Multivariable Adaptive Harmonic Steady-State Control for Rejection of   Sinusoidal Disturbances Acting on an Unknown System
  This paper presents an adaptive harmonic steady-state (AHSS) controller, which addresses the problem of rejecting sinusoids with known frequencies that act on a completely unknown multi-input multi-output linear time-invariant system. We analyze the stability and closed-loop performance of AHSS for single-input single-output systems. In this case, we show that AHSS asymptotically rejects disturbances. 
Mohammadreza Kamaldar and Jesse B. Hoagg
cs.SY