8

Concept of Stability and Routh-Hurwitz Criteria

8.1 CONCEPT OF STABILITY

System stability is one of the most important performance specification of a control system. A system is considered unstable if it does not return to its initial position but continues to oscillate after it is subjected to any change in input or is subjected to undesirable disturbance.

For any time invariant control system to be stable the following two conditions need to be satisfied. These are:

  1. The system will produce a bounded output for every bounded input;
  2. For no input, the output should tend to be zero, irrespective of any initial conditions.

Stability of a system may be referred to as absolute stability or in terms of relative stability. The term relative stability ...

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