A stability condition for STC with model mismatch

A stability condition is presented for a self-tuning control (STC) algorithm under the assumption that the estimation model order can be lower than the plant model order. The estimation rate is decided by a small positive real ε, which exists for stable STC if an operator H₂ is strictly positive real. An upper limit for ε is explicitly derived. Some implementation issues on the realization of such a stability condition are illustrated with simulation examples