Electromagnetic Transients Research Articles

A review of power system dynamic equivalents for transient stability studies

The increasing complexity of interconnected power system has brought challenges to detailed dynamic simulation in terms of computational effort. Therefore, for transient stability assessment, dynamic equivalents of parts of large-scale system are required to capture the electromagnetic transients. This paper presents a review of past research on dynamic equivalencing using coherency-based methods and system identification methods. Future topics are discussed to improve the state-of-art approaches.

Structure Preserving Aggregation Method for Doubly-Fed Induction Generators in Wind Power Conversion

An aggregation method is proposed that transforms the multiple DFIGs into an equivalent DFIG model that retains the major collective dynamic characteristics of a group of DFIGs. It is intended for Electromagnetic Transients Simulation (EMT). The aggregated machine can take into account different speeds and parameters of each of the individual DFIGs and the connecting impedance of individual DFIGs. Starting with a State Variable (SV) model of an individual DFIG, aggregation is carried out recursively, by combining two DFIGs at a time and then reducing the order of the aggregate to match the state variable equations of a single DFIG so that the steady state performances are identical. Validation is carried out by comparing the detailed electromagnetic transient (EMT) simulation of the unreduced system with the reduced aggregate system. It is shown that the proposed aggregation method accurately matches the steady state response and also accurately reproduces the dominant transient response of the unreduced system. As the aggregate DFIG has the same number of state variables as a single DFIG, the overall wind farms order is reduced significantly to increase the modelling and simulation efficiency.

ВИКОРИСТАННЯ ПРОГРАМНОГО ЗАБЕЗПЕЧЕННЯ ДЛЯ ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ МОДЕЛЮВАННЯ ЕНЕРГЕТИЧНИХ МЕРЕЖ

The article is devoted to the topical issue of power grid modeling. The article discusses positive and negative features of simulation programs. Particular attention is paid to the principles of the programs. Such programs as PSS®SINCAL from Siemens; ETAP from Operation Technology and PowerFactory from DIgSILENT GmbH are considered in the article. The PSS®SINCAL software specializes in designing networks from low to ultra-high voltage classes, in symmetrical and non-symmetrical modes of operation, takes into account the installation possibilities of compensating devices and gives recommendations for their installation locations. Basic models enabling mode calculations and shortcircuit calculations as well as simulation of electromagnetic transients are used as the basis of the PSS®SINCAL software. The basic modules include steady state calculations, calculations of short circuit currents, harmonics, system stability and electromagnetic transients. Particular attention is paid to the optimization and planning module, namely reactive power optimization. The module of reactive power optimization in PSS®SINCAL offers methods of optimizing existing equipment by finding the best switching points for reactive power compensation. ETAP software specializes in electrical network and power transmission design. ETAP Grid™ connects network design with detailed substation models, SCADA systems, and real-time transmission network management. This paper covers only 2 modules of ETAP software, namely transmission and distribution modules. PowerFactory captures the full range of functionality from standard features to highly sophisticated and advanced applications, including wind power, distributed generation, real-time modeling, and performance monitoring for testing of surveillance systems. This article reviews only 2 modules of the PowerFactory software, namely the electrical power transmission and distribution modules. The paper reviews the programs and concludes that Siemens' PSS®SINCAL software would be the most successful solution for modeling electric grids and accounting for the effects of compensating devices on voltage levels in electric grids.

Fault current and fault voltage analysis of power transmission systems with high penetration of inverter-based wind generators

This paper highlights the evolution of wind power sources in the modern energy scenario, emphasizing the impacts of inverter-based generators, namely Full-Converter and DFIG (Doubly-Fed Induction Generator), on fault currents and fault voltages in transmission systems. The studies were carried out through computer simulations, with an EMTP (Electromagnetic Transients Program) type software. A power system with high penetration of such renewable generations was modeled and several contingency scenarios were simulated in a transmission line that performs the connection of the wind power plant to the grid. The scenarios included the variation of parameters such as fault type, inception instant angles, resistance, and distance, to explore the main differences between the contributions to the fault of a wind power plant and conventional generation. Among the atypical analyzed characteristics, the following can be highlighted: the absence of the DC (Direct Current) component for Full-Converter generation, independent of fault inception instant angle and distance variation; low levels of the fault contributions at the wind power plant terminal; low levels of voltages at the wind power plant terminal, evidencing the high SIR (Source Impedance Ratio) characteristic of these generations; atypical relations between the fault resistance and measured currents; and others. The obtained results show the importance of further studies on the impacts of inverter-based generations on fault currents and voltages, allowing developments that are able to improve control and protection systems for grids with high penetration of this wind generation topologies

Development of practical allocation method for reactive power reference for wind farms through inner‐voltage restriction

This study considers the optimal reactive power dispatch strategy that minimizes electrical loss while working within the constraints of the internal layout voltage. Wind turbines (WTs) with a power converter system can promptly generate reactive power, and when a reactive power order arrives from the connected grid, an operator can assign a reactive power reference to each wind turbine. Recently, multiple objective functions in use have been based on centralized control, but their flexibility has been determined as inadequate for situations in which the voltage range of the wind turbine is also a factor. The designated constraints of the voltage fluctuation for each section have thus been considered by designing and applying an adaptive method. The main purpose of such a method is to use general dispatch optimization while maintaining the voltage of each connection point within operating range. The included case studies are designed using an electromagnetic transients program that checks both the voltage and loss of the entire wind farm. We tried to identify voltage violations and confirmed the effectiveness of the proposed method. This work thus attempts to confirm whether an objective function can be implemented while also adhering to a certain grid code.

Improving grid strength in a wide‐area transmission system with grid forming inverters

This paper summarizes Electromagnetic Transient (EMT) simulation studies using PSCAD/EMTDC undertaken to evaluate the capability and suitability of commercially available large scale Grid Forming Inverters (GFMI) to dampen oscillations in a real bulk power transmission network. Faults and a range of grid voltage oscillation frequencies are tested on GFMI and synchronous condenser (SC) models using single source equivalent network model and comparisons of transient, post fault and oscillatory rejection tests are presented. A critical credible fault in the West Murray Zone (WMZ) was simulated on a wide-area EMT model of the Australian National Electricity Market (NEM) to show the effectiveness of GFMI in providing system strength services and improving damping of network sub-synchronous control interactions (SSCI). Two scenarios were examined: Direct replacement of existing centralized synchronous condensers in the WMZ of the NEM, and a decentralized distribution of GFMI in the transmission network (treated as expansion or repowering solution for existing grid following inverter equipped solar farms). Simulation results show that commercially available GFMI are a viable option for improving system strength in a practical transmission system with a high proportion of Inverter Based Resources (IBR).

Mitigating High-Frequency Resonance in MMC-HVDC Systems Using Adaptive Notch Filters

Recently, high-frequency resonance (HFR) incidents have occurred in several MMC-HVDC projects. The resonance frequency highly depends on system conditions, making mitigation methods designed for specific scenarios ineffective once the grid condition changes. To address the issue, this paper proposes a novel HFR mitigation method based on adaptive notch filters (ANFs). The embedding positions of ANFs in the MMC control are optimally determined through impedance-based analysis. With the HFR frequency estimated by the interpolated discrete Fourier transform, the parameters of ANFs are adaptively tuned. The ANFs improve the damping performance of the captured HFR mode without affecting the dynamic characteristics at other frequencies. As a result, the HFR under varying grid conditions can be mitigated effectively. The effectiveness of the proposed method is verified through electromagnetic transient (EMT) simulations of an actual MMC-HVDC system.

Stability and Accuracy Analysis of a Distributed Digital Real-Time Cosimulation Infrastructure

Cosimulation techniques are gaining popularity amongst the power system research community to analyze future scalable smart grid solutions. However, complications such as multiple communication protocols, uncertainty in latencies are holding up the widespread usage of these techniques for the power system analysis. These issues are even further exacerbated when applied to digital real-time simulators (DRTSs) with strict real-time constraints for power hardware-in-the-loop (PHIL) tests. In this article, we present an innovative digital real-time cosimulation infrastructure that allows interconnecting different DRTS through the Aurora 8B/10B protocol to reduce the effects of communication latency and respect real-time constraints. The proposed solution synchronizes the DRTS interconnection by means of the IEEE 1588 precision time protocol (PTP) standard to align executions and results obtained by the cosimulated scenario. The ideal transformer method interface algorithm, commonly used in PHIL applications, is used to interface the DRTS. Finally, we present time-domain and frequency-domain accuracy analyzes on the obtained experimental results to demonstrate the potential of the proposed infrastructure. With the presented setup, a time step duration down to 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s is shown to be stable and accurate in running an electromagnetic transients cosimulated power grid scenario by interconnecting two commercial DRTS (i.e., RTDS NovaCor), extending the scalability of future smart grid real-time simulations.

Estimating transient rates from cosmological simulations and BPASS

ABSTRACT The detection rate of electromagnetic (EM) and gravitational wave (GW) transients is growing exponentially. As the accuracy of the transient rates will significantly improve over the coming decades, so will our understanding of their evolution through cosmic history. To this end, we present predicted rates for EM and GW transients over the age of the universe using Binary Population and Spectral Synthesis (bpass) results combined with four cosmic star formation histories (SFHs). These include a widely used empirical SFH of Madau &amp; Dickinson and those from three cosmological simulations: MilliMillennium, EAGLE, and IllustrisTNG. We find that the choice of SFH changes our predictions: transients with short delay times are most affected by the star formation rate and change up to a factor of 2, while long delay time events tend to depend on the metallicity evolution of star formation and can change the predicted rate up to an order of magnitude. Importantly, we find that the cosmological simulations have very different metallicity evolution that cannot be reproduced by the widely used metallicity model of Langer &amp; Norman, which impacts the binary black hole merger, stripped-envelope supernovae, and LGRBs in the local Universe most acutely. We recommend against using simple prescriptions for the metallicity evolution of the universe when predicting the rates of events that can have long delay times and that are sensitive to metallicity evolution.

Development of Imitation Model of an Electromechanical Energy Converter with a Solid Rotor in ANSYS RMxprt, Maxwell and Twin Builder

This paper presents the development of a platform for coupling modeling (cosimulation) of an electromechanical energy converter using Ansys Maxwell and Ansys Twin Builder. The researched electromechanical energy converter is based on the operation principle of an induction motor with an external hollow solid rotor. The paper reveals the specifics of modeling this type of special electric machine. In the work, step-by-step modeling of the machine in Ansys RMxprt, export of the model in Ansys Maxwell 2D and 3D with further co-simulation in Twin Builder was performed. It shows how to set up the project to import an object calculated by the finite element method from Ansys Maxwell into the Twin Builder sheet. Coupling simulation of an electromechanical energy converter with a stable three-phase power source was performed. The simulation model considers the presence of a step mechanical load during the run-up to the rated speed. Such structure of a coupling project gives better simulation results compared to the use of simulation models with concentrated parameters, based on the implementation of differential equations of electromagnetic transients using functional blocks. The obtained characteristics showed a high coincidence of the expected results according to the indicators of phase currents of the stator winding, moving torque and rotation speed. This paper will be useful for coupling modeling special-purpose electrical machines that are not available in the Ansys Twin Builder library as ready-made blocks.

A simplified model of Type‐4 wind turbine for short‐circuit currents simulation analysis

The electromagnetic transient (EMT) model of Type 4 wind turbine generator (WTG) requires a small simulation step, and cannot be simplified based on Thevenin-Norton theorem, which results in the low simulation efficiency of large-scale Type 4 WTG-based wind power plants (WPPs) widely connected to the power grid, bringing challenges to the short-circuit currents analysis in the research of protection. Therefore, in order to solve the problem of low simulation efficiency, a simplified model of Type 4 WTG is proposed based on the principle of internal active power balance of Type 4 WTG. The simplified model is represented by controlled voltage source, which eliminates the power electronic switch and DC-link, greatly simplifies the typical EMT model of Type 4 WTG, and does not require small simulation step. The simplified model has simple modelling process and high universality of modelling method. The simulation results show that the proposed model can accurately reflect the EMT characteristics of Type 4 WTG under fault. Compared with the typical EMT model, the simulation time of this simplified model is significantly reduced, and the EMT simulation efficiency of the power grid connecting with large-scale Type 4 WTG-based WPPs has been effectively improved.

Unified magnetic equivalent circuit-based model of two-core Sen transformer for low-frequency electromagnetic transients and its numerical calculation

This paper proposes a low-frequency electromagnetic transient model of two-core Sen transformer (TCST) based on unified magnetic equivalent circuit (UMEC) and also presents its numerical calculation procedure for revealing the internal electromagnetic characteristics of TCST. Firstly, the magnetic equivalent circuits of the two parts of TCST including series unit and exciting unit are established according to their associated iron-core structures. Secondly, the electromagnetic transient models about the two parts are deduced by the electromagnetic coupling relationship. Finally, the electromagnetic transient model of TCST can be obtained through the combination of the series unit and the exciting unit on the basis of the internal electrical connections between them. The saturation and hysteresis characteristics of the iron core are represented by the J-A model, and a cascaded R-L lumped circuit is used to depict the eddy current effect. The case studies have been carried out in the environment of MATLAB and PSCAD/EMTDC. The comparisons between the results from the numerical calculation and the time-domain simulation reveal the effectiveness of the proposed model. Furthermore, it is found that the current flowing through the tap-changer in TCST is about 50% of the corresponding current in single-core ST (SCST), which implies the former may have lower cost and higher reliability. Moreover, the actual step length of TCST is about 0.5 times smaller than that of SCST, which may lead to more accurate control performance for TCST.

Modified average‐value model for high‐performance fault transient simulation of AC‐DC hybrid power networks

Due to the complicated transients and the possibility of transition from a minor fault in AC subsystems to a severe blocking event of a high-voltage direct–current (HVDC) transmission line, the study of AC-DC hybrid power systems requires both efficient and accurate electromagnetic transient (EMT) simulation. However, the computational efficiency of such simulations is restrained by the switching events when detailed models of line-commutated converters (LCCs) are used. Recently the average-value modelling technique has been developed for accelerating the simulation while still accurately capturing the transient characteristics of line-commutated AC–DC converters. This study presents the application of the average-value model in the modelling of the LCC-HVDC system and gives a further discussion about the deficiency of the model. A modified interface and the corresponding soft-switching technique are proposed for enhancing the simulation performance of the LCC-HVDC model in the transition between normal and faulty operation. The model is tested on a series of LCC-based systems including a hybrid power system with four LCC-HVDC lines to verify its efficiency and accuracy. The results indicate that the developed model can accurately predict the transients of the system both in symmetrical and asymmetrical operation while being computationally efficient.

Active Cable Sheath Current-Based Protection Scheme for an Offshore HVAC Wind Transmission System

Due to the complex sending terminal structure of offshore wind transmission systems, conventional on-line monitoring-based protection cannot work well. The electromagnetic transient faults are also difficult to locate due to a short time span with fast characteristics that are affected by various power electronic devices and control algorithms. To solve the aforementioned problems, a new offshore wind transmission line protection scheme based on active detection of submarine cable sheath current is proposed. This method uses a normalized coding cooperation to realize the risk levels and failure locations of the transient defects, and then the sheath currents become a characteristic input data source, which can build a clear system protection boundary. Case studies using MATLAB and ATP simulations are carried out, where three types of transient faults represented by sheath currents are studied, i.e., loss of electrical continuity of grounding device, short circuit of segmented metal sheath of cable joint, and water immersion of junction box. Testing results illustrated that the proposed method could achieve fast fault detection and precise fault location of the electromagnetic transients. Moreover, compared with conventional wind farm protection techniques, it only needs to add few signal injection modules with high sampling frequency into the submarine optical fibers.

Application of the lumped parameter line model to simulate electromagnetic transients in three-phase transmission lines with vertical symmetry

In this paper, we propose a transmission line model to represent three-phase untransposed transmission lines with vertical symmetry. Here, we decouple a transmission line into its propagation modes using Concordia's matrix, which is the proper orthogonal form of Clarke's matrix that has its columns normalised. Due to the usage of Concordia's matrix, the transmission line is decoupled into two coupled modes and one uncoupled mode. We represent the uncoupled mode by a single-phase transmission line, and the coupled modes by a two-phase transmission line without vertical symmetry. We compute voltages and currents for the single-phase transmission line using the classic Lumped Parameter Model. Voltages and currents in the two-phase transmission line are calculated using a cascade of coupled L circuits pairs. Modal voltages and currents are then transformed back to the phase domain. We compare the results obtained with the proposed model to those obtained with two well-known time domain models, the classic modal lumped parameter model and the lumped parameter model available in the Alternate Transients Program ATP. Results show that the proposed model agrees with time-domain models and has the advantage that is developed in the time domain without needing any inverse transformations.

Transformer model with hysteresis for electromagnetic transients computation in the frequency domain

Transformer model with hysteresis for electromagnetic transients computation in the frequency domain

A tool for distributed collaborative electromagnetic transients studies allowing on-demand interaction

This work presents a computational architecture tool aimed to provide a distributed and collaborative environment for electromagnetic transients calculations. Through this tool, different systems, running on different computers in distributed locations, can connect using internet protocols to form large systems. Innovatively, it allows the integration between the subsystems to occur on-demand, which differentiates it from the existing proposals in the literature. Also, it allows user interaction with the power system during the simulation. Such features are demonstrated by means of case studies running on the tool on-demand mode of operation. The opportunities arisen from the tool are further presented using a case study for large systems, 3200 buses, 28 wind farms and 7 solar farms, and also using smaller subsystems, 39 Bus. The results comprise the simulations total running time, a brief discussion about the computers communication latency and the benefits through collaborative work the tool adds to the field of electromagnetic transients calculation.

Siting and sizing of synchronous compensator based on electromagnetic transient simulation

With the increasing load of power grid and the access of new energy sources and direct current lines, power grid voltage stability becomes increasingly prominent. Installing synchronous compensator is an option to supplement reactive power and improve voltage stability. Compared with other reactive power compensation equipment (SVC, SVG, etc.), synchronous compensators have advantages in service life, size, easy to maintenance and etc. Siting and sizing of synchronous compensator are critical for investment and voltage stability adjustment performance of the equipment. Considering that the power grid contains new energy and HVDC equipment, it is necessary to use electromagnetic transient (EMT) simulation to evaluate transient stability of a power system when the siting and sizing of a synchronous compensator was determined. In this paper, a method of siting and sizing the synchronous compensator based on voltage sensitivity index (VSI), severity index (SI) and EMT simulation is proposed. VSI of different bus in the system is calculated by injecting reactive power into each bus, and the suitable candidate bus location for compensator is obtained. Furthermore, the calculation of power grid fault severity index is designed, and the synchronous compensator sizing method with the SI as optimization objective is designed. An actual AC–DC hybrid power grid system with 1343 buses was used to test the proposed methods and testing results demonstrate the performance of the proposed method.

Asking for fast terminal voltage control in grid following plants could provide benefits of grid forming behavior

Conventional inverter based resource (IBR) plants generally have control loops with high bandwidth which enable them to maintain tight control of the active and reactive power injected by the IBR device into the grid. These control loops, if not tuned appropriately, can suffer from instability under reduced system stiffness. To bring about an increase in stability of a power network with large percentage of IBRs, recent research done around the world has resulted in the emergence of multiple different types of so-called grid forming inverter control architectures. But, in order for inverter manufacturers to break the circular (or chicken-and-egg) problem, exact performance requirements must be known, which can only be specified either through standards and/or interconnection requirements. Through the use of both electromagnetic transient (EMT) time domain and linearized state space small signal analysis, this paper will provide a way to define interconnection requirements that are agnostic to the specific type of grid forming or grid following IBR control. Further, the benefit of defining grid forming interconnection requirements even when short circuit ratio is not low will be showcased.

Shifted frequency‐based electromagnetic transient simulation for AC power systems in symmetrical component domain

Power systems are becoming more and more complicated. Traditional simulation tools such as transient stability programs and electromagnetic transients (EMT) programs are unable to meet the accuracy or efficiency requirements. This paper proposes a shifted frequency-based EMT (SFEMT) simulation in the symmetrical component-domain (abbreviated as SCSFEMT simulation) for the three-phase transmission system. The sequence-decoupled SCSFEMT modeling for the power system components is first presented based on the symmetrical component transformation. Then, the solution procedure of the presented SCSFEMT simulation algorithm is elaborated in detail based on the EMTP-type solution and multi-sequence Thevenin equivalence (MSTE). With the MSTE, the three sequence networks can be decoupled during the whole simulation. Thus, the dimension of the system is greatly reduced. Last, the accuracy and efficiency of the SCSFEMT simulation are validated on the 10-machine 39-bus New England system by comparing it with traditional EMT and SFEMT simulation. Test results show that the SCSFEMT simulation algorithm is much more efficient than traditional SFEMT simulation.