General impedance/admittance stability criterion for cascade system

Impedance-based stability criterions have been proved to be a very effective tool for the stability assessment when considering interaction between different modules. Two different stability criterions in the form of impedance ratio as Z_o/Z_i and Z_i/Z_o have been proposed for different system. However, the intrinsic relationship of these criterions has not been fully discussed. In this paper, the terminal characteristics of single module are focused. The physical meanings of terminal impedance and admittance are explained. Based on the physical understanding, different mathematical methods are derived for the stability prediction in cascade system. Through comparison, the advantage of proposed impedance/admittance stability criterion is analyzed as its convenience in mathematical calculation. As analyzed, the proposed impedance/admittance criterion can be used in the cascade system where existing impedance ratio type criterion can be used and the physical meaning of proposed criterion is clearer.