Renewable Energy from Wind Power-Control of Rotor Side Converters

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Dr. Nagy István
Department of Automation and Applied Informatics

Microgrid systems have changed the energy market and industry significantly. In order to take advantage of the possibilities, mainly renewable energy sources are used, especially photovoltaic panels, fuel cells, and wind turbines. In addition to the environmental protection aspect, this kind of distributed power generation creates some problems due to the fast development, such as energy storage, distribution, utilization, which present challenges for the developers. The wind turbines’ installations are essential for the renewable energy industry. For improved efficiency, these turbines are equipped with aerodynamical controls such as stall, pitch or yaw controls (I presented these controls in the mechanical part), and electromechanical controls such as rotor and grid side converter controls. In this paper the main focus is on the rotor side converters.

One of the most effective solutions for producing energy from wind is the generator type Doubly Fed Induction Generator (DFIG). This project aims to investigate this apparatus, including the theoretical basis of its operation, which I derived.

We start by discussing the operation of the variable speed generator, which can operate and harvest power from the wind above and below the rated wind speed as well as control the active and reactive power flow in its stator and rotor circuits. To investigate the behavior I created two models, representing the linear and the non-linear system. While I compare these models with each other in an assumed characteristic in some different operation point during the steady-state system, I investigate the dynamic processes in some aspects such as the change in torque or the appropriate components of the rotor voltages. The controlled variable is regulated using stator flux oriented vector control and studied for the two models. I present the independent controls of active and reactive power in the case of the linear model. By changing the load torque of the system, the displacement on the unstable characteristic can be examined if the reference values of the control loop, the mechanical speed, and the appropriate component of the rotor current are changed stepwise. I also present the phenomenon when only the load torque changes and the reference values do not. In this case the system operates in a new characteristic determined by the new values of the controllers. I explain and support by simulation results the operations in steady-state and during the dynamic processes in the case of open loop and closed loop. At the end of the project I present the operation of the pulse width modulation using the non-linear system.


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