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Figure 4.92: Operation states of three-phase BLDC spindle motor.
Therefore, the equation 4.89 is changed to
e A
e B
e C
=
=
=
E m sin (pω e t)=E m sin (θ)
E m sin (θ−120 )
E m sin (θ−240 )
(4.90)
The angular frequency is same as the angular speed of the motor, i.e., ω = Ω.
It is also assumed that the three phase windings are symmetric, the phase re-
sistances of the windings are same and equal to R a . The three phase windings
are Y-connected.
When the CC-BLDC mode is used, the drive current is kept constant in the
energized state as shown in the waveform of Figure 4.92. For the CV-BLDC
mode, the power transistors keep the line voltages of the motor terminals
constant during the energized state. The waveform representing one of the
terminal voltage is shown in Figure 4.93.
4.4.4.2 Optimal Commutation Angle for CC-BLDC Mode
For a three-phase spindle motor driven using constant current mode, the fol-
lowing equations describe the phase currents:
I m , α≤θ < α+2π/3
−I m , α+π≤θ < α+5π/3
0
i A (θ)=
(4.91)
, th rs
µ
I m , α−2π/3 ≤θ < α
θ−
3
−I m , α+π/3 ≤θ < α+π
0
i B (θ)=i A
=
(4.92)
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