Induction Generator Wind Turbine Research Articles

Electrical Discharge and Its Impact on Drivetrains of Wind Turbines

Defects in drivetrains of wind turbines are typically very costly due to the difficulty in accessing the defective components for repair and maintenance. Electrical discharge has been identified as one of the key root causes to defects in wind drivetrains. Improving the reliability of key wind turbine components has been attracting a great research interest since the launch of the first wind turbine. In this paper, a study to understand the electrical discharge and its impact on wind drivetrains is presented. The root cause of electrical discharge in wind turbines is discussed. A field test is carried out on 1.5-MW doubly fed induction generator wind turbines in practical environments. Suggestions are provided on the design of the wind turbine grounding and protection system to improve turbine reliability and reduce defect rates due to electrical discharge.

Maximum Energy Output of a DFIG Wind Turbine Using an Improved MPPT-Curve Method

A new method is proposed for obtaining the maximum power output of a doubly-fed induction generator (DFIG) wind turbine to control the rotor- and grid-side converters. The efficiency of maximum power point tracking that is obtained by the proposed method is theoretically guaranteed under assumptions that represent physical conditions. Several control parameters may be adjusted to ensure the quality of control performance. In particular, a DFIG state-space model and a control technique based on the Lyapunov function are adopted to derive the control method. The effectiveness of the proposed method is verified via numerical simulations of a 1.5-MW DFIG wind turbine using MATLAB/Simulink. The simulation results show that when the proposed method is used, the wind turbine is capable of properly tracking the optimal operation point; furthermore, the generator’s available energy output is higher when the proposed method is used than it is when the conventional method is used instead.

Reduced Cost of Reactive Power in Doubly Fed Induction Generator Wind Turbine System With Optimized Grid Filter

The modern grid requirement has caused that the wind power system behaves more like conventional rotating generators, and it is able to support certain amount of the reactive power. For a typical doubly fed induction generator (DFIG) wind turbine system, the reactive power can be supported either through the rotor-side converter or the grid-side converter. This paper first compares the current ripples and supportive reactive power ranges between the conventional L and optimized LCL filter, if the reactive power is injected from the grid-side converter. Then, the loss distribution is evaluated both for the generator and the wind power converter in terms of the reactive power done by the rotor-side converter or the grid-side converter with various grid filters. Afterward, the annual energy loss is also estimated based on yearly wind profile. Finally, experimental results of the loss distribution are performed in a down-scaled DFIG system. It is concluded that overexcited reactive power injected from the grid-side converter has lower energy loss per year compared to the overexcited reactive power covered by the rotor-side converter. Furthermore, it is also found that the annual energy loss could even become lower with the optimized filter and thereby more energy production for the wind turbine.

Symmetrical and asymmetrical low‐voltage ride through of doubly‐fed induction generator wind turbines using gate controlled series capacitor

This study proposes a new method to improve low-voltage ride through of the doubly-fed induction generator (DFIG) wind turbines (WTs) using gate-controlled series capacitor (GCSC) in series with the generator rotor. Using GCSC, as soon as a voltage dip occurs at the generator's terminals, the GCSC inserts its capacitor in series with the rotor, increasing the voltage seen by the rotor winding. Consequently, the rotor over-current is limited and transmission of the inrush energy to the rotor side converter is reduced. Moreover, by this method, the chopper is not required for protecting the DC-link capacitor. Unlike the Crowbar method, which control of the generator is lost during the fault, the proposed method in this study avoids the loss of control during the grid faults. To validate the effectiveness of the proposed method, extensive time-domain simulation is performed using MATLAB/SIMULINK on a 1.5 MW DFIG-based WT.

Performance of LR-type solid-state fault current limiter in improving power quality and transient stability of power network with wind turbine generators

Distributed generations (DGs) are predicted to perform an increasing role in the future power system. Expose of DGs can change the fault current during a grid disturbance and disturb the existing distribution system protection. Solid-state fault current limiters (SSFCLs) can provide a quick system protection during severe faults and are expected to advance the reliability and stability of the power system. SSFCLs are categorized into R- (resistive) and L- (inductive) types by the fault current limiting impedance. An L-type SSFCL is more effective in suppressing the voltage drop during faults. On the other hand, an R-type SSFCL is more effective in consuming the acceleration energy of generators during faults. Therefore, applying both functions lead to the improvement of the power quality and transient stability of the power system. This paper aims to investigate the performance of an inductive–resistive-type solid state fault current limiter (SSFCL-LR) that captures the features and advantages of inductive SSFCLs (SSFCL-Ls) and resistive SSFCLs (SSFCL-Rs) on an electric power network with the doubly-fed induction generator wind-turbine (DFIG-WT), which is a representative renewable energy source. Its connection to a power network simply increases the short-circuit current during a fault toward its maximum nominal level, which is closer to the rating of the circuit breaker, when compared to the case without the DFIG-WT system. This can aggravate the reliability of the overall power system. Detailed laboratory experiments and simulations are performed to demonstrate the capability of SSFCL-LR in simultaneously controlling the fault current, improving the power quality and enhancing the transient stability of the IEEE benchmark four-machine two-area system with induction generator wind turbines (IG-WT) and DFIG-WTs. PSCAD/EMTDC was used in order to analyze the power system characteristics of the SSFCL-LR unit.

Robust Control of Doubly Fed Induction Generator for Wind Turbine Under Sub-synchronous Operation Mode

This paper presents a modeling and a robust control of doubly fed induction generator for wind generation system. The whole system is presented in d-q-synchronous reference frame. The regulation of the electromagnetic torque, stator reactive power control and neuronal controller are applied in order to control the rotor currents of the DFIG. For to improve the controller robustness, the study is validated through simulation using software Matlab/Simulink, studies on a 1.5 MW DFIG wind generation system compared with conventional proportional integral controller. Performance and robustness results obtained will be presented and analyzed.

A Comparison of PI vs LPV Controllers for a Doubly-Fed Induction Generator in a Microgrid

State-space controllers have been central to modern control theory and are often preferred over classical controllers such as PI and lag-lead controllers. This is because they offer flexibility in design, such as being able to simultaneously incorporate performance and robustness requirements, and have a solid mathematical foundation. Recently, doubly-fed induction generators (DFIGs) for wind turbines have been modeled as linear parameter varying (LPV) systems, a special class of time-varying linear state-space systems, for which LPV state-space controllers can be designed. The LPV controllers have been introduced for DFIG mainly because of their novelty and that they can offer the typical advantages that come with state-space controllers. However, no comparison has yet been made regarding the control performance of LPV controllers versus more traditional PI controllers for DFIGs. In this paper, LPV controllers have been designed using linear matrix inequality (LMI) techniques and their performance is compared to PI controllers via simulation studies on a DFIG in a microgrid. Our study shows that if a mathematical model represents the DFIG accurately, then both controllers can be tuned to give comparable performance.

Improving Transient Stability in a Grid-Connected Squirrel-Cage Induction Generator Wind Turbine System Using a Fuzzy Logic Controller

A common problem in wind power plants involves fixed-speed wind turbines. In fact, being equipped with a squirrel-cage induction generator (SCIG), they tend to drain a relevant amount of reactive power from the grid, potentially causing voltage drops and possible voltage instability. To improve SCIG power quality and transient stability, this paper investigates a new control strategy for pitch angle control based on proportional-integral (PI) controller and a fuzzy logic controller (FLC), considering both normal and fault ride-through (FRT) schemes. In the literature, often, the mechanical torque output is assumed constant for a specific wind speed. This might not be accurate, because the mechanical torque-speed typical of a wind turbine depends also on the power coefficient or pitch angle. In this paper, an analytic model of transient stability is proposed using the equivalent circuit of the SCIG and using the concepts of stable and unstable electrical-mechanical equilibrium. The method has been evaluated by comparing the results obtained by the analytic method with the dynamic simulation. The results show that the proposed hybrid controller is effective at smoothing the output power and complying with FRT requirements for SCIG in the power system.

A novel MPPT method for enhancing energy conversion efficiency taking power smoothing into account

With the increasing capacity of wind energy conversion system (WECS), the rotational inertia of wind turbine is becoming larger. And the efficiency of energy conversion is significantly reduced by the large inertia. This paper proposes a novel maximum power point tracking (MPPT) method to enhance the efficiency of energy conversion for large-scale wind turbine. Since improving the efficiency may increase the fluctuations of output power, power smoothing is considered as the second control objective. A T-S fuzzy inference system (FIS) is adapted to reduce the fluctuations according to the volatility of wind speed and accelerated rotor speed by regulating the compensation gain. To verify the effectiveness, stability and good dynamic performance of the new method, mechanism analyses, small signal analyses, and simulation studies are carried out based on doubly-fed induction generator (DFIG) wind turbine, respectively. Study results show that both the response speed and the efficiency of proposed method are increased. In addition, the extra fluctuations of output power caused by the high efficiency are reduced effectively by the proposed method with FIS.

Adaptive Control With Reference Model of a Doubly Fed Induction Generator for Wind Turbine with Sliding Mode

Adaptive Control With Reference Model of a Doubly Fed Induction Generator for Wind Turbine with Sliding Mode

Optimal design of power system stabilizer for power systems including doubly fed induction generator wind turbines

This paper presents an evolutionary algorithm-based approach for optimal design of power system stabilizer (PSS) for multi-machine power systems that include doubly fed induction generator wind turbines. The proposed evolutionary algorithm is an improved particle swarm optimization named chaotic particle swarm optimization with passive congregation (CPSO-PC) applied for finding the optimal settings of PSS parameters. Two different eigenvalue-based objectives are combined as the objective function for the optimization problem of tuning PSS parameters. The first objective function comprises the damping factor of lightly damped electro-mechanical modes and the second one includes the damping ratio of these modes. The effectiveness of the proposed method to design PSS for the power systems including DFIG (Doubly Fed Induction Generator) is extensively demonstrated through eigenvalue analysis and time-domain simulations and also by comparing its simulation results with the results of other heuristic optimization approaches.

Discrete Fourier series-based dual-sequence decomposition control of doubly-fed induction generator wind turbine under unbalanced grid conditions

The doubly fed induction generator (DFIG) wind turbines (WTs) are widely installed as distributed generation utilities but their reliability is vulnerable to the grid disturbance, causing the second harmonics and associated low-frequency oscillations. This paper proposes a novel DFS-based dual-sequence decomposition control to mitigate the fatal oscillations and improve the DFIG's low-voltage ride-through (LVRT) capability under unbalanced grid conditions. The controller saturation phenomena under unbalanced conditions are first investigated. To overcome such saturation problem and its resultant oscillations, the positive and negative sequences are extracted by a fast sequence decomposition method using Discrete Fourier Series (DFS), irrespective of the operation being sub- or super-synchronous. A dual-loop control is integrated with the proposed sequence decomposition, using power balance for the minimization of the harmful torque pulsation and DC-link voltage fluctuation. In order to support the grid voltage during LVRT, an advanced reactive power control is further developed to capture more reactive power headroom by abandoning the active power generation with the mandatory absorption of the kinetic energy. Simulation results for a 9 MW DFIG WT system validate the effectiveness of the DFS-based dual-sequence decomposition design with the advanced reactive power control, demonstrating its mitigation of oscillations, and improvement of the LVRT capability to support the power grid.

Power System Oscillations Damping by Robust Decentralized DFIG Wind Turbines

This paper proposes a new robust decentralized power oscillation dampers (POD) design of doubly-fed induction generator (DFIG) wind turbine for damping of low frequency electromechanical oscillations in an interconnected power system. The POD structure is based on the practical 2 nd -order lead/lag compensator with single input. Without exact mathematical model, the inverse output multiplicative perturbation is applied to represent system uncertainties such as system parameters variation, various loading conditions etc. The parameters optimization of decentralized PODs is carried out so that the stabilizing performance and robust stability margin against system uncertainties are guaranteed. The improved firefly algorithm is applied to tune the optimal POD parameters automatically. Simulation study in two-area four-machine interconnected system shows that the proposed robust POD is much superior to the conventional POD in terms of stabilizing effect and robustness.

Fuzzy sliding mode control applied to a doubly fed induction generator for wind turbines

In this paper an indirect vector control using fuzzy sliding mode control is proposed for a double-fed induction generator (DFIG), applied for a wind energy conversion system in variable speed. The objective is to independently control the active and reactive power generated by the DFIG, which is decoupled by the orientation of the ux. The sliding mode controlnds its strongest justication for the problem concerning the use of a robust nonlinear control law for the model uncertainties. As far as the fuzzy mode control is concerned, it aims at reducing the chattering effect. The obtained results show the increasing interest of such control in this system

Dynamic Control of a DFIG Wind Farm Enhancing the Fault Ride-Through Capability

This study was interested in the control of a wind farm equipped with three doubly fed induction generator (DFIG) wind turbines. This wind power generation station was connected to the electrical grid which was subjected to different levels of symmetrical voltage sags. An advanced control strategy was designed in order to avoid the electrical problems which appear during this type of fault. The main purpose of this work was to enhance the fault ride-through capability for the DFIG wind turbine. Simulation results were presented to demonstrate the effectiveness of the proposed control method. Moreover, this approach presents attractive features compared to the conventional used strategies.

Sub-Synchronous Interaction Damping Control for DFIG Wind Turbines

This paper presents a damping control to mitigate sub-synchronous interactions (SSI) in doubly-fed induction generator (DFIG) wind turbines connected to series-compensated lines. This issue has gained attention due to the recent SSI phenomena reported in DFIG wind farms located near series capacitors. Two approaches which add a supplementary damping control signal are compared: one of them, integrated to the grid-side converter, and the other one, to the rotor-side converter. The SSI damping controls are designed using a multi-input multi-output state-space methodology. This allows to easily tune a high performance controller using several measurements and control inputs. Small- and large-signal stability analyses, robustness aspects, impact of the supplementary controls on the system modes, and influence of different operating conditions on the SSI are also discussed. The obtained results show that the supplementary control is able to properly damp the sub-synchronous oscillations of DFIG wind turbines by updating the existing DFIG control systems without the inclusion of expensive additional damping devices, and reducing the risk of wind generation tripping.

Modeling and Fault Analysis of Doubly Fed Induction Generators for Gansu Wind Farm Application

Wind power is developing rapidly as a means of handling the world's energy shortage and associated environmental problems. The Gansu provincial wind energy resources have around 237-GW wind power potential in China. In this paper, a study on key technologies of Hexi 750-kV power transmission line protections has been carried out. The project includes some characteristics, such as large-scale wind power, long-distance EHV lines, and so on. We used 49.5-MW doubly fed induction generator (DFIG) wind turbines in this project and different situations when a fault occurs in the presence of DFIG are studied and investigated. By the aid of stator-flux-oriented vector strategy, the system is modeled in PSCAD/EMTDC software on the basis of the real information from the wind farm site. The fault analysis is studied while the fault location is changed and the crowbar protection is ON/OFF. The data and information have been obtained by field experience of the wind farm in Gansu province. Also, the matrix pencil algorithm has been applied as a novel method in this project. This analysis can ease the protection issues and push the schedule to the next steps. With these results, we are able to adapt our system with smart grids and provide some novel methods to stabilize and control the wind farm.

Optimal Superconducting Coil Integrated Into DFIG Wind Turbine for Fault Ride Through Capability Enhancement and Output Power Fluctuation Suppression

The vital problems of the grid-connected doubly fed induction generator (DFIG) wind turbine are the fault ride through (FRT) capability and the output power fluctuation. To tackle these problems, this paper focuses on the optimization of the superconducting coil (SC) integrated into a dc link of the DFIG wind turbine for an enhancement of the FRT capability and a suppression of the output power fluctuation. The dcdc converter, which is used to control the exchanged energy between the SC and the system, is additionally connected between the grid side converter (GSC) and the rotor side converter. During normal operation, the SC acts as an energy storage device to exchange energy with the system so that the power fluctuation of the DFIG wind turbine can be alleviated. On the other hand, when severe faults occur in the system, the SC is used as the current limiting inductor to suppress both overcurrent in the rotor and stator, and overvoltage in the dc link of the DFIG. In the optimization, the inductance of the SC, the initial necessary stored energy in the SC, and the proportional integral (PI) parameters of the dcdc converter are tuned simultaneously so that both objectives can be achieved. Simulation study elucidates the control effect of the DFIG wind turbine with the optimal SC.

Modelación, Simulación y Control de Aerogeneradores con Generador de Inducción Doblemente Alimentado Utilizando Matlab

En este trabajo se presenta la modelación de los componentes aerodinámicos, mecánicos, eléctricos y de control del aerogenerador con generador de inducción doblemente alimentado (DFIG). La modelación es empleada para crear un programa en el software Matlab. Se utiliza el método de Runge Kutta de cuarto orden para solucionar las ecuaciones diferenciales existentes en la modelación. La estrategia de control del convertidor PWM bidireccional se base en la técnica de control vectorial que emplea marcos de referencia giratorios, la cual permite el control de las potencias activa y reactiva producidas por el DFIG. Se describe el proceso de inicialización del sistema aerogenerador con DFIG, para obtener las condiciones de estado estable antes de iniciar la simulación. Se analiza el comportamiento del aerogenerador con DFIG ante cambios de la velocidad del viento y fallas de corto circuito. Los resultados finales muestran que la potencia activa del DFIG varía de acuerdo al comportamiento de la velocidad del viento, mientras que la potencia reactiva permanece casi invariante. Los resultados obtenidos son comparados con los resultados del modelo del aerogenerador con DFIG existente en Simulink de Matlab.

Minimising losses of SEIG using constrained particle swarm optimisation considering voltage regulation

Induction generators are widely used in various applications since they offer distinct advantages over conventional synchronous machines, like a simplified design, installation at lower capital cost and substantial savings in operation and maintenance expenses. The wind turbine induction generator systems are proposed to supply isolated loads under widely varying conditions. These conditions are the wind speed and load variations. Under these varying conditions, there will be some changes in the terminal generated voltage. The terminal voltage can be regulated by adapting the value of excitation capacitance required for the induction generator. This paper presents a constrained particle swarm optimisation technique for minimising the power losses of self–excited induction generator with terminal voltage control under operating conditions by selecting the suitable capacitance required for generator excitation. Testing of the proposed technique over conventional particle swarm optimisation technique is performed. Results signify the supremacy of the proposed technique over conventional particle swarm optimisation technique.