Dynamic modeling, stability analysis and control of interconnected microgrids:A review

This paper reviews concepts of interconnected microgrids (IMGs) as well as compare and classify their modeling, stability analysis, and control methods. To develop benefits of isolated microgrids (MGs) such as reliability improvement and their renewable energy integration, they should be interconnected, share power, support the voltage/frequency of overloaded MGs, etc. Despite maximizing their benefits and decreasing weaknesses of isolated MGs, IMGs require maintaining stability in different operation modes and employing appropriate control methods. Moreover, a basic requirement for stability analysis and controller design is system modeling. Since many articles have addressed these topics on IMGs from different views, a comparison is necessary. Therefore, IMG dynamic modeling methods are classified and their main features and challenges are discussed. Then, stability analysis and control methods of IMGs are reviewed and compared. The provided review is supported by conceptual diagrams, classification tables, off-line and real-time simulations using MATLAB and OPAL-RT simulator for comparison. Furthermore, a data set is provided to study fundamentals as well as research gaps, which are addressed for future works

Advancements in converter-based frequency stability : recommendations for industrial applications

The burning of fossil fuels and related carbon emissions are driving the ongoing climate crisis. A critical path to fully decarbonise the power system is to enable low-carbon converter-interfaced devices to take on responsibility for the generation of electrical energy. However, a low-carbon electrical power system also requires the converters to provide the features that fossil-fuel-powered synchronous machines (SMs) conventionally provide to stabilise the electrical grid. The electrical frequency is one key system parameter that needs to be stabilised. Converter-based frequency stabilising solutions have been proposed but the nuance of their operation is not fully understood. Therefore, this thesis aims to address some of the critical hurdles that the solutions must overcome. The thesis initially outlines the technical characteristics that are required to provide inertial and droop responses. Academic and industrial data are assessed to identify the technologies that are techno-economically suited to provide the support. The impact of different controller choice for droop provision is assessed. Previous works have suggested that certain droop controllers are equivalent but often only consider the steady state. Models of Synchronverter and Grid-forming (GFM) Droop controlled ideal energy storage systems are assessed to identify the equivalence of the controllers’ frequency support. A tuning guide developed earlier in the thesis enables the controllers to provide equivalent inertial and droop responses but the dynamics of each controller are shown to be different. The impact of the GFM Droop’s cascaded controllers and its parametric tuning on the frequency support are then assessed and suggestions are made for their tuning. The industrial attempts to quantify useful inertial response are then assessed. Parametric sweeps of example GFM and grid-following (GFL) controllers are carried out to compare their full capability with the industrial specifications. A more detailed power system model is also used to validate the findings of the parametric sweeps and to assess the impact of the controllers’ properties on the system frequency. The study highlights that useful inertial provision is not unique to GFMs, that GFLs should not be subject to blanket disqualifications from inertial support, and that transient phase responses may require more consideration in converter dominated systems. Finally, the ability of system operators (SOs) to measure wind turbine (WT) based inertial support is assessed. Experimental data of a grid-connected wind farm are used to identify the impact that the wind has on the inertial response. A review is carried out to assess the methods that are currently available to measure WT inertial response (including the existing industrial standard). The accuracy of the existing methods are assessed using a model of a WT and its converters, which resolves the dynamics from wind energy source to grid. Two new approaches are proposed that improve the accuracy of WT inertial response measurement.The burning of fossil fuels and related carbon emissions are driving the ongoing climate crisis. A critical path to fully decarbonise the power system is to enable low-carbon converter-interfaced devices to take on responsibility for the generation of electrical energy. However, a low-carbon electrical power system also requires the converters to provide the features that fossil-fuel-powered synchronous machines (SMs) conventionally provide to stabilise the electrical grid. The electrical frequency is one key system parameter that needs to be stabilised. Converter-based frequency stabilising solutions have been proposed but the nuance of their operation is not fully understood. Therefore, this thesis aims to address some of the critical hurdles that the solutions must overcome. The thesis initially outlines the technical characteristics that are required to provide inertial and droop responses. Academic and industrial data are assessed to identify the technologies that are techno-economically suited to provide the support. The impact of different controller choice for droop provision is assessed. Previous works have suggested that certain droop controllers are equivalent but often only consider the steady state. Models of Synchronverter and Grid-forming (GFM) Droop controlled ideal energy storage systems are assessed to identify the equivalence of the controllers’ frequency support. A tuning guide developed earlier in the thesis enables the controllers to provide equivalent inertial and droop responses but the dynamics of each controller are shown to be different. The impact of the GFM Droop’s cascaded controllers and its parametric tuning on the frequency support are then assessed and suggestions are made for their tuning. The industrial attempts to quantify useful inertial response are then assessed. Parametric sweeps of example GFM and grid-following (GFL) controllers are carried out to compare their full capability with the industrial specifications. A more detailed power system model is also used to validate the findings of the parametric sweeps and to assess the impact of the controllers’ properties on the system frequency. The study highlights that useful inertial provision is not unique to GFMs, that GFLs should not be subject to blanket disqualifications from inertial support, and that transient phase responses may require more consideration in converter dominated systems. Finally, the ability of system operators (SOs) to measure wind turbine (WT) based inertial support is assessed. Experimental data of a grid-connected wind farm are used to identify the impact that the wind has on the inertial response. A review is carried out to assess the methods that are currently available to measure WT inertial response (including the existing industrial standard). The accuracy of the existing methods are assessed using a model of a WT and its converters, which resolves the dynamics from wind energy source to grid. Two new approaches are proposed that improve the accuracy of WT inertial response measurement

Instantaneous velocity field imaging instrument for supersonic reacting flows

The technical tasks conducted to develop and demonstrate a new gas velocity measurement technique for high enthalpy reacting flows is described. The technique is based on Doppler-shifted Planar Laser-induced Fluorescence (PLIF) imaging of the OH radical. The imaging approach permits, in principle, single-shot measurements of the 2-D distribution of a single velocity component in the measurement plane, and is thus a technique of choice for applications in high enthalpy transient flow facilities. In contrast to previous work in this area, the present program demonstrated an approach which modified the diagnostic technique to function under the constraints of practical flow conditions of engineering interest, rather than vice-versa. In order to accomplish the experimental demonstrations, the state-of-the-art in PLIF diagnostic techniques was advanced in several ways. Each of these tasks is described in detail and is intended to serve as a reference in supporting the transition of this new capability to the fielded PLIF instruments now installed at several national test facilities. Among the new results of general interest in LlF-based flow diagnostics, a detailed set of the first measurements of the collisional broadening and shifting behavior of OH (1,0) band transitions in H7-air combustion environments is included. Such measurements are critical in the design of a successful strategy for PLIF velocity imaging; they also relate to accurate concentration and temperature measurements, particularly in compressible flow regimes. Furthermore, the results shed new light on the fundamental relationship between broadening and energy transfer collisions in OH A(sup 2)Sigma(+)v(sup ') = 1. The first single-pulse, spectrally-resolved measurements of the output of common pulsed dye lasers were also produced during the course of this effort. As with the OH broadening measurements, these data are a significant aspect of a successful velocity imaging strategy, and also have potential implications for many other LIF measurement techniques. Our results indicated the need to modify the commercially available laser cavity in order to accommodate the constraints imposed by typical SCRAMJET combustion characteristics as well as to increase the instrument's velocity dynamic range to span an intra-image range in excess of 2 km/s. The various technical efforts were brought together in a series of experiments demonstrating the applicability of the technique in a high pressure, high temperature H2-air combustion system. The resultant images were compared with 2-D flow simulations in order to determine the accuracy of the instrument. Mean velocity imaging in flows with an axis of symmetry was demonstrated with an accuracy of +/- 50 m/s out of an intra-image dynamic range of 1600 m/s, including reversed flow. A more complex configuration amenable to single-shot imaging in flows without an axis of symmetry was also demonstrated. Limitations imposed by available equipment resulted in an accuracy of about +/- 200 m/s out of 1750 m/s in these demonstrations. Minor modifications to the present configuration were suggested to improve this performance. Each technical task is described in detail, along with significance of the results for the overall imaging velocimeter configuration. This report should allow the user community to integrate this new measurement capability in their existing instrumentation platforms

Calibration of Traffic Simulation Models using SPSA

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Γεωπληροφορική

Aeronautical Engineering. A continuing bibliography with indexes, supplement 156

This bibliography lists 288 reports, articles and other documents introduced into the NASA scientific and technical information system in December 1982

A Recursive Least-Squares Approach with Memorizing Factor for Deriving Dynamic Equivalents of Power Systems

In this research, a two-stage identification-based approach is proposed to obtain a two-machine equivalent (TME) system of an interconnected power system for transient stability studies. To estimate the parameters of the equivalent system, a three-phase fault is applied near and/or at the bus of a local machine in the original multimachine system. The electrical parameters of the equivalent system are calculated in the first stage by equating the active and reactive powers of the local machine in both the original and the predefined equivalent systems. The mechanical parameters are estimated in the second stage by using a recursive least-squares estimation (RLSE) technique with a factor called “memorizing factor”. The approach is demonstrated on New England 10-machine 39-bus system, and its accuracy and efficiency are verified by computer simulation in MATLAB software. The results obtained from the TME system agree well with those obtained from the original multimachine system

Calibration of Traffic Simulation Models using SPSA

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Γεωπληροφορική

Power system dynamic security analysis via decoupled time domain simulation and trajectory optimization

Electric power systems are subject to disturbances in the operation, and may encounter system failures such as power outages and blackouts due to disturbances. Power system security analysis plays an important role in improving the survivability to disturbances. This dissertation proposes advanced computational and optimization techniques that can be applied to mitigate instabilities in power systems subject to disturbances. The research work has been integrated into a general framework for power system dynamic security analysis. The proposed methods cover strategies for both power system instability assessment and control, and provide a fast simulation algorithm and coordinated optimization techniques to improve power system security. In the assessment phase of power system security analysis, a fast algorithm is proposed to identify power system dynamic behavior using decoupled time domain simulation method. Traditional time domain simulation algorithms can be categorized as explicit and implicit methods. While explicit methods are fast, the simulation results cannot be guaranteed to be correct for stiff dynamical systems. On the other hand, implicit methods may give correct qualitative behavior with slow performance. As a hybrid method, the proposed decoupled method improves the computational efficiency and achieves numerical stability of time domain simulation by combining the advantages of traditional explicit and implicit methods, and the decomposition is accomplished through invariant subspace partition with rigorous mathematical analysis. In mitigation phase of system security analysis, a coordinated control strategy based on trajectory optimization is proposed. Power system dynamic performance is improved by the proposed method within the constraints imposed on system transition. In addition to the equilibrium conditions, inequality constraints in power system dynamics such as voltage level are considered in the formulation and solved through penalty function method. As one of the applications, power quality such as voltage dip in power system dynamics can be improved. Cascading events may also be prevented by including transitional constraints in the trajectory optimization. Numerical examples of test power systems are presented to demonstrate the applications of the proposed methods

The development of a full probabilistic risk assessment model for quantifying the life safety risk in buildings in case of fire

In het kader van dit onderzoek is een probabilistisch model ontwikkeld dat het brandveiligheidsniveau van een gebouwontwerp kan kwantificeren en dit berekende veiligheidsniveau kan evalueren aan de hand van een vooraf gedefinieerd aanvaardbaar risicocriterium. De ontwikkelde methodiek kan zowel prescriptieve als op prestatie-gebaseerde ontwerpmethoden objectiveren door rekening te houden met de onzekerheid van ontwerpparameters en de betrouwbaarheid van veiligheidssystemen. Het model bestaat uit zowel een deterministisch als een probabilistisch gedeelte. Het deterministische kader is opgebouwd uit verschillende deelmodellen om zowel de verspreiding van brand en rook, als de interactie met evacuerende personen te simuleren. Verschillende deelmodellen zijn ontwikkeld om het effect van geïmplementeerde veiligheidsmaatregelen zoals detectie, sprinklers , rook- en warmteafvoersystemen, enz. mee in rekening te brengen. Het probabilistische kader is opgebouwd uit modellering van responsoppervlakken, steekproeftechnieken en ontwerp van grenstoestanden. De methodiek maakt gebruik van deze technieken om de nodige rekenkracht te beperken. Het uiteindelijke resultaat wordt vertaald naar een kans op sterfte, een individueel risico en een groepsrisico. De grote meerwaarde van de ontwikkelde methodiek is dat het mogelijk wordt om verschillende ontwerpmethodieken objectief met elkaar te vergelijken en het positieve effect van verbeterde veiligheidstechnieken en redundantie mee in rekening te brengen in het eindresultaat