Induction Generator Wind Turbine System Research Articles

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.

Data‐driven modelling of a doubly fed induction generator wind turbine system based on neural networks

In a wind power system, the wind turbine captures wind energy and converts it into electric energy through a coupled rotating generator. This renewable energy conversion system usually consists of a wind turbine, rotor, gearbox and mostly a doubly fed induction generator (DFIG). It is a complex non-linear multi-input multi-output system with many uncertain factors. Meanwhile, the dynamics of the system is quite dependent on the wind velocity. Traditional analytical methods are quite difficult to model such a complex system. The recently developed data-driven method can be a suitable modelling technique for such system. Using a large amount of input–output on-line measurement data from the selected months, neural networks and neuro-fuzzy networks are fully utilised to model the DFIG. Detailed analysis and comparisons with the classical system identification techniques are addressed to show the advantages of the data-driven DFIG modelling approach.

Transient Stability Study of a Reality 500kV Power System Using Statcom

Many of papers refers to study of application for Flexible Alternative Current transmission Systems (FACTS). Especially for using reactive compensators for 500kV power system in order to increase the static voltage stability margin and transient stability enhancement have considered. This paper presents a simulation model of the Static Synchronous Compensator (STATCOM) is developed to study its dynamic characteristics. The developed STATCOM is connected at the Point of Common Coupling (PCC) of the Doubly Fed Induction Generator (DFIG) wind turbine system connected to the weak distribution grid for steady state and dynamic voltage regulation purpose. The purpose of this paper is to solve the above problems in order to suggest a solution of the appropriate shunt compensator for a reality 500KV power system. Simulation results have shown that STATCOM helps to keep the steady state terminal voltage of the DFIG system to its rated voltage during the entire operation region of the DFIG. STATCOM maintains the fast voltage regulation (or voltage restoration) at the PCC during step change in reactive load causing voltage swelling or sagging. STATCOM does this by dynamically exchanging the reactive power with the power grid. The results of this work are of certain practical significance and applicable value.

Coordinated controller design of grid connected DFIG based wind turbine using response surface methodology and NSGA II

This paper presents a novel design procedure for the coordinated tuning of rotor side converter (RSC) and grid side converter (GSC) controllers of doubly fed induction generator (DFIG) wind turbine system. The RSC and GSC controller parameters are determined by simultaneously optimizing the controller performance indices. The performance indices considered are maximum peak overshoot (MPOSω), settling time (Tssω) of the generator speed and the maximum peak overshoot (MPOSVdc), maximum peak undershoot (MPUSVdc) and settling time (TssVdc) of DC link voltage. The coordinated controller design is carried out in two steps. First step is to arrive at the analytical expression that relates the performance indices and the controller parameters. This is achieved using response surface methodology (RSM) thereby saving significant computational time. In the second step the determination of controller parameters is posed as a constrained multiobjective optimization problem. The constrained multiobjective optimization problem is solved using NSGAII (nondominated sorting genetic algorithm II). The proposed methodology is tested on a sample system with DFIG based WECS. Simulation results demonstrate the effectiveness of the proposed methodology.

Maximum Output Power Tracking Control in Variable-Speed Wind Turbine Systems Considering Rotor Inertial Power

This paper proposes a new maximum power point tracking (MPPT) algorithm for variable-speed wind turbine systems, which takes advantage of the rotor inertia power. In this method, a proportional controller is added to the power control to effectively reduce the moment of inertia of the wind turbines, which can improve the fast performance of the MPPT control. The PSIM simulation and experimental results for a doubly-fed induction generator wind turbine system have proved the validity of the proposed algorithm.

Nonlinear model predictive controller with state observer for speed sensorless induction generator–wind turbine systems

In this article, the problem of tracking control for variable speed induction generator–wind energy conversion system is investigated using nonlinear predictive control. A rotor speed predictive control algorithm has been designed to control the angular speed of the machine in order to allow the wind energy conversion system to operate with maximum power extraction. The generator torque and uncertainties are estimated and injected into the control law to improve the tracking performance. Control action is carried out assuming that all the states are known by measurement. Then, a state observer is implemented and Lyapunov method is used to prove the global stability of the complete continuous control scheme. Simulation is carried out to verify the performance of the proposed control system.

Stator Current Harmonic Control With Resonant Controller for Doubly Fed Induction Generator

Voltage harmonics in the grid can introduce stator current harmonics in a doubly fed induction generator (DFIG) wind turbine system, which may potentially impact the generated power quality. Therefore, wind turbine current controllers need to be designed to eliminate the impact of grid voltage harmonics, especially low-order harmonics. This paper proposes a stator current harmonic suppression method using a sixth-order resonant controller to eliminate negative sequence fifth- and positive sequence seventh-order current harmonics. A stator current harmonic control loop is added to the conventional rotor current control loop for harmonic suppression. The overall control scheme is implemented in dq frame. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, an analysis of the steady-state error, and the dynamic performance, are discussed in this paper. Taking these effects into account, the parameters of the resonant controller can be designed and effectively damp the influence from the grid voltage harmonics. As a result, the impacts of the negative sequence fifth- and positive sequence seventh-order voltage harmonics on the stator current as well as the electromagnetic torque are effectively removed. Simulations and experiments are presented to validate the theoretical analysis.

Flicker Suppression Scheme for Variable-Speed Wind Turbine Systems

This paper proposes a strategy of flicker mitigation for doubly-fed induction generator (DFIG) wind turbine systems. In the weak grid system where the grid impedance ratio is low, the reactive power compensation only cannot suppress the flicker sufficiently due to the limited power capacity of the converters or the DFIG. For the full suppression of flickers, the active power smoothening using the energy storage system (ESS) needs to be utilized together with the reactive power compensation. The effectiveness of the proposed method is verified by PSCAD/EMTDC simulation results for a 2[MW] DFIG wind turbine system and by experimental results for a 3[kW] wind turbine simulator.

A Fault Ride-Through Technique of DFIG Wind Turbine Systems Using Dynamic Voltage Restorers

This paper proposes a low-voltage ride-through technique of a doubly fed induction generator (DFIG) wind turbine system using a dynamic voltage restorer (DVR). For effective control of the DVR, digital all-pass filters are used for extracting the positive-sequence component from the unbalanced grid voltage since they have the advantages of giving a desired phase shift and no magnitude reduction over conventional low- or high-pass filters. Using the positive-sequence component, the phase angles for the positive- and negative-sequence components of the grid voltage are derived. A control algorithm for the DVR that is dual voltage controllers only is implemented for the two sequence components in the dq synchronous reference frame. In order to achieve the power rating reduction of the DVR, the stator power reference for the DFIG is reduced during faults. In addition, a control scheme of pitch angle system is applied to stabilize the operation of the wind turbine system in the event of grid faults. PSCAD/EMTDC simulations show the effectiveness of the proposed technique and a feasibility of reducing the power rating of DVR for the fault ride-through capability of DFIG. The validity of the proposed control scheme for the DVR has also been verified by experimental results.

Improved LVRT Capability and Power Smoothening of DFIG Wind Turbine Systems

This paper proposes an application of energy storage devices (ESD) for low-voltage ride-through (LVRT) capability enhancement and power smoothening of doubly-fed induction generator (DFIG) wind turbine systems. A grid-side converter (GSC) is used to maintain the DC-link voltage. Meanwhile, a machine-side converter (MSC) is used to control the active and reactive powers independently. For grid disturbances, the generator output power can be reduced by increasing the generator speed, resulting in an increased inertial energy of the rotational body. Design and control techniques for the energy storage devices are introduced, which consist of current and power control loops. Also, the output power fluctuation of the generator due to wind speed variations can be smoothened by controlling the ESD. The validity of the proposed method has been verified by PSCAD/EMTDC simulation results for a 2 MW DFIG wind turbine system and by experimental results for a small-scale wind turbine simulator.

연계선로의 조건 변화에 따른 DFIG와 FSIG 풍력발전시스템의 운전특성 비교

This paper analyzes the steady-state output characteristics of variable-speed wind turbine systems using doubly-fed induction generators(DFIG) compared with fixed-speed induction generator(FSIG) wind turbine systems. It also presents simulations of a grid-connected wind turbine generation system for dynamics analysis on MATLAB/Simulink and compares the responses between DFIG and FSIG wind turbine systems with respect to wind speed variation, impedance changes and X/R ratio changes of interconnecting circuits. Simulation results show the variation of generator's active output, terminal voltage and fault currents at the interconnecting point. Case studies demonstrate that DFIG wind turbine systems illustrate better performance to 3-phase fault than FSIG's.

Flicker mitigation in a doubly fed induction generator wind turbine system

This paper describes a doubly fed induction generator (DFIG) control for wind energy generation. The DFIG model is established and the adopted control strategies for machine side and grid side converters are described. Flicker phenomenon is defined and its emission of variable speed wind turbine with DFIG during continuous operation is studied. Calculation of flicker severity is evaluated using flickermeter. Appropriate vector power control of the machine side converter is proposed and applied to achieve flicker mitigation.

Optimal controller design of a doubly-fed induction generator wind turbine system for small signal stability enhancement

Multi-objective optimal controller design of a doubly-fed induction generator (DFIG) wind turbine system using differential evolution (DE) is presented. A detailed mathematical model of DFIG wind turbine with a closed-loop vector control system is developed. Based on this, objective functions addressing the steady-state stability and dynamic performance at different operating conditions are implemented to optimise the controller parameters of both the rotor and grid-side converters. A superior ɛ-constraint method and method of adaptive penalties are applied to handle the multi-objective problem and the constraint with DE, respectively. Eigenvalue analysis and time-domain simulations are performed on a single machine infinite bus system as well as a nine-bus multi-machine system with two DFIG wind turbines to illustrate the control performance of the DFIG wind turbine with the optimised controller parameters. The electric energy productions of the studied DFIG wind turbine system with and without optimised controller parameters under turbulent wind speed are also demonstrated.

Modeling and Experimental Verification of Grid Interaction of a DFIG Wind Turbine

The response of the doubly fed induction generator (DFIG) wind turbine system to grid disturbances is simulated and verified experimentally. The results are compared to the response that a fixed-speed wind turbine would have given. A voltage sag to 80% (80% remaining voltage) is handled very well, which is not the case for a fixed-speed wind turbine. A second-order model for prediction of the response of DFIG wind turbines is derived, and its simulated performance is successfully verified experimentally. The power quality impact by the DFIG wind turbine system is measured and evaluated. Steady-state impact, such as flicker emission, reactive power, and harmonic emission, is measured and analyzed. It is found that the flicker emission is very low, the reactive power is close to zero in the whole operating range, and the current THD is always lower than 5%.