Figure 4.93: Line voltage waveforms of CV-BLDC mode.
⎩ I m , α−4π≤θ < α−2π/3
i C (θ)=i A
−I m , α−π/3 ≤θ < α+π/3
, th rs
In these equations, I m is the magnitude of the constant current delivered by
the power supply during the energized period. During the silent interval, the
phase current is set to zero.
T em (θ,α)= P m
e A (θ)i A (θ,α)+e B (θ)i B (θ,α)+e C (θ)i C (θ,α)
Since the current waveform is related to the commutation angle, both the
average torque and the torque ripple get affected when different commutation
angles are used. Figure 4.94 shows the EM-torques produced for two different
commutation angles, α=20 ◦ and α=20 ◦ .
The average EM torque produced by a spindle motor driven in the CC-
BLDC mode is
T em =
T em (θ,α)dθ =
i A (θ,α)e A (θ)dθ
E m I m sin(θ)dθ = 3
3E m I m