Overcoming eight drawbacks of the basic separation principl of state space control design

Separation principle implies that the state feedback control Kx(t) is designed assuming the system state x(t) is available. This principle has the following eight drawbacks. 1) The design of Kx(t)-control ignores the fact that a major effort, such as a separately designed observer, is needed to realize this control. 2) This design ignores the parameters of the realizing observer and the parameter C of the open loop system (A, B, C). 3) To guarantee the generation of such Kx(t) signal, a state observer is needed to generate all n elements of x(t), while the number of signals of Kx(t) is much less than n in non-trivial systems. 4) For most (A, B, C)´s, their state observers must have the feedback of system input, thus abandoning the well established output feedback compensator structure of classical control theory. 5) It is proven that for a practically designed Kx(t)-control, only an output feedback compensator can realize (if it can generate the signal Kx(t)) its loop transfer function and robustness properties. 6) The more important dynamic part is designed after the less important static output part, of the observer. 7) The only other existing basic form of control is static output feedback control KyCx(t), which is an extremely constrained Kx(t)-control (K must be linear combinations of only m rows of C). At the other extreme, no constraint is attached to the K of existing Kx(t)-control. 8) The order of KyCx(t)-control is fixed at zero, an extreme low, while the order of (state) observers of Kx(t)-control is fixed at least n-m, an extreme high. Each of these eight drawbacks is severe enough to demand a fundamental adjustment of separation principle of fifty years. This paper presents a simple and synthesized design approach that eliminates these drawbacks all at once. It is a scandal that this result is still little known to the control community.