Dynamic Study Of A System Consisting Of Two Terminal Boost Controlled Synchronous Generators For Variable Speed Wind Turbines (μελέτη Της Δυναμικής Συστήματος Ανεμογεννητριών Μεταβλητής Ταχύτητας Αποτελούμενου Από Δύο Τερματικά Με Σύγχρονες Γεννήτριες Ελεγχόμενες Από Μετατροπέα Ανύψωσης)

Abstract

This project deals with the investigation of variable speed control of a synchronous generator. The system under investigation consists of a synchronous generator, a rectifier, a boost-converter and a grid-connected DC/AC converter. Such a system might be an interesting option, especially for off-shore wind farms, in terms of losses, cost and complexity. The voltage at the DC side of the grid connected converter is kept constant using a proper control scheme at the DC/AC converter. The terminal voltage of the generator is controlled by changing the duty cycle of the IGBT at the boost-converter. Since the internally generated voltage of the generator and the rotor speed are directly related, controlling the terminal voltage results in controlling the rotor speed of the generator.In the report, different control schemes are tested for both speed and power control. A PWM control method has been compared to a new control strategy that was developed while the thesis was being elaborated. The new control strategy is based on hysteresis control. The results showed that better dynamic characteristics can be achieved using the new control scheme. Complementary to this scheme, a combination method has also been introduced, which involves hysteresis and excitation current control, in a way that the advantages of the two methods are combined.Additionally, loss investigation at the different components of the system has been carried out. It was found that the highest loss in the system is due to the generator. Further investigation is required for reducing the total loss of the system.Matlab/Simulink has been used for all the simulations carried out within this thesis.