Abstract
Doubly-fed induction generators (DFIGs) are widely used in wind energy conversion systems. The dynamic features of DFIGs make it important to focus on designing high-performance control schemes. However, the dynamic characteristics of such generators depend on nonlinear parameters, such as stator flux, stator current, and rotor current, which increase the overall system complexity. In addition, the DFIG Wind Energy Conversion Systems (WECSs) size is growing beyond 7 MW, which increases stress on both the mechanical drive train and the power circuits during connection to the grid. Such stress and dynamic features cannot be neglected. Therefore, robust controllers must be implemented which have the ability to support the dynamic frequencies of wind energy to ensure system stability in grid connection mode and during subsequent use. Conventional vector control configurations that use proportional-integral controllers have various drawbacks, such as parameter tuning difficulties, mediocre dynamic performance, and reduced robustness. In this study, we focused on improving DFIG synchronization to the grid by applying state feedback current controllers with a feedforward component to smooth the connection to the grid, as well as to improve the steady-state and transient characteristics of the controller. State feedback controllers are proposed to replace the proportional-integral controllers on both the rotor and grid sides. The proposed controller is designed using a multivariable system and feedforward control for input reference and incorporating disturbances into the control equations for fast synchronization and transient responses. To demonstrate the advantages of this controller, experimental studies are presented for both the transient and steady states.
Highlights
System Description In Doubly-fed induction generators (DFIGs)-based Wind Energy Conversion Systems (WECSs), when ignoring the stator core and copper losses, all active and reactive power is supplied by both the stator and rotor
The parameters of the wind turbine and DFIG can be found in Appendixes
The synchronization process to starts by the accelerating the ofwind turbine simulator which is Experiments were performed study performance the multivariable state controller mechanically coupled with the
Summary
In DFIG-based WECSs, when ignoring the stator core and copper losses, all active and reactive power is supplied by both the stator and rotor. A maximum power point tracker is typically implemented to maximize the stator active power, which is extracted from the wind turbine. Regarding the rotor rotational speed, rotor power can be either supplied to or drawn from the grid depending on the operating speed. The grid feeds the rotor when the rotor rotates at sub-synchronous speeds and the rotor current lags behind the rotor voltage by less than 90◦. At super-synchronous speeds, the rotor windings feed power to the grid and the rotor voltage jumps to nearly 180◦ ahead of the stator voltage, where the slip value is negative [29,30,31]
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