High Voltage Direct Current Networks Research Articles

Signal processing and artificial intelligence based HVDC network protection: A systematic and state-up-the-art review

In this modern era, the smart grid (SG) is progressively empowered for direct current (DC) power transmission, either at high voltage (HV) or at medium voltage (MV). The high voltage direct current (HVDC) transmission systems have a significant impact on the SG operation even though the integration of add-on green and renewable-based power generation (RPG). In this RPG era, the application of HVDC can be seen in the grid-connected remote offshore wind or photovoltaic (PV) based large RPG, and interconnections amongst the states or countries. In such a context, a smart grid inevitably is ridden with technical complexities (both control and protection viewpoints), and thus signals processing (SP) techniques along with artificial intelligence (AI) methods are considered very much important to understand, effectively plan, draw up plans, and drive the multifaceted electric power system. This paper presents an extensive review of HVDC network protection systems with special attention to SP and AI applications. This paper presents an extensive review of the suggested techniques in the past three decades and discussed the pros and cons of each method. Apart from that critical findings are discussed and analyzed along with the future scope of research toward the development of HVDC protection. This review tries to focus on the gap between the existing protection schemes and topology with the smart grid-based power system perspective and convey to the power engineers and researchers the possibilities of further research as a solution to the associated issues and challenges.

Fault Detection and VSC-HVDC Network Dynamics Analysis for the Faults in Its Host AC Networks

High-voltage direct current (HVDC) transmission is preferred over high-voltage alternating current (HVAC) for long power lines for asynchronous power grid interconnection and high-level renewable energy integration. The control and protection functions associated with HVDC systems help with fast and secure clearance of faults. The control and protection challenges in the embedded HVDC network are of great concern for the stable and secure operation of an HVDC network. The DC fault current may reach an extremely high level in a rather short period because of the low impedance in a DC system, which is dangerous for converters, and disturbances in the AC network directly influence the performance of the HVDC system. Sometimes, faults on the AC side may lead to disconnection or failure of the DC link, causing reliability problems as well as huge economic losses. AC and DC protection solutions are being developed for HVDC systems to enhance their sustainability and reliability. As such, AC and DC faults should be detected and cleared at a faster rate. Therefore, in this article, the feasibility of the synchro-squeezed transform (SST) is analyzed for detection purposes. For more accurate and faster detection, the signal is first decomposed using the empirical mode decomposition (EMD) technique, and then the SST is applied. A discrete Teager energy (DTE) spectrum is obtained with the processed signal, which works as the detection index. The algorithm shows low sampling frequency requirements, with higher efficiency and reliability for the purpose. PSCAD/EMTDC version 4.6 software and MATLAB 2022a software is used for the modeling and simulation.

A novel fault detection algorithm for high voltage DC networks

Faults in high voltage DC networks can lead to inefficient operation, power outage or even equipment damage. Therefore, several approaches have been proposed to monitor, detect, and handle such problems. Due to high currents during faults, run-time for detecting malfunctions is crucial. Thus, fast recognition of small deviations that might lead to an abnormal operation is quintessential in minimizing consequences. This work presents a novel fault-detection mechanism, which is based on locality-sensitive hashes and its run-time scales linearly with the number of analyzed samples. To detect a malfunction, the algorithm uses reference signals corresponding to the normal operating point. Yet, only 19 reference signals were sufficient and delivered results comparable to a system using 100. When having only 19 references, the detector’s runtime is below 0.15 ms for an analyzed signal of 400 samples. Apart from fault detection, the proposed mechanism can also be used to reduce the storage requirements of the monitoring system. For a later investigation of a faulty event, the monitoring system must store the samples containing signal degradation. Even some temporary small changes can yield valuable information regarding the cause of the fault. However, storing many samples inevitably leads to big storage units, which are costly. To address this issue, the proposed mechanism sends a criticality factor to the monitoring system, based on which the signal samples may be compressed or removed.

Evaluation of a Passive-Based Controller for Power Monitoring in Networks of High Voltage Transmission Lines in Direct Current with Voltage Source Converters (VSC–HVDC)

In this paper a tracking Passivity--based Control (PBC) for a multiterminal Voltage Source Converter based High Voltage Direct Current Network (VSC--HVDC) is evaluated. First, the system (an actual multiterminal HVDC) described as a Port Hamiltonian (PH) System and the controller are presented and subsequently three scenarios are proposed to evaluate the closed--loop behavior, namely: (i) load changes; (ii) generation changes and, (iii) DC--bus changes. Numerical simulations are carried out and results shown the robustness of the closed--loop to cope with these common disturbances.

A novel fault location strategy based on Bi‐LSTM for MMC‐HVDC systems

AbstractThe integration of modular multilevel converters (MMCs) with high voltage direct current (HVDC) transmission systems is an efficient method for transporting electricity from distant renewable energy sources to demand centres. However, MMC‐HVDC systems face reliability challenges during DC overcurrent faults, often caused by component failures that can lead to HVDC network shutdowns. Consequently, a reliable fault location approach is crucial for grid protection and restoration, aiding in fault isolation and alternate power flow identification. Conventional fault location methods struggle with manual protective threshold setting, susceptibility to fault resistance and noise, and the need for communication channels, resulting in signal delays. In multi‐terminal HVDC networks, fault location becomes even more complex due to poor selectivity and sensitivity in traditional schemes. This study proposes a robust fault location approach based on bidirectional long short‐term memory (bi‐LSTM). The method offers a simplified decision‐making model with low computational requirements, utilizing fault features from one end of the network, eliminating the need for a communication channel. Remarkably, this approach achieves high fault location accuracy, even with varying fault types, resistances, and noise levels, as demonstrated by an MSE of 0.006 and a percentage error below 1% in simulations conducted using a real‐time simulator with MATLAB/Simulink.

Allowing Large Penetration of Concentrated RES in Europe and North Africa via a Hybrid HVAC-HVDC Grid

Renewable energy sources (RESs) and electricity demand are not evenly distributed geographically across Europe. Thus, harvesting the wind energy from the north and solar energy from the south and delivering them to the demand in central Europe is a more viable solution. However, the present High-voltage alternating current (HVAC) transmission grids have been sometimes congested; thus, High-voltage direct current (HVDC) provides another possibility along the existing HVAC infrastructure. In this paper, we propose a hybrid HVAC-HVDC grid, allowing a large penetration of concentrated RES in Europe and North Africa. More specifically, the HVDC network is constructed to transfer wind and hydro electricity from northwestern Europe and solar electricity from north Africa, while the HVAC network is used to distribute electricity within each country or among adjacent areas. To quantitatively evaluate the feasibility and relevant performances, multiple dimensions of indicators are designed. Employing several European energy scenarios up to 2050, the performances of the proposed HVAC-HVDC infrastructure are analyzed and compared. The calculation results show that compared with the pure HVAC grid, the integrated HVAC-HVDC grid can significantly reduce greenhouse gas emissions and pollutants, leading to a further reduction in the number of deaths from air pollution. In addition, the HVAC-HVDC grids can accommodate a higher penetration of RES without causing infeasible power flows.

Battery Power Control Strategy for Intermittent Renewable Energy Integrated Modular Multilevel Converter-Based High-Voltage Direct Current Network

Modular multilevel converters (MMC) play a dominant role in integrating remotely located renewable energy resources (RER) over the high-voltage direct current (HVDC) transmission network. The fault ride-through capabilities of the MMC-HVDC network during low-voltage faults and the power fluctuation due to RER intermittency are the major obstacles to the effective integration of renewable energy. In response, this article proposes a local voltage-based combined battery energy control scheme for a PV-wind-battery connected MMC-HVDC system to regulate the HVDC-link voltage during low-voltage faults at the point of common coupling of alternating current grids and to reduce the intermittent RER power fluctuation. The proposed technique removes the dynamic braking resistor from the HVDC-link and smoothly integrates the RER without active power reduction of renewable energy under low-voltage faults. Symmetrical and unsymmetrical low-voltage faults have been conducted to validate the effectiveness of the proposed control scheme for the battery in mitigating surplus energy in the HVDC-link. Additionally, wind speed, solar radiation, and temperature have been changed to confirm the improved performance of the battery energy management system. The complete systems have been simulated and tested in a real-time digital simulator (RTDS) and using dSPACE-based controller hardware in a loop setup.

A Low-Voltage AC, Low-Voltage DC, and High-Voltage DC Power Distribution System with Grid: Design and Analysis

Low-voltage (LV) and high-voltage (HV) DC distribution systems are being investigated as alternatives due to the growth of DC distribution energy resources (DER), DC loads such as solar and wind power systems, and energy storage sources (ESSs). Furthermore, an HV/LV DC distribution system offers various advantages, including lower conversion losses, an easier connecting strategy for DC DERs, and less complex power management techniques. As renewable energy sources are increasingly incorporated into the electrical grid, it is important to create novel, effective approaches for connecting such sources and loads. It would hence be effective to merge DC distribution with AC distribution to fulfill the energy demands of both DC and AC consumers. To this end, this study proposes a multizone design with four buses: low-voltage direct current (LVDC), high-voltage direct current (HVDC), low-voltage alternating current (LVAC), and an electrical grid. A model of this system that covers crucial elements, including power systems, DER systems, and power electronic devices, to serve as a foundation for the analysis and design of this architecture is proposed. MATLAB/Simulink is used to conduct a simulation study to verify the performance of the proposed design. In this study, a hybrid electrical grid with an LVDC, HVDC, and LVAC distribution network test is used and implemented. Additionally, a transient and steady-state characteristic analysis of the test system is performed.

Small-signal stability analysis of the asymmetrical DC operation in HVDC networks

• Stability of interconnection of monopolar and bipolar HVDC stations is analysed. • A small-signal stability model for asymmetric DC operation studies is developed. • The model is validated with EMT dynamic simulation. • The findings are useful for systematic design of the HVDC grounding systems. • A controller is designed to enhance stability during asymmetric DC operation. The increase in High Voltage Direct Current (HVDC) projects favors their future interconnection to form regional networks, but this interconnection can be hindered by the lack of standardization in station's configuration and converter's differing grounding schemes. Whilst other studies have studied the effect of Direct Current (DC) asymmetrical operation, they are limited in their scope. This paper proposes a more realistic perspective, considering stations with different topologies, permanent DC asymmetries and the influence of the grounding systems. This more complex point of departure requires the re-examination of the modeling methods, from time-domain to frequency-domain. This paper proposes a small-signal stability model of the system, which is validated with the electromagnetic transient (EMT) dynamic simulations using PowerFactory. This model provides guidelines for designing the grounding impedance and allows the proper design of a specific controller to dampen the asymmetrical DC operation mode.

Stability Analysis and Control Design for Multiterminal HVDC Network With Power Flow Controller

The power flow control in high-voltage direct current (HVDC) grids can be improved by employing the interline dc power flow controller (IDCPFC). This article presents an improved control scheme using IDCPFC to balance power flow in the dc networks. In this work, a differential-mode transformer (DMT) is used in combination with a bidirectional buck converter to form a variable DMT. In comparison to the existing methods, the proposed system is scalable to higher voltages and powers, which makes it suitable for high-voltage dc transmission systems. Analysis of a small-signal model of the proposed method and design of compensator for improvement of transient behavior is performed. A simulation is performed with independent feed-forward and feedback control to show the effectiveness of the proposed method. The proposed method is also validated through a 600-W experimental prototype. The experimental results show that the current flow between lines is controlled for unbalance load conditions.

A Review on Multi-Terminal High Voltage Direct Current Networks for Wind Power Integration

With the growing pressure to substitute fossil fuel-based generation, Renewable Energy Sources (RES) have become one of the main solutions from the power sector in the fight against climate change. Offshore wind farms, for example, are an interesting alternative to increase renewable power production, but they represent a challenge when being interconnected to the grid, since new installations are being pushed further off the coast due to noise and visual pollution restrictions. In this context, Multi-Terminal High Voltage Direct Current (MT-HVDC) networks are the most preferred technology for this purpose and for onshore grid reinforcements. They also enable the delivery of power from the shore to offshore Oil and Gas (O&G) production platforms, which can help lower the emissions in the transition away from fossil fuels. In this work, we review relevant aspects of the operation and control of MT-HVDC networks for wind power integration. The review approaches topics such as the main characteristics of MT-HVDC projects under discussion/commissioned around the world, rising challenges in the control and the operation of MT-HVDC networks and the modeling and the control of the Modular Multilevel Converter (MMC) stations. To illustrate the challenges on designing the control system of a MT-HVDC network and to corroborate the technical discussions, a simulation of a three-terminal MT-HVDC network integrating wind power generation and offshore O&G production units to the onshore grid is performed in Matlab’s Simscape Electrical toolbox. The results highlight the main differences between two alternatives to design the control system for an MT-HVDC network.

Study of Hybrid Transmission HVAC/HVDC by Particle Swarm Optimization (PSO)

There are considerable power losses in Indonesia’s SUMBAGUT 150 kV transmission High Voltage Alternating Current Network (HVAC) system. These power losses and the voltage profile are critical problems in the transmission network system. This research provides one possible way to reduce power losses involving the use of a High Voltage Direct Current (HVDC) network system. Determining the location to convert HVAC into HVDC is very important. The authors of the current study used Particle Swarm Optimization (PSO) to determine the optimal location on the 150 kV SUMBAGUT HVAC transmission network system. The study results show that, before using the HVDC network system, the power loss was 68.41 MW. On the other hand, power loss with the conversion of one transmission line to HVDC was 57.31 MW for “Paya Pasir–Paya Geli” (efficiency 16.22%), 51.79 MW for “Paya Pasir–Sei Rotan” (efficiency 24.29%), and 60.8 MW for “Renun–Sisikalang” (efficiency 110.12%). The power loss with the conversion of two transmission lines to HVDC was 45.7 MW for “Paya Pasir–Paya Geli” and “Paya Pasir–Sei Rotan” (efficiency 33.19%), 44.95 MW for “Paya Pasir–Paya Geli” and “Renun–Sidikalang” (efficiency 26.98%), and 44.69 MW for “Paya Pasir–Sei Rotan” and “Renun–Sidikalang” (efficiency 34.67%). The power loss with the conversion of three transmission lines to HVDC was 38.71 MW for “Paya Pasir–Paya Geli,” “Paya Pasir–Sei Rotan,” and “Renun–Sidikalang” (efficiency 41.41%).

DC/DC Modular Multilevel Converters for HVDC Interconnection: A Comprehensive Review

High voltage direct current (HVDC) technology is a key component in power systems owing to huge benefits such as long-distance power transmission, lower losses, asynchronous grid interconnections, controllability, system availability, and limited short-circuit currents. HVDC transmission is a cost-effective method of transporting huge amounts of power across long distances with little loss. It can also link asynchronous alternative current (AC) networks while balancing the grid. DC/DC converters are one of the most important components for HVDC power transmission, and DC/DC modular multilevel converters (MMCs) are the backbone of HVDC grid interconnections. The DC/DC MMC is a highly regarded converter architecture for medium/high-voltage DC grid interconnection. DC/DC MMC topologies play a key role in modern HVDC networks with varying voltage levels. This paper’s fundamental aim is to offer a recent comprehensive review of HVDC topologies, current DC/DC modular multilevel converter (MMC) topologies for HVDC interconnection, and DC/DC MMC control techniques.

A Novel Medium-Voltage Hybrid-Cascaded DC–DC Converter With DC Fault-Blocking Capability and Reduced Switch Capacity

In this article, a medium-voltage nonisolated dc–dc converter with dc fault-blocking capability is proposed. The converter is designed to connect two high-voltage dc networks with varying voltage levels. The proposed converter is composed of a string of cascaded modules and two sets of series-connected switches. The cascaded modules have all the merits of modular design, and the series-connected switches avoid dynamic balancing issues due to the zero-voltage switching feature. The single-string structure of the proposed converter helps reduce the number of switches, power losses, and volume. The power efficiency of the converter is evaluated to be as high as 99.3%. The feasibility of the proposed converter is verified via 32-kV 22.5-MW simulations and 240-V 1.45-kW experiments.

Potential Contribution of the Grey Wolf Optimization Algorithm in Reducing Active Power Losses in Electrical Power Systems

Active power losses have the potential to affect the distribution of power flows along transmission lines as well as the mix of energy used throughout power networks. Grey wolf optimization algorithms (GWOs) are used in electrical power systems to reduce active power losses. GWOs are straightforward algorithms to implement because of their simple structure, low storage and computing needs, and quicker convergence from the constant decrease in search space. The electrical power system may be separated into three primary components: generation, transmission, and distribution. Each component of the power system is critical in the process of distributing electricity from where it is produced to where it is used by customers. By using the GWO, it is possible to regulate the active power delivered by a high-voltage direct current network based on a multi-terminal voltage-source converter. This review focuses on the role of GWO in reducing the amount of active power lost in power systems by considering the three major components of electrical power systems. Additionally, this work discusses the significance of GWO in minimizing active power losses in all components of the electrical power system. Results show that GWO plays a key role in reducing active power losses and consequently reducing the impact of power losses on the performance of electrical components by different percentages. Depending on how the power system is set up, the amount of reduction can be anywhere from 12% to 65.5%.

Fault protection of multiterminal HVDC networks: Impact of inductance

Multiterminal Voltage Source Converter (VSC) High Voltage Direct Current (HVDC) networks are developing rapidly worldwide, especially in China with urgent needs of long-distance power transmission. Currently, the interrupting capacity of available DC circuit breakers (DCCBs) is a key obstacle to the development of multiterminal VSC HVDC networks. Superconducting fault current limiters (SFCLs) can compensate for the limitation of DCCBs. Conventionally, a resistive SFCL is regarded as essential and sufficient, while an inductive one is less related and optional. However, pure resistance cannot effectively suppress the rising rate of fault current at the very early stage of a fault, resulting in unnecessary blocking of the converter. Adequate inductance is required for such SFCLs to curb rapidly increasing fault currents within the first few milliseconds, which is critical to DCCBs to isolate fault without interrupting other DC transmission lines. In this paper, we compared and analyzed the performances of SFCLs with different resistances and inductances in a four-terminal VSC HVDC network using PSCAD/EMTDC software. The results indicate that even resistance and inductance show different current limiting effects, but they are both necessary to realize effective SFCL function for multiterminal VSC HVDC networks. The outcomes of this paper are of significance in FCL design for multiterminal VSC HVDC networks.

Heuristic remedial actions in the reliability assessment of high voltage direct current networks

<p>Planning of high voltage direct current (HVDC) grids requires inclusion of reliability assessment of alternatives under study. This paper proposes a methodology to evaluate the adequacy of voltage source converter/VSC-HVDC networks. The methodology analyses the performance of the system using N-1 and N-2 contingencies in order to detect weaknesses in the DC network and evaluates two types of remedial actions to keep the entire system under the acceptable operating limits. The remedial actions are applied when a violation of these limits on the DC system occurs; those include topology changes in the network and adjustments of power settings of VSC converter stations. The CIGRE B4 DC grid test system is used for evaluating the reliability/adequacy performance by means of the proposed methodology in this paper. The proposed remedial actions are effective for all contingencies; then, numerical results are as expected. This work is useful for planning and operation of grids based on VSC-HVDC technology.</p>

Treating the Impacts of Connecting HVDC Link Converters with AC Power System Using Real-Time Active Power Quality Unit

The High Voltage Direct Current (HVDC) systems have been applied worldwide, due to important roles, technical benefits, and high efficiency. Usually, the HVDC network is a joining link between two separate and different technical properties of HVAC systems, which enhances its use. The joinpoint system that used to connect HVDC and HVAC links is a controlled converter circuit. Despite the importance of use and the significant benefits of the HVDC link, there are negative effects on the power quality of the electrical power of both systems connected on both ends of the HVDC network. The low quality of electric power has been addressed by known methods, whether traditional or modern. But the improvement is usually made with the assumption of load conditions and the need for the system to synthesize it. This research presents an innovative method based on real-time control strategy. This is performed by proposing dSPACE for controlling the Active Power Quality Unit (APQU). The proposed control strategy of the APQU includes a Modified Harmonics Pulse Width Modulation (MHPWM) algorithm in order to mitigate the line current THD and improve the effective power factor of the AC converter sides. The MHPWM is applicable for different nonlinear loads and can be implemented with APQU based on different topologies of H-bridge voltage source inverter. Simulation and practical results have been presented in this paper. The Experimental results are done based on real-time laboratory tests using dSPACE DS1103 board as a controller circuit. The presented results, under different operating loading conditions, show that the APQU provides almost unity power factor and significantly improving THD of the AC supply currents at both sides of the HVDC link controlled converters.

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

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

Minimization of Transmission Loss in Application of HVDC Networks under Load Increase Scenario

This study aims to analyze the effect of embedding HVDC (High Voltage Direct Current) on the voltage stability and power losses of the system. Sequential power flow is used to execute the combined AC-DC power flow by adjusting the estimation of DC slack bus injection to speed up convergence and to get more optimal results. Several systematic load increase scenarios are proposed in this study to provide stress loading on the system so that the performance of HVDC can be evaluated. This simulation was implemented on the IEEE 14-Bus System and IEEE 57-Bus System.