ABB ACS800-67LC, Hardware Manual

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Operation principle and hardware description 23
3
Operation principle and
hardware description
What this chapter contains
This chapter describes the operation principle and construction of the wind turbine
converter.
Operation principle
ACS800-67LC liquid-cooled wind turbine converter is used with induction generators with
wound rotor and slip rings, such as the ABB AMK series. The converter is connected
between the generator rotor and the power supply network. The converter can be installed
in a downtower cabinet, tower or in the nacelle.
Doubly-fed asynchronous generators are essentially wound rotor induction generators
with variable frequency excitation of the rotor circuit, incorporating rotor direct torque
control (DTC) via power converter. The rotor control is four-quadrant, allowing
independent control of real and reactive power flow in either direction (rotor to grid or grid
to rotor), or confined to unidirectional (grid to rotor) active power flow.
Induction generators have a gearbox for coupling the generator shaft to turbine hub, active
control of turbine blade pitch for maximizing production and controlling mechanical speed,
and variable speed operation depending on the rating of power converter relative to
turbine rating (typically ±30% of the generator synchronous speed).
In doubly-fed systems the stator circuit of the generator is connected to the power supply
network (grid) while the rotor circuit is connected to a converter via slip rings. In a doubly-
fed concept the size of the power converter is significantly smaller than in eg, full-power
concept because only one-third of the rated generator power is fed through the converter