ABSTRACT:
This
paper proposes a new position sensorless drive for brushless DC (BLDC) motors. Typical
sensorless control methods such as the scheme with the back-EMF detection
method show high performance only at a high speed range because the magnitude
of the back-EMF is dependent upon the rotor speed. This paper presents a new
solution that estimates the rotor position by using an unknown input observer
over a full speed range. In the proposed method, a trapezoidal back-EMF is
modelled as an unknown input and the proposed unknown input observer estimating
a line-to-line back-EMF in real time makes it possible to detect the rotor position.
In particular, this observer has high performance at a low speed range in that
the information of a rotor position is calculated independently of the rotor
speed without an additional circuit or complicated operation process.
Simulations and experiments have been carried out for the verification of the
proposed control scheme.
KEYWORDS:
1.
BLDC motor
2. Full
speed range
3. Sensorless
control
4. Unknown
input observer
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
EXPECTED SIMULATION RESULTS:
(a) Rotor
speed.
(b) Load
torque.
(c) Phase
current.
(d) Line-to-line
back-EMF.
(e) Commutation
function.
(f) Commutation
signal.
Fig.
2. Response waveforms at under step change of load torque. (Speed reference: 50
rpm, Load: 0.2 → 0.5 Nm).
(a) Rotor
speed.
(b) Load
torque.
(c) Phase
current.
(d) Line-to-line
back-EMF.
(e) Commutation
function.
(f)
Commutation signal.
Fig.
3. Response waveforms under step change of load torque. (Speed reference: 1650
rpm,
Load:
0.75 → 1.5 Nm).
(a) Rotor
speed.
(b) Speed
reference.
(c) Phase
current.
(d) Line-to-line
back-EMF.
(e) Commutation
function.
(f) Commutation signal.
Fig.
4. Response waveforms under step change of speed reference. (Load: 0.75 Nm,
Speed
reference:
50 → 1650 → 50 rpm).
CONCLUSION:
This
paper presented a new approach to the sensorless control of the BLDC motor
drives using the unknown input observer. This observer can be obtained
effectively by using the equation of augmented system and an estimated line-to-line
back- EMF that is modelled as an unknown input. As a result, the actual rotor
position as well as the machine speed can be estimated strictly even in the
transient state from the estimated line-to-line back-EMF. The novel sensorless
method using an unknown input observer can
v be achieved without additional circuits.
v estimate a rotor speed in real time for
precise control.
v make a precise commutation pulse even in
transient state as well as in steady state.
v detect the rotor position effectively over a
full speed range, especially at a low speed range.
v calculate commutation function with a noise insensitive.
v be easily realized for industry application by
simple control algorithm.
The
simulation and experimental results successfully confirmed the validity of the
developed sensorless drive technique using the commutation function.
REFERENCES:
[1]
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[2]
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[3]
S. Ogasawara and H. Akagi, “An approach to position sensorless drive for brushless
DC motors,” IEEE Trans. on Industry Applications, vol. 27, no. 5, pp.
928-933, 1991.
[4]
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[5]
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