Voltage harmonic suppression method and device for offshore wind power output system through hybrid commutation, terminal equipment and storage medium

Abstract

The invention discloses a voltage harmonic suppression method and device for offshore wind power through a hybrid commutation sending-out system, terminal equipment and a storage medium, and belongs to the field of offshore wind power, and the method comprises the steps: collecting a three-phase line voltage waveform of a diode uncontrolled rectification unit in the hybrid commutation sending-out system, carrying out the Fourier analysis, obtaining a line voltage fundamental component, and carrying out the voltage harmonic suppression of the three-phase line voltage waveform; the total harmonic distortion amount is calculated; whether the total harmonic distortion amount exceeds a preset threshold value or not is judged, if yes, the voltage at a PCC point in the hybrid commutation sending-out system is measured, and PCC voltage is obtained through measurement; and according to the PCC voltage, controlling an auxiliary converter in the hybrid commutation sending-out system to inject harmonic current into a diode uncontrolled rectification unit so as to eliminate the harmonic component of the PCC point voltage in the hybrid commutation sending-out system, and if not, maintaining the current operation state of the auxiliary converter unchanged. According to the invention, the problem of voltage harmonic waves existing in the hybrid commutation sending-out system in the prior art can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of offshore wind power, and in particular to a voltage harmonic suppression method and device for an offshore wind power hybrid converter transmission system, a terminal device and a storage medium. BACKGROUND

[0002] At present, offshore wind power is developing rapidly in the direction of large-scale and long-distance transmission. The hybrid transmission system based on diode uncontrolled rectifier unit and auxiliary converter has great advantages in cost and reliability.

[0003] When the hybrid converter transmission system is in steady state operation, the nature of the offshore wind turbine is closer to a current source, and the diode uncontrolled rectifier unit behaves as a harmonic voltage source on the AC side in steady state, resulting in a significant step waveform of the PCC voltage at the PCC point, and the voltage harmonic content increases significantly. This voltage harmonic not only directly affects the operation and control of the wind farm, but also generates harmonic currents of the corresponding frequency at the wind farm side, which further deteriorates the operation of the offshore wind farm and the power quality of the offshore AC power grid, and may even cause the wind turbine to be disconnected from the grid. SUMMARY

[0004] The present application provides a voltage harmonic suppression method and device for an offshore wind power hybrid converter transmission system, which can solve the voltage harmonic problem existing in the prior art hybrid converter transmission system.

[0005] To solve the above technical problems, an embodiment of the present application provides a voltage harmonic suppression method for an offshore wind power hybrid converter transmission system, comprising: Collecting the three-phase line voltage waveform of the diode uncontrolled rectifier unit in the hybrid converter transmission system; Performing Fourier analysis on the three-phase line voltage waveform to obtain a line voltage fundamental component; According to the line voltage fundamental component, the total harmonic distortion of the diode uncontrolled rectifier unit is calculated; determining whether the total harmonic distortion exceeds a preset threshold, If yes, the voltage at the PCC point in the hybrid converter transmission system is measured to obtain a PCC voltage, and according to the PCC voltage, the auxiliary converter in the hybrid converter transmission system injects a harmonic current into the diode uncontrolled rectifier unit to eliminate the harmonic component of the PCC point voltage in the hybrid converter transmission system, If not, the current operating state of the auxiliary converter is maintained unchanged.

[0006] Further, the calculation of the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage.

[0007] Further, the step of controlling the auxiliary converter in the hybrid converter-to-output system to inject harmonic current into the diode uncontrolled rectifier unit according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit.

[0008] Further, the extraction of harmonic voltage components of each frequency in the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter.

[0009] An embodiment of the present invention also provides a voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter, comprising: The waveform acquisition module is used to acquire the three-phase line voltage waveforms of the diode uncontrolled rectifier unit in the hybrid converter output system; The waveform analysis module is used to perform Fourier analysis on the three-phase line voltage waveform to obtain the fundamental component of the line voltage. The total harmonic distortion analysis module is used to calculate the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage. The harmonic suppression module is used to measure the voltage at the PCC point in the hybrid converter power transmission system when the total harmonic distortion exceeds a preset threshold, thereby obtaining the PCC voltage. Based on the PCC voltage, it controls the auxiliary converter in the hybrid converter power transmission system to inject harmonic current into the diode uncontrolled rectifier unit to eliminate the harmonic components of the PCC point voltage in the hybrid converter power transmission system. When the total harmonic distortion is determined not to exceed the preset threshold, the current operating state of the auxiliary converter is maintained unchanged.

[0010] Further, the calculation of the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage.

[0011] Further, the step of controlling the auxiliary converter in the hybrid converter-to-output system to inject harmonic current into the diode uncontrolled rectifier unit according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit.

[0012] Further, the extraction of harmonic voltage components of each frequency in the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter.

[0013] This application also provides a terminal device, including: One or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the voltage harmonic suppression method of the offshore wind power transmission system via hybrid converter as described in the above embodiments of the invention.

[0014] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the voltage harmonic suppression method for offshore wind power transmission via a hybrid converter system as described in the above embodiments of the invention.

[0015] The following benefits can be obtained by implementing the present invention: This invention provides a method, apparatus, terminal equipment, and storage medium for suppressing voltage harmonics in an offshore wind power transmission system via a hybrid converter system. The method first performs Fourier analysis on the three-phase line voltage waveforms of the diode uncontrolled rectifier unit in the hybrid converter system to obtain the fundamental component of the line voltage. Based on the fundamental component, the total harmonic distortion (THD) of the diode uncontrolled rectifier unit is calculated. When the THD exceeds a preset threshold, the voltage at the PCC point in the hybrid converter system is measured to obtain the PCC voltage. Based on the PCC voltage, the auxiliary converter in the hybrid converter system is controlled to inject harmonic current into the diode uncontrolled rectifier unit to eliminate the harmonic components of the PCC point voltage. Thus, by effectively eliminating voltage harmonics in the PCC voltage during steady-state operation of the hybrid converter system, the normal operation of the offshore wind farm is ensured. Attached Figure Description

[0016] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a voltage harmonic suppression method for an offshore wind power transmission system via hybrid converter, provided in a certain embodiment of this application. Figure 2 This is a schematic diagram of the structure of a hybrid converter power output system provided in a certain embodiment of this application; Figure 3 This is a system voltage and current diagram provided in one embodiment of this application, without considering the commutation process; Figure 4 This is a topology and line voltage waveform diagram of a diode uncontrolled rectifier unit provided in a certain embodiment of this application; Figure 5 This is a schematic diagram of harmonic voltage suppression provided in a certain embodiment of this application; Figure 6 This is a schematic diagram of harmonic voltage suppression control provided in a certain embodiment of this application; Figure 7 This is a simulation waveform diagram of the voltage and current of the offshore AC power grid before applying harmonic voltage suppression, provided in a certain embodiment of this application; Figure 8 This is a simulation waveform diagram of compensation for the 11th harmonic voltage provided in a certain embodiment of this application; Figure 9This is a simulation waveform diagram of compensation for the 13th harmonic voltage provided in a certain embodiment of this application; Figure 10 This is a simulation waveform diagram of simultaneous compensation for the 11th and 13th harmonic voltages provided in a certain embodiment of this application; Figure 11 This is a schematic diagram of the voltage harmonic suppression device of a hybrid converter transmission system for offshore wind power provided in a certain embodiment of this application; Figure 12 This is a schematic diagram of the structure of a terminal device provided in a certain embodiment of this application; The reference numerals for the accompanying drawings in the specification are as follows: Diode uncontrolled rectifier unit 1, auxiliary converter 2, high voltage DC bus 3, receiving-end MMC converter 4. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0020] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0024] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0025] See Figure 1 To address the voltage harmonic problem in existing hybrid converter power transmission systems, an embodiment of the present invention provides a method for suppressing voltage harmonics in an offshore wind power transmission system via a hybrid converter power transmission system, comprising: S1. Acquire the three-phase line voltage waveform of diode uncontrolled rectifier unit 1 in the hybrid converter output system; illustrative, see Figure 2 This is a schematic diagram of the specific structure of the hybrid converter transmission system described in this embodiment. The hybrid converter transmission system connects the offshore wind farm and the onshore AC power grid. Its purpose is to transmit the electricity generated by the offshore wind farm to the onshore AC power grid through the hybrid converter transmission system, thereby realizing the grid connection of the generated wind power. Specifically, one end of the diode uncontrolled rectifier unit 1 is connected to the offshore wind farm, and the other end of the diode uncontrolled rectifier unit 1 is connected to one end of the receiving-end MMC converter 4 through the high-voltage DC bus 3; the auxiliary converter 2 is connected to the offshore wind farm, and the other end of the receiving-end MMC converter 4 is connected to the onshore AC power grid.

[0026] Indicatively, to reduce the harmonic content of the diode uncontrolled rectifier unit 1 and improve the power factor of the system, multiple 6-pulse single diode bridges can be staggered by a certain phase and connected in series to construct a multi-pulse uncontrolled rectifier unit. The more pulses constructed, the lower the harmonic content and the higher the power factor of the diode uncontrolled rectifier unit 1. However, the number of power devices such as diodes will increase exponentially, and the manufacturing difficulty of the phase-shifting transformer will also increase exponentially. In this embodiment, after comprehensively considering the optimization benefits and economy, the diode uncontrolled rectifier unit 1 uses a 6-pulse single diode bridge. It is formed by connecting two 6-pulse diode bridges on the input side through a phase-shifting transformer and connecting them in parallel on the DC side to form a 12-pulse uncontrolled rectifier unit.

[0027] S2. Perform Fourier analysis on the three-phase line voltage waveform to obtain the fundamental component of the line voltage; illustrative, see Figure 3 This is the system voltage and current diagram without considering the commutation process. At this time, the AC voltage presents an ideal stepped waveform, while the DC current exhibits the characteristics of a 6-pulse wave. Specifically, assuming a constant DC voltage and a 120° square wave AC voltage, after acquiring the three-phase line voltage waveforms of the diode-uncontrolled rectifier unit 1 in the hybrid converter output system in step S1, and without considering the commutation process, Fourier decomposition of the three-phase line voltage waveforms yields: ; In the formula, This refers to the three-phase line voltage; This is the fundamental component of the line voltage; For harmonic order; This represents the upper limit of the harmonic order; ω is the angular frequency.

[0028] S3. Calculate the total harmonic distortion of the diode uncontrolled rectifier unit 1 based on the fundamental component of the line voltage; Schematic illustration, in the calculation of the fundamental component of the line voltage Then, it is necessary to extract each harmonic component and calculate its effective value, and then determine the degree of voltage harmonic pollution at the PCC point by calculating the total harmonic distortion of the diode uncontrolled rectifier unit 1.

[0029] In a preferred embodiment, calculating the total harmonic distortion of the diode uncontrolled rectifier unit 1 based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit 1 is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage. illustrative, see Figure 4 (a) is a topology diagram of the 12-pulse uncontrolled rectifier bridge in diode uncontrolled rectifier unit 1; see also Figure 4 (b) is the voltage waveform of diode uncontrolled rectifier unit 1 without considering the commutation process; Figure 4 (a) shows a dual-bridge 12-pulse converter that uses a three-winding transformer to offset the two single-diode bridges by 30°. Therefore, the total harmonic distortion of a hybrid converter output system actually using a 12-pulse uncontrolled rectifier unit can be calculated using a 6-pulse single-diode bridge. By comparing... Figure 3 and Figure 4 As can be seen from the waveform, the 12-pulse uncontrolled rectifier unit has 12 pulses in one cycle, with a total of 7 levels; Specifically, based on the fundamental component of the line voltage The effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of the line voltage at each frequency are calculated using the following formulas: ; In the formula, This represents the effective value of the fundamental line voltage of a hybrid converter output system using a 12-pulse uncontrolled rectifier unit. This indicates a hybrid converter output system using a 12-pulse uncontrolled rectifier unit. RMS value of subharmonic components; Specifically, based on the fundamental effective value of the line voltage and the effective values ​​of each harmonic component of the line voltage The total harmonic distortion of the diode uncontrolled rectifier unit 1 is calculated using the following formula: ; In the formula, This represents the total harmonic distortion.

[0030] S4. Determine whether the total harmonic distortion exceeds a preset threshold. If so, the voltage at point PCC in the hybrid converter power transmission system is measured to obtain the PCC voltage; based on the PCC voltage, the auxiliary converter 2 in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit 1 to eliminate the harmonic components of the PCC voltage in the hybrid converter power transmission system. If not, then the current operating state of the auxiliary converter 2 remains unchanged; Indicative, based on the calculated total harmonic distortion. Determine whether harmonic suppression is necessary; Total Harmonic Distortion (THD) The larger the value, the higher the harmonic content of the diode-controlled rectifier unit 1. When the total harmonic distortion is higher... When the voltage exceeds the preset threshold, harmonic suppression is required. If this voltage harmonic is not dealt with, the operation of the offshore wind farm and the power quality will deteriorate significantly. Specifically, the schematic diagram for harmonic voltage suppression is as follows: Figure 5 As shown, Figure 5 middle To actively inject harmonic current at the PCC point into auxiliary converter 2; This is the harmonic voltage source on the AC side of the diode uncontrolled rectifier unit 1. The PCC voltage on the AC side of diode uncontrolled rectifier unit 1; In a preferred embodiment, controlling the auxiliary converter 2 in the hybrid converter output system to inject harmonic current into the diode uncontrolled rectifier unit 1 according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter 2 in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit 1. Indicatively, when the auxiliary converter 2 actively injects a specific harmonic current into the diode uncontrolled rectifier unit 1 At that time, its equivalent impedance on the AC side The corresponding frequency of the reverse harmonic voltage is generated. This voltage is superimposed on the valve-side voltage of the diode uncontrolled rectifier unit 1, which can eliminate the harmonic components of the corresponding frequency in the PCC voltage. When suppressing the harmonic voltage, the auxiliary converter 2 needs to output and bear a larger harmonic current. The current source characteristics of the offshore wind farm mean a larger equivalent harmonic impedance. Therefore, the harmonic current injected into the PCC point by the auxiliary converter 2 mainly flows to the diode uncontrolled rectifier unit 1, and will not affect the power quality of the offshore wind farm current. On the contrary, due to the improvement of the PCC voltage quality, the harmonic distortion of the wind farm output current will be reduced, and the waveform quality of the current can be improved. Specifically, the suppression of harmonic voltage requires the extraction of harmonic components first; In a preferred embodiment, extracting the harmonic voltage components of each frequency in the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter. This embodiment utilizes a harmonic extraction algorithm based on synchronous rotating coordinate transformation to extract the harmonic voltage components of each frequency in the PCC voltage. Specifically, the PCC voltage is transformed in a synchronous rotating coordinate system, converting the harmonic voltage components of each frequency in the PCC voltage into DC components and the remaining components into AC components. Then, a low-pass filter (LPF) is used to extract the harmonic voltage components of each frequency from the mixed signal. Figure 6 (a) and Figure 6 (b) PCC voltage, The d-axis components of the harmonic voltage components at each frequency extracted from the PCC voltage are shown. The q-axis components of the harmonic voltage components at each frequency extracted from the PCC voltage; Then, the d-axis components of the harmonic voltage components of each frequency extracted from the PCC voltage are... and q-axis components After comparing and subtracting the value from the preset reference value, the result is sent to a PI controller. After processing by the PI controller and inverse coordinate transformation, the additional component of the voltage modulation signal that suppresses the corresponding harmonic is obtained. The harmonic current can then be calculated based on this additional component of the voltage modulation signal. The aforementioned auxiliary converter 2 actively injects a harmonic current ih of the corresponding frequency into the diode uncontrolled rectifier unit 1, thereby ultimately eliminating the voltage harmonic components of the corresponding frequency in the PCC voltage.

[0031] To better illustrate this application, a steady-state simulation model of the hybrid converter power transmission system was built based on a simulation platform. The offshore wind turbines were modeled using a convergent model, with an active power output of 100MW assumed during stable operation. The onshore REC employed conventional UDC-Q control, maintaining a constant DC bus voltage of 100kV.

[0032] Figure 7 The simulated voltage and current waveforms of the offshore AC power grid before applying harmonic voltage suppression are shown. Figure 7 (a) is the PCC voltage, with a THD of 7.58%, which has a large harmonic content, mainly the 11th and 13th harmonics. Figure 7 (b) represents the alternating current of the offshore wind field. Figure 7 (c) is the AC current for auxiliary converter 2. Figure 7 (d) represents the AC current of diode uncontrolled rectifier unit 1. It can be found that the THD of the AC current of the offshore wind farm, auxiliary converter 2 and diode uncontrolled rectifier unit 1 are all below 5%. This is because the offshore wind farm exhibits current source characteristics to the outside world, and the current harmonic content of the system is relatively lower. At this time, auxiliary converter 2 is mainly responsible for providing reactive current to maintain the voltage frequency stability of PCC.

[0033] Figure 8 and Figure 9 Simulation results for compensation of the 11th and 13th harmonic voltages are presented, respectively. Figure 8 (a) shows that the 11th harmonic of the PCC voltage is compensated at this time, and the voltage THD decreases from 7.58% to 5.24%, resulting in a significant improvement in power quality. Figure 8 (b) It can be seen that the wind farm basically does not compensate for harmonic currents at this time, and at the same time, by Figure 8 (c) As can be seen, at this time, in addition to outputting the fundamental reactive current, auxiliary converter 2 also outputs the 11th harmonic current to compensate for the harmonic voltage. Due to the large harmonic impedance of the offshore wind farm exhibiting current source characteristics, the harmonic current actively injected by auxiliary converter 2, such as... Figure 8 (d) shows that the main current flows through the DRU, which increases the harmonic content of its alternating current, and the current THD increases from 3.73% to 7.49%.

[0034] Figure 9 The simulation results shown are consistent with Figure 8 Similarly, the change from suppressing the 11th harmonic voltage to suppressing the 13th harmonic voltage demonstrates that the harmonic suppression method proposed in this application allows for the free selection of the desired harmonic voltage frequency without affecting the characteristics of other frequency voltages and currents. Figure 9 (a) It can be seen that the 13th harmonic of the PCC voltage is compensated at this time, and the total THD of the voltage decreases from 7.58% to 5.81%, resulting in a significant improvement in power quality. Figure 9 (b) It can be seen that the wind farm basically does not compensate for harmonic currents at this time, and at the same time, by Figure 9 (c) As can be seen, at this time, in addition to outputting the fundamental reactive current, auxiliary converter 2 also outputs the 13th harmonic current to compensate for the harmonic voltage. Due to the large harmonic impedance of the offshore wind farm exhibiting current source characteristics, the harmonic current actively injected by auxiliary converter 2, such as... Figure 9 (d) shows that the main current flows through the DRU, which increases the harmonic content of its alternating current, and the current THD increases from 3.73% to 5.88%.

[0035] Figure 10 Simulation results for simultaneous compensation of the 11th and 13th harmonic voltages. (From...) Figure 10 (a) It can be seen that the PCC voltage THD decreased from 7.58% to 3.16%, indicating a significant improvement in power quality while still meeting the 5% total harmonic content requirement. Figure 10 (b) It can be seen that the THD of the AC current in the wind farm decreased significantly, from 2.97% to 1.04%, indicating that the harmonic voltage suppression method proposed in this application not only does not affect the power quality of the AC current in the wind farm, but also further reduces its current harmonic content. Meanwhile, from Figure 10(c) As can be seen, at this time, in addition to outputting the fundamental reactive current, auxiliary converter 2 also outputs 11th and 13th harmonic currents to compensate for harmonic voltage. Due to the large harmonic impedance of offshore wind farms exhibiting current source characteristics, the harmonic current actively injected by auxiliary converter 2, such as... Figure 10 (d) shows that the main current flows through the DRU, increasing the harmonic content of its AC current, with the current THD increasing from 3.73% to 7.87%. In order to achieve harmonic voltage suppression, the auxiliary converter 2 withstands greater current harmonics, and the 11th and 13th harmonic contents in its output current are significantly increased, which leads to an increase in the capacity requirement of the auxiliary converter 2.

[0036] See Figure 11 This invention provides a voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter, comprising: The waveform acquisition module is used to acquire the three-phase line voltage waveforms of the diode uncontrolled rectifier unit in the hybrid converter output system; The waveform analysis module is used to perform Fourier analysis on the three-phase line voltage waveform to obtain the fundamental component of the line voltage. The total harmonic distortion analysis module is used to calculate the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage. The harmonic suppression module is used to measure the voltage at the PCC point in the hybrid converter power transmission system when the total harmonic distortion exceeds a preset threshold, thereby obtaining the PCC voltage. Based on the PCC voltage, it controls the auxiliary converter in the hybrid converter power transmission system to inject harmonic current into the diode uncontrolled rectifier unit to eliminate the harmonic components of the PCC point voltage in the hybrid converter power transmission system. When the total harmonic distortion is determined not to exceed the preset threshold, the current operating state of the auxiliary converter is maintained unchanged.

[0037] In a preferred embodiment, calculating the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage.

[0038] In a preferred embodiment, controlling the auxiliary converter in the hybrid converter-to-output system to inject harmonic current into the diode uncontrolled rectifier unit according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit.

[0039] In a preferred embodiment, extracting the harmonic voltage components of each frequency in the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter.

[0040] See Figure 12 One embodiment of this application also provides a terminal device, including: One or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the voltage harmonic suppression method of the offshore wind power transmission system via hybrid converter as described above.

[0041] The processor controls the overall operation of the terminal device to complete all or part of the steps of the voltage harmonic suppression method for offshore wind power transmitted via a hybrid converter system. The memory stores various types of data to support the operation of the terminal device. This data may include, for example, instructions for any application or method operating on the terminal device, as well as application-related data. The memory can be implemented using any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Read-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0042] In an exemplary embodiment, the terminal device may be implemented by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components to perform the voltage harmonic suppression method of the offshore wind power transmission system via hybrid converter as described in any of the above embodiments, and to achieve the same technical effect as the above method.

[0043] In another exemplary embodiment, a computer-readable storage medium including a computer program is also provided. When executed by a processor, the computer program implements the steps of the voltage harmonic suppression method for offshore wind power transmitted via a hybrid converter system as described in any of the foregoing embodiments. For example, the computer-readable storage medium may be the aforementioned memory including the computer program, which may be executed by a processor of a terminal device to perform the voltage harmonic suppression method for offshore wind power transmitted via a hybrid converter system as described in any of the foregoing embodiments, and achieve the same technical effects as the aforementioned method.

[0044] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for suppressing voltage harmonics in an offshore wind power transmission system via a hybrid converter, characterized in that, include: Acquire the three-phase line voltage waveforms of the diode-controlled rectifier unit in the hybrid converter output system; Fourier analysis was performed on the three-phase line voltage waveforms to obtain the fundamental component of the line voltage; The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the fundamental component of the line voltage. Determine whether the total harmonic distortion exceeds a preset threshold. If so, the voltage at the PCC point in the hybrid converter output system is measured to obtain the PCC voltage; Based on the PCC voltage, the auxiliary converter in the hybrid converter power supply system is controlled to inject harmonic current into the diode uncontrolled rectifier unit to eliminate harmonic components of the PCC point voltage in the hybrid converter power supply system. If not, then the current operating state of the auxiliary converter remains unchanged.

2. The voltage harmonic suppression method for offshore wind power transmission via a hybrid converter system as described in claim 1, characterized in that, The calculation of the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage.

3. The voltage harmonic suppression method for offshore wind power transmission via a hybrid converter system as described in claim 1, characterized in that, The step of controlling the auxiliary converter in the hybrid converter-to-output system to inject harmonic current into the diode uncontrolled rectifier unit according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit.

4. The voltage harmonic suppression method for offshore wind power transmission via a hybrid converter system as described in claim 3, characterized in that, The extraction of harmonic voltage components at each frequency from the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter.

5. A voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter, characterized in that, include: The waveform acquisition module is used to acquire the three-phase line voltage waveforms of the diode uncontrolled rectifier unit in the hybrid converter output system; The waveform analysis module is used to perform Fourier analysis on the three-phase line voltage waveform to obtain the fundamental component of the line voltage. The total harmonic distortion analysis module is used to calculate the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage. The harmonic suppression module is used to measure the voltage at the PCC point in the hybrid converter output system when the total harmonic distortion exceeds a preset threshold, and to obtain the PCC voltage. Based on the PCC voltage, the auxiliary converter in the hybrid converter power supply system is controlled to inject harmonic current into the diode uncontrolled rectifier unit to eliminate harmonic components of the PCC point voltage in the hybrid converter power supply system. When the total harmonic distortion is determined not to exceed the preset threshold, the current operating state of the auxiliary converter is maintained unchanged.

6. The voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter as described in claim 5, characterized in that, The calculation of the total harmonic distortion of the diode uncontrolled rectifier unit based on the fundamental component of the line voltage includes: Based on the fundamental component of the line voltage, the effective value of the fundamental wave of the line voltage and the effective values ​​of each harmonic component of the line voltage are calculated. The total harmonic distortion of the diode uncontrolled rectifier unit is calculated based on the effective value of the fundamental frequency of the line voltage and the effective values ​​of the harmonic components of each frequency of the line voltage.

7. The voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter as described in claim 5, characterized in that, The step of controlling the auxiliary converter in the hybrid converter-to-output system to inject harmonic current into the diode uncontrolled rectifier unit according to the PCC voltage includes: Extract the harmonic voltage components of each frequency from the PCC voltage; The harmonic voltage components of each frequency are subtracted from the preset reference values ​​of the corresponding frequencies. The error signals obtained by subtraction are processed by a preset PI regulator and coordinate inverse transformation to generate the three-phase harmonic voltage modulation additional components corresponding to each frequency harmonic. Based on the three-phase harmonic voltage modulation additional components corresponding to each harmonic frequency, the auxiliary converter in the hybrid converter power transmission system is controlled to inject harmonic current into the diode uncontrolled rectifier unit.

8. The voltage harmonic suppression device for an offshore wind power transmission system via hybrid converter as described in claim 7, characterized in that, The extraction of harmonic voltage components at each frequency from the PCC voltage includes: The PCC voltage is subjected to a coordinate transformation in a synchronous rotating coordinate system to obtain a mixed signal; wherein, the mixed signal includes an AC component and DC components corresponding to each frequency harmonic; The harmonic voltage components of each frequency are extracted from the mixed signal using a preset filter.

9. A terminal device, characterized in that, include: One or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the voltage harmonic suppression method for offshore wind power transmission via hybrid converter system as described in any one of claims 1-4.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the voltage harmonic suppression method of the offshore wind power transmission system via hybrid converter as described in any one of claims 1-4.

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