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

Voltage source PWM inverter for PMSM supply
The one leg of inverter consists of two transistor switches. A simple transistor switch
consist of feedback diode connected in anti-parallel with transistor. Feedback diode
conducts current when the load current direction is opposite to the voltage direction.
Assuming that the power devices are ideal: when they are conducting the voltage across
them is zero and they present an open circuit in their blocking mode. Therefore, each
inverter leg can be represented as an ideal switch. Its gives possibility to connect each
of the three motor phase coils to a positive or negative voltage of the dc link ( U ).
Thus the equivalent scheme for three-phase inverter and possible eight combinations of
the switches in the inverter are shown in Fig. 3.5.
DC
U
7
= 111
U
0
= 000
U DC
1 1
S
A
SB
1
S C
U DC
S
A
0 0
SB
0
S C
U
1
= 100
A B C
U
2
= 110
A B C
U
3
= 010
U DC
1
SA
0
SB
0
S C
U DC
1 1
S
A
SB
0
S C
U DC
0
S
A
1
SB
0
S C
U
4
= 011
A B C
U
5
= 001
A B C
U
6
= 101
A B C
U DC
0
SA
1
SB
1
S C
U DC
0
S
A
0
SB
1
S C
U DC
1
S
A
0
SB
1
S C
A B C
A B C
A B C
Figure 3.5 Possible switches state in VSI.
The six positions of switches ( U1 − U6) produce an output phase voltage equal ± 1/3 or
± 2/3 of the DC voltage. The last two ( U0,
U
7) give zero output voltage. The output
phase voltages produced by inverter are shown in Fig. 3.6a. and adequate line to line
voltage calculated in bellow formula also are presented in Fig. 3.6b.
UsAB = UsAN − UsBN
(3.1a)
UsBC = UsBN − UsCN
(3.1b)
UsCA = UsCN − UsAN
(3.1c)
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