Performance and Operation Management - Wind Energy Systems for Electric Power Generation - page 137

rotation stages, with input values of the rotor position angle ϕ r derived from a posi-

tion encoder and of the calculated voltage vector angle ϕ VS . In a decoupling stage

the actuating variables for the rotor are calculated in dq-frame, V Rdq , and subjected
to a vector rotation to V R in rotor frame. The converter is a VSI type with dc in-
termediate circuit. It is seen that V R supplies the control signals to the rotor side
inverter. The grid side inverter receives its PWM signals from a respective control.
The authors of [Mue02] have provided an example oscillogram of waveforms
during a time interval of 10 min for a 1,5 MW wind system, nominal speed at
1800 min − 1 , see Fig. 6.15. Note that below rated power the system is controlled
from the electric side, preferably to optimum speed tip ratio; the power is then lim-
ited to rated value by pitch control.
Other control methods, known from industrial applications may also be applied.
As an example [Sim97] describes a variable speed wind generation system where
fuzzy logic principles are used for efficiency optimization and performance en-
hancement; a cage induction generator feeds power via a double-sided pulse width
modulated converter into a utility grid or an autonomous system.

6.4 Basics of Operation Management

6.4.1 General

The operation management has to take care of a safe system performance. This
requires continuous measuring of the quantities relevant for the system state. When
specified limits are surpassed this must be checked. Faults must be detected and
emergency routines initiated if necessary.
This includes monitoring of the states of operation at standstill, running up, wait-
ing, performance under load and shutting down. Error states such as excess speed,
impermissible temperatures and short-circuits must be detected and starting of coun-
termeasures initiated. States of operation may be temporary or steady state.

6.4.2 States of Operation

System check
After activation of operation management the state of the system components is
checked. Any errors must be cleared before the next states are commanded. System
check is also made in operation before switching into other states.

Standstill
In the standstill state the rotor brake is on, rotors blades are in feathering direc-
tion (turned into the wind) while yawing is active, and the generator system is
switched off.