14 System description
The main components of a wind turbine system are presented in the picture below.
ACS800-67
ACS800-67 is air-cooled four-quadrant wind turbine converter for wind turbine
applications. The converter can be located up in the nacelle or in down tower of the wind
turbine.
The converter allows independent control of real and reactive flow in either direction (grid
to rotor), or confined to unidirectional (rotor to grid) real power flow. In doubly-fed systems
the stator circuit of the doubly-fed induction generator (DFIG) is connected via stator circuit
breaker to the 3-phase electrical power network while the rotor circuit is connected to a
wind turbine converter via slip rings.
When the rotor is accelerated by the wind and the speed is controlled by the pitch of the
blades, the converter can be controlled either in torque control mode or in active power
control mode. If rotor mechanical speed is within acceptable area, the converter can be
started. When the grid-side converter has charged the intermediate DC link properly
(MCB2 closed), and the rotor-side converter has magnetized the generator rotor properly
(correct voltage magnitude and phase sequence between the stator and grid), stator circuit
breaker/contactor can be closed (MCB3), and the converter is ready to operate and deliver
power to the 3-phase electrical power network.
In order to stop the converter, the breakers (MCB2 and MCB3) are opened and the rotor is
braked to standstill by pitch control and mechanical brakes. Block diagrams of the wind
turbine system are shown below. The system includes a doubly-fed AC induction
generator and the wind turbine converter.
Transformer
Generator
Yaw motors
Gear box
Blade
Nacelle
Rotor
Wind turbine control cabinet
Wind turbine converter
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