In the last decades, the increasing need for new clean and renewable sources of electric energy caused a great interest in alternative means to conventional power plants. Among them, the use of wind energy. In this context, the doubly-fed induction generator has been widely used with wind turbines worldwide due to the possibility of connecting its stator terminals directly to the electric power grid and its active and reactive power control possibility through electric power converters connected to its rotor terminals, which reduce the converters power capacity for up to 30% of the generator rated power. Thus, this dissertation aims to propose the generator active and reactive power control using sliding mode controllers using field-oriented control to perform independent power control. First, the performance of the proposed controller with the traditional PI power control controllers is compared through computer simulations connecting the generator to the electric grid through two converter topologies: with only the stator terminals connected to the grid and with the rotor terminals also connected to the grid through a back-to-back converter. Finally, the sliding mode controller was implemented on a laboratory assembly with only the generator stator terminals connected to the grid to prove the proposal.
The diversification of the energy supply associated with the increasing interest in clean energy sources make most of the countries seek new technologies that could meet these needs. In this way, there has been a large increase in the number of wind turbines connected to the network. Considering the technological development and consequent increase in their capacity, the impact of wind turbines upon the network has been considered increasingly important for both steady state and dynamic conditions. In view of that, this paper will present a dynamic analysis of the impacts, especially electromechanical transients, caused by doubly-fed induction generator (DFIG) based wind turbines connected to the transmission electrical system.
This paper proposes a decoupled control of active and reactive power for doubly-fed induction generators (DFIG) by using the rotor current control loop and sliding mode control (SMC). In order to decouple the active and reactive power generated, stator-fluxoriented vector control is applied. The sliding mode control strategy proposes is based on two sliding modes plus PI controllers whose main advantage is the easy implementation. Simulation and experimental results are presented to validate the proposed control scheme for a 2 kW DFIG during stator active and reactive power steps and rotor speed variation. During transient operation it is checked good dynamic response.
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