Sufficient Conditions for Minimum-Phase Second-Order Linear Systems
Several sufficient conditions are derived for a second-order linear system to be minimum phase. It is commonly known that a second-order linear system with collocated sensors and actuators is minimum phase. In general, this common knowledge is correct mathematically when the input influence matrix is the transpose of the output influence matrix. In this paper, we extend this knowledge to the case with noncollocated actuators and sensors. First, a conventional approach is used to prove some sufficient conditions of sensor and actuator locations for a system to be minimum phase. Second, a geometrical approach is introduced to discuss the sufficient conditions, and then used to derive other more useful sufficient conditions for a minimum-phase second-order linear system. Many illustrative examples are provided for the readers to better understand the theories developed in this paper.