HVDC - enabling the transition to an energy system based on renewables

Objectives : The world is getting more polluted day by day and living conditions are getting harder and harder. The Covid 19 process explains this situation even better. Global warming will show its effect more heavily if measures are not taken. There is a close relationship between global warming and the type and method of energy used. The use of fossil fuels by people pollutes the environment too much, and the use of alternative energy sources is gaining importance instead. Here, the issue of use and management of renewable energy sources comes to the fore. Turkey is a country with rich renewable energy resources and experience in cooperatives. In this study, it is aimed to reveal the current situation and problems of renewable energy cooperatives, which can be a model for managing Turkey’s renewable energy resources.Methods : In the study, a literature review method was used by examining domestic and foreign resources related to renewable energy and renewable energy cooperatives. Some of the data obtained were arranged in tables and used in the study.Results and Discussion : It is very important for Turkey to develop renewable energy resources and increase the share of renewable energy resources among other resources. Because Turkey is a developing country and its population is increasing day by day. It is essential to use renewable energy for the energy need of the increasing population and the least environmental pollution. Within the scope of 2023 targets in Turkey, it is planned to produce 34 thousand MW of hydroelectric, 20 thousand MW of wind energy, solar energy, 5 thousand MW, 1,000 MW of geothermal energy and 1,000 MW of geothermal energy and biomass energy. In order to achieve this goal, it is planned to invest approximately 60 billion dollars in renewable energy sources. Cooperatives are one of the most effective ways in which Turkey can use its renewable energy resources. Because cooperative is a method known to the Turkish society and it would be beneficial to transfer it to the renewable energy field.Conclusion Turkey is a developing country and its energy needs are increasing day by day. It is very important to use the renewable energy resources it has correctly and in a planned way. In this respect, it should be understood that renewable energy cooperatives are quite compatible with Turkey. Turkey should provide the necessary legal and administrative structure for the development of renewable energy cooperatives and develop it with financial support in order to make its increasing energy needs sustainable.

Recently, offshore wind farms have emerged as the most promising sector in the global renewable energy industry. The main reasons for the rapid development of offshore wind farms includes much better wind resources and smaller environmental impact (e.g., audible noise and visual effect). However, the current state of the offshore wind power presents economic challenges significantly greater than onshore. In this thesis, a novel interconnecting method for permanent magnet synchronous generator (PMSG)-based offshore wind farm is proposed, where cascaded pulse-width modulated (PWM) current-source converters (CSCs) are employed on both generator- and grid-side. With the converters in cascade to achieve high operating voltages, the proposed method eliminates the need for bulky and very costly offshore converter substation which is usually employed in voltage source converter (VSC) high voltage DC (HVDC)-based counterparts. Related research in terms of control schemes and grid integration are carried out to adapt the proposed cascaded CSC-based offshore wind farm configuration. The large distance between generator- and grid-side CSC in the proposed wind farm configuration addresses significant challenges for the system control. In order to overcome the problem, a novel decoupled control scheme is developed. The active and reactive power control on the grid-side converters are achieved without any exchange of information from the generator-side controller. Therefore, the long distance communication links between the generator- and grid-side converters are eliminated and both controllers are completely decoupled. At the same time, the maximum power tracking control is achieved for the generator-side converters that enable full utilization of the wind energy. Considering inconsistent wind speed at each turbine, a coordinated control scheme is proposed for the cascaded CSC-based offshore wind farm. In proposed control strategy, the wind farm supervisory control (WFSC) is developed to generate the optimized dc-link current control. This enables all the turbines to independently track their own MPPT even with inconsistent wind speed at each turbine. Grid integration issues, especially the fault ride-through (FRT) capability for the cascaded CSC-based offshore wind farm are addressed. Challenges in implementing existing FRT methods to the proposed offshore wind farm are identified. Based on this, a new FRT strategy using inherent short circuit operating capability of the CSC is developed. Moreover, the mitigation strategy is developed to ensure the continuous operation of the cascaded CSC-based offshore wind farm when one or more turbines fail to operate. Simulation and experimental verification for various objectives are provided throughout the thesis. The results validate the proposed solutions for the main challenges of the cascaded current source converter based offshore wind farm.

There is a trend towards increasing the use of renewable energy resources worldwide. In addition to countries' efforts to increase this with the help of laws, the industry is also trying to expand the use of RE since the vast majority of the emissions are produced by the industry. Although Türkiye has rich renewable energy resources, these resources cannot yet be used effectively. Renewable energy certificate is one of the latest methods to reduce greenhouse gas emissions with the help of market mechanisms. Although renewable energy certificate is a very incipient concept for Türkiye, it has a significant potential to encourage and promote the usage and investments of renewable energy. In this study, current trends, and future expectations regarding renewable energy certificate in Türkiye have been compiled in line with the opinions of renewable energy certification experts from sector. It is thought that such analysis will be a guide for the sector and lawmakers on this subject. It is expected that the increase in academic discussions on market-based carbon emission reduction approaches will both contribute to the awareness of industry and the success of policies of national certification institutions. In this way, the payments made by industrialists in Türkiye to certification institutions abroad can be prevented from increasing at a level that would affect the current account deficit in the long term.

The global energy transition is characterized by a shift from fossil fuels such as coal, oil, and natural gas to cleaner and more sustainable energy sources. It is emphasized that hydrogen energy has significant potential for the development of innovative business, international trade, and energy transition for a sustainable post-carbon future. Currently, most hydrogen is consumed locally, without significant volumes of interstate supplies. It is noted that the development of this market faces many technical challenges, including high costs of producing “green” hydrogen, technical difficulties with the infrastructure for its transportation and storage due to low density, and the need to create large-scale infrastructure. Demand for hydrogen is growing as it plays a key role in decarbonization and greenhouse gas emissions reduction, especially in heavy industry, transportation, and energy systems. In the short term, hydrogen trade will likely occur mainly between neighboring countries through pipelines, limiting the scope of international trade until cost-reducing technologies are developed. In the long term, as demand for green hydrogen grows, especially in Europe and Asia, the trend toward active trade in this resource will gradually change. According to the most optimistic forecasts, the global hydrogen market will gradually grow until 2030, and the volume of international hydrogen trade may reach 120 million tons per year. It has been theorized that hydrogen is becoming increasingly important in the global energy system, and the geopolitics of energy trade will inevitably change. Energy geopolitics has traditionally been dominated by fossil fuel exporters such as the Middle East and Russia. However, the transition to hydrogen has the potential to decentralize energy production, making countries with rich renewable energy resources, such as the Persian Gulf, North Africa, and parts of Europe, key players in the new hydrogen market. This underscores the importance of developing international hydrogen supply chains, particularly from regions rich in renewable energy sources, such as North Africa, the Middle East, and Australia. Institutional support for the energy transition for a sustainable post-carbon future is implemented at the global and macro levels. At the global level, through a system of rules and regulations for the international market, international trade agreements and customs regulation, and international coordination on the implementation of hydrogen quality and safety standards. At the macro level, through government institutions, regulatory frameworks, and hydrogen economy development strategies, which have already become an integral part of the energy plans of many countries seeking to achieve carbon neutrality, reduce greenhouse gas emissions, and improve energy security. It is substantiated that the hydrogen market will face a difficult path related to solving technical and economic issues. However, thanks to the development of innovative business and technological innovations, support from governments, private investors, and various stakeholder groups, this sector has a great chance to become a key player in the future energy landscape, playing an important role in the decarbonization of the global economy. Keywords: innovative business, institutional support, energy transition, hydrogen, global hydrogen economy, energy geopolitics, decarbonization, sustainable development, sustainable post-carbon future, green transition, green investments, technological innovation, international trade, emissions trading system, regulation, strategic interests, economic interests, strategy of hydrogen use for energy, energy strategy, strategizing the hydrogen economy, country strategies, global development triggers, trade policy, environmental policy, international trade agreements, customs regulation, international trade.

Energy consumption is the indicator of the development of a country. An adequate power supply is a prerequisite of sustainable development, where Bangladesh has been struggling. This study focuses on the technological barriers of renewable energy implementation in Bangladesh, which has salient renewable energy sources: biomass, solar power, solar photovoltaic (PV) cells, wind energy, and hydroelectricity. Despite having rich renewable energy resources, the country still depends on its gas and oil reserve for power generation. The geographic significance of installing new sustainable technologies like wind power and biomass power plants has been studied in this research. Besides, to profile the socio-economic barriers provoking behind the insurance of renewable energy sources for the mass population, a comprehensive survey was conducted with 200 individuals, including 50 experts on renewable energy research. Quantitative analysis of issues like the monthly electricity bill, types of power sources used up, public satisfaction, and consciousness, along with their concepts regarding sustainable technology fabrication to synthesize renewable energy, were conducted. Finally, all qualitative and quantitative outputs were statistically analyzed to figure out the actual status of renewable energy usage in Bangladesh's perspective simultaneously, which is vital for us to ensure new renewable energy sources to achieve environmental sustainability for the future.

The future development of energy islands in North Sea is going to assist the further growth of offshore wind farms in a territory characterized by rich wind energy resources. The development of offshore wind farms in Aegean Sea, which is characterized by high mean annual wind velocities, is in the initial phase while it is foreseen that by 2050 the electricity generated by offshore wind farms will have a high share in the energy mix in Greece. The future interconnection of the electric grids of the small islands in Aegean Sea with the grid of continental Greece is going to trigger the development of new renewable energy installations in these islands reducing the current use of oil-based fuels in them. The development of offshore wind farms in Aegean Sea could be combined with green hydrogen production, when it is profitable, while it could be also used in the future for electricity generation from sea waves. The future development of physical energy islands in the Archipelago combined with the development of offshore wind farms and the interconnection of the small islands' grids could promote the further development of the rich solar and wind energy resources in Aegean Sea assisting the de-carbonization of the Greek power system. The current work could be useful to policy makers, to local and regional authorities as well as to energy companies which are willing to invest in renewable energy systems in Aegean Sea.

In the international and regional interconnection of the power grid, submarine cable transmission engineering is a critical component for network construction and optimizing energy allocation. This paper describes the condition of the regional power grid interconnection of submarine cable projects around the world since the 1990's and the development trends of cross ocean power grid connection projects in different countries. It summarizes and analyses the electricity transmission method applied in submarine cable projects. It provides references and insights to the research for electricity transmission method used in the cross ocean interconnecting projects and to the choice of transmission method adopted in the interconnecting projects. It points out advantages and shortcomings of the direct current transmission system applied in submarine cable projects and the strong point that VSC HVDC is used in the submarine cable projects. In the process of achieving grid internationalization, regional power grid interconnection and optimal energy allocation, submarine cable transmission engineering is an important component for network construction. In recent years, with the development of international power transmission technology, together with the trend of economic integration, optimal allocation of energy and reducing the impact on the environment, the cross-sea power transmission, manufacturing technology of the submarine cable and submarine cable engineering technology continues to make progress. The construction of submarine cable is constrained by geographical construction conditions, ocean engineering conditions and construction equipment. The construction involves a wide range of technology with a large investment scale and complex techniques. This construction would be separated into two stages. The preparation stage includes engineering design, submarine cable routing, cable manufacturing and transportation. The construction stage is composed of submarine cable routing orientation, submarine cable laying, on-land equipment installation, test and commissioning and quality control of the work. The main elements of the submarine cable transmission project construction includes regional power grid interconnection across the waters, power supply to oceanic islands and an oil drilling platform and transport marine renewable energy through grid-connected. Impacted from international energy resource optimal utilization, improving national energy safety and reliability from each country and realizing power exchange among different countries, the submarine cable construction can continue to push the international energy structure change, establishing global energy structure for a further development.

The present paper describes an Electric Vehicle (EV) charging station that provides ancillary services to the main AC grid, as for example frequency support and synthetic inertia. Due to the Direct Current (DC) nature of these loads and the easier integration of renewable energies, a DC Microgrid is considered to power the charging station. Targeting both DC grid voltage stability and the capability to support the main AC grid, nonlinear control laws based on Lyapunov theory and backstepping are developed for local and primary control levels (droop control). The proposed controllers are validated via MATLAB-Simulink simulations in a 25 kW DC Microgrid with PV production, Vehicle to Grid (V2G) mode of operation, fast and slow vehicle charge, ancillary services to the AC main grid and islanded mode operation.

The paper considers a previously unreported control approach for the control of off-shore DFIG-based wind farm grid with line commutated HVDC connection. The method is applicable for wind farms based-on doubly fed induction generators (DFIGs) or generators interfaced with full-rated power electronic converters. The paper focused on DFIG- based generation. The proposed control scheme allows each wind turbine to share in the voltage and frequency control of the offshore grid. The classical approach of using droop characteristics for adjusting the voltage and frequency according to the power flow of each turbine is employed. In result, the offshore grid is controlled by each turbine using only the electrical variables of its local connection point. The proposed control approach is validated via PSCAD simulations of normal operation regime and of ride-through operation under loss of the main onshore AC grid. The results confirm very good active and reactive power sharing between wind-farm DFIGs while frequency and voltage deviations in the off-shore grid are very small.

DFIG-based offshore wind power plant connected to a single VSC-HVDC operated at variable frequency: Energy yield assessment

New connection constraints for the power network (Grid Codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic arrays. A solution for interconnecting such renewables to the main grid is to use storage systems and a Direct Current (DC) MicroGrid. A “Plug and Play” approach based on the “System of Systems” philosophy using distributed control methodologies is developed in the present work. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources like photovoltaic arrays, storage systems in different time scales like batteries and supercapacitors, and loads like electric vehicles and the main AC grid. The proposed scheme can easily be scalable to a much larger number of elements.

The change to a sustainable energy supply advances further development in grid interconnection, especially for offshore wind farms. This enables future wind farms to be interconnected by high voltage dc transmission grids. In this paper, a case study for dc grid with integrated offshore wind farms is studied and a system control is developed.

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

In this paper, a novel intelligent controller for grid connection of DC microgrids is presented. The proposed controller allows the bi-directional AC/DC converter, linking the DC microgrid to the main utility grid, to provide the main functionalities of an inverter. Such functions include bi-directional power flow control and independent control of both active power (P) and reactive power (Q). In addition, the developed controller acts as an intelligent active power filter (APF) to the main grid. This is because it autonomously detects any power quality problems, filters out load-created harmonics and compensates unbalances and/or DC offsets resulting from the local AC load connected at the point of common coupling (PCC). The objective of the controller is to force the AC grid currents at the PCC to be balanced three-phase currents with minor harmonics while maintaining its controllability of power flow regardless of the characteristics of the local AC load. The performance of the developed controller was examined under several extreme cases including: non-linear loads, distorted load currents, unbalanced and offset conditions. The results show that the developed controller succeeds to maintain bi-directional P/Q flow controllability, allows the inverter to provide ancillary services such as reactive power compensation or voltage control to the grid while simultaneously acting as an active power filter to assure improved power quality at the PCC under various loading conditions.

The ascertainment of the exhaustion of conventional energy sources has led human to search for new energy sources that are offered in abundance in the environment. One of them is wind energy, which although is already widely used on a global scale, in Greece is a relatively recent field of research. Wind energy is not only offered in the land parts of our planet, but also in the water, showing even greater growth prospects due to the existence of stronger winds. A wide field of utilization of this technology is therefore appeared, since most of the Earth's marine environment remains untapped to this day. Installing wind turbines at sea for the purpose of creating offshore wind farms is not an easy or quick task and it is a multifactorial decision-making issue, both in terms of choosing the right location and in terms of selecting the appropriate technical equipment. With the development of technology, installation costs and payback time of the investments are constantly improving, as is the case with any new technology, which is why more and more investors are attracted. According to studies, this technology is expected to develop significantly in the coming decades, capable of shaping a different energy situation on a global scale. In Greece, where the water landscape is abundant, an attempt has been made in the past to develop offshore wind farms in predetermined areas, but to date no one has started operating. A relevant energy study carried out on a developing project in the Diapontian Islands shows that even small-scale projects that can no longer fully meet the energy needs of large urban centers are able to contribute to increasing the share of domestic electricity production through renewable sources and more specifically through the wind, without this meaning that they are a panacea.