SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 5.3 – Torque control of sinusoidal motor; phase variable form.
The next step is to employ the inverse Clarke transform to change the three-phase sinusoidal
commutation block into an orthogonal two-phase one. This implements a controller in the
stationary reference frame, as shown in Figure 5.4. The references are generated using Equation
(5.3), where the factor of 3/2 comes from the fact that just two windings must produce the same
torque as the previous three. The current reference signals generated are those shown in Figure
5.8-b and Figure 5.8-c.
ref 3 ref
i I
2
ref 3 ref
i I
2
Figure 5.4 – Torque control in stationary reference frame.
sin( )
p r
cos( )
p r
Although only the stationary reference frame controller operates using the SV directly, both
versions accomplish the control shown in Figure 5.5, where the SVs are given by Equations (5.4)-
(5.5). As the rotor rotates, r increases and the sinusoidal commutator inherently produces three-
phase (or two-phase) values corresponding to a SV with angle /2 to ensure maximum
torque per current. When the current SV is aligned as such, torque is directly proportional to the
peak current.
r
(5.3)
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