Speed Loop

Before the design of speed loop is to be attempted, the current loop should be approximated by a suitable transfer function. The block diagram in Fig. 6 can be expressed by a transfer function, say G₂(s). Then G₂(s) = I_a(s)/I_R(s). Using G₂(s), the speed loop can be represented as shown in Fig. 7. Again a PI controller is used and it may be necessary to provide a filter in the path of speed feedback signal. The time constants are to be specified in seconds. In per unit notation, the value of K_M marked in Fig. 7 would be 1.

 
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