## 2 Literature Review  
### Wind Turbine Generators  
Like all electric generators, a wind turbine generator converts energy, known as wind mechanical energy, into electrical energy. Wind turbine generators are different from other grid-connected generators. The main difference is that a wind turbine generator has to work with wind energy that supplies fluctuating torque and mechanical power. There are different types of wind turbine generators, as follows:  
* Synchronous generator with field winding--a synchronous generator typically consists of a three-phase winding stator that feeds the external load and a rotor that generates a magnetic field. The rotor may be magnetically permanent or have an area winding system [16].
* Permanent magnetic synchronous generator--with this type of generator, the incremental converter controls the electromagnetic torque. The converter regulates the direct current (DC) connection voltage and controls the input power factor on the power supply side. One of its drawbacks involves using a diode rectifier, which increases the current and distortion range [17].  
* DFIG wired rotor generator--a DFIG controller can be a good solution for variable speed systems with a 30% synchronous speed change range. Furthermore, the power of the electronic power converter in these systems constitutes 20-30% of the total power of the generator, which contributes to lower losses compared to other types that operate at full power. Converter prices and costs are also reduced. The term \"doubly-fed\" refers to the stator supplying power to the power grid and the load, while the power converter generates the rotor voltage [18]. These systems have wide but limited operating speed ranges. The converter compensates for the difference in electrical and mechanical frequencies by injecting the variable frequency current into the rotor [19]. The power converters and controllers regulate the generator's behavior during both regular operation and faults. The advantages of a DFIG controller include the following: (a) the ability to control the reactive power, (b) the ability to independently control active and reactive capabilities, (c) the ability to be magnetized by the rotor, and (d) reactive power generation capability.
* DFIG all-control winding rotor generator--the controller used in these generators offers greater controllability flexibility than a traditional DFIG controller. These wind power systems are designed for wind farms located at sea and connected to neighboring land via sea cables. Other methods of integrating an induction generator into a grid include cycloconverters [20] and matrix converters [21]. The disadvantages of these systems include a low line power factor, high harmonic deviations in line and machine flow for cycloconverters, and the removal of DC capacitors in matrix converters. This type of converter is complex, and its technology needs to be more mature.
* Cage rotor induction generator--the stator windings in these generators are linked to the network via an electronic power converter. The stator converter control system regulates the electromagnetic torque and supplies the machine with reactive power [22]. The network side converter regulates the DC connection voltage and controls the active and reactive power transfer from the system to the network.
* A dual-stator winding induction generator [23]--the two stator windings are electrically isolated in these machines.
* Two-speed cage rotor induction generator--this type of generator increases the turbine's efficiency at low wind speeds, which is unsuitable for large wind farms because it cannot power the network [24].
* A DFIG field-oriented controller--this was used in Ref. [25] due to its ability to manage and optimize wind turbine speed and torque control. This controller divides the stator current into segments to produce the torque and flux.
* A DFIG vector control (VC) for grid and rotor side converters--this approach was suggested in [26], exploiting fuzzy controls such as Mamdani, Sugeno, and ANFIS.