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

Direct Torque Control with Space Vector Modulation
G
Ω _ closed
( z)
=
K
pΩ
( K + K )( z−
) aA
K + K
pΩ iΩ Ωd
pΩ
iΩ
2
pΩ
( z−1)( z − bz+ c)( z− 1) + ( KpΩ + KiΩ)( z−
) aAΩ
d
KpΩ
+ KiΩ
K
(5.91)
In many practical cases the digital filter is used in speed measurement loop (see Fig.
5.49).
Ω m _ ref
( z)
PI controller GΩ
( z)
C ( z)
Ω
Me_ ref()
z
D ( z)
Ω
M ( ) e
z
M ( ) L
z
ZOH
Control Plant
}
1
Js
Ω ( z m
)
Torque control loop
F ( z)
Ω
Digital Filter
Figure 5.49. Block scheme of speed control with digital filter in speed measurement loop
(discrete domain).
The transfer function FΩ ( s)
of first order low pass filter in s domain is expressed as:
FΩ () s =
1
s
+ 1
ω
i
(5.92)
2 ω
Where ωc
= 2π
fc
and f
c
is cut off frequency and tan(
cTs
ω
i
= ) [2]. In practice f
c
T 2
is selected in the range 20-250Hz
2( z −1)
Using the Tutsins’s approximation method s = for discretization process, the
Ts
( z+
1)
discrete transfer function of first order low pass filter can be expressed as:
Tsωi
2 −Tsωi
Where: a1
= , b1
=
2 + T ω 2 + T ω
s
i
Tsωi
( z + 1)
2 + T ω a ( z+
1)
FΩ
( z)
= =
z
2 T ω
s
s
s i
1
(5.93)
2 −Tsωi
−
z−
b1
+
i
s
i
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