## What are the main differences 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 is Dfig generator?

The DF generator (DFIG) is an asynchronous wound rotor slip ring machine where the rotor windings are connected to a small converter via slip rings and brushes. The generator feeds power both from the stator and also from the rotor.

### What is the difference between synchronous and asynchronous generators?

Permanent magnet synchronous generators require no rotor field excitation. The construction of asynchronous generators is less complicated than the construction of synchronous generators. Asynchronous generators require no brushes and thus no brush maintenance.

What is the principle of Dfig?

The principle of the DFIG is that stator windings are connected to the grid and rotor winding are connected to the converter via slip rings and back-to-back voltage source converter that controls both the rotor and the grid currents. Thus rotor frequency can freely differ from the grid frequency (50 or 60 Hz).

## 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’s the advantages of doubly fed induction generator?

The primary advantage of doubly-fed induction generators when used in wind turbines is that they allow the amplitude and frequency of their output voltages to be maintained at a constant value, no matter the speed of the wind blowing on the wind turbine rotor.

### What rotor is used in Dfig?

A seventh-order dynamic model [4] is used for the DFIG with rotor side converter. The model is derived from the voltage equations of an induction machine in a synchronous reference frame.

What is the difference between synchronous generator and induction generator?

An alternating or synchronous generator requires a separate DC excitation system, whereas an induction generator takes reactive powers from the powers system for field excitations. If induction generators are meant to supply standalone loads, a capacitors bank must be connected to supply reactive power.

## What is the difference between synchronous motor and induction generator?

Induction Motor. The fundamental difference between these two motors is that the speed of the rotor relative to the speed of the stator is equal for synchronous motors, while the rotor speed in induction motors is less than its synchronous speed.

Why Dfig is called doubly-fed?

A Doubly Fed Induction generator as its name suggests is a 3 phase induction generator where both the rotor and stator windings are fed with 3 phase AC signal. It consists of multi phase windings placed on both the rotor and stator bodies.

### What are the advantages of PMSG?

PMSG also has advantages of high efficiency and reliability, since external excitation and conductor losses are removed from the rotor. To supply the grid with active power at fixed voltage and frequency, the PMSG is connected to grid via a line power converter.

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.

## What is the difference between A DFIG and a PMG?

With high average-wind speeds, the DFIG turbine operates closer to the rated point, and can close the efficiency gap on PMGs to some extent. However, even during high average- wind speed, PMG still offers advantages over a DFIG in terms of installation, operation, maintenance and actualized value for money.

How does a DFIG system work?

The DFIG system therefore operates in both sub- and super-synchronous modes with a rotor speed range around the synchron ous speed. The stator circuit is directly connected to the grid while the rotor winding is connected via slip-rings to a three-phase converter.