Siemens MICROMASTER 411 - Manual (Page 126)

10 Engineering Information Issue 03/01
MICROMASTER 411 & COMBIMASTER 411 Operating Instructions
126 6SE6400-5CA00-0BP0
10.2.3 Ziegler-Nichols method of Optimization
The Ziegler-Nichols method is a means of calculating the Proportional gain and
Integral time by measuring the system response to a step change in open loop.
This is done by putting the inverter in frequency control and monitoring the
feedback signal. From the feedback response, the time before the system starts to
respond, L, and the dominant time constant, T, which is measured by estimating
when the system response would have reached its stationary value if the maximum
slope were maintained. (Typically measure to where the system response has
reached 85% of its final value). From L, T and the ratio between the frequency step
∆ f(as % of F
max
) to the feedback value change ∆ x (%), it is possible to calculate the
P and I terms for a PI control process as follows:
P gain = (0.9)(T)( ∆ f) / (L)( ∆ x)
I time = 3L
Example:
With the inverter in frequency control, a frequency step of 5 Hz is given and the
feedback signal monitored. To allow this, the following parameters are set:
P2200 = 0
P1120 = 0,0 s
P1121 = 0,0 s
P1080 = 50.0 Hz.
Figure 10-7 Response to 5 Hz step: L = 100 ms