Robust
Performance

qConsider a feedback system
with uncertain plant *P**D** *, the weighted sensitivity function is
defined as the transfer function from *d* to *e:
*

Suppose our performance objective is

||*T**ed**||*¥* =*sup*{||d||2 *£*1}** ||e||**2** *£*1
*

qSuppose *P**D** *Î *{(I+**D**W**2**)P: **D** *Î* **RH**¥** *,* *||*D*||¥ <1 *} *and *K* stabilizes *P*. Then the robust
performance is guaranteed if

Proof: