Direct Current Networks Research Articles

Direct current distribution network protection scheme based on inductive current limiting

Converter blocking in the case of pole-to-pole short circuit of the direct current (DC) distribution network can cause large-scale power outage and slow system recovery. Given this issue, a scheme of short circuit protection between poles of the DC distribution network based on the cooperation of fault current limiting module and DC circuit breaker is proposed in this paper. According to the inductive current limiting topology, the transient characteristics of the bridge arm current and the fault current on the DC side of the converter are analyzed, and the theoretical calculation method and selection principle of the current limiting inductor parameters are given. The proposed protection scheme can realize the fault ride-through of the converter during the pole-to-pole short circuit, reduce the scope of power outage and quickly restore the system. The simulation results under the PSCAD/EMTDC environment verify the correctness and feasibility of the protection scheme.

Small-Signal Stability Analysis for Multi-Terminal LVDC Distribution Network Based on Distributed Secondary Control Strategy

This paper presents a detailed and accurate small-signal analysis model for a four-terminal low-voltage direct current (LVDC) distribution network with distributed secondary control strategy. To tackle the contradiction between power sharing accuracy and average voltage recovery ability of voltage source converters (VSCs), a distributed secondary control strategy is adopted, which is based on average consensus algorithm and local voting protocol. Furthermore, to analyze the stability of LVDC distribution network based on the proposed distributed secondary control strategy, a detailed and accurate small-signal analysis model is formulated which is derived from various non-linear state-space sub-models. The time-domain simulation and electromagnetic simulation are carried out to verify the validity and accuracy of the proposed model. Based on this model, the influence rules of main eigenvalues are summarized with the variation of PI control and DC line parameters. Time-domain simulations conducted in PSCAD are used to validate the operational limits of the secondary controllers and DC line obtained from the small-signal stability analysis.

Optimal Power Dispatch in Direct Current Networks to Reduce Energy Production Costs and $$\hbox {CO}_2$$ Emissions Using the Antlion Optimization Algorithm

Optimal Power Dispatch in Direct Current Networks to Reduce Energy Production Costs and $$\hbox {CO}_2$$ Emissions Using the Antlion Optimization Algorithm

Implementation of DC voltage controllers on enhancing the stability of multi-terminal DC grids

Because of the increasing penetration of intermittent green energy resources like offshore wind farms, solar photovoltaic, the multi-terminal DC grid using VSC technology is considered a promising solution for interconnecting these future energies. To improve the stability of the multi-terminal direct current (MTDC) network, DC voltage control strategies based on voltage margin and voltage droop technique have been developed and investigated in this article. These two control strategies are implemented in the proposed model, a ±400 kV meshed multi-terminal MTDC network based on VSC technology with four terminals during the outage converter. The simulation results include the comparison and analysis of both techniques under the outage converter equipped with constant DC voltage control, then the outage converter equipped with constant active power control. The simulation results confirm that the DC voltage droop technique has a better dynamic performance of power sharing and DC voltage regulation.

Compensation method for parallel real-time EMT studies✰

The classical solution for computing electromagnetic transients (EMTs) in parallel relies on the propagation delay of transmission lines. The lines are used as decoupling elements to split the network into different tasks. When there is no natural delay or the delay is too short for the selected simulation time-step, other techniques have to be considered. This paper presents one of them. The compensation method is used in this paper for network decoupling for parallelization. A detailed implementation of this method is presented for real-time simulation. Performances are assessed in both offline and real-time environments with distribution and High Voltage Direct Current (HVDC) network test cases. Switching cases are also studied with HVDC power electronics devices. A Hardware-In-The-Loop (HIL) setup for an HVDC link in operation is also considered to validate the proposed method in a real-time environment.

Exact minimization of the energy losses and the CO2 emissions in isolated DC distribution networks using PV sources

This paper addresses the optimal location and sizing of photovoltaic (PV) sources in isolated direct current (DC) electrical networks, considering time-varying load and renewable generation curves. The mathematical formulation of this problem corresponds to mixed-integer nonlinear programming (MINLP), which is reformulated via mixed-integer convex optimization: This ensures the global optimum solving the resulting optimization model via branch & bound and interior-point methods. The main idea of including PV sources in the DC grid is to minimize the daily energy losses and greenhouse emissions produced by diesel generators in isolated areas. The GAMS package is employed to solve the MINLP model, using mixed and integer variables; also, the CVX and MOSEK solvers are used to obtain solutions from the proposed mixed-integer convex model in the MATLAB. Numerical results demonstrate important reductions in the daily energy losses and the harmful gas emissions when PV sources are optimally integrated into DC grid.

Stand-Alone Direct Current Power Network Based on Photovoltaics and Lithium-Ion Batteries for Reverse Osmosis Desalination Plant

Plummeting reserves and increasing demand of freshwater resources have culminated into a global water crisis. Desalination is a potential solution to mitigate the freshwater shortage. However, the process of desalination is expensive and energy-intensive. Due to the water-energy-climate nexus, there is an urgent need to provide sustainable low-cost electrical power for desalination that has the lowest impact on climate and related ecosystem challenges. For a large-scale reverse osmosis desalination plant, we have proposed the design and analysis of a photovoltaics and battery-based stand-alone direct current power network. The design methodology focusses on appropriate sizing, optimum tilt and temperature compensation techniques based on 10 years of irradiation data for the Carlsbad Desalination Plant in California, USA. A decision-tree approach is employed for ensuring hourly load-generation balance. The power flow analysis evaluates self-sufficient generation even during cloud cover contingencies. The primary goal of the proposed system is to maximize the utilization of generated photovoltaic power and battery energy storage with minimal conversions and transmission losses. The direct current based topology includes high-voltage transmission, on-the-spot local inversion, situational awareness and cyber security features. Lastly, economic feasibility of the proposed system is carried out for a plant lifetime of 30 years. The variable effect of utility-scale battery storage costs for 16–18 h of operation is studied. Our results show that the proposed design will provide low electricity costs ranging from 3.79 to 6.43 ¢/kWh depending on the debt rate. Without employing the concept of baseload electric power, photovoltaics and battery-based direct current power networks for large-scale desalination plants can achieve tremendous energy savings and cost reduction with negligible carbon footprint, thereby providing affordable water for all.

A Study of failure Multi-Term Central HVDC Conductors In Wind Power Transmission Systems

Wind power is developing quickly all throughout the planet as a methods for managing the world energy deficiency and related natural issues. Adaptable direct current (DC) transmission network innovation is a viable strategy for huge limit clean energy admittance to control grids, however the DC cut off identification for it is a troublesome issue for wind structure. The multiterminal dc wind farm is a promising geography with a voltage-source inverter (VSI) association at the coastal matrix. Voltage-source converters (VSCs) are robust to ac-side shortcoming conditions. Be that as it may, they are defenseless against dc deficiencies on the dc side of the converter. For the modular multilevel converter HVDC (MMC-HVDC) systems, when a solitary pole to-ground deficiency happens, the flaw current is little, and it is hard to recognize the issue rapidly. Two variable-speed age frameworks are thought of: doubly-fed induction generators (DFIGs) and perpetual magnet simultaneous generators (PMSGs) in light of their ubiquity these days for wind turbines scaling to a few MW frameworks. The impact of the wind power plant control technique in the short out conduct of the HVDC connect has likewise been contemplated. Results show that the elements of the wind power plant commitment to post to-ground shortcomings are somewhat more slow than those of the wind turbines current control circles. Consequently, the wind turbine front end converters can be utilized to diminish the pinnacle and normal estimation of the issue current in such a system.

Location of solar panels to the medium voltage direct current distribution network considering DC loads

The penetration of renewable energies of Direct Current (DC) to the Distribution Network of Direct Current of Medium Voltage (MVDC) is already a reality. Therefore, extensive planning is required for its location in the electrical network. The implementation of this energy brings great advantages to the system since it contributes to the reduction of losses, improvement of the voltage profile, greater reliability in the system since there is generation of the photovoltaic system installed and of the distribution company. This article was carried out through a bibliographic review of the bases IEEE Xplore, Science Direct, Taylor & Francis and related academic knowledge, identifying several positive and negative aspects of this new reality of renewable energy, in the same way it was analyzed the Energy Storage System (BESS) and the impact of Electric Vehicles (EV) on distribution networks.

Study and analysis of voltage source converter control stability for HVDC system using different control techniques

A Stable and highly reliable DC link voltage represents an important factor for efficient power transfer in high voltage direct current (HVDC) networks. In this framework, this paper investigates the control and stability analysis of voltage source converter (VSC) for DC link voltage regulation. To separately achieve the independent active and reactive power control, the system voltages and currents are represented in the synchronous reference frame. In order to optimally design the parameters of proportional-integral (PI) controller, the inner and outer loops’ transfer functions are thoroughly derived/developed. In addition,/moreover, in order to attain satisfactory/certain system performance, modulus optimum, symmetrical optimum pole placement control approaches are studied and implemented for the purpose of tuning the voltage/current controller gain parameters. In particular for the symmetrical optimum control method, the gain parameters of the DC-bus voltage are determined under different values of network impedance. Furthermore, the impact/influence of changing gain parameters on the DC-link voltage and poles/zeros movement are investigated. MATLAB/Simulink model is built and simulation studies are carried out to verify the introduced concepts.

A Full-Newton AC-DC Power Flow Methodology for HVDC Multi-Terminal Systems and Generic DC Network Representation

The use of Direct Current (DC) transmission links in power systems is increasing continuously. Thus, it is important to develop new techniques to model the inclusion of these devices in network analysis, in order to allow studies of the operation and expansion planning of large-scale electric power systems. In this context, the main objective of this paper is to present a new methodology for a simultaneous AC-DC power flow for a multi-terminal High Voltage Direct Current (HVDC) system with a generic representation of the DC network. The proposed methodology is based on a full Newton formulation for solving the AC-DC power flow problem. Equations representing the converters and steady-state control strategies are included in a power flow problem formulation, resulting in an expanded Jacobian matrix of the Newton method. Some results are presented based on HVDC test systems to confirm the effectiveness of the proposed approach.

Metaheuristic Based Solution for the Non‐Linear Controller of the Multiterminal High‐Voltage Direct Current Networks

The purpose of this study is to improve the P-I controllers of the voltage-source converters (VSC)-based multiterminal high voltage direct-current (MT-HVDC) networks. Since the VSCs are the non-linear elements of the MT-HVDC stations, the classical optimization methods, which approximately implement the linear model to optimize the P-I controllers of the VSCs, do not generate optimal results. Therefore, this paper presents a novel technique to optimize the VSC-based MT-HVDC grids’ P-I controllers by embedding the artificial bee colony (ABC) algorithm. The voltage-droop control method is employed at on-shore grids to ensure the active and reactive power balance within MT-HVDC networks. During an evaluation, achieved via a detailed four-terminal MT-HVDC model designed in PSCAD/EMTDC, the improved results obtained under different dynamic situations such as unbalance wind power generation, change in load demand at the on-shore side grids, and eventual VSC disconnection, respectively.

Multi-objective optimal power flow considering the multi-terminal direct current

Introduction. In recent years, transmission systems comprise more direct current structures; their effects on alternating current power system may become significant and important. Also, multi-terminal direct current is favorable to the integration of large wind and solar power plants with a very beneficial ecological effect. The novelty of the proposed work consists in the effects of the aforementioned modern devices on transient stability, thus turn out to be an interesting research issue. In our view, they constitute a new challenge and an additional complexity for studying the dynamic behavior of modern electrical systems. Purpose. We sought a resolution to the problem of the transient stability constrained optimal power flow in the alternating current / direct current meshed networks. Convergence to security optimal power flow has been globally achieved. Methods. The solution of the problem was carried out in MATLAB environment, by an iterative combinatorial approach between optimized power flow computation and dynamic simulation. Results. A new transient stability constrained optimal power flow approach considering multi-terminal direct current systems can improve the transient stability after a contingency occurrence and operate the system economically within the system physical bounds. Practical value. The effectiveness and robustness of the proposed method is tested on the modified IEEE 14-bus test system with multi-objective optimization problem that reflect active power generation cost minimization and stability of the networks. It should be mentioned that active power losses are small in meshed networks relative to the standard network. The meshed networks led to a gain up to 46,214 % from the base case.

On the mathematical modeling for optimal selecting of calibers of conductors in DC radial distribution networks: An MINLP approach

This paper addresses the problem of optimal conductor selection in direct current (DC) distribution networks with radial topology. A nonlinear mixed-integer programming model (MINLP) is developed through a branch-to-node incidence matrix. An important contribution is that the proposed MINLP model integrates a set of constraints related to the telescopic structure of the network, which allows reducing installation costs. The proposed model also includes a time-domain dependency that helps analyze the DC network under different load conditions, including renewable generation and battery energy storage systems, and different voltage regulation operative consigns. The objective function of the proposed model is made up of the total investment in conductors and the total cost of energy losses in one year of operation. These components of the objective function show multi-objective behavior. For this reason, different simulation scenarios are performed to identify their effects on the final grid configuration. An illustrative 10-nodes medium-voltage DC grid with 9 lines is used to carry out all the simulations through the General Algebraic Modeling System known as GAMS.

A Mixed-Integer Conic Formulation for Optimal Placement and Dimensioning of DGs in DC Distribution Networks

The problem of the optimal placement and dimensioning of constant power sources (i.e., distributed generators) in electrical direct current (DC) distribution networks has been addressed in this research from the point of view of convex optimization. The original mixed-integer nonlinear programming (MINLP) model has been transformed into a mixed-integer conic equivalent via second-order cone programming, which produces a MI-SOCP approximation. The main advantage of the proposed MI-SOCP model is the possibility of ensuring global optimum finding using a combination of the branch and bound method to address the integer part of the problem (i.e., the location of the power sources) and the interior-point method to solve the dimensioning problem. Numerical results in the 21- and 69-node test feeders demonstrated its efficiency and robustness compared to an exact MINLP method available in GAMS: in the case of the 69-node test feeders, the exact MINLP solvers are stuck in local optimal solutions, while the proposed MI-SOCP model enables the finding of the global optimal solution. Additional simulations with daily load curves and photovoltaic sources confirmed the effectiveness of the proposed MI-SOCP methodology in locating and sizing distributed generators in DC grids; it also had low processing times since the location of three photovoltaic sources only requires 233.16s, which is 3.7 times faster than the time required by the SOCP model in the absence of power sources.

Удосконалення системи управління гребними електрорушіями при плаванні в умовах хитавиці

У статті розглянуто питання управління судном з електрорушієм в умовах хитавиці. При ході судна в умовах хвилювання дизель-генератор працює в режимах перевантаження, що значно скорочує експлуатаційні характеристики пропульсивного комплексу. Аналіз хитавиці судна, вказує на випадковий характер постійно діючого обурення різної величини і тривалості. При роботі ГЕУ в таких умовах мають місце коливання моменту опору на гребному валу (якщо відсутнє відповідне регулювання збудження ГЕД), моментів опору на валах дизелів, що визначаються електромагнітними моментами генераторів. Квазістаціонарний характер зміни моменту пояснюється таким же характером зміни моменту опору обертанню гребного гвинта. Стабілізацію кутової швидкості можливо досягти зміною упору лопатей азіподу (ГРК), а, отже удосконалити систему управління ГРК.

Fault Diagnosis with Wavelet Packet Transform and Principal Component Analysis for Multi-terminal Hybrid HVDC Network

In view of the fact that the wavelet packet transform (WPT) can only weakly detect the occurrence of fault, this paper applies a fault diagnosis algorithm including wavelet packet transform and principal component analysis (PCA) to the inverter-side fault diagnosis of multi-terminal hybrid highvoltage direct current (HVDC) network, which can significantly improve the speed and accuracy of fault diagnosis. Firstly, current amplitude and current slope are used to sample the data, and the WPT is used to extract the energy spectrum of the signal. Secondly, an energy matrix is constructed, and the PCA method is used to calculate whether the squared prediction error (SPE) statistics of various signals that can reflect the degree of deviation of the measured value from the principal component model at a certain time exceed the limit to judge the occurrence of the fault. Further, its maximum value is compared to determine the fault types. Finally, based on a large number of MATLAB/Simulink simulation results, it is shown that the PCA method using the current slope as the sampled data can detect the occurrence of a ground fault with small transition resistance within 2 ms, and identify the fault types within 10 ms, without being affected by the sampling frequency.

Fault Location Using the Natural Frequency of Oscillation of Current Discharge in MTdc Networks

This paper discusses a novel fault location approach using single ended measurement. The natural dissipation of the circuit parameters are considered for fault location. A relationship between the damped natural frequency of oscillation of the transmission line current and fault location is established in this paper. The hybrid dc circuit breaker (dcCB) interrupts the fault current and the line current attenuates under the absence of any driving voltage source. The line capacitance discharges into the fault at a specific frequency of oscillation and rate of attenuation. Utilizing this information, the fault location in a multi-terminal direct current (MTdc) network can be predicted. A three terminal radial model of a MTdc is used for performance evaluation of the proposed method using Power System Computer Aided Design (PSCAD)/Electromagnetic Transients including dc (EMTdc).

Independent dual-beam control based on programmable coding metasurface

Programmable metasurfaces incorporating with tunable materials or components are emerging as an attractive option to realize reconfigurable manipulations of electromagnetic (EM) behaviors in real-time. Many efforts have been devoted to the realization of active EM manipulations of the metasurface and significant progress has been achieved, showing their unprecedented ability to arbitrarily manipulate wavefronts in dynamic functions. However, most of the existing multi-beam metasurfaces are based on passive building blocks, only possessing one or a few functions, which cannot provide tunable and independent multi-beam control, thus limiting their further uses in wireless communications. Hence, a 1-bit coding metasurface with high-efficiency, programmable, and independent multi-beam control is proposed in this paper, providing dynamic EM responses with real-time reconfigurability, and controlled by external digital circuits through direct current (DC) bias networks. Specifically, the meta-atom loaded with PIN diodes is employed to achieve independently tunable phase characteristics, thus complex EM functions can be manipulated by redistributing the spatial phases of the metasurface. Symmetric/asymmetric independent dual- and multi-beam manipulations are analyzed theoretically and simulated by EM software. Then as an experimental verification, a metasurface consisting of 14 × 14 meta-atoms is fabricated and tested in a standard microwave anechoic chamber, and the measured results accord well with the simulations. The proposed metasurface has promising ability to generate the arbitrary and independent multi-beams, which may largely enhance the information capacity of the metasurfaces, offering untapped potentials in wireless communication systems.

Metaheuristic Optimization Methods for Optimal Power Flow Analysis in DC Distribution Networks

In this paper is addressed the optimal power flow problem in direct current grids, by using solution methods based on metaheuristics techniques and numerical methods. For which was proposed a mixed integer nonlinear programming problem, that describes the optimal power flow problem in direct current grids. As solution methodology was proposed a master–slave strategy, which used in master stage three continuous solution methods for solving the optimal power flow problem: a particle swarm optimization algorithm, a continuous version of the genetic algorithm and the black hole optimization method. In the slave stages was used a methods based on successive approximations for solving the power flow problem, entrusted for calculates the objective function associated to each solution proposed by the master stage. As objective function was used the reduction of power loss on the electrical grid, associated to the energy transport. To validate the solution methodologies proposed were used the test systems of 21 and 69 buses, by implementing three levels of maximum distributed power penetration: 20%, 40% and 60% of the power supplied by the slack bus, without considering distributed generators installed on the electrical grid. The simulations were carried out in the software Matlab, by demonstrating that the methods with the best performance was the BH/SA, due to that show the best trade-off between the reduction of the power loss and processing time, for solving the optimal power flow problem in direct current networks.