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The purpose of this study is to provide data for the best possible circuit breaker allocation in power grids with HVDC transmission while taking circuit breaker failure into account. The lack of a suitable selection of HVDC circuit breakers is one of the primary obstacles to establishing an appropriate protection system for HVDC transmission. This research focuses on finding the optimal circuit breaker allocation strategy with respect to the transient response of the system, especially when the grid operator is using existing circuit breakers, rather than on the necessary steps to improve the technology of circuit breakers. Case studies are simulated using PSCAD/EMTDC in order to verify the transient response of the transmission system corresponding to the allocation of circuit breakers and the circumstance of circuit breaker failure. It is crucial to remember that there isn't a strategy that is always the best. Consequently, a detailed analysis of the suggested approach is required, taking into account the benefits and drawbacks from the standpoints of fault clearing, power system planning, and operational factors. In the context of HVDC transmission, the authors hope that their research will spark and start conversations about circuit breaker allocation strategies. [ABSTRACT FROM AUTHOR]

The rapid development of offshore wind farms (OWFs) calls for economical and reliable power transmission technology. This review paper focuses on the diode‐rectifier‐unit based high voltage direct current (DRU‐HVDC) transmission systems. The main technical features of DRU‐HVDC are highlighted and the comparisons with MMC‐HVDC and LCC‐HVDC are conducted. Considering the uncontrollability of DRU and the necessity of offshore wind turbines (WTs) to establish offshore network, the existing decentralized and centralized control strategies are reviewed in detail. For the fully‐grid‐forming converter, the operation principle of the P–V and Q–f power control is explained from the OWF‐DRU level and the WT level, respectively. For the partial‐grid‐forming converter, why the voltage control loop can be eliminated is analysed. Focusing on the start‐up issue caused by the unidirectional‐power‐flow characteristic of DRU, several start‐up solutions are reviewed, including medium voltage alternative current (MVAC) umbilical cable, auxiliary MMC, energy storage for WTs, auxiliary low voltage DC cable. Then considering different fault locations, the fault characteristic and protection of the DRU‐HVDC system is presented, including the offshore AC faults, DRU faults, HVDC faults and onshore AC faults. Finally, the future research topics worth exploring for DRU‐HVDC system are identified. [ABSTRACT FROM AUTHOR]

Modern electrical power networks make extensive use of high voltage direct current transmission systems based on voltage source converters due to their advantages in terms of both cost and flexibility. Moreover, incorporating a direct current link adds more complexity to the optimal power flow computation. This paper presents a new meta-heuristic technique, named self-adaptive bonobo optimizer, which is an improved version of bonobo optimizer. It aims to solve the optimal power flow for alternating current power systems and hybrid systems AC/DC, to find the optimal location of the high voltage direct current line in the network, with a view to minimize the total generation costs and the total active power transmission losses. The self-adaptive bonobo optimizer was tested on the IEEE 30-bus system, and the large-scale Algerian 114-bus electric network. The obtained results were assessed and contrasted with those previously published in the literature in order to demonstrate the effectiveness and potential of the suggested strategy. [ABSTRACT FROM AUTHOR]

Commutation failure (CF) is one of the most prevalent events in line-commutated converter-based high-voltage direct current (LCC–HVDC) systems. The frequent occurrence of CF poses a significant threat to the safe and stable operation of power grids. The commutation failure prevention control (CFPREV) is the main method to prevent the initial CF, which relies on the detection of a drop in AC voltage. However, its slow fault detection hinders the rapid response of post-fault control, thereby affecting the effectiveness of CF suppression. Therefore, this paper proposes a fast fault detection method based on Bayesian theory. This algorithm can calculate the conditional probability of each variable in a given dataset, effectively mitigating the impact of noise and errors in data to yield precise and dependable results. By processing the collected continuous data and calculating the probability of the existence of a fault point, it determines whether a fault occurs. Based on this method, an improved prevention strategy is proposed, which can effectively enhance the CF resilience of LCC–HVDC systems under AC faults. Finally, using the power systems computer-aided design (PSCAD) platform, the accuracy of the fault probability detection algorithm was verified based on actual engineering data. The effectiveness of the proposed strategy was further validated under three typical fault scenarios, leading to significant improvements: a 64.12% reduction in detection time for three-phase grounding faults, a 69.88% decrease for single line-to-ground faults, and a 36.84% improvement in phase-to-phase fault detection. Additionally, the overall performance of the strategy was thoroughly assessed through extensive simulations covering various fault cases within a selected range of typical faults. The simulations demonstrated the superiority of the proposed strategy in CF mitigation, with a significant reduction in incidents from 89 to 34 out of 150 tested scenarios. This highlights the robustness and reliability of the proposed strategy. [ABSTRACT FROM AUTHOR]

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the penetration of the high proportion of power electronics interfaced energy resources, the frequency stability issue in power systems is becoming increasingly prominent. This paper proposes a coordinated control strategy of multiple voltage source converter based high voltage direct current transmission (VSC‐HVDC) to simultaneously improve the transient frequency and steady‐state frequency after a severe disturbance. Firstly, a modified average system frequency response (MASFR) model is constructed with reserve power limitation, which takes into account the frequency responses of different types of generators (thermal, hydro and new energy resources). Secondly, according to the frequency stability requirements, the corresponding constraints, which consider the overload capacity of VSC‐HVDC, the AC transmission capacity and the frequency of AC grids on both sides of VSC‐HVDC, are formulated. Thirdly, for the transient frequency control, the coordinated optimization control model of multiple VSC‐HVDC is established, which aims to minimize the control energy considering the transient frequency threshold. For the steady‐state frequency control, the coordinated optimization control model is fomulated, which aims to minimize the control cost while considering the steady‐state frequency threshold. The two control schemes achieve seamless and smooth switching. Finally, the correctness and effectiveness of the proposed control strategy are verified in the improved IEEE 39 bus system. [ABSTRACT FROM AUTHOR]

This paper presents various control strategies to improve operations in two interconnected areas connected by a VSC‐HVDC transmission line. The main focus is on designing a central control system (CCS) that coordinates control units in both areas. In area 1, an AC voltage control unit is connected to the CCS. In area 2, three control units including a load power control unit, a fault detection unit, and an AC voltage control unit are also connected to the CCS. The CCS receives inputs from these units and generates commands for the DC voltage and active/reactive power control units on both sides of the DC line. The first proposed strategy addresses permanent voltage drops caused by load fluctuations in area 2. It adjusts the transmitted power from area 1 based on voltage variations in area 2. The second strategy focuses on mitigating faults in area 2 by injecting active and reactive power from area 1 during such events. The third strategy resolves transient voltage oscillations in both areas by controlling the reactive power of stations on either side of the DC line. Simulations using MATLAB‐SIMULINK demonstrate that these mechanisms successfully achieve their objectives. [ABSTRACT FROM AUTHOR]

Voltage Source Converter-based High-Voltage Direct Current Transmission (VSC-HVDC) is essential for integrating renewable energy sources and facilitating inter-regional power transmission. This study evaluates the reliability of control and protection devices within these systems, which are crucial for the stable operation of power grids. Humidity significantly affects both the operational conditions and lifespan of these devices. Previous studies, reliant on extensive full-condition fatigue testing, have lacked effective test models and detailed analyses of mechanisms. To address this gap, a humidity diffusion model was developed to comprehensively investigate moisture diffusion mechanisms. Using the insights gained, the Hallberg–Peck model was applied to predict the lifespan of these devices, quantitatively assessing how changes in humidity affect their reliability. This approach employs a stringent failure criterion, leading to a conservative predicted lifespan. This method achieved a prediction accuracy of 85.648% compared to the benchmarks in GB/T 2423.50-2012, validating the accuracy of our model and the effectiveness of our simulation technology under stringent conditions. This research provides vital theoretical data and serves as an essential tool for guiding the precise maintenance of equipment in varying environmental humidity levels. [ABSTRACT FROM AUTHOR]

Due to the high cost and complex challenges faced by offshore wind power transmission, economic research into offshore wind power transmission can provide a scientific basis for optimal decision-making on offshore wind power projects. Based on the analysis of the topology structure and characteristics of typical wind power transmission schemes, this paper compares the economic benefits of five different transmission schemes with a 3.6 GW sizeable onshore wind farm as the primary case. Research includes traditional high voltage alternating current (HVAC), voltage source converter high voltage direct current transmission (VSC-HVDC), a fractional frequency transmission system (FFTS), and two hybrid DC (MMC-LCC and DR-MMC) transmission scenarios. The entire life cycle cost analysis model (LCCA) is employed to thoroughly assess the cumulative impact of initial investment costs, operational expenses, and eventual scrap costs on top of the overall transmission scheme's total cost. This comprehensive evaluation ensures a nuanced understanding of the financial implications across the project's entire lifespan. In this example, HVAC has an economic advantage over VSC-HVDC in the transmission distance range of 78 km, and the financial range of a FFTS is 78–117 km. DR-MMC is better than the flexible DC delivery scheme in terms of transmission capacity, scalability, and offshore working platform construction costs in the DC delivery scheme. Therefore, the hybrid DC delivery scheme of offshore wind power composed of multi-type converters has excellent application prospects. [ABSTRACT FROM AUTHOR]

The power transmission system of Afghanistan is witnessing a significant shortage in terms of capacity, reliability, flexibility, and energy security. The goal of this paper was to identify and examine the associated issues, challenges, and opportunities for domestic transmission grid and power imports in the country. On these bases, proposals and recommendations were provided that can help the Afghan energy sector strategically enhance its transmission capacity and make the country's existing massive renewable energy potential exploitation feasible. The focus was on the expansion of high-voltage direct current transmission technology. The findings of the paper revealed that the utilization of high-voltage direct current, hybrid high-voltage alternating current, and high-voltage direct current transmission technologies can facilitate bulk power transmission and trade between south and central Asia, as well as regional energy sustainability, development, and security. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive performance analysis of power systems incorporating High Voltage Direct Current (HVDC) transmission lines, with a focus on the impact of integrating advanced Flexible AC Transmission Systems (FACTS) devices, namely Static Synchronous Series Compensator (SSSC) and Static Synchronous Compensator (STATCOM). This study evaluates key performance parameters, including Total Power Loss (TPL), Voltage deviation (Vdev), transmission efficiency, and corona loss, across three configurations, HVDC alone, HVDC with SSSC, and HVDC with STATCOM. Through simulations conducted using MATLAB or Simulink, the results demonstrate that the addition of SSSC and STATCOM significantly improves system performance by reducing power losses, enhancing voltage stability, and optimizing transmission efficiency. The analysis reveals that HVDC systems with SSSC outperform other configurations in terms of power loss reduction and voltage stability, while STATCOM improves voltage regulation and minimizes deviations. This study highlights the benefits of incorporating SSSC and STATCOM into HVDC systems for enhancing power system efficiency, stability, and operational reliability. [ABSTRACT FROM AUTHOR]

Nowadays, with the significant expansion of industrial growth, the bulk power requirement can only be satisfied through high-voltage direct current HVDC transmission. The converter transformer is the utmost vital part of the HVDC transmission. Pressboard insulation is most commonly used as interdisc insulation in converter transformers. During working conditions due to elevated temperature and different operational stresses, insulation material gets deteriorated. It may cause a risk to the life of the converter transformer. The effects of elevated temperatures as well as frequency on pressboard insulation of the converter transformer are examined in this study. The condition evaluation and morphological changes in pressboard insulation at elevated temperatures can evaluate with the help of frequency domain spectroscopy (FDS) and atomic force microscopy (AFM) techniques. The impact of elevated temperatures on insulation material can be analyzed based on surface roughness and dielectric parameters. In MATLAB Simulink environment, a dual winding single-phase converter transformers valve side star winding 60 discs model is constructed for impulse test. Based upon arrival time and velocity of traveling wave, insulation degradation location can be identified by using mathematical morphology. The simulation results demonstrate that the suggested method can notably located degradation across disc winding. [ABSTRACT FROM AUTHOR]

Recently, significant attention has been paid to the large-scale use of renewable energy through high-voltage direct current (HVDC) because of its economic feasibility. At the same time, the growing demand for electricity and the increasing penetration of renewable energy sources have prompted the electric power industry to explore methods to optimize the use of the existing grid infrastructure. Dynamic thermal line rating (DTLR) is a technique that allows transmission lines to operate at their maximum capacity, considering their real-time operating conditions. The majority of existing research on this topic has focused predominantly on employing DTLR in alternating current systems and exploring their applications. This study presents a novel approach by applying DTLR to HVDC transmission corridors, with the aim of maximizing the utilization of their capacity and facilitating increased integration of renewable energy. The performance of the proposed approach is evaluated by conducting a case study for an HVDC transmission line in Alberta, Canada. On average, the mean increase in ampacity above the static rating is 64% during winter and 34% during summer. This additional capacity can be used to integrate wind energy, replacing coal-fired generation. This leads to a significant reduction in greenhouse gas emissions, also quantified in this contribution. [ABSTRACT FROM AUTHOR]

Commutation failures in line commuted converter-based high voltage direct current (LCC-HVDC) transmission systems leads to an increase in the converter bus voltage of the rectifier station, thus resulting in AC transient overvoltage in the sending-end grid. The transient overvoltage could lead to the disconnection of renewable energy generation and threaten the stable operation of the sending-end grid. However, the influences of the coupling between AC and DC systems caused by the interaction between the active and reactive power of the sending-end grid, the AC bus voltage of the rectifier station, and the DC current are ignored. The AC transient overvoltage cannot be accurately suppressed. Therefore, in this study, the transient voltage characteristics of the rectifier station under a commutation failure of the inverter station are analyzed. The influence of LCC-HVDC control on the AC bus voltage of a rectifier station through the active and reactive power of the rectifier station is analyzed. A dynamic model of the AC bus voltage of a rectifier station under an AC-DC system coupling is established. The calculation method of the command value of the DC current of the rectifier station is proposed by a predictive control model, and an improved suppression method for AC transient overvoltage is proposed. The case studies show that the accuracy and effectiveness of the suppression of AC transient overvoltage are improved by considering the coupling between AC and DC systems. [ABSTRACT FROM AUTHOR]

The rapid growth of offshore wind power has resulted in a mismatch between generation and demand because of its variability. To quantify the maximum wind power penetration of the transmission network, the dispatchable region is defined as the largest region in the uncertainty space. The security distance is defined as the minimum distance from the operating point to the boundaries of the dispatchable region. System operators can use security distance as a metric to assess the flexibility of the power system. This paper proposes a method to construct the dispatchable region for the AC/DC hybrid system with VSC‐HVDC by outer convex relaxation firstly. The second‐order cone relaxation is employed to reformulate non‐convex and non‐linear power flow equations. Next, a polyhedral approximation is adopted to obtain the convex hull of the dispatchable region. Subsequently, an efficient algorithm known as adaptive constraint generation (Ad‐CG) is introduced to calculate the boundaries of the dispatchable region. Furthermore, solving the Chebyshev centre problem determines the minimal security distance. The modified IEEE 5‐bus and 39‐bus system is used for validating effectiveness of the proposed method and evaluating the impact of the converter reactive power compensation capacity and generation dispatch on the dispatchable region. [ABSTRACT FROM AUTHOR]

Increased demand in renewable power move towards the balancing conventional dependent energy source lead the increase in technical development in reliable power generation. This model contains the wind speed variation, capacity, uncertainty, and production are considered in system evaluations to bring the wind power to more sustainable energy. More reliable VSC HVDC technology in power transmissions for longer distances is preferred to transmit the renewable generated energy to remote end areas. Authors introduced particle swarm optimization method into the wind integrated HVDC System. The system is developed in MATLAB/Simulink to evaluate the wind power generation performance and Transmission performance. The simulation results are correlated and validated with the existing VSC HVDC link parameters. The supremacy in wind energy with particle swarm optimization performance is validated and more viable to integrate wind energy system with VSC HVDC system to transmit the reliable power to remote areas. [ABSTRACT FROM AUTHOR]

Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The power-electronics converters are increasingly applied in modern power system, which contains various sub-systems, such as renewable energy power plants and high voltage direct current transmission systems, etc. The electromagnetic transient simulation has been one of the important tools for the study of complex system containing large numbers of power converters. The coordination control of the power converters and corresponding power generation and load units is one of the challenges ensuring stability and obtaining optimal efficiency. However, the detailed modeling of the power converters considering the conduction and switching losses can cost a great number of computation resources, which makes it difficult to simulate a large system. This work proposed a current injection method for converter power loss representation, which can accurately consider the conduction and switching losses of the power-electronics switches with low computation complexity. A look-up table (LUT) of the power loss ratio is calculated before the simulation, and a current source representing the power loss is connected in parallel with the converter to track the reference loss generated by the look-up table. The proposed method can be combined with multiple converter modeling schemes, such as the two-resistance model, the switching-function model, and the average value model, etc. The topologies of the two-level converter and the modular multi-level converter (MMC) were used in the case studies to demonstrate the effectiveness of the proposed method. Compared to the device-level model, the simulation power loss deviation is 0.64% and 4.13% applying the current injection method model in the case studies of the two-level converter and the MMC. [ABSTRACT FROM AUTHOR]

The grid‐following control‐based hybrid cascaded high‐voltage direct current (HC‐HVDC) links may contribute to the worsening of inertia decline and instability issues, especially in situations characterized by a weak grid. To address the challenge, this paper proposes a grid‐forming (GFM) based optimal frequency support scheme (OFSS) for HC‐HVDC integrated wind farms. Firstly, a GFM control for hybrid converter is proposed and its stability under weak grid conditions is evaluated through a small‐signal model. Then, DC current–voltage droop control is introduced to the line commutated converter (LCC). This control approach ensures the consistency of reactive power in the LCC by regulating the DC voltage and current in the same direction, thereby mitigating AC voltage fluctuations. It also facilitates active power control in the LCC in response to grid frequency variations. Furthermore, the OFSS can convey the frequency of receiving‐end grid to the rectifier and wind farms without communication for precise power control. Finally, to validate the effectiveness of OFSS, a point‐to‐point HC‐HVDC and a 4‐machine test model are constructed on PSCAD/EMTDC. The OFSS significantly enhances the frequency support capability of HC‐HVDC links and improves the robustness in weak grid. [ABSTRACT FROM AUTHOR]

The transmission network of a power system is important in connecting interactions between the generation and distribution sides. A significant aspect in the power system profile is voltage improvement. This study intends to examine the impact of inserting High Voltage Direct Current (HVDC) on the system's voltage stability, network power losses and power transfer capacity of transmission network under several cases of load contingency. IEEE 57-Bus test system is used for testing the addition of HVDC transmission based on genetic algorithm. Modeling of point-to-point HVDC transmission and multi-terminal HVDC transmission is carried out using the Power System Simulator for Engineering (PSS/E) version 32 Package Program (A collection of computer programs and organized data files called PSS/E software was developed by Siemens PTI to handle the fundamental tasks of power system performance simulation work). The system's performance was compared with and without the HVDC inserted under different loading scenarios: 5%, 10%, and 20% of the total load. The comparative results can show that active power losses at the normal load case are reduced by 55.714% after inserting point to point HVDC topology, and after inserting multi-terminal HVDC topology reduced by 68.214%. Also, the reactive power losses reduce by 55.714% after inserting point to point HVDC topology and after inserting multi-terminal HVDC topology reduced by 66.830% at the same case. The results shown that inserting HVDC Transmission to the system gives better improvement in bus voltage profile and a significant reduction in total network power losses and increase in power transfer capacity of transmission network. The results also showed that multi-terminal HVDC transmission is better in voltage improvement and total power losses reduction when HVDC Transmission is added to the system. [ABSTRACT FROM AUTHOR]

High voltage direct current (HVDC) transmission is flexible towards the power control (produced by solar or wind) and can be transported over thousands of kilo meters with minimal losses over the high voltage alternative current (HVAC). It allows solar power to be integrated into the current power grid on a large scale. The author view in this article aims at providing an overview of methods used to integrate HVDC and solar systems. MATLAB/Simulink is used to simulate the solar power integration with HVDC transmission link. This article emphaises solar energy and grid integration, which results in quality and controlled electricity to the grid. Further the simulation studies are compared with real time data between the stations Pugalur AC grid (high solar energy region) and Thrissur AC grid (low solar energy region). Obtained results from the simulation, voltage and currents and power quality stresses the superiority towards the solar integration. The comparison studies enumerate the need to go situation for HVDC technology during the penetration of solar voltaic penetration into the utility network. [ABSTRACT FROM AUTHOR]

This research paper addresses the issue of enhancing the operational availability of NPC three-level converter-based high-voltage direct current (HVDC) transport systems during alternating current (AC) grid fault conditions. During short-circuit faults in power transmission lines, voltage sags can occur, causing fluctuations in the DC link voltage of converter systems. These voltage sags have the potential to induce a reversed power flow and trip the VSC-HVDC transmission system. The objective of this paper is to develop a nonlinear control technique that investigates the fault ride-through (FRT) capability of VSC-HVDC transmission system characteristics during voltage sag events. To achieve this, we conduct semi-experimental investigations using Processor-in-the-Loop (PIL) simulations and analyze the results. Symmetrical and asymmetrical voltage sag events with different remaining voltages are applied to an AC grid, and their effects are observed for varying durations. The proposed nonlinear control technique aims to mitigate the impact of voltage sags on the operational availability of HVDC transport systems. By analyzing the semi-experimental results, we aim to gain insights into the FRT capability of the VSC-HVDC transmission system. [ABSTRACT FROM AUTHOR]

This paper presents an innovative approach in line commutated converter-based high-voltage direct-current (LCC-HVDC) transmission line for recognizing the section of the faults. In this work, three adaptive neuro-fuzzy inference system (ANFIS) modules have been suggested to investigate the safety responsibilities in the LCC-HVDC line. The ANFIS-1 aims to ascertain the faults in both sections; ANFIS-2 is to distinguish the section of the fault; and ANFIS-3 is to recognize the characteristics of the fault. To ascertain the effectiveness of the ANFIS approach, it has been compared with the differential protection (DP), wavelet transform (WT), fuzzy and artificial neural network (ANN). Furthermore, the proposed methods have been tested by varying the fault resistance (up to 500 Ω), power angle (from 5 to 15 degrees), near and end faults, and changing the transmission line parameters (±15 %). The simulation outcomes are disclosed that the proposed ANFIS technique yields better performance than other studied methods in terms of percentage of accuracy, time of fault section recognition, and reach setting. [ABSTRACT FROM AUTHOR]

Empirical evidence suggests that marine animals perceive and orient to local distortions in the earth's natural magnetic field. Magnetic fields (MFs) generated by electrified underwater cables may produce similar local distortions in the earth's main field. Concern exists that these distortions may impact migration movements of MF-sensitive animals. The Trans Bay Cable (TBC) is a ± 200-kV, 400-megawatt, 85-km high-voltage direct current transmission line buried through San Francisco Bay (37° 56′ 8.81″ N, 122° 27′ 0.19″ W). Detections of adult green sturgeon implanted with acoustic transmitters were used from six cross-bay receiver arrays from 2006 to 2015 to investigate how inbound and outbound migration movements through lower portions of their route to/from upstream breeding grounds are related to the TBC's energization status (off/on) and other local environmental variables. Here, we assess how these variables impacted transit success, misdirection from the migration route, transit times, and migration path locations within stretches between the Bay's mouth and the start of the Sacramento River. Overall, there was varied evidence for any effect on migration behavior associated with cable status (off/on). A higher percentage of inbound fish successfully transited after the cable was energized, but this effect was nonsignificant in models including temperature. Outbound fish took longer to transit after cable energization. Inbound and outbound migration path locations were not significantly influenced by cable energization, but results suggest a potential subtle relationship between energization and both inbound and outbound paths. Overall, additional migration-based studies are needed to investigate the impact of anthropogenic cables on marine species. [ABSTRACT FROM AUTHOR]

The restoration control of the modern alternating current–direct current (AC–DC) hybrid power grid after a major blackout is difficult and complex. Taking into account the interaction between the line‐commutated converter high‐voltage direct current (LCC‐HVDC) and the AC power grid, this paper proposes a novel optimization method of restoration path to reconfigure the skeleton network for the blackout power grid. Based on the system strength, the supporting capability of the AC power grid for the LCC‐HVDC is first analysed from the aspects of start‐up and operation of LCC‐HVDCs. Subsequently, the quantitative relationship between the restoration path and the restoration characteristic of LCC‐HVDC is derived in detail based on the system strength indices of the short‐circuit capacity and the frequency regulation capability. Then, an optimization model of restoration path considering non‐tree paths is formulated and a feasible optimization algorithm is proposed to achieve the optimal path restoration scheme. A modified IEEE 39‐bus system and a partial power grid of Southwest China are simulated to show that the proposed method is suitable for the restoration of AC–DC power grids and can improve restoration efficiency. This research can be an important guidance for operators to rapidly restore the AC–DC power grid. [ABSTRACT FROM AUTHOR]

Assessment of reliability indices is important when availability and unavailability of the system or systems or components or group of components are to be assessed. There are various reliability indexes which are very important for overall performance of any complex engineering system. Reliability block diagram modeling is required to be formulated for evaluating different essential and important reliability parameters of any complex engineering system. In view of above, in this paper, reliability block diagram modeling of HVDC converter station is represented and formulated. The schematic diagram of the HVDC converter station is available in literature and based on that schematic diagram the modeling of HVDC converter station is formulated in this paper. After the reliability block diagram modeling of HVDC converter station, the mean time to failure (MTTF) of each and every components of HVDC converter station are also evaluated and represented in the result and discussion section. The reliability of each and every component of the HVDC converter station is evaluated and expressed in result section. Assessment of unavailability is also obtained and shown in result section. [ABSTRACT FROM AUTHOR]

Soil resistivity is the key parameter influencing resistance and potential distribution on the soil surface for grounding systems and electrodes for HVDC power transmission. The paper presents a novel approach that does not rely on analytical expressions or simplifications inherent in the Wenner and classical characterization methods for obtaining a layered soil model. The new method and corresponding computational tool are implemented as an iterative process using a finite element method coupled with a numerical parameter estimation solver. The novel method is applied on soil with a very thin and highly resistive surface layer compared to a resistivity of a lower layer, where accurate implementation of the classical method would require Wenner measurements for short electrode spacings a. Since the classical characterization methods rely on the assumption that the electrode driving depth b is much smaller than a, it is practically (physically) impossible to drive the electrodes to sufficiently small depth b. The application of the novel method and a comparison with the classical approach are presented on examples including normal soils, one hypothetical soil with a thin highly resistive surface layer, and one experimental desert location. The application of the proposed method leads to an extreme increase in the characterization accuracy for the case of ideal two-layer soil with thin high resistivity topsoil justifying considerable computational time. [ABSTRACT FROM AUTHOR]

In order to solve the problems of insufficient abilities to withstand transition resistance under remote faults and difficulties in identifying internal and external faults for HVDC transmission line protection, a new single-ended protection scheme based on time-domain convolutional power was proposed. In this scheme, the ratio of time-domain convolution power at different frequencies is used to detect internal and external faults, and the long window convolution power is used to form the pole selection criteria. Due to the integration of transient power fault characteristics at high and low frequencies, this scheme amplifies the characteristic differences between internal and external faults caused by DC line boundaries and has a strong ability to withstand transition resistance. Based on PSCAD/EMTDC, simulation verification was conducted on the Yunnan–Guangzhou ±800 kV HVDC project. The results show that the proposed single-ended protection scheme can effectively identify fault poles, as well as internal and external faults. It has strong resistance to transition resistance and certain anti-interference ability and has strong adaptability to DC line boundaries, which meets the protection requirements of HVDC transmission systems for high speed, selectivity and reliability. [ABSTRACT FROM AUTHOR]

A large‐scale AC/DC hybrid power network has recently been constructed in China because of the fast development of high voltage direct current (HVDC) technology. The receiving AC system must have sufficient system strength to guarantee the safe operation of the DC side. The paradox is that raising the AC side system's strength will increase the short‐circuit current (SCC) level, endangering the safety of the system. In order to resolve the contradiction between the system strength of multi‐infeed DC receiving‐end power networks and SCC, this paper proposes an optimal transmission switching strategy. Firstly, the system strength is characterised by the multi‐infeed short‐circuit ratio (MISCR), followed by constructing a comprehensive constraint set that considers the MISCR and SCC simultaneously. Secondly, to optimize SCC with MISCR and N−1 safety constraints, a mixed integer linear programming model is developed. Finally, to enhance the computing performance for large power systems, a new connectivity constraint set and decision space reduction techniques are provided. The proposed method is tested for effectiveness using the IEEE 30‐bus and IEEE 118‐bus systems. [ABSTRACT FROM AUTHOR]

To investigate the impact of incoming current from high-voltage direct current (HVDC) transmission grounding electrodes on nearby oil and gas pipelines operating in single-pole earth return mode, the pipeline interference was simulated considering cathodic protection for different conditions such as the distance between grounding electrode and pipeline, soil resistivity, pipeline coating resistance, and outer diameter of pipeline. An interference model of HVDC grounding electrode on pipeline was established by finite element method using COMSOL Multiphysics software and validated experimentally. The distribution of cathodic protection potential on pipeline caused by grounding electrode interference was derived. The results showed that the offset of cathodic protection potential on pipeline was increased with the increasing of grounding electrode current and soil resistivity, but decreased with the increasing of the distance between grounding electrode and pipeline, the outer diameter of pipeline, and the resistance of coating on pipeline. Some other anticorrosion measures were discussed. These findings can serve as a reference for optimizing pipeline cathodic protection system and grounding electrode siting. [ABSTRACT FROM AUTHOR]

This article explores the use of a multilevel multifunction inverter (MLMFI) to enhance the power transfer capacity in transmission networks. The MLMFI is controlled by a voltage control loop and a current control loop to optimize power extraction from a solar array and minimize harmonics. The proposed controller includes reactive power and damping controllers to improve power transfer capacity and transient stability. Simulation and experimental results confirm the effectiveness of the system, which increases power transfer capacity by 23% and improves the voltage profile by 9.5%, without the need for costly FACTS devices. [Extracted from the article]

In this paper, the problem of harmonic coupling between the converter transformer and the converter under the action of geomagnetically induced current (GIC) is proposed to be investigated. Firstly, a model of a 12‐pulse line commutated converter high voltage direct current (LCC‐HVDC) converter station based on harmonic state space (HSS) theory is established. Secondly, the harmonic components of the interaction between the AC‐side harmonic current and the DC‐side harmonic voltage are qualitatively analyzed by using the harmonic modulation theory. Through the simulation model and harmonic state space (HSS) calculation model, the harmonic coupling characteristics of power grid are analyzed. Finally, the harmonic current and voltage amplitude of AC / DC power grid under different GIC are calculated, and the characteristics and rules of AC / DC harmonic propagation are revealed. Among them, the amplitude of the 2nd harmonic current on the AC side and the 3rd harmonic current on the DC side increases linearly with the GIC. In addition, the 3rd and 9th harmonics on the AC side are also greatly affected by the magnetic bias of the converter. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BackgroundThe converter stations of high-voltage direct current (HVDC) transmission lines generate special total electric fields. At present, few investigations have been conducted on total electric fields in the workplace of converter stations from an perspective of occupational health. ObjectiveTo understand the current situation of total electric field strength in the workplace of converter stations. MethodsUsing purposive sampling, a calibrated HDEM-1 direct current (DC) total electric field strength measurement system was used to measure the total electric fields of 12 converter stations serving 6 DC lines in Southeast and Southwest China according to the Measurement method for total electric field strength and ion current density of the converter stations and DC transmission lines (DL/T 1089—2008). The results were evaluated according to occupational exposure limits recommended by The limits of electromagnetic environment at ±800 kV UHV DC converter station (DL/T 275—2012), the American Conference of Governmental Industrial Hygienists (ACGIH), and the International Commission on Non-Ionizing Radiation Protection (ICNIRP). ResultsA total of 615 check points were planned, the total electric field strength was 0.05-37.05 kV·m−1, and the median was 10.45 kV·m−1. The total electric field strength of 39 check points (6.3%) exceeded 25 kV·m−1 (the limits of ACGIH and ICNIRP), and the total electric field strength of 12 check points (2.0%) exceeded 30 kV·m−1 (the limit of DL/T 275—2012). There were statistically significant differences in the total electric field strength values and the proportions of exceeding 25 kV·m−1 between the neutral regions and the positive regions and between the neutral regions and the negative regions (P < 0.01). The proportion of total electric field strength exceeding 30 kV·m−1 in the negative regions was higher than that in the positive regions (P < 0.01). There were no significant differences in the total electric field strength of converter stations at different voltage levels and different altitudes (P > 0.05). There were no significant differences in the proportions of total electric field exceeding 25 kV·m−1 and exceeding 30 kV·m−1 in converter stations at different voltage levels and different altitudes (P > 0.05). ConclusionThe total electric field in some workplace of converter stations exceeds selected limits. Converter station operators may be exposed to high-strength total electric field for a short time.

The 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. [ABSTRACT FROM AUTHOR]

As one of the most common voltage/var‐related contingencies, commutation failures in hybrid AC/DC networks deteriorate the voltage profiles. Thus, systems may suffer from large‐scale cascading risks induced by the lack of dynamic reactive power support. Conventional power system planning usually aims to optimize the device capacity and location, ignoring the influences of intrinsic device parameters on high‐voltage direct current (HVDC) dynamics during commutation failures. If the intrinsic device parameters are also taken into account in the planning problem, it would allow for faster dynamic voltage/var support during system faults or disturbances to recover from voltage drops. However, considering the intrinsic parameters, allocations and capacities of a device, the optimal planning problem brings several challenges, such as scenario selections and computational burdens. To overcome these issues, an objective‐oriented scenario selection based power system planning approach is proposed in this paper. First, the detailed operations of converter stations are formulated both considering the steady state and system dynamics. Next, the quantitative relation between the power losses and deviation in system conditions is then derived to approximately describe the operational characteristics. Then, an objective‐oriented representative scenario selection method is introduced, aiming to reduce the number of selected scenarios, guaranteeing both computational accuracy and efficiency. Finally, a modified IEEE‐118 system is used to test the proposed algorithm, and the superiority and computational efficiency are observed by the simulation results. [ABSTRACT FROM AUTHOR]

The Modular Multilevel Converter High Voltage Direct Current Transmission (MMC-HVDC) technology is considered to be the most feasible choice for high-voltage and high-power transmission systems, and its flexibility and high controllability provide a new solution for renewable energy grid integration. The MMC topology contains a large number of capacitors, which enables it to provide a certain active inertia support for the connected AC system. Different from a synchronous machine, the active inertia control of an MMC can flexibly adjust a system's inertia-supporting power by changing the control parameters. By introducing a variation of the Sigmoid function with amplitude-limiting capability, this paper proposes an adaptive active inertia control strategy for the MMC-HVDC system. The proposed scheme adjusts the inertia constant adaptively according to the frequency change rate of the AC system, which can better respond to the frequency recovery performance. Finally, the MMC-HVDC simulation model is established in PSCAD/EMTDC to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive assessment for the small‐signal voltage stability of voltage source converter (VSC)‐HVDC systems supplying industrial loads represented by the induction motors (IMs) and provides a stability enhancement control for the VSCs. First, the steady‐state voltage stability is analysed to seek the factors that affect the existence of the stable equilibrium point. Then, the small‐signal voltage stability analysis is performed based on the developed linear model. Eigenvalue analysis is carried out to capture the critical factors that induce instability phenomena correlative to the system voltage. It demonstrates that decreasing either the proportional gain K of the VSC's PI controller or the electrical distance between the VSC and IM is detrimental to voltage stability. Next, the enhancement control strategy is elaborated. It adopts virtual reactance and virtual admittance control for the VSC to improve the voltage control capability. Finally, the effectiveness and robustness of the proposed enhancement control are validated via time‐domain simulations in a multi‐IM system supplied by VSC‐HVDC. [ABSTRACT FROM AUTHOR]

Frequency 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. [ABSTRACT FROM AUTHOR]

Converter blocking is a serious malfunction encountered in high voltage direct current (HVDC) transmission systems. During sending-end converter blocking, the resultant active power and reactive power surplus in the sending-end power system lead to a severe increase in bus voltage and grid frequency. Consequently, this poses a substantial threat to the stability of the power system. Traditional control techniques generally control the frequency and voltage separately, which makes it challenging to regulate them jointly. This research paper introduces a collaborative approach for optimal control of voltage and frequency to address this issue. State space models for converter bus voltage and grid frequency prediction are developed using the bus voltage sensitivity matrices and system swing equation. The regulation of the converter bus voltage and grid frequency are intrinsically integrated using the explicit model predictive control (EMPC). When blocking occurs and results in an increase in the converter bus voltage and grid frequency, the EMPC controller regulates the output of active power and reactive power from the wind farm to realize the cooperative regulation of the converter bus voltage and grid frequency. The applicability and effectiveness of this strategy have been confirmed through simulation studies. [ABSTRACT FROM AUTHOR]

This paper analyzes an accident of abnormal increase of pole bus differential current and pole differential current of a converter station caused by line fault of a ±800 kV extra high-voltage direct current transmission project. After a lightning strike caused a short circuit and grounding of the DC line, the sudden voltage change protection of the DC line was triggered and the DC full voltage restart was successful. The pole bus differential current and pole differential current of the converter station have reached the protection set but have not reached the protection delay set; therefore, the differential protection has not acted. This paper first introduces the configuration principles of pole differential protection, pole bus differential protection, and line voltage sudden change protection for extra-high voltage converter stations. Second, the operation of the DC protection under this fault was analyzed in detail, and the reasons for the occurrence of pole bus differential current and pole differential current were also analyzed in this paper. Then, the range of equipment that caused the abnormal increase in differential current was identified. Finally, the lightning strike model was built on the real-time digital system, and the fault was simulated and replicated. It was determined that the abnormal increase in differential current was caused by the discharge of the pole bus surge arrester caused by the second lightning strike on the DC line. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic power systems. Synchronization between the inverter and the grid needs to be achieved by a phase-locked loop (PLL), the performance of which determines the quality of power transmission. This paper proposes a PLL adapted to extremely harsh grid conditions. Firstly, the traditional synchronous reference frame PLL and the dual second-order generalized integrator (DSOGI-PLL) are analyzed, and the errors in phase-locking and the shortcomings of these two methods in the presence of DC components in the grid are pointed out. Secondly, based on the harmonic grid voltage, a repetitive control internal model is introduced by DSOGI to realize the real-time tracking and regulation of the harmonic signals in order to suppress the harmonic voltage disturbance. In addition, a DC bias elimination and frequency adaptive method is proposed to solve the problems of DC bias and grid voltage frequency fluctuation in order to achieve adaptive tracking of the grid phase. Finally, the superiority of the proposed strategy is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

This work presents a control strategy for integrating an offshore wind farm into the onshore electrical grid using a high-voltage dc transmission system based on modular multilevel converters. The proposed algorithm allows the high-voltage DC system to operate in grid-connected or stand-alone modes, with the second case supplying power to local loads. In either mode, the modular multilevel rectifier works as a grid-forming converter, providing the reference voltage to the collector network. During grid-connected operation, the modular multilevel inverter regulates the DC link voltage while the generating units are controlled to maximize power extracted from the wind turbines. Conversely, in the event of grid disconnection, the onshore modular multilevel converter takes over the regulation of the AC voltage at the point of connection to the grid, ensuring energy supply to local loads. Simultaneously, the generator controller transitions from tracking the maximum power of the wind turbines to regulating the DC link voltage, preventing excessive power injection into the transmission DC link. Additionally, the turbine pitch angle control regulates the speed of the generator. Mathematical models in the synchronous reference frame were developed for each operation mode and used to design the converter's controllers. A digital model of the wind power plant and a high-voltage dc transmission system was implemented and simulated in the PSCAD/EMTDC program. The system modeled includes two groups of wind turbines, generators, and back-to-back converters, in addition to a DC link with a rectifier and an inverter station, both based on modular multilevel converters with 18 submodules per arm, and a 320 k V /50 k m DC cable. Aggregate models were used to represent the two groups of wind turbines, where 30 and 15 smaller units operate in parallel, respectively. The performance of the proposed control strategy and the designed controllers was tested under three distinct scenarios: disconnection of the onshore converter from the AC grid, partial loss of a wind generator set, and reconnection of the onshore converter to the AC grid. [ABSTRACT FROM AUTHOR]

In the case of dispersed load consumption, Ultra‐high Voltage Direct Current (UHVDC) system in cascaded connection mode can significantly reduce the cost by building DC lines between different ends, but the communication delay caused by it brings challenges to the original control strategy. Therefore, the control strategy suitable for cascaded multi‐terminal UHVDC (CMT‐UHVDC) system is developed. In this paper, first of all, the operation characteristics, mathematical model, and adaptability of the original control strategy are discussed. Next, an autonomous master‐slave control strategy is proposed to maintain voltage balance without real‐time communication between high‐end and low‐end valves. Finally, based on the planning parameters of an actual project, the electromagnetic transient simulation model of the CMT‐UHVDC transmission system is established. Several working conditions and the practical influence of sampling deviation on the control performance are discussed and analyzed, which verifies the proposed control strategy's effectiveness. [ABSTRACT FROM AUTHOR]

Offshore wind farm (OWF) is considered as a perfect zero‐carbon energy source for the future power system. However, the growing offshore distance and water depth of OWF make the OWF HVDC transmission technique a more promising solution than HVAC due to higher cost‐efficiency and reliability. In this paper, the current situation of OWF‐HVDC projects is introduced at first. Then, novel converter topologies with the higher power density and cost‐efficiency are presented, including the hybrid modular multilevel converter (MMC), alternative arm converter (AAC), and diode rectifier (DR). Next, several OWF HVDC transmission system topologies are introduced, including terminal‐hybrid, station‐hybrid and all‐DC delivered system. Furthermore, the key technologies for OWF HVDC operation and control are summarized, including grid‐forming control strategy for offshore wind turbines, stability analysis method, corresponding stability enhancement measures and frequency support control strategies. Additionally, the fault ride‐through and protection strategies for different fault locations have been presented. Finally, the main conclusions and prospects for OWF HVDC are summarized. [ABSTRACT FROM AUTHOR]

High voltage direct current transmission based on a modular multilevel converter (MMC-HVDC) is an effective method to solve the grid connection of the new energy. A DC fault is an issue that must be solved for MMC-HVDC. This paper proposes a protection scheme for HVDC converters to quickly suppress DC fault current without increasing the operation loss. By employing a bypass arm in conjunction with a switch-type zero-loss current limiter (SZCL), most of the DC current in the bridge arm flows through the bypass arm so the fault current of the power devices is reduced. There are a number of main advantages of this scheme. The fault isolation time can be greatly shortened, the cost of the system is effectively reduced, the steady-state operation loss of the system does not increase, the operation of the AC-grid can be maintained stably when a DC fault occurs, and the overcurrent impulse to the AC-grid is reduced. The proposed scheme is applicable to two-terminal systems and the DC grid, especially for faults at the converter outlet of the DC grid. Simulation results using PSCAD/EMTDC show the superiority of the proposed scheme when compared with other schemes and a comparison of the costs shows the feasibility of the proposed scheme in practical applications. [ABSTRACT FROM AUTHOR]

With the rapid development of high-voltage direct current transmission systems and trends of miniaturization and integration of power and electronic equipment, higher requirements have been imposed on the key physical properties of insulating materials, such as their electrical insulation and thermal and mechanical properties. This has made research on the modification of epoxy resin by doping with nanoparticles a timely topic. In this paper, molecular dynamics simulations are used to study changes in various key physical properties of composites after doping epoxy resin with C60, C70, or the C60 derivatives phenyl-C61-butyric acid methyl ester ([60]PCBM) and bis-phenyl-C61-butyric acid methyl ester (Bis[60]PCBM). All doping treatments effectively reduced the thermal expansion coefficient, the free volume ratio, and relative permittivity; inhibited molecular chain segment motion; and increased thermal conductivity as well as Young's modulus, bulk modulus, and shear modulus. The effects on glass transition temperature were not significant. Furthermore, the analysis indicated that Bis[60]PCBM had the most prominent effects. Therefore, doping epoxy resin with Bis[60]PCBM may be an effective material modification solution for improving dielectric properties in the future. [ABSTRACT FROM AUTHOR]

The scarcity of drinking water is an increasingly pressing issue in many regions of the world, even in areas up till now considered developed. Climate change deprives many populations of the amount of water necessary for human consumption and traditional crops. Therefore, finding new water sources and making their usage more efficient and able to adapt to new environmental conditions without worsening the situation with further pollution is becoming mandatory. In the case study considered here, set on the Italian island of Vulcano in the Central Mediterranean, we propose the economic analysis and financial sustainability of plants for the desalination and recycled wastewater, powered by a DC-DC photovoltaic tracker system with silicon crystal panels sustained by a daily pack of lithium batteries. We present an estimation of the necessary budget, and propose a mix of traditional and innovative financial instruments to construct and analyse the economic trends of the installations over 30 years, considering the specific area price levels, salaries and interest rates. Finally, through the net present value index, we evaluate the financial sustainability of the entire operation, namely, identifying the circumstances when funding and building these plants in areas as remote as the one considered here is cost-effective. [ABSTRACT FROM AUTHOR]