Dynamic Modeling of a Wind Turbine System
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- Institutt for elkraftteknikk 
The objective of this paper is to derive a simple dynamic model of a wind turbine system, with focus on mechanical conditions. The investigated system is assumed to be a 10 MW reference wind turbine, with variable speed operations and a direct-drive permanent magnet synchronous generator. The model will include the mechanical dynamics where the joint inertia, the electromagnetic torque and the aerodynamic torque will influence the turbine rotational speed. Three different control strategies for the generator-side converter system will be investigated, where steady-state power flow equations are utilized to describe the system. The variable turbine rotational speed and demanded electric torque will influence the electrical quantities. The derived control strategies will be implemented in a wind turbine model in the computer tool MatLab/SIMULINK to perform several simulations with different wind speeds. Signals containing information about the armature current, terminal voltage, load angle and power output will be analyzed. The intended generator implemented in the model will be designed to deliver 10 MW to the grid, including losses in generator and converter. Voltage and current restrictions can cause a limitation on the desired delivered power output. The system should be optimized for operations at rated wind speed, but must be able to handle situations with high turbine rotational speed and possible grid faults. The desired induced torque will be delivered during ideal operations, maintaining steady-state operations for the wind turbine. Identical power output will be delivered from the three different control strategies implemented in the generator subsystem. Both the current and voltage values will be different causing various operating modes.A beneficial control strategy would be to minimize losses and maximize the power factor. The maximum voltage and current tolerance on the generator-side converter should be determined to minimize costs and weight, and maximize the turbine operations and security. At the same time the generator must be designed to handle the thermal stress caused by a high current value during high rotational speeds. A development where the mechanical structure and the electrical system are more integrated should be emphasized in future research.