Estudio del efecto de los huecos de tensión en el generador de inducción doblemente alimentado
- Autores: Alejandro Rolán Blanco
- Directores de la Tesis: Felipe Córcoles López (dir. tes.), Joaquín Pedra Durán (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2012
- Idioma: catalán
- Tribunal Calificador de la Tesis: José Roger Folch (presid.), Oriol Gomis Bellmunt (secret.), Luis Guasch Pesquer (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The aim of this doctoral thesis is to analyse the dynamic behaviour of the doubly-fed induction generator exposed to voltage sags. This electrical machine is mainly used in variable-speed wind turbines. Due to the noticeable increase in recent years in grid integration of wind turbine energy systems, the transmission system operators have developed the grid codes, which are the technical specifications that wind turbines have to achieve when a fault occurs. Faults are the most common causes that originate voltage sags. Therefore, the first step to ensure electricity supply continuity as well as to improve power quality when this kind of faults occur is to analyse the dynamic behaviour of the generator exposed to voltage sags. The stator of the doubly-fed induction generator is directly connected to the grid, whereas its rotor is connected by means of a power converter. The converter consists of a rectifier or rotor-side converter and an inverter or grid-side converter, which are linked by a DC bus. It is assumed that the rotor-side converter keeps constant the rotor current in the synchronous reference frame during the entire event. This hypothesis allows the electrical transient to be solved analytically. The voltage limit of the rotor-side converter is also taken into account in order to determine the situations where the rotor current can be controlled. This doctoral thesis is structured as follows. Firstly, the mathematical model of voltage sags is given. Secondly, both dynamic and steady-state models of the doubly-fed induction machine are obtained. Thirdly, the steady-state behaviour of the doubly-fed induction generator is analysed for different generated powers and it is studied, by means of an analytical approach, its electrical transient when exposed to voltage sags. The analytical results are validated by numerical integration of the system of equations with a MATLAB ode solver and by means of the PSpice circuit simulator. It is also carried out an exhaustive study of the effect that voltage sags cause on the doubly-fed induction generator, considering all the typologies (symmetrical and unsymmetrical voltage sags) and varying their parameters (duration and depth). Moreover, the fault-clearing process is taken into account, which has a strong influence on the voltage that the rotor-side converter requires to control the rotor current. The terms abrupt sag and discrete sag stand for voltage sags whose voltage recovery is produced instantaneously or in different steps, respectively. Finally, by means of an analytical study, which is validated by the simulation of different loads exposed to voltage sags, a grouping of voltage sags whose voltage recovery is produced in different steps is proposed. It is observed that from the fourteen discrete voltage sag types in the literature, it is enough to consider only five types. This is a significant advantage, as the number of simulations or laboratory tests carried out on an electrical device exposed to voltage sags is reduced.
