Adding Active Filtering Functionality to Doubly-fed Induction Generator (DFIG)-based Wind Turbines
Location: Greece
Publication date: 2006-02-27
Published in: European Wind Energy Conference 2006, Athens (Greece) - EWEC 2006

Local members

Alvaro Luna

PhD. Senior Researcher.

Jose Ignacio Candela

PhD. Senior Researcher. Project Responsible

External members

, Burgos. R.



In power systems, the integration of doubly-fed induction generator (DFIG) based wind turbines (WT) is increasing. This type of turbine uses a four-quadrant converter to link the rotor circuit of the generator to the grid. This converter in turn has a back-to-back structure, where the rotor-side inverter controls the currents in the generator in order achieve the maximum efficiency in the wind energy usage, while the front-end inverter controls the currents injected into the grid keeping constant the energy in the DC-bus.

The main goal of this paper is to extend the capabilities of the front-end inverter by means of adding an active filtering function to its controls. When the front-end inverter works in active-filter mode, the instantaneous active power oscillations associated to distorted loads are transformed into instantaneous energy variations in the DC-bus. Whether a DFIG-WT works in grid connected or stand-alone mode, the implementation of the active filtering function makes easier its control, since the voltage harmonics in the Point of Common-Coupling (PCC) are effectively attenuated and the oscillations in the instantaneous power consumed by nonlinear loads do not flow into the DFIG. 

The front-end inverter also can supply active power to the grid with unity power factor. The proper control of both front-end and rotor-side inverters regulates the active power sharing between the stator and the rotor of the DFIG. In the control of the DFIG-WT, this functionality increases the efficiency in the generation process by reducing its losses. Additionally, the dynamic behaviour of the generation system is improved because sudden fluctuations in the active power consumed in the grid are damped by the energy stored in the DC-bus, and hence cannot directly affect the DFIG.

The front-end inverter also can inject reactive power into the network. The proper sharing of the reactive power between the front-end inverter and the DFIG achieves minimum losses in the system.

This paper shows that the front-end inverter in the DFIG-WT can play a more important role in the generation process. Cancellation of current harmonics improves the behaviour of the power system and simplifies the control of the DFIG-WT. The control strategy proposed in this paper also achieves a faster response and a higher efficiency in the generation process.