High Voltage Direct Current Technology Research Articles

Offshore wind farms interfacing using HVAC-HVDC schemes: A review

Offshore wind farms (OWF) have emerged as a pivotal component in the transition towards renewable energy, offering substantial potential for reducing carbon emissions and enhancing energy security. Integration these offshore installations into the existing power grid present opportunities and challenges, particularly in terms of efficiency, stability, and cost-effectiveness. This review explores the interfacing of OWF with the power grid through High Voltage Alternating Current (HVAC) and High Voltage Direct Current (HVDC) schemes. This research offers a thorough examination of the latest technologies, and comparing the benefits and drawbacks of HVAC and HVDC systems for offshore wind applications. The review delves into various aspects, including technological advancements, economic considerations, and environmental impacts of HVAC and HVDC technologies. The review also addresses recent developments and contrasting viewpoints in the field, highlighting innovations and ongoing debates related to integrating OWF. By synthesizing recent studies and industry reports, this paper offers a balanced overview of the strengths and weaknesses associated with HVAC and HVDC schemes. It identifies critical areas for future research and provides recommendations for optimizing offshore wind farm integration. This review seeks to enhance understanding of current technologies and support decision-making in the development and deployment of offshore wind energy infrastructure.

Getting Ready for Multi-Vendor and Multi-Terminal HVDC Technology

Interoperable multi-vendor High-Voltage Direct-Current (HVDC) grids are a key enabler for the integration of renewable energy (in particular offshore wind) and its transmission over longer distances to consumers. However, most HVDC systems today are single-vendor and point-to-point. Various technical and non-technical aspects need to be considered, for example, (real-time) testing, legal aspects (intellectual property and regulation), and the multi-vendor interoperability process. This paper presents findings from the READY4DC project, which is a larger and open European effort involving diverse stakeholders, including HVDC manufacturers, transmission system operators, wind developers, academia, and research institutes. It summarizes key technical recommendations, emphasizing comprehensive interaction studies and the development of a structured legal framework to facilitate the development and operation of a multi-vendor, multi-terminal HVDC grid. The READY4DC project highlights the need for increased harmonization, transparent communication among stakeholders, and future-oriented research to ensure the robustness and interoperability of interconnected grids. Collaborative efforts are key for addressing technical complexities and advancing the deployment of multi-vendor multi-terminal HVDC technology.

Advancements and comparative analysis of high-voltage direct current transmission technologies

This paper outlines the fundamental principles of high-voltage direct current (HVDC) transmission, elucidating its two primary variants: current-source converter (CSC) HVDC and voltage-source converter (VSC) HVDC. It also undertakes a comparative analysis with high-voltage alternating current (HVAC) technologies, focusing on aspects such as power transmission efficiency and cost-effectiveness, drawing upon prior research findings. Additionally, the paper underscores the critical role of circuit-breakers (CB) as essential components for controlling HVDC systems. HVDC technology plays a pivotal role in augmenting AC transmission systems, facilitating the integration of large-scale renewable energy sources, and enhancing the efficiency of expansive power grids over considerable distances. Its continued evolution and refinement are highly probable, given its indispensable role in the energy landscape.

Voltage Source Converter based High Voltage Direct Current Transmission: A Comprehensive Review of Control Strategies, Developments and Trends

The continuous increasing progress in high power and high voltage semiconductor devices leads to have a substantial impact on optimization and effective management of electric grids. These developments have great influence on High Voltage Direct Current (HVDC) and flexible ac controller technologies. This article gives an outline of the innovations in Voltage source Converter (VSC) based HVDC technology. VSC based HVDC technology offers decent advantages which includes interconnection of asynchronous networks, bulk power transmission and voltage stability support. VSC based HVDC technology niche utilities to grab opportunities in incorporating large scale renewable energy sources to the grid, especially on shore /offshore wind energy to the grid. Furthermore, VSC-based HVDC technology is essential for maintaining voltage stability in networks of interconnected grids. In the face of changing loads and the incorporation of renewable energy, these systems help to maintain grid dependability and resilience by offering dynamic voltage management and wattless power support.This article highlights the transformative potential of VSC-based HVDC technology in modernizing and future-proofing electric grids. By leveraging the latest innovations in semiconductor devices and control technologies, VSC-based HVDC systems empower grid operators to overcome existing challenges and embrace the opportunities presented by the evolving energy landscape.

Economic viability assessments of high voltage direct current for wind energy systems

This research shows an economic assessment for decision-makers of high voltage direct current utilization in wind energy systems applied to a case study in Turkey. The increasing energy demand in Turkey can be supplied effectively by this transmission in long distances and leading the use of renewable energy sources. Thereby, wind energy systems are being one of the main developed renewable sources, but the economic feasibility of its feature has been demonstrated only in some cases. The transmission of wind energy is possible both inside a country and between the countries, depending on the deployments about the utilization of high voltage direct current technology, operating with renewable energy systems. Thus, life-cycle cost scenarios are proposed by recommending a 1,000 km length high voltage direct current overhead transmission line in optimum economic conditions between Canakkale and Samsun-Bafra to transport energy from wind farms. The economic feasibility of these systems can be proven by showing the comparison between investment cost and profit from the 25 years life-time of the project. A novel cumulative cash flow analysis is applied for this comparison employing the net present value. A voltage source converter and a current commuted converter are considered in the scenarios. The findings show that voltage source converter can be chosen for both overhead and cable transmission for wind energy systems with the need of government subsidies in the investment. Moreover, the possibility of the investment is discussed through economic terms, i.e., the positive externality, the opportunity cost and the economies of scale. Therefore, this study can be taken as a pre-model for both the other regions of Turkey and for the developing countries.

Overview and Assessment of HVDC Current Applications and Future Trends

High voltage direct current (HVDC) technology has begun to gather a high degree of interest in the last few decades, showing a fast evolution of achievable voltage levels, transfer capacities, and transmission lengths. All these changes occurred in a context in which power system applications are highly dependent on HVDC technologies such as energy generation from renewable sources (e.g., energy generated in offshore wind power plants), power exchanges between asynchronous networks, submarine cables, and long-length transmission overhead lines have become more common worldwide. This paper tries to summarize the current state of HVDC technologies, both voltage-source converters and current-source converters, the main components of converter substations, control strategies, key challenges arising from their use, as well as the future prospects and trends of HVDC applications. This paper represents the first step in setting the background information for analyzing the impact of a VSC-HVDC connection on the stability of the Romanian transmission network during steady-state and dynamic operation.

The Impact of HVDC on the Current and Future Energy Markets

Obvious technological and economic advantages of High Voltage Direct Current (HVDC) systems over traditional High Voltage Alternating Current (HVAC) systems are becoming increasingly attractive for long-distance transmission. Several research papers on HVDC transmission networks have been published. However, most of them are focused on specific geographic locations or system components. Nonetheless, this study gives a brief yet thorough overview and international assessment of HVDC transmission systems. The following are the important points to be covered in the paper: The state of the art of HVDC technology development, the benefits, economic comparisons, and constraints of HVDC systems, as well as the size of the international HVDC industry market and the impact of COVID-19 on the market, are all explored in-depth, along with a mathematical model for forecasting the evolution of market demand. According to market statistics, the Asia-Pacific region (APAC) is the biggest market and technical leader in HVDC technologies. In addition, the market for HVDC will continue to grow in the forecasted period.

Sizing and operation of a pure renewable energy based electric system through hydrogen

Today, in order to reduce the increase of the carbon dioxide emissions, a large number of renewable energy resources (RES) are already implemented. Considering both the intermittency and uncertainty of the RES, the energy storage system (ESS) is still needed for balancing and stabilizing the power system. Among different existing categories of ESS, the hydrogen storage systems (HSS) have the highest energy density, and are crucial for the RES integration. In addition, RES are located in faraway regions, and are often transmitted to the terminal consumption center through HVDC (high voltage direct current) due to its lower power loss. In this paper, we present a power supply system that achieves low-carbon emissions through combined HSS and HVDC technology. First, the combined HSS and the HVDC model are established. Secondly, the rule-based strategy for operating the HSS microgrid is presented. Then, an operating strategy for a typical network, i.e., the pure RES generation station-HVDC transmission-microgrids, is demonstrated. Finally, the best sizing capacities for all components are found by the genetic algorithm. The results prove the efficiency of the presented sizing approach for a pure RES electric system.

Operation and Challenges of Multi-Infeed LCC–HVDC System: Commutation Failure, AC/DC Power Flow, and Voltage Stability

This paper presents a detailed analysis of commutation failure, AC/DC power flow, and voltage stability of multi-infeed high-voltage direct current (HVDC). The use of HVDC power transmission technology has become common in modern power systems. During the past two decades, HVDC technology has been extensively used for long-distance bulk power transmission to remote areas. Throughout the world, the demand for power has drastically increased in recent years due to industrialization; such situations make HVDC an economic candidate because the distance between power generation plants and load areas is significantly very long. The line-commutated converter (LCC) technology-based HVDC system is well more mature than other available conversion schemes (i.e., voltage source converters), and it is widely used in high-power projects. China had approximately 50 HVDC–LCC links in 2020, and a single LCC-based link with the highest capacity is 12 GW. The installation of several HVDC links in an existing power network has led to a situation where two or more HVDC links terminate in the electric vicinity of each other’s AC network or even in same AC busbar. Such scenarios are termed multi-infeed HVDC system. Multi-infeed HVDC systems bring various challenges related to voltage stability, local and concurrent commutation failure, and AC/DC power flow. Here, the literature available on these phenomena of LCC-based HVDC is discussed for future research. The assumptions and drawbacks of various techniques used for investigating the mentioned phenomena are also highlighted.

AN ECONOMIC AND TECHNICAL REVIEW FOR THE UTILIZATION OF HVDC IN TURKEY AND IN THE WORLD

In recent years, it is seen that High Voltage Direct Current (HVDC) transmission line systems have come to the fore in the field of energy efficiency in the world. Therefore, it is predicted that analyzing the technological and economic advantages of HVDC transmission line systems will make an important contribution to energy efficiency policies. In this regard, this study aims to examine the technological and economic advantages of HVDC transmission systems through the historical development with applications in Turkey and in the world. In addition to this, it is expected that the evaluation of the effects of energy efficiency on the economy will bring a different perspective to the energy and economic literature. Therefore, it is thought that energy and economic policies for the spread of HVDC transmission line systems worldwide will be essential. The asymmetric distribution of natural energy sources in the world causes energy supply security problems in the countries such as Turkey in terms of high foreign dependence on energy. For this reason, it is necessary to meet the increasing energy demand and increase the existing capacity day by day. Besides, it is important to develop policies for efficient use of energy. HVDC technology is extremely important for a developing country like Turkey. Moreover, it is known that this energy transmission technology has become widespread in developed countries. Thereby, a technical comparison is done for investment costs of the transmission system in Germany. As a result, other than bringing economic benefits with the energy transmission of Turkey through HVDC, it has important potential for making energy transmission possible with her neighbors and European Union countries.

VSC-HVDC and Its Applications for Black Start Restoration Processes

System reliability is a measure of an electric grid system’s ability to deliver uninterrupted service at the proper voltage and frequency. This property of the electric system is commonly affected by critical processes, such as a total blackout. The electric system restoration is a complex process which consists of returning generators, transmission system elements, and restoring load following an outage of the electric system. However, the absence of a generator or unit of black start capabilities may worsen the duration and effects of blackouts, having severe consequences. Black start capability is important as it can reduce the interruption time, decrease the economic loss, and restart the power supply fast and efficiently. In recent years, several works have reported advances about the High Voltage Direct Current (HVDC) technology based on the Voltage-Source Converter (VSC) as an attractive and promising technology to increase black start capability. This paper is a review of the current studies of VSC-HVDC as black start power and discusses the advantages and limitations of recent methods. The major points addressed in this paper are as follows: the current theoretical approach of the black start process and the used HVDC technologies, the advantages of VSC-HVDC as black start power, a compressive review of the literature about the black start capabilities using VSC-HVDC technologies, and a description of the main methods recently used to provide an enhancement for restoration processes. Finally, this paper discusses new challenges and perspectives for VSC-HVDC links in order to provide an enhancement for restoration processes.

Selection of an IGCT for multilevel converters dedicated to high‐voltage direct current grid connection of offshore wind‐farms

Grid connection of remote offshore wind-parks uses high-voltage direct current technology and in order to reduce costs and losses and maximise profitability, semiconductor power losses must be minimised. To properly choose the semiconductors, it is necessary to estimate their losses for a large number of operating conditions. This article deals with a modelling approach to calculate power losses for many such operating conditions, based on measured semiconductor characteristics and the chosen multilevel modulation strategy. The case of the integrated gate-commutated thyristor is considered because, for a given device rating, it is possible to select an integrated gate-commutated thyristor benefiting from the best trade-off between on-state losses and turn-off losses, thus minimising the power losses of the two end-stations.

A PSO Optimal Power Flow (OPF) Method for Autonomous Power Systems Interconnected with HVDC Technology

High-voltage direct current (HVDC) technology has been the state of the art in power systems’ interconnections, especially for submarine installations. Multi-terminal HVDC networks and furthermore mixed AC–DC networks demand new operational modes. Techniques can be employed for the optimal operation of the whole interconnected system. In this article, an optimal power flow (OPF) technique is proposed for the steady state operation of such systems, which could be very useful in planning or scheduling of AC–DC networks. Particle swarm optimization (PSO) method has been employed to minimize the operational cost of the system. This cost includes fuel cost and investment for new transmission lines, while power losses are limited. This method-technique had been tested on real power AC power systems that are planned to be interconnected with HVDC systems. A detailed model of the simulated system was developed, and specific operational scenarios were examined.

An Overview of HVDC Technology

There is a growing use of High Voltage Direct Current (HVDC) globally due to the many advantages of Direct Current (DC) transmission systems over Alternating Current (AC) transmission, including enabling transmission over long distances, higher transmission capacity and efficiency. Moreover, HVDC systems can be a great enabler in the transition to a low carbon electrical power system which is an important objective in today’s society. The objectives of the paper are to give a comprehensive overview of HVDC technology, its development, and present status, and to discuss its salient features, limitations and applications.

Enabling thermal efficiency improvement and waste heat recovery using liquid air harnessed from offshore renewable energy sources

A novel approach using decoupled processes to harness offshore renewable energy, from marine hydrokinetics, ocean waves, wind, and solar to produce liquid air, is presented in this paper. Offshore renewables interconnection using submarine medium- and high-voltage direct current technologies are used to produce liquid air that can be transported to end-use locations using repurposed liquefied natural gas tankers. Two important possibilities arise from using the proposed technology. The first possibility allows the integration with conventional thermal cycles to improve efficiency. This approach can be used to leverage efficiencies of thermal systems that have already reached a plateau in the maximum achievable efficiency via design and operation optimization. The second possibility is related to the incorporation of low temperature cycles to recover waste heat from other thermal processes. This is important considering that waste heat accounts for more than 60% of the consumed energy in the United States. A detailed technical description of the complete cycle from cryogen generation to end-use of energy is provided. Estimation of efficiency enhancement for thermal plants using liquid air including waste heat recovery is presented.

Multi-time Scale Optimal Power Flow Strategy for Medium-voltage DC Power Grid Considering Different Operation Modes

Direct current (DC) power grids based on flexible high-voltage DC technology have become a common solution of facilitating the large-scale integration of distributed energy resources (DERs) and the construction of advanced urban power grids. In this study, a typical topology analysis is performed for an advanced urban medium-voltage DC (MVDC) distribution network with DERs, including wind, photovoltaic, and electrical energy storage elements. Then, a multi-time scale optimal power flow (OPF) strategy is proposed for the MVDC network in different operation modes, including utility grid-connected and off-grid operation modes. In the utility grid-connected operation mode, the day-ahead optimization objective minimizes both the DER power curtailment and the network power loss. In addition, in the off-grid operation mode, the day-ahead optimization objective prioritizes the satisfaction of loads, and the DER power curtailment and the network power loss are minimized. A dynamic weighting method is employed to transform the multi-objective optimization problem into a quadratically constrained quadratic programming (QCQP) problem, which is solvable via standard methods. During intraday scheduling, the optimization objective gives priority to ensure minimum deviation between the actual and predicted values of the state of charge of the battery, and then seeks to minimize the DER power curtailment and the network power loss. Model predictive control (MPC) is used to correct deviations according to the results of ultra short-term load forecasting. Furthermore, an improved particle swarm optimization (PSO) algorithm is applied for global intraday optimization, which effectively increases the convergence rate to obtain solutions. MATLAB simulation results indicate that the proposed optimization strategy is effective and efficient.

A power system restoration method using voltage source converter–high-voltage direct current technology, aided by time-series neural network with firefly algorithm

Voltage source converter (VSC)–high-voltage direct current (HVDC) has become a new trend for achieving an efficient and reliable bulk power transmission. The main challenges in VSC-HVDC link are the “soft-start-up” or the restoration of power after the system blackout, with over voltage and less response delay. In this paper, VSC-HVDC link with firefly Levenberg–Marquardt-trained artificial neural network (ANN), termed as ANN-FLM, is proposed to restore the power quickly. The simulation is performed by creating blackout in the system through the introduction of a three-phase fault. The performance analysis is made on VSC-HVDC with ANN-FLM in existing proportional integral controller. The simulated results provide faster restoration and independent control of real and reactive powers. The proposed method minimizes the over voltage to 98% in maximum point, 84% in phase A, 61% in phase B and 82% in phase C, when simulated.

A high voltage direct current transmission system : natural and selective harmonic cancellation

<p class="AbsKeyBibli"><span lang="EN-US">This study focused on the special High Voltage Direct Current technology. The context is given by combining two original solutions; the first solution, using a natural harmonic cancellation, consists to connect in series two classical frequency inverters which are coupled to the grid through a specific transformer connection. On the other hand, the second solution is achieved by using three, five or more level converters in square wave modulation, in order to eliminate some selective harmonics by optimizing a switching angle. The simulation and experimental results indicate that the proposed High Voltage Direct Current transmission systems offer high efficiency, unity power factor and better current and voltage quality with fewer harmonic.</span></p>

The hybrid model of VSC HVDC

The trend in semiconductor developments has made the high-voltage direct current (HVDC) technologies based on voltage source converters feasible. This type of convertor has a number of potential advantages compared with “classic” HVDC, but deep analysis should be carried out before its integration in electric power system. In this paper, the results of realization of the VSC HVDC model based on a concept of hybrid simulation of electric power system are presented. Hybrid concept combines three approaches of simulation: analog, digital and physical, combination of which allows to achieve a maximum efficiency. The obtained simulation results have confirmed an adequacy of the model and possibility to integrate it to the hybrid real-time simulator for carrying out various researches and analyses of the operation of large electric power system, including HVDC technologies, in real time without any decompositions and limitations.

Feasibility and Reliability Analysis of LCC DC Grids and LCC/VSC Hybrid DC Grids

Power system interconnections using high-voltage direct-current (HVDC) technologies between different areas can be an effective solution to enhance system efficiency and reliability. Particularly, the multi-terminal DC grids, that could balance and ensure resource adequacy, increase asset utilization and reduce costs. In this paper, the technical feasibility of building DC grids using the line commutated converter based (LCC) and voltage source converter based (VSC) HVDC technologies are discussed. Apart from presenting the technical challenges of building LCC DC grids and LCC/VSC hybrid DC grids, the reliability modeling and analysis of these DC grids are also presented. First, the detailed reliability model of the modular multi-level converters (MMCs) with series connected high-voltage and low-voltage bridges are developed. The active mode redundancy design is considered for the reliability model. To this end, a comprehensive whole system reliability model of the studied systems is developed. The reliability model of each subsystem is modeled in detail. Various reliability indices are calculated using this whole system reliability model. The impacts of the redundancy design of the MMCs on these indices are presented. The studies of this paper provide useful guidance for DC grid design and reliability analysis.