Offshore Wind Power Integration Research Articles

Composition and Control of a New Type of Hybrid Voltage-Source Converter Based on DRUs and FB-MMC for Large-Scale Offshore Wind Power Integration and Transmission

Composition and Control of a New Type of Hybrid Voltage-Source Converter Based on DRUs and FB-MMC for Large-Scale Offshore Wind Power Integration and Transmission

Improving short-term offshore wind speed forecast accuracy using a VMD-PE-FCGRU hybrid model

The integration of large-scale offshore wind power into the power grid presents significant challenges for grid operation and dispatch due to the variability and intermittency of offshore wind energy. However, non-stationarities and noise in wind speed time series pose challenges. This study proposes a VMD-PE-FCGRU methodology to address this challenge of predicting offshore wind speeds. Firstly, the Variational Mode Decomposition (VMD) algorithm decomposes the original wind speed signal, considering the strong fluctuations and high noise inherent to offshore wind energy. A corresponding performance evaluation index is established to assess the effectiveness of this deconstruction process. To further enhance the model's (GRU) ability to capture time series information, a Position Encoding layer (PE) has been added, and the network is deepened through a Fully Connected Neural Network (FCNN). This allows multi-dimensional time series features to be input into the Gated Recurrent Unit (GRU) network for forecast. The accuracy of the proposed method is then verified using measured historical data from the wind tower of an offshore wind farm in Guangdong. Experimental results demonstrate that the proposed method can accurately forecast short-term wind speeds for offshore wind farms, with a Mean Absolute Error (MAE) of 0.199 and a Mean Absolute Percentage Error (MAPE) of only 2.45%. Moreover, the qualified rate (r) reaches 100%, providing an accurate reference for real-time power grid dispatching and can inform decision-making for the integration of offshore wind power into the grid.

Analysis of the influence of large‐scale offshore wind power on the steady‐state voltage of the vicinity region of grid connection point

AbstractThe power characteristics of offshore wind power will change the regional power flow distribution and affect the regional voltage. Here, the direct‐drive wind turbine generator controlled by unity power factor is selected as the research object, and the influence of change of wind power on voltage at the grid connection point is analyzed from the simple integration model. Based on the two critical states of the external equivalent power of the grid connection point, an analytical expression of the output of wind power in the corresponding state is obtained, and the relationship among the critical state outputs, the output of wind power and the parameters at the grid connection point is drawn, hence the related influence laws is analyzed. The influence of change of wind power on voltage and regional reactive power and the reactance distribution of transmission lines near the grid connection point is considered to analyze the influence of offshore wind power on the vicinity region of grid connection point. The rationality of the conclusion is verified by study the cases of the integration of offshore wind power into Guangdong power grid, and some suggestions are put forward for the planning of offshore wind power integration.

Experimental Assessment of a Decentralized Control Strategy for a Back-to-Back Modular Multilevel Converter Operating in Low-Frequency AC Transmission

The Modular Multilevel Converter (MMC) has been widely used in high-power applications owing to its inherent advantages, including scalability, modularity, high-power density, and fault tolerance. MMCs have recently been used in Low-Frequency Alternating Current (LFAC) transmission, particularly in the integration of offshore wind power with onshore grids. However, LFAC applications produce significant voltage oscillations in floating capacitor voltages within the MMC. Early research efforts have successfully established and validated decoupled control strategies for LFAC-based MMC systems. However, validations are usually based on simulations or small-scale prototypes equipped with limited power cells. Consequently, this paper presents a decentralized voltage control strategy based on Nearest Level Control for an MMC-based LFAC system. Experimental results obtained with a 120-cell MMC prototype are presented to validate the effectiveness and operation of the MMC in LFAC applications.

Grid Integration of Offshore Wind Power: Standards, Control, Power Quality and Transmission

Grid Integration of Offshore Wind Power: Standards, Control, Power Quality and Transmission

Large-scale offshore wind energy integration by wind-thermal bundled power system: A case study of Yangxi, China

A large-scale offshore wind power integration has a reverse peak regulation effect on the electric load and requires newly built transmission corridors. This work adopts a wind-thermal (WT) bundled system for offshore wind power integration and transmission line capacity factor improvement. The Qingzhou I-VII offshore wind farms (5000 MW) and the Yangxi coal-fired power plant units #5, #6 (2 × 1240 MW) are taken as a case study. The offshore wind farms (OWF) act as the must-take generator to increase the renewable fraction while the thermal power plants (TPP) provide peak regulation service to trace the changing net load. The OWF and TPP share the transmission line and point of interconnection. The OWF integration level is determined by the 8760-h production simulation and the wind-thermal (W-T) capacity ratio is 1.4516:1 (3600 MW OWF) in the studied site. The curtailment rate, electricity shortage rate, transmission line capacity factor (CF), load following precision, renewable fraction, CO2 emission of WT-W3600 condition are 9.02%, 5.41%, 61.36%, 91.43%, 50.46%, 6.97 million ton/year. There is a trade-off relationship between renewable fraction and curtailment rate in the WT system which restricts higher OWF integration. The demand-side response technologies such as power-to-X and energy storage are required to break the trade-off relation and reduce the electricity shortage rate. The WT system is economically viable and the net present value (NPV), levelized cost of electricity (LCOE), internal rate of return (IRR) of WT-W3600 are 3.55 billion¥, 0.4859¥/kWh, 4.82%. Co-locating the OWF and the floating solar photovoltaic (PV) is the future direction that benefits the intensive exploitation of sea area and offshore renewable energy development.

Control and Capacity Design of Station-Hybrid HVDC System with DRU and MMC in Parallel for Offshore Wind Power Integration

Control and Capacity Design of Station-Hybrid HVDC System with DRU and MMC in Parallel for Offshore Wind Power Integration

Comprehensive optimization framework for transmission expansion planning with fractional frequency transmission system

AbstractThe Fractional Frequency Transmission System (FFTS) operates with low frequency to decrease the electrical length of AC transmission lines, consequently enhancing transmission capacity. The integration of renewable energy sources via FFTS will significantly impact power system planning. This paper presents a Fractional Frequency Transmission Expansion Planning (FF‐TEP) model, which considers the interaction between FFTS and the industrial‐frequency power grid. This model addresses the challenges posed by the integration of offshore wind power through FFTS, and takes several key factors into account, including the active power coupling of Modular Multilevel Matrix Converter (M3C), inverter capacity, and converter transformer capacity. To address the non‐convexity caused by AC power flow, this paper introduces a Genetic‐Particle Swarm Optimization algorithm (G‐PSO) with dynamic penalties tailored to the M3C structure. This approach incorporates both crossover and mutation operators from Genetic Algorithms (GA) into Particle Swarm Optimization (PSO). The penalty function dynamically adapts according to the M3C structure, resulting in improved global optimization while maintaining computational efficiency. The results of two case studies demonstrate that FFTS can significantly enhance transmission capacity while reducing cable charging power. This reduces investment costs and decreases voltage offset issues.

Large-scale offshore wind integration by wind-thermal-electrolysis-battery (WTEB) power system: A case study of Yangxi, China

Offshore wind power integration is a grand challenge due to the volatility, randomness and intermittency This work presents a wind-thermal-electrolysis-battery (WTEB) hybrid energy system designed to integrate large-scale offshore wind energy and reduce curtailment. The system composes of offshore wind farms (OWF), thermal power plants (TPP), electrolysis station, battery bank. The Qingzhou (geographic name) I-VII offshore wind farms (5000 MW) and the Yangxi (geographic name) coal-fired power plant units #5, #6 (2 × 1240 MW) are taken as a case study. The OWF is the indispensable generator and the renewable fraction increases with integration level. The TPP adjusts the load ratio to meet the changing net load. The electrolysis station consumes the excess electricity and the battery bank time-shifts the electricity to reduce the electrolyzer downtime. The recommended wind-thermal (W-T) capacity ratio is 1.452:1 in the studied case, namely 3600 MW OWF. The WTEB system breaks the trade-off relationship between renewable fraction (50.11%) and curtailment rate (1.48%) compared to traditional wind-thermal (WT) bundled system. The WPEB system improves the electricity shortage rate (4.74%), transmission line capacity factor (61.79%), load following precision (91.79%). The internal rate of return (IRR), levelized cost of electricity (LCOE), levelized cost of hydrogen (LCOH) of WTEB-W3600 are 34.70%, 0.5172 ¥/kWh, 29.76 ¥/kg. The WTEB hybrid energy system for a large-scale offshore wind power integration is first proposed and the techno-economic feasibility analysis proves the feasibility and forward-looking of the system. Collaborative capacity optimization of OWF, TPP, electrolysis station, battery can improve the system performance and economy. The wind-photovoltaic-thermal-electrolysis-battery (WPTEB) system co-locating the OWF and floating photovoltaic (PV) is an important development direction.

Harmonic filtering and fault ride‐through of diode rectifier unit and modular multilevel converter based offshore wind power integration

AbstractThe diode rectifier unit (DRU) is promising in offshore wind power integration due to its reliability and economy. Offshore AC voltage control is the key technology of the DRU‐based scheme. In this paper, a low‐cost offshore wind power integration system based on the DRU and the modular multilevel converter (MMC) in parallel on the rectifier side is proposed. The low‐capacity MMC rectifier is controlled to establish the offshore AC voltage amplitude and frequency, maintain all offshore wind active power transmitted by the DRU, and provide reactive power compensation and AC harmonic filtering for the DRU. Besides, the fault ride‐through strategies of both the offshore fault and the onshore fault are proposed. Moreover, the calculation method of the rated capacity of the MMC rectifier is derived. The time domain simulations of the hybrid system under typical operating conditions are investigated in PSCAD/EMTDC, and the feasibility of the proposed scheme is verified.

Numerical simulation of offshore wind power pile foundation scour with different arrangements of artificial reefs

The industrial integration of offshore wind power and marine ranches has been actively explored and developed in many countries. This emerging industrial synergy can significantly improve the ecological friendliness of offshore wind power and contribute to the development of the marine economy in the region. This industrial synergy is an important development direction for future offshore engineering. Artificial reefs (ARs) are critical components of marine ranches and are widely placed around offshore wind foundations (OWFs). The ARs can block the water flow and form a complex wake region behind it, which changes the original turbulence structure and reduces scour around the OWF. Therefore, determining the arrangement of ARs for scour protection around an OWF is of great engineering significance. In this study, a three-dimensional numerical model is established using a prototype of the first offshore wind power-marine ranch demonstration project in China. The turbulent change and sediment movement between the OWF and ARs are solved using the Reynolds-averaged Navier-Stokes (RANS) and sediment transport equations. Moreover, the variations in the maximum scour depth and scour volume around the OWF at different arrangements of ARs are explored. The results demonstrate that the arrangement of ARs weakens the horseshoe vortices in front of the OWF and destroys the vortex shedding behind the OWF, thereby producing a beneficial scour protection effect. Various arrangements of ARs have different effects on scour results around the OWF. Increasing the height of the AR could significantly reduce the scour results around the OWF and play an effective role in scour protection, followed by the tandem arrangement of ARs, whereas the parallel arrangement of ARs will produce negative scour effects. This study will serve a vital guiding role in the arrangement of ARs and practical significance for scouring protection around the OWF.

Modeling and Control of Modular Multilevel Matrix Converter for Low-Frequency AC Transmission

The modular multilevel matrix converter (M3C) is the core component in low-frequency AC (LFAC) transmission, which is a competitive scheme for offshore wind power integration. In this paper, the M3C control strategy with the reduced switching frequency SM voltage balancing method is proposed. First, based on the conventional αβ0 and dq transformations, the M3C mathematical model is derived. Then, the dual-loop control structure with outer loop and inner loop controllers commonly used in voltage source converters is applied to the M3C. The inner loop controller consists of the current tracking controller in the dq reference frame and the circulating current suppressing controller in the αβ0 reference frame; the outer loop controller is proposed for the offshore wind farm LFAC integration scenario. Additionally, according to the operating characteristics of full-bridge sub-modules (FBSMs), three characteristic variables are defined and a reduced switching frequency SM voltage balancing method based on the nearest level control (NLC) is proposed. Finally, time-domain simulations in PSCAD/EMTDC demonstrate the feasibility of the proposed control strategy.

Grid-Forming Control of Wind Turbines for Diode Rectifier Unit Based Offshore Wind Farm Integration

Offshore wind farms are the main trend of future wind power exploitation. The diode rectifier unit (DRU) shows great potential in offshore wind power integration due to its economy and reliability benefits, and stable AC voltage control of the offshore gird is the key technology of the DRU based scheme. In this paper, the sensitivities of the DRU based system are defined and the sensitivity calculation method is proposed. According to the sensitivity characteristics analysis, the relationship between the wind turbine (WT) active power (or reactive power) and the WT output voltage (or system frequency) is clarified. On this basis, a grid-forming control strategy for WT converters is proposed. The stable operation mechanism of the grid-forming WTs in the DRU based system is demonstrated according to the analysis of steady state operation point existence and small disturbance stability. The time domain simulations of two DRU based offshore wind farm integration systems are carried out in PSCAD/EMTDC, and the feasibility of the proposed grid-forming control is verified.

Design of Main Circuit Parameters for Modular Multilevel Matrix Converter in LFAC System

The low-frequency AC (LFAC) transmission is a competitive scheme for offshore wind power integration, in which the modular multilevel matrix converter (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C) is the key equipment. In this brief, the selection methods of the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C main circuit parameters are proposed. First, the maximum arm voltage is derived and the selection method of the sub-module (SM) number is established. Then, according to the switching function approach, the analytical expressions of the average SM capacitor current and the average SM capacitor voltage are derived. On this basis, the selection method of the SM capacitance is proposed. Additionally, the design principle of the arm inductance is proposed. Finally, a case is elaborated to illustrate the proposed M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C main circuit parameter selection methods and provide a reference for practical projects.

Dual-AC-port modular multilevel converter for hybrid frequency integration of offshore wind power: Modeling and control

Low frequency AC transmission system (LFAC) is a potential solution for deep-sea offshore wind power utilization besides HVAC and HVDC. Multi-port converter is the key device for the interconnection of hybrid frequency wind farms and power grid. An improved multi-port modular multilevel converter with dual AC ports and single DC port (DASD-MMC) is proposed as the key device for the interconnection among HVAC/HVDC/LFAC. The in-depth topology and working principle analysis are presented. The partitioned nearest level modulation method is proposed for high-voltage applications providing submodule capacitor voltage self-balancing ability. The mathematical model and the corresponding decoupling control strategy are presented afterward to realize the free power transfer among the three ports. To solve the output performance issues for hybrid HVAC and LFAC scenarios, an output current distortion suppression strategy is proposed with a novel cross-decoupling harmonic extraction method. Circulating current control strategy is presented with consideration of essential component analysis and calculation. Experiment and simulation validation and discussion are given, which show that the proposed DASD-MMC could provide a high quality hybrid frequency solution for offshore wind power collection and transmission.

Feasibility Study on Design of Offshore Wind Power Integration Single Pile Foundation

Feasibility Study on Design of Offshore Wind Power Integration Single Pile Foundation

Modular Combined DC-DC Autotransformer for Offshore Wind Power Integration with DC Collection

Offshore wind farms (OWFs) integration are attractive extensively for furnishing more robust power than land wind farms. This paper introduces a modular combined DC-DC autotransformer (MCAT), which contributes to the offshore wind power integration of DC grids with different voltage levels. Traditional DC transformers contains medium- or high-frequency converter transformers, which have the disadvantages of high manufacturing difficulty and cost. These shortcomings seriously affect the progress of commercial application of DC transformers. To solve these problems, in the proposed MCAT, converter transformers are replaced with a DC-isolation capacitor and a compensation inductor in series to reduce the footprint of offshore platforms and improve economy. Theoretical analysis is carried out for the MCAT operation principle. Selection methods of main circuit parameters for the MCAT are discussed in detail. Then, corresponding control strategies of the MCAT are proposed. Finally, the effectiveness of the proposed MCAT and its control strategies are validated by time domain simulations in PSCAD/EMTDC. The time-domain simulation results show the correctness of the main circuit parameters and the rationality of the MCAT control strategies.

Developing a long-lasting offshore wind business case towards a Dutch decarbonised energy system by 2050

The integration of large-scale offshore wind power in the energy system will have a major effect on electricity markets. It may lead to large market price volatility due to the inherent variability of wind energy in terms of power fluctuations, forecast errors and insufficient flexibility on the demand side. This study models future business cases for offshore wind farms in two reference national scenarios for the Netherlands, namely NECP2030 and TRANSFORM. Results show that the value of offshore wind in 2030, according to NECP scenario is 39.9 €/MWh, and that electricity price in the TRANSFORM scenario, which considers aggressive development towards a sustainable economy, is a high 104 €/MWh by 2050. To consider ways of improving the return on investment for offshore wind farms in future markets, an optimisation problem is defined, where the wind farm has the choice to either sell the generated electricity to the spot market or to an electrolyser. Results show a potential advantage in using an electrolyser to produce green hydrogen for offshore wind farms, with net profit of 41.4 M€, compared to when offshore wind farms sell electricity solely to the spot market, where the profits are 36 M€.

Techno-economic system analysis of an offshore energy hub with an outlook on electrofuel applications

The integration of cross-sectoral energy hubs into large-scale wind farms opens up existing structures to new applications and contributes to achieving renewable energy systems and climate protection targets. The offshore energy hub concept consists in establishing an artificially constructed energy conversion and distribution hub that addresses two energy-related markets by power supply to public grids and by potentially enabling the conversion of renewable electricity into hydrogen or ammonia and supplying it ashore. Hence, the energy hub concept enables smart integration of offshore wind power into gas grids. Power generation on demand from stored green gas is able to cover residual power loads at low carbon intensity. Electrofuel production provides also the opportunity to export renewable fuels for sectors with traditionally high greenhouse gas emissions, e.g., agriculture or transportation. In this contribution an energy hub system in the North Sea is modeled and simulated to determine production quantities and efficiencies of electricity, hydrogen and ammonia. When comparing the efficiencies of production, storage, and transport values of 45.1–65% for hydrogen and values of 52–52.3% for ammonia were determined. Re-conversion to electricity with fuel cells of both hydrogen and ammonia is less efficient and cost worthly than their use in electrofuel applications. Because of emerging and potential cost reductions a sensitivity analysis is performed where lower capital costs (50%) lead to cost reductions in hydrogen (42–45%) and ammonia production (40–42%). Results show that energy hubs can become sustainable pillars in future energy systems through improving cost-competitiveness of wind power.

Offshore wind power integration to support weak grid voltage for industrial loads using VSC-HVDC transmission system

This paper investigates the integration of the offshore wind power plant into the grid using voltage source converter high-voltage direct current (VSC-HVDC). The paper proposes both offshore and onshore converter stations control to support voltage variation in grid. Heavy industrial loads result in a weak grid. In this paper, the effect on industrial loads by the grid strength is shown. Then the paper proposes a solution for the grid voltage support for industrial loads connected to weak grids. The results showed that the increase of grid voltage from 0.7 pu to 1 pu at full load condition that provides a continuous operation without any interruption. The system was modelled using MATLAB/Simulink package.