilevel converter. The method described in this embodiment includes the following steps: Step S1: Obtain the topology parameters of the hybrid multi-infeed receiving-end power grid containing LCC and MMC, and establish a positive-sequence s-domain node admittance model.

[0042] Specifically, the AC line parameters (including line resistance and inductance), parallel capacitor parameters, filter branch parameters, LCC access node parameters, and MMC access node parameters of the receiving-end power grid are obtained. The MMC adopts a broadband voltage source equivalent model, and its high-frequency AC side equivalent impedance is: (1), In equation (1), The equivalent impedance of the AC side of the MMC. ,in To connect the equivalent resistance of the transformer, This is the equivalent resistance of the MMC bridge arm. ,in To connect the transformer leakage inductance, For MMC bridge arm reactance.

[0043] For a resistor-inductor branch connected in series in a power grid, its branch admittance is: (2), For a capacitor branch connected in parallel in a power grid, its branch admittance is: (3), In equations (2) and (3), For the admittance of the series resistor-inductor branch, For branch resistance, For the Laplace operator, For branch inductance, For the admittance of the parallel capacitor branch, It is a parallel capacitor.

[0044] Based on the above component parameters and admittance expressions, a positive-sequence s-domain node admittance model for the receiving-end power grid is established: (4), In equation (4), Let be the admittance matrix of the s-domain nodes in the positive order. The node voltage column vector, Inject a column vector of currents into the nodes.

[0045] Step S2: Calculate the power grid resonant modes based on the positive sequence s-domain node admittance model, and obtain the resonant frequency, characteristic roots and damping ratio of each resonant mode.

[0046] Specifically, the grid resonant mode corresponds to the non-zero root of the following equation: (5), In equation (5), This refers to matrix determinant operations.

[0047] To reduce the complexity of finding roots of high-order matrices, this embodiment first ignores the resistance and conductance parameters in the power grid, obtaining the undamped node susceptance matrix: (6), In equation (6), The imaginary unit, For the first The angular frequency of the resonant mode. Let be a real symmetric nodal susceptance matrix. Scan the target frequency band and solve: (7), Obtain the undamped resonant frequency Subsequently, in the complete damped network, a second-order rational function fit is performed on the current distribution ratio of the parallel branches near the resonant frequency: (8), In equation (8), For the current distribution ratio of parallel branches, , , , , These are the fitting coefficients. Solving the denominator polynomial yields the characteristic roots: (9), In equation (9), For the first Characteristic roots of a resonant mode For the real part of the characteristic root, Let be the resonant angular frequency corresponding to the imaginary part of the characteristic root. The damping ratio satisfies: (10) In equation (10), For the first Damping ratio of each resonant mode denoted as the absolute value of the real part of the characteristic root.

[0048] Step S3: Identify high-risk resonant modes based on the frequency deviation between the resonant frequency of each resonant mode and the characteristic harmonic frequency of the LCC, as well as the damping ratio. The high-risk resonant modes simultaneously satisfy the following conditions: the frequency deviation is not greater than the corresponding preset value and the damping ratio is not greater than the corresponding preset value.

[0049] Specifically, the LCC is a twelve-pulse converter, and its characteristic harmonic frequency satisfies: (11), In equation (11), The characteristic harmonic frequency of LCC It is a positive integer. Let be the fundamental frequency of the AC system. If the... The resonant modes simultaneously satisfy: (12), (13) This resonant mode is then identified as a high-risk resonant mode.

[0050] Step S4: Determine the MMC virtual damping access node based on the node voltage mode corresponding to the high-risk resonant mode, and set the angular frequency of the high-risk resonant mode as the target resonant angular frequency.

[0051] Specifically, the node voltage mode vector is extracted for high-risk resonant modes: (14) In equation (14), For the first The node voltage mode vector of each resonant mode. to They are respectively the 1st to the 1st Normalized voltage mode components of each node, This represents the number of nodes.

[0052] Select the node that satisfies the following formula as the priority damping access node: (15) In equation (15), For node sequence number, This represents the normalized voltage mode component of the node. When the MMC access node is a controllable node, it is selected from the set of controllable MMC access nodes. The largest node is used as the virtual damping access node, and the angular frequency of the corresponding high-risk resonant mode is set as the target resonant angular frequency. .

[0053] Step S5: Obtain the three-phase voltage at the common coupling point (PCC) on the AC side of the MMC, obtain the αβ stationary coordinate system voltage through Clarke transformation, and extract the target frequency harmonic voltage component through a bandpass filter with the target resonant angular frequency as the center angular frequency.

[0054] Specifically, the three-phase voltage is measured at the common coupling point PCC on the AC side of the MMC. , , After Clarke transform, the following is obtained Voltage in stationary coordinate system: (16) In equation (16), , , This refers to the three-phase voltage at PCC. and They are respectively shaft and Axis voltage component.

[0055] Harmonic voltage components of the target frequency are extracted using a second-order bandpass filter. (17) (18) In equations (17) and (18), For the target frequency harmonic voltage component, for Coordinate system voltage, The transfer function of a second-order bandpass filter. This is the filter bandwidth. In this embodiment... The range of values ​​is .

[0056] Step S6: Perform digital control delay phase compensation on the target frequency harmonic voltage component, generate a damping current command based on the parallel virtual resistor, and convert the damping current command into a damping voltage command.

[0057] Specifically, the phase compensation angle corresponding to the MMC digital control delay is: (19) In equation (19), For phase compensation angle, This is the MMC control cycle. The phase compensation matrix is: (20) In equation (20), and To compensate for the harmonic voltage components of the target frequency, and To compensate for the harmonic voltage components of the target frequency.

[0058] The damping current command is generated based on the principle of parallel virtual resistance: (twenty one), In equation (21), and For damping current command, The simulated parallel virtual resistance at the target resonant frequency. Let be the virtual conductance at the target resonant frequency, and .

[0059] Convert the damping current command to a damping voltage command: (twenty two), In equation (22), and This is a damping voltage command. This is the inner loop proportional gain of the MMC current. For example... Figure 2 As shown, the conversion is completed in the modulation wave bypass channel, and the PI integral element does not participate in the generation of the target frequency damping current.

[0060] Step S7: The damping voltage command is bypassed and superimposed on the modulation wave command of the MMC in the dq stationary coordinate system, so that the MMC is equivalent to a parallel virtual resistor at the target resonant frequency.

[0061] Specifically, the fundamental modulation voltage command in the dq coordinate system output by the MMC outer loop and the PI current inner loop is obtained through inverse Park transformation. and Before the nearest level modulation or carrier modulation, the damping voltage command is superimposed on the modulation voltage command: (twenty three), In equation (23), and For the final modulation voltage command, and This is the modulation voltage command output by the fundamental frequency control channel. The negative sign indicates that when the target frequency harmonic voltage of the PCC is a positive disturbance, the MMC outputs a corresponding modulation voltage adjustment, causing the target frequency harmonic current to flow into the MMC, forming a parallel conduction to absorb harmonic energy.

[0062] When multiple high-risk resonant modes exist, for Target resonant angular frequency Separate bandpass filter channels are set up, and the final modulation voltage command is generated using the following formula: (twenty four), In equation (24), This is the damping channel number. and For the first Damping voltage command output by each target frequency damping channel.

[0063] Example 2: This embodiment provides a grid resonance suppression system based on MMC virtual damping, used to implement the method described in Embodiment 1.

[0064] Example 3: like Figure 3 As shown, this embodiment provides an electronic device, which may include: at least one processor, at least one network interface, a user interface, a memory, and at least one communication bus.

[0065] The communication bus can be used to enable communication between the various components mentioned above.

[0066] The user interface may include buttons, and optional user interfaces may also include standard wired interfaces and wireless interfaces.

[0067] The network interface may include, but is not limited to, Bluetooth modules, NFC modules, Wi-Fi modules, etc.

[0068] The processor may include one or more processing cores. It connects various parts of the electronic device via various interfaces and lines, executing instructions, programs, code sets, or instruction sets stored in memory, and accessing data stored in memory to perform various functions and process data. Optionally, the processor can be implemented using at least one hardware form of DSP, FPGA, or PLA. The processor may integrate one or more of the following: CPU, GPU, and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor.

[0069] The memory may include RAM or ROM. Optionally, the memory may include a non-transitory computer-readable medium. The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor. The memory, as a computer storage medium, may include an operating system, a network communication module, a user interface module, and a suppression application program. The processor can be used to call the suppression application program stored in the memory and execute the steps of the power grid resonance suppression method mentioned in the foregoing embodiments.

[0070] Example 4: This embodiment provides a computer-readable storage medium storing instructions that, when executed on a computer or processor, cause the computer or processor to perform one or more steps as described in Embodiment 1. If the constituent modules of the above-described electronic device are implemented as software functional units and sold or used as independent products, they can be stored in the computer-readable storage medium.

[0071] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this specification are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., Digital Versatile Discs (DVDs)), or semiconductor media (e.g., Solid State Disks (SSDs)).

[0072] Those skilled in the art will understand that all or part of the processes in the method of Embodiment 1 described above can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks. Unless otherwise specified, the technical features of this embodiment and the implementation scheme can be combined arbitrarily.

[0073] Example 5: To verify the effectiveness of the grid resonance suppression method based on MMC virtual damping described in this specification, this embodiment builds an LCC-MMC hybrid multi-infeed receiving-end grid simulation model based on the PSCAD / EMTDC electromagnetic transient simulation platform, and uses the method described in Embodiment 1 for virtual damping control.

[0074] The main parameters of the simulation model are as follows: the rated line voltage of the AC system is 500 kV, and the fundamental frequency is 50 Hz; the LCC adopts a twelve-pulse converter with a rated DC voltage of 800 kV and a rated power of 2000 MW; the rated AC voltage of the MMC-HVDC is 525 kV, the rated DC voltage is 800 kV, the rated power is 2000 MW, and the control cycle is... , , .

[0075] Modal analysis yielded three resonant modes, with the second mode having a resonant frequency of 581.31 Hz and a damping ratio of 0.64%. This frequency lies between the 11th characteristic harmonic (550 Hz) and the 13th characteristic harmonic (650 Hz), satisfying... and Therefore, it was identified as a high-risk resonant mode.

[0076] Configure parallel virtual resistors at MMC access nodes Bandpass filter damping channels were deployed for the 11th and 13th harmonic frequencies, respectively. After applying virtual damping, the frequency of the second mode was adjusted from 581.31 Hz to 643.22 Hz, and the damping ratio increased from 0.64% to 38.49%; the damping ratio of the third mode increased from 0.52% to 6.39%. In the time-domain simulation, before control was implemented, the 11th harmonic voltage of the LCC access node was 33.20 kV, and the 11th harmonic voltage of the MMC access node was 27.31 kV; after control was implemented, the corresponding voltages were 10.27 kV and 3.34 kV, respectively. Before control was implemented, the 13th harmonic voltage of the LCC access node was 10.13 kV, and the 13th harmonic voltage of the MMC access node was 11.98 kV; after control was implemented, the corresponding voltages were 1.68 kV and 5.57 kV, respectively. The fact that the fundamental current deviation before and after the control input is less than 0.1% indicates that the modulation wave bypass injection channel did not change the MMC fundamental power transmission control target.

[0077] Figure 4 and Figure 5 The figures shown are waveforms comparing the node harmonic voltages before and after applying virtual damping as described in this embodiment. Based on the above, this embodiment verifies the effectiveness of the grid resonance suppression method based on MMC virtual damping described in this specification.

[0078] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0079] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0080] The foregoing description is merely an exemplary embodiment of the present invention and should not be construed as limiting the scope of the invention. Any equivalent changes and modifications made in accordance with the teachings of this invention are still within the scope of this invention. Those skilled in the art will readily conceive of embodiments of the invention upon considering the specification and practicing the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include knowledge or means in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of the invention are defined by the claims.

Claims

1. A method for suppressing grid resonance based on MMC virtual damping, characterized in that, Applied to LCC-MMC hybrid multi-infeed receiving-end power grids, the method includes the following steps: Obtain the topology parameters of the hybrid multi-feed receiving-end power grid and establish a positive-sequence s-domain node admittance model based on them; The resonant modes of the power grid are calculated based on the positive-sequence s-domain nodal admittance model, and the resonant frequency and damping ratio of each resonant mode are obtained. Based on the frequency deviation between the resonant frequency of each resonant mode and the characteristic harmonic frequency of the LCC, and the damping ratio of each resonant mode, high-risk resonant modes are identified. The high-risk resonant modes are those in which both the frequency deviation and the damping ratio are not greater than the corresponding preset values. Based on the node voltage mode corresponding to the high-risk resonant mode, determine the MMC virtual damping access node, and set the angular frequency of the high-risk resonant mode as the target resonant angular frequency; The three-phase voltage is obtained at the AC side common connection point of the MMC, and the stationary coordinate system voltage is obtained by Clarke transformation. The target frequency harmonic voltage component is extracted by passing it through a bandpass filter with the target resonant angular frequency as the center angular frequency. Digital control delay phase compensation is performed on the target frequency harmonic voltage component, a damping current command is generated based on the parallel virtual resistor, and the damping current command is converted into a damping voltage command; The damping voltage command is bypassed and superimposed onto the modulation wave command of the MMC in the stationary coordinate system, so that the MMC is equivalent to a parallel virtual resistor at the target resonant frequency.

2. The method according to claim 1, characterized in that, The damping voltage command is bypassed and superimposed onto the modulation wave command of the MMC in the stationary coordinate system, specifically as follows: The damping voltage command bypasses the MMC's inner current loop PI controller and is superimposed with the fundamental modulation voltage command output by the fundamental control channel in the stationary coordinate system to form the MMC's modulation wave command.

3. The method according to claim 1, characterized in that: When multiple high-risk resonant modes exist, multiple bandpass filter channels are set for the target resonant angular frequency of each high-risk resonant mode. Each bandpass filter channel outputs a damping voltage command corresponding to the target resonant frequency. The damping voltage commands are linearly superimposed and then bypassed and superimposed onto the modulation wave command of the MMC.

4. The method according to claim 1, characterized in that: The digital control delay phase compensation is a phase lead compensation. The compensation phase angle is determined based on the control cycle of MMC and the target resonant angular frequency, and the phase of the target frequency harmonic voltage component is rotated in a stationary coordinate system.

5. The method according to claim 1, characterized in that, The determination of the MMC virtual damping access node based on the node voltage mode corresponding to the high-risk resonant mode is specifically as follows: Obtain the normalized voltage mode components of each node in the node voltage mode vector of the high-risk resonant mode, select the nodes whose normalized voltage mode components are greater than or equal to a first preset threshold as priority damping access nodes, and determine the virtual damping access nodes in the MMC access node set.

6. The method according to claim 1, characterized in that: The preset value corresponding to the frequency deviation is 10%; The preset value corresponding to the damping ratio is 5.

7. The method according to claim 1, characterized in that, A damping current command is generated based on the parallel virtual resistance, and the damping current command is converted into a damping voltage command, specifically as follows: The damping current command is generated by multiplying the phase-compensated target frequency harmonic voltage component with the reciprocal of the parallel virtual resistance. The damping voltage command is generated by multiplying the damping current command by the proportional gain of the MMC current inner loop.

8. A power grid resonance suppression system based on MMC virtual damping, characterized in that, Used to implement the method as described in any one of claims 1 to 7.

9. An electronic device, the electronic device comprising a memory, a processor, and a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 7.

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 method as described in any one of claims 1 to 7.

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