Control Strategy Of Wind Turbine Research Articles

Model‐free adaptive learning control scheme for wind turbines with doubly fed induction generators

The classical control mechanisms of the wind turbines are generally based on precise modelling approaches to ensure robust and effective interplay between the wind turbines and the main power grids in both autonomous and grid-connected modes. This study presents an innovative intelligent control system for the doubly fed induction generator wind turbines. The proposed system uses model-free control polices. The online controller is based on a policy iteration reinforcement learning paradigm along with an adaptive actor-critic technique. It is shown to be robust against the turbine's high non-linearities and stochastic variations in the input–output conditions. These are associated with single and double rotor doubly fed large-scale induction generators driven by wind turbines in the range of 5–7 MW. The performance of the controller is validated against challenging scenarios of coexisting undesired situations like severe wind changes with load excursions and abrupt shifts in the loads.

Combined Primary Frequency Control Strategy of Permanent Magnet Synchronous Generator-Based Wind Turbine

To ensure the proper operation of power system, some independent system operators have specified that wind power plants should be able to manipulate power output for frequency control. This article presents a combined control scheme which exploits the self-capability of permanent magnet synchronous generator-based wind turbine to provide primary frequency response. Under normal condition, the wind turbine operates in de-loading mode to obtain the power reserve. Once frequency deviation is detected, the proposed control strategy can not only make use of the power reserve for frequency regulation by adjusting the rotor speed, but utilize the kinetic energy in rotor to provide frequency response as well. Besides, the energy stored in DC capacitor is also employed for frequency support. The simulation results reveal that the wind turbines with the proposed method can improve frequency performance under both constant wind speed condition and variable wind speed condition.

Active-Current Control of Large-Scale Wind Turbines for Power System Transient Stability Improvement Based on Perturbation Estimation Approach

This paper proposes an active-current control strategy for large-scale wind turbines (WTs) to improve the transient stability of power systems based on a perturbation estimation (PE) approach. The main idea of this control strategy is to mitigate the generator imbalance of mechanical and electrical powers by controlling the active-current of WTs. The effective mutual couplings of synchronous generators and WTs are identified using a Kron-reduction technique first. Then, the control object of each WT is assigned based on the identified mutual couplings. Finally, an individual controller is developed for each WT using a PE approach. In the control algorithm, a perturbation state (PS) is introduced for each WT to represent the comprehensive effect of the nonlinearities and parameter variations of the power system, and then it is estimated by a designed perturbation observer. The estimated PS is employed to compensate the actual perturbation, and to finally achieve the adaptive control design without requiring an accurate system model. The effectiveness of the proposed control approach on improving the system transient stability is validated in the modified IEEE 39-bus system.

Pitch Angle Control of Wind Turbine Using Adaptive Fuzzy-PID Controller

The control strategy for wind turbine is very important an equipage that diverts the kinetic energy of the wind to electrical power. The rotation speed control of wind turbine is necessary for highest degree energy capture and pitch angle advanced control planning depending on traditional PID cont

Study on Power Angle Stability of Wind-fire Hybrid Transmission System Controlled by Virtual Synchronous Machine

Wind-fire hybrid transmission system stability has always been a research hot spot, and as the wind turbine control strategy is more and more complex, the stability is more complicated. In recent years, the idea of virtual synchronous machine applied to the control scheme of wind turbines has been popularized, so it is necessary to discuss the power angle stability of wind-fire hybrid system considering the additional control of the wind turbines with the virtual synchronous machine. In this paper, a typical wind-fire hybrid transmission system model is established, and the operating characteristics of the wind turbine are analyzed and the wind turbine model is established. Then, a control strategy of virtual synchronous machine is proposed. At last, the power equivalence function of wind-fire hybrid transmission system is analyzed by Extended Area Equity Criterion (EEAC), and the simulation results in PSASP show that when the receiver is a strong system, the higher the wind-fire ratio, the better the system's angle stability is. The control of the virtual synchronous machine has less effect on the stability of the power angle. When the receiver is a weak system, with the increase of wind power ratio, the power angle stability first increases and then decreases, there is an optimal ratio, and the application of the virtual synchronous machine control can effectively enhance the system's power angle stability, thereby improving the optimal wind-fire ratio.

On wind turbine down-regulation control strategies and rotor speed set-point

The use of down-regulation or curtailment control strategies for wind turbines offers means of supporting the stability of the power grid and also improving the efficiency of a wind farm. Typically, wind turbine derating is performed by modifying the power set-point and subsequently, the turbine control input, namely generator torque and blade pitch, are acted on to such changes in the power reference. Nonetheless, in addition to changes in the power reference, derating can be also performed by modifying the rotor speed set-point. Thus, in this work, we investigate the performance of derating strategies with different rotor speed set-point, and in particular, their effect on the turbine structural fatigue and thrust coefficient were evaluated. The numerical results obtained from the high-fidelity turbine simulations showed that compared to the typical derating strategy, the derated turbines might perform better with lower rotor speed set-point but it is crucial to ensure such a set-point does not drive the turbine into stalled operations.

Comparative study of yaw and nacelle tilt control strategies for a two-bladed downwind wind turbine

The structural dynamics and response of a two bladed downwind wind turbine configuration using a tilt control concept is examined based on Computational Structural Dynamics CSD analysis Nacelle tilt angles of and degrees are investigated based on varying wind speeds in order to achieve the same rated power output Yaw angles of and degrees are examined with the purpose of comparing structural loads and displacements between two control methods The computed load effects reveal that the tower top and base shear forces are reduced significantly using the nacelle tilt control compared with the yaw control method The shear forces and bending moments at the blade root also show favorable outcomes at most nacelle tilt angles except for degrees

Fractional order sliding mode controller design for large scale variable speed wind turbine for power optimization

Based on wind speed, the operating regions of a wind turbine are divided into two parts: below‐rated wind speed (region II) and above‐rated wind speed (region III). This article presents a new control strategy for a variable speed wind turbine for the below‐rated wind speed category (region II). In this operating region, maximization of the conversion efficiency and capturing the maximum energy available in the wind are desirable. The controller is designed based on sliding mode control techniques and fractional order calculations. The sliding‐mode approach has been widely used in wind turbine systems due to the existence of nonlinearity and uncertainty in wind turbine dynamics. The fractional order sliding mode controller has the capacity to produce better performance in comparison to integer order sliding mode controllers due to higher degrees of freedom for tuning. The generator torque is used as the control input to vary the rotor speed in order to maximize energy conversion. To achieve this goal, the rotor angular speed must track the time variable reference value and, hence, fast variations in wind speed. This requires fast reactions on the part of design control. The fractional‐order sliding mode controller can have a good transition response, a low tracking error, and a very fast reaction against rapid variations in wind speed. The stability analysis of the suggested controller was provided using Lyapunov stability theory. Finally, the numerical simulation results are presented and compared with integer order sliding mode control to illustrate the effectiveness of the proposed method. The results show the better performance of the fractional‐order sliding mode controller in comparison to the integer order sliding mode controllers. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1901–1907, 2018

A Novel Constant Output Powers Compound Control Strategy for Variable-Speed Variable-Pitch Wind Turbines

The output power of wind turbine should be maintained at rated value when wind speed exceeds rated speed.However, the wind turbine is a system with large nonlinearity and time delay. Therefore, it is difficult for conventional linear controllers to realize effective control. In order to solve this problem, a combination of feedforward control with feedback control is developed. In feedback loop, feedback linearization theory is adopted to overcome the nonlinear features, and sliding mode algorithm is employed to improve the robustness of the system. On the other hand, in feedforward loop, a cerebellar model articulation controller is implemented to approximate the system. Furthermore, an improved credit assignment method is used to adjust the weight of the network. Together these procedures improve the effectiveness of the algorithm. Through this method, not only can the stability of the nonlinear model be ensured, but also the control lag caused by the time-delayed system can be compensated. Simulation results show that the feedforward-feedback compound control algorithm can both keep the output power at rated value and improve dynamic response speed, reduce adjustment time, has small steady-state error.

Aerodynamic load control strategy of wind turbine in microgrid

A control strategy is proposed in the paper to optimize the aerodynamic load of the wind turbine in micro-grid. In grid-connection mode, the wind turbine adopts a new individual variable pitch control strategy. The pitch angle of the blade is rapidly given by the controller, and the pitch angle of each blade is fine tuned by the weight coefficient distributor. In islanding mode, according to the requirements of energy storage system, a given power tracking control method based on fuzzy PID control is proposed. Simulation result shows that this control strategy can effectively improve the axial aerodynamic load of the blade under rated wind speed in grid-connection mode, and ensure the smooth operation of the micro-grid in islanding mode.

Inductance-Emulating Control for DFIG-Based Wind Turbine to Ride-Through Grid Faults

For doubly fed induction generator (DFIG)-based wind turbines, the rotor side of DFIG is prone to suffering from overcurrent during grid faults, due to large electromotive force (EMF) induced in the rotor circuit. To solve this problem, this paper proposes an inductance-emulating control strategy for DFIG-based wind turbine to suppress the postfault rotor current, thereby enhancing its low-voltage ride through capability. Under the proposed control strategy, once the grid fault is detected, the rotor side converter (RSC) is controlled to emulate an inductance. Furthermore, with proper inductance value, both the required rotor voltage and postfault rotor current can be reduced within the permissible ranges of RSC, thus the controllability of control system can be maintained during transient process. Moreover, the oscillation of electromagnetic torque can be effectively suppressed during transient state of both grid fault and fault recovery. Finally, the simulation and experimental results are presented to demonstrate the effectiveness of the proposed method.

The typhoon effect on the aerodynamic performance of a floating offshore wind turbine

The wind energy resource is considerably rich in the deep water of China South Sea, where wind farms have to face the challenge of extreme typhoon events. In this work, the typhoon effect on the aerodynamic performance of the 5MW OC3-Hywind floating offshore wind turbine (FOWT) system has been investigated, based on the Aero-Hydro-Servo-Elastic FAST code. First, considering the full field observation data of typhoon “Damrey” is a long duration process with significant turbulence and high wind speed, so one 3-h representative truncated typhoon wind speed time history has been selected. Second, the effects of both the (variable-speed and collective-pitch) control system of NREL 5 MW wind turbine and the motion of the floating platform on the blade aerodynamic performance of the FOWT system during the representative typhoon time history has been investigated, based on blade element momentum (BEM) theory (coupled with potential theory for the calculation of the hydrodynamic loads of the Spar platform). Finally, the effects of different wind turbine control strategies, control parameter (KP–KI) combinations, wave heights and parked modes on the rotor aerodynamic responses of the FOWT system have been clarified. The extreme typhoon event can result in considerably large extreme responses of the rotor thrust and the generated power due to the possible blade pitch angle error phenomenon. One active-parked strategy has been proposed for reducing the maximum aerodynamic responses of the FOWT system during extreme typhoon events.

Optimal Control and Operation Strategy for Wind Turbines Contributing to Grid Primary Frequency Regulation

This study introduces a frequency regulation strategy to enable the participation of wind turbines with permanent magnet synchronous generators (PMSGs). The optimal strategy focuses on developing the frequency support capability of PMSGs connected to the power system. Active power control is performed using maximum power point tracking (MPPT) and de-loaded control to supply the required power reserve following a disturbance. A kinetic energy (KE) reserve control is developed to enhance the frequency regulation capability of wind turbines. The coordination with the de-loaded control prevents instability in the PMSG wind system due to excessive KE discharge. A KE optimization method that maximizes the sum of the KE reserves at wind farms is also adopted to determine the de-loaded power reference for each PMSG wind turbine using the particle swarm optimization (PSO) algorithm. To validate the effectiveness of the proposed optimal control and operation strategy, three different case studies are conducted using the PSCAD/EMTDC simulation tool. The results demonstrate that the optimal strategy enhances the frequency support contribution from PMSG wind turbines.

A new control strategy for PMSG based wind turbine to improve power smoothing

This paper presents a new simple control strategy for direct driven PMSG wind turbines, using no wind speed sensor. There are several strategies for wind turbine control. Operation of different strategies in terms of power smoothing is compared. New strategy is proposed to have more power smoothing. Performance of the proposed strategy is evaluated by MATLAB/ Simulink simulations and its validity and effectiveness are verified.

A New Decentralized Pitch Control Scheme for Wind Turbines

Wind turbine rotor imbalances may be created by a multitude of causes, e.g. pitch misalignment, blade erosion. In such situations, machines experience undesired vibrations, which cannot be compensated or mitigated by the controllers generally adopted by industry today. This happens because the control action may be collective or both collective and cyclic, but, in order to cope with imbalances, it is necessary to employ a fully individual control which allows a blade to move independently from the others.In this paper we present a new individual pitch control algorithm able to simultaneously target the imbalance and reduce oscillating loads at frequencies multiple of the rotor revolution. The effectiveness of the proposed control is demonstrated in a high-fidelity simulation environment.

Predictive control of wind turbine for load reduction during ramping events

With increasing penetration of wind power, the impact of its intermittence and volatility on power systems becomes more severe. A predictive control strategy for wind turbines (WTs) is proposed to deal with wind power ramping events and reduce WT load on the blades. The blade load model is based on the Blade Element Momentum (BEM) theory. The generator speed and pitch angle are simultaneously regulated to realize the control objectives. A two-stage optimization is designed in order to reduce the computational complexity. The objectives of the first stage are minimizing the ramping rate and maximizing the power generation. A trade-off is made between the two contradictory objectives by setting weight coefficients. The second stage reduces the WT load and meanwhile guarantees the power reference from the first stage is tracked. Feedback is designed based on neural network prediction to compensate the error of the prediction model. Case studies with a 1.5MW WT were conducted to demonstrate the efficacy of the proposed predictive control strategy. Simulation results show that the proposed control can reduce the WT load during ramping events and the risk of ramping events.

Power fluctuation and power loss of wind turbines due to wind shear and tower shadow

The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to estimate the capacity and quality of the power generated by a wind turbine. First, wind speed models, particularly the wind shear model and the tower shadow model, are described in detail. The widely accepted tower shadow model is modified in view of the cone-shaped towers of modern large-scale wind turbines. Power fluctuation and power loss due to wind shear and tower shadow are analyzed by performing theoretical calculations and case analysis within the framework of a modified version of blade element momentum theory. Results indicate that power fluctuation is mainly caused by tower shadow, whereas power loss is primarily induced by wind shear. Under steady wind conditions, power loss can be divided into wind farm loss and rotor loss. Wind farm loss is constant at 3α(3α–1)R2/(8H2). By contrast, rotor loss is strongly influenced by the wind turbine control strategies and wind speed. That is, when the wind speed is measured in a region where a variable-speed controller works, the rotor loss stabilizes around zero, but when the wind speed is measured in a region where the blade pitch controller works, the rotor loss increases as the wind speed intensifies. The results of this study can serve as a reference for accurate power estimation and strategy development to mitigate the fluctuations in aerodynamic loads and power output due to wind shear and tower shadow.

Optimal Control with Stochastic Principles for Voltage Decoupling Control of a Wind Turbine

This paper presents new control strategies for a variable speed wind turbine (WT) which consists of a doubly fed asynchronous generator. In this kind of generators, the rotor windings are supplied with an appropriate voltage vr through a dc link. There are 2 converters: the rotor-side and the grid-side converter in the dc link. The right pulsation of the rotor-side converter defines the rotor voltage vr in such a way that both real power maximization from the wind speed and nominal voltage are secured at the same time. With all the flux dynamics inside the machine having been included in the generator model, there is a 2-input-2-output system. Based on the dq electric machines analysis theory, the proposed control scheme manages to create 2 single-input-single-output systems with the rotor voltage component in each axis responsible only for real power or voltage nominal value respectively. This is achieved through optimal control theory with the right definition of the cost function. A new control scheme that contains stochastic control principles is proposed for the grid-side controller in which the decoupling of the loops is achieved by means of the grid frequency being regarded as a ‘random’ variable to the voltage control loop and so it has no impact on it. The nonlinear system has been tested in the SIMULINK software under 3 tests: In the first test the wind speed changes and brings about an analogous alteration of the WT output. In the second test there is a short circuit in the grid. According to the new rules, the WT is not disconnected from the grid during the short circuit and continues to produce energy with a very smooth behavior. In the third test, there is a large load disturbance in the grid. Again the WT manages to supply the grid with electrical energy in a nice way. Under all tests the controllers seem to cooperate very well and the variations of the voltage and the frequency are within acceptable limits.

A New Compensation Control Strategy for Grid-connected Wind Turbine and Fuel Cell Inverters in a Microgrid

The use of a new control method for grid-connected inverters for reducing the output current harmonic distortion in a wide range of grid-connected distributed generation (DG) applications, including wind turbine (WT) and fuel cell (FC) inverters is proposed in this paper. The control method designed to eliminate main harmonics in a microgrid (MG) and between MG and point of common coupling (PCC) and responsible for the correction of the system unbalance. Another advantage of the proposed control method is that it can be easily adopted into the DG control system without the installation of extra hardware. The proposed control method is comprised of the synchronous reference frame method (SRF). Results from the proposed control method are provided to show the feasibility of the proposed approach.

Asymptotic tracking control for wind turbines in variable speed mode

This paper presents a variable speed control strategy for wind turbines in order to capture maximum wind power. Wind turbines are modeled as a two-mass drive-train system with generator torque control. Based on the obtained wind turbine model, variable speed control schemes are developed. Nonlinear tracking controllers are designed to achieve asymptotic tracking for a prescribed rotor speed reference signal so as to yield maximum wind power capture. Due to the difficulty of torsional angle measurement, an observer-based control scheme that uses only rotor speed information is further developed for global asymptotic output tracking. The effectiveness of the proposed control methods is illustrated by simulation results.