Direct Torque Control with Space Vector Modulation (DTC-SVM) of ...

Control methods of PM Synchronous motor
For many years the CTA control ( I
_
= 0 ) method has been a popular technique for a
sd
ref
long time because of simple control. This method was dedicated for surface permanent
magnet synchronous motor (SPMSM), where the magnetic saliency does not exist
[126]. So the maximum torque per ampere is obtained, when stator current vector is
shifted in respect to rotor flux vector 90 degree. However, in IPMSM, maximum torque
per ampere is obtained with torque angle more than 90 degree. This is because of
existence of reluctance torque component due to magnetic saliency (see subchapter
2.2.2). Therefore, the I
sd_
ref
should be negative value [44].
The main question is how or in which manner produce the reference currents in d-q
frame. Its leads to many realization of current control structure. Among them generally
we can distinguish two structures of current control loop. One of them is hysteresis
based control (Fig.4.7a) [3,52] and the second one is PI based current controllers
(Fig.4.7b).
Hysteresis based current control has following disadvantage such as [3]:
• measurement of three phase currents are required,
• three independent hysteresis current controllers are required,
• variable switching frequency is achieved,
• fast sampling time is required.
All this listed above disadvantage can be eliminate, when the PI current control are
used. This structure are mostly used in industrial application (Fig. 4.7b).
a)
U DC
M e _ ref
Fig. 4.5
I d _ ref
I q _ ref
d,q/ABC
I A _ ref
I B _ ref
I C _ ref
−
−
S A
S B
S C
Inverter
current
feedback
−
I A current
I
sensors
B
I C
rotor
position
sensor
PMSM
56