Sufficient condition for second-order linear systems having no zeros

摘要

Some of the model independent controllers such as the virtual passive controller require a minimum-phase system to start with the controller design process (Morris and Juang, 1994). Recently, Lin and Juang (1995) have presented some sufficient conditions for second-order linear systems to be minimum phase. However, if a second-order linear system has no zeros, then we can directly make a conclusion by using the definition of minimum phase (Chen, 1984), and thus we need not apply the sufficient conditions of Lin and Juang to determine whether this second-order linear system is minimum phase. Therefore, the purpose of this note is to propose a sufficient condition for second-order linear systems to have no zeros. Note that the work by Lin and Juang is very significant and excellent. It is hoped that the content of this note may serve as a complement of their work. [References: 3]