Wind power technology - Wind Power Integration: Connection and System Operational Aspects - page 74

P g + jQ g

v s

i g

Power
system

i s

v r

i r

C1

C2

AC/DC DC/AC

Crowbar
protection

Controller

Figure 3.18 Typical configuration of a DFIG wind turbine

w r > w s w r < w s

P P

Super synchronous
operation

Sub synchronous
operation

Figure 3.19 Super synchronous and sub synchronous operation of the DFIG wind

turbine

Operating in steady state the relationship between mechanical power, rotor
electrical power and stator electrical power in a DFIG is shown in Figure 3.20. In this
figure P m is the mechanical power delivered to the generator, P r is the power deliv-
ered by the rotor, P air gap is the power at the generator air gap and P s is the power
delivered by the stator. P g is the total power generated and delivered to the grid.
From Figure 3.20, it is seen that if the stator losses are neglected then

P air gap ¼ P s ð 3 : 17 Þ

and if we neglect the rotor losses then

P air gap ¼ P m P r ð 3 : 18 Þ