LAUSR

This study develops a framework for optimisation of rotor side converter (RSC) switching to eliminate lower-order harmonic injection of a doubly fed induction generator connected to a grid. A biogeography based optimisation (BBO) technique is used for this purpose. Three level inverters operating in either 120° or 180° modes at slip frequency are usually employed for the RSC to reduce switching losses. Non-sinusoidal rotor injected voltages by RSC generates undesirable stator harmonics based on the operating rotor speed. Induced harmonics in the stator are analysed and computed. A modified switching strategy is developed to reduce stator harmonics at different speeds. A BBO-based technique is used to compute the switching angles off-line controlled with minimum injected harmonics at closed intervals of modulation indices. These angles are stored in processor memory for an on-line application using mixed model equations which have low memory usage. Various simulations are executed and supported by suitable experiments with a practical machine for verification of the proposed model which provided satisfactory results.