Abstract
This article presents the modelling and assessment of a pulsating torque mitigation control strategy by using a tidal turbine emulator in a laboratory environment. Sudden changes and variability of the tidal flow velocity have the effect of creating pulsations on tidal current turbines. These pulsations have an adverse effect on tidal turbine fatigue and ultimate loading as well as the operation of the drivetrain. For the above reasons, a pulsating torque mitigation control strategy has been developed and tested which is based on modifying the reference maximum power point speed of the generator. This article presents the assessment of this pulsating torque mitigation control strategy in a laboratory setup. A 7 kW tidal current turbine is modelled in MATLAB/Simulink. The tidal turbine is emulated in the laboratory setup by using a torque-controlled induction motor. Results show the effectiveness of the method in a laboratory environment, the ability of the generator to accelerate and decelerate based on the speed controller commands and the difference between the pulsating torque mitigation control strategy and maximum power point operation (MPPO). In addition, the experimental results are compared with a Simulink model which will show the accuracy of the modelling process.
Highlights
A number of tidal current developers are planning or have installed demonstration arrays with a notable example the MeyGen project in the Inner Sound of the Pentalnd Firth in Scotland
The tidal current turbine system developed was emulated in the laboratory setup for two different test cases in order to assess the performance of the fatigue torque mitigation (FTM) control strategy compared to the maximum power point operation (MPPO) control strategy
At the same time that the experimental setup was operating, the SimPowerSystems Simulink model was simulated in real time with the same Vtidal. This is necessary in order to compare simulation and experimental results and understand possible limitations of the control strategy in the laboratory setup
Summary
A number of tidal current developers are planning or have installed demonstration arrays with a notable example the MeyGen project in the Inner Sound of the Pentalnd Firth in Scotland. For below rated power operation variations of the forces and the torque on a tidal current turbines have to be minimised in order to avoid blade lifetime reduction, unnecessary use of the pitching system and gearbox stress. By reducing mechanical torque variations through the speed controller of the generator and applying appropriate pitch control for the above rated power operation the unnecessary use of the pitching system can be avoided and the failure rates of the mechanical parts of the turbines minimised. In this paper a tidal current turbine is emulated in real time in the laboratory environment through a torque-controlled induction motor. Based on this input the ABB drive was generating the appropriate pulses for the active rectifier This process was modelled in the SimPowerSystems model by using a speed controller and implementing the zero d-axis controller (ZDC) for PMSM. The whole experimental process was monitored and controlled using the ControlDesk which acts as an interface between Simulink and the dSPACE controller
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