A Novel Technique for Rotor Side Converter Protection in Doubly Fed Induction Generators

Abstract

Recently, wind energy is considered as one of the most important energy resources and the growing share of the wind energy in the electrical grids made many countries introduced new grid codes to identify the responsibilities and rights of the wind farms during all grid conditions. Nowadays, the Doubly Fed Induction Generator (DFIG) becomes one of the most popular generators in variable wind turbine systems. The DFIG has the advantages of; low cost, low weight, and high efficiency. However, one of its main disadvantages is its sensitivity to the voltage dips. Therefore, there are various techniques were developed to protect the DFIG and enhance its performance during the faults so as to meet the grid codes requirements. In this thesis, DFIG theory was discussed along with its control techniques, also various protection techniques of the DFIG were discussed and their advantages and disadvantages are highlighted. Two novel proposed techniques in protecting DFIG`s Rotor Side Converter (RSC) are presented and discussed. To evaluate the behavior of the new proposed protection schemes, a network consisting of a 2MW wind turbine connected to an infinite bus bar via a 0.69 /20 kV transformer is considered using EMTDC/PSCAD software. A 3-phase to ground fault with different levels at the high voltage side of the transformer is introduced at different generator speeds. The results showed a noticeable enhancement in the DFIG performance when the proposed techniques are applied specially regarding rotor current and DC link voltage which have a direct effect on RSC and its components.