Alternative Approach to Alleviate Passivity Violations of Rational-Based Fitted Functions

This paper presents an efficient approach to enforce passivity of rational-based fitted systems. The origin of non-passivity is thoroughly reviewed and analyzed. The proposed approach identifies and modifies, from the original non-passive rational approximation, only the partial fractions that generate passivity violations. It is shown in this paper that these partial fractions generally correspond to out-of-band poles. As for proper-type rational approximations, a new method is proposed to force the constant matrix to be positive-definite. The proposed approach is verified via three case studies with highly non-passive conditions.