Controller saturation nonlinearity in doubly fed induction generator‐based wind turbines under unbalanced grid conditions

Abstract

Doubly fed induction generator (DFIG) is widely used in wind energy generation systems due to its costeffective, partially rated back-to-back power converters, variable rotor speed operation, and maximum wind power capture. The conventional design assumes balanced grid voltage and utilizes power protection for the power converters. The DFIG wind turbine is naturally one of the major components in distributed generations of the smart grid system. However, newly developed smart grid system is rich in unbalanced loads. This paper summarizes the limiter settings of controllers and explores the nonlinear behaviors of the DFIG-based wind power generation system with unbalanced loads. The generator rotor speed and an unbalanced load resistance are chosen as variation parameters. An emerging low-frequency linear-modulated oscillation at line second harmonic frequency with DC drifting is identified on the DC link voltage of the back-to-back power converters. In terms of second harmonic and the usually reported hazardous low-frequency oscillation, the saturation nonlinearity and over-modulation of the back-to-back power converter and its power flow are investigated and analyzed. The built-in detailed model of the DFIG wind energy generation system in MATLAB with SimPowerSystems library is used in this study.

Direct current grid‐based doubly‐fed induction generator wind turbines: Real‐time control and stability analysis

“…For the DFIG control in dq-frame with SFO, the d-axis is aligned with the stator flux vector, and hence 𝜓 sd = |𝜓 s | and 𝜓 sq = 0. From (5), T e in the SFO frame is given by…”

“…In the last three decades, various types of wind generation sources that are different in terms of mechanical and electrical structures have been introduced and exploited worldwide [2,3]. Among different types of wind turbines, DFIG-based wind turbines (DFIG-WTs) are well-known technology and widely used due to their cost-effective and variable speed operation [4][5][6]. Additionally, the DFIG-WTs through power electronics converters can provide the independent control of the real and reactive power with higher energy capture and less mechanical stress [4][5][6].…”

“…Among different types of wind turbines, DFIG-based wind turbines (DFIG-WTs) are well-known technology and widely used due to their cost-effective and variable speed operation [4][5][6]. Additionally, the DFIG-WTs through power electronics converters can provide the independent control of the real and reactive power with higher energy capture and less mechanical stress [4][5][6].…”

Experimental investigation on the control strategy of split source inverter for grid‐connected wind power generation system

“…Two control loops supervise the grid‐tied SSI. The current controller regulates the grid current and outer voltage regulator to control dc‐link capacitor voltage 51–54 …”

Sub‐synchronous control interaction in power grids including doubly fed induction generator based wind turbines

“…Nevertheless, the sub-synchronous resonance risk is an important concern regarding the series compensation employment [3][4][5][6]. Doublyfed induction generator (DFIG) based wind turbines (WTs) because of their cost effective and variable speed operation are widely used in wind power systems [7]. DFIG-based wind farms, because of direct connection of the stator to the grid, are more sensitive to the power grid disturbances such as resonance and distortion, voltage unbalance, voltage dip and fault [8].…”