Variable Speed Wind Turbine System Research Articles

Continuous-time multi-model predictive control of variable-speed variable-pitch wind turbines

ABSTRACTThe control objective for wind turbine control systems includes maximum power tracking, speed and power regulation and minimisation of mechanical loads. The operating region of a wind turbine is a function of the incoming wind speed and the control objective in each operating region differ significantly from the other. Therefore, a linear controller designed based on a model obtained at one operating point cannot guarantee stability and satisfactory performance across the whole operating regime of the turbine. In this paper, a continuous-time multi-model predictive controller is proposed for variable-speed variable-pitch wind turbine systems. Four controllers were designed using linearised models obtained at 4, 8, 11 and . A Bayesian probability inference function was used to make the transition between these controllers based on the errors between the system outputs and each operating point. Simulation studies based on a benchmark 5 MW wind turbine were used to demonstrate the performance of the proposed controller.

Detection of rotational periodic torque deviations in variable-speed wind turbine systems using disturbance observer and phase-locked loop

We discuss the detection of rotational periodic torque deviations in variable speed wind turbine systems. These deviations can be caused by faults in the system. The turbine torque is estimated with an observer and an estimate of the ideal aerodynamical torque is calculated. These torques are analysed using a phase-locked loop to detect deviations. The torque observer is based on the model of the turbine drive train. It is modelled as a two-mass-system with a flexible shaft. The design of the observer and the phase-locked loop are shown and their stability is discussed. Simulations show, that the presented concept is capable of detecting the amplitude of the deviations at different periodicities, online and for variable speed.

Robust Wind Speed Estimation and Control of Variable Speed Wind Turbines

AbstractIn this work, a robust control scheme for variable speed wind turbine system that incorporates a doubly feed induction generator is described. The sliding mode controller is designed in order to track the optimum wind turbine speed value that produces the maximum power extraction for different wind speed values. A robust sliding mode observer for the aerodynamic torque is also proposed in order to avoid the wind speed sensors in the control scheme. The controller uses the estimated aerodynamic torque in order to calculate the reference value for the wind turbine speed. Another sliding mode control is also proposed in order to maintain the dc‐link voltage constant regardless of the direction of the rotor power flow. The stability analysis of the proposed controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally, the simulation results show that the proposed control scheme provides a high‐performance turbine speed control, in order to obtain the maximum wind power generation, and a high‐performance dc‐link regulation in the presence of system uncertainties.

Robust Predictive Control for Direct-Driven Surface-Mounted Permanent-Magnet Synchronous Generators Without Mechanical Sensors

In this paper, an extended Kalman filter (EKF) is employed to estimate stator currents, rotor speed, rotor position, and mechanical torque of a direct-driven surface-mounted permanent-magnet synchronous generator (PMSG) based variable-speed wind turbine systems controlled by a robust predictive deadbeat (DB) algorithm. Therefore, the flux-oriented control of the PMSG is realized without mechanical sensors (i.e., no position encoders or speed transducers). The estimated stator currents are fed back to the prediction model in order to compensate the one-step delay caused by the digital controller and to reduce the total harmonic distortion of the stator currents. Thus, the torque ripples are also reduced. Furthermore, a simple disturbance observer is presented, which estimates the perturbations caused by parameter variations of the PMSG or by any unmodeled dynamics in order to enhance the robustness of the proposed DB algorithm. The proposed scheme is experimentally validated using a 14.5-kW PMSG and a dSPACE DS1007 real-time platform. Its performance is compared with that of the conventional DB control strategy for all operation conditions and under parameter variations of the PMSG.

An overall Control of BDFIG using Direct Power Control for WECS under Unbalanced Grid Voltage Conditions

The paper presents the complete modelling and control strategy of variable speed wind turbine system (WTS) driven brushless doubly fed induction generators (BDFIG). A back-to-back converter is employed for the power conversion exchanged between BDFIG and grid. The wind turbine is operated on the maximum power point tracking (MPPT) mode its maximum efficiency. The control strategy of CW stator side converter (MSC) combines the technique of MPPT and conventional direct power control. In the control system of the grid side converter (GSC) the direct power control based an improved switching table (IST-DPC has been used to maintain a constant DC-Link voltage and the reactive power is set to zero. In addition, the behaviours of BDFIG under unbalanced grid voltage conditions are studied and a power compensation scheme is developed to improve the power quality generation. Simulations results using MATLAB/SIMULINK are presented and discussed on a 3.5 KW BDFIG wind generation system based an cascaded doubly fed induction generator  demonstrate the effectiveness of the proposed control. several advantages, particularly providing sinusoidal line current when the supply voltage is not ideal.

Power Extraction Control of Variable Speed Wind Turbine Systems Based on Direct Drive Synchronous Generator in All Operating Regimes

Due to the increased penetration of wind energy into the electrical power systems in recent years, the turbine controls are actively occupied in the research. This paper presents a nonlinear backstepping strategy to control the generators and the grid sides of a Wind Farm System (WFS) based Direct Drive Synchronous Generator (DDSG). The control objectives such as Tracking the Maximum Power (TMP) from the WFS, pitch control, regulation of dc-link voltage, and reactive and active power generation at varying wind velocity are included. To validate the proposed control strategy, simulation results for 6-MW-DDSG based Wind Farm System are carried out by MATLAB-Simulink. Performance comparison and evaluation with Vector Oriented Control (VOC) are provided under a wide range of functioning conditions, three-phase voltage dips, and the probable occurrence of uncertainties. The proposed control strategy offers remarkable characteristics such as excellent dynamic and steady state performance under varying wind speed and robustness to parametric variations in the WFS and under severe faults of grid voltage.

Wind Farm Grid Integration Architecture using Unified Expandable Power Converter

This paper proposes a novel unified expandable low switch power electronic converter architecture for grid integration of direct drive variable speed wind turbine (VSWT) system using permanent magnet synchronous generator (PMSG). The proposed unified expandable power converter can interface two or more bidirectional output ports, such as wind generators, energy storages, and grid. The size of the power converter is compact because of fewer number of power electronic switches and protection devices, and its architecture is easily expandable to accommodate more outputs, i.e., in this case, the wind turbines. A generalized sequential space-vector modulation technique is developed based on the operational principle of the proposed converter to control the outputs autonomously in order to track the maximum power point for individual VSWTs-driven PMSGs. It is expected that the proposed approach will reduce the cost of power electronic converters in a wind farm, compared to both ac- and dc-link-based topologies, which are available for the moment.

Robust Control of Variable Speed Wind Turbine Using Quasi-Sliding Mode Approach

In this paper, a robust controller is designed for variable speed wind turbine (VSWT) system. The VSWT is an uncertain system having nonlinear dynamics. The irregular behavior of wind makes the system unstable. To overcome this problem, a nonlinear robust controller is designed using quasi-sliding mode approach (QSMC). The chattering effect is almost eliminated from the overall system. The obtained results are validated through simulation studies. The simulation results are compared with the conventional sliding mode controller to show the superior performance of the proposed control scheme.

Fuzzy Predictive Control of Wind Turbine Systems Via Singular Perturbation Theory

In this paper, the maximum power point tracking problem of variable-speed wind turbine systems is studied. The mechanical and electromagnetic dynamics of the wind turbine systems are both taken into account. Since the electromagnetic parts change much faster than the turbine part, the whole system is modeled in two time scales base on singular perturbation theory. And a T-S fuzzy model predictive control strategy is then developed. The controller is validated with a wind turbine simulator. The results have shown better performance in comparison with existing controllers.

A Complete Modeling and Control for Wind Turbine Based of a Doubly Fed Induction Generator using Direct Power Control

<span lang="EN-US">The paper presents the complete modeling and control strategy of variable speed wind turbine system (WTS) driven doubly fed induction generators (DFIG). A back-to-back converter is employed for the power conversion exchanged between DFIG and grid. The wind turbine is operated at the maximum power point tracking (MPPT) mode its maximum efficiency. Direct power control (DPC) based on selecting of the appropriate rotor voltage vectors and the errors of the active and reactive power, the control strategy of rotor side converter combines the technique of MPPT and direct power control. In the control system of the grid side converter the direct power control has been used to maintain a constant DC-Link voltage, and the reactive power is set to 0. Simulations results using MATLAB/SIMULINK are presented and discussed on a 1.5MW DFIG wind generation system demonstrate the effectiveness of the proposed control.</span>

A Novel Sliding Mode Control Scheme for a PMSG-Based Variable Speed Wind Energy Conversion System

This work proposes a novel control scheme for a variable speed wind turbine system based on the permanent magnet synchronous generator. Regions II and III for a wind speed profile are considered, hence the control is designed for maximizing the generated power from the wind turbine when the wind speed is below the nominal wind speed, and to saturate the generated power when the wind speed is above its nominal value in order to avoid damage to the system. Based on nonlinear models, the control scheme is also designed for introducing robustness to the closed-loop system. The pitch angle reference signal is also designed based on a mathematical model of the system, yielding in that way to a great performance of the wind turbine as predicted by the numeric simulations.

Değişken Hızlı Rüzgâr Türbinlerinde Kanat Ucu Hız Oranı Tabanlı Maksimum Güç İzleme Denetimi; Kapsamlı Bir Tasarım

The most primitive control method of wind turbines used to generate electric energy from wind is the fixed speed control method. With this method, it is not possible that turbine input power is transferred to grid at maximum rate. For this reason, Maximum Power Tracking (MPT) schemes are proposed. In order to implement MPT, the propeller has to rotate at a different speed for every different wind speed. This situation has led MPT based systems to be called Variable Speed Wind Turbine (VSWT) systems. In VSWT systems, turbine input power can be transferred to grid at rates close to maximum power. When MPT based control of VSWT systems is the case, two important processes come into prominence. These are instantaneously determination and tracking of MPT point. In this study, using a Maximum Power Point Tracking (MPPT) method based on tip speed ratio, power available in wind is transferred into grid over a back to back converter at maximum rate via a VSWT system with permanent magnet synchronous generator (PMSG). Besides a physical wind turbine simulator is modelled and simulated. Results show that a time varying MPPT point is tracked with a high performance.

Distributed FACTS stabilization scheme for efficient utilization of distributed wind energy systems

Summary Because of the growing usage of wind energy systems worldwide, more challenges in power quality and microgrid stabilization domains have emerged. In this paper, a new distributed FACTS-based green plug-switched filter capacitor (GP-SFC) filter is presented for efficient utilization of microgrid-connected wind energy systems. The primary goals are improving the energy use, stabilizing voltage dynamically, enhancing power quality, and improving the power factor at the common interface AC buses of the microgrid-connected wind system. The proposed GP-SFC topology is modelled and simulated using MATLAB/Simulink software. A dynamic multiloop error-driven controller is proposed for adjusting the pulse switching pattern of the variable speed wind turbine system. In addition to the low cost of the proposed GP-SFC filter, the results show that it can promote the use of wind energy system under load changes and temporary fault conditions. Besides, the proposed GP-SFC guarantees high-speed controllability while maintaining its capability for power factor correction and voltage support using its switched shunt capacitor. Also, the system performance with the proposed filter is compared with the system with a conventional D-STATCOM compensator. The results validate the effectiveness and robustness of the GP-SFC topology.

Uncertain Saturated Discrete‐Time Sliding Mode Control for A Wind Turbine Using A Two‐Mass Model

AbstractThe aim of this paper is to propose a new design variable speed wind turbine control by discrete‐time sliding mode approach. The control objective is to obtain a maximum extraction of wind energy, while reducing mechanical loads and rotor speed tracking combined with an electromagnetic torque. For this application, we designed a discrete time sliding mode control using the equivalent discrete time reaching law. Furthermore, a systematic and improved design procedure for uncertainties discrete‐time sliding mode control (SMC) with saturation problem is provided in this paper. The saturation constraint is reported on inputs vector. LMI technique and polytopic models are used in the design of the switching surface. To achieve some performance requirements and good robustness, in the sliding mode, the pole clustering method is investigated. Based on the unit vector control approach, a robust control is developed, then, to direct and maintain the system states onto the sliding manifold in finite time. Finally, a systematic design procedure for DSMC required to achieve a given performance level is provided and its effectiveness is varied by applying it to variable speed wind turbine systems.

Control of High-Power Wind Energy Conversion System Fed by Multi-level Converters

The progress of Variable Speed Wind Turbine Systems (VS-WTS) is currently focused in reaching higher power ratings (8MW). Also, medium voltage operation is at this power level, particularly at electrical network, a required feature. Consequently, high power medium-voltage multilevel converters for VS-WTS have been attracting more and more attentions. Nevertheless, most modern high-power VS-WTS consist of a large number of Wind Turbine Generators (WTGs) connected and operating simultaneously to reach the multi-megawatt level. This study presents a control strategy for a grid-connected onshore wind farm based Permanent Magnet Synchronous Generator (PMSG), where cascaded multilevel converters are employed on the generators and grid side. The generator-side converters provide speed control of the turbine-generator units to implement Maximum Power Point Tracking. The grid side Neutral Point diode Clamped (NPC) converter system regulates reactive and real power flow to the electrical network. So, it regulates the dc bus voltage and the ac side power-factor. The modulation technique for the proposed topology is developed from Space Vector Modulation. The overall control approaches of a rectifiers and an NPC are also described. Nonlinear Sliding Mode technique (NL-SM) with speed control and Vector Oriented Control are developed. To validate the proposed approaches, simulations are carried out on a high-power wind energy conversion system with multi-level converters and MATLAB/Simulink software. The simulation results demonstrate a good performance in diverse scenarios.

Efficient Direct Model Predictive Control for Doubly-Fed Induction Generators

In reality, heavy calculation burden is an obstacle for applying direct model predictive control (DMPC) schemes in industrial applications. To resolve this problem, this paper proposes a computationally efficient DMPC scheme for doubly-fed induction generators (DFIGs) based on variable-speed wind turbine systems (WTSs). The procedure of selecting the optimal switching vector is enhanced by calculating the reference voltage vector (VV) directly from the reference current. Then, the sector where this reference VV is located is identified. Finally, the cost function is evaluated only for three times to get the best switching action. Consequently, the necessity to test all candidates VVs will be avoided, which reduces the calculation burden of the conventional DMPC method. Control performance of the proposed efficient DMPC method is compared with the conventional DMPC by simulation results for all operation conditions. Furthermore, the performance of the proposed efficient DMPC is investigated under variations of the DFIG parameters and in case of unbalanced grid conditions.

Pitch angle control for grid-connected variable-speed wind turbine system using fuzzy logic: A comparative study

Pitch angle control is considered as a practical technique for power regulation above the rated wind speed. As conventional pitch control commonly the proportional–integral controller is used. However, the proportional–integral type may well not have suitable performance if the controlled system contains nonlinearities as the wind turbine system or the desired wind trajectory varied with higher frequency. In the presence of modeling uncertainties, the necessity of methods presenting controllers with appropriate performance as the advanced control strategies is inevitable. The pitch angle based on fuzzy logic is proposed in this work. We are interested to the development of a wind energy conversion system based on permanent magnet synchronous generator. The fuzzy logic controller is effective to compensate the nonlinear characteristics of the pitch angle to the wind speed. The design of the proposed strategy and its comparison with a conventional proportional–integral controller are carried out. The proposed method effectiveness is verified using MATLAB simulation results.

A Review on DC-DC Converters for PMSG based Standalone Variable Speed Wind Turbine System

A Review on DC-DC Converters for PMSG based Standalone Variable Speed Wind Turbine System

Encoderless Model Predictive Control of Doubly-Fed Induction Generators in Variable-Speed Wind Turbine Systems

In this paper, an encoderless finite-control-set model predictive control (FCS-MPC) strategy for doubly-fed induction generators (DFIGs) based on variable-speed wind turbine systems (WTSs) is proposed. According to the FCS-MPC concept, the discrete states of the power converter are taken into account and the future converter performance is predicted for each sampling period. Subsequently, the voltage vector that minimizes a predefined cost function is selected to be applied in the next sampling instant. Furthermore, a model reference adaptive system (MRAS) observer is used to estimate the rotor speed and position of the DFIG. Estimation and control performance of the proposed encoderless control method are validated by simulation results for all operation conditions. Moreover, the performance of the MRAS observer is tested under variations of the DFIG parameters.

UDE-based control of variable-speed wind turbine systems

ABSTRACTIn this paper, the control of a PMSG (permanent magnet synchronous generator)-based variable-speed wind turbine system with a back-to-back converter is considered. The uncertainty and disturbance estimator (UDE)-based control approach is applied to the regulation of the DC-link voltage and the control of the RSC (rotor-side converter) and the GSC (grid-side converter). For the rotor-side controller, the UDE-based vector control is developed for the RSC with PMSG control to facilitate the application of the MPPT (maximum power point tracking) algorithm for the maximum wind energy capture. For the grid-side controller, the UDE-based vector control is developed to control the GSC with the power reference generated by a UDE-based DC-link voltage controller. Compared with the conventional vector control, the UDE-based vector control can achieve reliable current decoupling control with fast response. Moreover, the UDE-based DC-link voltage regulation can achieve stable DC-link voltage under model uncertainties and external disturbances, e.g. wind speed variations. The effectiveness of the proposed UDE-based control approach is demonstrated through extensive simulation studies in the presence of coupled dynamics, model uncertainties and external disturbances under varying wind speeds. The UDE-based control is able to generate more energy, e.g. by 5% for the wind profile tested.