Dynamic Modeling and Control of DFIG-Based Wind Turbines Under Unbalanced Network Conditions

TLDR

The study analyzes and designs control strategies for a DFIG-based wind turbine operating under unbalanced network conditions, aiming to reduce stator current unbalance, torque, and power pulsations. The authors model the DFIG in positive and negative synchronous reference frames, define stator power and torque variations under negative sequence conditions, and implement a rotor‑current control strategy using dq reference frames, validated by EMTDC/PSCAD simulations of a 2‑MW turbine. The proposed control strategy eliminates the excessive oscillations seen with conventional vector control, achieving smoother active power, torque, and current operation under network unbalance.

Abstract

This paper presents an analysis and control design of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced network conditions. A DFIG system model in the positive and negative synchronous reference frames is presented. Variations of stator active and reactive powers and generator torque are fully defined in the presence of negative sequence voltage and current. Alternative DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. A rotor current control strategy based on positive and negative (dq) reference frames is used to provide precise control of the rotor positive and negative sequence currents. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system. It shows that conventional vector control of DFIG without considering network unbalance results in excessive oscillations on the stator active/reactive power, electromagnetic torque, and stator/rotor currents even with a small stator voltage unbalance. In contrast, with the proposed control strategy, enhanced system control and operation such as minimizing oscillations in either active power, or electromagnetic torque, or stator or rotor currents can be achieved