2.22.  STATE-VARIABLE DIAGRAM

The state-variable diagram provides a physical picture that is useful in understanding the state-variable concept. In addition, the differential equations relating the state variables are easily obtained by inspection of the diagram. A state-variable diagram consists of integrators, summing devices, and amplifiers. Outputs from the integrators denote the state variables. It should be noted that the state-variable diagram is the same as an analog computer simulation diagram [15].

Example 1. As an example of determining the state-variable diagram, consider a system whose transfer function is given by

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Dividing numerator and denominator by s3, to obtain the result in terms of integrators:

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Defining the error node of the control system to be E(s),

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Eq. (2.223) may be rewritten as follows:

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From Eq. (2.225) and the relation

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the state-variable diagram can easily be obtained as indicated in Figure 2.30*. The state variables are indicated in the diagrams as x1(t), ...

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