Environmental Engineering Reference
In-Depth Information
11.4.2 Fault Scenarios
The faults in the pitch system originate either from the internal faults in the system
or from the pitch control loop in the GSPI controller as this loop sets the reference
pitch angle. The bias and the gain faults in pitch sensor result in bias and gain in
the final blade pitch angle, while the complete failure of the pitch sensor results in
pitching the blade to feather. The pitch sensor fault also affects the GSPI pitch
control loop, as the faulty pitch measurement affects the choice of the scheduled
gains. Moreover, the generator speed faults will lead to either bias in the final
blade pitch angle or in actuator runaway on the system level. Therefore, only the
listed faults in Table 11.3 are considered.
Different magnitudes for each fault are simulated in order to estimate the
severity of the fault as function of its magnitude. Some magnitudes depend on the
corresponding environmental condition, other magnitudes are absolute. The
dependency of the fault on the environmental condition is introduced in order to
prevent losing rotor torque, which in turn will shut down the turbine (Table 11.4 ).
As the hydraulic pitch systems are common in utility-scale wind turbines, a
hydraulic system is considered in order to study the performance degradation fault
effects. The hydraulic pitch system consists of the main pump that provides the
hydraulic pressure to the system, a set of valves that have different tasks such as the
servo valves that control the position of the actuators and the blade pitch motion is
achieved through an actuator, e.g., cylinder (Fig. 11.8 ). The system is also provided
with a controller that accepts the error signal between the measured blade pitch
angle and the set reference one and issues the appropriate command to the servo
valves. The reference pitch angle is set by the baseline GSPI controller, and the basic
implementation of the pitch system controller could be a proportional gain [ 16 ].
The performance degradation of the hydraulic pitch system might rise from
different sources such as pump wear, hydraulic leakage, high air content in oil, and
pressure drop [ 15 , 20 ]. These faults lead to change in the system dynamics and
consequently to performance degradation, and in case of total failure, it leads to
actuator stuck in its current position. The change in the dynamics is pronounced by
varying the nominal natural frequency x n and damping ratio f of the system into
the new values x n ð c Þ and f ð c Þ where the parameter c is used to identify the fault
type shown in Table 11.5 .
Table 11.3 List of
considered pitch
system faults
Fault
code
Fault
Fault
type
Pitch
sensor
B
Bias
Incipient
C
Gain
Incipient
Pitch
system
D
Performance
degradation
Incipient
E
Actuator stuck
Abrupt
F
Actuator runaway
Abrupt
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