Performance and structural load analysis of small and medium wind turbines operating with active speed stall control versus pitch control

The objective of this paper is to investigate the performance pitch and active speed stall control, and their impact on the structural loads of small and medium wind turbines (SMWTs). Large wind turbines use blade pitching to limit the power at high wind speeds. For SMWTs, the cost and complexity of a blade pitching system are not justified, so that passive yaw, stall control, or a furling tail mechanism is used instead. However, the choice of a proper control concept is not straightforward for SMWTs. In this regard, it is important to take into account that the control strategy has a significant impact on the structural loads. Reducing the structural loads results in a longer lifespan and ensures the safe operation of the wind turbine in stormy wind gusts or fierce winds. In this study, a 10 kW wind turbine is operated with different control strategies to investigate the corresponding loads, both in uniform and turbulent winds. The simulation results show that controlling power around the rated value is feasible and stable for both control strategies. However, active speed stall control increases the bending moments at the blade root, while it lightens the tower base moments, in contrast to the pitch control

A data-driven approach using deep learning time series prediction for forecasting power system variables

This study investigates the performance of ‘Group Method of Data Handling’ type neural network algorithm in short-term time series prediction of the renewable energy and grid-balancing variables, such as the Net Regulation Volume (NRV) and System Imbalance (SI). The proposed method is compared with a Multi-layer Perceptron (MLP) neural network which is known as a universal approximator. Empirical validation results show that the GMDH performance is more accurate in compression with the most recent forecast which is provided by ELIA (Belgian transmission system operator). This study aims to practice the applicability of the polynomial GMDH-type neural network algorithm in time series prediction under a wide range of complexity and uncertainty related to the environment and electricity market

The impact of pitch-to-stall and pitch-to-feather control on the structural loads and the pitch mechanism of a wind turbine

This article investigates the impact of the pitch-to-stall and pitch-to-feather control concepts on horizontal axis wind turbines (HAWTs) with different blade designs. Pitch-to-feather control is widely used to limit the power output of wind turbines in high wind speed conditions. However, stall control has not been taken forward in the industry because of the low predictability of stalled rotor aerodynamics. Despite this drawback, this article investigates the possible advantages of this control concept when compared to pitch-to-feather control with an emphasis on the control performance and its impact on the pitch mechanism and structural loads. In this study, three HAWTs with different blade designs, i.e., untwisted, stall-regulated, and pitch-regulated blades, are investigated. The control system is validated in both uniform and turbulent wind speed. The results show that pitch-to-stall control enhances the constant power control for wind turbines with untwisted and stall-regulated blade designs. Stall control alleviates the fore-aft tower loading and the blades flapwise moment of the wind turbine with stall-regulated blades in uniform winds. However, in turbulent winds, the flapwise moment increases to a certain extent as compared to pitch-to-feather control. Moreover, pitch-to-stall control considerably reduces the summed blade pitch movement, despite that it increases the risk of surface damage in the rolling bearings due to oscillating movements with a small amplitude

Wind and solar intermittency and the associated integration challenges : a comprehensive review including the status in the Belgian power system

Renewable Energy Sources (RES) have drawn significant attention in the past years to make the transition towards low carbon emissions. On the one hand, the intermittent nature of RES, resulting in variable power generation, hinders their high-level penetration in the power system. On the other hand, RES can aid not only to supply much more eco-friendly energy but also it allows the power system to enhance its stability by ancillary service provision. This article reviews the challenges related to the most intermittent RES utilised in Belgium, that is, wind energy and solar energy. Additionally, wind speed and solar irradiance variations, which are the cause of wind and solar intermittency, are studied. Then, recent techniques to forecast their changes, and approaches to accommodate or mitigate their impacts on the power system, are discussed. Finally, the latest statistics and future situation of RES in the Belgian power system are evaluated

Flexible integration of energy-intensive CCU based processes and wind energy in the electrical power system

De klimaatverandering is de grootste uitdaging van deze eeuw. Het reduceren van de uitstoot van broeikasgassen en de transformatie naar een koolstof-arme economie staan hoog op de politieke agenda. Hernieuwbare energie, elektrische energienetten en CO2-gebaseerde technologie zijn essentieel om deze paradigma-verschuiving te realiseren. Een belangrijke CO2-gebaseerde technologie is 'Carbon Capture and Utilization' (CCU), waarmee CO2 wordt omgezet in nuttige chemische bouwstoffen. Het aandeel hernieuwbare energie zal significant toenemen tijdens de energie-transitie, om uiteindelijk bij een overwegend hernieuwbare energie productie uit te komen. Dit introduceert echter nieuwe uitdagingen om het elektrische energienet betrouwbaar en stabiel te houden. Bovendien verhoogt dit de belasting op klassieke energiecentrales om productie en consumptie te balanceren. Bijgevolg moet het systeem meer flexibel en adaptief worden teneinde om te gaan met een verhoogd aandeel hernieuwbare energie en energie-intensieve CO2-gebaseerde processen. Meer specifiek werd in dit doctoraat een regel- en beslissingssysteem ontwikkeld om een chemisch CCU proces optimaal te combineren met windenergie om het elektrisch energienet te ondersteunen als hybride systeem. Dit onderzoek levert daarmee een waardevolle bijdrage aan de ontwikkeling van het toekomstige energienet met een hoog aandeel aan hernieuwbare energiebronnen

An adaptive operational strategy for enhanced provision of frequency containment reserve by Wind Turbines : data-driven based power reserve adjustment

Due to the growing penetration of renewables, Wind Turbines (WT) are becoming increasingly crucial for grid balancing services, such as Frequency Containment Reserve (FCR). This study proposes an adaptive operational strategy that optimally accommodates the power reserve and controls the active power based on grid frequency uncertainties and stochastic wind variations. The proposed approach includes an end-to-end solution, considering fixed and percentage reserve methods, from estimating an appropriate reserve margin to the real-time computation of generator torque and pitch control setpoints in response to grid frequency variations. A real-time look-up table is incorporated to actively adjust the reserve and adapt the deloading rotor speed-power curve based on a short-term estimation of the grid frequency using a deep-learning technique. Applying the proposed strategy improves WTs’ FCR contribution by at least 3.3 times reserve in MW. Moreover, adaptive fuzzy-PI pitch-torque controllers are suggested to enhance the WT dynamic response and ensure smooth provision of FCR. Simulation results of a 5 MW-NREL offshore model show the improvement of the fuzzy-PI in power reference tracking, rotor speed regulation, and average studied mechanical load parameters in the range of 2.14–11.69%, 11.1%, and 8.81%, respectively, for an average of 250 kW reserve, confirming an overall improvement