HVDC Technology Research Articles

Fair Energy Trading in Blockchain-Inspired Smart Grid: Technological Barriers and Future Trends in the Age of Electric Vehicles

The global electricity demand from electric vehicles (EVs) increased by 3631% over the last decade, from 2600 gigawatt hours (GWh) in 2013 to 97,000 GWh in 2023. The global electricity demand from EVs will rise to 710,000 GWh by 2030. These EVs will depend on smart grids (SGs) for their charging requirements. Like EVs, SGs are a booming market. In 2021, SG technologies were valued at USD 43.1 billion and are projected to reach USD 103.4 billion by 2026. As EVs become more prevalent, they introduce additional complexity to the SG landscape, with EVs not only consuming energy, but also potentially supplying it back to the grid through vehicle-to-grid (V2G) technologies. The entry of numerous independent sellers and buyers, including EV owners, into the market will lead to intense competition, resulting in rapid fluctuations in electricity prices and constant energy transactions to maximize profit for both buyers and sellers. Blockchain technology will play a crucial role in securing data publishing and transactions in this evolving scenario, ensuring transparent and efficient interactions between EVs and the grid. This survey paper explores key research challenges from an engineering design perspective of SG operation, such as the potential for voltage instability due to the integration of numerous EVs and distributed microgrids with fluctuating generation capacities and load demands. This paper also delves into the need for a synergistic balance to optimize the energy supply and demand equation. Additionally, it discusses policies and incentives that may be enforced by national electricity carriers to maintain grid reliability and manage the influx of EVs. Furthermore, this paper addresses emerging issues of SG technology providing primary charging infrastructure for EVs, such as incentivizing green energy, the technical difficulties in integrating diverse hetero-microgrids based on HVAC and HVDC technologies, challenges related to the speed of energy transaction processing during fluctuating prices, and vulnerabilities concerning cyber-attacks on blockchain-based SG architectures. Finally, future trends are discussed, including the impact of increased EV penetration on SGs, advancements in V2G technologies, load-shaping techniques, dynamic pricing mechanisms, and AI-based stability enhancement measures in the context of widespread SG adoption.

Review of HVDC technologies for weak grid interconnectors

Review of HVDC technologies for weak grid interconnectors

Small signal analysis of DC voltage control based on a virtual resistance of DC/DC converter integrated in a multiterminal DC grid

AbstractThe future multi‐terminal direct‐current (MTDC) grid will require the interconnection of point‐to‐point high‐voltage (HV) DC links with different specifications such as DC voltage level, system grounding configuration and HVDC technology. To adapt these differences, it is obligatory for DC/DC converters to interconnect HVDC links. Additionally, they are capable of providing supplementary functionalities as they are highly controllable devices. In this article, a primary virtual resistance DC voltage controller associated with DC/DC converter is proposed for managing DC grid voltages of the interconnected HVDC grids, increasing the reliability of the system. The commonly known topology, Front‐to‐Front Modular Multilevel Converter (F2F‐MMC) is adopted for DC/DC converter. Time‐domain simulations are performed using EMTP software for validating the controller behaviour under power disturbances and large events of loss of one converter in a MMC‐based MTDC system. The converters are modelled using reduced order modelling (ROM) methodology. Apart from this, dynamic studies have been carried out using a linear state space model for small‐signal stability analysis of a HVDC system integrating DC/DC converter with a virtual resistance DC voltage controller. The results are examined through parametric sensitivity analysis.

Fault-Location Accuracy of Natural Frequencies Using Incomplete HVDC Station Models

This paper investigates how the accuracy of fault location estimated from a transmission line's natural frequencies is affected by imperfect modeling of HVDC power-converter sta- tions. These systems include a large number of devices each with specific frequency-dependent characteristics, as filters, reactors and surge protection systems. While it is well-known that location errors may ensue from inaccurate termination models, it is not clear to what extent location accuracy is affected when neglecting one or more of these devices. Results show significant differences depending on the kind of transmission line and the reactor inductance. Including reactors is found not to completely avoid errors, proving the need to take into account the reactive behavior of the converter, which strongly varies according to the HVDC technology. A notable source of errors is level repulsion between station and line resonances, a phenomenon observed when the converter station presents self resonances, e.g., due to DC filters and stray capacitances in reactors. Significant loss of sensitivity to the fault position is found in these cases, impairing fault-location resolution. The first, or dominant, natural frequency of the line is more strongly affected by all these phenomena, suggesting that the standard choice of using the dominant resonance may not be an optimal strategy. Higher-order resonances are instead found to be more robust against inaccurate converter models, and appear to be more suitable for accurate fault location in case of uncertainties about the converter model.

Converter for Voltage Source HVDC Links: Current Status and Future Challenges

This article discusses the current state of DC HVDC technology. The article describes the history of DC HVDC technology, starting with its early development as a voltage source, and then discusses the introduction of line-cutting into current designs. The article discusses control and co-ordination of transformers, as well as the need for a DC breaker to facilitate control of multiple plants. Recent developments in the design of DC circuit breakers are discussed. The importance of reliability is recognized, especially in relation to cables, and the issues surrounding cable design are explained. Ongoing and planned installations of VHF-VHF DC installations are described.

A decision-making method for the operation flexibility enhancement of hybrid cascaded MTDC

To enable the integration of large-scale renewable energy, hybrid HVDC technology, which combines the technical advantages of LCC-HVDC and VSC-HVDC, is being gradually deployed in the power grid nowadays. The operation of the Wu-dong-de Hybrid DC Project and the Jian-su Hybrid cascaded MTDC Project has proved its advantages. However, for the simultaneous application of different converter station technologies in the system, the control strategies become complex. Issuing appropriate control instructions to ensure system stability according to operational requirements is an issue that cannot be ignored in decision-making. Even under abnormal conditions, when the topology changes due to various failure scenarios, reasonable decision-making and precise control instruction definitions are required. To achieve flexible planning of the MTDC system, this paper presents a decision-making method for control strategies of a hybrid cascaded MTDC system, which analyzes the control strategy combinations selected for normal and abnormal conditions of the MTDC system. In addition, a control instruction calculating method and decision-making process for precise control in normal and abnormal control conditions is proposed. Simulation results based on a five-terminal hybrid cascaded MTDC in PSCAD/EMTDC have verified the effectiveness of the proposed method.

The Simulation Analysis and Countermeasures of LCC-HVDC Complementary Resonance

With the advancement of HVDC technology, the AC/DC hybrid grid has gradually emerged. The interaction and influence between AC and DC have become increasingly prominent, with the complementary resonance problem between AC and DC emerging as a hot research topic. In this paper, firstly, the phenomenon of LCC-HVDC complementary resonance is analyzed in both time and frequency domains, and a method for setting the saturation curve of the converter transformer in time domain simulation is proposed. Subsequently, targeting the actual LCC-HVDC complementary resonance, a hardware-in-loop simulation platform is constructed based on the actual HVDC control and protection equipment, and the actual field complementary resonance is reproduced. By simulating different operation modes, the operation range with a low risk of complementary resonance is determined. The influencing factors of complementary resonance are discussed and analyzed. Finally, through real-time simulation, the results show that the simulation method proposed in this article for setting the saturation curve of the converter transformer can accurately reflect the complementary resonance phenomenon between AC and DC caused by the saturation of the converter transformer. The countermeasures proposed in this article can effectively remove the complementary resonance between AC and DC and have been applied to the operation and control of actual power grids.

Design consideration for frequency containment reserve provisions by a multi‐terminal HVDC system

AbstractFrequency control is considered to be an important function of multi‐terminal HVDC (MTDC) systems. Sharing frequency containment reserves (FCRs) among interconnected AC systems using HVDC technology is particularly attractive in the European context. However, coordination of the contribution between systems with different sizes, quality requirements, and dynamic characteristics requires harmonized rules and well‐defined control strategies. If the controllers are not properly designed, they can lead to disproportional supports, noncompliance with the existing regulation framework, or even degradation of the frequency quality. This paper presents a general analytical methodology for assessing the compliance of MTDC grid control solutions to the essential requirements of the FCR framework, and then examines three different implementation solutions as illustrative examples to validate the method. Through this process, the interaction mechanisms behind each solution are analytically clarified. The performance analyses are then confirmed using load‐frequency models of CE, Nordic, and GB systems coupled with a three‐terminal DC system. It is revealed that, while certain control solutions result in insufficient performance with respect to the desired FCR provision, the newly proposed distributed solution for each pair of converters is the most compliant with the existing framework thanks to the highest degrees of freedom.

Electricity transportation using HVDC technology for Algerian southern sun power plants

Electricity transportation using HVDC technology for Algerian southern sun power plants

Multi-Objective Design Optimization for HVDC-LCC Converter Transformers: Analytical and FEA-Based Comparison

The emerging HVDC technology has been used for long-distance power transmission, increasing flexibility to the power systems, handling asynchronous interconnections, crossing long-distance submarine cables, unusual loading, and generation profiles, and improving energy market relations. The HVDC converter transformers are designed based on system parameters, that directly affect the core and windings geometries, thus the weight and operating losses. In a standard design process, the designer adjusts the active part dimensions, until the constructive and specified aspects, moreover, the technical standard restrictions, are satisfied. The paper’s main contribution is to formulate analytic equations, in a way that losses and weight can be obtained for several options of core and windings geometry. However, weight and losses are opposite objectives in the search for an optimal solution. Understanding this compromise between opposing goals is relevant to the equipment learning process. In this context, another significant contribution of the paper is to carry out a formal optimization process through the analytical formulation developed. To minimize the weight and operating losses, and subject to IEC standards and constructive restrictions, the multi-objective Genetic Algorithm has been used to search for the Pareto Frontier. Far beyond the chosen solution, the non-dominated frontier obtained for each transformer design, allows the designer to learn about the equipment and its operation, leading to a continuous improvement of the proposed methodology. The analytical formulation is validated by an alternative numerical methodology for winding harmonic losses and short-circuit impedance verification, providing meaningful confidence for the applied method.

A High Voltage Gain Capable MMC for Offshore Wind Farms: Frequency Component Analysis and Minimization of Capacitor Voltage Ripple

Modular multilevel converter (MMC) and HVdc technology together provide an indispensable solution to integrate offshore wind farms with onshore ac grid. However, the bulky size of MMC and voltage boosting transformers (VBTs) pose a big challenge to keep the footprint and cost of the onshore-platform low. With this background, a full-bridge submodule (SM) modified MMC and a suitably modified switching function are proposed, which utilize the negative SM voltage to achieve ac side voltage boosting. How much negative SM voltages are to be applied across the arms is determined by the group submodule ratio (GSR) parameter, introduced in the switching function. The acquired boosting ability not only shrinks the voltage boosting requirement of VBTs but also reduces the semiconductor switches (upto 10%) and/or the SM count (8%–30%). Analytical solutions derived for the SM capacitor sizing are also presented. The analysis is further utilized to obtain a novel circulating current injection scheme (CCIS), which utilizes phasor analysis to obtain the values of circulating current control parameters. The CCIS suppresses SM capacitor voltage ripple, especially fundamental, and reduces the capacitance requirement by 10%–15% for a wide range of GSR. Representative simulation results are showcased, and the theoretical claims are validated by hardware experiment.

The Latest Trend of VSC HVDC

There have been various discussions in Japan on how to introduce renewable energy toward the target of carbon neutrality in 2050. The “Interim Report for Network Master Plan” issued by the “Study Committee on Master Plans for Wide-Area Interconnection Systems and System Rules” on May 20, 2021 describes the possibility that large-scale, long-distance power transmission from power generation areas to large demand areas by high-voltage direct current transmission system (HVDC) is effective for mass introduction of renewable energy. The introduction of HVDC is already expanding overseas, such as in Europe, and the trend is accelerating. The background to this is that it has been demonstrated that strengthening interconnection by HVDC has economic rationality and that it brings various benefits to existing power systems such as strengthening resilience. This paper describes the latest trends in the HVDC market and technology.

The On-site Verification of Key Technologies for Kunbei-Liuzhou-Longmen Hybrid Multi-terminal Ultra HVDC Project

Hybrid high voltage direct current transmission (Hybrid HVDC) is a new type of HVDC technology developed in recent years. It combines the characteristics of large-capacity and low cost of the line commutated converters (LCC) and non-commutation failure and dynamic reactive power support of voltage sourced converters (VSCs) in one HVDC system. It has technical advantages in the fields of unidirectional power transmission and in the application of improving the stability of multi-infeed HVDCs, giving it broad application prospects. The Kunbei-Liuzhou-Longmen (KBL) project is the first hybrid ultra HVDC project. It was put into service on Dec. 27 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 2020. This paper introduces the KBL project, analyzes the operation characteristics of hybrid HVDC system, and provides on-site verification of KBL project, including operation of LCC-VSC hybrid system, ultra-high voltage VSC technology using the series of two valve groups, the DC fault ride-though of hybrid VSC without using DC breaker, the connection and disconnection of a third station, and etc.

Summary of Research on Intelligent Control algorithm and Application of Power system Automation

With the development of HVDC technology and the continuous progress of AC/DC hybrid power grid, the research of intelligent control in the direction of power system automation has made some progress and has a certain foresight. The power system automatic intelligent control technology algorithm discussed in this paper includes neural network, fuzzy control algorithm and genetic algorithm, application development and significance, through the development of related intelligent algorithms to provide some reference for the field.

Analysis of Fault Waveforms of Key Electrical Parameters in Hybrid Multi-terminal DC System

LCC-VSC hybrid multi terminal HVDC system combines the advantages of traditional HVDC and flexible HVDC technology, and becomes one of the new directions of HVDC development. In this paper, taking the Baihetan Jiangsu HVDC transmission project as an example, under the appropriate simplified model, the critical electrical stresses of the DC side faults of a typical LCC-VSC hybrid multi-terminal DC system are analyzed. The simulation results verify the correctness of the simplified analysis in this paper.

Impact of DFT-Based phasor estimation errors due to commutation failures of LCC-HVDC links on the protection of AC lines in the near vicinity

Commutation failure (CF) is an inherent issue for Line-Commutated Converter (LCC) HVDC technology. Whenever it happens, voltage and current waveforms throughout the AC system in the near vicinity of LCC-HVDC links become quite distorted. In this paper, it is assessed the impact of such kind of distortion on transient response of phasor estimation algorithms and, in turn, on the performance of AC transmission lines protection. Different discrete Fourier transform (DFT) based algorithms are implemented, and distance, differential and directional protection functions are evaluated. The obtained results reveal that phasor estimation errors arise whenever CFs take place, which may lead protection functions to misoperate, such that false trip command may be issued for external faults.

Standards lead and promote the application of green and safe HVDC technology

Standards lead and promote the application of green and safe HVDC technology

A Vision of HVDC Key Role Toward Fault-Tolerant and Stable AC/DC Grids

Massive off-shore wind integration in the European power system and the necessity to increase the power flows between asynchronous areas and inside continental Europe, call for HVDC transmission development and multiterminal-HVDC-based transmission. HVDC technology is highly controllable, but also sensitive to faults and degraded modes. Achieving an efficient and robust AC/DC transmission system requires to develop a vision of HVDC role and functionalities in different situations. In addition to HVDC converter core control functions and DC grid protection strategies, a coordinated DC grid control layer is beneficial to supervise control modes toward overall AC/DC transmission system security and stability, as well as to ensure converter controls interoperability. This article offers a vision of what a robust AC/DC network can be, based on control and protection strategies that can be implemented via HVDC converter capabilities.

Relaxations and approximations of HVdc grid TNEP problem

In recent years, the use of HVdc technology has increased and VSC technology has enabled the realization of HVdc grids. This calls for the development of new tools to solve the transmission network expansion planning (TNEP) model. A detailed representation of the dc grid TNEP problem is highly nonlinear and more complex than the traditional ac grid expansion problem due to extra constraints and additional decision variables from the converter station model. The present day industrial solvers have difficulties to tackle the resultant MINLP problem. Therefore, the linearized ‘DC’ approximation is often used in practice, which may not produce sufficiently accurate answers. In this paper, different relaxations and approximations of the dc grid TNEP problem are presented. The performance of each formulation is evaluated using eight test cases. Although there is no clear formulation that shows the best performance, LPAC approximation and SOC relaxations seem to provide better alternatives to ‘DC’ approximations. The developed formulations do not guarantee feasibility and a second corrective stage is required to obtain feasible solutions.

Modified Dual Active Bridge DC/DC Converter With Improved Efficiency and Interoperability in Hybrid LCC/VSC HVDC Transmission Grids

DC transmission grids are the promising electrical networks in the near future especially with the high penetration of large-scale renewables. This article proposes a modified version of the dual active bridge (DAB) dc/dc converter with ac link capacitors generating reactive power to compensate for nonactive power consumption, hence mitigating current stresses and losses to improve efficiency. The proposed topology also enables the connectivity of current source line-commutated HVDC and voltage source HVDC technologies particularly during power reversal; a feature which conventional DAB is incapable of doing. Analysis and detailed design of the proposed converter are addressed and a comparative performance analysis is carried out with conventional DAB. Converter principle of operation is explained and MATLAB/Simulink simulations are carried out to verify converter operation particularly under adverse conditions such as rated power reversal and dc fault conditions. A low-scale prototype substantiates the theoretical analysis and simulation results.