Control Properties, Definitions; Closed-Loop Control Characteristics - Siemens SINAMICS G130 Engineering Manual

SINAMICS S120
Engineering Information

Control properties, definitions

Criteria for assessing
control quality
Rise time
Characteristic angular
frequency -3 dB
Ripple
Accuracy

Closed-loop control characteristics

Servo control
Induction motor 1PH7/ 1PL6
without
encoder
Booksize format, pulse frequency 4 kHz, closed-loop torque control
125 μs
Controller cycle
Total rise time (rise -
time + dead time)
Characteristic -
angular frequency
-3 dB
Torque ripple -
Torque accuracy -
SINAMICS Engineering Manual – May 2008
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© Siemens AG
Explanations, definitions
The rise time is the period which elapses between a sudden change in the setpoint and the instant the
actual value first reaches the specified tolerance band (2%) around the setpoint.
The dead time is the period which elapses between an abrupt change in the setpoint and the moment
the actual value begins to increase. The dead time is partially determined by the read-in, processing
and output cycles of the digital closed-loop control. Where the dead time constitutes a significant
proportion of the rise time, it must be separately identified.
The limit frequency is a measure of the dynamic response of a closed-loop control. A pure sinusoidal
setpoint is input to calculate the limit frequency; no part of the control loop must reach the limit. The
actual value is measured under steady-state conditions and the ratio between the amplitudes of actual
value and setpoint is recorded.
"-3 dB limit frequency": Frequency at which the absolute value of the actual value drops by 3 dB (to
71 %) for the first time. The closed-loop control can manage frequencies up to this value and remain
stable.
The ripple is the undesirable characteristic of the actual value which is superimposed on the mean
value (useful signal). Oscillating torque is another term used in relation to torque. Typical oscillating
torques are caused by motor slot grids, by limited encoder resolution or by the limited resolution of the
voltage control of the IGBT power unit. The torque ripple is also reflected in the speed ripple as being
indirectly in proportion to the mass inertia of the drive. The ripple is also a measure of "differential"
accuracy and therefore also primarily defines the dynamic response to disturbances of the control
system.
Accuracy is a measure of the magnitude of the average, repeatable deviation between the actual value
and setpoint under nominal conditions. Deviations between the actual value and setpoint are caused by
internal inaccuracies in the measuring and control systems. External disturbances, such as temperature
or speed, are not included in the accuracy assessment. The closed-loop and open-loop controls should
be optimized with respect to the relevant variable.
Vector control
1PH7/ 1PL6 1PH7/ 1PL6
with without
incrementtal encoder
encoder
1024
.
pulses/rev
125 μs 250 μs
1.8 ms 3 ms
(0.8 + 1) (2 + 1)
600 Hz 250 Hz
1.5 % of M 2 % of M
rated rated
±3.5 % of ±2 %
M of M
rated rated
Notes
1PH7/ 1PL6
with incremental
encoder
1024 pulses/rev.
250 μs
2.2 ms With encoderless operation in speed operating
(1.2 + 1) range 1:10, with encoder 50 rpm and above up to
rated speed.
A dead time of 1 ms is the default setting for
PROFIBUS DP.
400 Hz With encoderless operation in speed operating
range 1:10. The dynamic response is enhanced by
an encoder feedback.
2 % of M With encoderless operation in speed operating
rated
range 1:20, with encoder 20 rpm and above up to
rated speed.
1.5 % of M Measured value averaged over 3s.
rated
With motor identification and friction compensation;
temperature effects compensated by KTY84 and
mass model. In torque operating range up to
±M . Approx. additional inaccuracy of ± 2.5% in
rated
field-weakening range.
Servo: Speed operating range 1:10 referred to
rated speed.
Vector: Speed operating range 1:50 referred to
rated speed.