Quantification Method and System for Harmonic Transmission of Offshore Wind Power Considering Insulation Aging of Submarine Cables

Abstract

The present invention discloses a method and system for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging, which relates to the field of harmonic transfer characteristic analysis. The method includes: dividing the severity levels of submarine cable insulation aging, and determining the insulation capacitance gain coefficient corresponding to each level of submarine cable; based on the cable aging detection results regularly obtained by the power grid company, determining the actual capacitance gain coefficient of the submarine cable insulation state; based on the actual capacitance gain coefficient, correcting the capacitance value of the submarine cable; establishing an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line, and estimating the grid-connected system harmonic resonance frequency causing harmonic current amplification and the harmonic current amplification coefficient at the grid connection point under the grid-connected system harmonic resonance frequency according to the corrected capacitance value of the submarine cable. The present invention significantly improves the accuracy of evaluating the resonance frequency and the severity of harmonic amplification of the offshore wind power grid-connected system, so as to be able to guide the effective suppression of harmonic resonance amplification.

Description

Technical Field

[0001] The present invention relates to the field of harmonic transfer characteristic analysis, and particularly to a method and system for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging. Background Art

[0002] In the past decade, a large number of offshore wind farms have been put into operation in the eastern coastal areas of China, and the safe transmission of offshore wind power has become particularly important. Due to its special geographical location, offshore wind power often needs to use long-distance (more than 10 kilometers) AC submarine cables to connect to the onshore power grid. For long submarine cable lines, the distributed capacitance effect is obvious, and it is easy to resonate with the inductive onshore power grid, resulting in serious amplification of harmonic current during the transmission process of submarine cables (referred to as submarine cables for short), deteriorating the power quality of the grid in the grid connection area, and increasing the risk of safe operation of equipment.

[0003] Therefore, accurately predicting the harmonic resonance frequency and quantifying the harmonic transfer characteristics (i.e., evaluating the severity of harmonic amplification) are of great significance for suppressing harmonic resonance amplification. However, the current methods for quantifying harmonic transfer characteristics are all based on the factory capacitance parameters of the cable and do not consider the influence of insulation aging on the capacitance value. During the entire life cycle of the cable, its capacitance value will increase with the increase of insulation aging, and when the insulation is close to damage, it can reach about 1.15 times of the factory parameters. The parameter changes caused by insulation aging have an important impact on the resonance amplification of cable harmonics.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing methods for quantifying harmonic transfer characteristics are all based on the factory capacitance parameters of the cable and do not consider the influence of insulation aging on the capacitance value, resulting in problems such as low accuracy in evaluating the resonance frequency and the severity of harmonic amplification of the offshore wind power grid connection system. The purpose of the present invention is to provide a method and system for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging. By considering the influence of submarine cable insulation aging on the cable capacitance value and performing parameter correction, the accuracy of evaluating the resonance frequency and the severity of harmonic amplification of the offshore wind power grid connection system will be significantly improved, thereby being able to guide the effective suppression of harmonic resonance amplification.

[0006] The present invention is realized through the following technical solutions:

[0007] In the first aspect, the present invention provides a method for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging, and the method includes:

[0008] Dividing the severity level of submarine cable insulation aging and determining the insulation capacitance gain coefficient corresponding to the submarine cable at each level;

[0009] Based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company, determine the actual capacitance gain coefficient of the submarine cable insulation status;

[0010] Based on the actual capacitance gain coefficient, correct the capacitance value of the submarine cable to obtain the corrected capacitance value of the submarine cable;

[0011] Establish an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line, and estimate the grid-connected system harmonic resonance frequency causing harmonic current amplification according to the corrected capacitance value of the submarine cable;

[0012] According to the grid-connected system harmonic resonance frequency, estimate the harmonic current amplification coefficient at the grid connection point under the grid-connected system harmonic resonance frequency.

[0013] Furthermore, divide the severity level of the submarine cable insulation aging, and determine the insulation capacitance gain coefficient corresponding to the submarine cable at each level, including:

[0014] Based on the severity of the insulation aging, divide the levels of the submarine cable into 5 grades; the grades include the first grade, the second grade, the third grade, the fourth grade, and the fifth grade; among them, the first grade is in good condition, the second grade is slightly aged, the third grade is moderately aged, the fourth grade is severely aged, and the fifth grade is in the state of insulation damage;

[0015] According to each grade, determine the insulation capacitance gain coefficient corresponding to the submarine cable at each level; among them, the insulation capacitance gain coefficients corresponding to the first grade, the second grade, the third grade, the fourth grade, and the fifth grade are 1.00, 1.04, 1.08, 1.12, and 1.15 respectively.

[0016] Furthermore, the expression of the corrected capacitance value of the submarine cable is: C0 = μC 0_ref ; where, C0 is the capacitance value of the actual submarine cable capacitance per unit length; C 0_ref is the capacitance value of the submarine cable at the time of factory shipment per unit length, that is, the capacitance value when the insulation is in good condition; μ is the actual capacitance gain coefficient.

[0017] Furthermore, establish an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line, and estimate the grid-connected system harmonic resonance frequency causing harmonic current amplification according to the corrected capacitance value of the submarine cable, including:

[0018] Equivalent the submarine cable line to a T-shaped circuit, and construct an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line;

[0019] Based on the equivalent circuit, when a series resonance occurs in the loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance of the submarine cable to the ground, the harmonic current in the loop (i.e., the harmonic current at the point of common coupling) will be severely amplified, and the series resonance frequency is estimated based on the series resonance frequency formula;

[0020] Substitute the corrected capacitance value of the submarine cable into the series resonance frequency formula, and use the Newton iteration method to solve the objective function of the harmonic resonance frequency to obtain the harmonic resonance frequency of the grid-connected system that causes the amplification of the harmonic current in the loop.

[0021] Furthermore, the series resonance frequency formula is:

[0022]

[0023] In the formula, j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; C0 is the capacitance value of the actual submarine cable per unit length; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the cable length; Z s is the equivalent harmonic impedance of the power grid; coth() is the hyperbolic cotangent function.

[0024] Furthermore, the equivalent harmonic impedance of the power grid is estimated based on the minimum short-circuit capacity of the busbar at the point of common coupling of the offshore wind farm. The expression of the equivalent harmonic impedance Z s is:

[0025]

[0026] In the formula, U N is the rated voltage of the busbar at the point of common coupling; S c is the minimum short-circuit capacity of the busbar; j is the imaginary unit; h is the harmonic resonance frequency.

[0027] Furthermore, the objective function for solving the harmonic resonance frequency is:

[0028]

[0029] In the formula, h is the harmonic resonance frequency, is the estimated value of the harmonic resonance frequency; j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable per unit length when it leaves the factory; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid.

[0030] Furthermore, the expression of the harmonic current amplification factor HI is:

[0031]

[0032] Z h = R0 + j2πhL0;

[0033] In the formula, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable at the time of factory per unit length; Z h is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

[0034] Second, the present invention also provides a quantization system for harmonic transfer of offshore wind power considering the insulation aging of submarine cables, and the system includes:

[0035] An insulation aging level division unit for dividing the severity level of the insulation aging of the submarine cable and determining the insulation capacitance gain coefficient corresponding to the submarine cable for each level;

[0036] An actual capacitance gain coefficient determination unit for determining the actual capacitance gain coefficient of the insulation state of the submarine cable based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company;

[0037] A cable capacitance value correction unit for correcting the capacitance value of the submarine cable based on the actual capacitance gain coefficient to obtain the corrected capacitance value of the submarine cable;

[0038] A first estimation unit for establishing an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line and estimating the harmonic resonance frequency of the grid-connected system that causes harmonic current amplification according to the corrected capacitance value of the submarine cable;

[0039] A second estimation unit for estimating the harmonic current amplification factor at the grid connection point under the harmonic resonance frequency of the grid-connected system according to the harmonic resonance frequency of the grid-connected system.

[0040] Further, the expression of the harmonic current amplification factor HI is:

[0041]

[0042] Z h = R0 + j2πhL0;

[0043] In the formula, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable per unit length at the time of factory shipment; Z h is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

[0044] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0045] The existing method does not consider the influence of insulation aging on the cable capacitance parameter (which can actually cause the capacitance to increase by 1.15 times), and the obtained harmonic resonance amplification result is only applicable to new cables. However, the method of the present invention can significantly improve the assessment accuracy of the resonance frequency and the severity of harmonic amplification in the offshore wind power grid connection system by considering the influence of cable insulation aging on the cable capacitance value and performing parameter correction, so as to be able to guide the effective suppression of harmonic resonance amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0047] Figure 1 is the flow chart of the method for quantifying harmonic transfer in offshore wind power considering submarine cable insulation aging of the present invention;

[0048] Figure 2 is the equivalent circuit diagram of the offshore wind power grid connection system via the submarine cable line of the present invention;

[0049] Figure 3 is the harmonic amplification coefficient diagram of the submarine cable under different insulation states of the present invention;

[0050] Figure 4 is the waveform diagram of the harmonic current at both ends under the condition of intact cable insulation obtained by the electromagnetic transient simulation model analysis of Embodiment 1 of the present invention;

[0051] Figure 5 is the waveform diagram of the harmonic current at both ends under the condition of damaged cable insulation obtained by the electromagnetic transient simulation model analysis of Embodiment 1 of the present invention;

[0052] Figure 6 is the structural block diagram of the system for quantifying harmonic transfer in offshore wind power considering submarine cable insulation aging of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0054] Embodiment 1

[0055] As Figure 1 shown, the present invention provides a method for quantifying harmonic transfer in offshore wind power considering submarine cable insulation aging. The method includes:

[0056] Step 1: Divide the severity levels of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable.

[0057] In this embodiment, Step 1 specifically includes:

[0058] Based on the severity of insulation aging, the levels of submarine cables are divided into 5 grades; the grades include the first grade, the second grade, the third grade, the fourth grade, and the fifth grade; among them, the first grade is in good condition, the second grade is slightly aged, the third grade is moderately aged, the fourth grade is severely aged, and the fifth grade is in an insulation damaged state;

[0059] According to each grade, determine the insulation capacitance gain coefficient corresponding to each level of submarine cable; among them, the insulation capacitance gain coefficients corresponding to the first grade, the second grade, the third grade, the fourth grade, and the fifth grade are 1.00, 1.04, 1.08, 1.12, and 1.15 respectively.

[0060] Step 2: Based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company, determine the actual capacitance gain coefficient of the submarine cable insulation state.

[0061] Step 3: Based on the actual capacitance gain coefficient, correct the capacitance value of the submarine cable to obtain the corrected capacitance value of the submarine cable.

[0062] In this embodiment, the expression for the corrected capacitance value of the submarine cable is: C0 = μC 0_ref ; where C0 is the capacitance value of the actual submarine cable capacitance per unit length; C 0_ref is the capacitance value of the submarine cable at the time of factory shipment per unit length, that is, the capacitance value when the insulation is in good condition; μ is the actual capacitance gain coefficient.

[0063] Step 4: Establish an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line. The equivalent circuit is as Figure 2 shown; and based on the corrected capacitance value of the submarine cable, estimate the harmonic resonance frequency of the grid-connected system that causes harmonic current amplification.

[0064] In this embodiment, Step 4 specifically includes:

[0065] Step 41: Equivalent the submarine cable line to a T-shaped circuit and construct the equivalent circuit of the offshore wind power grid-connected system via the submarine cable line;

[0066] Step 42: Based on the equivalent circuit, when a series resonance occurs in the loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance to the ground of the submarine cable, the harmonic current in the loop (i.e., the harmonic current at the grid connection point) will be severely amplified. At this time, estimate the series resonance frequency based on the series resonance frequency formula; where the series resonance frequency formula is:

[0067]

[0068] In the formula, j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; C0 is the capacitance value of the actual submarine cable per unit length; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the cable length; Z s is the equivalent harmonic impedance of the power grid; coth() is the hyperbolic cotangent function.

[0069] The equivalent harmonic impedance Z of the power grid in the above formula s can be estimated according to the minimum short-circuit capacity of the bus at the grid connection point of the offshore wind farm. The expression of the equivalent harmonic impedance Z of the power grid s is:

[0070]

[0071] In the formula, U N is the rated voltage of the bus at the grid connection point; S c is the minimum short-circuit capacity of the bus; j is the imaginary unit; h is the harmonic resonance frequency.

[0072] Step 43: Substitute the corrected capacitance value of the submarine cable into the series resonance frequency formula, solve the objective function of the harmonic resonance frequency, and obtain the harmonic resonance frequency of the grid-connected system that causes the amplification of the harmonic current in the loop.

[0073] Specifically, the objective function for solving the harmonic resonance frequency is:

[0074]

[0075] In the formula, h is the harmonic resonance frequency, is the estimated value of the harmonic resonance frequency; j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable per unit length when it leaves the factory; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the length of the submarine cable; Z sis the equivalent harmonic impedance of the power grid.

[0076] The solution of h belongs to an optimization problem and can be solved by the Newton iteration method. Since the submarine cable of the offshore wind farm is relatively long and the equivalent capacitance of the submarine cable is relatively large, the series resonance frequency is often not high. Therefore, the initial value of h can be set to 2.

[0077] Step 5: Estimate the harmonic current amplification factor at the grid connection point under the harmonic resonance frequency of the grid-connected system according to the harmonic resonance frequency of the grid-connected system.

[0078] In this embodiment, let the harmonic current at the wind power end of the submarine cable be The harmonic current at the grid connection end is Considering the cable distribution parameter characteristics and the insulation capacitance gain caused by insulation aging, the harmonic current amplification factor HI at the grid connection point under the harmonic resonance frequency h can be obtained:

[0079]

[0080] Z h = R0 + j2πhL0;

[0081] In the formula, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable when it leaves the factory per unit length; Z h is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

[0082] The specific implementation is as follows:

[0083] To illustrate in detail the method for quantifying harmonic transfer in offshore wind power considering the insulation aging of submarine cables provided in this embodiment, first, parameter settings are performed based on the Figure 2 equivalent circuit shown in the figure, and the harmonic resonance frequency and harmonic current amplification factor under different insulation states of the submarine cable are calculated using the method proposed in the present invention. Further, an electromagnetic transient simulation analysis model is built on the Matlab / Simulink platform to verify the effectiveness of the proposed method. Figure 2In this case, the wind farm is connected to the power grid based on a 220 kV submarine cable, and the grid connection point is Bus 2. The short-circuit capacity of the bus is set to 5000 MVA, the cable length is set to 50 km, and the electrical parameters when the cable insulation is intact are shown in Table 1. It should be noted that the reference capacity of the 220 kV bus given in the national standard "Power Quality - Harmonics in Public Power Grids" (GB / T 14549-93) is 2000 MVA, and the actual value can often reach several times the reference value. Therefore, it is reasonable to set the short-circuit capacity to 5000 MVA. The length range of the outgoing cable of a 220 kV offshore wind farm is generally 10 - 60 km. Therefore, the setting of the cable length is also reasonable.

[0084] Table 1 Electrical parameters per unit length of the cable

[0085] <![CDATA[U N (kV)]]> <![CDATA[R0(Ω)]]> <![CDATA[L0 (mH)]]> <![CDATA[C0(uF)]]> 220 0.018 0.306 0.168

[0086] Based on the harmonic resonance frequency calculation method proposed in the present invention, the resonance frequencies of the wind power grid-connected system under different cable insulation degrees are shown in Table 2.

[0087] Table 2 Resonance frequencies of the grid-connected system under different cable insulation degrees

[0088] Cable insulation status Intact Slightly aged Moderately aged Severely aged Insulation damaged Capacitance gain coefficient 1 1.04 1.08 1.12 1.15 Resonant frequency 5.8 5.7 5.6 5.5 5.4

[0089] As can be seen from Table 2, insulation aging affects the harmonic resonance frequency, and the more severe the insulation aging, the lower the harmonic resonance frequency. Since the above-mentioned harmonic resonance frequencies are all non-integer multiples and are close to the 5th harmonic, the harmonic resonance frequencies can be approximately regarded as the 5th harmonic. Based on the method proposed in the present invention, the amplification factors of the calculated 5th harmonic under different insulation degrees are as Figure 3 shown. Figure 3 In this case, under five different cable insulation states, the harmonic current amplification factors are 4.2, 4.7, 5.5, 6.5, and 7.5 respectively. Therefore, it can be seen that cable insulation aging has a significant impact on harmonic current amplification. The method proposed in the present invention can effectively reflect the harmonic amplification differences caused by insulation aging, which is also a major advantage of the method proposed in the present invention compared with the existing methods.

[0090] Furthermore, an electromagnetic transient simulation analysis model is built by selecting submarine cables in two insulation states (intact and damaged insulation) to verify the accuracy of the calculation results of the method proposed in the present invention. When the cable insulation is intact, the simulation results are as Figure 4 shown, Figure 4 in this case, the harmonic current amplitude at the initial end (wind power end) of the cable is 1 A, while the harmonic current amplitude at the end (grid connection end) is 4.2 A, indicating that the harmonic current is amplified by 4.2 times after current transfer, which is consistent with the Figure 3 theoretical calculation value in; when the cable insulation is damaged, the simulation results are as Figure 5 shown, Figure 5Among them, the harmonic current amplitude at the initial end of the cable is 1 A, while the harmonic current amplitude at the end is 7.5 A, indicating that the harmonic current is amplified by 7.5 times after being transmitted through the cable, which also coincides with the theoretical calculation value. Therefore, the electromagnetic transient simulation results verify the accuracy and effectiveness of the method proposed in the present invention for evaluating the severity of harmonic amplification when considering the insulation aging of offshore wind power cables, thereby enabling the effective suppression of harmonic resonance amplification.

[0091] Embodiment 2

[0092] As Figure 6 shown, the difference between this embodiment and Embodiment 1 is that this embodiment provides a quantization system for harmonic transmission in offshore wind power considering the insulation aging of submarine cables, and the functions of this system correspond one-to-one with the quantization method for harmonic transmission in offshore wind power considering the insulation aging of submarine cables in Embodiment 1. This system includes:

[0093] An insulation aging level division unit for dividing the severity level of submarine cable insulation aging and determining the insulation capacitance gain coefficient corresponding to each level of submarine cable;

[0094] An actual capacitance gain coefficient determination unit for determining the actual capacitance gain coefficient of the insulation state of the submarine cable based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company;

[0095] A cable capacitance value correction unit for correcting the capacitance value of the submarine cable based on the actual capacitance gain coefficient to obtain the corrected capacitance value of the submarine cable;

[0096] A first estimation unit for establishing an equivalent circuit of the grid-connected system of offshore wind power through the submarine cable line and estimating the harmonic resonance frequency of the grid-connected system causing harmonic current amplification according to the corrected capacitance value of the submarine cable;

[0097] A second estimation unit for estimating the harmonic current amplification coefficient at the grid connection point under the harmonic resonance frequency of the grid-connected system according to the harmonic resonance frequency of the grid-connected system.

[0098] As a further implementation, the expression of the harmonic current amplification coefficient HI is:

[0099]

[0100] Z h =R0 + j2πhL0;

[0101] In the formula, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable at the time of factory per unit length; Zh is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

[0102] Among them, the execution process of each unit can be carried out according to the process steps of the method for quantifying harmonic transfer of offshore wind power considering the insulation aging of submarine cables in Embodiment 1, and will not be elaborated one by one in this embodiment.

[0103] Since the influence of insulation aging is considered in the present invention, the resonance frequency of the offshore wind power grid connection system and the accuracy of evaluating the severity of harmonic amplification can be significantly improved, so as to guide the effective suppression of harmonic resonance amplification.

[0104] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. 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.) containing computer-usable program code.

[0105] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0106] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implement the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0107] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable apparatus to generate a computer-implemented process, thereby providing instructions for implementing the functions specified in one process or a plurality of processes and / or boxes Figure 1 in one or more processes and / or boxes Figure 1 steps for implementing the functions specified in one or more boxes.

[0108] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A quantization method for harmonic transfer of offshore wind power considering the insulation aging of submarine cables, characterized in that The method includes: Dividing the severity levels of the insulation aging of the submarine cable and determining the insulation capacitance gain coefficient corresponding to each level of the submarine cable; Based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company, determining the actual capacitance gain coefficient of the insulation state of the submarine cable; Based on the actual capacitance gain coefficient, correcting the capacitance value of the submarine cable to obtain the corrected capacitance value of the submarine cable; Establishing an equivalent circuit of the grid-connected system of the offshore wind power through the submarine cable line and estimating the harmonic resonance frequency of the grid-connected system that causes harmonic current amplification according to the corrected capacitance value of the submarine cable; According to the harmonic resonance frequency of the grid-connected system, estimating the harmonic current amplification coefficient at the grid connection point under the harmonic resonance frequency of the grid-connected system; The expression of the harmonic current amplification coefficient HI is: Z h = R0 + j2πhL0; Wherein, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable at the time of factory production per unit length; Z h is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

2. The method for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging according to claim 1, wherein Dividing the severity levels of the insulation aging of the submarine cable and determining the insulation capacitance gain coefficient corresponding to each level of the submarine cable includes: Based on the severity of the insulation aging, dividing the levels of the submarine cable into 5 grades; the grades include the first grade, the second grade, the third grade, the fourth grade, and the fifth grade; among them, the first grade is in good condition, the second grade is slightly aged, the third grade is moderately aged, the fourth grade is severely aged, and the fifth grade is in the state of insulation damage; According to each grade, determining the insulation capacitance gain coefficient corresponding to each level of the submarine cable; among them, the insulation capacitance gain coefficients corresponding to the first grade, the second grade, the third grade, the fourth grade, and the fifth grade are 1.00, 1.04, 1.08, 1.12, and 1.15 respectively.

3. The method for quantifying harmonic transmission of offshore wind power considering submarine cable insulation aging according to claim 1, wherein The expression for the corrected capacitance value of the submarine cable is: C0 = μC 0_ref ; where C0 is the capacitance value of the actual submarine cable per unit length; C 0_ref is the capacitance value of the submarine cable when it leaves the factory per unit length, that is, the capacitance value when the insulation is intact; μ is the actual capacitance gain coefficient.

4. The method for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging according to claim 1, wherein Establishing an equivalent circuit of the grid-connected system of the offshore wind power through the submarine cable line and estimating the harmonic resonance frequency of the grid-connected system that causes harmonic current amplification according to the corrected capacitance value of the submarine cable includes: Equivalenting the submarine cable line to a T-shaped circuit and constructing an equivalent circuit of the grid-connected system of the offshore wind power through the submarine cable line; Based on the equivalent circuit, when a series resonance occurs in the loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance to the ground of the submarine cable, the loop harmonic current will be severely amplified, and the series resonance frequency is estimated based on the series resonance frequency formula; Substituting the corrected capacitance value of the submarine cable into the series resonance frequency formula, and using the Newton iteration method to solve the objective function of the harmonic resonance frequency to obtain the harmonic resonance frequency of the grid-connected system that causes the loop harmonic current amplification.

5. The method for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging according to claim 4, characterized in that, The series resonance frequency formula is: Where j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; C0 is the capacitance value of the actual submarine cable capacitance per unit length; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the cable length; Z s is the equivalent harmonic impedance of the power grid; coth() is the hyperbolic cotangent function.

6. The method for quantifying harmonic transfer of offshore wind power considering submarine cable insulation aging according to claim 4, wherein The equivalent harmonic impedance of the power grid is estimated based on the minimum short-circuit capacity of the busbar at the grid connection point of the offshore wind farm. The expression of the equivalent harmonic impedance Z s is as follows: Where U N is the rated voltage of the grid connection point busbar; S c is the minimum short-circuit capacity of the busbar; j is the imaginary unit; h is the harmonic resonance frequency.

7. The method for quantifying harmonic transmission of offshore wind power considering submarine cable insulation aging according to claim 4, wherein The objective function for solving the harmonic resonance frequency is: where h is the harmonic resonance frequency, is the estimated value of the harmonic resonance frequency; j is the imaginary unit; L0 is the inductance parameter of the submarine cable per unit length; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable at the time of factory shipment per unit length; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid.

8. A harmonic transfer quantification system for offshore wind power considering the insulation aging of submarine cables, characterized in that The system includes: An insulation aging level division unit for dividing the severity levels of the insulation aging of the submarine cable and determining the insulation capacitance gain coefficient corresponding to each level of the submarine cable; An actual capacitance gain coefficient determination unit for determining the actual capacitance gain coefficient of the insulation state of the submarine cable based on the insulation capacitance gain coefficient and the cable aging detection results regularly obtained by the power grid company; A cable capacitance value correction unit for correcting the capacitance value of the submarine cable based on the actual capacitance gain coefficient to obtain the corrected capacitance value of the submarine cable; A first estimation unit is configured to establish an equivalent circuit of an offshore wind power grid-connected system via a submarine cable line, and estimate the grid-connected system harmonic resonance frequency that causes harmonic current amplification according to the corrected submarine cable capacitance value; A second estimation unit is configured to estimate the harmonic current amplification factor at the grid connection point under the grid-connected system harmonic resonance frequency according to the grid-connected system harmonic resonance frequency; The expression of the harmonic current amplification factor HI is as follows: Z h = R0 + j2πhL0; Wherein, is the harmonic current at the wind power end of the submarine cable; is the harmonic current at the grid connection end; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, where f is the harmonic frequency; μ is the actual capacitance gain coefficient; C 0_ref is the capacitance value of the submarine cable at the time of factory per unit length; Z h is the impedance per unit length of the submarine cable; sinh() is the hyperbolic sine function; l is the length of the submarine cable; Z s is the equivalent harmonic impedance of the power grid; cosh() is the hyperbolic cosine function; R0 is the cable resistance parameter per unit length.

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