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Electromagnetic Transient (EMT) simulation tools are typically developed using conventional procedural programming languages. On the other hand, modern high-level and equation-based programming languages, such as Modelica, are currently available. Modelica allows formulating models that are easy to develop, maintain and understand by expressing what needs to be computed without stating how it should be computed. This paper presents a Modelica-based simulator for electromagnetic transients. It is demonstrated that this approach offers significant advantages for developing sophisticated models. Computational performance and accuracy are compared to a conventional EMT-type simulation tool. [ABSTRACT FROM AUTHOR]

The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental registrations and numerical simulations of the transient overvoltages caused by single phase intermittent arc earth fault in 35 kV network with isolated neutral. Experimental laboratory investigation is performed in order to implement appropriate arc fault model for arcs with low and discontinuous current. Single phase to earth arc fault is created in field in 35 kV network. Numerical model of the system is created in EMTP-ATP software. Overvoltage waveshapes and overvoltage factors are calculated and compared to measured values. Good agreement between the measured and calculated results is achieved. [ABSTRACT FROM AUTHOR]

Grid modernization and innovations in clean energy are leading to a rapid increase in the penetration of inverter-based resources (IBRs) like wind power and solar photovoltaic (PV) plants in the bulk power system (BPS). To study the implications on BPS dynamics and mitigate potential risks to grid reliability, the second-generation generic renewable energy system model has been developed earlier. However, this model has three modules with 86 user-defined parameters and eight control flags to facilitate the utility-scale solar PV plant operation in different control modes. It presents a major challenge to the transmission system planning engineers. There is a critical need to identify the key parameters of the dynamic model that are highly sensitive to grid events causing large-scale voltage and frequency disturbances. In this work, a sensitivity analysis based on modified Sobol’ method is proposed for identification of the key parameters in the utility-scale solar PV plant model. The total Sobol’ sensitivity index captures even the higher-order effects of the variations in the parameters. Validation of the identified key parameters was carried out on a modified IEEE 9-bus system and 200-bus synthetic grid using PSS®E for plant-level control and local coordinated control operation of the solar PV plant. The reduced set of parameters identified in this work offer help to utility grid planning teams while conducting dynamic studies to meet the interconnection requirements. [ABSTRACT FROM AUTHOR]

Several models were successfully developed to reproduce the dynamic behavior of ZnO surge arrester, but the accuracy and reliability of these models are only evaluated for residual voltage calculations. This paper presents a model developed with the specific goal of achieving reliable and accurate modeling of the energy absorbed by a ZnO surge arrester during impulsive transients. To develop and test the model, an experimental database was built, composed of responses of ZnO varistors to current impulses. The database contains the response of varistors of different classes and manufacturers, subjected to current impulses with different waveforms and amplitudes. Then, using system identification techniques, a mathematical model was proposed and validated. The proposed model was successfully tested on the same circumstances that traditional models are used and its performance was compared with the most relevant existing ZnO model. The results indicate that the developed model is an overall valid model for ZnO surge arresters and that energy calculations performed with it are more accurate and reliable. [ABSTRACT FROM AUTHOR]

White-box models are detailed models for the investigation of the internal behavior of transformers during dielectric design. A new model of this type with significantly improved characteristics is presented in this paper. The model has been developed in state-space form, which is more flexible than an equivalent circuit and also makes it possible to optionally hide proprietary information on internal voltages. The proposed parameter determination methodology is very robust and allows the adequate representation of the damping. The methodology for determining inductive impedances and capacitances as a function of frequency using the Finite Element Method is described first. Then the fitting of the impedances obtained in the frequency domain by means of rational approximation functions is presented, which is based on the Vector Fitting algorithm in combination with Particle Swarm Optimization. The state-space model is obtained next, which is then used to perform time and frequency domain calculations. This new model has been successfully validated by comparison with measurements on a large power transformer used as case study during the activities of the JWG CIGRE A2/C4.52. [ABSTRACT FROM AUTHOR]

For low‐voltage autonomous microgrids, the essential goal is maintaining stable voltage and frequency throughout its network for the smooth operation of distributed loads. The other goal is to maintain proportionate power‐sharing between multiple sources connected through voltage source converters (VSCs). For the particular case of a heavily loaded microgrid, any further increase in demand poses new problems. The VSCs proximate to the loads may overshoot beyond its maximum ratings. Owing to which the stability of the power supply, as well as the longevity of VSCs, may get compromised. Also, these sources provide power under varying composite loading conditions comprising both linear and non‐linear loads resulting in unbalancing in its network. To overcome these problems, a decentralised fast terminal sliding mode control strategy for active power‐sharing between parallel VSCs has been proposed. A detailed mathematical model based on Lyapunov's stability theory‐based study is designed to establish the operating stability of the proposed controller. To validate the proposed control strategy, MATLAB‐based simulation results are provided for possible loading scenarios. A comparative study for performance evaluation between the proposed controller and a conventional proportional ‐integral‐based controller is further carried out. Finally, the performance of the proposed controller is also validated in real‐time scenario. [ABSTRACT FROM AUTHOR]

Contribution: A didactic methodology, based on analytical expressions and experimental validation, to describe the process of abrupt current interruption in a series RL circuit, that considers real passive components and uses a toggle switch as disconnecting device. Background: In undergraduate courses, circuits adopted in transient analysis usually assume electrical switches in their ideal form, disregarding electrical impedance and its variation over time. Texts and instructors rarely point out these simplifications, so students can become confused. There is thus a need for a suitable switch model that yields a behavior consistent with real devices, while permitting a mathematical formulation of the inductor current. Intended Outcomes: That students should understand electrical component modeling, and how models can represent the physical phenomena that occur in electrical circuits. Application Design: An experiment, designed to evaluate students’ perceptions of switch modeling, modeled a switch by using three different equivalent circuits of increasing complexity, to allow a more realistic simulation. Electrical switch modeling is described, with the models being based on measurements performed on a real circuit. Findings: Student performance was evaluated qualitatively through test scores, and quantitatively through a post-class questionnaire. The results indicate that 96.15% of the students were able to propose an accurate model of the electrical switch. [ABSTRACT FROM AUTHOR]

Switching AC filter may cause harmonic impact, which may lead to commutation failure of HVDC system. Here, the commutation failure mechanism of HVDC system caused by AC filter switching is studied. The circuit and mathematical model of the transient process simulation of filter switching are established, and the time-domain solution of the overvoltage of each filter including voltage reduction and distortion is given. The commutation failure mechanism of HVDC system is analysed based on the commutation failure analysis method of harmonic voltage and time area. The simulation results verify the effectiveness of the mechanism analysis of commutation failure caused by AC filter switching in HVDC system.

Coupled nonlinear oscillators, e.g., Kuramoto models, are commonly used to analyze electrical power systems. The cage model from statistical mechanics has also been used to describe the dynamics of synchronously connected generation stations. Whereas the Kuramoto model is good for describing high inertia grid systems, the cage one allows both high and low inertia grids to be modelled. This is illustrated by comparing both the synchronization time and relaxation towards synchronization of each model by treating their equations of motion in a common framework rooted in the dynamics of many coupled phase oscillators. A solution of these equations via matrix continued fractions is implemented rendering the characteristic relaxation times of a grid-generator system over a wide range of inertia and damping. Following an abrupt change in the dynamical system, the power output and both generator and grid frequencies all exhibit damped oscillations now depending on the (finite) grid inertia. In practical applications, it appears that for a small inertia system the cage model is preferable. [ABSTRACT FROM AUTHOR]

With increase of practical power system complexity, power system online stability assessment and control is more and more important. Application of the traditional model-driven methods is always limited by contradiction between accuracy and efficiency, while data-driven methods demonstrate strong abilities for the online decision-making support with advancement of various data mining techniques. Instead of direct application of data-driven methods in the power system, this paper first discusses feasible integration approaches for the model-driven and data-driven methods based on the existing achievements, and then, proposes to integrate both methods for the power system online frequency stability assessment and control. The integrated method consists of frequency dynamics prediction and load shedding procedure. In frequency dynamics prediction procedure, integration of system frequency response (SFR) model and the extreme learning machine (ELM)-based learning model is applied, where basic physical causality is kept in the SFR model and ELM is used to fit and correct error of the SFR. The ELM also plays a part in load shedding prediction model construction by digging out mapping relationship from samples. Finally, the proposed prediction and control scheme for the frequency stability is verified by simulations on WSCC 9-bus, New England 39-bus, and NPCC 140-bus system. Results show that the reliability, time efficiency, and accuracy are enhanced with the proposed method. [ABSTRACT FROM AUTHOR]

The absolute requirement to increase the amount of energy generation from renewable sources e.g., predominantly asynchronously connected wind turbines and photovoltaic installations, may in practice during transient events (where frequency changes are examined) excite oscillatory response of the power output of large grid connected synchronous generators. The response of such generators must be controlled either by varying the applied torque of a turbine or by altering the electromagnetic torque in the airgap. Choosing the latter, the adequacy of a voltage regulator, particularly that of the embedded power system stabilizer (PSS) circuit, is investigated using the IEEE PSS1A model for the automatic voltage regulator of a synchronous generator driven by a gas turbine. The response is obtained via closed form analytic solutions for both small (linear) and large (nonlinear) scale transient events in the energy grid system. In tandem with the analytical study, the behavior simulated with a computer model from MATLAB-SimPowerSystems is reviewed. [ABSTRACT FROM AUTHOR]

This paper presents a novel frequency-domain approach toward the control design for parallel grid-connected voltage source inverters (VSIs) with LCL output filters. The proposed method allows the controllers of multiple VSIs to be designed in a single step, and inherently attenuates the resonances introduced by the output filters and coupling effects while guaranteeing stability. Performance specifications such as desired closed-loop bandwidth, decoupling or robustness toward multi-model uncertainty can be specified through frequency-domain constraints. Furthermore, controllers can be designed in a plug-and-play fashion. The designed controllers are equivalent in structure to multi-variable PI controllers with filters. As the control design is based on the frequency response of the system, the algorithm is independent of the model order, which allows the use of large and high-order models. The performance of the method is demonstrated on a relevant example of a low-voltage distribution grid with five VSIs, and the results are validated both in numerical simulation using MATLAB/Simulink as well as in power-hardware-in-the-loop experiments. [ABSTRACT FROM AUTHOR]

Switching AC filter may cause harmonic impact, which may lead to commutation failure of HVDC system. Here, the commutation failure mechanism of HVDC system caused by AC filter switching is studied. The circuit and mathematical model of the transient process simulation of filter switching are established, and the time-domain solution of the overvoltage of each filter including voltage reduction and distortion is given. The commutation failure mechanism of HVDC system is analysed based on the commutation failure analysis method of harmonic voltage and time area. The simulation results verify the effectiveness of the mechanism analysis of commutation failure caused by AC filter switching in HVDC system. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to develop methods that would be able to predict transient voltage distribution along the insulated-multiconductor windings of electric equipment fed by frequency converters. Several electromagnetic (EM) challenges are presented with this desire. First, the resistance (R) and self-/mutual inductances (L,M) frequency-dependent parameters are accurately computed using the enforced electric total current process based on the finite-element (FE) formulation of the strongly coupled time-harmonic magnetic field and total current density equations model including skin and proximity effects. Second, the coupling capacitances (C) are computed from the FE electrostatic analysis using the floating electric scalar potential process. Finally, a realistic high-frequency electric circuit of the distributed (R, L, M, C) EM parameter matrices is formed in order to predict the turn-to-ground and turn-to-turn voltage transients. The numerical results obtained from the proposed models implemented under the MATLAB code are successfully verified by the corresponding laboratory test measurements. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive approach toward the design of primary and secondary controllers in low-inertia power grids with mixed lines and a large amount of inverter-interfaced generation. First, a complete dynamic phasor model is developed that represents the electromagnetic and electromechanic dynamics of lines, inverters, synchronous machines, and constant power loads. The model offers a straightforward way to combine white-, gray- and black-box models, and its structure lends itself well to control design. In a second step, it is shown how a recently developed robust fixed-structure control design method can be applied to the challenging and relevant problem of primary and secondary control in medium-and low-voltage grids. A comprehensive three-part simulation example demonstrates how frequency and voltage transient stability and performance can be achieved through a methodical design process. It is also shown how nonstandard performance specifications such as proportional power sharing can be directly incorporated in the design. Finally, a distributed secondary controller from the literature is reformulated and designed using the presented framework, and all results are validated in nonlinear simulation. [ABSTRACT FROM AUTHOR]

This paper presents the development and performance evaluation of a new approach for detecting voltage flicker events in power systems hosting distributed generating units. The proposed approach is based on extracting the magnitudes and phases of the different frequency sub-band contents present in the voltage signal(s). Desired magnitudes and phases are extracted by processing the voltage signal(s) using nine phaselet frames that are realized by a modulated filter bank. The modulated filter bank is designed using nine digital high-pass filters (HPFs), each of which implements one phaselet frame. The coefficients of HPFs are determined by bi-orthogonal phaselet basis functions. Extracted high-frequency sub-band contents provide signature information for accurate detection and quantification of voltage flickers. The performance of a phaselet transform based approach is experimentally tested for different conditions, including voltage flicker events that are triggered by an interconnected photovoltaic system. Performance results show accurate, reliable, and fast detection and quantification of voltage flickers, along with a negligible sensitivity to the source producing voltage flicker events. [ABSTRACT FROM AUTHOR]

When solving network algebraic equations during power system transient stability simulations, the nonzero elements in the independent vector and the elements needed in the solution vector are determined by the location of source nodes. Different kinds of source nodes will have a different influence on the solution process of the network equations. According to these features of source nodes, sparsity techniques, more specifically, the node ordering algorithm and sparse vector method, are improved in this paper. A new heuristic ordering algorithm is proposed to enhance the efficiency of the sparse vector method by reducing the number of nodes in the factorization path set of source nodes while maintaining the sparsity of the factorized matrix. A multipath sparse vector method is proposed to avoid the unnecessary computation in the iterative solution process of the network equations, whereby the idea of the method is to form different paths for different types of source nodes. Different paths are used to solve different elements in the solution vector. The correctness and effectiveness of these improvements is proven by the simulation results of three practical power systems (up to 13 490 nodes) and six IEEE examples (up to 162 nodes). [ABSTRACT FROM AUTHOR]

An expression of the compensation torque is derived to reduce the difference between the fifth-order generator model and the seventh-order model. It is appended to the swing equation in the fifth-order model, with the voltage equations and the flux linkage equations unchanged. Based on the singular perturbation theory, the stator transients are approximated. The fast current components of three rotor windings are represented by equivalent d- and q-axis stator current increments that create the same stator flux linkage. The relationship between this torque and damping is clarified from a physical viewpoint. Simulations on two systems show that the compensation torque reduces the model difference. The proposed damping preserving model overcomes the difficulty in determining the damping torque coefficient and is applicable to online transient stability analysis. [ABSTRACT FROM PUBLISHER]

This study exhibits the optimum design procedure to tune controller parameters for grid‐connected distributed generation system based on cuckoo search algorithm (CSA). To investigate the effectiveness of proposed algorithm, a grid‐tied photovoltaic (PV) system consisting of two power electronic converters controlled by five proportional integral (PI) controllers is chosen. Setting proper values for all the PI controllers is a complicated task, notably when the system is non‐linear. In this study, response surface methodology (RSM) is used to develop the mathematical design of the PV system which is required to apply the optimisation algorithm. To minimise the design efforts of RSM, an alternate approach based on artificial neural network is introduced to develop the mathematical model of the PV system which is another salient feature of this research. Moreover, two modifications in the CSA are proposed to extract optimum parameters for the controllers which are found suitable in power system applications. Both the transient and dynamic performances of the system with the optimum values obtained through CSA are studied for different types of grid fault conditions using PSCAD/EMTDC. The design values are compared with values obtained through genetic algorithm and bacterial foraging optimisation. Experimental validation is also given for the proposed method. [ABSTRACT FROM AUTHOR]

Six-phase electrical machines have received significant attention in the literature due to their use in special purpose applications (e.g., aircraft, naval, and vehicular systems). Recently, such machines have also been considered for renewable energy systems including wind generators. Modeling of such machines in commonly available transient simulation programs is not straightforward, especially when the machine model is interfaced with external inductive network and/or power electronic converters. The available modeling approaches include the classical qd 0 model, the coupled-circuit-phase-domain and the voltage-behind-reactance (VBR) models (each having its interfacing challenges). This paper extends the prior research in this area and proposes a constant-parameter VBR model that has a very convenient constant RL−branch interfacing circuit (even for salient pole machines), which makes it simple to implement in most state-variable-based simulations programs. The presented computer studies demonstrate significant numerical advantages of the new model over the existing alternative models. [ABSTRACT FROM PUBLISHER]

This paper proposes a new approach for power system transient stability simulation, which is based on a semi-analytical solution (SAS) of power system differential-algebraic equations. In this paper, an SAS is derived using the Adomian decomposition method as a closed-form explicit function of symbolic variables such as time, the initial state, and other variables on system conditions and; hence, it can directly give a power system's dynamic trajectory being accurate for a certain time window. Unlike a traditional numerical integration based simulation approach, the proposed new approach offline derives an SAS and online evaluates the SAS by plugging in values of symbolic variables for a series of time windows making up the desired simulation period. This paper further studies the maximum length of the time window for an SAS being accurate and proposes a divergence indicator for simulation using adaptive time windows. Implementation of this new approach on parallel computers is also studied. The new approach is validated through contingency simulation of the IEEE 10-generator 39-bus system with detailed generator models. [ABSTRACT FROM AUTHOR]

In a multiterminal HVDC network, dc circuit breakers (CBs) are required at each end of a line to selectively isolate a fault. Several CB concepts have been implemented in PSCAD, which differ significantly in their structure and performance. This paper describes the interaction of the different HVDC CB topologies with a meshed four-terminal network and assesses their performance in terms of maximum currents and voltages. The tradeoff between network parameters and CB requirements is analyzed. [ABSTRACT FROM PUBLISHER]

This paper studies the average value modelling (AVM) of medium frequency (200 Hz–2000 Hz) dc–dc converters, which are becoming increasingly important in high-power dc grids and distributing microgrids. The most convenient modelling is based on transfer function and power components which are available in common simulation platforms, such as PSCAD/EMTDC. However, these models are found to require very small simulation steps and the achieved time-domain accuracy is not satisfactory for medium frequency converters. The core issue of accuracy loss is identified and corresponding improvement is proposed. User written state-space models in the abc frame and the dq frame are analyzed in depth. Different solvers, including the Dommel's method, the Heun's method, and the Runge-Kutta method were adopted and compared in solving the state-space models. A high-power 2-kHz LCL dc-dc converter is taken as the test system. It is found that the AVM in the dq rotating frame based on the Runge-Kutta solver is able to generate very accurate time-domain responses compared to the detailed switching model with almost 100 times improvement in simulation speed. It is demonstrated that a dc-dc converter with 2-kHz inner ac circuit frequency can be accurately simulated at a 50-\mus time step. [ABSTRACT FROM PUBLISHER]

This paper proposes a new passive antiislanding method for three-phase (3φ) distributed generation units (DGUs). The proposed method is based on extracting signatures from the instantaneous 3φ apparent powers determined at the point of common coupling (PCC). This new method is found on the fact that the instantaneous 3φ apparent powers have components continuously exchanged between loads and sources. The islanding condition creates transient high-frequency components in the instantaneous 3φ apparent powers.These high-frequency components contain signature information capable of identifying the islanding condition. These transient high-frequency components can be extracted using the wavelet packet transform (WPT), when applied to the direct and quadrature (d-q-axis) components of the instantaneous 3φ apparent powers. The d-q WPT-based antiislanding method is implemented for testing on a 3φ permanent magnet generator-based wind energy conversion system. Test results demonstrate an accurate, fast, and reliable response to the islanding condition occurring when supplying different load types at different levels of power delivery to the host grid. [ABSTRACT FROM AUTHOR]

Transient stability of wind generation system is evaluated in terms of critical clearing time (CCT) of fault. CCT of a wind generation system connected to grid is calculated based on the maximum amount of time that the wind generation system remains connected to grid, without becoming unstable, when the grid is subjected to a fault. In the literature, the wind turbine model has been used for steady state analysis alone, that is, it is used for finding the initial operating mechanical torque output of the turbine. The turbine model is then completely neglected in case of transient stability analysis by assuming constant mechanical torque output for a particular wind speed. This may not be true, as the mechanical torque-speed characteristic of a wind turbine depends not only on the wind speed but also on the slip of the induction generator connected to the wind turbine. This paper explains the necessity of considering the wind turbine model for the transient stability and steady state analysis of grid connected induction generator based wind generation system. A detailed analysis has been done on the effect of various electrical and mechanical factors on CCT determination and the simulation results are presented. [ABSTRACT FROM PUBLISHER]

Simulation scheme constructed by transient models is widely used for interconnected power system studies. However, it has shortcomings when used in automatic generation control (AGC) and AGC relevant fields. In this paper, a novel simulation scheme designed for AGC and its relevant studies is presented. The scheme uses dynamic energy balancing equation and a single central frequency as core algorithm. Moreover, models described by algebraic equations are adopted instead of transient models described by differential equations. The simplified models reduce computational power requirement to about 3% of transient models and require fewer parameters. By ignoring transient dynamics and inter-area oscillations which are insignificant in AGC timescale, the presented scheme achieves high computational efficiency and acceptable accuracy making it acceptable for up to year-long simulation. At the end of the paper, comparative tests are performed to provide differences, validity and accuracy of proposed scheme. [ABSTRACT FROM PUBLISHER]

This is the first part of a two-paper series and presents the modeling methodology for all of the main components of a typical wind power plant for power system transient studies. The models developed are intended for investigation of the temporary overvoltages, switching overvoltages, and lightning overvoltages. The component models developed include the high-frequency models of the vacuum and SF6 circuit breakers, three core cables for the collector grid, and quad core cables for the wind turbine tower, turbine transformer, doubly fed asynchronous generator, and surge arrester. The models developed are wideband in nature and can be used for all studies, except the transformer model which requires two variations for the low–mid frequency range and mid–high frequency range. Detailed user-defined models developed for both vacuum and SF6 circuit breakers take account of the restrikes, reignitions, prestrikes, low-frequency high-current interruption, and high-frequency low-current interruption. The generator and transformer transient models include a representation of the various high-frequency capacitive couplings. The success criteria for each individual component model are discussed, and the model performance is validated against these criteria. [ABSTRACT FROM AUTHOR]

Shortcomings of the classical approach in describing magnetization processes in grain-oriented transformer steel is analyzed. A noniterative method of accounting for hysteresis and dynamic properties of transformer core is proposed. Fitting the model to catalog data is described. The method is illustrated by calculating inrush current produced by subsequent transformer energizations. [ABSTRACT FROM AUTHOR]

This paper proposes an optimized transmission line modeling (TLM) method for the real-time transient simulation of systems with multiple nonlinearities. The proposed method allows the simulation to be carried out with larger time-steps while maintaining the accuracy. A detailed case study of a nonlinear bridge circuit is presented to illustrate the advantages of the optimized TLM method in comparison with other methods. The new formulation is then implemented in real-time for the transient simulation of the nonlinear bridge. Real-time simulation results are validated by comparing them with experimental measurements. A second case study includes a power system with several surge arresters which is also simulated in real-time by the aid of the optimized TLM method and verified using offline simulation. [ABSTRACT FROM PUBLISHER]