Harmonic suppression method for offshore wind generating set

Abstract

The invention relates to an offshore wind generating set harmonic suppression method, which belongs to the technical field of offshore wind power harmonic suppression, and comprises the following steps: constructing an offshore wind generating set sequence impedance model, and outputting the positive sequence impedance of an offshore wind generating set; the method comprises the following steps: constructing sequence impedance models of an offshore wind generating set, a rectifier station and an inverter, respectively outputting positive sequence impedance of the offshore wind generating set, positive sequence impedance from the offshore wind generating set to the alternating current side of the rectifier station and positive sequence impedance from the direct current side of the rectifier station to the direct current side of the inverter, and further obtaining positive sequence impedance of a system and constructing open-loop and closed-loop transfer functions; and carrying out stability diagnosis by adopting a Nyquist reverse criterion. And if the diagnosis result is unstable, PI controller parameters are optimized based on the system positive sequence impedance, and accurate control of current and voltage of the inverter and the rectifier station is realized through the PI controller. Cooperative control of a current loop and a voltage loop is adopted, system harmonic wave changes are quickly responded, generation and amplification of harmonic waves are reduced, and the harmonic waves are effectively suppressed.

Description

Technical Field

[0001] This invention relates to a method for harmonic suppression of offshore wind turbine generators, belonging to the field of offshore wind power harmonic suppression technology. Background Technology

[0002] Against the backdrop of global energy transition and sustainable development, offshore wind power, as a clean and renewable energy source, is booming at an unprecedented pace. However, with the continuous expansion of offshore wind power systems and the increasingly widespread application of power electronics technology in this field, a series of technical challenges have gradually emerged, the most prominent of which is harmonic oscillation. Offshore wind power systems typically consist of numerous complex power electronic devices, such as converters, rectifiers, and inverters. While these devices achieve efficient power conversion and transmission, they inevitably become significant sources of harmonics. Harmonic oscillations not only degrade power quality and threaten the stable operation of the offshore wind turbine itself, but also negatively impact the safety and reliability of the entire power system.

[0003] Existing technologies, such as Chinese invention patent application publication number "CN119921384A", disclose a stability analysis method and system for offshore wind power grid-connected systems, including the following steps: acquiring real-time operating data of wind turbines and static var generators in the offshore wind power grid-connected system; inputting the real-time operating data into a preset offshore wind power grid-connected system impedance model, so that the offshore wind power grid-connected system impedance model calculates the first equivalent impedance of the offshore wind power grid-connected system based on the real-time operating data, wherein the offshore wind power grid-connected system impedance model is constructed based on the impedance models of various parts of the offshore wind power grid-connected system; obtaining the second equivalent impedance of the power grid based on a preset power grid harmonic impedance model or actual power grid harmonic scan values; and performing stability analysis on the offshore wind power grid-connected system based on the first and second equivalent impedances to improve the accuracy of stability judgment of the offshore wind power grid-connected system. The above patent mainly focuses on stability analysis through impedance models to provide data support for system oscillation risk assessment, but it does not form a closed-loop control optimization, making it difficult to dynamically adjust system parameters to suppress harmonics in actual operation. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a method for harmonic suppression of offshore wind turbine generators.

[0005] The technical solution of the present invention is as follows: A method for suppressing harmonics in offshore wind turbine generators 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. Construct open-loop and closed-loop transfer functions based on the positive-sequence impedance of the system; 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, and the current and voltage of the inverter and rectifier station are controlled by the PI controller to suppress the harmonics of the offshore wind turbine.

[0006] Preferably, the offshore wind turbine adopts the maximum power point tracking (MPPT) control mode.

[0007] Preferably, the specific steps for constructing the sequence impedance model of the offshore wind turbine generator 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.

[0008] Preferably, 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.

[0009] Preferably, 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.

[0010] Preferably, 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.

[0011] Preferably, the open-loop transfer function and closed-loop transfer function are constructed based on the positive-sequence impedance of the system, and 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.

[0012] Preferably, the PI controller uses a current loop and a voltage loop to control the current and voltage of the inverter and rectifier station.

[0013] Preferably, the specific steps for optimizing the parameters of the PI controller based on the positive sequence impedance of the system 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.

[0014] Preferably, 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 during AC side disturbance 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.

[0015] The present invention has the following beneficial effects: 1. This invention constructs sequence impedance models for offshore wind turbine generators, rectifier stations, and inverters respectively, accurately depicting the electrical characteristics of each component, especially modeling the generation and transmission characteristics of harmonics. The positive sequence impedance of the system calculated based on these models can more accurately reflect the propagation path and influence of harmonics in the system, providing a precise target for harmonic suppression.

[0016] 2. When the diagnostic result indicates instability, optimize the parameters of the PI controller based on the system's positive sequence impedance. By adjusting the proportional and integral coefficients of the current and voltage loops, the damping characteristics of the system can be changed, increasing the system's damping ratio, effectively suppressing harmonic oscillations, improving the system's stability under various operating conditions, and ensuring the normal operation of offshore wind turbines.

[0017] 3. This invention achieves precise control of the current and voltage of the inverter and rectifier station by optimizing the PI controller parameters. The coordinated control of the current loop and voltage loop can quickly respond to harmonic changes in the system, promptly adjust the current and voltage output, reduce the generation and amplification of harmonics, and thus more effectively suppress harmonics in offshore wind turbine generators, improving power quality. Attached Figure Description

[0018] Figure 1 This is a system topology diagram according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram illustrating the total harmonic distortion rate of the comparative algorithm in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the total harmonic distortion rate of the method described in the embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of the response curve in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0024] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0025] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0026] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0027] Example 1: See Figure 1 , Figure 1 middle This is the voltage loop reference voltage. The current is the reference current for the current loop, and the PLL is a phase-locked loop used to acquire the phase of the power grid. Both dq / abc and abc / dq are coordinate transformation modules, used to transform between the abc coordinate system and the dq rotating coordinate system in a three-phase AC system. This transformation allows impedance modeling to better reflect actual characteristics. SVPWM, or Space Vector Pulse Width Modulation, is used for switching control and reduces harmonic components during modulation.

[0028] A method for suppressing harmonics in offshore wind turbine generators includes the following steps: Perform modular sequence impedance modeling, construct sequence impedance models for offshore wind turbine generators separately, and output the positive sequence impedance of 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. Construct open-loop and closed-loop transfer functions based on the positive-sequence impedance of the system; 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, and the current and voltage of the inverter and rectifier station are controlled by the PI controller to suppress the harmonics of the offshore wind turbine.

[0029] The Nyquist inverse criterion is calculated by plotting the Nyquist curve of the loop gain, determining its wrapping direction and number around the "-1 point," and matching it with the number of poles in the right half-plane of the open loop: if the condition is met, the closed loop is stable; otherwise, it is unstable. (Prior art) Preferably, the offshore wind turbine adopts the maximum power point tracking (MPPT) control mode.

[0030] In the process of constructing the sequence impedance model of offshore wind turbine generators, the offshore wind turbine generator to inverter is equivalent to a constant power source.

[0031] Preferably, the specific steps for constructing the sequence impedance model of the offshore wind turbine generator 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, and expressed by the formula: ; ; In the formula, This represents the positive-sequence admittance of the inverter. This represents the positive sequence current of the inverter. This represents the positive sequence voltage of the inverter. Represents a complex frequency variable; The number of wind turbines in the offshore wind turbine generator set is determined. Based on the number of wind turbines and the positive sequence admittance, a sequence impedance model of the offshore wind turbine generator set is constructed, expressed by the formula: ; In the formula, This represents the positive-sequence impedance of an offshore wind turbine, and can also be understood as the transfer function of the offshore wind turbine. This indicates the number of wind turbines in an offshore wind turbine generator set.

[0032] Preferably, 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.

[0033] Preferably, 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. Calculate the output voltage of the 12-pulsating diode rectifier bridge using the converter transformer's operating data and the rectifier station's DC output current. The formula is as follows: ; In the formula, This indicates the output voltage of the 12-pulsating diode rectifier bridge. This represents the effective value of the AC port voltage of the converter transformer under no-load conditions. This represents the equivalent leakage reactance parameter of the converter transformer, with a value range of 0.1-0.25 pu. This indicates the DC output current of the rectifier station; The active power transmission capacity of the AC port of the rectifier station is calculated based on the output voltage of the 12-pulse diode rectifier bridge, and expressed by the formula: ; In the formula, This indicates the amount of active power transmitted at the AC port of the rectifier station. This indicates the output current of the 12-pulse diode rectifier bridge; Correspondingly, the reactive power interaction at the AC port of the rectifier station is expressed by the formula: ; In the formula, This represents the reactive power exchange quantity at the AC port of the rectifier station. This indicates the commutation overlap angle of a phase-shifting transformer; Commutation overlap angle The dynamic balance equation with the DC voltage output from the rectifier station ensures efficient and stable commutation, avoiding issues caused by commutation overlap angle. The abnormal DC voltage drop and commutation loss maintain the active power transmission at the AC port of the rectifier station. Commutation overlap angle A smaller angle results in a higher power factor and lower losses; commutation overlap angle The conference supports more reactive power, but this increases losses. Therefore, to achieve maximum active power transmission... The commutation overlap angle needs to be maintained. Near the minimum value within the allowable range. The harmonic complementary suppression equation of the 12-pulsating diode rectifier bridge and filter reduces reactive power loss and heat loss caused by harmonics by increasing the harmonic order for targeted filtering, thereby increasing the proportion of active power in the system's equivalent impedance; the reactive power compensation and power factor balance equation maintains the power factor close to 1 through devices such as STATCOM, avoiding a decrease in the proportion of active power caused by reactive power imbalance.

[0034] Based on the active power transmission volume 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, expressed by the following formula: ; In the formula, Indicates DC capacitor The voltage rating, Indicates the turns ratio of a phase-shifting transformer. This represents the primary voltage of the phase-shifting transformer. This represents the leakage reactance of the phase-shifting transformer; ; The above equation is in At that time, the maximum active power transmission amount is obtained. ,like Then the voltage rating needs to be increased. ,like Then the voltage rating needs to be reduced. .

[0035] The MMC shore-land platform is not limited to the MMC-HVDC system; the DR-HVDC used in this embodiment is also suitable for accessing the MMC shore-land platform. In fact, the MMC shore-land platform here refers to a type of landside converter station based on a modular multilevel converter (MMC), which can be widely used in different DC transmission system structures.

[0036] The MMC shore-land platform is a power conversion and transmission system platform built around the Modular Multilevel Converter (MMC) as its core equipment. It enables flexible and efficient interconnection of DC and AC power, featuring modular design, strong scalability, flexible and stable operation, and good adaptability to grid disturbances. It is widely used in various application scenarios such as large-scale grid connection of new energy sources, long-distance offshore wind power transmission, and interconnection of DC and AC power grids.

[0037] Voltage rating and active power transmission The following equality constraints must also be satisfied, expressed as a formula: ; In the formula, This represents the equivalent impedance of a DC cable, with a value ranging from 170 to 210 Ω.

[0038] ; In the formula, This represents the steady-state voltage value of the MMC shore-landing platform; The resistance of the MMC shore-land platform is calculated using the active power transmission amount, the equivalent impedance of the DC cable, and the voltage rating of the DC capacitor, and is expressed by the following formula: ; In the formula, This indicates the resistance of the MMC shore-landing platform; 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, expressed by the formula: ; ; In the formula, The fundamental frequency, 50 Hz, is the lowest natural frequency in periodic vibrations or waves, and it determines the fundamental frequency characteristics of the vibration or wave. This represents the positive sequence impedance of a 12-pulsating diode rectifier bridge, and can also be understood as the transfer function of the 12-pulsating diode rectifier bridge. Represents the imaginary unit. Indicates will The transfer function of the offshore wind turbine is called as a parameter; The equivalent impedance parameters of the filter and reactive power compensator are determined. Based on these 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, expressed by the formula: ; In the formula, Indicates parallel operation, This represents the positive-sequence impedance from the offshore wind turbine generator to the AC side of the rectifier station, and can also be understood as the transfer function from the offshore wind turbine generator to the AC side of the rectifier station. This represents the equivalent impedance parameter of the filter and the reactive power compensator, with a value range of [value missing]. arrive .

[0039] Preferably, 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 admittances of the positive-sequence voltage disturbance to the positive-sequence current disturbance and the positive-sequence current disturbance to the positive-sequence voltage disturbance are determined based on the disturbance components of the positive-sequence current and the positive-sequence voltage disturbance, and are expressed by the following formula: ; ; ; ; In the formula, It represents the admittance of the response of positive-sequence voltage disturbance to positive-sequence current. This represents the disturbance component of the positive sequence current of the inverter. This represents the disturbance component of the positive sequence voltage of the inverter. It represents the admittance of the response of positive-sequence current disturbance to positive-sequence voltage. Represents a complex frequency variable. Indicates the frequency of the disturbance signal. Indicates conjugate operation; 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, respectively, and are expressed by the following formula: ; ; ; In the formula, This represents the admittance of the response to the negative sequence current in response to the positive sequence voltage disturbance. This represents the admittance of the response to a negative-sequence current disturbance in response to a positive-sequence voltage disturbance. This represents the disturbance component of the negative sequence current 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, respectively, and are expressed by the following formula: ; ; ; In the formula, This represents the admittance of the DC-side current response to a positive-sequence voltage disturbance. This represents the admittance of the DC-side current disturbance in response to the positive-sequence voltage. This represents the disturbance component of the DC-side current of the inverter; The positive-sequence admittance from the DC side of the rectifier station to the DC side of the inverter is calculated based on the positive-sequence voltage disturbance response to positive-sequence current, the positive-sequence current disturbance response to positive-sequence voltage, the positive-sequence voltage disturbance response to negative-sequence current, the negative-sequence current disturbance response to positive-sequence voltage, the positive-sequence voltage disturbance response to DC-side current, the positive-sequence current disturbance response to positive-sequence voltage, and the positive-sequence impedance from the offshore wind turbine generator to the AC side of the rectifier station. This is expressed by the following formula: ; In the formula, This represents the positive-sequence admittance from the DC side of the rectifier station to the DC side of the inverter; Based on DC capacitor The positive-sequence impedance of the inverter's DC side is obtained by calculating the rated voltage and the positive-sequence admittance from the DC side of the rectifier station to the DC side of the inverter, and is expressed by the formula: ; In the formula, This represents the positive-sequence impedance on the DC side of the inverter, and can also be understood as the transfer function on the DC side of the inverter. This represents the equivalent output power of an offshore wind turbine, with a value ranging from 1.5 to 2 MVA. This represents the equivalent inductance of a DC cable, with a value ranging from 0.1 to 1H. The inverter sequence impedance model is constructed based on the positive sequence impedance of the DC side of the inverter, and expressed by the formula: ; In the formula, This represents the positive-sequence impedance from the DC side of the rectifier station to the DC side of the inverter, and can also be understood as the transfer function from the DC side of the rectifier station to the DC side of the inverter. (DC capacitance) The value is 130mF.

[0040] Preferably, the open-loop transfer function and closed-loop transfer function are constructed based on the positive-sequence impedance of the system, and 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, and expressed by the formula: ; ; In the formula, This represents the negative-sequence admittance of the inverter. This represents the negative sequence current of the inverter. This represents the negative sequence voltage of the inverter; The inverter's sequence admittance matrix is ​​constructed based on the negative-sequence admittance and positive-sequence admittance, and is expressed by the formula: ; In the formula, Represents the inverter's sequential admittance matrix; The closed-loop transfer function is constructed based on the inverter-sequence admittance matrix and the system positive-sequence impedance, and is expressed by the following formula: ; ; In the formula, This represents the positive-sequence impedance of the system, and can also be understood as the transfer function from the offshore wind turbine to the AC power grid. Represents the closed-loop transfer function. Represents the identity matrix; The 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, and is expressed by the following formula: ; In the formula, This represents the open-loop transfer function.

[0041] Preferably, the PI controller uses a current loop and a voltage loop to control the current and voltage of the inverter and rectifier station.

[0042] The current loop acts as the inner loop to achieve a fast dynamic response, while the voltage loop acts as the outer loop to maintain the system's energy steady state. Both loops are adaptively adjusted by the parameters of the PI controller to achieve impedance reshaping and harmonic oscillation suppression under all operating conditions.

[0043] Preferably, the specific steps for optimizing the parameters of the PI controller based on the positive sequence impedance of the system are as follows: The poles of the denominator of the system's positive-sequence impedance are determined, and the damping ratio is calculated based on these poles. The specific steps are as follows: The positive-sequence impedance of the system can be expressed in fractional form as follows: ; In the formula, The denominator represents the positive-sequence impedance of the system. The molecule representing the positive-sequence impedance of the system; Determine the poles of the denominator of the system's positive-sequence impedance, specifically the poles of the denominator. The point with a value of 0 is represented by the formula: ; In the formula, Indicates the number of poles. Indicates the first An extreme point, Indicates the pole index; If multiple poles exist Then take the pole with the largest real part. ; Based on the pole with the largest real part The damping ratio is calculated and expressed by the formula: ; ;

[0044] In the formula, Indicates the damping ratio. Indicates the attenuation coefficient. Indicates the damped oscillation frequency. This represents a function that takes the real part. Indicates a function with its imaginary part taken; The damping ratio is used as a priori constraint for tuning to define the feasible region of the PI parameter and provide a stability margin.

[0045] Determine the current when the AC side of the inverter is disturbed, and optimize the current loop proportional coefficient and current loop integral coefficient based on the current and damping ratio when the AC side of the inverter is disturbed, so that the current loop maintains the target damping, suppresses current spikes and improves disturbance immunity under the conditions of load change and grid resistance change. If it is phase a, then the formula is expressed as: ; If it is phase b electricity, then the formula is expressed as: ; If it is phase c electricity, then the formula is expressed as: ; In the formula, Indicates the integral coefficient of the current loop. This represents the proportionality coefficient of the current loop. This represents the filter inductance, taken as 0.3mH. This indicates the control bandwidth; the control bandwidth range for the current loop is 100-300. This represents the phase a current when there is a disturbance on the AC side of the inverter. This represents the b-phase current during AC side disturbances in the inverter. This represents the c-phase current when there is a disturbance on the AC side of the inverter. The closed-loop transfer function of the current loop, constructed based on the current loop proportional coefficient and current loop integral coefficient, controls the current of the inverter and rectifier station, as expressed by the formula: ; In the formula, Represents the open-loop transfer function. The closed-loop transfer function represents the current loop. The voltage loop proportional coefficient and voltage loop integral coefficient are optimized based on the aforementioned damping ratio, and coordinated with the current loop damping to reduce the resonance risk caused by phase coupling between the inner and outer loops, as expressed by the formula: ; In the formula, Indicates the voltage loop integral coefficient. This represents the voltage loop proportionality coefficient. This indicates the filter capacitor, with a value of 0.3mF, and the control bandwidth range of the current loop is 10-30. Based on the voltage loop proportional coefficient and voltage loop integral coefficient, a closed-loop transfer function is constructed to control the voltage of the inverter and rectifier station, expressed by the formula: ; In the formula, This represents the closed-loop transfer function of the voltage loop.

[0046] Based on the symmetry characteristics of AC voltage, only the phase a current when the AC side of the inverter is disturbed is selected as the analysis example. The calculation methods for the phase b current and phase c current when the AC side of the inverter is disturbed are the same as those for the phase a current when the AC side of the inverter is disturbed, so they will not be repeated here.

[0047] Preferably, the specific steps for determining the current during AC side disturbances in the inverter are as follows: Obtain the instantaneous three-phase voltage and current at the inverter ports. Based on these instantaneous voltage and current, construct a DC voltage disturbance model and output the DC-side voltage disturbance of the inverter, expressed by the formula: ; In the formula, Indicates the port voltage conversion factor. Indicates the port current conversion factor. This represents the instantaneous three-phase voltage at the inverter port. This represents the instantaneous three-phase current at the inverter port. This indicates DC-side voltage disturbance in the inverter; The steady-state rated value of the inverter's AC side current is calculated based on the inverter's DC-side voltage disturbance, positive-sequence admittance, and negative-sequence admittance, and is expressed by the formula: ; In the formula, This represents the steady-state rated value of the phase a current on the AC side of the inverter. The signal quantity representing the duty cycle of phase a. The signal quantity representing the voltage of phase a; The current disturbance of the inverter's 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 transfer at the AC port of the rectifier station, and is expressed by the formula: ; In the formula, This represents the current disturbance of phase a current on the AC side of the inverter. This represents the duty cycle signal, with a value range of 0%-100%. The current during AC side disturbance is calculated based on the steady-state rated value of the inverter's AC side current and the current disturbance of the inverter's AC side current, and is expressed by the formula: .

[0048] See Figure 2-3 , Figure 2 To compare the total harmonic distortion rate of the algorithm (specifically, a PI controller with fixed parameters), Figure 3 The total harmonic distortion (THD) using the method described in this embodiment is 1.31%, which is 12.58% lower than that of the comparative algorithm (13.89%). Simultaneously, the amplitude of each harmonic is significantly reduced across the entire frequency band, verifying the harmonic suppression effect and effectiveness of the method described in this embodiment.

[0049] See Figure 4 The display shows the response curve of the inverter AC side voltage after being disturbed. The blue curve represents the response before PI parameter optimization, and the red curve represents the response after optimization. Unlike the existing technology of "no closed-loop control optimization", it achieves the fast response advantage of "current loop + voltage loop coordinated control". Figure 4 The horizontal axis represents time.

[0050] Example 2: This embodiment provides an electronic device that stores a computer program, which, when executed by a processor, implements the harmonic suppression method for offshore wind turbine generators as described in any embodiment of the present invention.

[0051] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural 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, where a, b, and c can be single or multiple.

[0052] Those skilled in the art will recognize that the units and algorithm steps described in the embodiments disclosed herein can be implemented using electronic hardware, computer software, or a combination of electronic hardware and software. Whether these functions are implemented 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 this application.

[0053] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0054] In the several embodiments provided in this application, any function, if implemented as a software functional unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0055] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

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 to 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 to 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 transfer function and closed-loop transfer function are constructed based on the positive-sequence impedance of the system. The stability of the open-loop transfer function and closed-loop transfer function 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, and the current and voltage of the inverter and rectifier station are controlled by the PI controller to suppress the harmonics of the offshore wind turbine.

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 6, characterized in that, 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.

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

9. The method for harmonic suppression of offshore wind turbine generators according to claim 8, characterized in that, 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.

10. The method for harmonic suppression of offshore wind turbine generators according to claim 9, characterized in that, 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 at the AC port of the rectifier station. The current during AC side disturbance 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.

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