Individual Wind Turbine Generators Research Articles

Partial repowering analysis of a wind farm by turbine hub height variation to mitigate neighboring wind farm wake interference using mesoscale simulations

Repowering augments the power generation capacity of a wind farm in order to enhance the exploitation of the high mean wind speed regions. In this study, a partial repowering strategy has been discussed for an onshore commercial-scale wind farm with deteriorated performance under the influence of wakes originating from upstream wind farms. The mesoscale Weather Research and Forecasting (WRF) model with Wind Farm Parameterization has been employed to evaluate the wind speed and power deficit observed by the individual wind turbine generators. Wakes induced by the upstream wind farms are observed to cause a reduction in wind speed and power output by up to 15% and 35%, respectively. The predicted power was also validated by the observed data for each turbine generator. The hub heights of selected wind turbines with the highest power deficit are varied to alleviate the influence of upstream wind farm wake interference. Power output and wind shear profiles have been evaluated at new hub heights of 61.5 m and 100 m, and results are compared with the existing hub height turbine generators at 80 m. Power output reduced by up to 12% at the lower hub height of 61.5 m as compared to the default case, while an increase of about 13.6% is observed for the 100 m hub height case. A mean increase of 7.5% is estimated in the total wind power generation from the wind farm under evaluation. This paper presents a theoretical and engineering platform for partial repowering of wind farms with depleted generation due to inter-farm wake interaction.

Equivalent modeling of wind energy conversion considering overall effect of pitch angle controllers in wind farm

The correct electric power fluctuation process of a wind farm is essential for the operation and studying of the power grid integrated with wind power. A complete wind energy conversion model, that should take both the spatial effects and the overall effect of all the pitch angle controllers into account, is required to convert the wind fluctuation into the electric power fluctuation. Although some equivalent models have been proposed in previous studies, there is no simple solution for equivalently modeling the non-synchronous actions of the pitch angle controllers in individual wind turbine generators. This study found the relationship between the overall effect of all the pitch angle controllers and the spatial effects of the wind farm and presented a theoretical derivation of the frequency-domain equivalent modeling method. The proposed modeling method is the simplest way to obtain the equivalent model of the complete wind energy conversion process of a wind farm with consideration of all the spatial effects and the overall effects of all the pitch angle controllers. The only input signal of the proposed equivalent model is the speed of the wind before entering the wind farm, which is called the “original incoming wind speed” and the only output signal is the total power of the wind farm. In this proposed equivalent modeling method, a discrete transfer function for representing both the wind energy conversion process, and all the spatial effects of a wind farm, can be obtained, first through a wind process below the rated wind speed. Second, a compensation factor for calculating a “compensation wind speed” of the original incoming wind can be obtained through a wind process that partly exceeds the rated wind speed. Using this compensation wind speed, a compensation power with negative values can be obtained to represent the total reduced power caused by the pitch angle controllers in individual wind turbine generators. A frequency-domain equivalent model has been identified and validated by field measurements of an actual wind farm. The normalized root-mean-squared error of the model is less than 8% over the entire wind process, and the maximum error of the power ramp rate in 10 min is less than 5 MW. Finally, an example is provided to demonstrate the online use of the proposed model to convert the forecasted wind speed into output power of a wind farm in ultra-short-term wind power forecast.

Control Strategies for Enhancing Frequency Stability by DFIGs in a Power System with High Percentage of Wind Power Penetration

Nowadays, regarding high percentage of wind power penetration in power systems, operating conditions of power system necessitates wind turbine generators (WTGs) to contribute in frequency regulation of the system, similar to the conventional units. To reach this goal, active power output of WTGs must be controlled, but this issue distances the operating conditions of WTGs from maximum power point tracking (MPPT) mode. This paper initially presents a completed model of doubly fed induction generator (DFIG) for dynamic studies in frequency stability analysis. Next, a coordinated control strategy to regulate active power command set point (Pcmd) for individual WTGs in a wind farm (WF) and a control strategy to regulate wind power output of DFIG upon operator’s request is presented. Stability is assured under different wind conditions in the proposed control strategy. Individual WTGs set point allocation is performed applying fuzzy logic controller (FLC), while emotional learning based intelligent controller is used in regulation of the coefficient in the DFIG to reach the best stability conditions. Simulation results, performed on a test system consisting of both conventional units and WTGs, validate the effectiveness of the proposed control strategy in comparison with other mentioned solutions.

Primary frequency regulation by deloaded wind turbines using variable droop

This paper introduces a method to improve the primary frequency contribution of grid connected variable speed wind turbine generators (WTGs). Using their energy reserve margins, deloaded WTGs are controlled to provide relief to the grid during depressed frequency conditions. The frequency support from individual WTGs is regulated based on the available reserve, which depends on the prevailing wind velocities. By continuously adjusting the droop of the WTG in response to wind velocities, its primary frequency response is significantly improved in terms of reduced stresses on WTGs during low wind speeds. The impact of variable droop operation on two aspects of WTG operation is investigated-primary frequency contribution and smoothening power fluctuations caused due to changes in wind speed. Also highlighted is the usefulness of this control when adopted by wind farms.

Dynamic model of wind energy conversion systems with PMSG-based variable-speed wind turbines for power system studies

In order to study the impact of a wind farm on the dynamics of the power system, a significant issue is to develop appropriate equivalent models that allow characterizing the dynamics of all individual wind turbine generators (WTGs) composing the park. In this sense, with the advance of power electronics, direct-driven permanent magnet synchronous generators (PMSGs) have drawn increased interest to wind turbine manufacturers due to their advantages over other variable-speed WTGs. These include the possibility of multi-pole design with a gearless construction that offers slow speed operation and reduced maintenance since no brushes are used, elimination of the excitation system, full controllability for maximum wind power extraction and grid interface, and easiness in accomplishing fault-ride through and grid support. In this way, this paper presents a comprehensive dynamic equivalent model of a wind farm with direct-driven PMSG wind turbines using full-scale converters and its control scheme. The proposed simplified modelling is developed using the state-space averaging technique and is implemented in the MATLAB/Simulink environment. The dynamic performance of the wind farm and its impact on the power system operation is evaluated using the phasor simulation method.

Output Power Leveling of Wind Farm Using Pitch-angle Control with Fuzzy Neural Network

There are concerns in regards to wind power generation as its output constantly, as well as considerably, varies. This article presents a control strategy for wind farms consisting of a wind turbine with variable pitch. In order to reduce output power fluctuation of wind farms, smoothed wind-farm output power command is determined by wind condition and fuzzy neural network. In addition, individual wind turbine generators are controlled by output power command derived from wind-farm output power command and coordination control for each wind turbine generator. Simulation results using an actual detailed model for wind-farm systems show the effectiveness of the proposed method.

Supercapacitor Energy Storage for Wind Energy Applications

As wind energy reaches higher penetration levels, there is a greater need to manage intermittency associated with the individual wind turbine generators. This paper considers the integration of a short-term energy storage device in a doubly fed induction generator design in order to smooth the fast wind-induced power variations. This storage device can also be used to reinforce the dc bus during transients, thereby enhancing its low-voltage ride through (LVRT) capability. The topology is evaluated in terms of its ability to improve the performance both during normal operation and during transients. Results show that when storage is sized based upon the LVRT requirement, it can effectively damp short-term power oscillations, and it provides superior transient performance when compared with conventional topologies