Offshore wind power harmonic transmission quantification method and system considering submarine cable insulation aging

Abstract

The invention discloses an offshore wind power harmonic transmission quantification method and system considering submarine cable insulation aging, and relates to the field of harmonic transmission characteristic analysis. The method comprises the following steps: dividing the insulation aging severity level of the submarine cable, and determining an insulation capacitance gain coefficient corresponding to each level of submarine cable; determining an actual capacitance gain coefficient of the insulation state of the submarine cable based on cable aging detection results regularly acquired by a power grid company; correcting the capacitance value of the submarine cable based on the actual capacitance gain coefficient; and establishing an equivalent circuit of an offshore wind power grid-connected system through the submarine cable line, estimating a grid-connected system harmonic resonant frequency causing harmonic current amplification according to the corrected submarine cable capacitance value, and estimating a harmonic current amplification coefficient of a grid-connected point under the harmonic resonant frequency of the grid-connected system. According to the method, the evaluation accuracy of the resonant frequency and harmonic amplification severity of the offshore wind power grid-connected system is remarkably improved, so that effective suppression of harmonic resonance amplification can be guided.

Description

Technical Field

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

[0002] In the past decade, a large number of offshore wind farms have been put into operation in my country's eastern coastal areas, 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, causing the harmonic current to be seriously amplified during the transmission process of the submarine cable (referred to as submarine cable), deteriorating the power quality of the grid in the grid-connected area, and increasing the risk of safe operation of equipment.

[0003] Therefore, accurately estimating 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 harmonic transfer characteristics quantification methods are based on the factory capacitance parameters of the cable, and do not consider the impact 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. When the insulation is close to damage, it can reach about 1.15 times the factory parameters. The parameter changes caused by insulation aging have an important impact on the resonant amplification of cable harmonics.

[0004] In view of this, this application is hereby filed. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing harmonic transfer characteristic quantification methods are based on the factory capacitance parameters of the cable, and do not consider the influence of insulation aging on the capacitance value, resulting in the low accuracy of the evaluation of the resonant frequency and harmonic amplification severity of the offshore wind power grid-connected system. The purpose of the present invention is to provide an offshore wind power harmonic transfer quantification method and system taking into account the insulation aging of the submarine cable. By considering the influence of the submarine cable insulation aging on the cable capacitance value and performing parameter correction, the accuracy of the evaluation of the resonant frequency and harmonic amplification severity of the offshore wind power grid-connected system will be significantly improved, thereby guiding the effective suppression of harmonic resonance amplification.

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

[0007] In a first aspect, the present invention provides a method for quantifying offshore wind power harmonic transmission taking into account the aging of submarine cable insulation, the method comprising:

[0008] Divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable;

[0009] According to the insulation capacitance gain coefficient, based on the cable aging test results regularly obtained by the power grid company, the actual capacitance gain coefficient of the submarine cable insulation state is determined;

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

[0011] Establish an equivalent circuit of the offshore wind power grid-connected system via submarine cable lines, and estimate the harmonic resonance frequency of the grid-connected system that causes harmonic current amplification based on the corrected submarine cable capacitance value;

[0012] According to the harmonic resonance frequency of the grid-connected system, the harmonic current amplification factor of the grid-connected point under the harmonic resonance frequency of the grid-connected system is estimated.

[0013] Furthermore, the severity level of submarine cable insulation aging is divided into different levels, and the insulation capacitance gain coefficient corresponding to each level of submarine cable is determined, including:

[0014] Based on the severity of insulation aging, submarine cables are divided into five levels: level 1, level 2, level 3, level 4 and level 5. Level 1 is intact, level 2 is slightly aged, level 3 is moderately aged, level 4 is severely aged, and level 5 is insulation damaged.

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

[0016] Furthermore, the corrected submarine cable capacitance value is expressed as: 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 per unit length when it leaves the factory, that is, the capacitance value when the insulation is intact; μ is the actual capacitance gain coefficient.

[0017] Furthermore, an equivalent circuit of the offshore wind power grid-connected system via a submarine cable line is established, and based on the corrected submarine cable capacitance value, the harmonic resonance frequency of the grid-connected system causing harmonic current amplification is estimated, including:

[0018] The submarine cable line is equivalent to a T-type circuit, and an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line is constructed;

[0019] Based on the equivalent circuit, when the loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance of the submarine cable to the ground undergoes series resonance, the loop harmonic current (that is, the harmonic current at the grid connection point) will be severely amplified, and the series resonance frequency is estimated based on the series resonance frequency formula;

[0020] The corrected submarine cable capacitance value is substituted into the series resonant frequency formula, and the Newton iteration method is used 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.

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

[0022]

[0023] Wherein, j is an 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, 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 grid equivalent harmonic impedance is estimated based on the minimum short-circuit capacity of the busbar at the offshore wind farm connection point. s The expression is:

[0025]

[0026] Where U N is the rated voltage of the busbar 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.

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

[0028]

[0029] 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 factory per unit length; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, 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 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 grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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] In a second aspect, the present invention further provides an offshore wind power harmonic transmission quantification system taking into account the aging of submarine cable insulation, the system comprising:

[0035] The insulation aging level division unit is used to divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable;

[0036] An actual capacitance gain coefficient determination unit, used to determine an actual capacitance gain coefficient of the insulation state of the submarine cable according to the insulation capacitance gain coefficient and based on the cable aging detection results regularly obtained by the power grid company;

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

[0038] The first estimation unit is used to establish an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line, and estimate the harmonic resonance frequency of the grid-connected system causing harmonic current amplification based on the corrected submarine cable capacitance value;

[0039] The second estimation unit is used to estimate the harmonic current amplification factor of the grid connection point under the harmonic resonance frequency of the grid connection system according to the harmonic resonance frequency of the grid connection system.

[0040] Furthermore, the expression of 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 grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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 effect of insulation aging on cable capacitance parameters (which can actually cause the capacitance to increase by 1.15 times), and the obtained harmonic resonance amplification results are only applicable to new cables. However, the method of the present invention, by considering the effect of cable insulation aging on cable capacitance and making parameter corrections, will significantly improve the accuracy of the evaluation of the resonant frequency and harmonic amplification severity of the offshore wind power grid-connected system, thereby being 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, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0047] Figure 1 This is a flow chart of the offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation in the present invention;

[0048] Figure 2 It is an equivalent circuit diagram of the offshore wind power grid-connected system via a submarine cable line of the present invention;

[0049] Figure 3 It is a diagram of harmonic amplification factor of the submarine cable of the present invention under different insulation conditions;

[0050] Figure 4 The harmonic current waveform diagram at both ends of the cable when the insulation is intact is obtained based on the electromagnetic transient simulation model analysis of Example 1 of the present invention;

[0051] Figure 5 The harmonic current waveform diagram at both ends of the cable under the condition of insulation damage obtained by analyzing the electromagnetic transient simulation model according to Example 1 of the present invention;

[0052] Figure 6 This is a structural block diagram of the offshore wind power harmonic transmission quantification system taking into account the aging of submarine cable insulation in the present invention. DETAILED DESCRIPTION

[0053] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0054] Example 1

[0055] like Figure 1 As shown, the present invention provides a method for quantifying offshore wind power harmonic transmission taking into account the aging of submarine cable insulation, the method comprising:

[0056] Step 1, classifying the severity level of submarine cable insulation aging, and determining 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, submarine cables are divided into five levels: level 1, level 2, level 3, level 4 and level 5. Level 1 is intact, level 2 is slightly aged, level 3 is moderately aged, level 4 is severely aged, and level 5 is insulation damaged.

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

[0060] Step 2, according to the insulation capacitance gain coefficient, based on the cable aging test 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 submarine cable capacitance value to obtain a corrected submarine cable capacitance value;

[0062] In this embodiment, the expression of the corrected submarine cable capacitance value 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 per unit length when it leaves the factory, that is, the capacitance value when the insulation is intact; μ is the actual capacitance gain coefficient.

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

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

[0065] Step 41, equating the submarine cable line to a T-type circuit, and constructing an equivalent circuit of an offshore wind power grid-connected system via a submarine cable line;

[0066] Step 42, based on the equivalent circuit, when the loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance of the submarine cable to the ground undergoes series resonance, the loop harmonic current (that is, the harmonic current at the grid connection point) will be severely amplified. At this time, the series resonance frequency is estimated based on the series resonance frequency formula; wherein the series resonance frequency formula is:

[0067]

[0068] Wherein, j is an 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, 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 is s It can be estimated based on the minimum short-circuit capacity of the busbar at the offshore wind farm grid connection point, and the equivalent harmonic impedance Z of the power grid s The expression is:

[0070]

[0071] Where U N is the rated voltage of the busbar 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, substituting the corrected submarine cable capacitance value into the series resonant frequency formula, solving the target function of the harmonic resonant frequency, and obtaining the harmonic resonant frequency of the grid-connected system that causes the loop harmonic current to be amplified.

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

[0074]

[0075] 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 factory per unit length; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, 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 is an optimization problem and can be solved by Newton's iteration method. Since the submarine cables of offshore wind farms are long, the equivalent capacitance of the submarine cables is large, and the series resonance frequency is often not high, the initial value of h can be set to 2.

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

[0078] In this embodiment, the harmonic current at the wind power end of the submarine cable is The grid-connected harmonic current is Considering the cable distributed 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 grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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] In order to explain in detail the offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation provided in this embodiment, firstly based on Figure 2 The parameters of the equivalent circuit shown in the figure are set, and the harmonic resonance frequency and harmonic current amplification factor under different submarine cable insulation conditions are calculated using the method proposed in the present invention. An electromagnetic transient simulation analysis model is further built in the Matlab / Simulink platform to verify the effectiveness of the proposed method. Figure 2In the example, the wind farm is connected to the grid based on a 220kV submarine cable, the connection point is bus 2, the bus short-circuit capacity is set to 5000MVA, the cable length is set to 50km, and the electrical parameters when the cable insulation is intact are shown in Table 1. It should be noted that the national standard "Power Quality Public Grid Harmonics" (GB / T 14549-93) gives a 220kV bus reference capacity of 2000MVA, and the actual value can often reach several times the reference value, so it is reasonable to set the short-circuit capacity to 5000MVA, and the length of the 220kV offshore wind farm transmission cable is generally in the range of 10 to 60km, so the setting of the cable length is also reasonable.

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

[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 frequency of the wind power grid-connected system under different cable insulation levels can be obtained as shown in Table 2.

[0087] Table 2 Resonance frequency of grid-connected system under different cable insulation levels

[0088] Cable insulation status intact Slight aging Moderate aging Severe aging Insulation damage Capacitor gain factor 1 1.04 1.08 1.12 1.15 Resonance frequency 5.8 5.7 5.6 5.5 5.4

[0089] It can be seen from Table 2 that insulation aging affects the harmonic resonance frequency, and the more serious the insulation aging, the lower the harmonic resonance frequency. Since the above harmonic resonance frequencies are all non-integer times and are adjacent to the 5th harmonic, the harmonic resonance frequency can be approximately regarded as the 5th. Based on the method proposed in the present invention, the calculated amplification factor of the 5th harmonic at different insulation levels is as follows Figure 3 shown. Figure 3 In the data of 5 different cable insulation conditions, the harmonic current amplification factors are 4.2, 4.7, 5.5, 6.5 and 7.5 respectively. Therefore, it can be seen that the cable insulation aging has a significant effect on the harmonic current amplification. The method of the present invention can effectively reflect the harmonic amplification difference caused by insulation aging, which is also a major advantage of the method proposed in the present invention over the existing methods.

[0090] Furthermore, two submarine cables with two insulation states (intact and damaged) were selected to build an electromagnetic transient simulation analysis model 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 follows: Figure 4 As shown, Figure 4 In the figure, the harmonic current amplitude at the initial end of the cable (wind power end) is 1A, while the harmonic current amplitude at the end (grid-connected end) is 4.2A, indicating that the harmonic current is amplified by 4.2 times after current transmission, which is consistent with Figure 3 The theoretical calculation value in is consistent; when the cable insulation is damaged, the simulation results are as follows Figure 5 As shown, Figure 5In the simulation, the harmonic current amplitude at the initial end of the cable is 1A, while the harmonic current amplitude at the end is 7.5A, indicating that the harmonic current is amplified by 7.5 times after being transmitted through the cable, which is also consistent with the theoretical calculation value. Therefore, the electromagnetic transient simulation results verify the accuracy and effectiveness of the proposed method in assessing the severity of harmonic amplification when considering the aging of offshore wind power cable insulation, thereby guiding the effective suppression of harmonic resonance amplification.

[0091] Example 2

[0092] like Figure 6 As shown, the difference between this embodiment and embodiment 1 is that this embodiment provides an offshore wind power harmonic transmission quantification system taking into account the aging of submarine cable insulation, and the system corresponds to the offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation in embodiment 1 in a one-to-one manner. The system includes:

[0093] The insulation aging level division unit is used to divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable;

[0094] An actual capacitance gain coefficient determination unit, used to determine an actual capacitance gain coefficient of the insulation state of the submarine cable according to the insulation capacitance gain coefficient and based on the cable aging detection results regularly obtained by the power grid company;

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

[0096] The first estimation unit is used to establish an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line, and estimate the harmonic resonance frequency of the grid-connected system causing harmonic current amplification based on the corrected submarine cable capacitance value;

[0097] The second estimation unit is used to estimate the harmonic current amplification factor of the grid connection point under the harmonic resonance frequency of the grid connection system according to the harmonic resonance frequency of the grid connection system.

[0098] As a further implementation, the expression of harmonic current amplification factor 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 grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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 executed according to the process steps of the offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation in Example 1, and will not be repeated one by one in this embodiment.

[0103] Since the present invention takes the influence of insulation aging into consideration, the accuracy of evaluating the resonant frequency and harmonic amplification severity of an offshore wind power grid-connected system can be significantly improved, thereby being able to guide the effective suppression of harmonic resonance amplification.

[0104] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A quantification method for offshore wind power harmonic transmission taking into account the aging of submarine cable insulation, characterized in that: The method includes: Divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable; According to the insulation capacitance gain coefficient, based on the cable aging test results regularly obtained by the power grid company, the actual capacitance gain coefficient of the insulation state of the submarine cable is determined; Based on the actual capacitance gain coefficient, correct the submarine cable capacitance value to obtain a corrected submarine cable capacitance value; Establishing an equivalent circuit of an offshore wind power grid-connected system via a submarine cable line, and estimating a harmonic resonance frequency of the grid-connected system that causes harmonic current amplification based on the corrected submarine cable capacitance value; According to the harmonic resonance frequency of the grid-connected system, a harmonic current amplification factor of the grid-connected point at the harmonic resonance frequency of the grid-connected system is estimated.

2. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 1 is characterized in that: Divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable, including: Based on the severity of insulation aging, the submarine cables are divided into five levels; the levels include the first level, the second level, the third level, the fourth level and the fifth level; among which, the first level is intact, the second level is slightly aged, the third level is moderately aged, the fourth level is severely aged, and the fifth level is insulation damaged; According to each level, the insulation capacitance gain coefficient corresponding to each level of submarine cable is determined; wherein the insulation capacitance gain coefficients corresponding to the first level, the second level, the third level, the fourth level and the fifth level are 1.00, 1.04, 1.08, 1.12 and 1.15 respectively.

3. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 1 is characterized in that: The expression of the corrected submarine cable capacitance value 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 per unit length when it leaves the factory, that is, the capacitance value when the insulation is intact; μ is the actual capacitance gain coefficient.

4. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 1 is characterized in that: Establishing an equivalent circuit of an offshore wind power grid-connected system via a submarine cable line, and estimating the harmonic resonance frequency of the grid-connected system causing harmonic current amplification based on the corrected submarine cable capacitance value, including: The submarine cable line is equivalent to a T-type circuit, and an equivalent circuit of the offshore wind power grid-connected system via the submarine cable line is constructed; Based on the equivalent circuit, when a loop composed of the equivalent harmonic impedance of the power grid and the harmonic impedance of the submarine cable to the ground undergoes series resonance, the loop harmonic current will be severely amplified, and the series resonance frequency is estimated based on the series resonance frequency formula; The corrected submarine cable capacitance value is substituted into the series resonant frequency formula, and the objective function of the harmonic resonant frequency is solved by the Newton iteration method to obtain the harmonic resonant frequency of the grid-connected system that causes the loop harmonic current to be amplified.

5. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 4 is characterized in that: The series resonant frequency formula is: Wherein, j is an 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, 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 offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 4 is characterized in that: The grid equivalent harmonic impedance is estimated based on the minimum short-circuit capacity of the busbar at the offshore wind farm grid connection point. s The expression is: Where U N is the rated voltage of the busbar 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.

7. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 4 is characterized in that: 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 factory per unit length; coth() is the hyperbolic cotangent function; h is the harmonic resonance frequency, and h = f / 50, 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. The offshore wind power harmonic transmission quantification method taking into account the aging of submarine cable insulation according to claim 1 is characterized in that: The expression of the harmonic current amplification factor HI is: From h =R0+j2πhL0; In the formula, is the harmonic current at the wind power end of the submarine cable; is the grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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.

9. Offshore wind power harmonic transmission quantification system taking into account the aging of submarine cable insulation, characterized in that: The system includes: The insulation aging level division unit is used to divide the severity level of submarine cable insulation aging and determine the insulation capacitance gain coefficient corresponding to each level of submarine cable; An actual capacitance gain coefficient determination unit, configured to determine an actual capacitance gain coefficient of the insulation state of the submarine cable according to the insulation capacitance gain coefficient and based on the cable aging detection results regularly obtained by the power grid company; A cable capacitance value correction unit, used to correct the submarine cable capacitance value based on the actual capacitance gain coefficient to obtain a corrected submarine cable capacitance value; The first estimation unit is used to establish an equivalent circuit of an offshore wind power grid-connected system via a submarine cable line, and estimate a harmonic resonance frequency of the grid-connected system that causes harmonic current amplification according to the corrected submarine cable capacitance value; The second estimation unit is used to estimate the harmonic current amplification factor of the grid-connected point at the harmonic resonance frequency of the grid-connected system according to the harmonic resonance frequency of the grid-connected system.

10. The offshore wind power harmonic transmission quantification system taking into account the aging of submarine cable insulation according to claim 9, characterized in that: The expression of the harmonic current amplification factor HI is: From h =R0+j2πhL0; In the formula, is the harmonic current at the wind power end of the submarine cable; is the grid-connected harmonic current; j is the imaginary unit; h is the harmonic resonance frequency, and h = f / 50, 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 when it leaves the factory; 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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