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- Design and test cascade compensator
- Simulated system for accurate
results
- Built-in compensator gain –
only passive external components needed
- Built-in signal sources
Introduction
Practical feedback control
systems are often required to satisfy design specifications
in the transient as well as steady state regions. This is
usually not possible by selecting good quality components
alone, due to basic physical limitations and characteristics
of these components. Cascade compensation is most commonly
used for this purpose and the design of compensation networks
figures prominently in any course on automatic control systems.
Due to the absence of any laboratory experience, however,
the concepts of compensation remain rather vague. This unit
has been designed to enable the students to go through the
complete design procedure and finally verify the performance
improvements provided by compensation.
A simulated second order system with variable
gain is taken as the ‘unsatisfactory system’.
Simulated system has the advantage of predictable performance
which is necessary if the verification of the results is to
be meaningful. Built-in variable frquency square wave and
sine wave generators are provided for time domain and frequency
domain testing of the system. The frequency may be varied
in the range 25Hz – 800Hz and its value read on a built-in
frequency meter on the panel. Although most practical control
systems have bandwidth upto a few Hz only, a higher bandwidth
has been chosen for the simulated system to facilitate viewing
on a CRO. A pre-wired amplifier makes the implementation of
the compensation network extremely simple. Only a few passive
components need plugging into the circuit. Lead and lag networks
may be designed and tested on the set-up using both frequency
domain and s-plane procedures.
The experimental set-up is accompanied by
the supporting literature which becomes of vital importance
as a major part of the experiment involves theoretical design
of compensation networks. Although a complete coverage of
design philosophy is not feasible in this document, all efforts
have been made to describe the salient features and design
steps of the four problems listed above. Also included is
a typical design, explicitly covered with compensation network
parameter calculation and final results
Experiments
- Lag compensation in the frequency domain
- Lead compensation in the frequency domain
- Lag compensation in the s-plane
- Lead compensation in the s-plane
To start with, a suitable ‘uncompensated
system’ is chosen, either by an arbitrary setting of
the gain control potentiometer or by setting it to result
in a given value of overshoot as seen by step response test.
Next a set of specifications - both transient and steady state
- are prescribed as an objective by the teacher. The design
may then be carried out by one of the above techniques and
the results verified by a step response or frequency response
testing
All the above design problems may be undertaken
for a very wide range of design specifications. Notice that
the implementation of the compensation network has been made
very convenient by a prewired amplifier with calibrated gain.
Features & Specifications
- Simulated ‘uncompensated’
system having adjustable damping. Peak percent overshoot
MP, variable from 20% to 50%, and steady state error variables
from 50% to 0.5%
- Compensation network implementation through
built-in variable gain amplifier. Gain is adjustable from
1 to 11
- Built-in square and sine wave generators
for transient and frequency response studies.
- Frequency adjustable from 25Hz –
800Hz (approx.)
- 110V±10%, 50Hz mains operation
- Complete in all respects, except a measuring
CRO

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