Low Order Rational Approximations To The Delay Operator

Consideration is given to three rational approximants to the delay operator including the Pade approximants. The Pade approximants, in general, give rise to unstable system performance and, hence, are not satisfactory. The second approximant arises from a direct solution of systems with delay. The third is of the form (1 + sT)N. Low-order approximants of either of the later two types are generally satisfactory.