115 - 23/May/97
Having a constant amplitude of phase currents, the current vector will rotate at
ω
r, having a
constant amplitude along the period. Hence, conditions of obtaining ripple-free
electromagnetic torque are fulfilled. The torque generation and the current control loops are
conditioned by the shaft sensor, which is giving the rotor speed and the rotor position
information. An application of synchronous motor calls for an absolute position sensor, in
order to set the current angle
θ
i between the magnetomotive force and the rotor flux.
DBM is designed to interface with resolvers as the motor shaft sensors. Details of the
speed/position sensing are described in par. 5.4 . In Fig. 1,
θ
r stands for the angular
displacement of the rotor flux with respect to the phase A winding of the stator. Assuming the
speed of rotation
ω
r,
θ
θ
ω
r
0
t.
=
+
Electromotive forces, induced in the stator windings will be:
e
e
e
A
B
C
=
+
=
−
=
−
Ψ
Ψ
Ψ
r
r
r
r
r
r
r
r
r
/ 2)
/ 6)
/ 6)
ω
θ
π
ω
θ
π
ω
θ
π
cos(
cos(
cos(
5
In order to obtain the magnetomotive force vector as described in the Fig. 1, the stator phase
currents has to be:
i
I
i
I
i
I
A
s
B
s
C
s
=
+
=
+ −
=
+ −
cos(
cos(
cos(
θ
θ
θ
θ
π
θ
θ
π
r
i
r
i
r
i
)
/ 3)
/ 3)
2
4
(1)
(2)
(3)
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