Design and Development of Flight Controller for Kite-based Wind Power Generation Systems

Abstract

Wind power can significantly contribute to transitioning from fossil fuels to renewable energies. Airborne Wind Energy (AWE) technology is one of the approaches to tapping the power of high-altitude wind. Kite Power System (KPS) is a type of AWE technology which uses tethered kites to harness the power in the wind at higher altitudes. The main advantage of KPS over Conventional Wind Turbines (CWT) is that the KPS eliminates the need for a structure and rotating blades, significantly reducing the size and materials needed. Also, kites can reach much higher altitudes than CWT, which can harness the power from much stronger winds. The study of the dynamics of KPS is fundamental in researching and developing a commercial-scale system. Unlike CWTs, where the blades rotate in a circular motion, the kites are controlled to follow figure-eight trajectories in the crosswinds. The kites harness power from the wind and transfer the aerodynamic force through the tethers to the ground. The reeling-out tether rotates the generator at the ground station to generate electric power. As the tether length is finite, the kite is depowered and reeled in at the end of the limit by consuming a fraction of generated power. The cycle of operation repeats and is called as pumping cycle kite power system. KPS is one of the solutions contributing towards clean and green energy production in the renewable energy mix, which is the sole motivation of this research work. The KPS has challenges that must be addressed to develop it as a commercially viable product. The power from the kites depends on the tether force of the kite in the figure-eight trajectory. The tether force of a kite depends on the wind velocity and the kite’s orientation to the wind vector in the figure-eight trajectory. This research presents an experimental measurement of the pulling force of an Airush Lithium 12 m2 kite with a constant tether length of 24 m in a coastal region. The position and orientation data of the kite is obtained from the sensors mounted on the kite. The flight dynamics of the kite are studied using multiple field tests under steady and turbulent wind conditions. In this research, a physical model (PM), Artificial Neural Network (ANN) and Long Short-Term Memory (LSTM) deep neural network algorithms are proposed to estimate the tether force of the kite with experimental validation. The performance of the proposed methods is studied using Root Mean Square Error (RMSE), Mean Absolute Error (MAE), and R2 evaluation methods. The potential of KPS can be realized by scaling the model to a commercialscale power generation device. Testing an actual KAWECS or a location with suitable wind conditions is only sometimes a trusted opportunity for conducting esearch. A KAWECS emulator is developed based on a Permanent Magnet Synchronous Machine (PMSM) drive coupled with a generator to mimic the kite’s behaviour in wind conditions. The KPS is simulated using a MATLAB-SIMULINK environment with various power ranges and wind conditions. The satellite wind speed data at 10 m and 50 m above ground with field data of the kite’s figureof-eight trajectories are used to emulate the kite’s characteristics in the dynamic wind conditions. Another challenge in the KPS is the steering controller, which controls and flies a kite in figure-eight crosswind motion. The kite consists of two power lines and two control lines, the power lines are connected together, and the kite delivers most of the force through the power lines. The left and right control lines are used to steer the kite by a differential movement of both lines. The kite steer controller mimics the differential movement of the kite control lines to steer the kite. The force exerted on the control lines by the kite is essential in designing the kite steering actuators. A kite steering controller’s design and development methodology is explained and validated using experimental analysis under steady and turbulent wind conditions. The power consumed to control the kite and the power generation aspects of the KPS is also analyzed. The results of this research will promote the use of KAWECS as it can provide reliable and seamless energy flow, enriching wind energy exploitation under various installation environments.