An adaptive damping control method for flexible DC converter stations

Abstract

The present invention relates to the field of flexible direct current (HVDC) transmission technology, specifically providing a method for adaptive damping control in a flexible direct current (DC) converter station. The method comprises: acquiring angular frequencies from preset sampling points and calculating angular frequency derivatives based on the angular frequencies of five adjacent sampling points; confirming that the angular frequency or angular frequency derivative does not meet dynamic conditions; calculating adaptive virtual damping based on the angular frequency derivatives and updating the damping parameters of a virtual synchronous machine; calculating adaptive virtual inertia based on the adaptive virtual damping and steady-state operating parameters of the virtual synchronous machine; and calculating a compensation value based on the adaptive virtual damping and adaptive virtual inertia. The present invention achieves accurate control of the damping of the flexible direct current (DC) converter station and improves compensation accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current (DC) transmission, and in particular relates to an adaptive damping control method for a flexible DC converter station. Background Art

[0002] In recent years, flexible DC transmission (FDC) projects have been continuously constructed, with increasing capacity and voltage levels. However, high-frequency oscillations have repeatedly occurred in actual projects, seriously impacting the safe and stable operation of the system. High-frequency oscillations in FDC systems are primarily caused by system control link delays and voltage feedforward, reducing system damping and stability margins. Virtual synchronous generator control (VSG) simulates the damping and inertia characteristics of synchronous machines and is an important measure for improving the stability of FDC systems. While introducing rotor mechanical equations into system control can improve stability, it also introduces issues such as slower response speed and increased frequency disturbances.

[0003] The existing virtual inertia control method constructs a new energy storage microgrid; by configuring a supercapacitor in the new energy storage microgrid, electric energy is quickly released / absorbed; by introducing a high-pass filter in the new energy storage microgrid, the DC bus voltage is kept stable; and the inertia control of the new energy storage microgrid is achieved through the supercapacitor and the high-pass filter.

[0004] This approach is complex to operate, costly, and lacks adaptive adjustment capabilities. Therefore, a new damping control method for flexible DC converter stations is needed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides an adaptive damping control method for a flexible DC converter station to solve the above-mentioned technical problems.

[0006] The present invention provides an adaptive damping control method for a flexible DC converter station, comprising:

[0007] Collecting angular frequencies from a preset sampling point and calculating angular frequency derivatives based on the angular frequencies of five adjacent sampling points;

[0008] Confirm that the angular frequency or angular frequency derivative does not meet the dynamic conditions;

[0009] Calculating adaptive virtual damping according to angular frequency derivatives and updating the damping parameters of the virtual synchronous machine;

[0010] Calculate the adaptive virtual inertia based on the adaptive virtual damping and the parameters of the virtual synchronous machine during steady-state operation;

[0011] A compensation value is calculated based on the adaptive virtual damping and the adaptive virtual inertia.

[0012] In an optional embodiment, collecting the angular frequency from a preset sampling point and calculating the angular frequency derivative based on the angular frequencies of five adjacent sampling points includes:

[0013] The angular frequency of the PCC sampling voltage is extracted by Fourier analysis;

[0014] Five adjacent sampling points are obtained according to the selection principle of the first-order five-point formula, and the derivative of the angular frequency dω / dt is calculated by the first-order five-point formula.

[0015] In an optional embodiment, five adjacent sampling points are obtained according to the selection principle of the first-order five-point formula, and the derivative of the angular frequency dω / dt is calculated by the first-order five-point formula, including:

[0016] Take two adjacent sampling points on both sides of the sampling point under investigation. If there are less than two sampling points on one side, use the sampling points on the other side to supplement them.

[0017] The derivative value of the angular frequency at the observation point is calculated using the first-order five-point formula, which is:

[0018] ,

[0019] ,

[0020] ,

[0021] ,

[0022] ,

[0023] Where h represents the sampling interval, f(x0) is the angular frequency of the first sampling point, f(x1) is the angular frequency of the second sampling point, f(x2) is the angular frequency of the third sampling point, f(x3) is the angular frequency of the fourth sampling point, and f(x4) is the angular frequency of the fifth sampling point. The complete application process is: at time x0, sample f(x0), f(x 1~4 ) is 0, m0 is the derivative at this time; at x1 moment, sampling f(x1), f(x0) has a value, f(x 2~4 ) is 0, m1 is the derivative at this time; at x2, sample f(x2), f(x0) and f(x1) have values, f(x 3、4) is 0, m2 is the derivative at this time; at time x3, f(x3) is sampled, f(x0), f(x1), and f(x2) have values, f(x4) is 0, m3 is the derivative at this time; at time x4, f(x4) is sampled, f(x0), f(x1), f(x2), and f(x3) have values, m4 is the derivative at this time; at time x5, f(x5) is sampled, f(x1), f(x2), f(x3), and f(x4) have values, m5 is the derivative at this time.

[0024] In an optional embodiment, confirming that the angular frequency or the angular frequency derivative does not satisfy the dynamic condition includes:

[0025] If the difference between the angular frequency and the preset expected angular frequency does not exceed a preset first threshold, and the angular frequency derivative does not exceed a preset second threshold, it is determined that the angular frequency and the angular frequency derivative meet the dynamic conditions, and there is no need to compensate for the virtual inertia and virtual damping;

[0026] If the difference between the angular frequency and the preset expected angular frequency exceeds a preset first threshold, or the angular frequency derivative exceeds a preset second threshold, it is determined that the angular frequency or the angular frequency derivative does not meet the dynamic condition, and the virtual inertia and virtual damping need to be compensated.

[0027] In an optional embodiment, calculating the adaptive virtual damping according to the angular frequency derivative and updating the damping parameters of the virtual synchronous machine includes:

[0028] Set virtual damping according to the standard voltage frequency and standard voltage amplitude of the power grid D p ;

[0029] According to the static stability condition and virtual damping D p Calculating virtual inertia J 0;

[0030] Calculate the adaptive virtual damping based on the virtual damping and the angular frequency derivative.

[0031] In an optional embodiment, the virtual damping is set according to the standard voltage frequency and standard voltage amplitude of the power grid. D p ,include:

[0032] Assuming the grid voltage frequency changes by ±1Hz and the system output active power changes by 100%, the calculation formula for virtual damping is:

[0033] ;

[0034] Among them, Δ P max is the maximum value of active power change, Δ ohmax is the maximum value of the frequency variation.

[0035] In an optional embodiment, according to the static stability condition and the virtual damping D p Calculating virtual inertia J 0, including:

[0036] The relationship between the virtual inertia, the virtual damping and the cutoff frequency is obtained according to the system loop gain at the active loop cutoff frequency. The calculation formula of the virtual inertia is:

[0037] ;

[0038] in, D p represents virtual damping, f cp represents the system cutoff frequency, oh n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, E n is the effective value of the output voltage of the virtual synchronous machine when it is working in steady state. V g is the grid voltage, X s is the system impedance;

[0039] The system phase margin requirement is used as a constraint for selecting virtual inertia and cutoff frequency. The system phase margin requirement is:

[0040] ;

[0041] in, D p represents virtual damping, f cp represents the system cutoff frequency, oh n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, PM req is the system phase margin requirement.

[0042] In an optional embodiment, the adaptive virtual damping is calculated based on the virtual damping and the angular frequency derivative, including:

[0043] Adaptive virtual damping D v The calculation formula is:

[0044] ;

[0045] in, Dp is the standard value of virtual damping in the current system, k D is the damping adjustment coefficient.

[0046] In an optional embodiment, the adaptive virtual inertia is calculated based on the adaptive virtual damping and the parameters of the virtual synchronous machine during steady-state operation, including:

[0047] Adaptive virtual inertia J v The calculation formula is:

[0048] ;

[0049] in, D v represents the adaptive virtual damping, f cp represents the system cutoff frequency, oh n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, E n is the effective value of the output voltage of the virtual synchronous machine when it is working in steady state, V g is the grid voltage, X s is the system impedance, k J Indicates the inertia adjustment coefficient;

[0050] Among them, the calculation expression of the ReLU function is:

[0051] .

[0052] In an optional embodiment, calculating the compensation value based on the adaptive virtual damping and the adaptive virtual inertia includes:

[0053] Substituting the adaptive virtual damping and the adaptive virtual inertia into the control equation of the virtual synchronous machine;

[0054] Obtain the angular frequency and angular frequency derivatives of the power system using adaptive virtual damping and adaptive virtual inertia,

[0055] A voltage reference value is calculated based on the angular frequency and the angular frequency, and a voltage and current are modulated based on the voltage reference value.

[0056] The beneficial effect of the present invention is that the adaptive damping control method for a flexible DC converter station provided by the present invention configures virtual inertia and damping through angular frequency and its derivative, thereby improving the anti-interference ability and dynamic performance of the virtual synchronous machine. First, the system angular frequency is measured, and the angular frequency derivative is calculated based on the system angular frequency. Secondly, the virtual damping is set according to the relevant standards of the power grid, and the virtual inertia is calculated based on the static stability condition and the virtual damping. Next, the system state is judged by the angular frequency and the derivative of the angular frequency. If the system does not meet the dynamic requirements, the virtual damping and virtual inertia under the static stability condition are adopted; if the system meets the dynamic requirements, the adaptive virtual damping compensation value is calculated based on the angular frequency and its derivative, and the adaptive virtual inertia compensation value is calculated based on the virtual damping compensation value, and then the system state is re-judged until the system meets the dynamic requirements. The present invention adopts the activation function commonly used in neural networks in the calculation process of adaptive virtual damping and inertia. The control scheme has a simple structure and is easy to implement, which improves the dynamic performance and anti-interference ability of the system; no additional equipment such as supercapacitors is required, which helps to reduce costs.

[0057] In addition, the present invention has a reliable design principle, a simple structure and a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0059] Figure 1 It is a schematic principle diagram of a method according to an embodiment of the present invention.

[0060] Figure 2 is a schematic flow chart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0063] Please refer to Figure 1 First, the inductor current and inductor voltage at the point of common coupling (PCC), as well as the grid-side voltage and current, are sampled. The voltage and current in the abc coordinate system are transformed into the dq coordinate system through coordinate transformation. Secondly, the angular frequency of the PCC sampled voltage is extracted through Fourier analysis, and the derivative of the angular frequency is calculated using the five-point formula. The adaptive virtual inertia and damping are calculated based on the angular frequency and its derivative and input into the virtual synchronous machine control module. Then, the instantaneous power is calculated using the sampled values, and the frequency and amplitude reference values ​​are calculated using the active loop and reactive loop to obtain the reference value of the system output voltage. Finally, through dual closed-loop control of voltage and current, a sub-sine wave of a specific frequency is injected into the modulation wave to generate a pulse width modulation signal that acts on the flexible DC converter station.

[0064] For details, please refer to Figure 2 The adaptive damping control method for a flexible DC converter station includes the following steps:

[0065] Step S1: Measure the power system angular frequency oh .

[0066] Step S2: Get five adjacent sampling points according to the selection principle of the first-order five-point formula, and calculate the derivative of the angular frequency using the first-order five-point formula. dω / dt The principle for selecting sampling points for the first-order five-point formula is: generally, two adjacent sampling points are selected on both sides of the sampling point under investigation. If there are less than two sampling points on one side, the sampling points on the other side are used to supplement them.

[0067] The first-order five-point formula is:

[0068] ,

[0069] ,

[0070] ,

[0071] ,

[0072] ,

[0073] Where h represents the sampling interval, f(x0) is the angular frequency of the first sampling point, f(x1) is the angular frequency of the second sampling point, f(x2) is the angular frequency of the third sampling point, f(x3) is the angular frequency of the fourth sampling point, and f(x4) is the angular frequency of the fifth sampling point. The complete application process is: at time x0, sample f(x0), f(x 1~4 ) is 0, m0 is the derivative at this time; at x1 moment, sampling f(x1), f(x0) has a value, f(x 2~4 ) is 0, m1 is the derivative at this time; at x2, sample f(x2), f(x0) and f(x1) have values, f(x 3、4 ) is 0, m2 is the derivative at this time; at moment x3, f(x3) is sampled, f(x0), f(x1), and f(x2) have values, f(x4) is 0, m3 is the derivative at this time; at moment x4, f(x4) is sampled, f(x0), f(x1), f(x2), and f(x3) have values, m4 is the derivative at this time; at moment x5, f(x5) is sampled, f(x1), f(x2), f(x3), and f(x4) have values, m5 is the derivative at this time, and so on.

[0074] Step S3: According to the grid standard, the grid voltage frequency is between 49Hz~51Hz, the grid voltage amplitude is between 90%~110% of the rated voltage amplitude, and the virtual damping is set. D p The principle of setting virtual damping according to the relevant standards of the power grid is: if the grid voltage frequency changes by ±1Hz, the system output active power changes by 100%. The calculation formula of the virtual damping is:

[0075]

[0076] Among them, Δ P max is the maximum value of active power change, Δ oh max is the maximum value of the frequency variation.

[0077] Step S4: Calculate virtual inertia based on static stability conditions and virtual damping J 0. The method for calculating the virtual inertia based on the static stability condition and the virtual damping is as follows: the relationship between the virtual inertia and the virtual damping and the cutoff frequency is obtained based on the system loop gain at the active loop cutoff frequency. The calculation formula of the virtual inertia is:

[0078]

[0079] in, D p represents virtual damping, f cprepresents the system cutoff frequency, oh n 、 E n is the angular frequency and effective value of the output voltage of the virtual synchronous machine when it is working in steady state. V g is the grid voltage, X s is the system impedance.

[0080] Furthermore, the selection of virtual inertia and cutoff frequency needs to ensure the system phase margin requirement, which is:

[0081]

[0082] in, D p represents virtual damping, f cp represents the system cutoff frequency, oh n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, PM req is the system phase margin requirement.

[0083] Step S5: If the system angular frequency and its derivative respectively satisfy | oh-oh ref | ≤ K ω and | dω / dt | ≤ K dω , it is determined that the system meets the dynamic requirements and there is no need to compensate for the virtual inertia and damping, and the process goes to step S9; if the system angular frequency does not meet the | oh-oh ref | ≤ K ω or its derivative does not satisfy | dω / dt | ≤ K dω , it is determined that the system does not meet the dynamic requirements and the process goes to step S6. Wherein, is the preset expected angular frequency, K ω is the first threshold value set, K dω is the set second threshold.

[0084] Step S6: When the system does not meet the dynamic requirements and is in a divergent state, according to the derivative of the angular frequency dω / dt Computing adaptive virtual damping D vAnd update the damping parameters of the virtual synchronous machine. The adaptive virtual damping is calculated based on the angular frequency and its derivative D v The calculation formula is:

[0085] ;

[0086] in, D p is the standard value of virtual damping in the current system, k D is the damping adjustment coefficient.

[0087] Step S7: Adaptive virtual damping D v Calculate the dynamic reference value of virtual inertia, and then calculate the adaptive virtual inertia through the ReLU function J v And update the inertia parameters of the virtual synchronous machine. J v The calculation formula is:

[0088] ;

[0089] in, D v represents the adaptive virtual damping, f cp represents the system cutoff frequency, oh n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, E n is the effective value of the output voltage of the virtual synchronous machine when it is working in steady state, V g is the grid voltage, X s is the system impedance, k J Indicates the inertia adjustment factor.

[0090] Furthermore, the calculation expression of the ReLU function is:

[0091] .

[0092] Step S8: Measure the angular frequency of the power system using adaptive virtual damping and adaptive virtual inertia oh And calculate its derivative dω / dt .

[0093] Step S9: The system adopts virtual damping under static stability conditions D p and virtual inertiaJ 0.

[0094] Although the present invention has been described in detail with reference to the accompanying drawings and in conjunction with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A method for adaptive damping control of a flexible DC converter station, characterized in that: include: Collecting angular frequencies from a preset sampling point and calculating angular frequency derivatives based on the angular frequencies of five adjacent sampling points; Confirm that the angular frequency or angular frequency derivative does not meet the dynamic conditions; Calculating adaptive virtual damping according to angular frequency derivatives and updating the damping parameters of the virtual synchronous machine; Calculate the adaptive virtual inertia based on the adaptive virtual damping and the parameters of the virtual synchronous machine during steady-state operation; calculating a compensation value based on the adaptive virtual damping and the adaptive virtual inertia; Calculate the adaptive virtual damping according to the angular frequency derivative and update the damping parameters of the virtual synchronous machine, including: Set virtual damping according to the standard voltage frequency and standard voltage amplitude of the power grid D p ; According to the static stability condition and virtual damping D p Calculating virtual inertia J 0; Calculate adaptive virtual damping based on virtual damping and angular frequency derivative; Calculate adaptive virtual damping based on virtual damping and angular frequency derivative, including: Adaptive virtual damping D v The calculation formula is: ； in, D p is the virtual damping standard value under the current system, k D is the damping adjustment coefficient, dω / dt is the angular frequency derivative, and ω is the angular frequency; The adaptive virtual inertia is calculated based on the adaptive virtual damping and the parameters of the virtual synchronous machine during steady-state operation, including: Adaptive virtual inertia J v The calculation formula is: ； in, D v represents the adaptive virtual damping, f cp represents the system cutoff frequency, ω n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, E n is the effective value of the output voltage of the virtual synchronous machine when it is working in steady state, V g is the grid voltage, X s is the system impedance, k J Indicates the inertia adjustment coefficient; Among them, the calculation expression of the ReLU function is: 。 2. The method according to claim 1, characterized in that The angular frequency is collected from a preset sampling point, and the angular frequency derivative is calculated based on the angular frequencies of five adjacent sampling points, including: The angular frequency of the PCC sampling voltage is extracted by Fourier analysis; Five adjacent sampling points are obtained according to the selection principle of the first-order five-point formula, and the derivative of the angular frequency dω / dt is calculated by the first-order five-point formula.

3. The method according to claim 2, characterized in that According to the selection principle of the first-order five-point formula, five adjacent sampling points are obtained, and the derivative of the angular frequency dω / dt is calculated by the first-order five-point formula, including: Take two adjacent sampling points on both sides of the sampling point under investigation. If there are less than two sampling points on one side, use the sampling points on the other side to supplement them. The derivative value of the angular frequency at the observation point is calculated using the first-order five-point formula, which is: ， ， ， ， ， Where h represents the sampling interval, f(x0) is the angular frequency of the first sampling point, f(x1) is the angular frequency of the second sampling point, f(x2) is the angular frequency of the third sampling point, f(x3) is the angular frequency of the fourth sampling point, and f(x4) is the angular frequency of the fifth sampling point. The complete application process is: at time x0, sample f(x0), f(x 1~4 ) is 0, m0 is the derivative at this time; at x1 moment, sampling f(x1), f(x0) has a value, f(x 2~4 ) is 0, m1 is the derivative at this time; at x2, sample f(x2), f(x0) and f(x1) have values, f(x 3、4 ) is 0, m2 is the derivative at this time; at time x3, f(x3) is sampled, f(x0), f(x1), and f(x2) have values, f(x4) is 0, m3 is the derivative at this time; at time x4, f(x4) is sampled, f(x0), f(x1), f(x2), and f(x3) have values, m4 is the derivative at this time; at time x5, f(x5) is sampled, f(x1), f(x2), f(x3), and f(x4) have values, m5 is the derivative at this time.

4. The method according to claim 1, wherein Verify that the angular frequency or angular frequency derivative does not meet dynamic conditions, including: If the difference between the angular frequency and the preset expected angular frequency does not exceed a preset first threshold, and the angular frequency derivative does not exceed a preset second threshold, it is determined that the angular frequency and the angular frequency derivative meet the dynamic conditions, and there is no need to compensate for the virtual inertia and virtual damping; If the difference between the angular frequency and the preset expected angular frequency exceeds a preset first threshold, or the angular frequency derivative exceeds a preset second threshold, it is determined that the angular frequency or the angular frequency derivative does not meet the dynamic condition, and the virtual inertia and virtual damping need to be compensated.

5. The method according to claim 4, characterized in that Set virtual damping according to the standard voltage frequency and standard voltage amplitude of the power grid D p ,include: Assuming the grid voltage frequency changes by ±1Hz and the system output active power changes by 100%, the calculation formula for virtual damping is: ； Among them, Δ P max is the maximum value of active power change, Δ ω max is the maximum value of the frequency variation.

6. The method according to claim 5, characterized in that According to the static stability condition and virtual damping D p Calculating virtual inertia J 0, including: The relationship between the virtual inertia, the virtual damping and the cutoff frequency is obtained according to the system loop gain at the active loop cutoff frequency. The calculation formula of the virtual inertia is: ； in, D p represents virtual damping, f cp represents the system cutoff frequency, ω n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, E n is the effective value of the output voltage of the virtual synchronous machine when it is working in steady state. V g is the grid voltage, X s is the system impedance; The system phase margin requirement is used as a constraint for selecting virtual inertia and cutoff frequency. The system phase margin requirement is: ； in, D p represents virtual damping, f cp represents the system cutoff frequency, ω n is the angular frequency of the output voltage of the virtual synchronous machine when it is working in steady state, PM req is the system phase margin requirement.

7. The method according to claim 1, characterized in that Calculating a compensation value based on the adaptive virtual damping and the adaptive virtual inertia includes: Substituting the adaptive virtual damping and the adaptive virtual inertia into the control equation of the virtual synchronous machine; Obtain the angular frequency and angular frequency derivatives of the power system using adaptive virtual damping and adaptive virtual inertia, A voltage reference value is calculated based on the angular frequency and the angular frequency, and a voltage and current are modulated based on the voltage reference value.

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