ABSTRACT:
Sensorless control methods are commonly employed to
derive the rotor position and speed information indirectly in permanent magnet
(PM) brushless motor drives. Thereinto, the simple yet effective flux observer
method is extensively applied in a wide range of applications. However, damper
cage is sometimes employed in the rotor of certain PM brushless motor.
Normally, high order current harmonic components occur in such damper cage
during operations. The introduction of these extra current contents can
significantly hinder the performance of conventional flux observer. By applying
Park transformation, the fundamental harmonic components of stator phase
currents, flux linkages, and voltages during steady-state operation, become
constants under rotor synchronous reference frame, while the currents in the
rotor damper cage are still alternating. In this paper, an improved flux observer
method is proposed to filter the harmonic contents under the rotor synchronous
reference frame for PM brushless motor with rotor damper cage. The validity and
performance of the proposed flux observer are verified by both numerical analysis
and experimental results.
KEYWORDS:
1.
Flux observer
2.
Mathematical model
3.
PM BLD motor
4.
Damper cage
5.
Harmonic components
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
The
harmonic components of the stator currents of the PM BLDC motor affect the accuracy
of the flux observer-based sensorless control method. Moreover, some BLDC
motors employ a damper cage or similar structure (such as the shield outside
magnets, or the metal retaining sleeve) in the rotor. Since the currents in the
damper cage cannot be measured, the flux observer-based sensorless control
method is not readily applicable to such BLDC motors. Considering that the
damper cage makes the stator currents have more harmonic components, an
improved flux observer model is proposed. It is under the d-q synchronous
rotating reference frame, so that all the fundamentals of voltage, current and
flux linkage become DC components, whilst the harmonics of the stator currents
and rotor cage currents are still AC components and can be easily eliminated
with low pass filters. Using the left DC components (i.e., the fundamental
components), the rotor position can be estimated accurately. According to the numerical
analysis and experiment results, it is verified that 1the improved flux
observer method works well for the BLDC motor with a damper cage, and the error
between the observed and actual rotor position is sufficiently small.
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[3]
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