Microgrid is becoming an attractive concept to meet the increasing demands for energy and deal with air pollutions. Distributed energy sources (DERs) in Microgrid are usually interfaced with the utility grid by inverters, so the characteristics of Microgrid stability are much different from that of a traditional grid. However, the classifications, guidelines, and analysis method of Microgrid stability are well behind of the Microgrid development. In this paper, a Microgrid stability classification methodology is proposed on the basis of the of Microgrid characteristics investigation, which considers the Microgrid operation mode, types of disturbance and time frame. Then a comprehensive review of the body of research on Microgrid stability is presented in order to identify and advance the field. Finally, some challenges and suggestions of Microgrid stability for further researches are discussed.

Microgrid stability: Classification and a review

Radial MV networks voltage regulation with distribution management system coordinated controller

CIGRE WG C4.605 : “Modelling and aggregation of loads in flexible power networks”

This paper presents the development of the dynamic equivalent model of an active distributed network (ADN) based on the grey-box approach. The equivalent model of an ADN comprises a converter-connected generator and a composite load model in parallel. The grey-box approach was chosen for model development as it incorporates prior knowledge about the ADN structure into the model, makes the model more physically relevant and intuitive than black-box or white-box models, and potentially improves the accuracy of the model. The dynamic equivalent model is presented in the seventh-order nonlinear state space format. It was initially loosely developed from the algebraic and differential equations describing assumed typical components of an ADN. Various static load models, dynamic load compositions, fault locations and a diverse range of distributed generation types and scenarios are considered in order to establish the generic range of model parameters for an ADN. The model is intended for the use in large power system stability studies.

Generic Model of Active Distribution Network for Large Power System Stability Studies

This paper presents a comprehensive survey on application of various conventional, optimization and artificial intelligence (AI) based computational techniques for impact assessment of optimally placed and coordinated control of distributed generations (DGs) and flexible AC transmission systems (FACTS) controllers in power systems (PSs). This review work is presented from the viewpoint of different performance criterion enhancement of PSs such as minimization of active and reactive power losses and reduction of cost of system, more flexible operation and control, increase overall system energy efficiency, increase reliability of system, relieved transmission and distribution congestion, enhance power quality (PQ) of system, improve the voltage profile (VP), increase the loadability of systems, increase available power transfer capacity (APTC) of system, enhance PS stability, reduce PS oscillations, improve environmental GHG conditions and provide the reactive power support in emergency case such as under fault, sudden change in field excitation of alternators or load increase in PSs. This paper also presents the current status of the various conventional, optimization, and AI computational techniques for optimally placed and coordinated control of DG and FACTS controllers in PSs for enhancement of PSs performance parameters. Authors strongly believe that this survey will be very much useful to the researchers, scientific engineers, industrial persons working in this area to find out the relevant references and current state of the art.

A survey on impact assessment of DG and FACTS controllers in power systems

Nowadays the number of dispersed generators (DGs) is growing rapidly. This change will greatly influence power system dynamics. A distribution network, where DGs are connected to the grid, cannot be considered as passive anymore. Therefore, in the future it will not be possible to use simple equivalents of distribution networks for power system dynamic modelling, as it was done before. At the same time, the whole power system cannot generally be represented in a detailed manner for dynamic studies because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. A brief review of existing techniques is provided here, and the dynamic reduction using Hankel norm approximation is performed for a 10 kV distribution network, which includes DG of different types.

Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation

Apart from the positive technical consequences like reducing losses, the increasing penetration of distributed generation (DG) units connected to the distribution network, has lead to the increase of the short-circuit (sc) currents and the fault level. Therefore it is important to know the contribution of each unit. This paper presents the available analytical equations to calculate the short-circuit current, and makes a comparison between the IEC 60909 and the results obtained by the simulations in a test network that incorporates these units.

/pdf/overview-of-short-circuit-contribution-of-various-4k8b8l40km.pdf

Overview of short-circuit contribution of various Distributed Generators on the distribution network

The paper describes a possible network topology of an autonomous operating network as well as several control activities in normal and disturbance operation, their interaction with network performance and their modelling. The three described control processes are: predefined exchange of power, optimization of voltage profile, and keeping stability during disturbances. The paper focuses on the theoretical aspects of new network design and control. INTRODUCTION OF AUTONOMOUS NETWORKS The expected growth of dispersed generation results in a more complex operation of low and medium voltage grids. Examples of this complexity are: uncertainty of power flows, strong variation of voltage magnitude, possible reversed power flow and variations in short circuit currents and their influence on protection. Furthermore the use of power electronics in the connection of the generation units can result in an increase of harmonic levels and challenges in maintaining stability of the controls. But on the other hand the combination of power electronics and controllable power sources like storage, small gas turbines and fuel cells will help managing these problems in the future. It is even possible that this results in improved performances of the network.

/pdf/self-controlling-autonomous-operating-power-networks-39ka2e35q7.pdf

Self controlling autonomous operating power networks

Nowadays the number of dispersed generators (DG) is growing rapidly. This change will greatly influence the power system dynamics. A distribution network, where DG are connected to the grid, cannot be considered as passive anymore. So in future it will not be possible to use simple equivalents of distribution networks for power system dynamic modeling as it was done before. In dynamic studies whole power system cannot be represented in detailed manner because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. In this paper brief review of existing techniques has been done, and afterwards dynamic reduction using balanced truncations has been performed for a small distribution network consisting of DG of different type

http://ieeexplore.ieee.org/iel5/10666/33649/01600593.pdf

Dynamic reduction of distribution networks with dispersed generation

In this paper transient stability of an existing 10 kV distribution network with combined heat and power plants, microturbines and wind turbines is analyzed. In order to do this, dynamic models of the network and generators have been created and simulations for faults at different network locations have been done. From the analysis it appears that the most critical parameter, which influences transient stability in the test network, is the inertia of a microturbine. Simulations have shown that there is linear relationship between inertia constant of microturbine and critical clearing time. After that it has been checked that the protection of DG satisfies transient stability requirements. In the end, the possibility for providing DG support to the network during and after disturbances using fault ride-through concept has been considered and simulations illustrate that DG protection can guarantee transient stability in this case as well.

A. Ishchenko

Papers

Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation

Overview of short-circuit contribution of various Distributed Generators on the distribution network

Self controlling autonomous operating power networks

Dynamic reduction of distribution networks with dispersed generation

Transient Stability Analysis of Distribution Network with Dispersed Generation