Search

This article presents an application of neural network-based Model Predictive Control (MPC) to improve the wind turbine control system's performance in providing frequency control ancillary services to the grid. A closed-loop Hammerstein structure is used to approximate the behavior of a 5MW floating offshore wind turbine with a Permanent Magnet Synchronous Generator (PMSG). The multilayer perceptron neural networks estimate the aerodynamic behavior of the nonlinear steady-state part, and the linear AutoRegressive with Exogenous input (ARX) is applied to identify the linear time-invariant dynamic part. Using the specific structure of the Cascade Hammerstein design simplifies the online linearization at each operating point. The proposed algorithm evades the necessity of nonlinear optimization and uses quadratic programming to obtain control actions. Eventually, the proposed control design provides a fast and stable response to the grid frequency variations with optimal pitch and torque cooperation. The performance of the MPC is compared with the gain-scheduled proportional-integral (PI) controller. Results demonstrate the effectiveness of the designed control system in providing Frequency Containment Reserve (FCR) and frequency regulation in the future of power systems.

As the share of renewable energy sources increases, the grid frequency becomes more unstable. Therefore, grid balancing services will become more important in the future. Dedicated devices can be installed close to the point where off-shore wind farms are connected to the transmission grid on land. There, they can be used to attenuate power variations, reduce congestion and offer grid balancing. The provision of these ancillary services can create considerable additional economic revenue. In this study, the provision of the primary reserve by means of a large hydrogen electrolyser of 25 MW is investigated for the specific case of the Belgian transmission system. The revenue of the provision of the frequency containment reserve (FCR) is analysed on a techno-economic model, including capital costs, operational costs, the revenue of the generated hydrogen and oxygen products and the ancillary service income. The revenue depends strongly on the contracted power band. Therefore, it is optimised to yield maximum revenue. The results show that providing FCR creates considerable additional revenue. Therefore, a large electrolyser can be a good candidate to buffer excess renewable energy into green gas while simultaneously providing the grid support.

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.

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.

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.

Wind turbines are one of the most rapid growing and promising technologies for renewable power generation today. However, the share of wind energy in the global energy mix is almost entirely attributed to large turbines. Despite their unique merits, small wind turbines remain a marginal phenomenon, as they lack the technological maturity of their large counterparts. They often have a disappointing energy yield, and consequently, poor economic viability. However, it was observed from test field data that turbines with a higher ratio of rotor size to drivetrain power perform better. This rises the question whether a different design methodology, tailored to the specifics of small turbines, would result in a performance improvement. Therefore, this article presents a techno-economic optimisation method specifically for small wind turbines. Parametrised technical and economic models are integrated within a co-design optimisation process, with maximum economic performance as primary goal. A cost model of the turbine was constructed by collecting price data from wind turbine manufacturers and manufacturers of their main components. The results of the optimisation process confirm that the economic performance can indeed be greatly increased by significantly increasing the ratio of rotor size to drivetrain power.

As the share of renewable energy sources increases, the grid frequency becomes more unstable. Therefore, grid balancing services will become more important in the future. Dedicated devices can be installed close to the point where off-shore wind farms are connected to the transmission grid on land. There, it can be used to attenuate power variations, reduce congestion and offer grid balancing. These ancillary services can create significant economic revenue. In this paper, the provision of primary reserve by means of a large hydrogen electrolyser of 25 MW is investigated for the specific case of the Belgian transmission system. The electrolyser is used to convert water and excess power to hydrogen gas, which is injected into the natural gas grid. The revenue for Frequency Containment Reserve (FCR) provision is analysed on a techno-economic model, including capital costs, operational costs, the revenue of the generated hydrogen and oxygen products and the ancillary service income. The revenue depends strongly on the contracted power-band. Therefore, it is optimised to yield maximum revenue. The results show that providing FCR creates a considerable revenue. Therefore, a large electrolyser can be a good candidate to buffer excess renewable energy into green gas while simultaneously providing grid support.

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.

This paper proposes the use of an active yaw system to protect small and medium wind turbines in the high wind zone from overloading. The active yaw system turns the rotor partially out of the wind to decrease the turbine power. The dependency of the power on the yaw angle is modeled by the third power of the cosine of the yaw angle. A proper controller is configured based on on-off control of the yaw mechanism. A supplementary rotor speed control is required to avoid static instability. The proposed power limitation strategy is simulated in dynamic situations. The step response simulations show that a yaw rate of the order of 3°/s is required to properly limit the power. Simulations using a realistic wind profile demonstrate that the system can cope with the fluctuating nature of the wind.