Hardware Reference
In-Depth Information
Figure 4.91: Current vector in the 6-step and 12-step.
4.4.4.1 The Optimal Commutation Angle of Spindle Motor
The back-EMF of a spindle motor can be de
fi
ned by the expression in equation
4.89. Back-EMF of one of the phases is shown in Figure 4.92.
⎨
e
A
= E
m
sin (ω
e
t)
e
B
= E
m
sin
¡
¢
ω
e
t −
2
3
(4.89)
¡
¢
⎩
ω
e
t +
2
3
e
C
= E
m
sin
When the BLDC drive mode is used, the exciting state spans over 120
◦
in
the space domain, and the silent state spans over 60
◦
. However, the commu-
tation angle α could be set at different value in the motor operation as shown
in Figure 4.92.
Varying the commutation angle αaffects the performance of the motor. It is
important to
fi
nd the commutation angle that results in optimal performance of
the motor. Optimal performance means the use of minimum effective current
to produce the required electromagnetic torque. Under this condition, the
copper loss is minimum while generating the required torque. In the analysis
presented below, the speed of the motor is assumed constant and the effects
of the spindle motor inductance are assumed negligibly small. Moreover, for
simplicity and conciseness of analysis, the magnetic pole-pair is set to one.
