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The trend toward higher switching frequency and larger scale of power electronic systems poses challenges for real-time simulation. This article presents an event-driven hardware-in-the-loop (ED-HIL) simulation framework that does not rely on the small fixed simulation step-size related to the switching frequency. ED-HIL framework can improve the calculation efficiency by positioning switch events and using variable simulation step-size. Further, a parallel acceleration and circuit partitioning (PACP) solver is proposed based on this framework. The PACP solver partitions the circuit with energy storage elements and ensures that the partitioning does not introduce simulation distortion by using the higher order derivatives of the energy storage elements. Meanwhile, it achieves a process-level paralleling through a shared memory architecture in order to accelerate the simulation. As a result, the proposed PACP solver based on the ED-HIL framework can achieve about three times the simulation scale of a commercial FPGA-based real-time simulator at 1/16 the hardware cost under the same conditions. An accurate real-time HIL example of a power electronic transformer with 32 switches at a switching frequency of 20 kHz has been implemented on a personal computer. The simulation results are analyzed by comparing with experiment, offline software, and commercial real-time simulator. [ABSTRACT FROM AUTHOR]

The integration of uncertain photovoltaics (PVs) and flexible loads leads to uncertainties in the power system dynamic simulation results. Furthermore, geographically close PV farms are correlated and may exhibit nonlinear correlations. This article proposes a copula-based sparse polynomial chaos expansion (PCE) framework for quantifying the impacts of uncertain dynamic PVs and loads on power system dynamic simulations and stability. The dynamics include both PV and load stochasticity and those governed by differential and algebraic equations. The copula statistics are utilized to accurately characterize the dependence structure of PVs and further used to develop the copula-PCE for quantifying the impacts of uncertain PVs and loads. A probabilistic TSI is also developed to assess the uncertainties from PVs and loads on the system stability. To address the cases, where both stable and unstable conditions coexist, a preprocessing step via sample classification is proposed. The effects of different dependence structures of PVs and different numbers of uncertain sources are investigated. Comparison results with other methods on the modified IEEE 39- and 118-bus systems, including the Monte Carlo method, Latin hypercube sampling, and traditional PCE without consideration of uncertain input correlations show that the proposed method is able to accurately quantify the uncertain dynamic simulations and transient system stability while being computationally efficient. [ABSTRACT FROM AUTHOR]

The OPA (ORNL-PSERC-Alaska) model has been widely used in cascading failure simulations to predict likely and plausible sequences of cascading failures. This letter focuses on an algorithmic approach to enhance the OPA model whose main engine is based on quasi-steady-state models without considering the impact of collective transient dynamics of the entire system on the sequence of cascading failures. In particular, the enhanced OPA model incorporates dynamically induced cascading failures in fast time scales, which allows it to capture more realistic and detailed cascading scenarios. In this work, we outline the enhanced OPA model and provide simulation results to illustrate its feasibility with the realistic test network. [ABSTRACT FROM AUTHOR]

Voltage source converter (VSC) is fundamental and critical in renewable energy integration and transmission and has become ubiquitous in power systems. For the design and operation of power systems with VSCs, electromagnetic transient (EMT) simulation is indispensable. However, a large number of VSCs in power systems cause a high time-consuming issue in EMT simulation. This article proposes a fast EMT simulation model for VSCs with arbitrary topology based on switch-state prediction. The accurate switch-state prediction has two steps: Preliminary switch-state prediction and simultaneous switching prediction. It avoids the iterative computation required to obtain a feasible switch-state combination in the traditional EMT simulators. Extensive tests on different types of VSCs and a dc microgrid demonstrate that the proposed fast model significantly improves the EMT simulation efficiency of power systems with VSCs. [ABSTRACT FROM AUTHOR]

In this work we present a novel technique, based on a trust-region optimization algorithm and second-order trajectory sensitivities, to compute the extreme trajectories of power system dynamic simulations given a bounded set that represents parametric uncertainty. We show how this method, while remaining computationally efficient compared with sampling-based techniques, overcomes the limitations of previous sensitivity-based techniques to approximate the bounds of the trajectories when the local approximation loses validity because of the nonlinearity. We present several numerical experiments that showcase the accuracy and scalability of the technique, including a demonstration on the IEEE New England test system. [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]

Power system planning is essential for ensuring development of a safe and stable power system. Articles on power system planning have been published in recent decades. In this paper, bibliometric analysis is applied to power system planning to identify its basic characteristics, and to summarize the research hotspots and trends. A total of 4562 publications were obtained from the Web of Science during 1971–2020. The 4562 publications cover 8136 keywords, 1526 journals, 107 countries/territories, and 2519 institutions. IEEE Transactions on Power Systems is the key journal in power system planning; USA, China, and England are the countries that dominate publication production. Research hotspots and trends were analyzed using author-keyword co-occurrence analysis and keyword burst detection. Four clusters were identified and topics from Cluster I (central nodes as power system stability and transient stability) and Cluster IV (central nodes as power system simulation and economics) are important for power system planning research. However, their relative popularities have declined over the past two decades. This indicates that Cluster II (central nodes as renewable energy, wind power, and energy storage) and Cluster III (central nodes as distributed generation and smart grids) will be the focus of future research. [ABSTRACT FROM AUTHOR]

Accurate evaluating the lightning induced voltages of distributed networks has been the subject for several decades. The technique on the interface between the field-to-line coupling model and power system simulators are of particular interest. In this article, a solution of the Agrawal's field-to-line coupling model is derived and an easy-to-implement macro-model is developed. Combining with the “Frequency Dependent (Phase) Model” component included in PSCAD, the proposed macro-model can be directly integrated into PSCAD to evaluate the lightning induced voltages on the overhead lines. The validity and efficiency of the proposed method is demonstrated by several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of the metal-oxide arrester to the lightning induced voltages are discussed. [ABSTRACT FROM AUTHOR]

With the development of dc renewable power generation and dc power consumption, more and more attention has been paid to residential low-voltage dc (RLVDC) power systems in recent years because of their advantages in conversion efficiency and control flexibility. Meanwhile, there are still some obstacles and challenges in the practical application of RLVdc due to the lack of standardization. One of the most important issues in RLVdc standardization progress is the voltage level standard. In this article, a comparative study on the performance of different RLVdc system voltage levels is presented. The main purpose of the article is to provide a voltage level selection guidance for energy prosumers and equipment manufacturers interested in RLVdc systems. The voltage levels commonly used in academia and industry, from 220 to 750 V, are compared and analyzed considering their influence on compatibility, topology, power supply capability, and safety. The article contains a research surveys, market statistics, power system simulations, and calculations with simplified models. The results of the comparative study show that ±375 V is optimal for the RLVdc system in cases with large power ratings and voltage levels below 240 V are suitable for RLVdc systems with special safety requirements. [ABSTRACT FROM AUTHOR]

Hydrogen-integrated transportation and power systems (HTPS) will become an important way to achieve the goal of carbon neutrality. As an important coupling unit of HTPS, the business mechanism of hydrogen fueling stations (HFS) is an important starting point for improving system economy and promotion value. This article proposed an interaction mechanism between HFS and HTPS and hydrogen and fuel cell EVs (HFEVs) in smart cities for HFS pricing strategies. First, we construct the framework of the HTPS interaction mechanism based on the basic combination of HTPS. Then, the interactive model of HTPS is constructed, including the scheduling model of HTPS, the pricing model of HFS and the response model of HFEVs. Finally, an HTPS system is constructed based on the improved IEEE 33-node power distribution system for simulation and analysis. The results show that the interaction mechanism and pricing strategy can improve the economics of HTPS and HFS, the operating cost of HTPS has been reduced by approximately 5.57%, the operating income of HFS has increased by approximately 4.17%. [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]

Resilient distributed coordination control is studied on multiarea power systems with low inertia under hybrid attacks, including denial-of-service (DoS) attack and deception attack. The communication among various areas under the DoS attack is deteriorated to switching residual topologies whose time characteristic is modeled by model-dependent average dwell time (MDADT). Deception attack with malicious strategy targeting at negative feedback control is modeled by a sign function. To obtain resilience performance of the power system under low inertia and hybrid attacks, resilient distributed scheme combining load-frequency control (LFC) with virtual inertia control (VIC) is proposed. Then, resilient frequency control problem of the studied power system is converted to $H_{\infty }$ control of the switched nonlinear system. By employing the Lyapunov stability theory and switched system method, the resilient conditions are given by the lower bound of the average dwell time of each residual topology and the upper bound of deception attacks. Furthermore, a linear matrix inequality (LMI) technique is used to design the distributed resilient control gains of the LFC-VIC scheme. Finally, a simulation of four-area power systems is carried out to verify the validness of our theory. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to dynamic phasor-based transient stability simulation. The proposed method is based on the modified nodal analysis (MNA) approach to circuit simulation, which is used to construct continuous differential-algebraic equations (DAEs). The proposed method makes use of the stamp technique, which makes it possible to construct a general purpose MNA-based simulator. Stamp-based models for common power system components are derived in this work. A new MNA-based synchronous machine model is presented, which represents machines as nonlinear inductances instead of subtransient equivalents. The resultant continuous DAEs are numerically solved using the general purpose variable step and variable order library IDA. Simulation results from the IEEE 68 bus test system, a real 400 bus power system, and the IEEE 39 bus test system with an embedded HVdc transmission system demonstrate that the proposed method is suitable for large ac networks with power electronic devices. The results demonstrate good agreement between the proposed method and electromagnetic transient (EMT) simulation. The results also demonstrate that the proposed method is fast and scalable with CPU times that are up to 200 times faster than EMT simulation. [ABSTRACT FROM AUTHOR]

Modeling grounding systems is necessary for the calculation of ground potential rise (GPR), power system simulations and insulation coordination studies. In this work, a methodology for estimating equivalent circuit parameters through the optimization of the time-domain impulse response was developed. It allows to obtain equivalent circuits with positive parameters that accurately represent grounding systems considering both effects related to frequency and soil ionization. Additionally, linear and nonlinear equivalent circuits for calculating the impulse response of typical grounding systems were proposed. The Nelder-Mead optimization method was applied to adjust the circuit parameters. For evaluating the methodology developed and the proposed models, data from impulse current tests was used. It was found that the use of nonlinear circuits increases the accuracy of the simulated response, resulting in errors of less than 4% in the estimation of GPR. The proposed methodology allows obtaining representative circuits of typical grounding systems used in the electrical system. The circuits can be used for systemic studies and calculation of GPR considering short-circuit or lightning currents. [ABSTRACT FROM AUTHOR]

This paper outlines a novel loss of excitation (LOE) protection scheme for synchronous generators (SGs) based on reactive power increment (RPI) strategy and tracking the variation of SG output voltage (VSG). When variation of the VSG exceeds lesser than a specified threshold value, the proposed RPI strategy is triggered and VSG deviation is analyzed. For RPI execution, generated reactive power by SG (QSG) is shifted in increment direction. Following the applying RPI strategy, the VSG does not have any increasing changes during LOE events due to lack of excitation system to provide the required field current; while for Non-LOE (NLOE) events, VSG will be increased. Therefore, this provided feature by RPI strategy can properly and immediately cluster all LOE/NLOE events even under worst-scenarios. Due to power quality issues, the value of the shifted reactive power (ΔQSG) is considered small as much as possible. Meanwhile, it does not require any extra devices for execution. The exhaustive simulation studies on the power system prove that, the proposed scheme is quite reliable for clustering all LOE/NLOE events, and is much faster than other available methods. [ABSTRACT FROM AUTHOR]

This article introduces a novel multirate cosimulation architecture that overcomes previous challenges integrating faster real-time, microseconds-scale, power-hardware-in-the-loop (PHIL) with larger scale but slower, real-time, seconds-scale, quasi-static time-series (QSTS) simulation. Specifically, an intermediate reduced-equivalent electromagnetic transient (EMT) model duplicates the key power system topology to capture high-speed dynamics and converge hardware-power system interactions between QSTS updates. Exchanging multidimensional parameter vectors (loads, control status, etc.) between the QSTS and EMT models enables capturing the interactions of the rich, high-node-count (thousands of electrical nodes) QSTS model with the hardware. This architecture offers full spatial resolution from QSTS, including individual load dynamics, actual distribution management system controls, and nodal voltages. Simultaneously, the intermediate EMT model provides more detailed high-speed transients of key distributed energy resource hardware interactions. In addition, we use careful PHIL interface design and the exchange of complex power data, rather than current, to further improve performance. This cosimulation architecture is demonstrated by testing a simulated distribution system with an interconnected 500-kVA advanced photovoltaic (PV) inverter in PHIL. The architecture successfully captured PV local volt–volt ampere reactive (volt-VAR) control interactions with the larger network under time-varying electrical and weather conditions. [ABSTRACT FROM AUTHOR]

With continuing advances in high-performance parallel computing platforms, parallel algorithms have become powerful tools for development of faster than real-time power system dynamic simulations. In particular, it has been demonstrated in recent years that parallel-in-time (Parareal) algorithms have the potential to achieve such an ambitious goal. The selection of a fast and reasonably accurate coarse operator of the Parareal algorithm is crucial for its effective utilization and performance. This paper examines semi-analytical solution (SAS) methods as the coarse operators of the Parareal algorithm and explores performance of the SAS methods to the standard numerical time integration methods. Two promising time-power series-based SAS methods were considered; Adomian decomposition method and Homotopy analysis method with a windowing approach for improving the convergence. Numerical performance case studies on 10-generator 39-bus system and 327-generator 2383-bus system were performed for these coarse operators over different disturbances, evaluating the number of Parareal iterations, computational time, and stability of convergence. All the coarse operators tested with different scenarios have converged to the same corresponding true solution (if they are convergent) and the SAS methods provide comparable computational speed, while having more stable convergence to the true solution in many cases. [ABSTRACT FROM AUTHOR]

The transience and unpredictability of processes in electric power systems (EPS) determine complexity of its control. This problem is especially relevant for EPS with renewable energy sources and flexible alternating current transmission systems technologies. Automatic control systems simplify the solution of this problem. Despite this, many issues related to EPS state control are solved by power system operators. Decision support systems (DSS) are applying to increase efficiency of operators work. However, existing algorithms in practice are inoperable in some cases: unrealizable decisions are formed, or decision cannot be found at all, etc. Another important problem is impossibility to preliminarily verify the proposed solution. In this regard, operators can additionally use EPS simulators, which are usually limited either by the size of simulated scheme or by the details of equipment mathematical models. The limitations are a consequence of numerical methods using, which are badly applicable for large-scale power systems simulation. In this article, a novel DSS has been developed based on a hybrid approach to EPS modeling combining properties and capabilities of several simulation techniques: analog, physical and digital. The implicit integration of differential equations in analog way makes possible modeling faster than real time. Such opportunity allows operator to verify more decisions and select the most effective ones. The algorithm for DSS application has been developed and described in the article. The properties and capabilities of the developed DSS are confirmed by experimental studies and tests in a real EPS. [ABSTRACT FROM AUTHOR]

In transient stability simulators such as PSS/E, the bus frequency is estimated using a window of (positive-sequence) phasor angle measurements. A digital filter is often used to account for the filtering effect in actual measurement devices and to eliminate sudden changes during frequency computations. Although transient stability simulators label the filtered angle derivative as the “frequency,” the frequency provided by such programs does not match actual measurements reported by phasor measurement units (PMUs), which makes it difficult to gauge the validity of studies (e.g., wide-area event detection and control applications) that are based on such simulations. In this paper, we implement a frequency computation method directly using positive phasor angles provided by simulators. The proposed method is tested on two systems extensively and validated against the measurements of an actual PMU. The improved frequency measurements closely match PMU responses. Cross-validation results also suggest the method may be used for other systems without conducting full time-domain simulations. [ABSTRACT FROM AUTHOR]

The paper presents accurate and simple dynamic model of a supercapacitor bank system for power system dynamics studies. The proposed model is derived from a detailed RC circuit representation. Furthermore, a complete control system of the supercapacitor bank is also presented. The proposed model is easy to integrate in any power system simulation software and consists of only up to four standard datasheet parameters. The performance of the proposed model in grid frequency control and low-voltage ride through is illustrated on IEEE 14-bus test system in DIgSILENT PowerFactory. It is shown that in case of transient stability simulations the ideal (simplified) model of the supercapacitor can be used while in case of frequency control the ideal representation may not always be appropriate. [ABSTRACT FROM AUTHOR]

Safe and effective exploitation of lithium ion (Li-ion) batteries requires advanced battery management systems. This article proposes a computationally efficient, control-oriented model of a Li-ion cell. The model describes the spatial nature of both the chemical species and temperature dynamics in a computationally efficient way. The method takes advantage of the algebraic structure that arises from the distributed nature of the model. We show that, by discretizing the model partial differential equations with a finite difference method, the coupling equations take a semiseparable structure for which an efficient algebra exists. This approach yields an efficient modeling tool that can be employed to design model-based estimation and control algorithms. The proposed model is validated against a high order computational fluid dynamics model showing accuracy and efficiency. [ABSTRACT FROM AUTHOR]

As the importance of renewable energy increases, the capacity of dispersed generations (DGs) has increased worldwide. However, the connection of DGs in the power distribution system can cause the fault current to increase as well as malfunction of the overcurrent relay (OCR) due to the reverse directional fault current. As the countermeasure to limit the fault current in the power distribution system with DG, though the superconducting fault current limiter (SFCL) is reported to be more effective, the research on the protection algorithm of the protective relay considering the application of SFCL is preferentially required. In this paper, the correction method of the OCR using voltage components for application of SFCL in a power distribution system with DG was suggested. To verify the effectiveness of the suggested method, the fault simulation for the power distribution system with DG including the OCR and the SFCL was performed. By applying the proposed correction method in the OCR, the protection coordination of OCRs for the application of SFCL in power distribution system with DG was confirmed to be improved through the suppression of the malfunction of the OCR. [ABSTRACT FROM AUTHOR]

Switching processes of voltage source converters can emit significant high-frequency distortions of frequencies between 5 to 20 kHz. Furthermore, the distortions can partly propagate from the place of their origin into a medium voltage system via capacitive coupling of power transformers. The origin, parameters, and propagation process of distortions were clarified by a numerical simulation of a 1-MW photovoltaic power plant connected to the medium voltage distribution grid. The determined results provided input data for the following accelerated aging test setup. The main idea behind the accelerated aging tests was to confirm the effect of the high-frequency distortions on the degradation rate of cable insulation systems. The tests were performed on cable samples, with terminations mounted on each end, which were split into three groups. The first sample group was stressed by increased power frequency voltage and by maximum operating temperature. The second group was stressed similarly, but with superposed high-frequency distortions present. The last group was not stressed to provide reference values for the other groups. Partial discharge, dissipation factor, and breakdown voltage measurements were carried out on both aged groups. The results indicate that cable insulation degradation progresses faster under power frequency voltage with superposed high-frequency distortions. [ABSTRACT FROM AUTHOR]

Geomagnetic Disturbance (GMD) impacts a power system by causing the circulation of quasi-dc Geomagnetically-induced Currents (GICs) in transmission lines and high-voltage transformer windings leading to transformer saturation, increased reactive power losses, and voltage regulation problems. Utility planners use various analysis methods and simulation tools to analyze GMD system impacts. These techniques can be broadly categorized into load-flow-based (LF), transient stability type (TS), and electromagnetic transient type (EMT) methods. These methods are based on different modeling assumptions and solution techniques. There is a need for evaluation of these assumptions and cross-examination of results to ensure their accuracy. Such an evaluation is essential to ensure that planners performing required GMD vulnerability assessments have confidence in the results. This paper evaluates the LF, TS, and EMT methods through cross-examination of their results. The objective is to identify their limitations, assess the consistency of their results, and provide assumptions on their use for analysis of GMD system impacts. The study is conducted in consistence with the North American Electric Reliability Corporation (NERC) GMD guidelines and standards. [ABSTRACT FROM AUTHOR]

This paper analyses the frequency stability of ac grids in the presence of non-dispatchable generation and stochastic loads. Its main goal is to evaluate conditions in which the system is robust to large, persistent active power disturbances without recurring to time-domain simulations. Considering the ongoing energy transition to more renewable sources, defining robustness boundaries is a key topic for power system planning and operation. However, much of the research on long-term studies has not dealt with robust dynamic constraints, while short-term analyses usually depend on time-consuming simulations to evaluate nonlinearities. To bridge this gap, the authors derive an algebraic equation that provides sufficient conditions for robust frequency stability in ac power systems and a relationship among four key quantities: the maximum active power perturbation, the minimum system damping, the steady-state and the transient frequency limits. To achieve this goal, it uses a nonlinear average-model of the ac grid and Lyapunov's direct method extended by perturbation analysis requiring only limited knowledge of the system parameters. The algebraic calculations are validated using time-domain simulations of the IEEE 39-bus test system and results are compared to the traditional Swing Equation model. [ABSTRACT FROM AUTHOR]

Computer-aided analysis is playing an important role in the design and control of power electronic systems. A discrete-state event-driven (DSED) framework with state-space modeling has been proposed recently for accurate and efficient off-line simulation. Nevertheless, automated equation formulation for arbitrary circuits is also required to develop the DSED framework toward general simulation software. However, the traditional state equation generation method is very time-consuming, especially for large-scale systems due to the variable topologies brought by switching events. In this article, an automated semi–symbolic state equation generation method is proposed. Based on the switching function modeling of basic switching legs, an explicit function from switching states to state equation matrices is given, which reduces the computational cost without sacrificing any accuracy. The operating and topological characteristics of power electronics systems are utilized for further optimization. The proposed method greatly increases the simulation efficiency of power electronic systems, especially for large-scale systems. Two cases of the 2 MW 4-port solid-state transformers with different system scales are simulated with the proposed method under the DSED framework. About 700-fold and 1200-fold acceleration is achieved compared with one fast-speed commercial software, where the proposed method contributes 50-fold and 110-fold acceleration in the two cases, respectively. [ABSTRACT FROM AUTHOR]

This article presents the innovative control scheme of renewable ancillary services to support the system operation of a bulk power system with high penetration of renewable energy. The smart inverters of PV systems can be controlled to adjust the renewable generation of real and reactive power according to the variation of system voltage and frequency. The dispatch control of renewable ancillary services is integrated with the energy management system to achieve the coordination control of renewable energy and synchronous generators. The sensitivity factors of renewable system was applied to determine the generation curtailment for the mitigation of line overloading. The ancillary service of reactive power compensation by renewable energy was considered to improve the system voltage quality. The emergency generation control of renewable systems with fast ramping up capability was applied to illustrate the effectiveness of renewable ancillary service to improve the system frequency response after sudden generator tripping. Based on the computer simulation of an actual power system with large renewable energy to be integrated, the functions of virtual synchronous generators by the photovoltaic systems and wind farms have to be applied to ensure the successful steady-state operation and to improve the system transient stability for severe disturbance contingency. [ABSTRACT FROM AUTHOR]

This paper proposes a data-driven cooperative method for load frequency control (LFC) of the multi-area power system based on multi-agent deep reinforcement learning (MA-DRL) in continuous action domain. The proposed method can nonlinearly and adaptively derive the optimal coordinated control strategies for multiple LFC controllers through centralized learning and decentralized implementation. The centralized learning is achieved by MA-DRL based on a global action-value function to quantify overall LFC performance of the power system. To solve the MA-DRL problem, multi-agent deep deterministic policy gradient (DDPG) is derived to adjust control agents’ parameters considering the nonlinear generator behaviors. For implementation, each individual controller only needs local information in its control area to deliver optimal control signals. Numerical simulations on a three-area power system and the fully-modeled New-England 39-bus system demonstrate that the proposed method can effectively minimize control errors against stochastic frequency variations caused by load and renewable power fluctuations. [ABSTRACT FROM AUTHOR]

The reliability of power systems with high penetration of renewables, a fast response mechanism, and precise decision-making scheme is more important than ever. This study presented a novel scheme that utilizes the predicted frequency nadir after a generation trip event to initiate necessary ancillary services such as fast spinning reserve units, energy storage units, and demand responses to restore the frequency back to the secure operating range. The proposed scheme coordinates Under-Frequency Load Shedding (UFLS) with ancillary services in the sense that the unnecessary load shedding can be avoided. By using the proposed scheme, the system becomes more resilient against disturbances, and the actions of load shedding are minimized. In this scheme, the frequency data is captured by phasor measurement units (PMUs), and a frequency nadir prediction algorithm is proposed. We demonstrate the effectiveness of the proposed scheme by using 1700-bus power system simulations and realistic frequency data from real generation trip events captured by a laboratory micro-phasor measurement unit (μPMU). [ABSTRACT FROM AUTHOR]

The field-programmable gate array (FPGA) based hardware-in-the-loop (HiL) test, which minimizes the time-step of the real-time simulation below 500 ns, is an enabling technology for the development of the control unit of high-power electronic systems (HPE). In order to improve the time performance of FPGA-based HiL, this article proposes a novel parallel structure using the predictive behavior of the power electronic system. With this structure, we design an improved system-level solver applied to HPE. A piecewise insulated-gate bipolar transistor (IGBT) model is used to determine the state of the switch, offering a quasi-realistic model of the power converter. A parallel integration method is also implemented to solve the status of the circuit elements. Moreover, the proposed parallel structural can execute both the IGBT model and circuit element model at the same time, thus, reducing the simulation time-step significantly. The numerical accuracy of the solution, the architecture design, and the issue of the parallel computation are discussed in detail. An ac–dc–ac topology is presented as a case study. At last, a 25 ns time step in the National Instruments FlexRIO platform is achieved. Results comparison with the reference model is also identified and discussed. [ABSTRACT FROM AUTHOR]

In this article, an approach is proposed for the online diagnostic analysis of power electronic converters utilizing real-time, probabilistic digital twinning. Under this approach, a digital twin (DT) of a power converter is defined as a real-time, probabilistic simulation model with stochastic (random) variables, developed using generalized polynomial chaos expansion. The DT models are partitioned in perspective of control layers for power converter subsystems in the approach, with emphasis on the application and converter control layers. Real-time executed solvers of these divided probabilistic DT models are embedded into power converter controllers running on field programmable gate array (FPGA) computing devices. Using a monitoring system, the real-time probabilistic DTs at each control layer and the corresponding physical twins of the power converter are compared by the controllers to determine if the power converter is operating within probable behavior. Knowing the large computational cost of probabilistic modeling, the resource usage and timing of real-time DT solvers on modern FPGAs is reported for common power electronic converter topologies, showing the approach is feasible and able to perform probabilistic real-time simulation of smaller power converters in perspective of application and converter control layers using ≤ 2 μs time steps, with as low as 70 ns steps; while staying embeddable within FPGA-based controllers. To highlight the capabilities of the proposed approach, a case study is presented using a probabilistic DT in the application layer controller of a pair of converters to comparatively monitor their behavior and corresponding controller action under hardware-in-the-loop testing. [ABSTRACT FROM AUTHOR]

The article proposes a computationally efficient and robust method for estimating impulse or frequency response in the context of black-box multiple-input-multiple-output linear model identification of large power systems from simulations. The proposed approach is validated in conjunction with two realization algorithms – ERA method that is based on the established Ho-Kalman procedure for minimal realization, and the relatively new Loewner matrix based method. Practical aspects of identification in presence of numerical noise and nonlinearities are discussed. Study cases presented in the article include a linear model equivalent of a large-scale power system and the full-scale nonlinear transient model of the Eastern Interconnection. [ABSTRACT FROM AUTHOR]

Voltage stability assessment on a deterministic direction of loading variation may provide misleadingly high values of voltage stability margin due to uncertainties in load forecast. On the other hand, by disregarding loading forecast information and computing the worst case scenario, we may obtain unrealistic and very conservative margin values. This paper proposes a new voltage stability index that takes place between these two approaches. In this proposal, a set of credible loading variation directions is considered and the closest bifurcation point is determined within this set. A fast method for computation of this index is also proposed. The method is able to detect both saddle-node and limit-induced bifurcations. The efficiency of the proposed method is confirmed by means of numerical simulation on different power systems. [ABSTRACT FROM AUTHOR]

The operational security of power systems for wind farm (WF) integration becomes more important as the penetration of wind generation increases. A WF may contain hundreds of wind turbines (WT) and thus the power system simulations based on the complex model of a WT consume much time. This article proposes an equivalent WF model with the frequency-regulation function. The main research works include the establishment of the generic model of a WT, the development of single- and multimachine equivalent models for a large WF, the clustering of WTs based on the developed nonlinear wake model and the fuzzy C-means (FCM) clustering algorithm, the integration of the frequency-regulation function into the equivalent WF model, and the validation of the developed equivalent WF model by various operating scenarios. The results demonstrate that the proposed multimachine equivalent method based on the FCM clustering provides a more accurate model than a single-WT equivalent model. Consequently, the research results provide a solution for simulating a large-scale wind power integration, providing efficient, accurate, and fast steady-state and dynamic analyses. [ABSTRACT FROM AUTHOR]

This paper proposes a time-domain method to calculate the fault response in multiterminal dc (MTdc) grids and the performance of hybrid dc breakers. The proposed method, based on traveling waves: 1) provides a sound representation of fault performance by considering all created traveling waves; 2) introduces a new approach to estimate the reflection coefficients; and 3) provides an approximation of the worst case fault location. Then, based on the analytical results, three parameters of the hybrid dc circuit breaker, i.e., current limiting reactor, arrester rated voltage, and time delay are optimally selected with respect to maximum overcurrent, maximum overvoltage, fault clearance time, and energy absorption in arresters through multiobjective optimization. Accuracy and performance of the proposed method are evaluated and verified by time-domain simulation studies in the power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) environment using frequency-dependent models. The results confirm reasonable accuracy of the proposed fault performance calculation and represent a further step towards optimized design of hybrid dc circuit breakers. [ABSTRACT FROM AUTHOR]

Parameter identification facilitates the improvement of the accuracy of power system simulation. However, for complex models of electrical equipment, it is impossible to simultaneously identify all the parameters. Inaccurate values of the nontarget parameters (NTPs) will affect the identification accuracy of the target parameters (TPs). However, no suitable methods are available in the parameter identification process to assess and handle this adverse impact. Therefore, a probabilistic preassessment method (PPM) is proposed to assess the possible identification accuracy of the TPs when the NTPs are inaccurate. PPM can provide more useful quantitative information than traditional sensitivity analysis for selecting the disturbance form, the observation variable, and the TPs that can be accurately identified. Then, a statistical identification process (SIP) is proposed to eliminate the dependence of the traditional parameter identification method on accurate NTPs. In SIP, parameter identification is repeated by using random values of the NTPs. Then, the mean value of the high-probability identification results is selected as the final result. Some of the identification results can be adjusted according to the PPM result to further improve the accuracy. The proposed methods were successfully used to identify the parameters of a two-mass drive train model of a DFIG wind turbine generator under the assumption that the generator and controller parameters are unknown. [ABSTRACT FROM AUTHOR]

An efficient and accurate multi-scale induction machine model for simulating diverse transients in power systems is developed and validated. Voltages, currents, and flux linkages are described through analytic signals that consist of real in-phase and imaginary quadrature components, covering only positive frequencies of the Fourier spectrum. The stator is modeled in the abc phase coordinates of an arbitrary reference frame whose rotating speed is adjusted by a simulation parameter called shift frequency. When the reference frame is stationary at a zero shift frequency, then the model processes instantaneous signals to yield natural waveforms. When the reference frame is set to rotate at the synchronous frequency of the electric network, then the Fourier spectra of the analytic signals are shifted by this synchronous frequency to become dynamic phasors that allow for efficient envelope tracking. The shift frequency can be adapted during simulation. For any rotor position and independent of the variation of the magnetizing inductances with saturation, the induction machine model appears as a Norton current source with constant inner admittance in the abc phase domain to support the integration with simulators that represent the electric network in the abc phase domain. The analysis of test cases covering diverse transients substantiates the claims made in terms of accuracy and efficiency across different time scales. [ABSTRACT FROM AUTHOR]

This paper emphasizes the importance of including unbalanced distribution systems for voltage stability studies in power systems. The paper aims to: discuss the various simulation methods for power system analysis; highlight the need for modeling unbalanced distribution system for accurate load margin assessment; demonstrate the influence of net-load unbalance (NLU) on voltage stability margin (VSM). We also share a T&D co-simulation interface with commercial power system solvers. The distribution system is evolving rapidly with high proliferation of distributed energy resources (DERs); these are not guaranteed to proliferate in a balanced manner and uncertainty resulting due to these DERs is well acknowledged. These uncertainties cannot be captured or visualized without representing the distribution system in detail along with the transmission system. We show the impact of proliferation of DERs in various 3-phase proportions on voltage stability margin through T&D co-simulation. We also study the impact of volt/VAR control on voltage stability margin. This analysis is only possible by representing the distribution system in detail through T&D co-simulation. Higher percentage of net-load unbalance (NLU) in distribution system aggravates the voltage stability margin of the distribution system, which can further negatively influence the overall voltage stability margin of the system. [ABSTRACT FROM AUTHOR]

Low frequency electromechanical oscillations can pose a threat to the stability of power systems if not properly addressed. This paper proposes a novel methodology to damp these inter-area oscillations using loads, the demand side of the system. In the proposed methodology, loads are assigned to an aggregated cluster whose demand is modulated for oscillation damping. The load cluster control action is obtained from an optimal output feedback control (OOFC) strategy. The paper presents an extension to the regular OOFC formulation by imposing a constraint on the sum of the rows in the optimal gain matrix. This constraint is useful when the feedback signals are generator speeds. In this case, the sum of the rows of the optimal gain matrix is the droop gain of each load actuator. Time-domain simulations of a large-scale power system are used to demonstrate the efficacy of the proposed control algorithm. Two different cases are considered: a power imbalance and a line fault. The simulation results show that the proposed controllers successfully damp inter-area oscillations under different operating conditions and with different clustering for the events considered. In addition, the simulations illustrate the benefit of the proposed extension to the OOFC that enable load to provide a combination of droop control and small signal stability augmentation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel non-iterative method to solve power system differential algebraic equations (DAEs) using the differential transformation, which is a mathematical tool able to obtain power series coefficients by transformation rules instead of calculating high order derivatives and has proved to be effective in solving state variables of nonlinear differential equations in our previous study. This paper further solves non-state variables, e.g., current injections and bus voltages, directly with a realistic DAE model of power grids. These non-state variables, nonlinearly coupled in network equations, are conventionally solved by numerical methods with time-consuming iterations, but their differential transformations are proved to satisfy formally linear equations in this paper. Thus, a non-iterative algorithm is designed to analytically solve all variables of a power system DAE model with ZIP loads. From test results on a Polish 2383-bus system, the proposed method demonstrates fast and reliable time performance compared to traditional numerical approaches including the implicit trapezoidal rule method and a partitioned scheme using the explicit modified Euler method and Newton Raphson method. [ABSTRACT FROM AUTHOR]

This paper presents the development and validation of a new oscillatory component load (OCL) model for a measurement-based real-time estimation of dynamic load model parameters. The proposed OCL model has been derived from a second-order differential equation that considers three necessary components, namely static, exponential recovery, and damped oscillatory components. The performance evaluation of the proposed OCL model has been demonstrated through DIgSILENT PowerFactory-based dynamic power system simulations, real-time substation data captured from phasor measurement units located at the primary substations of Leadenham, Holwell, and Regent Street cities, and real-time transient voltage events data provided by the EirGrid. Further, the effectiveness of the proposed OCL model has been assessed by comparing its performance with that of the existing exponential recovery load model. A new flexible and efficient SynchroHub platform, developed at the University of Manchester for real-time data acquisition, processing and visualization, has been used for the real-time estimation of dynamic load model parameters. The validation results revealed the efficacy of the proposed OCL model in tracking both the first as well as the subsequent oscillations of dynamic load model response of the power system for both the steady state as well as transient operating conditions accurately. [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 large amount of power electronic submodules and semiconductor switching events in the Modular Multilevel Converter (MMC) introduces several challenges for efficient and accurate Electro-Magnetic Transient (EMT) simulation. Research efforts have focused on developing Average Value Models (AVMs) of MMC that enable fast and accurate dynamic simulation of the converter. This paper proposes a universal blocking-module-based AVM, which can simulate the MMC of different submodule types and provide accurate results for the MMC operating in both blocking and de-blocking modes. An analytical approach is included in the model to calculate the semiconductor losses of different submodule types in the MMC. The proposed model is validated against a detailed switching-based model and the state-of-the-art AVMs in a 41-level two-terminal MMC-HVDC system. [ABSTRACT FROM AUTHOR]

The objective of this paper is to develop and analyse a variable speed hydropower (VSHP) model that can aid the design of controllers that maximize the utilization of power plant for the provision of ancillary services, considering the limitations given by the hydraulic system. The model is tested and analysed with more or less conventional controllers to identify critical modes, adverse interactions or other limitations that must be taken into account in the future design of potentially multivariable or more advanced controllers for VSHP. Dynamic tests are performed by simulating step responses in power demand and by comparing responses of the model with the VSHP and with a conventional hydropower plant. A participation factor-based interaction analysis shows that there are no strong dynamic couplings between the hydraulic system of the VSHP and the rest of the grid. This simplifies the tuning of the control system. However, the analysis concludes that some oscillatory modes associated with the hydraulic system become significantly more excited when operating at variable speed; which is due to the larger deviation in turbine rotational speed. Extra awareness when designing the control system is therefore needed to keep the hydraulic system variables within their limits. [ABSTRACT FROM AUTHOR]

The wind speeds of each wind turbine generator (WTG) are the basis for establishing an aggregated model of a wind farm for power system transient simulation. However, the commonly obtained operation data of the wind farm do not include the wind speeds of each WTG. Thus, a modeling method for the wind speeds of the WTGs of same moment inside the wind farm was proposed. A wind speed combination model (WSCM) is established via K-means clustering from the sorted field-measured wind speed data, which can provide reasonable wind speeds for each WTG when aggregate modeling the wind farm. Subsequently, an improved two-step clustering method of the WTGs was proposed, by which the WTGs are initially clustered according to whether they enter low voltage ride through (LVRT) mode or not. An “N-1 VS One” aggregated model and the binary search algorithm were used to quickly and correctly predict whether a WTG in the wind farm enters LVRT mode under a grid fault. The case study demonstrates the satisfactory performance of the WSCM and the necessity of clustering the WTGs according to whether they enter or do not enter LVRT mode for obtaining an accurate aggregated model of the wind farm. All the data, models, and programs that are used in this paper can be found at IEEE Dataport, DOI: 10.21227/dqyk-t852. [ABSTRACT FROM AUTHOR]

Accurate and efficient simulation of power electronic systems is challenging due to their hybrid nature consisting of continuous states and discrete events. In this paper, a comprehensive discrete state event-driven (DSED) framework is proposed for offline simulation of such hybrid dynamic systems. Two key elements of the proposed comprehensive DSED simulation framework that contribute to the significant improvements in numerical accuracy and computational efficiency are a flexible adaptive algorithm for flexible integration of continuous states and an event-driven mechanism for efficient locating of discrete events. The proposed DSED simulation framework is applied to a 50-kVA solid-state transformer and a multileg full-bridge Class-D amplifier to verify its accuracy and efficiency by comparisons with experimental waveforms and simulated waveforms of Simulink and PLECS. Up to 100-fold and 10-fold improvements in simulation speed are achieved at the same level of numerical accuracy compared with Simulink and PLECS, respectively. [ABSTRACT FROM AUTHOR]

In this paper we present a solution for real-time multi-FPGA simulation of energy conversion systems based on the Latency-Based Linear Multistep Compound (LB-LMC) simulation approach. The approach relies on a nodal decomposition approach derived from multiport network analysis, and fast parallel communication between Field Programmable Gate Array (FPGA) devices. The results presented in this paper –using a microgrid example– demonstrate how the developed real-time platform overcame the resource scalability limit of single FPGA solvers while achieving a time step size of 100 nanoseconds. [ABSTRACT FROM AUTHOR]

Earth faults occur frequently in power distribution systems and they are usually accompanied by an arc. This is a big hazard to the power distribution systems. Effective early detection is difficult to achieve using conventional methods, which brings inconvenience to fault location and maintenance. In order to solve this problem, a sensitive triggering algorithm should be equipped in the detection device. By analyzing the zero-sequence voltage under normal conditions and fault conditions, a discrete wavelet transform-based triggering algorithm is proposed in this paper. A great number of waveforms simulated by the PSCAD/EMTDC software are used to test the algorithm and two other traditional algorithms, and the results are analyzed and compared. In addition, the curves recorded in the physical simulation systems and the field power distribution systems are input into the proposed algorithm to test its adaptability. For testing whether the algorithm could achieve real-time triggering, a device is designed to carry the algorithm program. These experiments show that the proposed algorithm has high reliability and it can meet the needs of real-time monitoring. [ABSTRACT FROM AUTHOR]