Efficient extraction of wind energy Under unbalanced and distorted grid Conditions

Abstract

Modern high power Wind Electric Conversion (WEC) systems are capable of adjustable speed operation. Key advantages of variable speed wind generators compared to fixed speed generators are cost effectiveness and the ability to generate electricity even during lower wind speeds. The Doubly Fed Induction Generator (DFIG) based WEC systems are more favorable than squirrel cage induction machine and synchronous machine based variable speed schemes. The advantages include constant frequency-variable speed operation, four quadrant real and reactive power flows, reduced power electric converter rating and low power converter losses. newlineAs wind electric systems are normally connected to weak (lower X/R ratio) rural distribution grids, unbalanced load and asymmetric grid faults give rise to grid imbalances. This occurrence results in negative sequence flux linkages leading to damage of mechanical components. This dissertation focuses on two separate modest control strategies of DFIG based WEC system with Matrix Converter (MC) under unbalanced and harmonic grid conditions. Tedious sequence decomposition process and complex reference computations are avoided in the proposed control strategies. The conventional dc link back-to-back converter is replaced by MC due to their minimum energy storage requirements, bi-directional energy flows and fully controllable input power factor. newline