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As the penetration level of converter-based generators (CBGs) continues to grow in electric power systems, their impact on power system dynamics and control becomes increasingly significant. Maintaining a stable operation of the CBGs is becoming more and more critical. Since their controls and dynamic behaviour differ from synchronous generators, in this study, the transient stability mechanism of CBGs is analysed and the key influencing factors are identified and investigated. Moreover, a stability margin index, which can be obtained analytically, is proposed to identify potential transient stability issues of CBGs and can be used as a screening technique before conducting time-consuming electromagnetic simulation studies. This index can be used for both planning and operations studies and it outperforms the state-of-the-art index of short circuit ratio that is presently used to identify potential CBG instabilities due to weak grid scenarios. Dynamic simulations on a real power system model have been conducted to validate the accuracy and applicability of the proposed stability margin index. [ABSTRACT FROM AUTHOR]

Matrix converter has become one of the research hotspots of power electronic converter due to its excellent input and output characteristics and adjustable power factor. To study the stability of the matrix converter grid-connected system, the harmonic linearisation method is adopted to model the positive and negative sequence output impedance models of the matrix converter grid-connected system. The stability of the system is analysed by judging whether the plot of the ratio of the input impedance to the positive and negative sequence output impedance satisfies the Nyquist stability criterion. Also, an impedance remodelling method based on the positive sequence impedance is proposed to improve the stability of the system. Finally, the simulation verification is carried out by MATLAB/Simulink. The simulation results prove the correctness of the theoretical analysis and the feasibility of the impedance remodelling method. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to perform small-signal analysis of an offshore ac network, which is formed by interconnecting several offshore wind power plants. The offshore ac network is connected with different onshore ac grids using point-to-point voltage-source-converter high-voltage direct current (VSC-HVDC) transmission links. In such a network, each offshore VSC-HVDC converter operates in grid-forming mode. In this paper, the offshore VSC grid-forming control is enhanced by using a frequency and voltage droop scheme in order to establish a coordinated grid control among the offshore converters. A small-signal model of the offshore ac network is developed that includes the high-voltage alternating current cables' model, the converters' current, and voltage-control model, the frequency droop scheme, and the voltage droop scheme. Based on this model, an eigenvalue analysis is performed in order to study the influence of the frequency and voltage droop gains on overall offshore ac network stability. Finally, theoretical analysis is validated by performing nonlinear dynamic simulation. [ABSTRACT FROM PUBLISHER]

The stability of electric power system (EPS) insures energy security of consumers. Therefore, saving the stability of EPS is the main task for professionals around the world. For its solution, a variety of activities is used. This publication deals with the description of the authors' experience for solving the task in the Tyumen power system. The hybrid real‐time power system simulator (HRTSim) developed in Tomsk Polytechnic University was used as a platform for research carrying out. The study presents the research result fragments of the momentary and sustained fast turbine valving control (FTVC) which is one of the most effective ways of an automatic emergency control of power units in the thermal power station. Using the simulator HRTSim, one of the greatest challenges of electric power industry in Russia has been solved, i.e. FTVC adequate setting of the power units in the thermal power station Surgut GRES‐2 in the Tyumen power system. An FTVC operation largely determines the reliability and stability of the EPS. Therefore, an incorrect setting may result in substantial disturbance or disruption of the stability that already occurred in the past. The adequacy of turbine and FTVC simulations is verified by comparing it with the real data. [ABSTRACT FROM AUTHOR]

Utility power distribution system analysis has traditionally been performed considering only the primary or medium-voltage system. Distributed energy resources are increasingly being located on the secondary, or low voltage, side of the distribution transformer, requiring the low-voltage system to be included in the analysis. However, most distribution system models do not include secondary circuits or they are modeled with limited detail. In the absence of the appropriate model data, secondary circuits models commonly rely on simplifications such as single-phase models, constant power factor, etc. This paper highlights the implications of some of these assumptions and provides guidance in terms of how more accurate secondary models are needed. This paper shows that split-phase secondary circuits can be modeled accurately with single-phase equivalents under perfectly balanced conditions. It also shows that assuming constant power factor or using smart meter measurements with practical 15 min, or larger, time granularity can lead to considerable errors in simulated secondary circuit losses or voltages. [ABSTRACT FROM PUBLISHER]

In order to reduce the online calculations for power system simulations of transient stability, and dramatically improve numerical integration efficiency, a transient stability numerical integration algorithm for variable step sizes based on virtual input is proposed. The method for fully constructing the nonhomogeneous virtual input for a certain integration scheme is given, and the calculation method for the local truncation error of the power angle for the corresponding integration scheme is derived. A step size control strategy based on the predictor corrector variable step size method is proposed, which performs an adaptive control of the step size in the numerical integration process. The proposed algorithm was applied to both the IEEE39 system and a regional power system (5075 nodes, 496 generators) in China, and demonstrated a high level of accuracy and efficiency in practical simulations compared to the conventional numerical integration algorithm. [ABSTRACT FROM AUTHOR]

A concept of sensitive line set is presented in this paper, aiming to enhance the ability of resilient power system to prevent and resist the external extreme disturbances. Furthermore, a new fault chain model is established, in order to obtain the above sensitive line set. The fault chain, calculated by this fault chain model, is consisted of the initial segment and the middle segment. The index of bus load rate for the initial and the middle segments is presented firstly to reflect the load condition of a system in the fault chain model. Besides, other indices, such as historical fault statistics, line load degree, and correlation coefficient in the initial segment and power flow transfer, sequent overload of lines, and damage of transmission sections in the middle segment, are concerned and normalized to predict all the fault chains. Then, the sensitive line set can be obtained after the risk calculation and level assessment for the fault chains. The set can become the basis for controlling process of resilient power system during the accident preventing and resisting stages. Finally, the rationality of the proposed sensitive line set is demonstrated via 39 bus system. [ABSTRACT FROM AUTHOR]

Dynamic response of loads has a significant effect on system stability and directly determines the stability margin of the operating point. Inherent uncertainty and natural variability of load models make the stability assessment especially difficult and may compromise the security of the system. We propose a novel mathematical “robust stability” criterion for the assessment of small-signal stability of operating points. Whenever the criterion is satisfied for a given operating point, it provides mathematical guarantees that the operating point will be stable with respect to small disturbances for any dynamic response of the loads. The criterion can be naturally used for identification of operating regions secure from the occurrence of Hopf bifurcation. Several possible applications of the criterion are discussed, most importantly the concept of robust stability assessment (RSA), that could be integrated in dynamic security assessment packages and used in contingency screening and other planning and operational studies. [ABSTRACT FROM PUBLISHER]

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]

We define here a new parallel simulation method designed for real-time execution. This method is highly parallelizable and scalable, and the simulation execution time is fully predictable, which is very important for real-time execution. The stability conditions for the method are defined. Furthermore, we show how to define appropriate flow variable injections so that this method can be extended to multiphysic applications and how to implement multirate time step in the defined method. Finally, we present simulation tests that validate the presented method. [ABSTRACT FROM AUTHOR]

Short-term voltage stability is an increasing concern in today's power systems due to the growing penetration of induction motors. This paper proposes a systematic method for optimal placement of dynamic VAR support against short-term voltage instability. The problem is formulated as a multi-objective optimization model minimizing two conflicting objectives: 1) the total investment cost and 2) the expected unacceptable short-term voltage performance subject to a set of probable contingencies. STATCOM is employed for its stronger dynamic VAR support capability. Indices for quantifying the short-term voltage stability and the related risk level are proposed for problem modeling. Candidate buses are selected based on the concept of trajectory sensitivity. Load dynamics are fully considered using a composite load model containing induction motor and other typical components. A relatively new and superior multi-objective evolutionary algorithm called MOEA/D is introduced and employed to find the Pareto optimal solutions of the model. The proposed method is verified on the New England 39-bus system using industry-grade models and simulation tool. [ABSTRACT FROM AUTHOR]

Several studies have recently reported the capability of doubly-fed induction generator (DFIG) wind farms in improving the dynamic performance of power systems. Since wind farms are more often located far from the system conventional generation centers, local signals do not comprise enough content for damping inter-area oscillations. This paper presents a particle swarm optimization (PSO)-based wide-area damping controller (WADC) for the DFIG wind farms. The proposed controller is designed with a centralized nature on the basis of latest technological development of wide-area measurement system (WAMS). Damping both inter-area and local oscillatory modes are intended in the design process. The most challenging deficiency against WAMS real-time applications is the variable communication latency which can deteriorate the system stability if not properly accounted for in the controller design process. The proposed WADC hence incorporates effective means to compensate for the destructive characteristics of WAMS delayed signals. The PSO technique is applied to normalize and optimize the parameters of WADC. A set of comprehensive case studies are conducted on a 16-bus six-machine test system and the obtained numerical evidences are thoroughly discussed. [ABSTRACT FROM AUTHOR]

With the increasing penetration of variable renewable generations, independent system operators (ISOs)/regional transmission organizations (RTOs) are faced with new challenges for the secure and economic operation of power systems. This paper proposes an effective approach for deriving robust solutions to the security-constrained unit commitment (SCUC) problem, which considers load and wind uncertainties via interval numbers. Different from most robust optimization-based SCUC approaches in literature which explore robust unit commitment (UC) solutions for immunizing against the worst economic scenario in terms of the highest minimum dispatch cost, the proposed robust SCUC model minimizes operation cost for the base case while guaranteeing that the robust UC and dispatch solutions could be adaptively and securely adjusted in response to uncertain intervals. Thus, the proposed model achieves smaller unit commitment costs while maintaining the solution robustness as compared with literature. In addition, the proposed model describes base case dispatches and corrective actions in uncertain intervals, which is more consistent with the current day-ahead and real-time markets. Furthermore, besides budget constraints used in literature, this paper also considers load and wind variability correlations in constructing uncertain intervals, which would eliminate unlike-to-happen scenarios and further limit the level of conservatism of the robust solution. The proposed robust SCUC model is solved by Benders decomposition, which decomposes the original problem into a master UC problem for the base case and subproblems for the base case network evaluation and the security checking for uncertain intervals. Feasibility cuts are generated and fed back to the master problem for further iterations when violations are identified in subproblems. Numerical case studies on the modified IEEE 118-bus system illustrate the effectiveness of the proposed robust SCUC model for the secure and economic operation of power systems under various uncertainties. [ABSTRACT FROM AUTHOR]

This paper presents a fully analog demonstrator based on power system emulation for high-speed power system stability analysis. A benchmark using a fixed two-machine topology has been implemented. The characteristics of the emulated components (i.e., generators and transmission lines) are reprogrammable and short circuits can be emulated at different distances from the generator. This first realization is limited to transient stability analysis, as the main focus during design was put on computation speed. Indeed, the emulated phenomena are 10\thinspace000 times faster than real time. Moreover the authors aim to emphasize that such highly dedicated computation architectures are not only competitive in terms of speed, but also in terms of modularity. [ABSTRACT FROM PUBLISHER]

Abstract: This article studies accurate and detailed hydro turbine and governor models, and implements these models in Power System Analysis Toolbox (PSAT)—a free and open source software. The implementation of these models in PSAT is approached using a general methodology, which is described in detail. To evaluate the performances of the developed hydro turbine and governor models, simulation studies are carried out on test systems of different scales, from a single-machine infinite-bus (SMIB) system to a larger system which includes 20 generators. Further more, transient stability analysis and small signal stability analysis are carried out to assess the performance of the implemented models. [Copyright &y& Elsevier]

This paper proposes voltage-shift acceleration control for islanding detection of distributed-generation (DG) inverters. The proposed method is conceptually based on a traditional dq-based voltage positive feedback control. A main improvement of the proposed control is that the anti-islanding performance and its impact on inverter output control can be consistent regardless of inverter operation points. An analytical approach based on a small-signal model of an inverter controller is used to prove the proposed control. Also, an analytical design method is proposed to obtain proper control gain that satisfies two conflicting issues: successful anti-islanding and limited impact on inverter control. Simulation and experimental tests were conducted to validate the proposed detection algorithm and its design method. In addition, simulation results on a two DGs system are shown to investigate the performance in multiple DGs operation. [ABSTRACT FROM AUTHOR]

In this paper, we present a new Matlab-based toolbox for power system analysis, called MatDyn. It is open-source software, and available for everyone to download. Its design philosophy is based on the well-known open-source Matlab toolbox MATPOWER , but its focus is transient stability analysis and time-domain simulation of power systems, instead of steady-state calculations. [ABSTRACT FROM AUTHOR]

Parameters of power system models, in particular load models, are seldom known exactly, yet dynamic security assessment relies upon simulation of those uncertain models. This paper proposes a computationally feasible approach to assessing the influence of uncertainty in simulations of power system dynamic behavior. It is shown that trajectory sensitivities can be used to generate accurate first-order approximations of trajectories that arise from perturbed parameter sets. The computational cost of obtaining the sensitivities and perturbed trajectories is minimal. The mathematical structure of the trajectory approximations allows the effects of uncertainty to be quantified and visualized using worst-case analysis and probabilistic approaches. [ABSTRACT FROM AUTHOR]

To achieve better performance for the controlled system, the rule table of a fuzzy logic based controller is often determined by trial and error. To simplify this time-consuming task, a standardized rule table that can be used in a fuzzy logic control design procedure is developed in this paper. To demonstrate its applicability, the design technique proposed in this paper is employed to design a fuzzy logic based power system stabilizer. Details of the design procedure and results of performance studies with the proposed stabilizer are given in the paper. [ABSTRACT FROM AUTHOR]

Repeated simulations have been most widely applied in analyzing the sensitivities of the power system dynamics with respect to controller inputs. This approach is computationally intensive and it does not explicitly show the physical insights. A transfer function matrix based approach is proposed in this letter for control input sensitivity analysis. A bottom up method is also presented to build the respective transfer function matrix. The effectiveness of the method is demonstrated through case studies. [ABSTRACT FROM AUTHOR]

The paper deals with the small-signal stability analysis of aircraft ac frequency-wild power systems representing a real ac-dc hybrid distribution architecture with a multiplicity of actuators, aircraft loads, and bus geometries. The $dq$ modelling approach is applied to derive individual power system component models and to constitute the corresponding generalized power system model as a powerful and flexible stability analysis tool. The element models can be interconnected in an algorithmic way according to a variety of the architecture selected. Intensive time-domain simulation and experimental results are used to verify the theoretical results. It is also shown how the proposed approach can be used to predict instability due to possible variations in operating points and system parameters. [ABSTRACT FROM AUTHOR]