What is doubly-fed induction generator?
What is doubly-fed induction generator?
The doubly-fed induction generator (DFIG) with the back-to-back converter is a system frequently used in wind turbines. Traditional wind turbines have fixed turning speeds, while DFIG enables wind turbines to operate with various range of speeds.
What is the difference between induction generator and doubly-fed induction generator?
The difference between a regular asynchronous generator and a DFIG is that the prior is rotor excited whereas the latter is externally excited with an ac-dc-ac convertor. The 3 phase ac input current causes the flux field of the rotor to have an apparent rotation with respect to the rotor.
What is the advantage of double fed induction generator?
It can operate like a synchronous generator and at variable speed, although its stator is directly connected to the grid. The converter can adequately control the voltage (phase and magnitude) that is applied to the rotor and as a consequence control the magnetic field’s frequency or speed.
What is sub synchronous mode in doubly-fed induction generator?
DFIGs are almost classical induction machines that two typical operation modes: the subsynchronous mode (during this mode the rotor absorb power) and the supersynchronous mode (during this mode the rotor generate power). This is mainly due to the slip sign.
What is difference between Dfig and PMSG?
In present scenario there are primarily two types of generators used in WECS namely Doubly Fed Induction Generator(DFIG) used for geared operation for variable speeds and fixed speeds and Permanent Magnet Synchronous generator(PMSG) can operate gearless.
What system is Dfig used?
Doubly Fed Induction Generator (DFIG) are widely used in wind energy generation systems because of high efficiency and independent control of active and reactive power using partial capacity converters.
What are the disadvantages of doubly-fed induction generator?
However, one of the main disadvantages of DFIG is that it is very sensitive to grid faults. To analysis dynamic behaviors of DFIG during grid faults, a model including wind wheel, wind speed, drive train, generator, and converters has been proposed.
Why PMSG is used in wind turbine?
Particularly, PMSG is direct drive, has slow rotation speed, does not have rotor current, and can be used without gearbox. The high efficiency and low maintenance will reduce the cost that is the most concern to invest.
What is squirrel cage induction generator?
The squirrel cage induction generator (SCIG) is attached to the wind turbine by means of a gearbox. The SCIG stator windings are connected to a back to back full power converter. The wind turbine is responsible for transforming wind power into kinetic energy.
What is subsynchronous speed?
Abstract: In the sub-synchronous mode, series-connected wound-rotor induction motor can run at a speed below the synchronous speed with self-starting capability in a manner similar to that of the normal mode of operation of an induction motor.
What is Supersyncronous speed?
Abstract: The name “super synchronous” has been given to a certain type of motor, not because the motor operates above synchronous speed but because it has the ability to develop super torque in starting.
Why Pmsg is used in wind turbine?
What is a doubly-fed induction generator (DFIG)?
This chapter introduces the operation and control of a Doubly-fed Induction Generator (DFIG) system. The DFIG is currently the system of choice for multi-MW wind turbines. The aerodynamic system must be capable of operating over a wide wind speed range in order to achieve optimum aerodynamic efficiency by tracking the opti mum tip-speed ratio.
What is the steady-state equivalent of the doubly fed induction machine?
Figure 15.4. Steady-state–equivalent circuit of the doubly fed induction machine referred to the stator with stator frequency. a = N s N r; R r = I r a. Source: Author.
What is a cascaded doubly-fed induction machine?
The cascaded doubly-fed induction machine consists of two doubly-fed induction machines that are connected mechanically through the rotor and electrically through the stator circuits as shown in Fig. 9.
How does the DFIG change the speed of the generator rotor?
The DFIG can change the speed of the generator rotor by means of controlling the frequency of the rotor field current. When a fault occurs on the grid side and the rotor is accelerated, it can keep the speed of the rotor rotating magnetic field at the synchronous speed via reducing the frequency of the rotor field current.