Example H5.3
MATLAB code for example 5.3 from the book "Regeltechniek voor het HBO"
Improving system behaviour through feedback
- Date : 02/03/2022
- Revision : 1.0
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Table of Contents
Direct current generator
In figure 5.6 a greatly simplified version of a direct current generator can be seen. The output signal is the voltage 
to feed a load.
to feed a load.The generator is driven at a rotationspeed of n and the so called excitation current 
is supplied by the voltage source 
. In this case the following applies:
is supplied by the voltage source . In this case the following applies: 1) 
, and in s-notation:
, and in s-notation: 
with 
sec.2) 
(
constant)
( constant)From 1) and 2): 
with 
and sec
with and sec So the system behaves as a first order process.
In many applications (e.g. emergency power installations) 
must remain as constant as possible, even if the generator load or the speed n or the voltage 
vary. The question is: how can we improve this without having to make expensive and drastic changes? Of course we can adjust 
(by switching resisters on or off), or adjust by taking it from a voltage divider. Much better is to make the current 
dependent on the output voltage by means of voltage negative feedback (see figure 5.7a). The block diagram of this type of feedback is shown in figure 5.7b. Here applies:
must remain as constant as possible, even if the generator load or the speed n or the voltage vary. The question is: how can we improve this without having to make expensive and drastic changes? Of course we can adjust (by switching resisters on or off), or adjust by taking it from a voltage divider. Much better is to make the current dependent on the output voltage by means of voltage negative feedback (see figure 5.7a). The block diagram of this type of feedback is shown in figure 5.7b. Here applies:
with 
and 
and As a result of the feedback we see the gain 
and time constant 
have become smaller. So the system reacts faster, but the gain of the total system has become smaller. This is a general characteristic of negative feedback.
and time constant have become smaller. So the system reacts faster, but the gain of the total system has become smaller. This is a general characteristic of negative feedback.If in figure 5.7a decreases because of a lower speed or higher load or lower , the excitation current is automatically increased and this causes to increase (see formula 5.2).
decreases because of a lower speed or higher load or lower , the excitation current is automatically increased and this causes to increase (see formula 5.2).