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Power distribution systems with a high share of Variable Renewable Energy Sources (VRE) face problems due to the variability, uncertainty, and non-dispatchable nature of VRE. This paper reviews and discusses the pertinent challenges arising for steady state operation of future distribution systems with a large share of weather-dependent renewable energy sources. The substantially increased amount of VRE in future distribution networks transforms them into highly weatherdependent networks with limited real-time observability. Challenges of such networks, like sustained over-voltage, increased power losses in the network, growing stress upon the existing network assets and changing interactions with the upstream grid, are addressed in the paper. Illustrations from past research and practical demonstrations of these challenges are presented to emphasize the severity of the problems. [ABSTRACT FROM AUTHOR]

This paper analyses impact of different load types on voltage stability of a power system with wind power. To analyse voltage stability, dynamic as well as static static voltage stability assessment are performed. Dynamic model of wind turbine based on Type 4A IEC 61400-27-1 is used to develop an aggregated wind power plant model including the wind power collection system. Polynomial load model is used to represent different load types, namely, constant impedance, constant current and constant power loads. With respect to voltage stability assessment, eigenvalue analysis is used for static voltage stability assessment to determine stability of a particular operating point. Voltage collapse proximity indicator is used as dynamic voltage stability assessment tool to analyse the proximity of an operating point from voltage collapse. Impact of load type on voltage stability is discussed. Impact of reactive power support from wind power plant for the different load types is analysed and discussed. From the case studies performed, it is observed that effect of reactive power support from WPP varies depending on the load type. Results show that distance to instability for the same reactive power support from WPPs can be greater in case of voltage dependent loads than that of constant power loads. [ABSTRACT FROM AUTHOR]

This paper presents the modelling and the control architecture of two different hybrid power plant topologies, e.g. AC and DC coupled Wind-Solar-Storage based Hybrid Power Plants. Dynamic models of different individual assets are briefly described in the paper. A set of simulations are carried out in order to verify and demonstrate the performance of the dynamic models and of the hybrid power plant control dispatch strategy for different control functionalities - namely, maximum power point tracking, delta control and balance control. An overview of the modelling challenges and complexities of ancillary services provisions from hybrid power plants is provided and discussed. [ABSTRACT FROM AUTHOR]

In this paper, an optimization methodology, which uses a heuristic algorithm, is developed in order to maximize the active power generation of wind power plants in distribution networks during maintenance situations. Traditionally, distribution system operators are not taking risks during the maintenance operation by shutting down wind power plants while the reconfiguration is performed. However, the developed methodology presented that the active power outputs of wind power plants' can be curtailed instead of shutdown operation while keeping the distribution network in design and stability limits. Further studies and developments are performed in Danish funded NetVind project to improve the operation of a real distribution network with a high penetration of wind power by exploiting control capabilities of wind power plants. [ABSTRACT FROM AUTHOR]

This paper describes an optimization study of wind power plants' inertial response for different wind speed and penetration levels in power systems. The paper is presenting an optimization method employing a genetic algorithm with an objective function, where the frequency nadir, the seconddip value and the time to reach the frequency steady state are taken into account. As the genetic algorithm is a minimization algorithm, distinct weighting factors of each component enables the adjustment of the optimization according to different specific requirements defined by transmission system operators. The results presented that for the above rated wind speed and medium wind speed operating regions, wind power plants can provide support to the frequency control and improve the performance regarding the frequency nadir and time to reach the steady state. However, the operation region which is closed to the rated wind speed can create a second frequency dip after the nadir. [ABSTRACT FROM AUTHOR]

A reduced grid model of a transmission system with a number of central power plants, consumption centers, local wind turbines and a large offshore wind farm is developed and implemented in the simulation tool PowerFactory (DIgSILENT). The reduced grid model is given by Energinet.dk, Transmission System Operator of Denmark (TSO) for Natural Gas and Electricity, to the Danish Universities and the Risø National Laboratory. Its intended usage is education and studying of interaction between electricity-producing wind turbines and a realistic transmission system. Focus in these studies is on voltage stability issues and on the ride-through capability of different wind turbine concepts, equipped with advanced controllers, developed by the Risø National Laboratory. [ABSTRACT FROM AUTHOR]

The recent plans for the deployment of renewable energy in Denmark require new integrated regulation strategies, making renewable energy to be a key technology in the development of future power systems towards fossil and nuclear free energy generation. Accordingly, the bulk addition of large scale renewable generations to a power system should not be detrimental to the overall stability of the power system. In order to analyze the impact of the renewable generation on power systems, and also to explore the capability of these renewable generation plants, several projects have been conducted recently in Denmark. This paper describes a new ongoing Danish research project RePlan, which has as main objective to investigate the provision of ancillary services, like frequency/active power, voltage/reactive power support from wind power plants (WPP) and photovoltaic (PV) plants, incorporating communication properties in the control loops and using existing forecast techniques. It is intended to analyze the possibility to exploit and coordinate the ancillary services from these plants, identifying and analyzing their capabilities and limitations in respect to their coordination. [ABSTRACT FROM AUTHOR]

This article gives an overview of power system services provided by HVDC-connected wind power plants. With the help of a large set of references, the state-of-art in the field is discussed, with particular focus on VSC-based HVDC technology, and, where relevant, possible alternative solutions. This allows understanding where industry and academia stand as of today and trace the line for future work in the subject. Sample simulation results from the authors' own work are also used to elucidate some of the concepts. The following services are within scope: active power balance control, AC voltage control, power oscillation damping and fault-ridethrough. [ABSTRACT FROM AUTHOR]

This paper presents a wind farm aggregation method that is based on rescaling the output of a single wind turbine, and on an equivalent wind speed calculated as the average wind of the wind speeds for the individual wind turbines. The proposed aggregation method is simple and straightforward, whereas the effect of the wind distribution inside the farm is in focus. The wind farm aggregated model is built based on a simplified generic variable speed wind turbine model suitable for dynamic active power studies. The performance of the aggregated model is assessed in comparison with the detailed representation of the wind farm in terms of active power output. The results have shown that the use of the proposed aggregated wind farm model instead of the detailed model is meaningful, as it is a good approximation without compromising the accuracy of the results. [ABSTRACT FROM AUTHOR]

Secure power system operation of a highly wind power integrated power system is always at risk during critical weather conditions, e.g. in extreme high winds. The risk is even higher when 50% of the total electricity consumption has to be supplied by wind power, as the case for the future Danish power system in 2020. This paper analyses and compares the performance of the future Danish power system during extreme wind speeds, where wind power plants are either controlled through a traditional High Wind Shut Down storm controller or a new High Wind Ride Through storm controller. For this purpose, the power system model has been developed that represents the relevant dynamic features of power plants and compensates for power imbalances caused by the forecasting error during critical weather conditions. The regulating power plan, as an input time series for the developed power system model, is provided by the hour-ahead power balancing model, i.e. Simulation power Balancing model (SimBa. The regulating power plan is prepared from day-ahead power production plan and hourahead wind power forecast. The wind power (forecasts and available) are provided by the Correlated Wind power fluctuations (CorWind) model, where the wind turbine storm controllers are also implemented. [ABSTRACT FROM AUTHOR]

A first study of voltage stability with relevant amount of Voltage Sourced Converter based High Voltage Direct Current (VSC-HVDC) transmission is presented, with particular focus on the converters' behaviour when reaching their rated current. The detrimental effect of entering the current limitation on the Power-Voltage (PV) curves at a load bus is exemplified on a three-bus system, proposing a method to model the converters in current limiting mode through ideal current sources. The influence of the current magnitude and angle on the reduced stability margin is analysed and results show that, when the current limit is reached, despite the detrimental effect brought about by an increased equivalent transmission impedance, the loss of stability margin can be minimised by proper control of the converter. [ABSTRACT FROM PUBLISHER]