ABSTRACT:
In this paper, a novel rotor speed estimation method
using model reference adaptive system (MRAS) is proposed to improve the
performance of a sensorless vector control in the very low and zero speed
regions. In the classical MRAS method, the rotor flux of the adaptive model is
compared with that of the reference model. The rotor speed is estimated from
the fluxes difference of the two models using adequate adaptive mechanism.
However, the performance of this technique at low speed remains uncertain and the
MRAS loses its efficiency, but in the new MRAS method, two differences are used
at the same time. The first is between rotor fluxes and the second between
electromagnetic torques. The adaptive mechanism used in this new structure
contains two parallel loops having Proportional-integral controller and
low-pass filter. The first and the second loops are used to adjust the rotor
flux and electromagnetic torque. To ensure good performance, a robust vector control
using sliding mode control is proposed. The controllers are designed using the
Lyapunov approach. Simulation and experimental results show the effectiveness
of the proposed speed estimation method at low and zero speed regions, and good
robustness with respect to parameter variations, measurement errors, and noise
is obtained.
KEYWORDS:
1.
Induction
motor
2.
Lyapunov
function
3.
Model
reference
4.
Adaptive
system (MRAS)
5.
Sensorless
control
6.
Speed
estimation
7.
Vector
control
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Block diagram of the new MRAS observer.
EXPECTED SIMULATION RESULTS:
Fig.
2. Speed estimation error.
Fig.
3. Speed tracking error.
Fig.
4. Rotor flux.
Fig.
5. Load torque and Rs variations.
Fig.
6. Classical MRAS observer: Reference, actual, and estimated speed
for
load torque and Rs variations.
Fig.
7. Classical MRAS observer: Zoom of Reference, actual, and estimated
speed
for load torque and Rs variations.
Fig.
8. Speed of induction motor.
Fig.
9. Speed zoom.
Fig.
10. Speed estimation error.
Fig.
11. Speed tracking error.
In
this paper, a new MRAS rotor speed observer was proposed to improve the
performance of sensorless vector controller of induction machine. The control
robustness is achieved by a sliding-mode controller and its stability is proved
using a Lyapunov approach. Simulation and experimental results for different
speed profiles had shown, on the one hand, that the proposed new MRAS observer
was able to estimate accurately the actual speed at low and zero speed when the
conventional MRAS observer is limited. On the other hand, the robustness of the
proposed observer regarding load torque and stator resistance variations,
especially at low and zero speed, is much better than the classical observer.
REFERENCES:
[1]
J. W. Finch and D. Giaouris, “Controlled AC electrical drives,” IEEE Trans.
Ind. Electron., vol. 55, no. 2, pp. 481–491, Feb. 2008.
[2]
J.-I. Ha and S.-K. Sul, “Sensorless field-orientation control of an induction machine
by high-frequency signal injection,” IEEE Trans. Ind. Appl., vol. 35,
no. 1, pp. 45–51, Jan./Feb. 1999.
[3]
C. Caruana, G.M. Asher, and M. Sumner, “Performance of high frequency signal
injection techniques for zero-low-frequency vector control induction machines
under sensorless conditions,” IEEE Trans. Ind. Electron., vol. 53, no.
1, pp. 225–238, Feb. 2006.
[4]
F. Peng and T. Fukao, “Robust speed identification for speed-sensorless vector
control of induction motors,” IEEE Trans. Ind. Appl., vol. 30, no. 5,
pp. 1234–1240, Sep./Oct. 1994.
[5]
C. Schauder, “Adaptive speed identification for vector control of induction motors
without rotational transducers,” IEEE Trans. Ind. Appl., vol. 28, no. 5,
pp. 1054–1061, Sep./Oct. 1992.
