Comparison of SCIG and DFIG Wind Turbines during Variable Wind Speed

Abstract

The Renewable energy sources, which have been expected to be a promising alternative energy source, can bring new challenges when it is connected to the power grid. However, the generated power from renewable energy source is always fluctuating due to environmental condition. In the same way Wind power injection into an electric grid affects the power quality due to the fluctuation nature of the wind and the comparatively new types of its generators. Fixed speed wind turbine equipped with Squirrel cage induction generator has the advantages of being simple, robust and reliable. However, it also contains some disadvantages of uncontrollable reactive power output, mechanical stress and limited power quality control. Owing to its fixed speed operation, fluctuations in wind speed are further transmitted as fluctuations in the mechanical torque and then in the electrical power output. In order to overcome the above mentioned problems associated with fixed-speed wind turbine system and to maximize the wind energy capture, variable speed wind turbines based on Doubly fed induction generator are becoming employed.Keywords: Doubly fed induction generator (DFIG), Flicker, Power quality, Squirrel cage induction generator (SCIG), wind turbine I. INTRODUCTIONWind energy is one of the most cost-effective energy sources to produce electricity among various renewable energy sources. However, the generated power from renewable energy source is always fluctuating due to environmental condition. In the same way Wind power injection into an electric grid affects the power quality due to the fluctuation nature of the wind and the comparatively new types of its generators [2]. As the wind power penetration into the grid is increasing quickly, the influence of wind turbines on the power quality is becoming an important issue. One of the important power quality aspects is flicker. Flicker causes irritation to the consumer at the receiving end and results in a serious limitation for weak networks where the flicker effect can emerge. IEC 61400-21 describes procedures for determining the power quality characteristics of wind turbines. There are numerous of factors that affect flicker emission of grid-connected wind turbines during continuous operation, such as wind characteristics (e.g. mean wind speed, turbulence intensity) and grid conditions (e.g. short circuit capacity, grid impedance angle, load type) [7]. The type of wind turbine also has influence on flicker emission. Fixed-speed wind turbine system use a multistage gearbox and a standard squirrel-cage induction generator (SCIG), directly connected to the grid. The speed is not controllable and variable only over a very narrow range, in which only speeds higher than the synchronous speed are possible for generator operation. The fixed speed concept means that wind speed fluctuations are directly translated into electromechanical torque variations, this causes high mechanical and fatigue stresses on the system (turbine blades, gearbox and generator), and may result in swin...

Voltage Control and Braking System of a DFIG during a Fault

“…This kinetic energy is converted into useful power through wind turbines. Furthermore, transmission lines help to supply power for mills, home, hospitals, farm, school, industries and many more business applications on different scales, [1,2]. It is also the source for generating sustainable, clean and green energy.…”

“…The DFIG system is popular system that is used worldwide over others generators [1]. Doubly-fed generator rotors are typically wound rotor type with 2 to 3 times the noumber of turns of the stator [3].…”

Transient stability analysis of IEEE 9-bus system integrated with DFIG and SCIG based wind turbines

“…SCIG has been considered since it is also a very well-known type of generator, but researchers haven't used it as much. It is a robust and stable generator with mechanical simplicity, greater efficiency, and low maintenance [8]. As for DFIG, the rotor uses a back-to-back power converter; the converter's rate is about 25% -35% of the generator rating [8].…”

“…It is a robust and stable generator with mechanical simplicity, greater efficiency, and low maintenance [8]. As for DFIG, the rotor uses a back-to-back power converter; the converter's rate is about 25% -35% of the generator rating [8].…”