The L2-gain almost disturbance decoupling problem for SISO nonlinear systems is formulated. Sufficient conditions are identified for the existence of a parametrized state feedback controller such that the L2-gain from disturbances to output can be made arbitrarily small by increasing its gain. The controller is explicity constructed using a Lyapunov-based recursive scheme. Sufficient conditions for the solvability of the H∞ almost disturbance decoupling problem and the explicit construction of teh controller are given for a more restrictive class of nonlinear systems.
Marino, R., Respondek, W., van der Schaft, A., & Tomei, P. (1994). Nonlinear H-infinity almost disturbance decoupling. Systems and control letters, 23(23), 159-168. https://doi.org/10.1016/0167-6911(94)90001-9