Standards Development
This document applies to offshore wind farms grid-connected via VSC-HVDC with a voltage level of 110kV and above. It provides a uniform method for harmonic evaluation of offshore wind farms grid - connected via VSC-HVDC.
The indices evaluated in this document include: 2nd to 40th harmonics and 40th to 60th supraharmonics. The evaluation methods are categorized into predictive evaluation and monitoring - based evaluation.
This document specifies the general requirements, evaluation procedure, data collection, evaluation methods, and report structure for harmonic evaluation of offshore wind farms grid -connected via VSC-HVDC. Offshore wind farms connected to the power system through other voltage levels and other transmission methods may refer to the implementation.
As of the end of 2024, over fifty VSC-HVDC transmission projects have been commissioned in multiple countries including Germany, the United Kingdom, and China. The global cumulative installed capacity of offshore wind power has reached 86.2 GW, with VSC -HVDC interfaced offshore wind farms achieving a delivery scale at the 10 GW level. By 2028, it is projected that 13 additional VSC-HVDC-connected offshore wind farm systems will be deployed globally, including 3 new systems in China.
In a VSC-HVDC-connected offshore wind farm system, multiple wind turbines are interconnected simultaneously, and interactions between the power electronic converters of wind turbines and the VSC-HVDC transmission system lead to coupled power quality distur bance phenomena within the offshore wind farm grid-connected via VSC-HVDC. Therefore, it is imperative to conduct a comprehensive harmonic evaluation specific to such systems.
During the planning and feasibility study phase of an offshore wind farm grid -connected via VSC- HVDC, a predictive evaluation of harmonics shall be performed. The investors of offshore wind farms and VSC-HVDC transmission systems shall utilize the evaluati on results to identify potential harmonic risks in advance and implement mitigation measures. The predictive evaluation report shall be submitted to the grid operator prior to project commissioning.
During the commissioning phase of an offshore wind farm grid -connected via VSC-HVDC, a monitoring-based evaluation of harmonics shall be conducted. During the operation phase of such systems, a monitoring-based evaluation shall be initiated when equipment failures or grid anomalies caused by harmonics occur, or when there is ambiguity in harmonic source identification. The evaluation shall provide technical bases for power generation enterprises and grid operators to analyze the root cause and implement corrective actions.
Grid codes in many countries mandate wind farms to perform power quality assessments, including harmonic evaluation, prior to grid connection approval. However, thorough investigation reveals the current absence of harmonic assessment standards applicable to offshore wind farms interconnected via VSC-HVDC systems. Concurrently, the following limitations persist in renewable energy-related power quality evaluation methodologies:
(1) The existing standards have defined calculation methods for harmonic indices; however, they do not align with the practical requirements for harmonic evaluation workflows in offshore wind farm projects. Critical gaps remain, including the lack of stand ardized evaluation procedures and harmonized measurement protocols.
(2) Current standards specify harmonic calculation methods for AC -connected wind turbines but fail to address scenarios where wind farms are grid-connected via long-distance submarine cables or land cables. The influence of cable characteristics (e.g., dis tributed capacitance) on harmonic propagation mechanisms is not considered.
(3) Existing frameworks do not regulate supraharmonic evaluation (40 -60th harmonics) for offshore wind farms grid-connected via VSC-HVDC.
(4) Current standards are limited to AC grid-connection scenarios and have not considered the influence of VSC-HVDC systems on harmonic emission profiles and resonance propagation paths.
This proposal aims to facilitate the harmonization of harmonic evaluation standards across various national grid codes, and to establish harmonized evaluation frameworks for countries lacking such standards. Additionally, it enables investors in offshore wind farms and VSC -HVDC transmission systems to proactively identify potential harmonic -related risks, thereby mitigating equipment degradation risks and improving project cost-effectiveness. It ensures power quality compliance of grid-supplied electricity, enhancing end-user experience; provides enhanced power supply quality for neighboring consumers, safeguarding operational efficiency and reliability of industrial equipment. Furthermore, through the implementation of this document, operational data will be accumulated over time, offering field-validated datasets for equipment manufacturers to optimize equipment immunity levels against harmonics.
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