Siemens SINAMICS DCM 6RA80, Часто задаваемые вопросы, Страница: 70 / 79

70
Structure diagram of the entire armature control loop with an example
Speed controller with a lower-level current controller and DC motor as the load.
A
n*: speed setpoint, nact: speed actual value, I*: current setpoint, Iact: actual current value;
Ust: control voltage, U
A
: armature voltage, EMF: induced motor voltage,
I
A
: armature current motor, T
t
: dead time due to power system cycles,
T
M
: mechanical ramp-up time constant; M
L
: load torque, n
M
: the motor speed
n-controller: speed controller, i-controller: current controller
K
A
, T
A
: PT1 element due to armature circuit inductance and armature circuit resistance;
Kp: controller gain, Tn: controller reset time
Example:
B6C circuit, line voltage Us:3AC400 V, armature circuit inductance motor L
M
: 0.5 mH,
rmature circuit resistance motor R
M
: 0.02 ohm, inductance of smoothing reactor L
G
: 1 mH,
resistance of smoothing reactor R
G
: 5 mOhm, cable deemed negligible.
Voltage drop commutating reactor: Vimp = 4%,
Line frequency: 50 Hz, rated armature current I
AN
: 600 A, rated armature voltage U
AN
: 420 V,
firing angle range = 90 degrees for 100% in the calculation of the software
Parameters of the dead-time element:
Ideal no-load direct voltage = Udi = Us * 1.35 = 540 V
The trigger firing angle for rated armature voltage
2
is derived from the cosine function of
the control characteristic: cos
2
= U
AN
/ Udi = 420 / 540 = 0.778 yields
2
approx. 39 degrees
K
t
= / (
1
–
2
) = 90 / (90 – 39) = 1.76
Mean (statistical) dead time for 6-pulse bridge connection (p=6) and 50 Hz:
T
t
= 20 ms / p = 20 / 6 = 3.33 ms, half of which is postulated as the statistical dead time:
T
t
= 1.66 ms
Parameters of the lag element:
R
A
= R
M
+ R
G
+ R
S
, d
x
= 0.5 * Vimp = 0.02; R
S
= d
x
* Udi / I
AN
= 0.02 * 540 / 600 = 0.018
R
A
= 0.02 + 0.005 + 0.018 = 0.043
Armature circuit inductance L
A
= L
M
+ L
G
= 1.5 mH
Armature circuit gain:
K
A
= U
AN
/ (I
AN
* R
A
) = 440 / (600*0.043) = 16.3
Armature time constant = L
A
/ R
A
= 1.5*10
-3
/ 0.043 = 0.0349 s = 34.9 ms = T
1
If the set current limit is greater than I
AN
, this peak current must be substituted in the
formulas. This also applies to the torque M
MN
for the mechanical ramp-up time constant T
M
.
M
L
-nact
n
M
K
t
, T
t
K
A
, T
A
Kp2, Tn2
Kp, Tn
T
M
Dead
i-controller
n-controller
n*
I*
I
A
-Iact
Uctr
l
U
A
-EMF
....MOTOR