A sensorless control strategy for automatic start‐up and grid‐synchronization of doubly fed induction generator in wind energy conversion system

Abstract

SummaryIn a wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG), a fast and smooth automatic synchronization of the DFIG with the utility grid is always desirable. Additionally, elimination of the need for a speed encoder makes the synchronization process much more reliable. This paper proposes a modified voltage controller‐based automatic grid‐synchronization strategy for the DFIG‐WECS using a rotor‐current‐dependent model‐reference‐adaptive‐system (MRAS) for rotor‐speed/position estimation. A V/f control‐based starting strategy is used to start the DFIG. An improved decoupled DFIG stator voltage controller is proposed to enhance the transient response during the DFIG grid synchronization. The modified controller is implemented in a grid‐voltage‐oriented reference frame to synchronize the DFIG‐stator with the grid. A robust modified MRAS with higher noise immunity and reduced machine parameter dependency is used to estimate the rotor‐speed/position during synchronization control. To validate the performance of the proposed strategy, a DFIG‐based WECS is modeled and simulated using an OPAL‐RT real‐time simulator, where a motor‐generator setup is modeled to have an equivalent WECS configuration. As compared with the latest reported work, this approach reduces the synchronization time by 16.99% while ensuring a smooth synchronization with no stator inrush‐current, even without any speed/position encoder.