A two-degree-of-freedom design of optimal servosystems for general reference signals

A two-degree-of freedom design of optimal servosystems for reference signals governed by linear time-invariant differential equations is proposed. First, an optimal tracking problem is considered as an optimal regulator problem for a variation system which is defined around the steady state behavior determined by the reference signal. Then, a servo compensator is applied to the resultant tracking system in order to cope with modeling errors of the plant and disturbance inputs to the plant. To preserve the optimal tracking property under no modeling error or no disturbance input, complementary feedforward and feedback are employed to cancel the effect of the servo compensator in such an ideal case