Parallel Operation of DFIGs in Three Phase Four Wire Autonomous Wind Energy Conversion System
ABSTRACT This paper deals with a control algorithm for two parallel operated Doubly Fed Induction Generators (DFIGs) driven by wind turbines in a three phase four wire autonomous system feeding local loads. The proposed Autonomous Wind Energy Conversion System (AWECS) is using back to back connected Pulse Width Modulated (PWM) Insulated Gate Bipolar Transistors (IGBTs) based voltage source converters (VSCs) with a battery energy storage system (BESS) at their dc link. The system utilizes separate rotor side converters for each DFIG for maximum power tracking (MPT) through its rotor speed control. However a common dc bus and battery bank, and stator side converter are used for voltage and frequency control (VFC) at the stator terminals of the DFIGs. A delta star transformer is connected between the stator side converter and the stator terminals of DFIGs for optimizing the voltage of dc bus, and the load side neutral is connected to the neutral of the star side of the transformer. The proposed electro-mechanical system is modeled and simulated in MATLAB using Simulink and Sim Power Systems (SPS) set toolboxes. The performance of the proposed AWECS is presented to demonstrate its capability of maximum power tracking, stator voltage and frequency control, harmonic elimination, load balancing and load leveling.