Doubly Fed Induction Generator Systems For Variable Speed Wind Turbine

1. Doubly Fed Induction Generator Systems For Variable Speed Wind Turbine Modern Instrumentation Project with lab view 2009 AdolpheKazadi

2. The fundamental feature of the DFIG is that the power processed by the power converter is only a fraction of the total wind turbine power, and therefore its size, cost and losses are much smaller compared to a full size power converter.

3. All electric machines are categorized as either Singly-Fed with one winding set that actively participates in the energy conversion process or Doubly-Fed with two active winding sets. Although sometimes described as doubly-fed, the wound-rotor induction machine (either Krämer drive where the slip power from rotor is lost in resistors or subsynchronousScherbius drive where the slip power is fed back to AC line) and the field-excited synchronous machine are singly-fed machines because only one winding set actively participates in the energy conversion process. to make variable-speed operation possible. Due to the converter that is needed, the price of variable-speed turbines tends to be higher than constant speed turbines. A straightforward way to obtain variable speed is to connect a converter directly between the stator circuit of the generator and the grid. This converter has to be designed for the rated power of the turbine. An alternative concept, shown in Fig. 1, is a wind turbine with a doubly-fed induction generator (DFIG), where the converter is connected to the rotor windings. Compared to the turbines with the converter connected to the stator, the DFIG has a number of advantages. The converter is much cheaper, as the inverter rating is typically 25% of total system power, while the speed range of the generator is 33% around the synchronous speed. Also, the inverter filters are much cheaper as they are also rated at 25% of the total power. Further, power-factor control can be implemented at lower cost, because the DFIG basically operates similar to a synchronous generator [2].

5. The stator electric values are indicated by the subscript s and the rotor electric values are indicated by the subscript r. u is a voltage, R is a resistance, i is a current, λ is a flux linkage. ω is the stator electrical frequency and s is the rotor slip Ls , Lr and M are respectively the stator and the rotor leakage inductance and the mutual inductance between the stator and the rotor. J where ωr is the rotor speed and ω1 stator frequency