Electromagnetic Transients Research Articles

Direct collapse of exceptionally heavy black holes in the merger-driven scenario

ABSTRACT We revisit the conditions present in supermassive discs (SMDs) formed by the merger of gas-rich, metal-enriched galaxies at redshift z ∼ 10. We find that SMDs naturally form hydrostatic cores which go through a rapidly accreting supermassive star phase, before directly collapsing into massive black holes via the general relativistic instability. The growth and collapse of the cores occurs within ∼5 × 105 yr from the formation of the SMD, producing bright electromagnetic, neutrino and gravitational wave transients with a typical duration of a few minutes and, respectively, a typical flux and a typical strain amplitude at Earth of ∼10−8 erg s−1 cm−2 and ∼4 × 10−21. We provide a simple fitting formula for the resulting black hole masses, which range from a few 106 to 108 M⊙ depending on the initial SMD configuration. Crucially, our analysis does not require any specific assumption on the thermal properties of the gas, nor on the angular momentum loss mechanisms within the SMD. Led by these findings, we argue that the merger-driven scenario provides a robust pathway for the rapid formation of supermassive black holes at z > 6. It provides an explanation for the origin of the brightest and oldest quasars without the need of a sustained growth phase from a much smaller seed. Its smoking gun signatures can be tested directly via multimessenger observations.

Evaluating chemically homogeneous evolution in stellar binaries: electromagnetic implications – ionizing photons, SLSN-I, GRB, Ic-BL

ABSTRACTWe investigate the occurrence of rapid-rotation-induced chemically homogeneous evolution (CHE) due to strong tides and mass accretion in binaries. To this end, we generalize the relation in Packet to calculate the minimum angular momentum (AM) accretion required by a secondary star to experience accretion-induced CHE. Contrary to traditionally assumed 5–10 per cent accretion of initial mass (Z ≲ 0.004, M ≳ 20 M⊙) for spinning up the accretor (resulting in CHE), this value can drop to ∼2 per cent for efficient AM accretion, while for certain systems it could be substantially larger. We conduct a population study using bpass of evolving stars under the influence of strong tides in short-period binaries and also account for the updated effect of accretion-induced spin-up. We find accretion CHE (compared to tidal CHE) to be the dominant means of producing homogeneous stars even at 10 per cent AM accretion efficiency during mass transfer. Unlike tidal CHE, it is seen that CH stars arising due to accretion can retain a larger fraction of their AM till core collapse. Thus, we show that accretion CHE could be an important formation channel for energetic electromagnetic transients like gamma-ray bursts, Ic-BL (SLSN-I, Ic-BL) under the collapsar (magnetar) formalism, and a single CH star could lead to both the transients under their respective formation scenario. Lastly, we show that under the current treatment of CHE, the emission rate of ionizing photons by such stars decreases more rapidly at higher metallicities than previously predicted.

Droop control for district heating networks: Solution for temperature control of multi-energy system with renewable power supply

In a district heating system, the flow of heated water transfers enthalpy from the generation side to the load side. It is thus critical to maintain the supply temperature at a desired level. However, with the rise of renewable energy sources in the district heating network, the temperature of the heated water tends to be disturbed. This calls for a deployment of thermal energy storage. To effectively exploit the flexibility of thermal energy storage, the relationship between the temperature of the district heating water and the power sharing with other thermal energy resources is considered in this paper. Based on this relationship, the concept and realization of a droop control for the district heating network is proposed. It is shown how the droop characteristic between the temperature of the heated water and the power sharing of the thermal energy storage for the district heating network is developed in analogy to the droop control used in an electrical dc network. The droop characteristic so supports the control of a district heating network. The theoretical considerations are complemented by application to a residential district heating network model to illustrate the functionality of the control. The studies are conducted with the program PSCAD, which is otherwise typically used for simulating electromagnetic transients.

Hybrid Parallel-in-Time-and-Space Transient Stability Simulation of Large-Scale AC/DC Grids

The increasing complexity of modern AC/DC power systems poses a significant challenge to a fast solution of large-scale transient stability simulation problems. This paper proposes the hybrid parallel-in-time-and-space (PiT+PiS) transient simulation on the CPU-GPU platform to thoroughly exploit the parallelism from time and spatial perspectives, thereby fully utilizing parallel processing hardware. The respective electromechanical and electromagnetic aspects of the AC and DC grids demand a combination of transient stability (TS) simulation and electromagnetic transient (EMT) simulation to reflect both system-level and equipment-level transients. The TS simulation is performed on GPUs in the co-simulation, while the Parareal parallel-in-time (PiT) scheduling and EMT simulation are conducted on CPUs. Therefore, the heterogeneous CPU-GPU scheme can utilize asynchronous computing features to offset the data transfer latency between different processors. Higher scalability and extensibility than GPU-only dynamic parallelism design is achieved by utilizing concurrent GPU streams for coarse-grid and fine-grid computation. A synthetic AC/DC grid based on IEEE-118 Bus and CIGRÉ DCS2 systems showed a good accuracy compared to commercial TSAT software, and a speedup of 165 is achieved with 48 IEEE-118 Bus systems and 192 201-Level detail-modeled MMCs. Furthermore, the proposed method is also applicable to multi-GPU implementation where it demonstrates decent efficacy.

Transmission distribution coordination for DER fault ride through support

Rapid renewable energy sources (RESs) deployments in transmission and distribution networks have changed power systems’ operation and control mechanisms. This fundamental shift makes the interaction between transmission and distribution systems more sensitive and requires robust TSO–DSO coordination to ensure system stability and ancillary services for the entire network. This paper uses an electromagnetic transient (EMT) simulation tool using a real-time digital simulator (RTDS) to investigate the dynamic transmission–distribution coordination with a high share of RESs in fault ride-through (FRT) capability of distributed energy resources (DERs). Then, the paper implements fault current injection (FCI), incorporating inverter-based resources (IBRs) in the transmission system to support dynamic voltage responses for the distribution system. Different reactive current control schemes are examined to evaluate the FRT performance of DERs under different fault locations. Additionally, hardware in the loop simulation for the under-voltage protection relay is implemented to validate the low-voltage ride-through capability of DERs. The comparison results show that the transmission system can provide dynamic voltage support for the distribution system through FCI from IBRs to help DER ride through. The FCI from the transmission system also significantly enhances fault-induced delayed voltage recovery of voltage-sensitive load in the distribution system.

Model predictive control and protection of MMC-based MTDC power systems

Meshed offshore grids (MOGs) present a viable option for a reliable bulk power transmission topology. The station-level control of MOGs requires faster dynamics along with multiple objective functions, which is realized by the model predictive control (MPC). This paper provides control, and protection design for the Modular Multilevel Converter (MMC) based multi-terminal DC (MTDC) power system using MPC. MPC is defined using a quadratic cost function, and a dqz rotating frame voltage inputs are represented using Laguerre orthonormal functions. MPC has been applied for the control of both grid forming and grid following converters in a four-terminal MTDC setup, implemented for real-time Electromagnetic Transient (EMT) simulation. By applying numerous time-domain simulations, the advantages of the MPC when dealing with AC and DC side disturbances are investigated. The investigation highlights the MPC’s inherent feature of fast response and high damping during- and post-disturbance, which is compared to the traditional PI controller performance. The analysis provides a comprehensive insight into the transient behavior of the MTDC during disturbances.

Electromechanical Energy Converter Imitation Model in SciLab

The paper shows the implementation of simulation models of an electromechanical energy converter on the example of an induction motor with a squirrel-cage rotor in the SciLab environment and its graphic library Xcos for building structural diagrams. Despite the existence of simulation programs such as Simulink and ANSYS Twin Builder, SciLab is completely free, which is an advantage for use in an academic environment and in scientific research. Despite SciLab being free and significantly different from existing paid software, this program allows to create complex models and has a powerful built-in programming language. This paper shows how, using SciLab blocks, to build a simulation model of an induction motor with a squirrel-cage rotor, based on the differential equations of electromagnetic transients. The construction of models for the mode of direct start from a source of stable three-phase power supply is considered. An example of a code program in SciLab for determining the parameters of an induction motor with a squirrel-cage rotor, necessary for simulation, only from the motor rated data, is shown separately. The work will be useful to researchers who intend to use free software to solve complex problems.

MGRIT-Based Multi-Level Parallel-in-Time Electromagnetic Transient Simulation

In this paper, we present an approach for multi-level parallel-in-time (PinT) electromagnetic transient (EMT) simulation. We evaluate the approach in the context of power electronics system-level simulation. While PinT approaches to power electronics simulations based on two-level algorithms have been thoroughly explored in the past, multi-level PinT approaches have not yet been investigated. We use the multigrid-reduction-in-time (MGRIT) method to parallelize a dedicated EMT simulation tool which is capable of switching between different converter models as it operates. The presented approach yields a time-parallel speed-up of up to 10 times compared to the sequential-in-time implementation. We also show that special care has to be taken to synchronize the time grids with the electronic components’ switching periods, indicating that further research into the usage of different models from adequate model hierarchies is necessary.

Power system stability improvement considering drive train oscillations of virtual synchronous generator‐regulated type‐4 wind turbines

The type-4 wind turbine generators (WTGs) can provide inertial frequency response by implementing the virtual synchronous generator (VSG) concept. However, unstable torsional oscillations (TOs) would be induced in the multi-mass-spring drive-train which can destabilize the entire power system. In this study, participation factor analyses are performed for a power system inclusive of a thermal unit and aggregated WTG system. The system's eigenvalues are characterized and the possible detrimental impacts of TOs on the inertia provision process and overall power system stability are demonstrated and the related stability limits are identified. A comprehensive active torsional oscillations damper (CA-TOD) and a supercapacitor-based energy storage system (ESS) are presented and discussed to implement the CA-TOD. A state of charge (SoC) regulator is also employed to set the reference speed difference for the turbine-generator. Small-signal studies and electro-magnetic transient (EMT) simulations are performed to evaluate the functionality of the CA-TOD and SoC controller and estimate their impacts on the system's dynamics. The robust performance of the CA-TOD is compared to the band-pass filter-based TOD by sweeping key control parameters of the VSG and emulating drive-train parameter uncertainty. Key results are cross-verified by EMT simulations of a multimachine power system.

Experimental and numerical investigation of magneto-plasma optical properties toward measurements of opacity relevant for compact binary objects

Electromagnetic transients known as kilonovae (KN), are among the photonic messengers released in the post-merger phase of compact binary objects, for example, binary neutron stars, and they have been recently observed as the electromagnetic counterpart of related gravitational-wave (GW) events. Detection of the KN signal plays a fundamental role in the multi-messenger astronomy entering in a sophisticated GW-detecting network. The KN light curve also delivers precious information on the composition and dynamics of the neutron-rich post-merger plasma ejecta (relying on r-process nucleosynthesis yields). In this sense, studying KN becomes of great relevance for nuclear astrophysics. Because of the highly heterogeneous composition, plasma opacity has a great impact both on radiative transport and spectroscopic observation of KN. Theoretical models attempting in encoding the opacity of this system often fail, due to the complexity of blending plethora of both light- and heavy-r nuclei transition lines, requesting for more complete atomic database. Trapped magneto-plasmas conceived in PANDORA could answer to these requests, allowing experimental in-laboratory measurements of optical properties and opacities, at plasma electron densities and temperatures resembling early-stage plasma ejecta’s conditions, contributing to shed light on r-process metallic species abundance at the blue-KN diffusion time. A numerical study has been recently performed, supporting the choice of first physics cases to be investigated and the design of the experimental setup. In this article, we report on the feasibility of metallic plasmas on the basis of the results from the systematic numerical survey on optical spectra computed under non-local thermodynamic equilibrium (NLTE) for several light-r nuclei. Results show the great impact of the NLTE regime of laboratory magneto-plasmas on the gray opacity contribution contrasted with those under the astrophysical LTE assumption. A first experimental attempt of reproducing ejecta plasma conditions has been performed on the operative Flexible Plasma Trap (FPT) at the INFN-LNS and here presented, together with first plasma characterization of density and temperature, via non-invasive optical emission spectroscopy (OES). The measured plasma parameters have supported numerical simulations to explore optical properties of NLTE gaseous and metallic plasmas, in view of the near-future plasma opacity measurements through spectroscopic techniques. The novel work so far performed on these under-dense and low-temperature magneto-plasmas, opens the route for the first-time to future in-laboratory plasma opacity measurements of metallic plasma species relevant for KN light curve studies.

A Testing Tool for Converter-Dominated Power System: Stochastic Electromagnetic Transient Simulation

To investigate the impact of uncertain variability and provide a rigorous testing environment for converter-dominated power systems, this article develops a testing tool called stochastic electromagnetic transient simulation. The tool is derived from the stochastic differential equation (SDE) representing the stochastic process of parameter migration. By inheriting the principle of companion circuit, the dynamic companion circuits of the lumped elements with parameter migration are further established. Combined with the analysis of the numerical stability in discrete simulation as well as the stability of the continuous system with parameter migration, a numerical algorithm that is compatible with the electromagnetic transients program (EMTP) framework is designed, as well as a C program package. The verification results on a grid-connected three-phase two-level rectifier and a two-terminal dc distribution system demonstrate that the developed tool can simulate the parameter migrations and the stimulated system dynamic process simultaneously, which can also be used to efficiently reflect the real performance of various control subsystems and their coordination in extreme cases.

Improved Dynamic State Estimation Based Protection on Transmission Lines in MMC-HVDC Grids

In this paper, an improved dynamic state estimation (DSE) based protection (DSEBP) scheme is proposed for transmission lines in MMC-HVDC grids. Firstly, a dynamic model of the protection zone (DC line of interest) is constructed using differential and algebraic equations. The impact of frequency dependent line parameters is mitigated through the utilization of the “line mode” transmission line model. Then, a novel Runge-Kutta (RK) discretization scheme is proposed to consider the dynamics of the control variables during electromagnetic transients, yielding reduced discretization error as compared to the conventional RK scheme. Finally, the batch mode regression framework based DSE is developed to formulate the protection logic considering errors of both measurements and historical estimates. Numerical experiments have shown that the proposed DSEBP scheme can dependably detect and trip internal faults, and securely ignore the external faults. The proposed scheme achieves improved reliability and operational speed as compared with the existing DSEBP schemes. The proposed scheme only requires a typical sampling rate of 10k samples per second, has the robustness to measurement noises, and the calculation burden is low enough for practical implementations.

Comprehensive Analysis of Transient Overvoltage Phenomena for Metal-Oxide Varistor Surge Arrester in LCC-HVDC Transmission System with Special Protection Scheme

This paper proposes a systematic and deterministic method for metal-oxide varistor (MOV) surge arrester selection based on the comprehensive analysis in line-commutated converter (LCC)-based high-voltage direct current (HVDC) transmission systems. For the MOV surge arrester, this paper investigates several significant impacts on the transient overvoltage (TOV) phenomena, which is affected by practical factors such as an operating point of the LCC-HVDC system, synchronous machine operating status of the power system, AC passive filter trip, and communication delay in a special protection system (SPS). In order to determine an appropriate rating of surge arrester, especially for TOV, this paper considers a pattern, magnitude, and duration of TOV based on various fault scenarios in an electrical power system with an LCC-HVDC system. A screening study method with 60 Hz and RMS-based balance system is conducted for examining a wide range of fault scenarios, and then for the specific test cases that need a detailed analysis, electro-magnetic transient (EMT)-based analysis models are developed with an approvable boundary setting method through the equivalent network translation tool. A detailed EMT study is subsequent based on the distinguished cases; as a result, the exact number of metal-oxide resistor stacks could be obtained through the detailed TOV study according to this procedure. The efficacy of the selection method from the proposed procedure based on the comprehensive analysis are verified on a specific power system with a 1.5 GW DC ± 500 kV symmetric monopole LCC-HVDC transmission system.

HVDC grid fault location method using genetic algorithm on reconstructed frequency-domain voltage profiles

This paper presents a novel frequency domain based fault location method for High Voltage Direct Current (HVDC) grids. The method relies only on short data windows (below two milliseconds) of single-ended voltage measurements, thus rendering the technique practically applicable to HVDC grids employing high-speed circuit breakers. Based on the available post-fault voltage traces, a frequency domain profile of voltage transfer function is initially constructed, which is then iteratively evaluated against theoretical voltage profiles, synthesized with the use of travelling wave principles. The evaluation routine is based on a genetic algorithm (GA) regime, which once terminated indicates a close approximation to the feeder’s fault location. The result of this process is further refined using a weighted averaging function to obtain the final fault distance estimation. The performance of the proposed method is demonstrated using comprehensive electromagnetic transient (EMT) simulation studies conducted on a four-terminal meshed HVDC grid using PSCAD/EMTDC. The results revealed that the method can estimate the fault location with high accuracy for all transmission media types, including hybrid lines that comprise of cable and overhead line segments. Moreover, it has been found that the method maintains its accuracy for very long transmission lines, highly-resistive faults and different fault types.

GPU and CPU-Based Parallel FDTD Methods for Frequency-Dependent Transmission Line Models

Finite-difference time-domain (FDTD) is a popular method utilized for solving frequency-dependent transmission line structures. It is also conveniently applicable to nonuniform wires. The FDTD algorithm discretizes the transmission line problem into a finite number of space-segments and solve for the voltage and current of each segment at every time-step. Therefore, they inherently involve more computations per timestep than conventional terminal based models. In this letter, parallel implementations of a modified FDTD algorithm for a frequency-dependent transmission line problem using multicore CPU and GPU architectures are proposed in order to increase its computational efficiency. Accuracy and performance of the parallel FDTD methods are discussed with examples. The results indicate that a speedup of a few folds compared to serial execution is achieved by the parallel implementation using multicore CPU architecture whereas a massive speedup is achieved by using GPU. The proposed model is also suitable for modelling transmission lines in massively parallel electromagnetic transient (EMT) simulation methods.

Stabilizing Inverter-Based Transmission Systems: Power hardware-in-the-loop experiments with a megawatt-scale grid-forming inverter

This article presents what the authors believe to be the first experimental verification of the ability of grid-forming (GFM) inverters to stabilize a transmission electric power system that is otherwise unstable. The experiments described here were performed using power hardware-in-the-loop (PHIL) simulation to connect a megawatt-scale battery inverter to a real-time electromagnetic transient (EMT) simulation of the near-future Maui power system. This allows the dynamic interactions between the inverter and the power system to be observed without putting the real power system at risk. The ability to use the actual inverter hardware removes the need to rely on a computer model approximation of the inverter’s behavior.

A Data-Driven Method for Prediction of Post-Fault Voltage Stability in Hybrid AC/DC Microgrids

Faults are extreme events that canadversely affect the voltages in islanded microgrids. This paper provides a new data-driven methodology for timely prediction of the post-fault voltage stability in hybrid AC/DC microgrids. The proposed method performs a binary classification with delay constraints by processing sequences of the short-time mean squared deviations using a deep learning system. The deep learning system consists of a bidirectional long short-term memory network whose output is a probabilistic voltage instability indicator. When the value of the indicator is non-zero, persistent voltage disturbances are most likely to occur even after the fault clearance. The proposed method enables the microgrid to carry out remedial or preventive actions, such as event-triggered protection and control of distributed energy resources (DERs), which are advantageous to the resilient operation of the microgrids. Extensive and detailed electromagnetic transient (EMT) simulations of a low-voltage hybrid AC/DC microgrid benchmark are analyzed, and the results confirm the effectiveness of the proposed method for online prediction and fast voltage regulation.

Dynamic Security Optimization for N-1 Secure Operation of Hawai‘i Island System With 100% Inverter-Based Resources

Reliable power system operation with 100% inverter-based resources (IBRs) is an unsolved and challenging problem. One of the most challenging factors is ensuring power system stability after N-1 contingencies. This paper presents a promising solution using an operator support system (OSS) to enable stable operation of power system with up to 100% IBR generation. The OSS consists of two components. First is dynamic security assessment to evaluate the system resiliency, and identify critical N-1 contingencies that could endanger the system. The second component, as the key technology behind the OSS, is dynamic security optimization (DSO). The DSO optimizes the control parameters of generators and inverters to improve the stability of the system towards the identified N-1 contingencies. The key to system with 100% IBRs, as emphasized in many recent studies, is to establish the grid frequency reference using grid-forming (GFM) inverters. We show through high-fidelity Electro-Magnetic-Transient (EMT) simulations of the future generation models of Hawai‘i Island system with 100% IBR capacity that a system with 100% IBRs can be operated stably with the help of GFM inverters, and appropriate controller parameters can be found by DSO for the inverters. The DSO is verified via 28 critical N-1 contingencies of Hawai‘i Island system identified by Hawaiian Electric. The simulation results verify the effectiveness of DSO, and show significant stability improvement from DSO.

EMTP/MODELS와 외부프로그램 연계를 통한 성능향상 방안 연구

Analyzing the electromagnetic transient of power systems is an important research field for power system analysis. for this, EMTP/ATPDraw is one of the programs for analysis. ATPDraw has elements for various electromagnetic and systematic analysis. however, there are limitations in nonlinear algebra or numerical analysis. therefore, in this paper, uses EMTP/ATPDraw

Measurement of electromagnetic environment of hybrid DC circuit breaker during bipolar short circuit fault

Hybrid DC circuit breakers (DCBs) have recently been used to break short-circuit fault currents to ensure safety in flexible DC transmission projects. However, electromagnetic transients from DCB operation can interfere with the secondary equipment and cause malfunctions. In this paper, the bipolar short-circuit test, which is the first short-circuit test for DC transmission line in flexible DC project in the world, has been carried out in the 200 kV HVDC converter station equipped with two hybrid DCBs. The transient magnetic field near the secondary equipment in the DCB hall were measured, and its characteristics were discussed. Furthermore, the relationships among the space magnetic field, the short-circuit current and the action of the power electronic equipment in the DCB were also analyzed The main findings are as follows. During the bipolar short-circuit process, the maximum space magnetic field intensity near the secondary device is 109 A/m, and the maximum rising rate of the magnetic field waveform is about 350 A/m/ms. The magnetic field strength reached its peak value at the moment when the DCB was blocked, as well as the short-circuit current. It can be indicated that the DCB can cut off the short-circuit fault current accurately and reliably. The results can provide reference for the immunity evaluation and anti-interference protection of secondary equipment, and its optimal arrangement in the DCB hall.