Dynamic fault simulation of wind turbines using commercial simulation tools

This paper compares the commercial simulation tools: PSCAD, PowerFactory, Simpow and PSS/E for analysing fault sequences defined in the Danish grid code requirements for wind turbines connected to a voltage level below 100 kV. Both symmetrical and unsymmetrical faults are analysed. The deviations and the reasons for the deviations between the tools are stated. The simulation models are implemented using the built-in library components of the simulation tools with exception of the mechanical drive-train model which had to be user-modelled in PowerFactory and PSS/E

Wind Turbine Models for Power System Stability Studies

The purpose of this thesis is to develop dynamic models of wind turbines for power system stability studies. More specifically, the wind turbine models are mainly intended for voltage and frequency stability studies.In developing the wind turbine models, each part of the wind turbines are examined to define relevant behaviors that significantly influence the power system response. Correspondingly, mathematical models of these parts are then presented with various possible levels of detail. Simplified models for each part of the wind turbines are evaluated against more detailed models to provide a clear understanding on how model simplifications may influence result validity and simulation efficiency. In order to obtain confident results, the wind turbine models are then validated against field measurement data. Two different cases of validation are then presented. Based on the measurement data of two different wind turbines, most typical behaviors of the wind turbines are discussed. Finally, both conformity and nonsimilarity between simulation results of the wind turbine models and the field measurement data are elaborated.Two different methods of predicting stator transient current of a wind turbine generator following a fault are presented. The first method implements a modified fifth-order model of an induction generator which is developed to be compatible with the fundamental frequency network model. The second method utilizes an analytical method in combination with the third-order model of an induction generator. A solution for the implementation of wind turbine models that require a simulation time step smaller than the standard simulation time step is also proposed in the thesis.In order to comprehend behaviors of wind turbines subject to different power system stability phenomena, a number of simulations are performed in the power system simulation tool PSS/E with the standard simulation time step of 10 ms. Each stability phenomenon are simulated using different wind turbine models. The simulation results are evaluated to determine the most appropriate wind turbinemodel for each particular power system stability study. It is concluded that a fixed-speed wind turbine model consisting of the third-order model of an induction generator and the two-mass model of a drive train is a compromised solution to provide a single wind turbine model for different types of power system stability studies.The thesis also presents aggregated models of a wind farm with fixed-speed wind turbines. The result of the simulations are validated against field measurement data

Dynamic Models of Wind Turbines

The impact of wind power generation in the power system is no longer negligible. Therefore, there is an urgent need for wind turbine models that are capable of accurately simulating the interaction between wind turbines or wind farms and the power system. One problem is that no standardized model of wind turbines for power system stability studies is currently available. In response to this problem, generic dynamic models of wind turbines for stability studies are proposed in this thesis. Three wind turbine concepts are considered; fixed-speed wind turbines (FSWTs), doubly fed induction generator (DFIG) wind turbines and full converter wind turbines (FCWTs).The proposed models are developed for positive-sequence phasor time-domain dynamic simulations and are implemented in the standard power system simulation tool PSS/E with a 10 ms time step. Response accuracy of the proposed models is validated against detailed models and, in some cases, against field measurement data. A direct solution method is proposed for initializing a DFIG wind turbine model. A model of a dc-link braking resistor with limited energy capacity is proposed, thus a unified model of an FCWT for a power system stability analysis can be obtained.The results show that the proposed models are able to simulate wind turbine responses with sufficient accuracy. The generic models proposed in this thesis can be seen as a contribution to the ongoing discourse on standardized models of wind power generation for power system stability studies.Aggregated models of wind farms are studied. A single equivalent unit representation of a wind farm is found to be sufficient for most short-term voltage stability investigations. The results show that non-linearities due to maximum power tracking characteristics and saturation of electrical controllers play no important role in characterizing wind farm responses. For a medium-term study, which may include wind transport phenomena, a cluster representation of a wind farm provides a more realistic prediction.Different influencing factors in designing dynamic reactive power compensation for an offshore wind farm consisting of FSWTs are also investigated. The results show that fault ride-through capability of the individual turbines in the wind farm utilizing an active stall control significantly reduces the requirement for the dynamic reactive power compensation

Factors Influencing Design of Dynamic Reactive Power Compensation for an Offshore Wind Farm

This paper investigates factors that influence the design of dynamic reactive power compensation (DRPC) for an offshore wind farm consisting of fixed-speed wind turbines.Several influencing factors are considered including DRPC device types and locations, network strength, and fault ride-through (FRT) capability of individual wind turbines in the wind farm. The DRPC alternatives discussed in this paper comprise of a STATCOM and an SVC. It is found that the exclusion of wind turbine FRT capability results in too large DRPC size estimation. In the case of wind turbines equipped with FRT capability, it was found that the investment cost for both STATCOM and SVC options are comparable. The study also emphasizes the necessity of performing dynamic analysis to correctly design the size andlocation of the DRPC device

Aggregated Models of a Large Wind Farm Consisting of Variable Speed Wind Turbines for Power System Stability Studies

Abstract—The main purpose of this paper is to present aggregation methods of a large wind farm consisting of variable speed wind turbines. Doubly fed induction generator (DFIG) and full power converter wind turbine concepts are considered in this study. The investigation emphasizes on short-term voltage stability studies. Influences of unequal distribution of wind speed across the wind farm on the response accuracy of the aggregated models are investigated. Non-linearities due to maximum power tracking (MPT) characteristics of the wind turbines in the wind farm are also taken into account. The study concludes that a two-machine equivalent representation of a large wind farm is sufficient for short-term voltage stability investigations. This assumption remains valid even if power output discrepancies among the wind turbines are large

Comparison of Control Schemes of Wind Turbines with Doubly Fed Induction Generator

Validity of wind turbine model for power system stability studies has been important as the penetration of wind power generation in the power system increases significantly.Variable speed wind turbines with doubly fed induction generator (DFIG) are the most common technologies used in today’s wind power generation. So far, there is no agreement on generic model of this type of wind turbine. Different control schemes of wind turbine with DFIG have been presented in many publications. However, comparisons of the different control schemes and their influences on the stability study are rarely found in the papers. This paper investigates different control schemes implemented in wind turbine with DFIG for power stability studies, which include the speed/power controls and the pitch controls

Comparison of Control Schemes of Wind Turbines with Doubly Fed Induction Generator

Validity of wind turbine model for power system stability studies has been important as the penetration of wind power generation in the power system increases significantly.Variable speed wind turbines with doubly fed induction generator (DFIG) are the most common technologies used in today’s wind power generation. So far, there is no agreement on generic model of this type of wind turbine. Different control schemes of wind turbine with DFIG have been presented in many publications. However, comparisons of the different control schemes and their influences on the stability study are rarely found in the papers. This paper investigates different control schemes implemented in wind turbine with DFIG for power stability studies, which include the speed/power controls and the pitch controls

Aggregated Models of a Large Wind Farm Consisting of Variable Speed Wind Turbines for Power System Stability Studies

Abstract—The main purpose of this paper is to present aggregation methods of a large wind farm consisting of variable speed wind turbines. Doubly fed induction generator (DFIG) and full power converter wind turbine concepts are considered in this study. The investigation emphasizes on short-term voltage stability studies. Influences of unequal distribution of wind speed across the wind farm on the response accuracy of the aggregated models are investigated. Non-linearities due to maximum power tracking (MPT) characteristics of the wind turbines in the wind farm are also taken into account. The study concludes that a two-machine equivalent representation of a large wind farm is sufficient for short-term voltage stability investigations. This assumption remains valid even if power output discrepancies among the wind turbines are large

Dynamic Response of Grid-Connected Wind Turbine with Doubly Fed Induction Generator during Disturbances

The use of the Doubly-fed Induction Generator (DFIG) in large wind turbines (MW-class) is growing rapidly. In order to investigate the dynamic response of a wind turbine with DFIG connected to the power system during grid disturbance, a model has been developed. This model includes aerodynamics, the mechanical drive train, the induction generator as well as the control parts. The response of the system during grid disturbances is studied. An inclusion of saturation effect in the generator during faults is included as well