3-DEGREE-OF-FREEDOM JOINT H2/H-INFINITY OPTIMAL CONTROLLERS

The solution is dealt with of the discrete-time LQ stochastic tracking and servo problems for a general system configuration. It is shown that the resultant solution is in the form of a three-degree-of-freedom (3DOF) controller when the vector of the exogenous signal is extended to include accessible disturbances. In particular, it is shown that a separation property between feedback, reference and accessible disturbance feedforward actions, proved for 2DOF optimal LQ stochastic control scheme, also holds true for the general system configuration here considered. Further, this separation property can be suitably extended, when a linear control law is assumed, to the minimax LQ stochastic tracking and servo problems.