Environmental Engineering Reference
In-Depth Information
The corresponding frequency is
K v
L N C N ,
ω o =
ω o , there is
which is called the outer loop frequency. For a given
2
o L N C N .
K v = ω
If the voltage controller K v
is tuned according to this formula, then the transfer function (11.5)
becomes
s
1
C N .
=
o ·
T ( s )
s 2
+
s
ω i + ω
The Bode plot is shown in Figure 11.7 for different
ω o . It consists of three parts A, B and C.
When K v or
ω o is increased, the left part A moves towards right while the length of the middle
part B is shortened and the right part C remains almost unchanged (when K v or
ω o is not
extremely large), and the shift
becomes smaller. When C N is decreased, parts B and C move
up and part A extends while the length of part B is shortened, and the shift
ε
ε
becomes larger.
Hence, in order to reduce the shift
ω o ) and larger C N are needed. Moreover,
the left part A of the Bode plot should move towards the right as close as possible to the right
part C. The extreme case is to choose
ε
, larger K v
(or
ω o = ω i .
This makes use of the full physical capability of the controller. The corresponding Bode plot
is shown as the thick line in Figure 11.7 and the voltage controller is obtained with
i L N C N .
K v = ω
(11.8)
ω i
0
g
-20
B
-40
A
ω o =0.5 ω i
C
ω o =0.0025
ω i
-60
ω o =
ω i
-80
10 -3
10 -2
10 -1
10 0 10 1
Frequency (rad/sec)
10 2
10 3
10 4
10 5
10 6
Figure 11.7 Bode plot for the voltage loop
 
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