Compensation is the adjustment of a system in order to satisfy the given specifications.
Performance specifications: control systems are designed to perform specific tasks. The requirements imposed upon the control system are usually spelled out as performance specifications. They generally relate to accuracy, relative stability, and speed of response.
For routine design problems, the performance specifications may be given in terms of precise numerical values. In other cases, the may be given partially in terms of precise numerical values and partially in terms of qualitative statements. In the latter case, the specifications may have to be modified during the course of design since the given specifications may never be satisfied (because of conflicting requirements) or may lead to a very expensive system.
Generally speaking, the performance specifications should not be more stringent than necessary to perform the given task. If the accuracy at steady-state operation is of prime importance in a given control system, then we should not require unnecessarily rigid performance specifications on the transient response since such specifications will require expensive components. Remember that the most important part of control system design is to state the performance specifications precisely so that they will yield an optimal control system for the given purpose.
Modern Control Engineering, Ogata, 1970.
