Airflow Rate Control of Oscillating Water Column for Maximising Wave Energy Capture

Abstract

The stalling effect in Oscillating Water Column OWC well turbine$-$based limits the power generated. This issue is solved by controlling the airflow rate, where the peak waves is predicted and accordingly the airflow speed is reduced. This paper introduces a control approach for maximising the power captured by an OWC equipped with well turbine and Doubly Fed Induction Generator DFIG. The function of control scheme is to regulate the rotational speed and this is achieved by controlling the airflow rate in the chamber of OWC. The airflow speed is estimated using information of wave parameters and employed for controlling the airflow coefficient. A sensor is used to measure the pressure in the OWC chamber to avoid damage that could occur during strong turbulent ocean. The dynamic of OWC is nonlinear in nature and it is intricate, thus its plant is simplified and linearised so as to apply the control scheme. Since the input to the system is rotational speed of well turbine along with the airflow speed and the output is DFIG rotor speed and the electromagnetic torque. The torque is directly linked to the rotor flux, the plant is derived according to that relation. PID controller is used for controlling the airflow rate and pole placement is used to determine the gains of this controller. In addition, Particle Swarm Optimisation PSO and Bat Algorithm Optimisation BAO are also used to obtain the exact gain values and the performance is compared. The airflow rate controller set the reference of rotor speed which would be used to control the rotor speed of DFIG. The torque of the generator is controlled as well along with rotor flux by implementing Direct Torque Control DTC. The system has simulated under various pressure conditions and the results show well dynamic response in terms of controlling the airflow rate, DFIG rotor speed, torque and power. In addition, the turbine provides torque without stalling as the air valve is activated during sever pressure and restore its state when the pressure in OWC chamber is decreased to a specific value, thus continuous operation is ensured alongside with maximising the captured power.