This paper presents a novel design process of
decoupled PI current controller for permanent magnet synchronous generator
(PMSG)-based wind turbines feeding a grid-tied inverter through back-to-back
converter. Specifically, the design methodology consists of combining disturbance
observer-based control (DOBC) with feedback linearization (FBL) technique to
ensure nominal transient performance recovery under model uncertainty. By simplifying
the DOBC under the feedback linearizing control, it is shown that the composite
controller reduces to a decoupled PI current controller plus an additional term
that has the main role of recovering the nominal transient performance of the
feedback linearization, especially under step changes in the reference.
Additionally, an anti windup compensator arises naturally into the controller when
considering the control input saturation to design the DOBC. This permits to remove the effect of
the saturation blocks required to limit the control input. The proposed control
scheme is implemented and validated through experimentation conducted on
22-pole, 5 kW PMSG. The results revealed that the proposed technique can
successfully achieve nominal performance recovery under model uncertainty as
well as improved transient performances under control saturation.
KEYWORDS:
1.
Anti-windup
scheme
2.
Disturbance
observer
3.
Nominal
performance recovery
4.
Permanent
magnet synchronous generator (PMSG)
5.
PI controller
6.
Renewable
energy
7.
Wind energy
conversion system
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Configuration of a direct-drive PMSG-based WECS connected
to
the host grid.
Fig.
2. System’s response under the composite controller consisting of the feedback
controller (13) and the PI-DO (34)–(37). The controller was tested experimentally
using the block diagram of Fig. 3. Specifically, the PI-DO (34)–(37) was
evaluated with and without the consideration of the reference jump .
Fig.
3. System’s response under the composite controller consisting of the feedback
controller (13) and the DOBC (25). The controller was tested experimentally
using the block diagram depicted in Fig. 2.
Fig.
4. System’s response under a conventional PI current controller [17].
Fig. 5. Performance evaluation of the proposed PI-DO under model uncertainty.
Fig.
6. Experimental results: Performance testing of the proposed PI current
controller under MPPT algorithm, with id (2 A/div), iq (4 A/div), ia (10
A/div), ws (5 [m/s]/div), iga (6 A/div), r (50 [rpm/min]/div), and time (400
ms/div)
CONCLUSION:
This
paper has presented a novel design of decoupled PI controller to enhance the
transient performance for the current control of PMSG-based wind turbine. The
proposed controller technique was established by combining a DOBC with feedback
linearizing control law. It turns out that the composite controller has a
decoupled PI-like structure plus two additional parts. The first part is
basically an anti-windup compensator, while the second part uses the reference
jump information to cancels out the effect of the sudden step changes in the
power demand on the transient response. This modification of the decoupled PI
controller permits to guarantee zero steady-state error without sacrificing the
nominal transient performance specified by the state feedback controller. This
salient feature cannot be achieved under the existing decoupled PI controller, particularly
when the model parameters are not accurate. Experimental tests have been
performed, and the results support the use of the reference jump information to
improve the transient performance under the decoupled PI controller. Therefore,
the proposed approach provides practitioners with an alternate method in
designing a robust decoupled PI current controller for PMSG-based wind energy conversion
system.
REFERENCES:
[1]
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