Investigation of microgrids supplied by renewables

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Supervisor:
Dr. Stumpf Péter Pál
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 this paper the state of art of electricity network is presented including the types of distribution networks and a short overview of the High-Voltage Direct Current (HVDC) transmission.

There are two basic types of microgrids: AC and DC microgids and both of them has many advantages and disadvantages as well. After a short description the operation of these microgrids are presented in this project.

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 and electromechanical controls such as rotor and grid side converter controls. In this paper the main focus is on the rotor side converters and the grid side converters. During my studies I was very closely involved in these topic and I am very interested in this theme.

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.

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 using rotor side converters. The basics of this control strategy is the stator flux oriented vector control. This control system is implemented into Matlab/Simulink environment and the steady-state and dynamic transient processes are studied by changing the input signals: the load torque and the mechanical speed of the wind turbine and the appropriate component of the rotor current (the required stator reactive power). The grid side converter control system is presented and implemented also. This control system regulates the value of the DC link, which is between the two converters, and the grid reactive power. The basics of this control scheme is the grid voltage oriented vector control. The steady-state and transient processes are investigated also, where the input signals are the prescribed value of the DC link and the required grid reactive power.

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