Harmonic compensation and power flow energy storage scheduling method based on wind power plant grid connection

Abstract

The invention discloses a harmonic compensation and power flow energy storage scheduling method based on wind power plant grid connection. The method comprises the following steps that S1, an ETAP builds a wind power grid connection simulation model according to a grid structure of a wind power plant grid connection power grid; s2, inputting power generation data of a wind power plant into the wind power integration simulation model, and generating a power flow curve by the wind power integration simulation model according to the power generation data; s3, performing reactive compensation and energy storage scheduling on the wind power plant according to the power flow curve, and collecting a generated scheduling harmonic wave a; s4, superposing the dispatching harmonic wave a with an inherent rectification harmonic wave b of a rectifier in the wind power plant to obtain a total harmonic wave c, and performing harmonic wave content analysis on the total harmonic wave c by FFT to generate a harmonic wave content diagram of the rectifier; and S5, performing harmonic compensation on the wind power plant according to the harmonic content diagram of the rectifier. Reactive compensation can stabilize the power grid voltage and improve the stability of the power grid voltage. The combined filtering device can reduce the impact of harmonic waves on the power grid, thereby improving the safety, stability and reliability of the power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a harmonic compensation and tidal energy storage scheduling method based on wind farm grid connection. Background Art

[0002] Wind energy is known as one of the most valuable green and environmentally friendly new energy sources in the 21st century. my country is a region with abundant wind energy reserves, but the utilization of wind energy resources has been slow. With the continuous improvement of economic level, human awareness of environmental protection has gradually increased, and people pay more attention to the quality of life. The development of green and environmentally friendly new energy has become the development direction of the energy industry. As one of the green and environmentally friendly new energy sources, the development and construction of wind farms is very necessary. At the same time, the development of wind power, especially the localization of wind power equipment, can drive and promote the rapid development of machinery, electrical appliances, manufacturing, service industry and related industries.

[0003] However, wind energy is an intermittent energy source. The active power and reactive power of wind farms will change with the wind speed, and the output power of wind farms fluctuates widely. At the same time, the generators in wind turbines are of various types, which can be asynchronous generators, synchronous generators, or doubly fed induction generators. Therefore, the reactive power characteristics are complex, and the power grid will produce voltage deviations. When the voltage deviation is too large, it will bring a series of hazards to the operation of electrical equipment and power systems, such as increased excitation current of transformers and mutual inductors, increased core temperature rise, accelerated insulation aging, and reduced power supply capacity of the power grid.

[0004] At the same time, since wind farms realize power conversion functions through frequent disconnection of power electronic devices, their input-output relationship shows obvious nonlinear characteristics, and factors such as nonlinear loads in wind farms will cause harmonics when wind power is connected to the grid. This harmonic has an impact on the safety, stability and reliability of the power grid, which is mainly manifested in the use of grid resonance, grid power supply interruption, expansion of accident scope, grid decoupling, etc.; in addition, the harm to equipment should not be underestimated, which is mainly manifested in heat, vibration noise, insulation, zero-crossing problems, etc., thereby endangering the safe and stable operation of motors, transformers, switches, protection, and automatic devices. Summary of the invention

[0005] The purpose of the present invention is to provide a harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection, which can balance the wind power flow, prevent large fluctuations in grid voltage, and reduce the impact of harmonics on the grid, thereby improving the safety, stability and reliability of the grid.

[0006] The key to the harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection is to include the following steps:

[0007] S1: ETAP builds a wind power grid-connected simulation model based on the grid structure of the wind farm;

[0008] S2: inputting the power generation data of the wind farm into the wind power grid-connected simulation model, and the wind power grid-connected simulation model generates a power flow curve according to the power generation data;

[0009] S3: Perform reactive power compensation and energy storage dispatching on the wind farm according to the power flow curve, and collect dispatching harmonics a generated thereby;

[0010] S4: superimpose the dispatching harmonic a with the rectifier harmonic b inherent in the wind farm rectifier to obtain the total harmonic c, perform harmonic content analysis on the total harmonic c by FFT, and generate a harmonic content map of the rectifier;

[0011] S5: Perform harmonic compensation on the wind farm according to the harmonic content diagram of the rectifier.

[0012] The above method can balance the wind power flow, prevent large fluctuations in grid voltage, and reduce the impact of harmonics on the grid, thereby improving the safety, stability and reliability of the grid.

[0013] Furthermore, the wind power grid-connected simulation model includes at least one wind farm, each of which is provided with a wind farm bus, each of which is provided with a static VAR compensator, and each wind farm bus is connected to a substation through a wind farm transformer, and cables of all wind farms are connected to the same substation;

[0014] At least one wind turbine is arranged in each wind farm, and each wind turbine collects electric energy to the wind farm bus through a wind turbine transformer.

[0015] Construct an equivalent power grid of all wind farms and substations.

[0016] Furthermore, each group of the power flow curves includes an active curve and a reactive curve, wherein the active curve correspondingly displays the active power change of any one of the cables, and the reactive curve correspondingly displays the reactive power change of the same cable;

[0017] When the reactive power of any one of the cables increases significantly, all the static VAR compensators connected to the same cable perform reactive power compensation on the corresponding wind farm, and the reactive power compensation capacity is less than the installed capacity of the corresponding wind farm transformer.

[0018] Reactive power compensation can stabilize the grid voltage, improve the stability of the grid voltage, prevent the grid power supply capacity from decreasing, and reduce the failure rate of electrical equipment and power systems.

[0019] Furthermore, the calculation formula of the compensation capacity ΔQ is:

[0020]

[0021] Among them, S d is the output capacity of any cable, PF1 is the system power factor before compensation, and PF2 is the system power factor after compensation.

[0022] Furthermore, the energy storage scheduling is to store electric energy higher than the average active power of the same cable through the energy storage device when the active power of any of the cables is higher than the average active power of the same cable, and to release the stored electric energy when the active power of the same cable is lower than the average active power of the same cable, so that the output active power value of the same cable is within the fluctuation range of the average active power of the same cable;

[0023] The energy storage device stores energy in the form of battery energy storage or hydrogen production energy storage.

[0024] The energy storage device manages the active power of all cables. When the average active power is set to 100%, the electric energy is stored in the energy storage device in the seasons or months with abundant wind power, and the electric energy stored in the energy storage power station is released in the seasons or months with relatively weak wind power.

[0025] When the average active power is set to daily or weekly, the electric energy is stored and released based on the average value of the previous day or week;

[0026] The energy storage device evenly allocates the active power of all cables, making the active power curves of all cables stable, reducing the voltage fluctuation amplitude of the power grid, and improving the safety, stability and reliability of the power grid.

[0027] Furthermore, the energy storage capacity of the energy storage device is greater than or equal to the total capacity of the energy storage scheduling;

[0028] The total capacity S of the energy storage dispatch c The calculation formula is:

[0029]

[0030] Where n is the total number of cables. is the maximum power scheduling of the jth cable, t is the charging time, and ρ is the attenuation coefficient.

[0031] Furthermore, the maximum power scheduling P of any of the cables r The calculation formula is:

[0032]

[0033] Among them, max is the maximum value, P max is the maximum active power of the cable, P minis the minimum active power of the cable, P a is the average active power of the cable, and σ is the allowable fluctuation percentage of the average active power.

[0034] Furthermore, the harmonic compensation is to filter the voltage of any one of the wind farm buses by means of a combined filtering device;

[0035] The combined filtering device is provided with four single-tuned filters and one high-pass filter, the four single-tuned filters respectively filter out the 5th, 7th, 11th and 13th harmonics in the harmonic content diagram of the rectifier, and the high-pass filter filters out the 13th and above harmonics in the harmonic content diagram of the rectifier;

[0036] The combined filter device is installed at the outgoing line of all wind farm busbars.

[0037] The 5th, 7th, 11th, 13th harmonics and harmonics above the 13th order have a greater impact on the power grid, and will affect the safety, stability and reliability of the power grid. By filtering out the 5th, 7th, 11th, 13th harmonics and harmonics above the 13th order through a combined filtering device, the impact of harmonics on the power grid can be reduced, thereby improving the safety, stability and reliability of the power grid.

[0038] Furthermore, the capacitance C of the single tuned filter D The calculation formula is:

[0039]

[0040] Among them, Q CN is the capacitance C D The installed capacity, h is the harmonic order, ω1 is the power frequency, U CN is the capacitance C D Rated voltage;

[0041] Among them, the capacitor C D Installation capacity Q CN The calculation formula is:

[0042]

[0043] Among them, U CN is the capacitance C D Rated voltage, X C1 is the fundamental capacitance value, h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, I h is the hth harmonic current;

[0044] Among them, the capacitor C D Rated voltage U CN The calculation formula is:

[0045]

[0046] Where h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, HRU h is the content of the hth harmonic voltage, U1 is the fundamental rated voltage, and Q is the quality factor;

[0047] Among them, the content of h harmonic voltage is HRU h The calculation formula is:

[0048]

[0049] Among them, I h is the hth harmonic current, X C1 is the fundamental wave capacitive reactance value, h is the harmonic order, U1 is the fundamental wave rated voltage, and Q is the quality factor;

[0050] The inductance L of the single tuned filter D The calculation formula is:

[0051]

[0052] Among them, h is the harmonic order, ω1 is the power frequency, C D is the capacitance of the single tuned filter;

[0053] The single tuned filter resistance R D The calculation formula is:

[0054]

[0055] Among them, h is the harmonic order, ω1 is the power frequency, L D is the inductance of the single tuned filter and Q is the quality factor.

[0056] Furthermore, the capacitor C of the high-pass filter G The calculation formula is:

[0057]

[0058] Among them, U1 is the fundamental rated voltage, h is the total harmonic number, ω1 is the power frequency, k is the initial harmonic number, I i is the i-th harmonic current;

[0059] The high pass filter resistor R G The calculation formula is:

[0060]

[0061] Among them, h is the total harmonic number, ω1 is the power frequency, C G is the capacitance of the high-pass filter;

[0062] The inductance L of the high-pass filter G The calculation formula is:

[0063] L G =mR G C G

[0064] Among them, m is the loss coefficient of the filter to the fundamental wave. The smaller its value is, the smaller the loss of the filter to the fundamental wave is. G is the resistance of the high-pass filter, C G is the capacitor of the high-pass filter.

[0065] Beneficial effects: 1. Reactive power compensation can stabilize the grid voltage, improve the stability of the grid voltage, prevent the grid power supply capacity from decreasing, and reduce the failure rate of electrical equipment and power systems.

[0066] 2. The energy storage device manages the active power of all cables. In seasons or months with abundant wind, electric energy can be stored in the energy storage device, and in seasons or months with relatively weak wind, the electric energy stored in the energy storage power station can be released, so as to evenly allocate the active power of all cables and make the active power curve of all cables tend to be stable, reduce the voltage fluctuation amplitude of the power grid, and improve the safety, stability and reliability of the power grid.

[0067] 3. The combined filtering device can filter out the 5th, 7th, 11th, 13th harmonics and harmonics above 13th, reducing the impact of harmonics on the power grid, thereby improving the safety, stability and reliability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a flow chart of the harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection;

[0069] Figure 2 It is a schematic diagram of the grid structure simulation model;

[0070] Figure 3 is a schematic diagram of the active power curve of the first cable Bus2 for one year;

[0071] Figure 4 is a schematic diagram of the reactive power curve of the first cable Bus2 for one year;

[0072] Figure 5 is a schematic diagram of the active power curve of the second cable Bus3 for one year;

[0073] Figure 6 is a schematic diagram of the reactive power curve of the second cable Bus3 for one year;

[0074] Figure 7 is a schematic diagram of the active power curve of the third cable Bus4 for one year;

[0075] Figure 8 is a schematic diagram of reactive power curve of the third cable Bus4 for one year;

[0076] Fig. 9 is a parameter diagram of the first static VAR compensator;

[0077] Fig.10 is a parameter diagram of the second static VAR compensator;

[0078] Fig.11 is a parameter diagram of the third static VAR compensator;

[0079] Fig.12 Schematic diagram of parameters of the fourth and fifth static VAR compensators;

[0080] Fig.13 This is a schematic diagram of the voltage fluctuation curve of the substation;

[0081] Fig.14 is the harmonic content diagram of the rectifier;

[0082] Fig.15 This is a schematic diagram of data before fifth harmonic compensation of the second cable Bus3;

[0083] Fig.16 This is a schematic diagram of the data after the 5th harmonic compensation of the second cable Bus3. DETAILED DESCRIPTION

[0084] The specific implementation manner and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0085] like Figure 1 As shown, the harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection includes the following steps:

[0086] S1: ETAP, a comprehensive analysis software system for power electrical analysis and power management, builds a grid structure simulation model based on the grid structure of the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm connected to the power grid;

[0087] like Figure 2As shown, the first wind farm in the grid structure simulation model is provided with a first wind farm bus Bus5 with a voltage level of 35kV, a first static VAR compensator SVC1 is provided on the first wind farm bus Bus5, and the first wind farm bus Bus5 is connected to a first cable Bus2 with a voltage level of 110kV through a first wind farm transformer T1, the first cable Bus2 is connected to a substation bus Bus1 of a substation, and the voltage level of the substation bus Bus1 is 110kV;

[0088] The first wind farm is provided with a plurality of first wind turbines, each of which collects electric energy to the first wind farm bus Bus5 through the first wind turbine transformer;

[0089] The second wind farm is provided with a second wind farm bus Bus6 with a voltage level of 35 kV, a second static VAR compensator SVC2 is provided on the second wind farm bus Bus6, and the second wind farm bus Bus6 is connected to a second cable Bus3 with a voltage level of 110 kV through a second wind farm transformer T2, and a plurality of second wind turbines are provided in the second wind farm, and each second wind turbine collects electric energy to the second wind farm bus Bus6 through the second wind turbine transformer;

[0090] The third wind farm is provided with a third wind farm bus Bus7 with a voltage level of 35 kV, a third static VAR compensator SVC3 is provided on the third wind farm bus Bus7, and the third wind farm bus Bus7 is connected to the second cable Bus3 through a third wind farm transformer T3, and a plurality of third wind turbines are provided in the third wind farm, and each third wind turbine collects electric energy to the third wind farm bus Bus7 through a third wind turbine transformer;

[0091] The second cable Bus3 is connected to the substation bus Bus1;

[0092] The fourth wind farm is provided with a fourth wind farm bus Bus8 with a voltage level of 35 kV, a fourth static VAR compensator SVC4 is provided on the fourth wind farm bus Bus8, and the fourth wind farm bus Bus8 is connected to a third cable Bus4 with a voltage level of 110 kV through a fourth wind farm transformer T4, and a plurality of fourth wind turbines are provided in the fourth wind farm, and each fourth wind turbine collects electric energy to the fourth wind farm bus Bus8 through a fourth wind turbine transformer;

[0093] The fifth wind farm is provided with a fifth wind farm bus Bus9 with a voltage level of 35kV, a fifth static VAR compensator SVC5 is provided on the fifth wind farm bus Bus9, and the fifth wind farm bus Bus5 is connected to a third cable Bus4 with a voltage level of 110kV through a fourth wind farm transformer T4, and a plurality of fifth wind turbines are provided in the fifth wind farm, and each fifth wind turbine collects electric energy to the fifth wind farm bus Bus9 through a fifth wind turbine transformer;

[0094] The third cable Bus4 is connected to the substation bus Bus1.

[0095] S2: inputting the wind power generation data of the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm into the grid structure simulation model, and the wind power grid connection simulation model generates the power flow curve of the first cable Bus2, the power flow curve of the second cable Bus3 and the power flow curve of the third cable Bus4 respectively according to the wind power generation data of the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm;

[0096] S3: According to the power flow curve of the first cable Bus2, the power flow curve of the second cable Bus3 and the power flow curve of the third cable Bus4, reactive power compensation and energy storage scheduling are performed on the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm respectively, and the first rectifier in the first wind farm, the second rectifier in the second wind farm, the third rectifier in the third wind farm, the fourth rectifier in the fourth wind farm and the fifth rectifier in the fifth wind farm are collected respectively, thereby generating the first scheduling harmonic a1, the second scheduling harmonic a2, the third scheduling harmonic a3, the fourth scheduling harmonic a4 and the fifth scheduling harmonic a5;

[0097] like Figure 2 , Figure 4 As shown, the power flow curve of the first cable Bus2 includes the active curve and reactive curve of the first cable Bus2 in the past year. According to the reactive curve of the first cable Bus2, it can be seen that the reactive power of the first cable Bus2 increases significantly from August to November, and the first static VAR compensator SVC1 performs reactive compensation for the first wind farm.

[0098] like Figure 5 , Figure 6As shown, the power flow curve of the second cable Bus3 includes the active power curve and reactive power curve of the second cable Bus3 in the past year. According to the reactive power curve of the second cable Bus3, it can be seen that in July and August, the reactive power of the first cable Bus2 increased significantly, and the second static VAR compensator SVC2 and the third static VAR compensator SVC3 performed reactive power compensation for the second wind farm and the third wind farm respectively;

[0099] like Figure 7 , Figure 8 As shown, the power flow curve of the third cable Bus4 includes the active power curve and reactive power curve of the third cable Bus4 in the past year. According to the reactive power curve of the third cable Bus4, it can be seen that in July and August, the reactive power of the third cable Bus4 increases significantly, and the fourth static VAR compensator SVC4 and the fifth static VAR compensator SVC5 perform reactive power compensation for the fourth wind farm and the fifth wind farm respectively;

[0100] The calculation formula of the compensation capacity ΔQ is:

[0101]

[0102] Among them, S d is the output capacity of any cable, PF1 is the system power factor before compensation, and PF2 is the system power factor after compensation.

[0103] like Fig. 9 As shown, the parameters of the first static VAR compensator SVC1 are set as follows: the voltage rating is 35 kV, the maximum voltage is 35 kV*100%, the minimum voltage is 35 kV*0%, and the reference voltage is 35 kV*100%;

[0104] The inductive rated capacity is 3Mvar, the inductive rated current is 49.487A, and the inductive rated conductance is 0.002 Siemens;

[0105] The capacitive rated capacity is 3Mvar, the capacitive rated current is 49.487A, and the capacitive rated conductance is 9999.999 Siemens;

[0106] The maximum inductive rated capacity is 3Mva, the maximum inductive rated current is 49.487A, and the maximum inductive slope is 0;

[0107] The maximum capacitive rated capacity is 3Mvar, the maximum capacitive rated current is 49.487A, and the maximum capacitive slope is 12%.

[0108] like Fig.10As shown, the parameters of the second static VAR compensator SVC2 are set as follows: the rated voltage is 35 kV, the maximum voltage is 35 kV*100%, the minimum voltage is 35 kV*0%, and the reference voltage is 35 kV*100%;

[0109] The inductive rated capacity is 40Mvar, the inductive rated current is 659.829A, and the inductive rated conductance is 0.033 Siemens;

[0110] The capacitive rated capacity is 40Mvar, the capacitive rated current is 659.829A, and the capacitive rated conductance is 9999.999 Siemens;

[0111] The maximum inductive rated capacity is 40Mva, the maximum inductive rated current is 659.829A, and the maximum inductive slope is 0;

[0112] The maximum capacitive rated capacity is 40Mvar, the maximum capacitive rated current is 733.143A, and the maximum capacitive slope is 90%.

[0113] like Fig.11 As shown, the parameters of the third static VAR compensator SVC3 are set as follows: the rated voltage is 35 kV, the maximum voltage is 35 kV*100%, the minimum voltage is 35 kV*0%, and the reference voltage is 35 kV*100%;

[0114] The inductive rated capacity is 30Mvar, the inductive rated current is 494.872A, and the inductive rated conductance is 0.024 Siemens;

[0115] The capacitive rated capacity is 30Mvar, the capacitive rated current is 494.872A, and the capacitive rated conductance is 9999.999 Siemens;

[0116] The maximum inductive rated capacity is 30Mva, the maximum inductive rated current is 494.872A, and the maximum inductive slope is 0;

[0117] The maximum capacitive rated capacity is 30Mvar, the maximum capacitive rated current is 549.857A, and the maximum capacitive slope is 90%.

[0118] like Fig.12 As shown, the parameters of the fourth static VAR compensator SVC4 and the fifth static VAR compensator SVC5 are consistent, and the parameters are set as follows: the voltage rating is 35 kV, the maximum voltage is 35 kV*100%, the minimum voltage is 35 kV*0%, and the reference voltage is 35 kV*100%;

[0119] The inductive rated capacity is 41Mvar, the inductive rated current is 676.325A, and the inductive rated conductance is 0.033 Siemens;

[0120] The capacitive rated capacity is 41Mvar, the capacitive rated current is 676.325A, and the capacitive rated conductance is 9999.999 Siemens;

[0121] The maximum inductive rated capacity is 41Mva, the maximum inductive rated current is 676.325A, and the maximum inductive slope is 0;

[0122] The maximum capacitive rated capacity is 41Mvar, the maximum capacitive rated current is 3299.145A, and the maximum capacitive slope is 20.5%.

[0123] like Fig.13 As shown, after the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm are added with reactive power compensation, the voltage fluctuation amplitude of the substation bus Bus1 is greatly reduced.

[0124] like Figure 3-Figure 8 As shown, the active power curves of the first cable Bus2, the second cable Bus3 and the third cable Bus4 fluctuate greatly, so an energy storage station is provided, which stores the electric energy whose active power of the first cable Bus2 is higher than the average active power of the first cable Bus2, the electric energy whose active power of the second cable Bus3 is higher than the average active power of the second cable Bus3 and the electric energy whose active power of the third cable Bus4 is higher than the average active power of the third cable Bus4, and releases the stored electric energy when the active power of the first cable Bus2 is lower than the average active power of the first cable Bus2, the active power of the second cable Bus3 is lower than the average active power of the second cable Bus3 and the active power of the third cable Bus4 is lower than the average active power of the third cable Bus4, so that the output active power values ​​of the first cable Bus2, the second cable Bus3 and the third cable Bus4 are respectively within the fluctuation range of the average active power of the first cable Bus2, the second cable Bus3 and the third cable Bus4;

[0125] The energy storage capacity of the energy storage station should be greater than or equal to the total capacity of the energy storage dispatch. The total capacity of the energy storage dispatch is S c The calculation formula is:

[0126]

[0127] Where n is the total number of cables. is the maximum power scheduling of the jth cable, t is the charging time, and ρ is the attenuation coefficient.

[0128] The maximum power scheduling P of any cable rThe calculation formula is:

[0129]

[0130] Among them, max is the maximum value, P max is the maximum active power of the cable, P min is the minimum active power of the cable, P a is the average active power of the cable, and σ is the allowable fluctuation percentage of the average active power.

[0131] S4: the first scheduling harmonic a1, the second scheduling harmonic a2, the third scheduling harmonic a3, the fourth scheduling harmonic a4, and the fifth scheduling harmonic a5 are respectively superimposed with the first rectifier harmonic b1 inherent in the first rectifier, the second rectifier harmonic b2 inherent in the second rectifier, the third rectifier harmonic b3 inherent in the third rectifier, the fourth rectifier harmonic b4 inherent in the fourth rectifier, and the fifth rectifier harmonic b5 inherent in the fifth rectifier to obtain the first total harmonic c1, the second total harmonic c2, the third total harmonic c3, the fourth total harmonic c4, and the fifth total harmonic c5, and FFT performs harmonic content analysis on the first total harmonic c1, the second total harmonic c2, the third total harmonic c3, the fourth total harmonic c4, and the fifth total harmonic c5 to generate harmonic content graphs of the first rectifier, the second rectifier, the third rectifier, the fourth rectifier, and the fifth rectifier;

[0132] S5: performing harmonic compensation on the first wind farm, the second wind farm, the third wind farm, the fourth wind farm and the fifth wind farm respectively according to the harmonic content diagrams of the rectifiers of the first rectifier, the second rectifier, the third rectifier, the fourth rectifier and the fifth rectifier;

[0133] The harmonic compensation is to filter the voltages of the first wind farm bus Bus5, the second wind farm bus Bus6, the third wind farm bus Bus7, the fourth wind farm bus Bus8 and the fifth wind farm bus Bus9 respectively through five groups of combined filtering devices;

[0134] Fig.14 The typical characteristics of the harmonic components of the power grid are shown, with the fundamental amplitude of 565.7 and the total harmonic distortion rate THD as high as 29.89%. This shows that the system has a high harmonic content, especially low-order odd harmonics, such as the 5th and 7th, which occupy a major proportion in the harmonic spectrum and have a greater impact on power quality.

[0135] As the harmonic order increases, the harmonic amplitude decreases rapidly, which is in line with the general law of harmonic generation in power electronic equipment. However, high-order harmonics may still cause electromagnetic interference or local resonance problems in equipment.

[0136] Therefore, each of the combined filtering devices is provided with four single-tuned filters and one high-pass filter, the four single-tuned filters filter out the 5th, 7th, 11th, and 13th harmonics respectively, and the high-pass filter filters out harmonics above the 13th order;

[0137] The capacitance C of the single tuned filter D The capacitance L of the single tuned filter D The resonant frequency is When the single tuned filter has low resistance to the harmonics with the same cut-off frequency, it can filter out the frequency and the resonant frequency f h Same harmonic currents;

[0138] Single tuned filter at ω h =hω1, when Z h =R h When the harmonic current is h, it is an ideal harmonic condition. At this time, the hth harmonic current mainly passes through the low resistance R h Divide the current and let the harmonic current flow into the filter branch with the same resonant frequency and hth harmonic frequency. For harmonic currents of other frequencies, due to Z h >>R h , the single tuned filter shunts very little harmonic current of other frequencies, so the single tuned filter can filter out the hth harmonic; where ω h is the resonant frequency, h is the harmonic number, ω1 is the power frequency, Z h is the total impedance at the hth resonant frequency, R h is the resistance of the single tuned filter in the resonant state.

[0139] The resonant frequency of a single tuned filter is ω h When the capacitor C D Installation capacity Q CN The calculation formula is:

[0140]

[0141] Among them, U CN is the capacitance C D Rated voltage, X C1 is the fundamental wave capacitive reactance value;

[0142] Capacitor C of single tuned filter D In addition to the harmonic current, there is also part of the fundamental current generated by the power frequency voltage, so the capacitor C D Installation capacity Q CN To pass the verification, it must meet the overvoltage requirements, overcurrent requirements and capacity balance requirements.

[0143] Under overvoltage check, the capacitor C D Installation capacity QCN The calculation formula is:

[0144]

[0145] Among them, U CN is the capacitance C D Rated voltage, X C1 is the fundamental wave capacitive reactance value;

[0146] Among them, the capacitor C D Rated voltage U CN The calculation formula is:

[0147]

[0148] Where h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, HRU h is the content of the hth harmonic voltage, U1 is the fundamental rated voltage, and Q is the quality factor;

[0149] Among them, the content of h harmonic voltage is HRU h The calculation formula is:

[0150]

[0151] Among them, I h is the hth harmonic current, X C1 is the fundamental wave capacitive reactance value, h is the harmonic order, U1 is the fundamental wave rated voltage, Q is the quality factor, Q=[30,60];

[0152] Among them, the fundamental capacitance value X C1 The calculation formula is:

[0153] X C1 =R h hQ (4)

[0154] Among them, R h is the resistance of the single tuned filter in the resonant state, h is the harmonic order, Q is the quality factor, Q = [30, 60];

[0155] Under over-current check, the capacitor C D Installation capacity Q CN The calculation formula is:

[0156]

[0157] Among them, U CN is the capacitance C D The rated voltage, h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, Ih is the hth harmonic current;

[0158] Under capacity balance check, the capacitor C D Installation capacity Q CN The calculation formula is:

[0159]

[0160] Among them, U CN is the capacitance C D The rated voltage, h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, I h is the hth harmonic current;

[0161] The capacitance C is calculated by the above three verification methods respectively. D Installation capacity Q CN , and select the largest value among the three methods as the capacitance C D Installation capacity Q CN Then calculate the capacitance C D of:

[0162] The capacitance C of the single tuned filter D The calculation formula is:

[0163]

[0164] Among them, Q CN is the capacitance C D The installed capacity, h is the harmonic order, ω1 is the power frequency, U CN is the capacitance C D Rated voltage;

[0165] Then according to the capacitor C D Calculate the inductance L of the single tuned filter D and resistor R D ;

[0166] The inductance L of the single tuned filter D The calculation formula is:

[0167]

[0168] Among them, h is the harmonic order, ω1 is the power frequency, C D is the capacitance of the single tuned filter;

[0169] The single tuned filter resistance R D The calculation formula is:

[0170]

[0171] Among them, h is the harmonic order, ω1 is the power frequency, L D is the inductance of the single tuned filter and Q is the quality factor.

[0172] Example 1: Taking the design of a single tuned filter for filtering out the fifth harmonic of a wind farm bus as an example, the actual operating voltage upper limit value U M 35kV;

[0173] According to the above formula (2), the single tuned filter capacitance C that filters out the fifth harmonic of the wind farm bus can be calculated: D Rated voltage U CN for:

[0174]

[0175] According to the above formula (1), formula (5), and formula (6), we can respectively obtain:

[0176] Under overvoltage check, the capacitance C of the single tuned filter that filters out the 5th harmonic of the wind farm bus D Installation capacity Q CN for:

[0177]

[0178] Capacitor C of the single tuned filter that filters out the fifth harmonic of the wind farm bus under overcurrent check D Installation capacity Q CN for:

[0179]

[0180] Under the capacity balance check, the capacitance C of the single tuned filter that filters out the 5th harmonic of the wind farm bus D Installation capacity Q CN for:

[0181]

[0182] Under overvoltage check, current check and capacity balance check, the maximum value of the calculated result is selected as the capacitance C of the single tuned filter that filters out the 5th harmonic of the wind farm bus. D Installation capacity Q CN , and then substitute into formula (7) to obtain the capacitance C of the single tuned filter that filters out the fifth harmonic of the wind farm bus D ;

[0183]

[0184] Then according to the capacitance C of the single tuned filter that filters out the fifth harmonic of the wind farm busD The inductance L of the single tuned filter that filters out the fifth harmonic of the wind farm bus can be obtained by using formula (8) and formula (9) respectively. D and the resistance R of the single tuned filter that filters out the fifth harmonic of the wind farm bus D ;

[0185]

[0186] Using a 6-pulse rectifier as the load, by simulating the current waveform of the power data, the current waveform and total harmonic distortion rate THD content of the 5th harmonic of the wind farm bus with a voltage level of 35kV are as follows Fig.15 As shown, from Fig.15 It can be seen that due to the high content of the 5th harmonic in the rectifier load, the total harmonic distortion rate THD is also high, up to 5.82%.

[0187] The above calculation results are used as the parameters of the single tuned filter of the 5th harmonic of the wind farm bus with a voltage level of 35kV. After filtering the 5th harmonic, the current waveform of the power data is simulated. The current waveform and total harmonic distortion rate THD content of the 5th harmonic of the wind farm bus with a voltage level of 35kV are as follows: Fig.16 As shown in the figure, the content of the 5th harmonic is greatly reduced, and its total harmonic distortion rate THD is also reduced to 2.56%, meeting the index requirements of the power grid. The total harmonic distortion rate THD of the 7th harmonic, which has the largest content among the remaining harmonics, is also reduced to less than 2%.

[0188] In summary, the single tuned filter can effectively reduce the fifth harmonic content in the power grid, effectively suppress the harmonics in the 35kV bus current of the wind farm, and help improve the power quality of the power grid.

[0189] A high-pass filter, in simple terms, is a filter that passes high and resists low, and is also called an amplitude reduction filter. The basis for judging the high or low of a signal is the cutoff frequency. A high-pass filter has low resistance to signals above the cutoff frequency, providing a path for these signals. In a relatively large filtering project, it is difficult to design a set of single-tuned filters for each harmonic from an economic point of view. Therefore, a high-pass filter is usually used in combination with a single-tuned filter, so that a single-tuned filter can be used to filter out harmonics of a specific order, and a high-pass filter can be used to filter out higher harmonics that cannot be filtered out by a single-tuned filter. This not only achieves the filtering effect, but is also relatively cheap in terms of cost.

[0190] The cutoff frequency of the high-pass filter should not be too high, otherwise the filtering effect cannot be achieved, nor should it be too low, otherwise the loss of the high-pass filter will increase.

[0191] The high-pass filter capacitor C G The calculation formula is:

[0192]

[0193] Among them, U1 is the fundamental rated voltage, h is the total harmonic number, ω1 is the power frequency, k is the initial harmonic number, I i is the i-th harmonic current;

[0194] The high pass filter resistor R G The calculation formula is:

[0195]

[0196] Among them, h is the total harmonic number, ω1 is the power frequency, C G is the capacitance of the high-pass filter;

[0197] The inductance L of the high-pass filter G The calculation formula is:

[0198] L G =mR G C G (12)

[0199] Among them, m is the loss coefficient of the filter to the fundamental wave. The smaller its value is, the smaller the loss of the filter to the fundamental wave is. G is the resistance of the high-pass filter, C G is the capacitor of the high pass filter.

[0200] In addition to installing the combined filter device at the wind farm bus outlet, a 12-pulse rectifier can be used instead of a 6-pulse rectifier and devices such as IGBTs with better harmonic suppression performance can be selected to reduce the generation of harmonics.

Claims

1. A harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection, characterized in that: The following steps are involved: S1: ETAP builds a wind power grid-connected simulation model based on the grid structure of the wind farm; S2: inputting the power generation data of the wind farm into the wind power grid-connected simulation model, and the wind power grid-connected simulation model generates a power flow curve according to the power generation data; S3: Perform reactive power compensation and energy storage dispatching on the wind farm according to the power flow curve, and collect dispatching harmonics a generated thereby; S4: superimpose the dispatching harmonic a with the rectifier harmonic b inherent in the wind farm rectifier to obtain the total harmonic c, perform harmonic content analysis on the total harmonic c by FFT, and generate a harmonic content map of the rectifier; S5: Perform harmonic compensation on the wind farm according to the harmonic content diagram of the rectifier.

2. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 1 is characterized in that: The wind power grid-connected simulation model includes at least one wind farm, each wind farm is provided with a wind farm bus, each wind farm bus is provided with a static VAR compensator, and each wind farm bus is connected to a substation through a wind farm transformer, and cables of all wind farms are connected to the same substation; At least one wind turbine is arranged in each wind farm, and each wind turbine collects electric energy to the wind farm bus through a wind turbine transformer.

3. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 2 is characterized in that: Each group of power flow curves includes an active curve and a reactive curve, wherein the active curve shows the change of active power of any cable, and the reactive curve shows the change of reactive power of the same cable; When the reactive power of any one of the cables increases significantly, all the static VAR compensators connected to the same cable perform reactive power compensation on the corresponding wind farm, and the reactive power compensation capacity is less than the installed capacity of the corresponding wind farm transformer.

4. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 3 is characterized in that: The calculation formula of the compensation capacity ΔQ is: Among them, S d is the output capacity of any cable, PF1 is the system power factor before compensation, and PF2 is the system power factor after compensation.

5. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 3 is characterized in that: The energy storage scheduling is to store electric energy higher than the average active power of the same cable through the energy storage device when the active power of any of the cables is higher than the average active power of the same cable, and release the stored electric energy when the active power of the same cable is lower than the average active power of the same cable, so that the output active power value of the same cable is within the fluctuation range of the average active power of the same cable; The energy storage device stores energy in the form of battery energy storage or hydrogen production energy storage.

6. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 5 is characterized in that: The energy storage capacity of the energy storage device is greater than or equal to the total capacity of the energy storage scheduling; The total capacity S of the energy storage dispatch c The calculation formula is: Where n is the total number of cables, P rj is the maximum power scheduling of the jth cable, t is the charging time, and ρ is the attenuation coefficient.

7. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 6 is characterized in that: The maximum power scheduling P of any of the cables r The calculation formula is: Among them, max is the maximum value, P max is the maximum active power of the cable, P min is the minimum active power of the cable, P a is the average active power of the cable, and σ is the allowable fluctuation percentage of the average active power.

8. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 2 is characterized in that: The harmonic compensation is to filter the voltage of any one of the wind farm buses by means of a combined filtering device; The combined filtering device is provided with four single-tuned filters and one high-pass filter, the four single-tuned filters respectively filter out the 5th, 7th, 11th and 13th harmonics in the harmonic content diagram of the rectifier, and the high-pass filter filters out the 13th and above harmonics in the harmonic content diagram of the rectifier; The combined filter device is installed at the outgoing line of all wind farm busbars.

9. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 8 is characterized in that: The capacitance C of the single tuned filter D The calculation formula is: Among them, Q CN is the capacitance C D The installed capacity, h is the harmonic order, ω1 is the power frequency, U CN is the capacitance C D Rated voltage; Among them, the capacitor C D Installation capacity Q CN The calculation formula is: Among them, U CN is the capacitance C D Rated voltage, X C1 is the fundamental capacitance value, h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, I h is the hth harmonic current; Among them, the capacitor C D Rated voltage U CN The calculation formula is: Where h is the harmonic order, U M is the upper limit of the actual operating voltage of the wind farm busbar, HRU h is the content of the hth harmonic voltage, U1 is the fundamental rated voltage, and Q is the quality factor; Among them, the content of h harmonic voltage is HRU h The calculation formula is: Among them, I h is the hth harmonic current, X C1 is the fundamental wave capacitive reactance value, h is the harmonic order, U1 is the fundamental wave rated voltage, and Q is the quality factor; The inductance L of the single tuned filter D The calculation formula is: Among them, h is the harmonic order, ω1 is the power frequency, C D is the capacitance of the single tuned filter; The single tuned filter resistance R D The calculation formula is: Among them, h is the harmonic order, ω1 is the power frequency, L D is the inductance of the single tuned filter and Q is the quality factor.

10. The harmonic compensation and power flow energy storage scheduling method based on wind farm grid connection according to claim 8, characterized in that: The high-pass filter capacitor C G The calculation formula is: Among them, U1 is the fundamental rated voltage, h is the total harmonic number, ω1 is the power frequency, k is the initial harmonic number, I i is the i-th harmonic current; The high pass filter resistor R G The calculation formula is: Among them, h is the total harmonic number, ω1 is the power frequency, C G is the capacitance of the high-pass filter; The inductance L of the high-pass filter G The calculation formula is: L G =mR G C G Among them, m is the loss coefficient of the filter to the fundamental wave. The smaller its value is, the smaller the loss of the filter to the fundamental wave is; R G is the resistance of the high-pass filter; C G is the capacitor of the high pass filter.

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