Fixed Speed Wind Turbine Research Articles

Analysis on Dgs Connection in a Developed Model of Doubly-Fed Wind Energy System

recent years, wind energy has become one of the most important and promising sources of renewable energy, which demands additional transmission capacity and better means of maintaining system reliability. The evolution of technology related to wind systems industry leaded to the development of a generation of variable speed wind turbines that present many advantages compared to the fixed speed wind turbines. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The stator of the generator is directly connected to the grid while the rotor is connected through a back-to-back converter which is dimensioned to stand only a fraction of the generator rated power. To harness the wind power efficiently the most reliable system in the present era is grid connected doubly fed induction generator. The rotor side converter (RSC) of DFIG usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The additional freedom of reactive power generation by the GSC is usually not used due to the fact that it is more preferable to do so using the RSC. However, within the available current capacity the GSC can be controlled to participate in reactive power generation in steady state as well as during low voltage periods. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. In this paper we focus on analysing a wind turbine system using MATLAB SimPower Systems. The machine used was a doubly fed induction generator (DFIG).As protection against short circuit transients, the crowbar protection was modelled. General terms: DFIG, Fault Ride Through, Grid.

Stability Augmentation of Wind Farm using Variable Speed Permanent Magnet Synchronous Generator

This paper presents a new control strategy of variable speed permanent magnet wind generator for stability augmentation of wind farm including fixed speed wind turbine with Induction Generator (IG). A new control scheme is developed for two levels back-to-back converters of Permanent Magnet Synchronous Generator (PMSG), by which both active and reactive powers delivered to the grid can be controlled easily. To avoid the converter damage, the DC link protection controller is also proposed in order to protect the dc link circuit during fault condition. To evaluate the control capability of the proposed controllers, simulations are performed on two model systems composed of wind farms connected to an infinite bus. From transient and steady state analyses by using PSCAD/EMTDC, it is concluded that the proposed control scheme is very effective to improve the stability of wind farm for severe network disturbance and randomly fluctuating wind speed.

Steady-state Solution of Fixed-speed Wind Turbines Following Fault Conditions Through Extrapolation to the Limit Cycle

A methodology to efficiently calculate the steady-state solution of fixed-speed induction generator (FSIG) based wind turbines, using a Newton algorithm and a Numerical Differentiation (ND) process for the extrapolation to the limit cycle is presented. This approach can be extremely useful in the development of steady-state studies of modern large-scale power systems with significant share of wind power based on FSIGs. A conventional Brute Force (BF) procedure is applied for comparison purposes to demonstrate the efficiency of the proposed methodology. The study involves the starting sequence of wind turbines and also the transient behavior of a single wind turbine after a disturbance. The simulations are conducted using a modeling platform developed by the authors to analyze power networks with high penetration of renewable sources.

Simultaneous STATCOM and Pitch Angle Control for Improved LVRT Capability of Fixed-Speed Wind Turbines

A robust multivariable controller with the objective of enhancing the low-voltage ride-through (LVRT) capability of wind farms with fixed-speed induction generators is presented in this paper. The nonlinear dynamics of the wind generator is represented as a linear system and a norm-bounded nonlinear uncertain term, derived from the Cauchy remainder of the Taylor series. The designed robust controller provides acceptable postfault performance for both small and large perturbations. Large disturbance simulations demonstrate that the designed controller enhances voltage stability as well as transient stability of the system during low-voltage ride-through transients and thus enhances the LVRT capability of fixed-speed wind generators.

Wind energy conversion with a variable-ratio gearbox: design and analysis

Variable-speed wind turbines are able to adapt to low wind speeds and therefore have greater efficiency than fixed-speed turbines during partial-load operation. Unfortunately, the high cost and low reliability of the electronics that enable variation in speed have discouraged this mode of operation for distributed wind turbines. Alternatively, a Variable-Ratio Gearbox (VRG) can be integrated into the fixed-speed wind turbine to facilitate operation with a discrete set of variable speeds that boost efficiency. The VRG concept is based upon mature technology taken from the automotive industry and is characterized by low cost and high reliability. In this paper, a model-based design methodology is introduced to study the performance gain of integrating a VRG into a fixed-speed stall-regulated wind turbine system. The results demonstrate how this device can improve the efficiency of the fixed-speed turbine in the partial-load region and the potential to use the VRG to limit power in the full-load region where pitch control is often used.

Design of an AC-DC-AC converter for wind turbines

In this study, a Simulink simulation is realized for a converter system that is located between fixed-speed wind turbine and grid. The 3-phase output voltage has been modelled as a squirrel cage induction generator output as being the most widely used generator type in wind turbines. The output line voltages of wind turbine has been converted to DC using a 12-pulse uncontrolled rectifier, and applied to the inverter that is controlled using sinusoidal pulse width modulation. The DC-AC conversion using three-level SPWM controlled inverter has been realized in this study, which is performed using Matlab/Simulink. The output harmonics of the designed converter system, which is based on a 10 kW wind turbine, have been minimized adjusting the values such as modulation index (mi) and switching frequency (fsw). The THD ratio of line currents has been decreased to 0.03% at the inverter output, while it was 8.38% at the turbine output. The minimum THD ratios of harmonic analysis are 0.03% for line-to-line currents and 1.11% for line-to-line voltages. The measured THD ratios are proper to IEEE-519 standards. Using a controlled rectifier will minimize the harmonic contents for the designed and analyzed system. Copyright © 2010 John Wiley & Sons, Ltd.

Investigation of maximum wind power extraction using adaptive virtual lookup-table approach

With the advance of power electronic technology, direct-driven permanent magnet synchronous generators (PMSG) have increasingly drawn interests to wind turbine manufacturers. Unlike a fixed-speed wind turbine, the maximum power extraction of a PMSG wind turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction strategies. In an environment integrating all the three characteristics, it is found in this paper that the existing commercial lookup-table maximum power extraction mechanism suitable to a DFIG wind turbine is not suitable to a PMSG wind turbine. Through the integrative study of all the three characteristics, this paper proposes a novel PMSG maximum power extraction design. The special features of the proposed strategy include (i) an adaptive virtual lookup-table approach for PMSG maximum power extraction and (ii) an implementation of the peak power-tracking scheme based on a novel direct-current vector control configuration. The proposed maximum power extraction mechanism with a nested speed- and current-loop control structure is built by using MatLab SimPowerSystems. Simulation studies demonstrate that the proposed PMSG peak power-tracking strategy has superior performance in various aspects under both stable and gust wind conditions. Copyright © 2010 John Wiley & Sons, Ltd.

Wind generator annual energy output estimation considering grid voltage and frequency variations

At present the energy output, for different types of wind turbine generating units (WTGUs), is estimated from either the wind turbine mechanical power output or from its power curve. The power curve of a wind turbine is a graph that gives the power output of the turbine at various wind speeds over which the turbine operates which is generally provided by the manufacturer. The energy output estimated considering the mechanical power output neglects generator efficiency. Although the energy output computed using the electric power output considers the generator efficiency, this method does not take into account the effect of grid voltage and frequency variations on the wind turbine generator efficiency. This paper proposes a method for computing the energy output of the fixed speed wind turbine considering the grid voltage and frequency variations. In this method, the annual wind speed and frequency distribution or their variations are quantized into equal/unequal intervals. The total annual energy output is then estimated by computing the power output of the wind turbine generator for a given average wind speed and frequency. Copyright © 2010 John Wiley & Sons, Ltd.

Doubly Fed Induction Generator Maximum Wind Power Extraction Study Through Integrated Steady-state and Close-loop Control Evaluation

A doubly fed induction generator wind turbine is a variable-speed wind turbine widely used in the modern wind power industry. Unlike a fixed-speed wind turbine, the maximum power extraction of the turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction control strategies. This article presents a doubly fed induction generator maximum power extraction study through the integrated steady-state and transient close-loop control evaluation approach so as to benefit the development of enhanced peak power tracking control techniques for variable-speed wind turbines. The generator characteristics are examined for different d-q control conditions; the peak power tracking and extracted wind power characteristics of the turbine blades versus generator slip are presented. Then, all three characteristics are analyzed in a joint environment to investigate doubly fed induction generator maximum power extraction principles. A nested current- and speed-loop control structure is developed using the stator-flux-oriented frame, which is then used to evaluate factors that may affect doubly fed induction generator peak power tracking control performance. Simulation studies are conducted to investigate how doubly fed induction generator maximum power extraction is influenced by wind turbine electrical and aerodynamic characteristics, different peak power tracking control designs, and variable and gusting winds.

Steady-state solution of fixed-speed wind turbines following fault conditions through extrapolation to the limit cycle

A methodology to efficiently calculate the steady-state solution of fixed-speed induction generator (FSIG) based wind turbines, using a Newton algorithm and a Numerical Differentiation (ND) process for the extrapolation to the limit cycle is presented. This approach can be extremely useful in the development of steady-state studies of modern large-scale power systems with significant share of wind power based on FSIGs. A conventional Brute Force (BF) procedure is applied for comparison purposes to demonstrate the efficiency of the proposed methodology. The study involves the starting sequence of wind turbines and also the transient behavior of a single wind turbine after a disturbance. The simulations are conducted using a modeling platform developed by the authors to analyze power networks with high penetration of renewable sources.

Quasi-Steady-State Analysis on the Effect of the STATCOM on FRT Performance of Fixed Speed Wind Turbines

This paper analyzes the effect of the STATCOM on the improvement of the Fault Ride Through (FRT) capability of the fixed speed wind turbines(FSWTs). The steady-state models of the wind farm components, such as induction generator, capacitor bank, and the STATCOM, are developed based on the simplified equivalent circuit. Especially, the STATCOM is modeled as a controllable current source and a method that analytically determines the magnitude of the injection current is developed. For the quasi-steady-state(QSS) analysis, the steady-state model of the generator and STATCOM are merged with the dynamic model of drive train. The QSS simulation with the STATCOM shows that the STATCOM can enhance the FRT performance by improving the characteristics of the FSWTs.

Added Value of Power Control in Improving the Integration of Wind Turbines in Weak Grid Conditions

For economical reasons, wind turbine systems must be located in favourable sites generating a higher pro- ductivity. These are often located in areas with weak electric grid infrastructures. The constraints related to this type of grids limit the penetration levels of wind energy. These constraints are mainly related to power quality in the grid as well as the economical aspects of the project. In this study, we take into account the slow voltage variations and the flicker phenomenon. The models used are based on the development of a set of relations derived from engineering knowledge related to both technical and economical points of view. The maximal penetration level of a fixed speed wind turbine system is determined for a given grid. The power control has been investigated to improve wind turbine system integration. Obtained results show the necessity to adapt technological choices to the requirements of weaker grids. Penetration levels and wind turbine cost may be greatly improved using variable speed systems.

Dynamic behavior and transient stability analysis of fixed speed wind turbines

This paper analytically investigates the dynamic behavior of fixed speed wind turbines (FSWTs) under wind speed fluctuations and system disturbances, and identifies the nature of transient instability and system variables involved in the instability. The nature of transient instability in FSWT is not similar to synchronous generators in which the cause of instability is rotor angle instability. In this paper, the study of dynamic behavior includes modal and sensitivity analysis, dynamic behavior analysis under wind speed fluctuation, eigenvalue tracking, and using it to characterize the instability mode, and investigating possible outcomes of instability. The results of theoretical studies are verified by time domain simulations. It is found that the instability occurs due to the mechanical dynamics and the instability is closely related to increasing of generator slip.

Modelling and control of variable speed wind turbines for power system studies

AbstractModern wind turbines are predominantly variable speed wind turbines with power electronic interface. Emphasis in this paper is therefore on the modelling and control issues of these wind turbine concepts and especially on their impact on the power system. The models and control are developed and implemented in the power system simulation tool DIgSILENT. Important issues like the fault ride‐through and grid support capabilities of these wind turbine concepts are addressed. The paper reveals that advanced control of variable speed wind turbines can improve power system stability. Finally, it will be shown in the paper that wind parks consisting of variable speed wind turbines can help nearby connected fixed speed wind turbines to ride‐through grid faults. Copyright © 2009 John Wiley & Sons, Ltd.

Análise de estabilidade de geradores de indução utilizados em turbinas eólicas de velocidade fixa

Neste trabalho, analisa-se o desempenho dinâmico de dois métodos para melhorar a estabilidade de turbinas eólicas de velocidade fixa, equipadas com geradores de indução, conectadas em redes de distribuição de energia elétrica, durante contingências no sistema elétrico. O primeiro método se baseia na compensação dinâmica de potência reativa, para o qual foram utilizadas duas tecnologias: compensação via SVC (Static Var Compensator) e compensação via DSTATCOM (Distribution Static Synchronous Compensator). O segundo se baseia no controle de ângulo de passo das hélices das turbinas eólicas. O desempenho desses geradores durante curtos-circuitos trifásicos é analisado para se verificar o impacto do uso de diferentes sinais de controle nos dispositivos eletrônicos e mecânicos. De forma geral, os dispositivos de compensação dinâmica tiveram melhor desempenho quando controlados por tensão terminal, e os mecânicos, utilizando a velocidade do rotor ou uma combinação de sinais (tensão terminal e potência elétrica).

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 and location of the DRPC device.

Low voltage ride through capability enhancement of wind turbine generator system during network disturbance

The energy capacitor system (ECS), composed of power electronic devices and electric double layer capacitor to enhance the low voltage ride through (LVRT) capability of fixed speed wind turbine generator system (WTGS) during network disturbance, is discussed. Control scheme of ECS is based on a sinusoidal pulse width modulation voltage source converter and DC–DC buck/boost converter composed of insulated gate bipolar transistors. Two-mass drive train model of WTGS is adopted because the drive train system modelling has great influence on the characteristics of wind generator system during network fault. Extensive analysis of symmetrical fault is performed with different voltage dip magnitudes and different time durations. Permanent fault because of unsuccessful reclosing is also analysed, which is one of the salient features of this study. A real grid code defined in the power system is considered and LVRT characteristic of WTGS is analysed. Finally, it is concluded that ECS (20 MW) can significantly enhance the LVRT capability of grid connected WTGS (50 MW) during network disturbance, where simulations have been carried out by using PSCAD/EMTDC.

Response of Fixed Speed Wind Turbines to System Frequency Disturbances

This paper analyzes the impact of system frequency variations on the steady-state operation point of fixed speed induction generators used in wind turbine generation systems (WTGS). An analytic method to predict the values of angular speed, torque and current during and after a frequency disturbance is presented. The proposed method as well permits to establish the operation limits in order to keep the WTGS connected during frequency variations and therefore to adjust protection relay settings.

Integration of space vector pulse width modulation controlled STATCOM with wind farm connected to multimachine power system

In this work, dynamic and transient characteristics of a multimachine power system connected with two wind farms composed of fixed speed wind turbine generator systems (WTGS) are analyzed. At each wind farm the terminal one space vector pulse width modulation controlled voltage source converter based static synchronous compensator (STATCOM) is considered to be connected. The capacitor bank capacity of fixed speed wind generator is reduced by certain percentages when a STATCOM is integrated at a wind farm terminal. As wind speed is always fluctuating, the terminal voltage of a fixed speed wind generator also fluctuates randomly, which has an adverse effect on the rest of the power system. It is reported that the STATCOM with a reduced capacitor bank can decrease the voltage fluctuations of the multimachine power system as well as wind generator terminals. Moreover, it is shown that a STATCOM can also enhance the transient stability of induction and synchronous generators when a network disturbance occurs in the power system. Since shaft system modeling of a wind turbine has a significant effect on the transient stability analysis of WTGS, a two-mass shaft model is adopted in this study. Both of the symmetrical and the unsymmetrical faults are analyzed in light of the real wind farm grid code. The transient performance of a STATCOM on the network is evaluated by the transient stability index based on the total kinetic energy of generators. For dynamic performance evaluation, real wind speed data are used in the simulation. Finally, it is concluded that the STATCOM can enhance both dynamic and transient stability of wind farms connected with a multimachine power system.

Control Algorithm for Coordinated Reactive Power Compensation in a Wind Park

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The penetration level of wind energy is continuously growing, and it is especially relevant in European countries such as Denmark, Germany, and Spain. For this reason, grid codes in different countries have been recently revised, or are now under revision in order to integrate this energy in the network taking into account the security of supply. This paper is related to reactive compensation, which is one aspect usually included in these codes. On the other hand, a great number of installed wind parks are formed by fixed speed wind turbines equipped with induction generators. The typical scheme for reactive compensation in this kind of wind parks is based on capacitor banks locally controlled in each machine. This configuration makes very difficult to follow the requirements of the new grid codes. To overcome this problem, a configuration with a central controller that coordinates the actuation over all the capacitor steps in the wind park is proposed in this paper. A central controller algorithm that is based on a dynamic programming is presented and evaluated by means of simulation. At this time, the proposed scheme has been installed at the Sotavento Experimental Wind Park (Spain) and it is currently being tested. </para>