Search

This paper explores an integration of virtual synchronous generators into voltage source converter–based VSC‐HVDC systems to enhance grid stability and performance. VSGs emulate the inertia and damping characteristics of traditional synchronous generators, thereby providing essential frequency support and improving transient stability during disturbances. The study focuses on design considerations, control strategies, and the impact of VSG incorporation on system dynamics. Through detailed simulations and analyses, it is demonstrated that VSGs can significantly reduce the rate of change of frequency during transient events, thus enhancing the overall robustness and reliability of VSC‐HVDC systems. In addition, the practical challenges of implementing VSG‐based control are addressed, and solutions are proposed to optimize system integration and performance. [ABSTRACT FROM AUTHOR]

The worldwide promotion of carbon-neutral policies is leading to a continuously growing percentage of electricity being derived from renewable energy, which makes it feasible to design power systems composed of 100% renewable energy in the future. The question of how to realize stable transmission for 100% renewable energy-integrating grids under different operating conditions needs to receive more attention. Voltage source converter-based high-voltage direct current (VSC-HVDC) technology is one of the prospective solutions for large-scale renewable energy integration due to its unique dominance in areas such as independent reactivity and active control. In this study, we design a novel, 100% renewable energy system through grid integration via a VSC-HVDC system structure and a control strategy. Unlike in other research, a mixed control strategy based on grid-forming control (PSL) and grid-following control (GFL) is developed to realize smooth switching in order to ensure secure transmission and consistent operation when the operating conditions of the 100% renewable energy-integrating grid changes. The simulation results indicate that the proposed system structure and control could stabilize renewable energy transmission under normal operation conditions and provide necessary grid support under different system disturbances. [ABSTRACT FROM AUTHOR]

Over the past few decades, wind energy has expanded to become a widespread, clean, and sustainable energy source. However, integrating offshore wind energy with the onshore AC grids presents many stability and control challenges that hinder the reliability and resilience of AC grids, particularly during faults. To address this issue, current grid codes require offshore wind farms (OWFs) to remain connected during and after faults. This requirement is challenging because, depending on the fault location and power flow direction, DC link over- or under-voltage can occur, potentially leading to the shutdown of converter stations. Therefore, this necessitates the proper understanding of key technical concepts associated with the integration of OWFs. To help fill the gap, this article performs an in-depth investigation of existing alternating current fault ride through (ACFRT) techniques of modular multilevel converter-based high-voltage direct current (MMC-HVDC) for OWFs. These techniques include the use of AC/DC choppers, flywheel energy storage devices (FESDs), power reduction strategies for OWFs, and energy optimization of the MMC. This article covers both scenarios of onshore and offshore AC faults. Given the importance of wind turbines (WTs) in transforming wind energy into mechanical energy, this article also presents an overview of four WT topologies. In addition, this article explores the advanced converter topologies employed in HVDC systems to transform three-phase AC voltages to DC voltages and vice versa at each terminal of the DC link. Finally, this article explores the key stability and control concepts, such as small signal stability and large disturbance stability, followed by future research trends in the development of converter topologies for HVDC transmission such as hybrid HVDC systems, which combine current source converters (CSCs) and voltage source converters (VSCs) and diode rectifier-based HVDC (DR-HVDC) systems. [ABSTRACT FROM AUTHOR]

To achieve simple and reliable single-phase grounding fault protection on the AC side of VSC-HVDC systems， this paper focuses on systems where the neutral point of the converter valve's AC side is impedance-grounded. The zero-sequence fundamental component on the AC side and the common-mode component on the DC side are analyzed， and analytical expressions for the zero-sequence fundamental voltage and current at both the faulted and non-faulted terminals during a metallic grounding fault are derived. For VSC-HVDC systems utilizing third harmonic injection modulation， the phase characteristics of the longitudinal third harmonic voltage induced by this modulation are examined， and expressions for the third harmonic voltage and current are derived. Based on this analysis， protection criteria using the zero-sequence fundamental voltage and third harmonic voltage at neutral point are proposed to detect grounding faults and determine their location， along with the corresponding setting calculation method. Simulation results under various operating conditions show that the protection mechanism correctly activates when a grounding fault occurs at the protection installation terminal and does not operate erroneously when faults occur at other terminals.

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.)

Copyright of Electric Power is the property of 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.)

As the penetration of the integrated intermittent and fluctuating new energy (e.g., wind and photovoltaic power) increases, the conventional grid- following voltage source converter (VSC)-based high voltage direct current (HVDC) transmission system faces the problem of interactive instability with the grid. A novel grid-forming control strategy is proposed to overcome these issues, which adopts the dynamics of a DC capacitor to realize the function of self- synchronization with the grid. Moreover, the per-unit DC voltage can automatically track the grid frequency, acting as a phase-locked loop. Next, the small-signal model of the grid-forming VSC-HVDC system is established, and the stability of the system is analyzed using the eigen-value analysis method and the complex power coefficient method. In addition, the stabilization controller is proposed for the grid-forming (GFM) control structure, which further enhances the grid-forming VSC-HVDC system's stability and helps it operate stably under both stiff and weak grid conditions. Research results show that the VSC-HVDC system under the proposed grid-forming control can work stably in both stiff and weak grids. The grid-forming VSC-HVDC system is robust and can maintain stable operations with a large range variation of the parameters in the current and voltage control loop. Simulations are carried out on the PSCAD/EMTDC platform to verify the proposed grid-forming control strategy. [ABSTRACT FROM AUTHOR]

Current researches mainly focus on the participation of wind farms in primary frequency regulation, including overspeed load shedding control, propeller control and their coordinated control, etc. The frequency support is realized by reserving reserve capacity of wind turbines, but the influence of the dynamic characteristics of maximum power point tracking (MPPT) on the overall frequency regulation characteristics of wind turbines during frequency support is ignored. To this end, firstly, the frequency response model of the system is constructed, and the main factors that affect the frequency dynamic characteristics are revealed. Secondly, the principle of the grid-forming VSC with the function of self-inertial synchronization is introduced, the influence of the dynamic characteristics of MPPT on the frequency regulation characteristics of the wind turbine generator is clarified. Finally, based on the PSCAD/EMTDC electromagnetic transient simulation software platform, the influence of the dynamic characteristics of MPPT on the frequency regulation characteristics are verified by combining the inertia self-synchronous network control technology. The simulation results indicate that with the increase of setting of droop control, the decrease of output power of MPPT becomes large so as to weaken the frequency support capability. [ABSTRACT FROM AUTHOR]

With the gradual emergence of trends such as the asynchronous interconnection of power grids and the increasing penetration of renewable energy, the issues of ultra-low-frequency oscillations and low-frequency stability in power grids have become more prominent, posing serious challenges to the safety and stability of systems. The voltage-source converter-based HVDC (VSC-HVDC) interconnection is an effective solution to the frequency stability problems faced by regional power grids. VSC-HVDC can participate in system frequency stability control through a frequency limit controller (FLC). This paper first analyses the basic principles of how VSC-HVDC participates in system frequency stability control. Then, in response to the frequency stability control requirements of the sending and receiving power systems, a droop FLC strategy is designed. Furthermore, a multi-objective optimization method for the parameters of the droop FLC is proposed. Finally, a large-scale electromagnetic transient simulation model of the VSC-HVDC interconnected power system is constructed to verify the effectiveness of the proposed droop FLC method. [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]

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.)

In VSC-HVDC system for new energy island， surplus power consumption in the system during fault ride-through （FRT） is achieved by employing grouped AC energy-dissipating resistors of equal capacity. However， the presence of an excessively powered resistor group can inflict severe impacts on the system. Therefore， a novel optimal configuration method for energy-dissipating resistors with different capacities based on progression conversion and the switching strategy are proposed. Firstly， the operational characteristics of the grouped AC energy-dissipating resistors of equal capacity are analyzed. Subsequently， multiple groups of AC energy-dissipating resistors with varying capacities， collectively equivalent to the total capacity of the VSC-HVDC system， are configured， and different combinations of the resistors are employed to obtain varying dissipating powers. Finally， a model of the integrated grid is constructed and validated using the PSCAD/EMTDC simulation platform. Simulation results demonstrate that the proposed method and switching strategy enhance the precision of resistor switching， mitigate system impacts， shorten fault recovery time， and precisely consumes surplus power during fault ride-through.

For the VSC-HVDC system transmitting new energy， poor parameter matching between the new energy controller and the VSC-HVDC controller can lead to sub-synchronous and super-synchronous oscillation. To address this， an open-loop strategy based on virtual synchronous generator （VSG） control has been adopted. This strategy eliminates the inner and outer loops and the phase lock of traditional closed-loop control methods， optimizing the impedance characteristics of the VSC-HVDC system and reducing the risk of sub-synchronous and super-synchronous oscillations of new energy. It is also compatible with both islanded and grid-connected operating modes. To address bipolar power imbalance and excessive short-circuit current after faults in open-loop control， bipolar power balancing and fault ride-through （FRT） strategies have been proposed. The effectiveness of the proposed VSG control and FRT strategies has been validated through RTDS simulations.

To delve into the mechanism behind wideband oscillation instability in voltage source converter based high voltage direct current （VSC-HVDC） transmission system and swiftly assess system stability with precision， a modeling method and a stability criterion based on z-domain impedance are proposed. Firstly， employing precise discretization techniques， a z-domain impedance model is established for voltage-source converters considering phase-locked loops （PLLs）， inner-current loop， and voltage feedforward control， along with a z-domain impedance model for AC grids in a global coordinate system. Subsequently， a criterion for generalized forbidden zone is proposed using Gershgorin circle theorem to analyze the impact of phase-locked loops and line impedances on system stability. Finally， simulation analysis is conducted on the VSC-HVDC system to demonstrate the effectiveness of the proposed generalized impedance criterion.

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.)

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.)

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.)

The data presented in this paper are related to the paper entitled "Optimal Estimation of Under-Frequency Load Shedding Scheme Parameters by Considering Virtual Inertia Injection", available in the Energies journal. Here, data are included to show the results of an Under-Frequency Load Shedding (UFLS) scheme that considers the injection of virtual inertia by a VSC-HVDC link. The data obtained in six cases which were considered and analyzed are shown. In this paper, each case represents a different frequency response configuration in the event of generation loss, taking into account the presence or absence of a VSC-HVDC link, traditional and optimized UFLS schemes, as well as the injection of virtual inertia by the VSC-HVDC link. Data for each example contain the state of the relay, threshold, position in every delay, load shed, and relay configuration parameters. Data were obtained through Digsilent Power Factory and Python simulations. The purpose of this dataset is so that other researchers can reproduce the results reported in our paper. Dataset: 10.5281/zenodo.11371324 Dataset License: Creative Commons Attribution 4.0 International (CC BY 4.0) [ABSTRACT FROM AUTHOR]

In this paper, a simplified model of voltage source converter-based high-voltage direct current (VSC-HVDC) link is proposed that is effective in the analysis of multi-machine systems, even when crucial applications of the link are involved. The model is derived by eliminating the DC dynamics, including the converter-related impedances as a part of the AC system transmission network and obtaining the converter currents in a straightforward manner. Case studies are conducted on 4-machine, 10-bus and 16-machine, 68-bus systems to prove the accuracy of the model. The study clearly indicates the model's ability to reproduce the influence of VSC controllers, impact of variable power levels and effects of multiple HVDC links in a system. It is further verified for significant VSC-HVDC applications. The model is effective at handling frequency support of asynchronous systems and can be applied to VSC-HVDC connected offshore wind farms feeding multi-machine systems. It is demonstrated that the proposed model can be efficiently used for analysis of large AC systems embedded with VSC-HVDC links with lesser modeling complexity and computation time. [ABSTRACT FROM AUTHOR]

The VSC-based HVDC networks have become a reliable candidate for integrating renewable energy resources over long distances. However, the development of these networks faces protection challenges against DC short-circuit faults, where fault detection in these networks is at top of the issues. This paper proposes a fast fault identification strategy based on the Interior-Angle analysis between the powers of the DC-link capacitor and the protected DC-line. In the proposed scheme, first, the time-domain mathematical expression of the power signals is extracted, and second, the angle analysis of the power signals through the normalized interior-product approach is carried out. Accordingly, a fast fault identification index is introduced that detects the fault conditions in about 1.0 msec. The presented strategy only relies on conventional voltage/current measurements and does not require any extra sensor. Moreover, it can discriminate the faulted branch from the healthy ones with a considerable safety margin. To validate the performance of the proposed method, a complete set of fault scenarios are investigated on a bipolar meshed multi-terminal VSC-HVDC network. It is shown that the proposed method appropriately detects the pole-to-ground and pole-to-pole DC faults at different locations with zero and high resistance faults.

The worldwide promotion of carbon-neutral policies is leading to a continuously growing percentage of electricity being derived from renewable energy, which makes it feasible to design power systems composed of 100% renewable energy in the future. The question of how to realize stable transmission for 100% renewable energy-integrating grids under different operating conditions needs to receive more attention. Voltage source converter-based high-voltage direct current (VSC-HVDC) technology is one of the prospective solutions for large-scale renewable energy integration due to its unique dominance in areas such as independent reactivity and active control. In this study, we design a novel, 100% renewable energy system through grid integration via a VSC-HVDC system structure and a control strategy. Unlike in other research, a mixed control strategy based on grid-forming control (PSL) and grid-following control (GFL) is developed to realize smooth switching in order to ensure secure transmission and consistent operation when the operating conditions of the 100% renewable energy-integrating grid changes. The simulation results indicate that the proposed system structure and control could stabilize renewable energy transmission under normal operation conditions and provide necessary grid support under different system disturbances.

Summary: Voltage source converter‐based high voltage direct current (VSC‐HVDC) transmissions are commonly employed to deliver as much inertial and primary frequency regulation (PFR) power as possible to a frequency‐disturbed system to ensure stable operation, which causes the unreasonable application of limited frequency regulation resources. Hence, this paper, based on online inertia estimation results, presents a novel method to determine the virtual inertia and droop parameters (MDVID) for VSC‐HVDC to weaken this deficiency. Firstly, the measured ambient active power and frequency variation data are applied as input and output of the auto‐regressive moving average with extra input (ARMAX) identification model, which is used to obtain the effective inertia of the studied system. Next, compared with the expected system dynamic frequency response characteristics under disturbance, the required and quantitative variation of the studied system inertia and droop parameters is acquired through the system frequency response (SFR) model. Then, the obtained variation of inertia and droop parameters is assigned to VSC‐HVDC based on the ratio of the rated capacity of the studied system to that of VSC‐HVDC. Finally, the simulation results confirmed the predominance of the proposed MDVID compared with other strategies in the event of a fault and step load variation. [ABSTRACT FROM AUTHOR]

Summary: A Robust H2$$ {H}_2 $$ Nonlinear Fuzzy Decentralized Controller (H2$$ {H}_2 $$ RNFDC) is proposed to improve the overall robustness and tracking ability of a VSC‐HVDC link. The studied system is considered as composed by two overlapping nonlinear subsystems. The nonlinear interaction between the two subsystems is treated as a disturbance rejection problem by fuzzy control techniques. First, the Takagi Sugeno (TS) fuzzy model is adopted for fuzzy modeling of the uncertain nonlinear system. Next, new stability conditions for a generalized class of uncertain HVDC systems are derived from robust control techniques based on Linear Matrix Inequalities (LMIs). The design method employs the so‐called Parallel Distributed Compensation (PDC) to obtain H2$$ {H}_2 $$ RNFDC gains based on LMIs.The efficiency and robustness of the proposed controllers are analytically proven and tested through validation simulations. The main contributions of this paper are: (i) resilience: in case of failure of one converter or loss of measures or controls, the control of the other converter is not affected; (ii) robustness is improved in order to provide good responses in case of network variations and HVDC line parameters changes; (iii) fuzzy techniques are adopted to handle nonlinearities and changes of operating conditions. The proposed H2$$ {H}_2 $$ RNFDC is compared with Fuzzy H 2$$ {}_2 $$ Decentralized State Feedback Control (H2$$ {H}_2 $$ NFDC) and H∞$$ {H}_{\infty } $$ Linear Decentralized Control (H∞$$ {H}_{\infty } $$ LDC) in simulation to illustrate the control synthesis and its effectiveness. [ABSTRACT FROM AUTHOR]

Current researches mainly focus on the participation of wind farms in primary frequency regulation, including overspeed load shedding control, propeller control and their coordinated control, etc. The frequency support is realized by reserving reserve capacity of wind turbines, but the influence of the dynamic characteristics of maximum power point tracking (MPPT) on the overall frequency regulation characteristics of wind turbines during frequency support is ignored. To this end, firstly, the frequency response model of the system is constructed, and the main factors that affect the frequency dynamic characteristics are revealed. Secondly, the principle of the grid-forming VSC with the function of self-inertial synchronization is introduced, the influence of the dynamic characteristics of MPPT on the frequency regulation characteristics of the wind turbine generator is clarified. Finally, based on the PSCAD/EMTDC electromagnetic transient simulation software platform, the influence of the dynamic characteristics of MPPT on the frequency regulation characteristics are verified by combining the inertia self-synchronous network control technology. The simulation results indicate that with the increase of setting of droop control, the decrease of output power of MPPT becomes large so as to weaken the frequency support capability.

DC fault current limiters can rapidly restrict the rise of fault currents， but attention needs to be paid to their dynamic current-limiting characteristics during fault impact. To address this， a study on the fault impact characteristics of a resistive-type current limiter is conducted. Firstly， mathematical expressions for the DC voltage and the withstandable fault current before and after the limiter is connected are theoretically analyzed and derived. Subsequently， a high-current DC impact platform is established， and a laboratory prototype of the current limiter is developed. A limiter model is built on the MATLAB/Simulink platform to conduct simulation analysis of the impact characteristics. Finally， high-current impact tests are performed on the resistive-type current limiters with single-coil and multi-coil parallel structures. Simulation and experimental results indicate that with increasing fault impact， the limiters’ resistance rises more rapidly and to a greater extent after reaching the critical limits， resulting in a more effective current-limiting performance. Additionally， at lower impact voltages， the current-limiting resistance exhibits a rapid rise followed by a decrease trend.

When unbalanced faults such as single-phase voltage drop occur in the power grid, VSC-HVDC will fail or become unstable due to sudden changes in amplitude, phase, frequency, etc. of the power grid voltage. Therefore, the role of PLL in a non-ideal power grid is particularly important, but often PLL needs to make a compromise between dynamic response and system stability. Therefore, this paper proposes a free-PLL control strategy under non ideal power grid. First, according to the power transmission model of VSC-HVDC under power grid imbalance, the control command required by the inverter is given, which is determined in the environment free-PLL. Therefore, PLL is not required to retrace the phase of the grid voltage. In addition, in order to overcome the impact of the sudden change of power grid frequency on the free-PLL strategy, a frequency locking strategy is proposed in the free-PLL environment, the response time is about 1 grid cycle. Finally, in order to verify the effectiveness and correctness of the proposed strategy, the VSC-HVDC system’s active power transmission stability is guaranteed when the grid voltage encounters different degrees of single-phase sags.

Voltage source converter based high voltage direct current transmission (VSC-HVDC) is widely adopted in the power system with new energy sources, but with the problem of fast rise of fault current. Magnetic saturation fault current limiter (MSFCL) suppresses the rise of short-circuit current by increasing the inductance value, which has the advantages of high speed and no additional control. However, the change of inductance will affect the detection of VSC-HVDC system fault, may leading to missed or incorrect removal of the fault and causing harm. Based on this problem, this paper proposes a fault detection method used in VSC-HVDC system considering MSFCL, which has fast detection speed, high sensitivity and reliability. The proposed method is robust to short-circuit resistance variation and can locate faults external and internal. Firstly, we establish the short-circuit equivalent circuit of VSC-HVDC system. Then we establish the differential equation and solve it, to obtain the analytical expression of voltage across MSFCL. Furthermore, we proposed a short circuit fault detection method based on the rise rate of the voltage across MSFCL. Finally we establish a four port VSC-HVDC system simulation model to prove that the method is effective. The results show that compared with traditional methods, the proposed method has faster detection speed. The proposed method is independent of the power flow direction, can identify the short circuit fault with large short-circuit resistance of 500 Ω and can discriminate the faulty branch from the healthy ones accurately.

The Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) technology has become the development direction of new energy grid-connected, DC power transmission and island power supply technology in the future due to its superior characteristics. The effective and reliable control method is important to realize the stable operation of VSC-HVDC system during disturbances. However, the common adopted control scheme for VSC-HVDC system lacks of superior dynamic response when system suffers external disturbances. Although some relatively new control methods have been continuously proposed and applied to the VSC-HVDC system, such as no-beat control, fuzzy control, sliding mode control and repetitive control, etc., they usually depend on detailed and exact system model. This paper focuses on the feedback linearization and disturbance compensation methods in VSC-HVDC system. Firstly, the mathematical model of VSC-HVDC system in dq coordinate system with modeling errors and external disturbances is derived. Secondly, in order to improve the dynamic response and robustness of the control, the feedback linearization and disturbance compensation method is used and designed to realize the decoupling control of the VSC-HVDC system. Finally, the VSC-HVDC system with conventional control and the proposed control is compared and analyzed on the PSCAD/EMTDC simulation platform. The results show that the proposed controller based on feedback linearization and disturbance compensation principle has better dynamic performance and higher robustness of regulation performance.

Henan Power Grid is located in the north of Central China Power Grid. During its energy transition, thermal power units will be decommissioned on a large scale. Therefore, the scale of the new energy grid connection and regional external power will be further greatly increased to match the load growth demand. Under this background, Henan Power Grid plans to introduce the third HVDC (High Voltage Direct Current). Based on the actual data and the current operation status of Henan Power Grid, this paper proposes an analysis strategy about VSC-HVDC (Voltage Source Converter HVDC) to improve the support capability of the receiving power grid with multi-infeed HVDC. In recent years, VSC-HVDC technology has emerged with the strengths of flexible power regulation and strong voltage support. This paper firstly analyzes the VSC-HVDC power transmission characteristics and clarifies the mechanism of the VSC-HVDC power regulation. Then, based on the actual planning of Henan power grid, the influence of two feed-in schemes (LCC-HVDC (Line Commutated Converter HVDC) and VSC-HVDC) on the voltage stability of power grid and the number of subsequent commutation failures of other conventional DC are compared and analyzed under the three-phase short-circuit fault of AC lines near HVDC terminal location by using PSD-BPA simulation software. The results show that the VSC-HVDC scheme can effectively alleviate the voltage fluctuation (duration within 1 s and fluctuation number within 2 times) after the fault and restrain the number of subsequent commutation failures of conventional DC(with 2 times and even none).

[Introduction] Due to its flexibility and rapid control ability, voltage source converter based high voltage direct current (VSC-HVDC) technology can be used in asynchronous grid interconnection, renewable energy grid-connection, and urban grid power supply. In this paper, the flexible and compact interconnection scheme of urban power grid is proposed to realize the interconnection and improve safety and stability of the urban power grid. [Method] According to the current situation of the power grid, and considering the difficulty of implementing new transmission lines in urban areas and the difficulty of controlling the construction period, the site selection and interconnection scheme were carried out from the perspective of exploiting potential of existing substations and transmission lines. The interconnection scale was determined comprehensively by combining the system requirements, the transmission capacity of the original lines, and the feasibility of capacity increase transformation. Due to the shortage of urban land, compact equipment and indoor compact layout was recommended. [Result] The flexible and compact back-to-back converter station is adopted to realize the interconnection, significantly reduce the short-circuit current level of the system and improve the security and stability of the urban power grid. The compact design which can save about 40% of the space is adopted to meet the need to alleviate the scarcity of urban land resources. [Conclusion] The compact and flexible interconnection proposed plays a good role in guiding the application of VSC-HVDC technology in urban power grid interconnection and has high reference value.

[Introduction] Due to the dense load, complex grid structure, and close electrical connections in the Guangdong power grid area, there are three major problems for a long time: the risk of large-scale power outages, the interaction between AC and DC, and the excessive short-circuit current, making it difficult to meet the needs of future power load development and flexible system regulation.[Method] To address the above issues, a high-performance VSC-HVDC (Voltage Source Converter-based High Voltage Direct Current) back-to-back project was constructed in the core area of Guangdong Power Grid, and a new generation of high-performance VSC-HVDC back-to-back technology was studied and adopted. The VSC-HVDC interconnection control of complex power grids, the development of highly reliable and high-performance converter valves, and the design of green and efficient converter stations were deeply studied. The upgrade of VSC-HVDC back-to-back technology was achieved. [Result] The project successfully achieved automatic control of asynchronous power flow, significantly reducing the link delay of the control and protection system, developed high-performance and highly reliable VSC-HVDC converter valves, and optimized the design in terms of noise reduction, loss reduction, water conservation, and other aspects of the converter station. A comprehensive perception system for the converter station was built, achieving intelligent operation and maintenance. At present, the project is running well. [Conclusion] The VSC-HVDC back-to-back project of Guangdong Power Grid has solved the three major stability problems faced by the multi DC feeder receiving end grid for a long time and enhanced the long-term safe and reliable power supply capacity of the Guangdong-Hong Kong-Macao Greater Bay Area.

This paper proposes a voltage source converter (VSC) control strategy for the high voltage direct current (HVDC) transmission systems compensating the harmonic components. For VSC-HVDC AC system accounted for a relatively large share of the 5th, 7th, 11th, 13th and other low harmonics. A selective harmonic current control strategy based on vector proportional integral (VPI) regulator in dq coordinate system is proposed on the basis of PI control. In which, PI is used to control the DC component of the current error, while VPI is used to suppress the multiplicative fluctuations of the current error. Unlike the proportional-integral resonant (PIR) regulator, the VPI contains a second-order numerator that achieves the ideal 0° phase delay of the closed-loop transfer function of the control system at the set resonant frequency point, so its control accuracy for harmonic currents is better than that of the PIR. A two-terminal VSC-HVDC system is built using Simulink software, and current compensation simulations are performed for three control methods: conventional PI, PIR and PI parallel VPI schemes. The superior harmonic suppression performance of VPI is verified by comparing the harmonic content.

Voltage source converter-based high-voltage direct current (VSC-HVDC) transmission systems are becoming increasingly popular for long-distance power transmission due to their numerous advantages. However, the fault ride-through (FRT) capabil-ity of VSC-HVDC systems during AC faults remains a key challenge that needs to be addressed to ensure their uninterrupted operation under challenging grid conditions. This paper presents and analyzes a novel nonlinear control scheme based on a robust sliding mode control approach to improve the FRT capability of VSC-HVDC systems. The proposed control scheme based on the modification of the converter’s active power to make it more sensitive to any changes in voltage magnitude at the points of common coupling (PCCs) on the AC side. This helps to maintain the DC voltage sta-bility and prevent the converter from tripping during AC faults. The performance of the proposed control scheme is evaluated using a series of ex-perimental investigations using a digital signal processor (DSP) within Processor-in-the-Loop (PIL) quasi-real-time simulation. The PIL simulations closely examine the system’s response to AC faults with varying remaining voltages and durations. The results demonstrate that the proposed control scheme can effectively improve the FRT capability of VSC-HVDC systems and ensure their stable operation during AC faults.

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.)

Under-frequency load shedding (UFLS) schemes are the latest safety measures applied for safeguarding the integrity of the grid against abrupt frequency imbalances. The overall inertia of electrical power systems is expected to decrease with an increased penetration of renewable energy as well as elements connected through power electronic interfaces. However, voltage source converter-based high voltage direct current (VSC-HVDC) links can provide virtual inertia through a control loop that allows for a reaction to occur at certain frequency fluctuations. This paper evaluates a UFLS scheme that considers the injection of virtual inertia through a VSC-HVDC link. A genetic algorithm (GA) is used to determine the location of the UFLS relays, the activation threshold of each stage, the delay time and the percentage of load shedding at each stage. It was found that the virtual inertia causes the nadir to delay and sometimes reach a greater depth. Furthermore, the implemented GA approximates the frequency response to the limits set with the constraints, reducing the load shedding but achieving a steeper nadir and a lower steady-state frequency level than traditional UFLS. The simulations were performed using the IEEE 39-bus test system. [ABSTRACT FROM AUTHOR]

High voltage direct current (HVDC) systems provide important advantages; among them the ability to transmit enormous amounts of electrical power over great distances at low cost. As a result, planners of power systems consider it as a viable choice for power transmission and interconnection of asynchronous networks. Depending on HVDC grids, continental/super grids have been recently constructed to promote global economic development. The study described in the paper focuses on the behavior of a voltage sourced converter (VSC) based HVDC transmission system comprising three arms-neutral point clamped (NPC) converters interconnecting two asynchronous alternating current (AC) networks. In addition, the system components, and the vector control strategy of active/reactive powers and direct current (DC) bus voltage are simulated in MATLAB/Simulink under varying situations by adjusting the controller's settings. The study records and analyzes AC/DC voltages and active/reactive powers at two converter stations under varying power and voltage conditions. The results of the study provide key performance indicators, such as settling time (tsett), steady state error (SSE), overshot/undershoot (OS%/US%), and correlation factor (CF), which demonstrate the robustness of the system's control. [ABSTRACT FROM AUTHOR]

Abstract The intermittent access of renewable energy sources leads to a significant increase in fault short‐circuit currents in power grid. DC superconducting fault current limiters (SFCL) can limit short‐circuit currents in flexible DC transmission systems, which work in combination with direct current circuit breaker (DCCBs) to protect the grid system effectively. However, for the parameter design of DC superconducting fault current limiter (DCSFCL), it is difficult to balance the economics of the device and its adaptability to different fault situations. In this paper, a cross‐mapping design methodology for the DCSFCL is proposed and applied in the Nan'ao flexible DC transmission project, China. A cross‐mapping method is designed combining the critical parameters of DCSFCL and the system parameters. A three‐terminal simulation model of the flexible DC transmission system is constructed through MATLAB/Simulink and the design process of DCSFCL parameters is introduced. A cyclic calculation approach is proposed for the design of DCSFCL parameters through three fault conditions of the power system. Meanwhile, impact current short‐circuits test and artificial ground short‐circuit test were conducted on the prototype. Test results show that the designed DCSFCL meets the requirements of practical applications.

The data presented in this paper are related to the paper entitled “Optimal Estimation of Under-Frequency Load Shedding Scheme Parameters by Considering Virtual Inertia Injection”, available in the Energies journal. Here, data are included to show the results of an Under-Frequency Load Shedding (UFLS) scheme that considers the injection of virtual inertia by a VSC-HVDC link. The data obtained in six cases which were considered and analyzed are shown. In this paper, each case represents a different frequency response configuration in the event of generation loss, taking into account the presence or absence of a VSC-HVDC link, traditional and optimized UFLS schemes, as well as the injection of virtual inertia by the VSC-HVDC link. Data for each example contain the state of the relay, threshold, position in every delay, load shed, and relay configuration parameters. Data were obtained through Digsilent Power Factory and Python simulations. The purpose of this dataset is so that other researchers can reproduce the results reported in our paper.