A method for harmonic suppression of an offshore wind turbine generator system

Abstract

The present application relates to a kind of offshore wind generator harmonic suppression method, belong to offshore wind power harmonic suppression technical field, including the following steps: offshore wind generator sequence impedance model is constructed, and the positive sequence impedance of offshore wind generator is output;Offshore wind generator, rectifier station, inverter sequence impedance model is constructed, respectively offshore wind generator positive sequence impedance, offshore wind generator to rectifier station alternating current side positive sequence impedance, rectifier station DC side to inverter DC side positive sequence impedance are output, to obtain system positive sequence impedance and construct open loop and closed loop transfer function, using Nyquist reverse criterion carries out stability diagnosis.If the diagnosis result is unstable, based on system positive sequence impedance optimization PI controller parameter, by PI controller realizes to inverter and rectifier station current, voltage accurate control.Current loop and voltage loop are used for collaborative control, quickly respond to system harmonic variation, reduce harmonic generation and amplification, effectively suppress harmonic.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for suppressing harmonics of an offshore wind turbine, and belongs to the technical field of offshore wind power harmonic suppression. BACKGROUND

[0002] Under the background of global energy transformation and sustainable development, offshore wind power, as a clean and renewable energy utilization form, is developing at an unprecedented speed. However, with the continuous expansion of offshore wind power system scale and the increasing application of power electronic technology in this field, a series of technical challenges have gradually emerged, of which the most prominent is the harmonic oscillation problem. Offshore wind power systems are usually composed of a large number of complex power electronic devices, such as converters, rectifiers, and inverters, etc. These devices, while achieving efficient conversion and transmission of electric energy, inevitably become an important source of harmonics. Harmonic oscillation not only reduces power quality, but also threatens the stable operation of offshore wind turbines and has a negative impact on the safety and reliability of the entire power system.

[0003] The prior art, such as Chinese patent application for invention with publication number "CN119921384A", discloses a stability analysis method and system for offshore wind power grid-connected system, including the following steps: obtaining real-time operation data of wind turbines and static var devices of offshore wind power grid-connected system; inputting the real-time operation data into a pre-set offshore wind power grid-connected system impedance model to make the offshore wind power grid-connected system impedance model calculate a first equivalent impedance of the offshore wind power grid-connected system according to the real-time operation data, wherein the offshore wind power grid-connected system impedance model is constructed according to the impedance models of each part of the offshore wind power grid-connected system; obtaining a second equivalent impedance of the power grid according to a pre-set power grid harmonic impedance model or actual power grid harmonic scanning value; performing stability analysis on the offshore wind power grid-connected system according to the first equivalent impedance and the second equivalent impedance to improve the accuracy of stability judgment of the offshore wind power grid-connected system. The above-mentioned patent mainly focuses on stability analysis through impedance model to provide data support for system oscillation risk assessment, but does not form a closed-loop control optimization, which is difficult to dynamically adjust system parameters to suppress harmonics in actual operation. SUMMARY

[0004] In order to solve the problems existing in the prior art, the present application proposes a method for suppressing harmonics of an offshore wind turbine.

[0005] The technical solution of the present application is as follows:

[0006] A method for suppressing harmonics of an offshore wind turbine, comprising the following steps:

[0007] constructing a positive sequence impedance model of the offshore wind turbine generator system to output the positive sequence impedance of the offshore wind turbine generator system;

[0008] constructing a positive sequence impedance model of the rectifier station to output the positive sequence impedance from the offshore wind turbine generator system to the AC side of the rectifier station;

[0009] constructing a positive sequence impedance model of the inverter to output the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter;

[0010] obtaining the system positive sequence impedance based on the positive sequence impedance of the offshore wind turbine generator system, the positive sequence impedance from the offshore wind turbine generator system to the AC side of the rectifier station, and the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter;

[0011] constructing an open-loop transfer function and a closed-loop transfer function based on the system positive sequence impedance;

[0012] diagnosing the stability of the open-loop transfer function and the closed-loop transfer function by using the Nyquist inverse criterion;

[0013] if the diagnosis result is unstable, optimizing the parameters of the PI controller based on the system positive sequence impedance, and controlling the current and voltage of the inverter and the rectifier station by the PI controller to suppress the harmonics of the offshore wind turbine generator system.

[0014] Preferably, the offshore wind turbine generator system adopts a maximum power point tracking (MPPT) regulation mode.

[0015] Preferably, the step of constructing the positive sequence impedance model of the offshore wind turbine generator system comprises the following steps:

[0016] obtaining the positive sequence current and the positive sequence voltage of the inverter;

[0017] calculating the positive sequence admittance of the inverter based on the positive sequence current and the positive sequence voltage;

[0018] determining the number of wind turbines of the offshore wind turbine generator system, and constructing the positive sequence impedance model of the offshore wind turbine generator system based on the number of wind turbines and the positive sequence admittance.

[0019] Preferably, the rectifier station is a diode rectifier-based high-voltage direct current transmission system (DR-HVDC).

[0020] The high-voltage direct current transmission system (DR-HVDC) comprises at least two groups of parallel 12-pulse diode rectifier bridges.

[0021] Each group of 12-pulse diode rectifier bridges is constructed by connecting two groups of 6-pulse diode rectifier bridges through a phase-shifting transformer with a phase shift of 30°.

[0022] Preferably, the step of constructing the positive sequence impedance model of the rectifier station comprises the following steps:

[0023] Obtaining the operation data of the converter transformer and the phase-shifting transformer, and calculating the output voltage of the 12-pulse diode rectifier bridge based on the operation data of the converter transformer and the DC output current of the rectifier station;

[0024] Calculating the active power transmission of the AC port of the rectifier station based on the output voltage of the 12-pulse diode rectifier bridge;

[0025] Determining the equivalent impedance of the DC cable, the voltage rating of the DC capacitor and the phase-shifting transformer ratio based on the active power transmission and the operation data of the phase-shifting transformer, and calculating the resistance of the MMC onshore platform based on the active power transmission, the equivalent impedance of the DC cable and the voltage rating of the DC capacitor;

[0026] Constructing the 12-pulse diode rectifier bridge impedance model based on the resistance of the MMC onshore platform and the sequence impedance model of the offshore wind turbine generator set, and outputting the positive sequence impedance of the 12-pulse diode rectifier bridge;

[0027] Determining the equivalent impedance parameters of the filter and the reactive compensator, and constructing the sequence impedance model of the rectifier station based on the equivalent impedance parameters, the phase-shifting transformer ratio and the positive sequence impedance of the 12-pulse diode rectifier bridge.

[0028] Preferably, the sequence impedance model of the inverter is constructed, and the specific steps are as follows:

[0029] Obtaining the disturbance component of the positive sequence current, the disturbance component of the negative sequence current, the disturbance component of the DC side current and the disturbance component of the positive sequence voltage of the inverter;

[0030] Determining the response admittance of the positive sequence voltage disturbance to the positive sequence current and the response admittance of the positive sequence current disturbance to the positive sequence voltage based on the disturbance component of the positive sequence current and the disturbance component of the positive sequence voltage of the inverter;

[0031] Determining the response admittance of the positive sequence voltage disturbance to the negative sequence current and the response admittance of the negative sequence current disturbance to the positive sequence voltage based on the disturbance component of the negative sequence current and the disturbance component of the positive sequence voltage of the inverter;

[0032] Determining the response admittance of the positive sequence voltage disturbance to the DC side current and the response admittance of the DC side current disturbance to the positive sequence voltage based on the disturbance component of the DC side current and the disturbance component of the positive sequence voltage of the inverter;

[0033] Calculating the positive sequence admittance from the DC side of the rectifier station to the DC side of the inverter based on the response admittance of the positive sequence voltage disturbance to the positive sequence current, the response admittance of the positive sequence current disturbance to the positive sequence voltage, the response admittance of the positive sequence voltage disturbance to the negative sequence current, the response admittance of the negative sequence current disturbance to the positive sequence voltage, the response admittance of the positive sequence voltage disturbance to the DC side current, the response admittance of the DC side current disturbance to the positive sequence voltage and the positive sequence impedance from the offshore wind turbine generator set to the AC side of the rectifier station.

[0034] calculating positive sequence impedance of the inverter DC side based on the voltage rating of the DC capacitor and the positive sequence admittance from the rectifier DC side to the inverter DC side;

[0035] constructing an inverter sequence impedance model based on the positive sequence impedance of the inverter DC side.

[0036] Preferably, open loop transfer function and closed loop transfer function are constructed based on the system positive sequence impedance, and the specific steps are as follows:

[0037] obtaining negative sequence current and negative sequence voltage of the inverter;

[0038] calculating negative sequence admittance of the inverter based on the negative sequence current and the negative sequence voltage;

[0039] constructing an inverter sequence admittance matrix based on the negative sequence admittance and the positive sequence admittance of the inverter;

[0040] constructing a closed loop transfer function based on the inverter sequence admittance matrix and the system positive sequence impedance;

[0041] constructing an open loop transfer function based on the system positive sequence impedance and the positive sequence impedance of the 12-pulse diode rectifier bridge.

[0042] Preferably, the PI controller controls the current and voltage of the inverter and the rectifier station by using current loop and voltage loop.

[0043] Preferably, the parameters of the PI controller are optimized based on the system positive sequence impedance, and the specific steps are as follows:

[0044] determining the poles of the denominator of the system positive sequence impedance, and calculating damping ratio based on the poles;

[0045] determining the current when the inverter AC side is disturbed, and optimizing the current loop proportional coefficient and the current loop integral coefficient of the current loop based on the current when the inverter AC side is disturbed and the damping ratio;

[0046] constructing a closed loop transfer function of the current loop based on the current loop proportional coefficient and the current loop integral coefficient to control the current of the inverter and the rectifier station;

[0047] optimizing the voltage loop proportional coefficient and the voltage loop integral coefficient of the voltage loop based on the damping ratio;

[0048] constructing a closed loop transfer function of the voltage loop based on the voltage loop proportional coefficient and the voltage loop integral coefficient to control the voltage of the inverter and the rectifier station.

[0049] Preferably, the current when the inverter AC side is disturbed is determined, and the specific steps are as follows:

[0050] Obtain three-phase instantaneous voltage of inverter port and three-phase instantaneous current of inverter port, construct a DC voltage disturbance model based on the three-phase instantaneous voltage of inverter port and three-phase instantaneous current of inverter port, and output inverter DC side voltage disturbance.

[0051] Based on the inverter DC side voltage disturbance, the positive sequence admittance of the inverter and the negative sequence admittance of the inverter, the steady-state rated value of the inverter AC side current is calculated and obtained.

[0052] Based on the positive sequence admittance from the rectifier station DC side to the inverter DC side and the active power transmission amount of the rectifier station AC port, the current disturbance of the inverter AC side current is calculated and obtained.

[0053] Based on the steady-state rated value of the inverter AC side current and the current disturbance of the inverter AC side current, the current of the inverter AC side during disturbance is calculated and obtained.

[0054] The present application has the following beneficial effects:

[0055] 1. The present application respectively constructs the sequence impedance model of offshore wind turbine generator, rectifier station and inverter, accurately depicts the electrical characteristics of each part, especially the generation and transmission characteristics of harmonics. Based on the system positive sequence impedance calculated by the model, the propagation path and influence degree of harmonics in the system can be more accurately reflected, and accurate targets are provided for harmonic suppression.

[0056] 2. When the diagnosis result is unstable, the parameters of the PI controller are optimized based on the system positive sequence impedance. By adjusting the proportional coefficient and integral coefficient of the current loop and voltage loop, the damping characteristics of the system can be changed, the damping ratio of the system can be increased, the harmonic oscillation can be effectively suppressed, the stability of the system under various working conditions can be improved, and the normal operation of the offshore wind turbine generator can be ensured.

[0057] 3. The present application realizes accurate control of the current and voltage of the inverter and rectifier station by optimizing the parameters of the PI controller. The cooperative control of the current loop and voltage loop can quickly respond to the harmonic changes in the system, timely adjust the output of the current and voltage, reduce the generation and amplification of harmonics, so as to more effectively suppress the harmonics of offshore wind turbine generator and improve the power quality. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 The system topology of the embodiment of the present application is shown.

[0059] Figure 2 The total harmonic distortion rate diagram of the comparative algorithm of the embodiment of the present application is shown.

[0060] Figure 3 The total harmonic distortion rate diagram of the method of the embodiment of the present application is shown.

[0061] Figure 4 The response curve schematic diagram for the embodiment of the present application. DETAILED DESCRIPTION

[0062] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0063] It should be understood that the step numbers used herein are only for the convenience of description, and are not intended to limit the execution sequence of the steps.

[0064] It should be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and the appended claims of the present application, the singular forms "a", "an" and "the" are intended to include the plural forms, unless the context clearly indicates otherwise.

[0065] The terms "comprise" and "include" indicate the presence of described features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0066] The term "and / or" means any combination of one or more of the associated listed terms and all possible combinations thereof, and includes these combinations.

[0067] Embodiment one:

[0068] Referring to Figure 1 , Figure 1 in is a voltage ring reference voltage, is a current ring reference current, PLL is a phase-locked loop for collecting grid phase . Both dq / abc and abc / dq are coordinate transformation modules, which are used to realize the transformation between abc coordinate system and dq rotating coordinate system in a three-phase alternating current system. Through the transformation, the impedance modeling can be more in line with the actual characteristics. SVPWM is a space vector pulse width modulation, which is used for switching control and reduces harmonic components in the modulation process.

[0069] A harmonic suppression method for an offshore wind turbine generator system, comprising the following steps:

[0070] Carrying out modular sequence impedance modeling, respectively constructing sequence impedance models of the offshore wind turbine generator system, and outputting positive sequence impedance of the offshore wind turbine generator system;

[0071] constructing a positive sequence impedance model of the rectifier station, outputting the positive sequence impedance from the AC side of the offshore wind turbine to the rectifier station;

[0072] constructing a positive sequence impedance model of the inverter, outputting the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter;

[0073] obtaining the system positive sequence impedance based on the positive sequence impedance of the offshore wind turbine, the positive sequence impedance from the offshore wind turbine to the AC side of the rectifier station, and the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter;

[0074] constructing an open-loop transfer function and a closed-loop transfer function based on the system positive sequence impedance;

[0075] adopting the Nyquist inverse criterion to diagnose the stability of the open-loop transfer function and the closed-loop transfer function;

[0076] if the diagnosis result is unstable, optimizing the parameters of the PI controller based on the system positive sequence impedance, and controlling the current and voltage of the inverter and the rectifier station through the PI controller to suppress the harmonics of the offshore wind turbine.

[0077] The Nyquist inverse criterion draws the Nyquist curve of the loop gain, calculates the encircling direction and the number of the " -1 point", and matches the number of the poles in the right half plane in the open loop: if the condition is met, the closed loop is stable; otherwise, it is unstable. (Prior art)

[0078] Preferably, the offshore wind turbine adopts a maximum power point tracking (MPPT) regulation mode.

[0079] In the process of constructing the positive sequence impedance model of the offshore wind turbine, the offshore wind turbine to the inverter is equivalent to a constant power source.

[0080] Preferably, the steps of constructing the positive sequence impedance model of the offshore wind turbine are as follows:

[0081] obtaining the positive sequence current and the positive sequence voltage of the inverter;

[0082] calculating the positive sequence admittance of the inverter based on the positive sequence current and the positive sequence voltage, and expressing it in a formula as follows:

[0083] ;

[0084] ;

[0085] In the formula, Y is the positive sequence admittance of the inverter, Y is the positive sequence admittance of the inverter, I is the positive sequence current of the inverter, V is the positive sequence voltage of the inverter, ω is a complex frequency variable;

[0086] determining the number of wind turbines of the offshore wind turbine generator system, constructing an offshore wind turbine generator system sequence impedance model based on the number of wind turbines and the positive sequence admittance, and formulating as:

[0087] ;

[0088] In the formula, represents the positive sequence impedance of the offshore wind turbine generator system, which can also be understood as the transfer function of the offshore wind turbine generator system, represents the number of wind turbines of the offshore wind turbine generator system.

[0089] Preferably, the rectifier station is a diode rectifier-based high-voltage direct current transmission system DR-HVDC;

[0090] The high-voltage direct current transmission system DR-HVDC includes at least two groups of parallel 12-pulse diode rectifier bridges.

[0091] Each group of 12-pulse diode rectifier bridges is constructed by connecting two groups of 6-pulse diode rectifier bridges through a phase-shifting transformer with a phase shift of 30°.

[0092] Preferably, the rectifier station sequence impedance model is constructed, and the specific steps are:

[0093] Obtaining the operating data of the converter transformer and the phase-shifting transformer, calculating the output voltage of the 12-pulse diode rectifier bridge through the operating data of the converter transformer and the direct current output current of the rectifier station, and formulating as:

[0094] ;

[0095] In the formula, represents the output voltage of the 12-pulse diode rectifier bridge, represents the effective value of the AC port voltage of the converter transformer under no-load working condition, represents the equivalent leakage reactance parameter of the converter transformer, and the value interval is 0.1-0.25pu, represents the direct current output current of the rectifier station;

[0096] Calculating the active power transmission amount of the AC port of the rectifier station based on the output voltage of the 12-pulse diode rectifier bridge, and formulating as:

[0097] ;

[0098] In the formula, represents the active power transmission amount of the AC port of the rectifier station, represents the output current of the 12-pulse diode rectifier bridge;

[0099] Correspondingly, the reactive power interaction of the AC port of the rectifier station is expressed by the formula:

[0100] ;

[0101] In the formula, represents the reactive power interaction of the AC port of the rectifier station, represents the commutation overlap angle of the phase-shifting transformer;

[0102] The commutation overlap angle and the dynamic balance equation of the DC voltage output by the rectifier station ensure efficient and stable commutation process, avoid DC voltage drop and commutation loss caused by abnormal commutation overlap angle , and maintain the active power transmission of the AC port of the rectifier station , the commutation overlap angle is small, which leads to high power factor and low loss; the commutation overlap angle is large, which supports more reactive power but increases loss, so as to realize the maximum active power transmission , the commutation overlap angle needs to be maintained near the minimum value within the allowed range. The harmonic complementary suppression equation of the 12-pulse diode rectifier bridge and the filter performs targeted filtering by improving the harmonic order, reduces the reactive loss and heating loss caused by harmonics, and improves the proportion of active components in the equivalent impedance of the system; the reactive power compensation and power factor balance equation maintains the power factor close to 1 through devices such as STATCOM, avoiding the decrease of active power proportion caused by reactive imbalance.

[0103] Based on the active power transmission and the operation data of the phase-shifting transformer, the equivalent impedance of the DC cable, the voltage rating of the DC capacitor, and the transformation ratio of the phase-shifting transformer are determined, which are expressed by the formula:

[0104] ;

[0105] In the formula, represents the voltage rating of the DC capacitor, represents the transformation ratio of the phase-shifting transformer, represents the primary side voltage of the phase-shifting transformer, represents the leakage reactance of the phase-shifting transformer;

[0106] ;

[0107] When the above equation is , the maximum active power transmission is obtained, if , the voltage rating needs to be improved, if , the voltage rating needs to be reduced​ .

[0108] The MMC land platform is not limited to the MMC-HVDC system, and the DR-HVDC adopted in the embodiment is also applicable to the MMC land platform. In fact, the MMC land platform herein generally refers to a land-side converter station based on a modular multilevel converter (MMC) and can be widely applied to different DC power transmission system structures.

[0109] The MMC land platform is a power conversion and transmission system platform constructed based on a modular multilevel converter (MMC) as a core device. It can realize flexible and efficient interconnection of DC and AC power, has the characteristics of modular design, strong expansibility, flexible and stable operation, and good adaptability to power grid disturbances, and is widely applied to new energy large-scale grid connection, long-distance offshore wind power transmission, and DC and AC grid interconnection and other application scenarios.

[0110] voltage rating and active power transmission The following equation constraints also need to be met, which are expressed in formulas as follows:

[0111] ;

[0112] In the formula, represents the equivalent impedance of the DC cable, and the value range is 170-210Ω.

[0113] ;

[0114] In the formula, represents the steady-state voltage of the MMC land platform;

[0115] The resistance of the MMC land platform is calculated and obtained based on the active power transmission, the equivalent impedance of the DC cable, and the voltage rating of the DC capacitor, which is expressed in a formula as follows:

[0116] ;

[0117] In the formula, represents the resistance of the MMC land platform;

[0118] Based on the resistance of the MMC land platform and the sequence impedance model of the offshore wind turbine generator, a 12-pulse diode rectifier bridge impedance model is constructed, and the positive sequence impedance of the 12-pulse diode rectifier bridge is output, which is expressed in a formula as follows:

[0119] ;

[0120] ;

[0121] wherein, represents the fundamental frequency, 50 Hz, is the lowest inherent frequency in periodic vibration or fluctuation, which determines the basic frequency characteristics of vibration or fluctuation, represents the positive sequence impedance of the 12-pulse diode rectifier bridge, and can also be understood as the transfer function of the 12-pulse diode rectifier bridge, represents the imaginary unit, represents the transfer function of the offshore wind turbine generator system, calling the transfer function of the offshore wind turbine generator system as a parameter;

[0122] determining the equivalent impedance parameters of the filter and the reactive compensator, constructing a rectifier station sequence impedance model based on the equivalent impedance parameters, the shift transformer ratio and the positive sequence impedance of the 12-pulse diode rectifier bridge, and expressing it in a formula as:

[0123] ;

[0124] wherein, represents parallel operation, represents the positive sequence impedance of the offshore wind turbine generator system to the AC side of the rectifier station, and can also be understood as the transfer function of the offshore wind turbine generator system to the AC side of the rectifier station, represents the equivalent impedance parameters of the filter and the reactive compensator, and the value range is to .

[0125] Preferably, the step of constructing the inverter sequence impedance model comprises the following steps:

[0126] obtaining the disturbance component of the positive sequence current, the disturbance component of the negative sequence current, the disturbance component of the DC side current and the disturbance component of the positive sequence voltage of the inverter;

[0127] determining the response admittance of the positive sequence voltage disturbance to the positive sequence current and the response admittance of the positive sequence current disturbance to the positive sequence voltage based on the disturbance component of the positive sequence current and the disturbance component of the positive sequence voltage of the inverter, and expressing it in a formula as:

[0128] ;

[0129] ;

[0130] ;

[0131] ;

[0132] wherein, represents the response admittance of the positive sequence voltage disturbance to the positive sequence current, represents the disturbance component of the positive sequence current of the inverter, a disturbance component indicative of a positive sequence voltage of the inverter, a response admittance indicative of a positive sequence current disturbance on the positive sequence voltage, a complex frequency variable, a frequency indicative of the disturbance signal, a conjugate operation;

[0133] determining, based on the disturbance component of the negative sequence current of the inverter and the disturbance component of the positive sequence voltage, a response admittance of the positive sequence voltage disturbance on the negative sequence current and a response admittance of the negative sequence current disturbance on the positive sequence voltage, formulated as:

[0134] ;

[0135] ;

[0136] ;

[0137] wherein, a response admittance of the positive sequence voltage disturbance on the negative sequence current, a response admittance of the negative sequence current disturbance on the positive sequence voltage, a disturbance component indicative of a negative sequence current of the inverter;

[0138] determining, based on the disturbance component of the DC side current of the inverter and the disturbance component of the positive sequence voltage, a response admittance of the positive sequence voltage disturbance on the DC side current and a response admittance of the DC side current disturbance on the positive sequence voltage, formulated as:

[0139] ;

[0140] ;

[0141] ;

[0142] wherein, a response admittance of the positive sequence voltage disturbance on the DC side current, a response admittance of the DC side current disturbance on the positive sequence voltage, a disturbance component indicative of a DC side current of the inverter;

[0143] calculating, based on the response admittance of the positive sequence voltage disturbance on the positive sequence current, the response admittance of the positive sequence current disturbance on the positive sequence voltage, the response admittance of the positive sequence voltage disturbance on the negative sequence current, the response admittance of the negative sequence current disturbance on the positive sequence voltage, the response admittance of the positive sequence voltage disturbance on the DC side current, the response admittance of the DC side current disturbance on the positive sequence voltage and the positive sequence impedance from the offshore wind turbine generator system to the AC side of the rectifier station, a positive sequence admittance from the DC side of the rectifier station to the DC side of the inverter, formulated as:

[0144]

[0145] In the formula, represents the positive sequence admittance from the rectifier DC side to the inverter DC side;

[0146] Based on the voltage rating of the DC capacitor and the positive sequence admittance from the rectifier DC side to the inverter DC side, the positive sequence impedance of the inverter DC side is calculated and obtained, which is expressed in the formula as:

[0147]

[0148] In the formula, represents the positive sequence impedance of the inverter DC side, which can also be understood as the transfer function of the inverter DC side, represents the equivalent output power of the offshore wind turbine, with a value range of 1.5-2MVA, represents the equivalent inductance of the DC cable, with a value range of 0.1-1H;

[0149] Based on the positive sequence impedance of the inverter DC side, the inverter sequence impedance model is constructed, which is expressed in the formula as:

[0150]

[0151] In the formula, represents the positive sequence impedance from the rectifier DC side to the inverter DC side, which can also be understood as the transfer function from the rectifier DC side to the inverter DC side, and the value of the DC capacitor is 130mF.

[0152] Preferably, based on the system positive sequence impedance, the open-loop transfer function and the closed-loop transfer function are constructed, and the specific steps are as follows:

[0153] The negative sequence current and the negative sequence voltage of the inverter are obtained;

[0154] Based on the negative sequence current and the negative sequence voltage, the negative sequence admittance of the inverter is calculated and obtained, which is expressed in the formula as:

[0155]

[0156]

[0157] In the formula, represents the negative sequence admittance of the inverter, represents the negative sequence current of the inverter, represents the negative sequence voltage of the inverter;

[0158] Based on the negative sequence admittance and the positive sequence admittance of the inverter, the inverter sequence admittance matrix is constructed, which is expressed in the formula as:

[0159] ​​​​​ ;

[0160] wherein, represents the inverter sequence admittance matrix;

[0161] Based on the inverter sequence admittance matrix and the system positive sequence impedance, a closed-loop transfer function is constructed, which is expressed as:

[0162] ;

[0163] ;

[0164] wherein, represents the system positive sequence impedance, which can also be understood as a transfer function from the offshore wind turbine generator system to the AC power grid, represents the closed-loop transfer function, represents the unit matrix;

[0165] Based on the system positive sequence impedance and the positive sequence impedance of the 12-pulse diode rectifier bridge, an open-loop transfer function is constructed, which is expressed as:

[0166] ;

[0167] wherein, represents the open-loop transfer function.

[0168] Preferably, the PI controller controls the current and voltage of the inverter and rectifier station by using a current loop and a voltage loop.

[0169] The current loop realizes fast dynamic response as an inner loop, and the voltage loop maintains system energy steady state as an outer loop. Both of them realize impedance reshaping and harmonic oscillation suppression under all working conditions through adaptive adjustment of the parameters of the PI controller.

[0170] Preferably, the parameters of the PI controller are optimized based on the system positive sequence impedance, and the specific steps are as follows:

[0171] The poles of the denominator of the system positive sequence impedance are determined, and the damping ratio is calculated based on the poles, and the specific steps are as follows:

[0172] The system positive sequence impedance is expressed in fractional form as:

[0173] ;

[0174] wherein, represents the denominator of the system positive sequence impedance, represents the numerator of the system positive sequence impedance;

[0175] The poles of the denominator of the system positive sequence impedance are determined, and the poles are specifically the points of the denominator which are 0, and are expressed as:

[0176] ;

[0177] wherein, denotes the number of poles, denotes the th pole, denotes the pole index;

[0178] If there are multiple poles , the pole with the largest real part is taken;

[0179] Based on the pole with the largest real part , the damping ratio is calculated and obtained, which is expressed by the formula:

[0180] ;

[0181] ;

[0182]

[0183] wherein, denotes the damping ratio, denotes the decay coefficient, denotes the decay oscillation frequency, denotes the real part function, denotes the imaginary part function;

[0184] The damping ratio is used as a set prior constraint to define the PI parameter feasible region and provide a stable margin.

[0185] The current at the time of disturbance on the AC side of the inverter is determined, and the current loop proportional coefficient and the current loop integral coefficient of the current loop are optimized based on the current at the time of disturbance on the AC side of the inverter and the damping ratio, so that the current loop maintains the target damping, suppresses the current peak, and improves the disturbance resistance under the conditions of load mutation and network resistance change;

[0186] If it is a-phase power, the formula is expressed as:

[0187] ;

[0188] If it is b-phase power, the formula is expressed as:

[0189] ;

[0190] If it is c-phase power, the formula is expressed as:

[0191] ;

[0192] wherein, denotes the current loop integral coefficient, represents the current loop proportional coefficient, represents the filter inductance, taking 0.3mH, represents the control bandwidth, the control bandwidth interval of the current loop is 100-300, represents the a-phase current when the inverter AC side is disturbed, represents the b-phase current when the inverter AC side is disturbed, represents the c-phase current when the inverter AC side is disturbed;

[0193] Based on the current loop proportional coefficient and the current loop integral coefficient, the closed-loop transfer function of the current loop is constructed to control the current of the inverter and the rectifier station, which is expressed by the formula:

[0194] ;

[0195] In the formula, represents the open-loop transfer function, represents the closed-loop transfer function of the current loop;

[0196] Based on the damping ratio, the voltage loop proportional coefficient and the voltage loop integral coefficient of the voltage loop are optimized, and the current loop damping is coordinated and optimized to reduce the resonance risk caused by the phase coupling of the inner and outer loops, which is expressed by the formula:

[0197] ;

[0198] In the formula, represents the voltage loop integral coefficient, represents the voltage loop proportional coefficient, represents the filter capacitance, taking 0.3mF, and the control bandwidth interval of the current loop is 10-30;

[0199] Based on the voltage loop proportional coefficient and the voltage loop integral coefficient, the closed-loop transfer function of the voltage loop is constructed to control the voltage of the inverter and the rectifier station, which is expressed by the formula:

[0200] ;

[0201] In the formula, represents the closed-loop transfer function of the voltage loop.

[0202] Based on the symmetry characteristics of the AC voltage, only the a-phase current when the inverter AC side is disturbed is selected as an analysis example, the calculation methods of the b-phase current when the inverter AC side is disturbed and the c-phase current when the inverter AC side is disturbed are consistent with the a-phase current when the inverter AC side is disturbed, so they are not described here.

[0203] Preferably, the specific steps for determining the current when the inverter AC side is disturbed are as follows:

[0204] The three-phase instantaneous voltage of the inverter port and the three-phase instantaneous current of the inverter port are acquired, a DC voltage disturbance model is constructed based on the three-phase instantaneous voltage of the inverter port and the three-phase instantaneous current of the inverter port, and the inverter DC side voltage disturbance is output, which is expressed by a formula as follows:

[0205] ;

[0206] In the formula, denotes a port voltage conversion coefficient, denotes a port current conversion coefficient, denotes the three-phase instantaneous voltage of the inverter port, denotes the three-phase instantaneous current of the inverter port, denotes the inverter DC side voltage disturbance.

[0207] The steady-state rated value of the inverter AC side current is calculated based on the inverter DC side voltage disturbance, the positive sequence admittance of the inverter and the negative sequence admittance of the inverter, and is expressed by a formula as follows:

[0208] ;

[0209] In the formula, denotes the steady-state rated value of the inverter AC side a-phase current, denotes a signal quantity of the a-phase duty ratio, denotes a signal quantity of the a-phase voltage.

[0210] The current disturbance of the inverter AC side current is calculated based on the positive sequence admittance from the rectifier station DC side to the inverter DC side and the active power transmission amount of the rectifier station AC port, and is expressed by a formula as follows:

[0211] ;

[0212] In the formula, denotes the current disturbance of the inverter AC side a-phase current, denotes a duty ratio signal, and the value range is 0%-100%;

[0213] The inverter AC side current at the disturbance time is calculated based on the steady-state rated value of the inverter AC side current and the current disturbance of the inverter AC side current, and is expressed by a formula as follows:

[0214] .

[0215] Referring to Figures 2-3 , Figure 2 is the total harmonic distortion rate of the comparative algorithm (specifically, a PI controller with fixed parameters), Figure 3The total harmonic distortion rate of the method described in the embodiment is 1.31%. Compared with the comparative algorithm (13.89%), the total harmonic distortion rate is reduced by 12.58%. At the same time, the amplitude of each harmonic is significantly reduced in the full frequency band, verifying the harmonic suppression effect and effectiveness of the method described in the embodiment.

[0216] Referring to Figure 4 The response curve of the AC side voltage of the inverter after the disturbance is shown in FIG. 6. The blue curve represents the response before the PI parameter optimization, and the red curve represents the response after the optimization. Unlike the prior art "no closed-loop control optimization", the method of the embodiment realizes the fast response advantage of "current loop + voltage loop cooperative control". Figure 4 The abscissa of FIG. 6 represents time.

[0217] Embodiment two:

[0218] The embodiment provides an electronic device having a computer program stored thereon, the computer program being executed by a processor to implement the offshore wind turbine harmonic suppression method according to any one of the embodiments of the application.

[0219] In the embodiments of the present application, "at least one" means one or more, and "multiple" means two or more. The association relationship of the associated objects is described by "and / or", which means that there can be three kinds of relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it. "At least one of the following" and the like means any combination of these items, including any combination of single or multiple items. For example, at least one of a, b and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, wherein a, b, and c can be single or multiple.

[0220] Those of ordinary skill in the art can realize that the units and algorithm steps described in the embodiments disclosed herein can be realized by electronic hardware, computer software and a combination of electronic hardware and computer software. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0221] Those skilled in the art can clearly understand that, for the convenience and brevity of the description, the specific working processes of the above-described system, device and unit can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0222] In several embodiments provided in the present application, any function, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application or the parts of the technical solutions that essentially contribute to the prior art or the parts of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in the embodiments of the present application. The aforementioned storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0223] The above description is only some embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields, based on the content of the specification and drawings of the present application, are also included in the patent protection scope of the present application.

Claims

1. A method for harmonic suppression in offshore wind turbine generators, characterized in that, Includes the following steps: Construct a sequence impedance model for offshore wind turbine generators and output the positive sequence impedance of the offshore wind turbine generators. Construct a rectifier station sequence impedance model and output the positive sequence impedance from the offshore wind turbine generator to the AC side of the rectifier station; Construct an inverter sequence impedance model and output the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter. The positive sequence impedance of the system is obtained based on the positive sequence impedance of the offshore wind turbine, the positive sequence impedance from the offshore wind turbine to the AC side of the rectifier station, and the positive sequence impedance from the DC side of the rectifier station to the DC side of the inverter. The open-loop and closed-loop transfer functions are constructed based on the positive-sequence impedance of the system. The specific steps are as follows: Obtain the negative sequence current and negative sequence voltage of the inverter; The negative sequence admittance of the inverter is calculated based on the negative sequence current and negative sequence voltage. Construct the inverter sequence admittance matrix based on the negative sequence admittance and positive sequence admittance of the inverter; Construct a closed-loop transfer function based on the inverter sequence admittance matrix and the system positive sequence impedance; An open-loop transfer function is constructed based on the system's positive-sequence impedance and the positive-sequence impedance of the 12-pulsating diode rectifier bridge. The stability of the open-loop and closed-loop transfer functions is diagnosed using the Nyquist inverse criterion. If the diagnosis result is unstable, the parameters of the PI controller are optimized based on the positive sequence impedance of the system. The specific steps are as follows: Determine the poles of the denominator of the system's positive-sequence impedance, and calculate the damping ratio based on these poles; Determine the current when the inverter's AC side is disturbed, and optimize the current loop proportional coefficient and current loop integral coefficient based on the current when the inverter's AC side is disturbed and the damping ratio. Based on the current loop proportional coefficient and current loop integral coefficient, a closed-loop transfer function of the current loop is constructed to control the current of the inverter and rectifier station. The voltage loop proportional coefficient and voltage loop integral coefficient are optimized based on the damping ratio. Based on the voltage loop proportional coefficient and voltage loop integral coefficient, a closed-loop transfer function of the voltage loop is constructed to control the voltage of the inverter and rectifier station. The specific steps for determining the current during AC side disturbances in the inverter are as follows: Obtain the three-phase instantaneous voltage and three-phase instantaneous current at the inverter port, construct a DC voltage disturbance model based on the three-phase instantaneous voltage and three-phase instantaneous current at the inverter port, and output the DC-side voltage disturbance of the inverter. The steady-state rated value of the inverter AC side current is calculated based on the inverter DC side voltage disturbance, the inverter positive sequence admittance, and the inverter negative sequence admittance. The current disturbance of the inverter AC side current is calculated based on the positive sequence admittance from the DC side of the rectifier station to the DC side of the inverter and the active power transmission amount at the AC port of the rectifier station. The current of the inverter AC side under disturbance is obtained by calculating the steady-state rated value of the inverter AC side current and the current disturbance of the inverter AC side current. Harmonics in offshore wind turbines are suppressed by controlling the current and voltage of the inverter and rectifier station through a PI controller.

2. The harmonic suppression method for offshore wind turbine generators according to claim 1, characterized in that, The offshore wind turbine adopts the maximum power point tracking (MPPT) control mode.

3. The harmonic suppression method for offshore wind turbine generators according to claim 1, characterized in that, The specific steps for constructing the sequence impedance model of offshore wind turbine generators are as follows: Obtain the positive sequence current and positive sequence voltage of the inverter; The positive-sequence admittance of the inverter is calculated based on the positive-sequence current and positive-sequence voltage. The number of wind turbines in the offshore wind turbine generator set is determined, and a sequence impedance model of the offshore wind turbine generator set is constructed based on the number of wind turbines and the positive sequence admittance.

4. The method for harmonic suppression of offshore wind turbine generators according to claim 3, characterized in that, The rectifier station is a high-voltage direct current transmission system (DR-HVDC) based on diode rectifiers. The high-voltage direct current transmission system DR-HVDC includes at least two sets of parallel 12-pulse diode rectifier bridges; Each group of 12-pulse diode rectifier bridges is constructed by connecting two groups of 6-pulse diode rectifier bridges through a transformer with a 30° phase shift.

5. The method for harmonic suppression of offshore wind turbine generators according to claim 4, characterized in that, The specific steps for constructing the rectifier station sequence impedance model are as follows: Obtain the operating data of the converter transformer and the phase-shifting transformer, and calculate the output voltage of the 12-pulsating diode rectifier bridge by using the operating data of the converter transformer and the DC output current of the rectifier station. The active power transmission of the AC port of the rectifier station is calculated based on the output voltage of the 12-pulse diode rectifier bridge. Based on the active power transmission and the operating data of the phase-shifting transformer, the equivalent impedance of the DC cable, the voltage rating of the DC capacitor, and the turns ratio of the phase-shifting transformer are determined, and the resistance of the MMC shore-land platform is calculated using the active power transmission, the equivalent impedance of the DC cable, and the voltage rating of the DC capacitor. Based on the resistance of the MMC onshore platform and the sequence impedance model of the offshore wind turbine, a 12-pulsating diode rectifier bridge impedance model is constructed, and the positive sequence impedance of the 12-pulsating diode rectifier bridge is output. The equivalent impedance parameters of the filter and the reactive power compensator are determined. Based on the equivalent impedance parameters, the phase-shifting transformer ratio, and the positive sequence impedance of the 12-pulsating diode rectifier bridge, a rectifier station sequence impedance model is constructed.

6. The method for harmonic suppression of offshore wind turbine generators according to claim 5, characterized in that, The specific steps for constructing the inverter sequence impedance model are as follows: Obtain the disturbance components of the positive sequence current, negative sequence current, DC side current, and positive sequence voltage of the inverter. The response admittance of positive sequence voltage disturbance to positive sequence current and the response admittance of positive sequence current disturbance to positive sequence voltage are determined based on the disturbance components of positive sequence current and positive sequence voltage of the inverter. The response admittance of the positive-sequence voltage disturbance to the negative-sequence current and the response admittance of the negative-sequence current disturbance to the positive-sequence voltage are determined based on the disturbance components of the negative-sequence current and the positive-sequence voltage disturbance of the inverter. The response admittance of the positive-sequence voltage disturbance to the DC-side current and the response admittance of the DC-side current disturbance to the positive-sequence voltage are determined based on the disturbance components of the DC-side current and the positive-sequence voltage of the inverter. The positive sequence admittance from the DC side of the rectifier station to the DC side of the inverter is obtained based on the positive sequence voltage disturbance response admittance, the positive sequence current disturbance response admittance, the positive sequence voltage disturbance response admittance, the negative sequence current disturbance response admittance, the positive sequence voltage disturbance response admittance to the DC side current, the DC side current disturbance response admittance, and the positive sequence impedance from the offshore wind turbine generator to the AC side of the rectifier station. The positive sequence impedance of the inverter DC side is calculated based on the voltage rating of the DC capacitor and the positive sequence admittance from the DC side of the rectifier station to the DC side of the inverter. The inverter sequence impedance model is constructed based on the positive sequence impedance of the DC side of the inverter.

7. The method for harmonic suppression of offshore wind turbine generators according to claim 1, characterized in that, The PI controller uses current loop and voltage loop to control the current and voltage of the inverter and rectifier station.

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