Series compensation capacitor oscillation suppression method and system based on impedance remodeling

Abstract

The invention discloses a series compensation capacitor oscillation suppression method and system based on impedance remodeling, and relates to the technical field of power electronics, and the method comprises the steps: carrying out the modeling of a low-voltage flexible DC power transmission system, obtaining an impedance model of the system, and achieving the preliminary control of a virtual synchronous machine; drawing a Bode diagram according to the impedance model of the system, and analyzing the stability of the system by applying a Nyquist stability criterion; optimization control is carried out according to the system stability, the sequence impedance of the virtual synchronous machine is detected again, and corresponding correction is carried out; and restoring the virtual inertia of the virtual synchronous machine to an initial value, and detecting the output current of the system by substituting into the adjusted optimization control to verify the effectiveness of the optimization control. Through optimization control and impedance correction, the adaptability and robustness of the system are improved, and unstable phenomena such as subsynchronous oscillation are avoided.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a method and system for suppressing oscillation of a series compensation capacitor based on impedance reshaping. Background Art

[0002] Unlike traditional synchronous power transmission grids that can provide inertia and frequency modulation capabilities when facing disturbances, power electronic transmission technology lacks damping suppression capabilities when facing disturbances. Therefore, when facing grid disturbances, it often couples with disturbance signals, line impedance or other power electronic devices to produce spontaneous oscillations. In order to improve the anti-disturbance capability of the power grid, the new power system incorporates power electronic transmission technology based on virtual synchronous generators (VSG) into the architecture. VSG technology provides damping support for the power grid by simulating the rotational inertia and inertia time constant in the synchronous machine grid to ensure safe and stable operation of the system.

[0003] Affected by the endowment characteristics of my country's new energy resources, most new energy power plants are built far away from the power load. In order to achieve the goal of smoothly transmitting new energy power generation resources, series compensation capacitor technology is often used to reduce transmission line losses to improve line utilization efficiency. However, the introduction of series compensation capacitor technology is prone to coupling with line impedance and VSG impedance to produce subsynchronous oscillations, affecting the safe operation of the power grid. Existing research on subsynchronous oscillation problems is mostly based on introducing new control loops to change the circuit response feedback link, and rarely considers optimizing the VSG control loop. How to suppress system oscillation problems and improve system operation stability by optimizing the control loop has become a technical problem that needs to be solved. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above existing problems, the present invention is proposed.

[0006] Therefore, the present invention provides a method and system for suppressing oscillation of a series compensation capacitor based on impedance reshaping, which can solve the problems mentioned in the background technology.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a method for suppressing oscillation of a series compensation capacitor based on impedance reshaping, which includes modeling a low-voltage flexible direct current transmission system, obtaining an impedance model of the system, and realizing preliminary control of a virtual synchronous machine;

[0009] Draw a Bode plot based on the impedance model of the system and apply the Nyquist stability criterion to analyze the system stability;

[0010] Performing optimization control according to the system stability, re-detecting the sequence impedance of the virtual synchronous machine, and making corresponding corrections;

[0011] The virtual inertia of the virtual synchronous machine is restored to its initial value, and the output current of the system is detected by substituting it into the adjusted optimal control to verify the effectiveness of the optimal control.

[0012] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping described in the present invention, wherein: the low-voltage flexible direct current transmission system includes a virtual synchronous machine and a series compensation capacitor circuit;

[0013] The preliminary control of the virtual synchronous machine includes simulating the moment of inertia and inertia time constant in the synchronous machine power grid, providing damping support for the power grid, and obtaining the virtual synchronous machine impedance model and the series compensation circuit impedance model for subsequent stability analysis;

[0014] The moment of inertia and inertia time constant in the simulated synchronous machine network include:

[0015] The motion equation and modulation part of the synchronous machine are simulated to calculate and obtain the virtual inertia and damping coefficient parameters. The calculation formula is as follows:

[0016]

[0017] Among them, P set and P e are the mechanical power and electromagnetic power of the virtual synchronous machine, T set is the mechanical torque, T e is the electromagnetic torque, J and D p are the virtual inertia and virtual damping coefficient of the virtual synchronous machine, ω is the angular frequency of the virtual synchronous machine, ω n is the rated angular frequency, and ω n =2πf n , θ is the virtual synchronous machine power angle, Q set Reactive power set for the virtual synchronous machine, D q is the reactive inertia of the virtual synchronous machine, V nom and V are the rated voltage rms and output voltage rms respectively, E m is the effective value of the voltage of the virtual synchronous machine, K is the inertia coefficient, and s is the differential operator;

[0018] According to the virtual synchronous machine main control, the power angle reference value θ is obtained to generate a three-phase modulation signal s a 、s b 、s c , the calculation formula is as follows:

[0019]

[0020] Among them, V dc is the DC terminal voltage.

[0021] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping of the present invention, wherein: the impedance model of the system obtained includes:

[0022] The impedance model of the virtual synchronous machine is constructed by harmonic linearization method to obtain the positive and negative sequence impedance model of the system.

[0023] Inject a positive and negative sequence signal with an amplitude much lower than the reference voltage amplitude and observe the response of the positive and negative sequence current signals;

[0024] The ratio of the voltage frequency domain signal to the current frequency domain signal is converted into an impedance value to obtain the positive and negative sequence impedance values. The calculation formula is as follows:

[0025]

[0026] M(s)=1 / (Js 2 +D p s)

[0027] When sampling delay is considered, the calculation formula of K(s) is as follows:

[0028]

[0029] Among them, V p 、V n are the frequency domain components of the positive and negative sequence voltage disturbances, I p ,I n are the frequency domain components of the positive and negative sequence current responses, V1 and I1 are the fundamental frequency voltage and current amplitudes, is the initial phase of the fundamental frequency current, L f is the filter inductance of the virtual synchronous machine, arcsin[P e ω n L f / (E m V1)] is the power angle of the virtual synchronous machine, ω v and ω i are the cutoff frequencies of the voltage and current sampling low-pass filters, T s is the switching period, K(s) is the controller gain;

[0030] The series compensation circuit is modeled and the series compensation circuit model formula is as follows:

[0031] Z series (s)=1 / (sC1)+R1

[0032] Among them, C1 and R1 are filter capacitor and filter resistor respectively.

[0033] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping described in the present invention, wherein: the series compensation circuit model also includes:

[0034] The filter capacitor circuit is included in the series compensation circuit model, and the filter capacitor circuit and the series compensation circuit are combined into the grid impedance. The calculation formula is as follows:

[0035] Z g (s)=(sL g +R g +1 / (sC2))||(1 / (sC1)+R1)

[0036] Among them, L g and R g They are the equivalent inductance and equivalent resistance on the grid side respectively, and C2 is the series compensation capacitor on the grid side.

[0037] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping of the present invention, wherein: the analysis system stability includes:

[0038] Calculate the frequency response using impedance model parameters according to the obtained impedance model;

[0039] Draw the frequency response curve to form a Bode diagram;

[0040] Based on the Bode plot, determine the open-loop transfer function of the system;

[0041] Apply the Nyquist stability criterion to determine the stability of the system;

[0042] If the system is unstable, the optimization control based on impedance reshaping is applied to adjust the parameters of the virtual synchronous machine so that the system meets the stability requirements;

[0043] The parameters of the virtual synchronous machine are adjusted through impedance reshaping optimization control to suppress subsynchronous oscillations.

[0044] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping of the present invention, wherein: the corresponding correction includes:

[0045] By adding the impedance reshaping controller and modifying the transfer function, the transfer function is modified to:

[0046]

[0047] Among them, T1 and T2 are the adjustable parameters of the proposed impedance reshaping controller;

[0048] At the same time, the virtual synchronous machine sequence impedance using the impedance reshaping controller is modified as follows:

[0049]

[0050] M(s)=1 / (J(s)s 2 +Ds).

[0051] As a preferred solution of the series compensation capacitor oscillation suppression method based on impedance reshaping of the present invention, wherein: the verification of the effectiveness of the optimization control includes:

[0052] After troubleshooting, restore the initial value of virtual inertia of the virtual synchronous machine;

[0053] Record the current virtual inertia value and restore the virtual inertia to the initial setting;

[0054] Bring the adjusted optimized control parameters into the virtual synchronous machine control system to detect the output current;

[0055] Run the system, record the output current value, and compare the output current value with the system design requirements;

[0056] By detecting the output current of the system, the effectiveness of the optimized control is verified to ensure that the system operates stably under the new control parameters;

[0057] Verify system stability based on test results;

[0058] If the system is stable, the optimized control parameters are recorded as the final solution;

[0059] If the system is unstable, further adjust the control parameters until the system is stable.

[0060] In a second aspect, the present invention provides a series compensation capacitor oscillation suppression system based on impedance reshaping, which includes: an impedance modeling module, a judgment and analysis module, an optimization control module, and a verification and optimization module;

[0061] The impedance modeling module is used to model the low-voltage flexible direct current transmission system, obtain the impedance model of the system, and realize the preliminary control of the virtual synchronous machine;

[0062] The judgment and analysis module is used to draw a Bode diagram according to the impedance model of the system and apply the Nyquist stability criterion to analyze the stability of the system;

[0063] The optimization control module is used to perform optimization control according to the system stability, re-detect the sequence impedance of the virtual synchronous machine, and make corresponding corrections;

[0064] The verification optimization module is used to restore the virtual inertia of the virtual synchronous machine to an initial value, and to detect the output current of the system by substituting the adjusted optimization control into the optimized control to verify the effectiveness of the optimization control.

[0065] In a third aspect, the present invention provides a computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: when the processor executes the computer program, the steps of a method for suppressing oscillation of a series compensation capacitor based on impedance reshaping are implemented.

[0066] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, the steps of a method for suppressing oscillation of a series compensation capacitor based on impedance reshaping are implemented.

[0067] Compared with the prior art, the beneficial effects of the present invention are as follows: by modeling the low-voltage flexible direct current transmission system and realizing preliminary control of the virtual synchronous machine, the foundation for the operation of the system is laid, and the effectiveness of the subsequent optimization control is ensured; by drawing the Bode diagram and applying the Nyquist stability criterion to analyze the system stability, the stability of the system at different frequencies is effectively judged; through optimization control and impedance correction, the adaptability and robustness of the system are improved, and the occurrence of unstable phenomena such as subsynchronous oscillations is avoided; finally, by restoring the initial value of the virtual inertia and detecting the system output current, the effectiveness of the optimization control is verified, ensuring that the system can remain stable and efficient in actual operation, and achieving the ultimate goal of suppressing the oscillation of the series compensation capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0069] Figure 1 A method flow chart of a series compensation capacitor oscillation suppression method and system based on impedance reshaping provided by an embodiment of the present invention;

[0070] Figure 2 An internal structural diagram of a computer device of a method and system for suppressing oscillation of a series compensation capacitor based on impedance reshaping provided by an embodiment of the present invention;

[0071] Figure 3A topology control structure diagram of a series compensation capacitor oscillation suppression method and system based on impedance reshaping provided by an embodiment of the present invention;

[0072] Figure 4 A structural diagram of an oscillation suppression method of a series compensation capacitor based on impedance reshaping and a system provided in accordance with an embodiment of the present invention;

[0073] Figure 5 An impedance Bode diagram of a series compensation capacitor oscillation suppression method based on impedance reshaping and an oscillation suppression method of the system provided by an embodiment of the present invention;

[0074] Figure 6 A simulation diagram of a first oscillation suppression method of a series compensation capacitor oscillation suppression method and system based on impedance reshaping provided by an embodiment of the present invention;

[0075] Figure 7 A simulation diagram of a second oscillation suppression method of a series compensation capacitor oscillation suppression method based on impedance reshaping and a system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0076] In order to make the above-mentioned purposes, features and advantages of the present invention more understandable, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0077] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0078] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0079] Example 1

[0080] Reference Figure 1-Figure 7 , which is the first embodiment of the present invention, provides a method for suppressing oscillation of a series compensation capacitor based on impedance reshaping, comprising:

[0081] The present application provides a method that can effectively solve the above-mentioned problems. Next, multiple embodiments will be combined to explain in detail how to implement the series compensation capacitor oscillation suppression method based on impedance reshaping;

[0082] Figure 1 A method flow chart of a series compensation capacitor oscillation suppression method and system based on impedance reshaping is shown, including:

[0083] S1: Model the low-voltage flexible DC transmission system, obtain the impedance model of the system, and realize the preliminary control of the virtual synchronous machine;

[0084] Furthermore, the low-voltage flexible DC transmission system includes a virtual synchronous machine and a series compensation capacitor circuit. The virtual synchronous machine control simulates the moment of inertia and inertia time constant in the synchronous machine power grid to provide damping support for the power grid, and finally obtains the impedance model of the virtual synchronous machine and the series compensation circuit for subsequent stability analysis.

[0085] Furthermore, the motion equation and modulation part of the synchronous machine are simulated to calculate and obtain the virtual inertia and damping coefficient parameters. The calculation formula is as follows:

[0086]

[0087] Among them, P set and P e are the mechanical power and electromagnetic power of the virtual synchronous machine, T set is the mechanical torque, T e is the electromagnetic torque, J and D p are the virtual inertia and virtual damping coefficient of the virtual synchronous machine, ω is the angular frequency of the virtual synchronous machine, ω n is the rated angular frequency, and ω n =2πf n , θ is the virtual synchronous machine power angle, Q set Reactive power set for the virtual synchronous machine, D q is the reactive inertia of the virtual synchronous machine, V nom and V are the rated voltage rms and output voltage rms respectively, E m is the effective value of the voltage of the virtual synchronous machine, K is the inertia coefficient, and s is the differential operator;

[0088] The power angle reference value θ is obtained by the virtual synchronous machine main body control, generating a three-phase modulation signal s a 、s b 、s c , the calculation formula is as follows:

[0089]

[0090] Among them, V dc is the DC terminal voltage.

[0091] Furthermore, the impedance modeling of the virtual synchronous machine is carried out through the harmonic linearization method to obtain the positive and negative sequence impedance model of the system;

[0092] Inject a positive and negative sequence signal with an amplitude much lower than the reference voltage amplitude and observe the response of the positive and negative sequence current signals;

[0093] The ratio of the voltage frequency domain signal to the current frequency domain signal is converted into an impedance value to obtain the positive and negative sequence impedance values. The calculation formula is as follows:

[0094]

[0095] M(s)=1 / (Js 2 +D p s)

[0096] When sampling delay is considered, the calculation formula of K(s) is as follows:

[0097]

[0098] Among them, V p 、V n are the frequency domain components of the positive and negative sequence voltage disturbances, I p ,I n are the frequency domain components of the positive and negative sequence current responses, V1 and I1 are the fundamental frequency voltage and current amplitudes, is the initial phase of the fundamental frequency current, Lf is the filter inductance of the virtual synchronous machine, arcsin[P e ω n L f / (E m V1)] is the power angle of the virtual synchronous machine, ω v and ω i are the cutoff frequencies of the voltage and current sampling low-pass filters, T s is the switching period, K(s) is the controller gain;

[0099] The series compensation circuit is modeled and the series compensation circuit model formula is as follows:

[0100] Z series (s)=1 / (sC1)+R1

[0101] Among them, C1 and R1 are filter capacitor and filter resistor respectively;

[0102] Further, such as Figure 3 As shown in the figure, the filter capacitor circuit has not been included in the impedance model. To facilitate the subsequent impedance analysis, the filter capacitor circuit and the series compensation circuit are combined into the grid impedance. The calculation formula is as follows:

[0103] Z g(s)=(sL g +R g +1 / (sC2))||(1 / (sC1)+R1)

[0104] Among them, L g and R g are the equivalent inductance and equivalent resistance on the grid side respectively, and C2 is the series compensation capacitor on the grid side;

[0105] So far, through Figure 3 The analysis of the circuit shown in the figure obtains the impedance model of the virtual synchronous machine control and series compensation circuit.

[0106] It should be noted that by modeling the low-voltage flexible DC transmission system and realizing the preliminary control of the virtual synchronous machine, the foundation for the operation of the system is laid, ensuring the effectiveness of the subsequent optimization control; by drawing the Bode diagram and applying the Nyquist stability criterion to analyze the system stability, the stability of the system at different frequencies is accurately judged, which helps to discover potential unstable factors and guide the optimization control; the optimization control and impedance correction improve the adaptability and robustness of the system, avoiding the occurrence of unstable phenomena such as subsynchronous oscillation; finally, by restoring the initial value of the virtual inertia and detecting the system output current, the effectiveness of the optimization control is verified, ensuring that the system can remain stable and efficient in actual operation, and achieving the ultimate goal of suppressing the oscillation of the series compensation capacitor. These steps not only solve the uncertainty problem in traditional technologies, but also significantly improve the dynamic response performance and anti-interference ability of the system, providing a reliable optimization control solution.

[0107] S2: Analyze the stability of the system by drawing the Bode diagram and applying the Nyquist stability criterion. If the system stability does not meet the requirements, apply the optimization control based on impedance reshaping to adjust the parameters of the virtual synchronous machine to ensure the stability of the system;

[0108] Further, according to the impedance model obtained in step S1, a Bode diagram of the system is drawn;

[0109] Drawing the Bode plot of a system involves,

[0110] Using the impedance model parameters, calculate the frequency response;

[0111] Draw the frequency response curve to form a Bode diagram;

[0112] Based on the Bode plot, determine the open-loop transfer function of the system;

[0113] Apply the Nyquist stability criterion to determine the stability of the system;

[0114] If the system is unstable, the optimization control based on impedance reshaping is applied to adjust the parameters of the virtual synchronous machine so that the system meets the stability requirements;

[0115] Through impedance reshaping optimization control, the parameters of the virtual synchronous machine can be adjusted to suppress subsynchronous oscillations.

[0116] S3: After applying the optimized control, re-detect the sequence impedance of the virtual synchronous machine and make corresponding corrections as needed;

[0117] Further, corresponding amendments may be made as needed, including:

[0118] By adding an impedance reshaping controller and modifying the transfer function, the adjusted virtual synchronous machine sequence impedance meets the system design requirements. The transfer function is modified as follows:

[0119]

[0120] Among them, T1 and T2 are the adjustable parameters of the proposed impedance reshaping controller;

[0121] At the same time, the virtual synchronous machine sequence impedance using the impedance reshaping controller is modified as follows:

[0122]

[0123] M(s)=1 / (J(s)s 2 +Ds)

[0124] This suppression method starts from the unstable working point during oscillation and adjusts the parameters of the virtual synchronous machine to avoid unstable operation of the system.

[0125] S4: The virtual inertia of the virtual synchronous machine is restored to its initial value. By substituting the adjusted optimized control into the system, the output current of the system is detected to verify the effectiveness of the optimized control.

[0126] Further, after the fault is eliminated, the initial value of the virtual inertia of the virtual synchronous machine is restored;

[0127] Record the current virtual inertia value and restore the virtual inertia to the initial setting.

[0128] Bring the adjusted optimized control parameters into the virtual synchronous machine control system to detect the output current;

[0129] Run the system, record the output current value, and compare the output current value with the system design requirements;

[0130] By detecting the output current of the system, the effectiveness of the optimized control is verified to ensure that the system operates stably under the new control parameters;

[0131] Verify system stability based on test results;

[0132] If the system is stable, the optimized control parameters are recorded as the final solution;

[0133] If the system is unstable, further adjust the control parameters until the system is stable.

[0134] Further, as attached Figure 3 As shown, by calculating the impedance of the virtual synchronous machine and the impedance of the series compensation circuit, the impedance Bode diagram can be obtained, as shown in Figure 5 As shown (VSG control impedance diagram is shown by the dashed and solid lines, and the impedance value of the series compensation circuit is shown in the figure), it can be seen that at 32Hz, the impedance of the virtual synchronous machine intersects with the impedance amplitude of the series compensation circuit, and the difference in the impedance phase angle at this time is 182°, that is, the phase angle margin here exceeds 180°. According to the Nyquist stability criterion, the system will oscillate at this time. At this time, the virtual synchronous machine optimization control proposed in this patent is put into use, and the specific parameter calculation method of the optimization control is as follows Figure 1 By putting into optimization control, the impedance value of the virtual synchronous machine optimization control at this time can be calculated and the Bode diagram can be drawn as shown in the dotted line. It can be seen that after the optimization control is put into use, the system phase angle changes from 180° to 163°, and the phase angle margin is less than 180°. According to the Nyquist stability criterion, by putting into virtual synchronous machine optimization control, the system operation stability can be effectively improved.

[0135] Furthermore, the present embodiment also provides a series compensation capacitor oscillation suppression system based on impedance reshaping, comprising: an impedance modeling module, a judgment and analysis module, an optimization control module, and a verification and optimization module;

[0136] The impedance modeling module is used to model the low-voltage flexible DC transmission system, obtain the impedance model of the system, and realize the preliminary control of the virtual synchronous machine;

[0137] The judgment and analysis module is used to draw a Bode diagram according to the impedance model of the system and apply the Nyquist stability criterion to analyze the stability of the system;

[0138] The optimization control module is used to perform optimization control according to the system stability, re-detect the sequence impedance of the virtual synchronous machine, and make corresponding corrections;

[0139] The verification optimization module is used to restore the virtual inertia of the virtual synchronous machine to its initial value, and to detect the output current of the system by substituting the adjusted optimization control into it to verify the effectiveness of the optimization control.

[0140] This embodiment also provides a computer device, which may be a terminal, and its internal structure diagram may be as shown in FIG. Figure 2As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a comprehensive evaluation method suitable for orderly access of large-scale distributed power sources is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse.

[0141] This embodiment further provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the following steps are implemented: modeling a low-voltage flexible direct current transmission system, obtaining an impedance model of the system, and implementing preliminary control of a virtual synchronous machine;

[0142] Draw a Bode plot based on the impedance model of the system and apply the Nyquist stability criterion to analyze the system stability;

[0143] Performing optimization control according to the system stability, re-detecting the sequence impedance of the virtual synchronous machine, and making corresponding corrections;

[0144] The virtual inertia of the virtual synchronous machine is restored to its initial value, and the output current of the system is detected by substituting it into the adjusted optimal control to verify the effectiveness of the optimal control.

[0145] Example 2

[0146] Reference Figure 1 - Figure 2 , which is the second embodiment of the present invention, provides a method for suppressing oscillation of a series compensation capacitor based on impedance reshaping. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0147] In this embodiment, a low-voltage flexible direct current transmission system is modeled, and a series compensation capacitor oscillation suppression method based on impedance reshaping is applied for optimization control. The specific steps are as follows:

[0148] A low voltage flexible DC transmission system is selected, including a virtual synchronous machine and a series compensation capacitor circuit.

[0149] Determine the basic parameters of the system, such as mechanical power, torque, impedance, etc. of the virtual synchronous machine.

[0150] Prepare necessary measurement equipment, including voltage and current sensors and data acquisition system.

[0151] By simulating the moment of inertia and inertia time constant in the synchronous machine network, damping support is provided for the power grid.

[0152] The virtual inertia and damping coefficient parameters are calculated and obtained to form a virtual synchronous machine impedance model and a series compensation circuit impedance model.

[0153] The harmonic linearization method is used to model the impedance of the virtual synchronous machine and obtain the positive and negative sequence impedance models of the system.

[0154] Inject positive and negative sequence signals, observe the response of the current signal, and convert it into impedance value.

[0155] The impedance model parameters are used to calculate the frequency response, draw the Bode plot, and apply the Nyquist stability criterion to determine the system stability.

[0156] If the system is unstable, the optimization control based on impedance reshaping is applied to adjust the parameters of the virtual synchronous machine so that the system meets the stability requirements.

[0157] The controller is reshaped by adding impedance, modifying the transfer function and the impedance of the virtual synchronous machine sequence.

[0158] After troubleshooting, restore the initial value of the virtual inertia of the virtual synchronous machine and record the current virtual inertia value.

[0159] The adjusted optimized control parameters are brought into the virtual synchronous machine control system to perform output current detection.

[0160] Run the system, record the output current value, compare it with the system design requirements, verify the effectiveness of the optimized control, and ensure stable operation of the system.

[0161] Table 1 Test result record

[0162]

[0163] It can be seen from the above test result record table that through the series compensation capacitor oscillation suppression method based on impedance reshaping, the various parameters of the system have been significantly improved before and after optimization. The specific analysis is as follows:

[0164] Mechanical power and electromagnetic power: Before optimization, the mechanical power and electromagnetic power of the virtual synchronous machine were 45kW and 46kW respectively, while after optimization, they were increased to 50kW and 48kW. This shows that through optimized control, the energy transfer efficiency of the system has been significantly improved and the power loss has been significantly reduced.

[0165] Mechanical torque and electromagnetic torque: Before optimization, the mechanical torque and electromagnetic torque of the system were 190Nm and 192Nm respectively, while after optimization, they were restored to 200Nm and 195Nm. This shows that the optimized control effectively improves the torque output of the system and enhances the power performance of the system.

[0166] Virtual inertia and virtual damping coefficient: Through optimization control, the virtual inertia is 0.45kg·m 2 Restored to 0.5kg·m 2 , and the virtual damping coefficient is also restored from 0.009N·m·s to 0.01N·m·s. The recovery of these parameters indicates that the inertia and damping performance of the system have been effectively restored, which helps to improve the dynamic response performance of the system.

[0167] Output current: The output current of the system before optimization was 285 A, and after optimization it was increased to 300 A. This shows that through optimization control, the output current of the system has been effectively improved, and the current transmission has become more stable.

[0168] System stability: Before optimization, the system was unstable due to parameter mismatch and impedance instability. Through optimization control based on impedance reshaping, the impedance model parameters and frequency response parameters of the system were significantly improved, and finally the stable operation of the system was achieved.

[0169] In summary, the stability and performance of the low-voltage flexible DC transmission system can be significantly improved through the series compensation capacitor oscillation suppression method based on impedance reshaping. Compared with the prior art, the method of the present invention has obvious creativity and novelty, which can not only effectively suppress subsynchronous oscillations, but also improve the energy transfer efficiency and dynamic response performance of the system.

[0170] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0171] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt 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.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0172] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0173] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0174] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0175] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0176] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A series compensation capacitor oscillation suppression method based on impedance reshaping, Features: Including modeling the low-voltage flexible DC transmission system, obtaining the impedance model of the system, and realizing the preliminary control of the virtual synchronous machine; Draw a Bode plot based on the impedance model of the system and apply the Nyquist stability criterion to analyze the system stability; Performing optimization control according to the system stability, re-detecting the sequence impedance of the virtual synchronous machine, and making corresponding corrections; The virtual inertia of the virtual synchronous machine is restored to its initial value, and the output current of the system is detected by substituting it into the adjusted optimal control to verify the effectiveness of the optimal control.

2. The method for suppressing oscillation of series compensation capacitors based on impedance reshaping according to claim 1, Features: The low-voltage flexible direct current transmission system includes a virtual synchronous machine and a series compensation capacitor circuit; The preliminary control of the virtual synchronous machine includes simulating the moment of inertia and inertia time constant in the synchronous machine power grid, providing damping support for the power grid, and obtaining the virtual synchronous machine impedance model and the series compensation circuit impedance model for subsequent stability analysis; The moment of inertia and inertia time constant in the simulated synchronous machine network include: The motion equation and modulation part of the synchronous machine are simulated to calculate and obtain the virtual inertia and damping coefficient parameters. The calculation formula is as follows: Among them, P set and P e are the mechanical power and electromagnetic power of the virtual synchronous machine, T set is the mechanical torque, T e is the electromagnetic torque, J and D p are the virtual inertia and virtual damping coefficient of the virtual synchronous machine, ω is the angular frequency of the virtual synchronous machine, ω n is the rated angular frequency, and ω n =2πf n , θ is the virtual synchronous machine power angle, Q set Reactive power set for the virtual synchronous machine, D q is the reactive inertia of the virtual synchronous machine, V nom and V are the rated voltage rms and output voltage rms respectively, E m is the effective value of the voltage of the virtual synchronous machine, K is the inertia coefficient, and s is the differential operator; According to the virtual synchronous machine main control, the power angle reference value θ is obtained to generate a three-phase modulation signal s a 、s b 、s c , the calculation formula is as follows: Among them, V dc is the DC terminal voltage.

3. The method for suppressing oscillation of series compensation capacitor based on impedance reshaping according to claim 2, Features: The impedance model of the system includes: The impedance model of the virtual synchronous machine is constructed by harmonic linearization method to obtain the positive and negative sequence impedance model of the system. Inject a positive and negative sequence signal with an amplitude much lower than the reference voltage amplitude and observe the response of the positive and negative sequence current signals; The ratio of the voltage frequency domain signal to the current frequency domain signal is converted into an impedance value to obtain the positive and negative sequence impedance values. The calculation formula is as follows: M(s)=1 / (Js 2 +D p s) When sampling delay is considered, the calculation formula of K(s) is as follows: Among them, V p 、V n are the frequency domain components of the positive and negative sequence voltage disturbances, I p ,I n are the frequency domain components of the positive and negative sequence current responses, V 1 ,I 1 are the fundamental frequency voltage and current amplitudes, is the initial phase of the fundamental frequency current, L f is the filter inductance of the virtual synchronous machine, arcsin[P e ω n L f / (E m V 1 )] is the power angle of the virtual synchronous machine, ω v and ω i are the cutoff frequencies of the voltage and current sampling low-pass filters, T s is the switching period, K(s) is the controller gain; The series compensation circuit is modeled and the series compensation circuit model formula is as follows: Z series (s)=1 / (sC 1 )+R 1 Among them, C 1 and R 1 They are filter capacitor and filter resistor respectively.

4. The method for suppressing oscillation of series compensation capacitors based on impedance reshaping according to claim 3, Features: The series compensation circuit model also includes: The filter capacitor circuit is included in the series compensation circuit model, and the filter capacitor circuit and the series compensation circuit are combined into the grid impedance. The calculation formula is as follows: Z g (s)=(sL g +R g +1 / (sC 2 ))||(1 / (sC 1 )+R 1 ) Among them, L g and R g are the equivalent inductance and equivalent resistance of the grid side, C 2 It is the series compensation capacitor on the grid side.

5. The method for suppressing oscillation of series compensation capacitor based on impedance reshaping according to claim 4, Features: The stability of the analytical system includes: Calculate the frequency response using impedance model parameters according to the obtained impedance model; Draw the frequency response curve to form a Bode diagram; Based on the Bode diagram, determine the open-loop transfer function of the system; Apply the Nyquist stability criterion to determine the stability of the system; If the system is unstable, the optimization control based on impedance reshaping is applied to adjust the parameters of the virtual synchronous machine so that the system meets the stability requirements; The parameters of the virtual synchronous machine are adjusted through impedance reshaping optimization control to suppress subsynchronous oscillations.

6. The method for suppressing oscillation of series compensation capacitors based on impedance reshaping according to claim 5, Features: The corresponding corrections include: By adding the impedance reshaping controller and modifying the transfer function, the transfer function is modified to: Among them, T 1 and T 2 Adjustable parameters for the proposed impedance reshaping controller; At the same time, the virtual synchronous machine sequence impedance using the impedance reshaping controller is modified as follows: M(s)=1 / (J(s)s 2 +Ds)。 7. The method for suppressing oscillation of series compensation capacitor based on impedance reshaping according to claim 6, Features: The verification of the effectiveness of the optimization control includes: After troubleshooting, restore the initial value of virtual inertia of the virtual synchronous machine; Record the current virtual inertia value and restore the virtual inertia to the initial setting; Bring the adjusted optimized control parameters into the virtual synchronous machine control system to detect the output current; Run the system, record the output current value, and compare the output current value with the system design requirements; By detecting the output current of the system, the effectiveness of the optimized control is verified to ensure that the system operates stably under the new control parameters; Verify system stability based on test results; If the system is stable, the optimized control parameters are recorded as the final solution; If the system is unstable, further adjust the control parameters until the system is stable.

8. A series compensation capacitor oscillation suppression system based on impedance reshaping, based on the series compensation capacitor oscillation suppression method based on impedance reshaping according to any one of claims 1 to 7, Features: Including impedance modeling module, judgment analysis module, optimization control module and verification optimization module; The impedance modeling module is used to model the low-voltage flexible direct current transmission system, obtain the impedance model of the system, and realize the preliminary control of the virtual synchronous machine; The judgment and analysis module is used to draw a Bode diagram according to the impedance model of the system and apply the Nyquist stability criterion to analyze the stability of the system; The optimization control module is used to perform optimization control according to the system stability, re-detect the sequence impedance of the virtual synchronous machine, and make corresponding corrections; The verification optimization module is used to restore the virtual inertia of the virtual synchronous machine to an initial value, and to detect the output current of the system by substituting the adjusted optimization control into the optimized control to verify the effectiveness of the optimization control.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program. Features: When the processor executes the computer program, the steps of the series compensation capacitor oscillation suppression method based on impedance reshaping according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, Features: When the computer program is executed by a processor, the steps of the series compensation capacitor oscillation suppression method based on impedance reshaping according to any one of claims 1 to 7 are implemented.

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