A FURTHER STUDY OF POSITIVE-NEGATIVE FEEDBACK CONTROL SYSTEMS.

The design and performance of positive-negative feedback P-NF switching control systems, which switch back and forth between direct positive- and negative-feedback modes, are investigated with the ultimate objective of developing a P-NF system which can satisfy certain common performance requirements better than either a linear negative-feedback LN-F system or a bang-bang switching control system. A simple technique for improving the performance of the sampling P-NF system is developed. It is asserted and demonstrated that, by inserting simple gain compensators in the positive- and negative- feedback loops, the step-input response time and the systems bandwidth can be simultaneously reduced. To compare the controller complexity and the performance of a sampling P-NF system with those of an ideal bangbang system, a bang-bang controller is designed for a typical plant to respond to step-function inputs without overshooting. It is concluded that the sampling P-NF switching control system is unique among non-linear and switching control systems in that its step-input transient response and its sinusoidal-input frequency response both obey the homogeneity principle.