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The voltage‐source virtual synchronous generator is a grid‐forming type power electronic control technology and is able to support converters that have the ability of inertial, primary frequency and voltage regulation. Firstly, the authors build the small‐signal model of the voltage‐source virtual synchronous generator and conventional converters, compare and analyse the characteristics of the high‐frequency resonance modes, the results show that the voltage‐source virtual synchronous generator has almost the same high‐frequency resonance characteristics as the conventional converter. Secondly, the different control parameters and power grid strength that affect the high‐frequency resonance characteristic are analysed with eigenvalue, and the mechanism of voltage‐source VSG that caused high‐frequency resonance is derived. The leading factor that causes high‐frequency resonance is power grid strengths, and the authors proposed introducing virtual impedance into the front‐end channel of the current inner loop control strategy to suppress resonance for the voltage‐source virtual synchronous generator based on the theoretical analysis with the small‐signal model and eigenvalue analysis. In addition, the electromagnetic transient simulation model and RT‐LAB controller‐in‐loop platform are built, and the simulation and experiment results indicate the effectiveness of the virtual impedance control strategy. [ABSTRACT FROM AUTHOR]

Modern power grid is evolving towards carbon neutrality by deploying increasing amount of renewable energy resources. However, the impact of renewable generation on power system planning and operation is not sufficiently investigated, especially the capability of renewable penetrated power systems to resist and recover from major disturbances, which is a critical concern for system operators. Novel metrics and evaluation methodologies are needed to depict systems' ability in response to events caused by natural disasters, and quantitatively evaluate system performance in various time scales. In this paper, operational resilience metrics are proposed for power systems with penetration of renewable energy resources based on transient stability principles. A systematic methodology is proposed to quantitatively assess the evolution of system performance during various stages of the disaster process. Based on the proposed metrics, a resilience‐oriented disaster management strategy is designed and validated using the modified IEEE 39‐bus test system. The simulation results demonstrate the validity of the proposed metrics and strategy, and show that the system resilience is enhanced during the mitigation of fault conditions. [ABSTRACT FROM AUTHOR]

Renewable energy communities are considered as key elements for transforming the present fossil fuel-based energy systems of islands into renewable-based energy systems. This study shows how renewable energy communities can be deployed in the Maltese context to achieve higher penetration of residential-scale photovoltaic systems. Case studies for five renewable energy communities in the Maltese LV distribution network have been analyzed in detail. A novel community battery energy storage sizing strategy was proposed to determine the optimal storage capacity at each energy community. The main objective of the community battery storage in each REC is to minimize the reverse power injection in the grid (minimize the total reverse energy and reverse peak power values), as well as to reduce the peak evening electricity demand. The optimal sizes for communal BESSs were determined to be of 57 kWh (EC 1), 55 kWh (EC 2), 31 kWh (EC 3), 37 kWh (EC 4) and 10 kWh (EC 5), respectively. The community storage systems were observed to reduce the overall impact of all five energy communities on the grid infrastructure. Power system simulations were performed for a typical spring day to evaluate the impact of communal BESS placement on the node voltages for all five energy communities. The results showed that the community storage was more effective at reducing the node rms voltage magnitudes when deployed at the end of the respective energy communities, rather than at the beginning of the community. During peak generation hours, reductions of up to 0.48% in the node rms voltage magnitudes were observed. This contrasts with reductions of only 0.19% when the community storage was deployed at the beginning of the energy communities. [ABSTRACT FROM AUTHOR]

The power grid is transforming with large amounts of distributed energy resource (DER) integration that is impacting the bulk power system planning and operations. Grid regulators have identified that traditional power system analysis techniques are challenged under the changing grid conditions. Transmission and distribution (T&D) co-simulation is an effective methodology to accurately account for the changing power-grid. A scalable multitimescale T&D (SMTD) co-simulation framework is developed with commercial transmission system solver that can handle large-scale system models, and distribution system solver that can model the distribution systems in detail with dynamic models of load and DER. In this article, PSS/E and GridLAB-D are combined using a Python interface with Hierarchical Engine for Large-scale Infrastructure Co-Simulation software to enable T&D co-simulation. This framework is scalable and parallel computing compatible that enables large-scale system simulation and adoption of T&D co-simulation by the industry and utilities. The SMTD cosimulator is designed to integrate with existing system models and new ones. The article also highlights functional specifications for the T&D co-simulation solvers and models along with providing the algorithms for the steady state, quasi-steady state, and dynamic T&D co-simulation. In context of changing power grid, future power grid planning, validation of controls under critical contingencies and validation of various wide area monitoring and controls can effectively utilize the proposed framework that can capture the T&D interactions accurately. The SMTD cosimulator can also be used to generate realistic synthetic measurement-data with noise and packet drop for uncommon grid events enabling development and validation of power system data analytics and controls. [ABSTRACT FROM AUTHOR]

Recently, with the increased intermittent renewable energy penetration, many power grids have been incorporated into a large‐scale long‐distance UHV AC–DC hybrid system. In the actual grid, power disturbances, such as DC blocking faults and trip‐off of wind turbines, often occur, resulting in power shortages and large frequency fluctuations. However, the existing approaches to assess the system frequency security are not reliable. This paper proposes an analytic formula for the system frequency response based on a generic system frequency‐response (SFR) model, which can be applied to modern large‐scale power systems. First, a generic SFR model with a reasonable structure is designed according to the parameter determination strategy. Second, according to the transfer function in the model, the time‐domain analytic formula of the frequency response is obtained by realizing the inverse Laplace transform. Moreover, four main indexes are established to represent the characteristics of the frequency dynamic process in different periods, and these indexes are qualitatively and quantitatively analysed. Finally, the New England 10‐unit 39‐bus power system and East China Power Grid are considered to demonstrate the key features of the proposed method. The results show that the proposed analytic assessment method can be effectively adopted in several applications. [ABSTRACT FROM AUTHOR]

Time-synchronized estimates acquired using the Wide Area Measurement System (WAMS) have substantially helped enhance the health of the modern power grid. WAMS data when used in conjunction with appropriate tools can aid in the timely detection of power system events. With the continuous expansion of the WAMS network, identification of events and narrowing down on their location is emerging as a serious challenge for power system operators. Therefore, in this paper an event detection and localization tool is developed which analyzes data obtained from multiple Phasor Measurement Units (PMUs) installed throughout the WAMS network in order to identify the occurrence of an event. The effectiveness of this tool is demonstrated using practical signals from the ISO-NE power system and simulation based signals obtained from a 4-machine 10-bus system. Occurrence of an event is flagged by comparing the wavelet energy and standard deviation values of a PMU signal against a threshold. An event localization algorithm based on the number of PMUs involved in the event detection stage is proposed. Based on the presented algorithm, disturbances are classified as local or wide-spread events. Finally, a method to identify a loss-of-synchronism condition using phase angle difference (PAD) signals obtained across transmission lines is also proposed. • An event detection, localization and classification method is proposed. • Multiple-PMU data is processed in order to identify the occurrence of an event. • Events are classified employing the "considerable excursion" criteria. • Method to predict loss-of-synchronism condition using PAD signals is also proposed. [ABSTRACT FROM AUTHOR]

The complexity of most power grid simulation algorithms scales with the network size, which corresponds to the number of buses and branches in the grid. Parallel and distributed computing is one approach that can be used to achieve improved scalability. However, the efficiency of these algorithms requires an optimal grid partitioning strategy. To obtain the requisite power grid partitionings, the authors first apply several graph theory based partitioning algorithms, such as the Karlsruhe fast flow partitioner (KaFFPa), spectral clustering, and METIS. The goal of this study is an examination and evaluation of the impact of grid partitioning on power system problems. To this end, the computational performance of AC optimal power flow (OPF) and dynamic power grid simulation are tested. The partitioned OPF-problem is solved using the augmented Lagrangian based alternating direction inexact Newton method, whose solution is the basis for the initialisation step in the partitioned dynamic simulation problem. The computational performance of the partitioned systems in the implemented parallel and distributed algorithms is tested using various IEEE standard benchmark test networks. KaFFPa not only outperforms other partitioning algorithms for the AC OPF problem, but also for dynamic power grid simulation with respect to computational speed and scalability. [ABSTRACT FROM AUTHOR]

Submarine cables are indispensable for offshore wind farms (OWFs) connected to a power grid. The submarine cable can cause certain degrees of impact on the system performance due to its different lengths, characteristics, electrical parameters, etc. This paper employs the power-system simulation software of Power System Simulator for Engineering (PSS/E) for modeling a future-scheduled OWF, i.e., a large-scale doubly-fed induction generator-based OWF of 200 MW, connected to Jang-Bin distribution substation of Taiwan Power System through five feeders, five circuit breakers, two step-up power transformers, a commercial submarine cable, and an underground cable. This paper simulates and compares the electrical quantities of the studied OWF with different operating capacities under various lengths of three types of commercial submarine cable. The transient surge peak voltages at the common bus of the OWF and the bus of Jang-Bin distribution substation subject to the switching of one of the five circuit breakers of the studied OWF under different lengths of the three types of commercial submarine cable are also compared using the power-system simulation software of ATPDraw in Alternative Transients Program (ATP) version of Electromagnetic Transients Program (EMTP). [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVDC) systems are increasingly incorporated into today's AC power grids, necessitating optimal power flow (OPF) tools for the analysis, planning, and operation of such hybrid systems. To this end, we introduce hynet, a Python-based open-source OPF framework for hybrid AC/DC grids with point-to-point and radial multi-terminal HVDC systems. hynet's design promotes ease of use and extensibility, which is supported by the particular mathematical model and software design presented in this paper. The system model features a unified representation of AC and DC subgrids as well as a concise and flexible converter model, which enable the compact description of a hybrid AC/DC power system and its OPF problem. To support convex relaxation based OPF solution techniques, a state space relaxation is introduced to obtain a unified OPF formulation that is analogous to the OPF of AC power systems. This enables the direct generalization of relaxation-related results for AC grids to hybrid AC/DC grids, which is shown for the semidefinite and second-order cone relaxation as well as associated results on exactness and locational marginal prices. Finally, hynet's object-oriented software design is discussed, which provides extensibility via inheritance and standard design patterns, and its robust and competitive performance is illustrated with case studies. [ABSTRACT FROM AUTHOR]

• The dynamic simulation of converter-populated power systems requires of models that provide an accurate response over a wide frequency range. • The proposed converter modeling approach allows straightforward interconnectivity with other components defined by wideband representations. • Measurement-based model reconstruction sets the basis for data-driven models that consider variation of operational conditions over time. Power-electronic converters are essential elements for the effective interconnection of renewable energy sources to the power grid, as well as to include energy storage units, vehicle charging stations, microgrids, etc. Converter models that provide an accurate representation of their wideband operation and interconnection with other active and passive grid components and systems are necessary for reliable steady state and transient analyses during normal or abnormal grid operating conditions. This paper introduces two Laplace domain-based approaches to model buck and boost DC-DC converters for electromagnetic transient studies. The first approach is an analytical one, where the converter is represented by a two-port admittance model via mode averaging and inclusion of switching effects. The second approach consists of reconstructing the two-port admittance model of the converter from terminal measurements for a series of tests. The performance of both approaches is evaluated against EMTP simulations, with very close results. [ABSTRACT FROM AUTHOR]

With the increasing penetration of grids with high levels of stochastic resources, the development of innovative computing tools is necessary in order to obtain risk-based power generation estimations by evaluating the stochasticity of primary sources (wind, solar, and river flow). Optimal planning and secure grid operation are new challenges facing modern power systems. The new, impactful, and tractable formulations/algorithms contained in this issue are applicable to all industries where smart grids and intermittent renewable energy resources are being used. [Extracted from the article]

Highlights • A general framework for model validation from frequency perspective is proposed. • New parameters, Frequency Ramp Rate (FRR) and Activity Range (AR), are introduced. • A quantitative assessment method is proposed for the model validation process. • Proposed framework is implemented successfully for a large and real power grid. • The steps of implementation are clarified through detailed results and discussion. Abstract This paper proposes a quantitative model validation framework from the frequency perspective in which some of the technical issues of the process are solved. Two influential parameters of the process, namely the frequency ramp rate and activity range are introduced. A new quantitative assessment method including indices development and threshold calculation method is proposed. In order to reduce the complexities and efforts, all the capabilities of the existing models are initially tried (as approach 1) and upon its failure, more complex models are developed and employed (as approach 2). After discussing the theoretical aspects, the implementation steps and effectiveness of the process are demonstrated by applying the framework to a large and real power system. Some solutions for the practical issues are proposed and implemented. Since the simulation results of the first approach exceed some specified thresholds, the second approach is followed. Quantitative assessment of the second approach proves that the simulation results satisfy the specified thresholds for all incidents. The prominent and vital effect of different influential parameters and improving actions of the process are also demonstrated on the validated model. [ABSTRACT FROM AUTHOR]

This paper develops a comprehensive dynamic-phasor-based small-signal model for the modular multilevel converter (MMC) system under unbalanced grid conditions, which takes into consideration the dynamics of the MMC system under a balanced grid condition as well as the other emerging internal harmonics produced by the unbalanced grid components and more complex controllers. The small-signal model is validated by comparing the time-domain responses from a detailed electromagnetic transient (EMT) simulation in PSCAD/EMTDC. Based on the eigen-analysis and PSCAD-based time-domain simulation studies, this paper reveals the poorly damped modes that cause unstable oscillations in MMC system under the unbalanced grid conditions. From the results, more poorly damped modes involved in the internal harmonics are emerging under unbalanced grid conditions compared with the modes under the balanced grid conditions, and can highly impact the system dynamic behaviors by the selection of the control parameters. It is also shown that, under the unbalanced grid conditions, the feasible region of the control parameters of the vector current control gets narrowed indicating the reduction of the stability margin, smaller (larger) value of proportional (integral) gain of the circulating current suppressing controller can enhance the system stability, and larger values of the proportional and integral gains of the negative-sequence current suppressing control can result in the harmonic instability of the MMC system. Besides, the parameters of multiple complex-coefficient filters for positive- and negative-sequence components extraction also have a big impact on the small-signal stability of the MMC system and are required to be properly selected. [ABSTRACT FROM AUTHOR]

Measurements from the on-board systems of marine vessels are increasingly available for data analysis and are growing in importance as the ship industry enters a phase of digitalization. The purposes of the data analysis from vessels in operation include the verification of the power system design in general and improvement of the electrical power load analysis in particular. In this paper, we show how to extract valuable information from the data-driven operational profile analysis, which reveals the real power demand, and how the vessel was operated. Using the real power range analysis, we emphasize the significance of rarely occurring high power demands, which are critical for power system design and optimization. We propose a methodology for the quantification of variability in the generated power, which explains the tails of probability distributions of a power signal based on signal decomposition. The proposed methodology makes use of the data and it can facilitate the selection of the optimal size, number, and configuration of generators or batteries when designing new power systems. Measurements from a data collection system are used to demonstrate the methodology for dynamic positioning mode of the operation of a platform supply vessel. [ABSTRACT FROM AUTHOR]

This paper describes the use of large electric grids in university electric power system courses. Since much actual power system information is not publicly available, the application of public domain synthetic grids developed by the authors is presented including a 2000-bus grid. Discussion of the educational applications utilized in a senior level class are given for power flow analysis and sensitivity, economic dispatch, contingency analysis, optimal power flow (OPF), security-constrained OPF, transient stability, and real-time dynamic operations. In each of these, the application of the large synthetic grids give students insights and experience with cases closer to actual power systems in complexity and size. [ABSTRACT FROM AUTHOR]

This study examines a modal condition to cause inter-area, low-frequency, electromechanical power oscillations in an interconnected power system with two subsystems. The modal condition being examined is the closeness of two electromechanical oscillation modes from each subsystem on the complex plane, which is referred to as open-loop modal resonance. The analysis in this study indicates that under the condition of open-loop modal resonance, the electromechanical oscillation modes of the interconnected power system are located at approximately opposite positions on the complex plane with respect to the resonant electromechanical oscillation modes of the subsystems. Hence, when open-loop modal resonance occurs, one electromechanical oscillation mode of the interconnected power system must have reduced damping. In this study, the damping reduction in the inter-area, low-frequency power oscillations caused by open-loop modal resonance is demonstrated using example power systems. An incident of inter-area, low-frequency electromechanical power oscillations that occurred in an actual large-scale power system in China is examined. The examination results indicate that the poorly damped, inter-area, low-frequency power oscillation incident was caused by open-loop modal resonance. [ABSTRACT FROM AUTHOR]

The paper proposes a new adaptive approach to power system model reduction for fast and accurate time-domain simulation. This new approach is a compromise between linear model reduction for faster simulation and nonlinear model reduction for better accuracy. During the simulation period, the approach adaptively switches among detailed and linearly or nonlinearly reduced models based on variations of the system state: it employs unreduced models for the fault-on period, uses weighted column norms of the admittance matrix to decide which functions to be linearized in power system differential-algebraic equations for large changes of the state, and adopts a linearly reduced model for small changes of the state. Two versions of the adaptive model reduction approach are introduced. The first version uses traditional power system partitioning where the model reduction is applied to a defined large external area in a power system and the other area defined as the study area keeps full detailed models. The second version applies the adaptive model reduction to the whole system. The paper also conducts comprehensive case studies comparing simulation results using the proposed adaptively reduced models with the linearly reduced model and coherency-based reduced model on the Northeast Power Coordinating Council 140-bus 48-machine system. [ABSTRACT FROM AUTHOR]

The system frequency response (SFR) model describes the average network frequency response after a disturbance and has been applied to a wide variety of dynamic studies. However, the traditional literature does not provide a generic, analytical method for obtaining the SFR model parameters when the system contains multiple generators; instead, a numerical simulation-based approach or the operators’ experience is the common practice to obtain an aggregated model. In this paper, an analytical method is proposed for aggregating the multi-machine SFR model into a single-machine model. The verification study indicates that the proposed aggregated SFR model can accurately represent the multi-machine SFR model. Furthermore, the detailed system simulation illustrates that the SFR model can also accurately represent the average frequency response of large systems for power system dynamic studies. Finally, three applications of the proposed method are explored, with system frequency control, frequency stability, and dynamic model reduction. The results show the method is promising with broad potential applications. [ABSTRACT FROM AUTHOR]

Interarea power oscillation damping enhancement in large interconnected power systems is often accomplished using supplementary controls at the synchronous machines involved and with the use of flexible ac transmission system devices. The power system literature has demonstrated that wide area signals could be more effective than the local signals for these controllers. In some cases where phasor measurement units are used, all the required control signals may not be available. To alleviate these cases, control signals are obtained using estimated signals from a “dynamic state estimator,” and a robust supplementary controller is deployed. In this paper, the cited strategy is illustrated using a static var compensator. The feasibility of the proposed method has been demonstrated on the IEEE 50-generator test system. [ABSTRACT FROM AUTHOR]

Abstract This paper addresses the potential multi-energy arbitrage opportunities for distributed multi-energy systems that arise from shifting the supply across input energy vectors and across plant components. This allows flexible decrease/increase of the electricity input from the grid to provide power system ancillary services, while maintaining the end-use energy demand at a constant level and thus without affecting the consumers' comfort. The benefits of the distributed multi-energy system participation in providing ancillary services for the reserve market are assessed by means of specifically defined multi-energy profitability maps. A novel indicator is introduced to quantify the electricity reduction that corresponds to the maximum profit of the distributed multi-energy system during the provision of the ancillary service. Numerical results that show the effectiveness of the proposed approach and the profitability map usage for a trigeneration system are discussed on two selected illustrative cases. From these cases, it is possible to identify the variety of conditions leading to the maximum profitability of the ancillary service provision in function of the economic parameters (availability fee and exercise fee) and of the amount of input electricity reduction. The most significant result is that, depending on the availability and exercise fees, the maximum profit may be obtained in some cases for an input electricity reduction lower than the maximum reduction that may be provided as the technical limit. This happens especially in the summer period, when the higher cooling demand and the presence of alternative solutions to provide cooling energy give more possibilities to perform energy shifting. Highlights • Distributed multi-energy systems provide multi-energy arbitrage opportunities. • The multi-energy arbitrage framework for ancillary services provision is presented. • Multi-energy profitability maps are introduced to assess profits and break-even conditions. • A novel indicator quantifies the input electricity reduction at maximum profit. • The proposed energy shifting strategy does not affect the consumers' comfort. [ABSTRACT FROM AUTHOR]

System health assessment becomes ever more important as consumers take for granted the apparent infallible character of power supply and the extremely high costs of prolonged down times. A system that achieves minimum operational disruptions becomes a target for all grid operators. This paper tackles the system heath issue in distribution networks by evaluating overall network losses. Using a genetic algorithm, the system health is evaluated considering key elements within the network operation. [ABSTRACT FROM AUTHOR]

Power system simulation is an important means to study the dynamic behavior, to ensure the safety and stability, and to optimize the operation of a power grid. Pure physical simulation and digital simulation have their own advantages and disadvantages. A three-phase four-wire hybrid simulation platform integrating the advantages of both the digital simulation and physical simulation is developed by combining the physical simulation system and real-time digital simulator. The platform is rated at 400 V and 50 kVA with the short-circuit capacity of 500 kVA and can supply ten times the rated current to support the simulation of various short-circuit faults. An improved interface algorithm based on an ideal transformer model is proposed to extend the stability region of a hybrid simulation. Hybrid simulation experiments are conducted under two cases, and the comparison with the digital simulation demonstrates the performance of this platform and the potential applied to a modern power system. This platform has been equipped in a key laboratory of smart power grid technology. [ABSTRACT FROM PUBLISHER]

Summary: In view of frequent multi‐machine power system oscillations in power grid which may cause traditional oscillation blocking and re‐opening schemes to be completely invalid, a distance protection oscillation blocking and re‐opening scheme in multi‐machine power system oscillation scenes is proposed in this paper. First, the ride‐through trajectory of measured impedance in multi‐machine power system oscillation cases and its effect on the operation characteristic of distance protection is analyzed, and the oscillation blocking scheme is formed by combining the operation status information of protection components on 2 line ends. And then, in the oscillation blocking duration, by calculating the estimated error of the dynamic phasor of measured current at the relaying point, the protection re‐opening scheme for symmetrical fault during oscillation is established. Finally, simulation tests on PSCAD in 3‐machine system and IEEE 39‐bus system verify that the proposed scheme could reliably block the protection when oscillation occurs in multi‐machine power system, and re‐open the protection accurately and reliably when symmetrical fault occurs during oscillation. [ABSTRACT FROM AUTHOR]

Rooftop photovoltaic (PV) hosting capacity has become a concern for utilities in scenarios of high penetration due to impacts on voltage quality, such as over/undervoltage and voltage unbalance, and on equipment loading (conductors and transformers). This paper uses a simplified Monte Carlo-based method to analyze this issue, which is applied to 50 000 real low-voltage (LV) systems. Results show that it is possible to perform a risk-based analysis of hosting capacity by means of a lognormal distribution. Furthermore, overvoltage is found to be the most restrictive impact of PV integration; such information can help to guide utility actions to avoid technical violations. Extensive sensitivity studies are also presented to quantify the effects of several factors on the PV hosting capacity. The effects of number of customers with PV generators, PV power factor, voltage magnitude on the medium-voltage system, load level, and conductor impedances are investigated. It is also shown that the hosting capacity for the entire utility can be estimated by performing simulations only on 1% of the circuits randomly selected. In addition to providing a comprehensive overview of PV hosting capacity in real systems, the method can be used by utilities to improve the management of LV systems with high PV penetration. [ABSTRACT FROM PUBLISHER]

The interconnected time-delay power system has become an important issue for the open communication network. Meanwhile, due to the output power fluctuation of integrated wind energy, load frequency control (LFC) for power system with variable sources and loads has become more complicated. The novel decentralised sliding mode (SM) LFC strategy is proposed for multi-area time-delay power system with significant wind power penetration. The appropriate switching surface gain is selected to assure the stability of power system with mismatched uncertainties. The SM controller is constructed to satisfy the hitting condition. At last, the SM controller is proved by using the real-time digital simulator device under different case of time delay, wind penetration, load disturbance and operating point. The test results show that the proposed SM LFC can reduce frequency deviation and tie-line power fluctuation effectively. [ABSTRACT FROM AUTHOR]

With wide applications of power electronic devices in modern power systems, simulation using traditional electromechanical and electromagnetic tools suffers low speed and imprecision. Multi-rate methods can enhance efficiency of simulation by decreasing the scale of systems in small time-steps. However, the existing traditional methods for multi-rate simulation suffer the problems of instability and simulation errors. These have hindered the application of multi-rate simulation in power industry. Therefore theoretical evaluation on different multi-rate simulation methods is crucial to understand the feasibility and limitation of the methods, and to contribute to overcome the drawbacks of the traditional methods. In this paper, the multi-rate simulation performance based on two traditional technologies and a Modified Thevenin Interface are evaluated to provide an overall feasibility of multi-rate algorithms in the power simulation. The Modified Thevenin Interface is proposed to overcome the drawbacks in synchronization. Three theorems are proposed and proved for theoretically analyzing the stability of the simulation methods. Error analyses of the multi-rate methods are performed to identify the relationships between errors and simulation conditions. Besides, the accuracy and efficiency performance in a practical project of VSC-MTDC shows the feasibility and necessity by using multi-rate simulation. Through the theoretical analysis, the issues of stability and accuracy of multi-rate simulation for the DC grids have been better understood, based on which an improved simulation algorithm has been proposed to overcome these issues. Long-term system dynamics of large-scale systems containing DC grids and fast transients of HVDC converters can be investigated simultaneously with high speed and sufficient accuracy. [ABSTRACT FROM AUTHOR]

POWER plants are subject to introduce disturbances in the power grid, resulting from interactions with the dynamical behavior of the energy source subsystem. In the case of hydropower plants when used to compensate for variations of power generation and consumption, instabilities or undesirable disturbances may arise. They may be caused by phenomena such as part load vortex rope pulsations in the draft tube of Francis turbines. This may affect the dynamical behavior of the power plant and lead to troublesome interactions with the grid. This paper presents a case study of an existing hydropower plant that illustrates the effects of pressure pulsations due to vortex rope precession on the draft tube of Francis turbines. It also showcases possible solutions to the mitigation of the effects of this disturbing hydraulic phenomenon over the operation of the generators and electrical system. The investigated system is a 1-GW hydropower plant (4 × 250 MW units). The assessment of the power swings is performed through modal analysis combined with frequency-domain and time-domain simulations, which are then compared with onsite measurements. [ABSTRACT FROM AUTHOR]

• One of the concerns on this implementation is imbalance supply and demand which resulting power congestion that might cause instability of power system operation. • This paper presents the algorithm to solve power congestion in the power line during high penetration solar photovoltaic (PV) to the grid. • In this study the optimization approach is done using multiple mitosis genetic algorithm. • Power flow simulation is done using Power system simulation for engineers (PSSE) software. • This study is useful to the planning division of power system engineer to consider the option to avoid power congestion in the grid before the integration of large-scale solar farm. Large scale solar PV plant has been actively implemented in many countries. One of the concerns on this implementation is imbalance supply and demand which resulting power congestion that might cause instability of power system operation. This paper presents the algorithm to solve power congestion in the power line during high penetration solar photovoltaic (PV) to the grid. In this study the optimization approach is done using Multiple mitosis genetic algorithm (MMGA) to choose the best line to receive the excess power from the congested line and the system used to test the algorithm for 3 different scenarios is IEEE 30 bus test systems. Power flow simulation is done using Power system simulation for engineers (PSSE) software. Simulation results show that the excess power exist in the power line during high penetration solar PV are solved by rerouting the excess power to the available best adjacent line found using MMGA. This study is useful to the planning division of power system engineer to consider the option to avoid power congestion in the grid before the integration of large-scale solar farm. [ABSTRACT FROM AUTHOR]

The increasing fuel price has led to high operational cost and therefore, advanced optimal dispatch schemes need to be developed to reduce the operational cost while maintaining the stability of grid. This study applies an improved heuristic approach, the improved Artificial Bee Colony (IABC) to optimal power flow (OPF) problem in electric power grids. Although original ABC has provided robust solutions for a range of problems, such as the university timetabling, training neural networks and optimal distributed generation allocation, its poor exploitation often causes solutions to be trapped in local minima. Therefore, in order to adjust the exploitation and exploration of ABC, the IABC based on the orthogonal learning is proposed. Orthogonal learning is a strategy to predict the best combination of two solution vectors based on limited trials instead of exhaustive trials, and to conduct deep search in the solution space. To assess the proposed method, two fuel cost objective functions with high non-linearity and non-convexity are selected for the OPF problem. The proposed IABC is verified by IEEE-30 and 118 bus test systems. In all case studies, the IABC has shown to consistently achieve a lower cost with smaller deviation over multiple runs than other modern heuristic optimization techniques. For example, the quadratic fuel cost with valve effect found by IABC for 30 bus system is 919.567 $/hour, saving 4.2% of original cost, with 0.666 standard deviation. Therefore, IABC can efficiently generate high quality solutions to nonlinear, nonconvex and mixed integer problems. [ABSTRACT FROM AUTHOR]

This paper presents a subsea DC collection grid with renewable power parks which inherently has robust DC fault protection and flexible expansion capability. By virtue of the applied DC/DC converter and the proposed DJ-Index Clamping control, different sections of the subsea grid are functionally interconnected and in the meantime decoupled in the event of DC faults. The faults are selectively isolated without the need for fast DC circuit breakers and system recovery from the faulty DC intertie branch is achieved by a coordinated operation strategy on DC/DC converters and DC disconnectors (or standard AC circuit breakers). A 200-MW test system is presented which consists of two 100-MW renewable energy sources (tidal stream and wind) and DC collection/transmission grids. The simulation results confirm the N-1 security of the presented topology and good control performance over a range of DC faults. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The need for accelerating power grid simulation through high performance computing (HPC) has long been recognized, and prior efforts have been devoted to developing one-off parallel computing applications for particular power grid functions. Non-transferable software codes and duplicated implementations in these prior efforts are a major barrier to more widespread HPC adoption in power grid applications. Modern HPC hardware and architecture require significant computing expertise for application development. The GridPACK™ software framework described in this paper provides an HPC-compatible software structure to access modern parallel solvers and HPC-ready modules for common components in power grid simulation applications. GridPACK hides the HPC details and enables power system developers to focus on applications instead of computational details. Several example applications of GridPACK are presented to demonstrate the capabilities of GridPACK and the performance of HPC simulations with large power grid networks. Examples discussed include: a dynamic simulation application capable of running a 17,156-bus Western Electricity Coordinating Council (WECC) system in a computational speed faster than real time (e.g., under 30 s for a 30-s simulation), a static contingency analysis application using a task manager, and a dynamic contingency analysis application utilizing two levels of parallelism. These example applications illustrate GridPACK's capabilities to support different types of simulations within a unified framework and to support reuse of transferable software codes across power grid applications. The computational results indicate strong performance improvements for power grid simulations with GridPACK. [ABSTRACT FROM AUTHOR]

Generic electrical simulation models of wind power generation have been developed as standards, such as the IEC 61400-27-1, to be used by wind industry, system operators, and academia for power system stability studies. In this paper, the IEC type 3 wind turbine model with wind turbine level voltage controller and with wind power plant level power factor controller is validated based on field measurements from a 52-MW wind power plant. In addition to the validation of the IEC type 3 wind turbine and wind power plant controller models, a comparison of the validation approaches, which are the full grid and play-back simulation, is provided together with a survey of the existing validation studies and recommendations for future modeling and validation tasks. The implemented IEC models are tuned to match the measurements accurately and the validated values for the control parameters of the reference wind power plant model are given. [ABSTRACT FROM PUBLISHER]

DC faults in HVDC grids lead to quickly increasing currents which should be interrupted sufficiently fast to prevent damage to power-electronics components. Although several primary relaying algorithms for HVDC grids have been proposed, fast backup relaying algorithms are needed to ensure system reliability when primary protection fails. This paper proposes a local backup relaying algorithm for HVDC grids, which leads to a short delay between primary and backup protective actions. The proposed algorithm, consisting of breaker and relay failure subsystems, uses classifiers which detect primary protection malfunctions based on the voltage and current waveforms associated with dc breaker operation. The algorithm initiates the detection of uncleared faults during primary protection operation, which results in accelerated actions by the backup protection after primary protection failure. The proposed algorithm is applied to a four-terminal HVDC grid. Study results show that the proposed algorithm accurately detects uncleared faults, identifies the source of primary protection malfunction, and expedites backup protective actions by operating during the fault current interruption interval of the primary protection. [ABSTRACT FROM PUBLISHER]

A challenge raised in today's power system is assessing the system protection security and dependability after the topology has been changed due to relay operation upon the occurrence of cascading faults or intentional operator switching action. This paper proposes an automated setting calculation module which could be used to review the adequacy of the distance relay settings following network topology changes. The calculation procedure is broken down into blocks which could be processed in parallel in order to improve the computation speed. A new concept called distance of impact is proposed to reduce the computational burden by conducting the calculations on a limited portion of the network affected by the topology change. The module performance is tested on a synthetic IEEE 118-bus and real-life Alberta transmission operator systems. A sensitivity analysis in the form of N-2 contingency impact on the network relay settings coordination is conducted on the test systems. [ABSTRACT FROM PUBLISHER]

This paper presents a new approach in adaptive out-of-step (OOS) protection settings in power systems in real time. The proposed method uses extended equal area criterion (EEAC) to determine the critical clearing time and critical clearing angle of the system, which are vital information for the OOS protection setting calculation. The dynamic model parameters and the coherency groups of the system for EEAC analysis are determined in real time to ensure that the newly calculated settings suit with the prevalent system operating condition. The effectiveness of the method is demonstrated in simulated data from a 16-machine 68-bus system model. [ABSTRACT FROM PUBLISHER]

Some potential adverse impacts of high photovoltaics (PV) penetration on the power grid are an increasing number of tap operations, over-voltages, and large and frequent voltage fluctuations and PV power ramps. The ability to create realistic PV input profiles with high spatial and temporal resolution is crucial to assess these impacts. This paper proposes a unique method to improve the accuracy of feeder hosting capacity studies using (1) high resolution PV generation profiles from sky imagers, (2) quasi-steady state distribution system simulation, and (3) distribution models created from utility data. Solar penetration levels, defined as ratio of peak PV output to peak load demand, from 0% to 200% and various cloud conditions are considered. Three conclusions were drawn: (1) the impacts of high PV penetration depend on feeder topology and characteristics; (2) the use of a single PV generation profile overestimates the tap operation number up to 260% resulting from an overestimation of power ramp rates and magnitudes – therefore, multiple realistic profiles should be used; and (3) distributed PV resources increase the feeder hosting capacity significantly compared to a centralized setup. [ABSTRACT FROM AUTHOR]

Synchronization with the power system is an essential part of control of grid-connected converters. This paper proposes a grid-voltage sensorless synchronization and control scheme for a converter equipped with an LCL filter, measuring only the converter currents and the dc voltage. A discrete-time pole-placement design method is used to formulate an adaptive full-order observer for the estimation of the frequency, angle, and magnitude of the grid voltage. The proposed discrete-time design method enables straightforward implementation and suits low sampling rates better than its continuous-time counterpart. The analytically derived design is experimentally validated, and the results demonstrate rapid convergence of the estimated quantities. Moreover, the experimental tests show that grid-voltage sensorless operation is possible under balanced and unbalanced grid disturbances and distorted grid conditions. [ABSTRACT FROM PUBLISHER]

• Modelling framework for automatic load frequency control studies of AC/DC grids. • It is aimed to slow transients caused by load/generation imbalances. • It is based on a suitable linear modelling of the VSC-based transmission grid. • Results are validated versus PSCAD with errors inferior to 3% This paper introduces an efficient simulation framework for automatic load frequency control (ALFC) studies of VSC-based AC/DC power grids. It is aimed at slow transients caused by large megawatt imbalances occurring either in the AC systems or DC grid. These studies involve the coordinated action of the primary and secondary control loops of power plants, ones requiring long simulation times ranging from various tens of seconds to minutes. To address these overly challenging AC/DC power system simulations, the developed modelling framework resorts to suitable linear models, i.e., VSC dynamic controls are devised to conform to the slow dynamics featuring the ALFC. The most fundamental dynamics of AC systems, DC grid and VSC stations are compiled with reasonable precision. This is demonstrated using a three-terminal, multilevel VSC-based HVDC system implemented in the PSCAD simulation package for comparative purposes; both solutions are shown to concur very well because root mean squared errors inferior to 3% are obtained. The practicality of this effective simulation framework is also demonstrated by studying a five-terminal VSC-based transmission grid facing large power imbalances imposed by load disconnections and VSC outages. [ABSTRACT FROM AUTHOR]

The increasing use of electronic converters is making possible the development of more sustainable, efficient, and reliable electric power systems, but it is also introducing new challenges that need to be addressed. Power system stability is one of them since the converter multiscale coupling between control loops and the mutual effects of multiple converters make the traditional approaches and specialized software available not fully adequate. In this context, this paper presents a software tool called CSTEP capable of carrying out small- and large-signal stability analysis for electric power systems strongly dominated by electronic converters. By utilizing the tool description, the paper provides the reader with a systematic methodology to obtain the system dynamic representation, and with some software tools for the analysis of the large and small-signal stability. Finally, the validity and functionality of CSTEP have been tested with the implementation of three use cases: a simple ac use case to illustrate the application of the system algorithm step by step, an IEEE 5-bus use case to validate the tool with already established commercial software and a more realistic system based on a medium voltage CIGRÉ benchmark to highlight the potential applications of the tool. The results show that, unlike existing tools that simplify or neglect the electric part of the grid (filters, line impedances, etc.), CSTEP can predict power system instabilities caused by the interactions of fast control loops of electronic converters with the electric part. [ABSTRACT FROM AUTHOR]

• Reliability analysis applied to composite systems through weather conditions. • Weather conditions considered windstorms, lightning storm, high temperatures and fire under the transmission line • Increased failure rate during weather conditions. • Applied to assess the reliability of the modified IEEE-RTS system with a Brazilian database. • Weather conditions have significant effects on system reliability and it is essential to involve external weather conditions in the reliability assessment. Power systems are undergoing transformations in order to address the intermittent power challenges due to the strong growth of renewable generating units, decrease vulnerability to failures and improve their resilience in order to provide service that is more reliable. In this context, one of the main concerns is related to the potential consequences of failures caused by rare and difficult-to-predict adverse weather events. The growing increase in severe weather events makes the assessment of such events increasingly important to prepare the system for these disasters. In this work, we originally propose to combine failure rate models due to adverse weather with an optimum power flow-based simulation system. The model is solved by a custom Monte Carlo scheme to quantify the impact of weather events on the reliability of the power grid. The approach is demonstrated with reference to the IEEE-RTS network test case. [ABSTRACT FROM AUTHOR]

A method of modifying existing grid-connected inverter models for use in droop-controlled microgrids is presented. The modification involves combination with a model of a grid-forming inverter to accurately represent the coupling between complex power, bus voltage, and frequency. The combination is performed after the individual models are linearized, adding little in terms of computational complexity. The method is applicable to any three-phase inverter operating in a grid-supporting capacity and is scalable for any number of parallel inverters at the same point of connection. To examine the modification process and its effect on model performance, a generic grid-tied inverter model is derived and used as a test case. The newly derived model is modified according to the proposed method. The validity of this process is assessed through comparisons of model predictions—both from before and after modification—to results of hardware experiments. A simple design example is given to demonstrate the application of this process in the design of inverters in distributed-generation-based microgrids. [ABSTRACT FROM PUBLISHER]

In this paper, a new multi-agent control system (MACS) is proposed for smart distribution networks. It can: 1) eliminate the feeders' congestion, 2) globally correct voltage violations, and 3) coordinate the operation of reactive power control devices. In performing its functions, the MACS must prevent overstress on the substation voltage regulator tap changer under all operating conditions, and avoid selective active power curtailment from DG units. This can help to improve reliability, economic revenue, and power quality. A fuzzy rule-based system is employed for decision-making support in MACS. The proposed MACS can achieve the self-healing requirement of smart distribution network. It eliminates feeders' congestion by properly reconfiguring the distribution network. Meanwhile, it amends most of voltage violation problems by coordinated operation of voltage control devices in the distribution system. The MACS overcomes the severe voltage violation problems via distribution network reconfiguration. It is applied to the IEEE 33-bus test feeder. A full dynamic model is constructed using a parallel MATLAB-JADE simulation arrangement. Comparative performance evaluations of the MACS and other schemes are presented under various conditions. [ABSTRACT FROM AUTHOR]

The need for new generation systems has motivated the development of microgrids. This new concept may provide significant benefits such as losses reduction, high degree of efficiency and reliability to the transmission and distribution networks. This paper presents generalities about microgrids, including general structure and different topologies. Also an original methodology for facilitating its design and evaluation is proposed. Finally, the microgrid located at the Parque Tecnológíco de Guatiguará at the Universidad Industrial de Santander, is analyzed and an operation analysis is included for different operations stages of loads and generation, the performance of operation of storage systems, the interaction with the grid and an energy balance for all the system. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for detecting parasitic dc components in ac grids. The method uses a parallel-connected sensing reactor and a low-cost digital signal processor. From the reactor current, the algorithm derives a sum of even harmonics, considering at the same time their phase shift with respect to the fundamental. The method is insensitive to the measurement noise and offset, and it does not require additional passive filters. Precision better than 100 \muV in 0.4-kV grids is maintained over a wide range of ac voltages. This paper details the detection method, provides the guidelines for the reactor design, and includes the key implementation details related to the signal acquisition—sampling and digital processing. High precision of the new sensor is thoroughly verified on an experimental setup connected to a 0.4-kV grid. [ABSTRACT FROM AUTHOR]

This paper demonstrates a novel cosimulation architecture that integrates hardware testing using power hardware-in-the-loop (PHIL) techniques with larger-scale electric grid models using off-the-shelf non-PHIL software tools. This test bed for distributed integration enables utilities to study the impacts of emerging energy technologies on their system and manufacturers to explore the interactions of new devices with existing and emerging devices on the power system, both without the need to convert existing grid models to a new platform or to conduct in-field trials. This paper describes an implementation of this architecture for testing two residential-scale advanced solar inverters at separate points of common coupling (PCCs). The same hardware setup is tested with two different distribution feeders (IEEE 123 and 8500 node test systems) modeled using GridLAB-D. In addition to simplifying testing with multiple feeders, the architecture demonstrates additional flexibility with hardware testing in one location linked via the Internet to software modeling in a remote location. In testing, the inverter current, real and reactive power, and PCC voltage are well captured by the cosimulation platform. Testing of the inverter advanced control features is currently somewhat limited by the software model time step (1 s) and tested communication latency (24 ms). These limitations could be overcome using faster modeling and communication within the same cosimulation architecture. [ABSTRACT FROM PUBLISHER]

Growing utilization of distributed generations in the power system may lead to protection problems. Therefore, in the conventional methods, DGs should be disconnected from the grid in the fault condition. In the case of high penetration of DGs, this strategy leads to voltage sag problem. In this paper, the inverter based DGs are properly controlled in the fault condition instead of disconnecting from the grid. This approach is called fault ride through strategy. The simulation results show that the fault current is kept in the desired range by using the proposed algorithm and the protection coordination before connection of DG remains intact even after the connection of DG. In addition, the voltage sag is improved due to DGs reactive power injection during the fault condition. Moreover, this method has not any additional cost because the proposed control strategy is carried out on the interfaced inverter and there is no need to use additional elements. [ABSTRACT FROM AUTHOR]