Modeling and experimental analysis of grid-connected six-phase induction generator for variable speed wind energy conversion system

Abstract

In this paper, an advanced control for grid-connected asymmetrical six-phase induction generator (ASIG) in variable speed wind energy conversion system (WECS) is proposed. It involves a detailed model of ASIG, a six-phase converter for machine side control, and a three-level converter for grid side control. ASIG consists of two three-phase sets spatially space shifted by thirty electrical degrees. This configuration offers higher power in the same machine frame, more reliability, and robustness when compared to the conventional three-phase induction generator (TPIG). Back to back connected voltage source converters (VSCs) are utilized for interfacing ASIG with the grid. Efficient control strategies are applied to generator side and grid side converters. Two machine side converters connected in parallel are operated with an advanced rotor field oriented control (RFOC) for maximum power point tracking (MPPT). RFOC is achieved by involving six PI controllers. It mainly focuses on removal of unbalanced currents between two sets of three-phase windings. Three-level grid side converter is controlled for maintaining DC link voltage, and to regulate the flow of reactive power between grid and generator. Experimental investigation of the proposed method is performed with 1.5-hp, six-pole, six-phase induction generator reconfigured from an existing three-phase induction machine. Generated power is supplied to the grid at unity power factor. Validating results indicating power flow, grid voltage and grid current are also exhibited. Paper also presents a comparative analysis of ASIG with conventional TPIG.