induction generator (DFIG)-based WECS in MATLAB/Simulink. The
obtained results are compared with the traditional PI controller [9]
and Fuzzy-PI controller [44]. To demonstrate the effectiveness of
the proposed control scheme, the overshoot of frequency devia-
tion, settling time and Integration of Time multiplied by Absolute
Error (ITAE) will be used to evaluate the control performance.
Finally, the robust performance testing based on Monte-Carlo
approach is carried out.
The rest of the paper is organized as follows: in Section 2 the
principle of DFIG-based WECS control issue based on the frequency
change is presented. Then, power system models used for frequen-
cy regulation test are proposed. The control strategy proposed is
described in Section 3. Simulation results and discussions are
shown in Section 4. Finally, conclusions are given in Section 5.
2. Models for LFC
The DFIG-based WECS has the ability to generate power with
variable mechanical speed and extract the kinetic energy stored
to support the frequency regulation [6]. Details about the principle
of frequency control for DFIG-based WECS and the models adopted
by the LFC for the power systems with DFIG-based WECS will be
presented in this section.
2.1. The principle of frequency control for DFIG-based WECS
In this paper, the wind power generation based on DFIG-based
WECS is considered.
In steady state, in order to maintain a desired speed holds. How-
ever, the electronic converter is able to control the active power
output arbitrarily, and almost instantly, by resorting to the kinetic
energy stored in the rotational masses. This translates into a
change in the rotational speed, which can take place only for a
short period of time in order to assure that remains inside its
operational limits.
Fig. 1 depicts the most commonly used variable-speed machi-
nes for wind energy conversion systems. p
in
= p
out
holds in order
to maintain a desired speed
x
e
in steady state. However, the active
power output can be controllable for the electronic converter dis-
cretionarily, and almost instantly, by resorting to the kinetic ener-
gy stored in the rotational masses. This is translated into a change
in the rotational speed,
x
e
that can take place only for a short peri-
od of time with its operational limits inside [33].
Two important features of the above mentioned WECS must be
taken into account to develop a control strategy:
As a result of depending on the wind, the primary power source
cannot be controlled.
Wind generators can provide varying active power.
The frequency control strategy for DFIG-based WECS used in this
paper relies on a conventional primary regulation, when the WECS
performs in a transient way. As mentioned above, wind generators
only can perform in a transient manner utilizing the stored kinetic
energy. In this approach, inertia of WECS contributes to that of the
rest of the power system, which is different from the inertial control
in earlier works. Since WECS hold the capability of fast power injec-
tion, the frequency regulation can take advantage of their faster
response [33]. Previous works do not exploit the advantage, making
non conventional generators behave like conventional generators
[34]. Adopted DFIG-based WECS takes advantage of their faster
response to support the LFC, as provided in Fig. 2. As the system
Fig. 2. The frequency control strategy for DFIG-based WECS.
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