Direct Power and Torque Control of AC/DC/AC Converter-Fed ...

3. Vector Control Methods of AC/DC/AC Converter-Fed IM Drives – A Review
Tab. 3. 1. Optimal switching table.
S
Ψ
S
M Sector 1 Sector 2 Sector 3 Sector 4 Sector 5 Sector 6
1
U Sc2
(1,1,0)
U Sc3
(0,1,0)
U Sc4
(0,1,1)
U Sc5
(0,0,1)
U Sc6
(1,0,1)
U Sc1
(1,0,0)
1
0
U Sc7
(1,1,1)
U Sc0
(0,0,0)
U Sc7
(1,1,1)
U Sc0
(0,0,0)
U Sc7
(1,1,1)
U Sc0
(0,0,0)
-1
U Sc6
(1,0,1)
U Sc1
(1,0,0)
U Sc2
(1,1,0)
U Sc3
(0,1 0)
U Sc4
(0,1,1)
U Sc5
(0,0,1)
1
U Sc3
(0,1,0)
U Sc4
(0,1,1)
U Sc5
(0,0,1)
U Sc6
(1,0,1)
U Sc1
(1,0,0)
U Sc2
(1,1,0)
0
0
U Sc0
(0,0,0)
U Sc7
(1,1,1)
U Sc0
(0,0,0)
U Sc7
(1,1,1)
U Sc0
(0,0,0)
U Sc7
(1,1,1)
-1
U Sc5
(0,0,1)
U Sc6
(1,0,1)
U Sc1
(1,0,0)
U Sc2
(1,1,0)
U Sc3
(0,1,0))
U Sc4
(0,1,1)
The main known drawbacks of the DTC are:
• high and variable switching frequency, which produces high VSI power
losses,
• violence of polarity consistency rules,
• start and low speed operation problems,
• steady states operation error,
• torque pulsation,
• flux and torque estimation problems.
Therefore, in the literature there is a lot of work which have a goal to improve the
features of the DTC, for instance, modified switching table. Other method produces
additional active vector as a sum of the nearest one. Finally, another kind of three
levels of hysteresis controller is proposed as in [18], [34], [60].
In spite of these disadvantages the DTC is very interesting for researcher thanks to
its advantages as follows:
• simple control structure,
• independent of rotor parameter,
• inherently motion-sensorless,
• excellent dynamic performance of torque control loop,
• no current control loops,
• no coordinates transformations,
• separate modulator is not needed.
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