ABSTRACT:
Participation
of the wind turbine generators (WTGs) in the frequency regulation service is an
appealing issue in order to consider the safe increasing of the wind power
generation. The droop and virtual inertia control are the most popular approaches
that facilitate the WTGs to provide frequency regulation. However, the
intermittent nature of the wind complicates the implementation of these methods
and has impacts on the wind turbine stability and may cause violation of the
allowed power reserve and minimum turbine rotor speed. Therefore, in this
paper, a control approach based on the dynamic de-loading technique is
proposed, where the wind turbine operating curve is dynamically adjusted in the
response of the frequency deviation throughout controlling the turbine
tip-speed ratio which helps the turbine provide steady-state power sharing
within the reserved power as well as the transient response within its
stability criteria. In addition, the inertial response based on a dynamic gain
is suggested. The inertial weighting gain has been formulated where it is continuously
regulated in the response of rotor speed and reflects the amount of available
kinetic energy in the rotating mass. The effectiveness of the proposed control
approaches is verified throughout the comparisons of the results with the fixed
inertial gain control and the droop control. The simulation results confirm
that the combined control of the proposed tip-speed ratio and dynamic inertia
control improve the overall system dynamic behavior in terms of frequency
response and turbine stability.
KEYWORDS:
1. Variable
speed wind turbine
2. Frequency regulation
3. De-loading
4. Inertia
response
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
This
study focused on the frequency regulation capability of VSWTs. A tip-speed
ratio control is presented, where the wind turbine operating curve is
dynamically adjusted in the response of frequency deviation. Furthermore, inertial
response based on a dynamic gain is suggested, where the inertial weighting
gain is continuously regulated in the response of the rotor speed and reflects the
amount of available kinetic energy. According to the proposed control strategy,
the wind turbine can provide frequency regulation effectively up to rated wind
speed (over-speed control zone).However, above rated wind speed, the wind
turbine will be operated at rated power and cannot provide frequency regulation
supports. The proposed control strategy has been analyzed at different load
step disturbances at up- and down-frequency events along the over-speed control
zone. Also, the proposed control methods are compared with the two different
implementations of the droop control and the inertial control. The results proved
that the proposed dynamic tip-speed ratio control has the ability to improve
frequency nadir and steady state frequency while ensuring stable operation of
the wind turbine. Moreover, the proposed control approaches ensure stable
operations of the wind turbine even at low wind speed at 7.5 m/s and high step
disturbances of 0.15 pu. The proposed control strategy can be extended in the future
to be valid for all wind speed ranges and also can be extended to help the WTGs
to participate in the load frequency control.
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