# An Output Feedback Stabilizer for MIMO Nonlinear Systems with Uncertain Input Gain: Nonlinear Nominal Model

## TL;DR

This paper introduces an output feedback stabilizer for MIMO nonlinear systems with uncertain input gain, capable of handling nonlinear gain functions and ensuring semi-global practical stability.

## Contribution

It extends existing controllers to systems with nonlinear, state-dependent input gain matrices by modifying disturbance observer-based output feedback control.

## Key findings

- The proposed controller achieves semi-global practical stability.
- It effectively handles nonlinear, state-dependent input gain matrices.
- The method exploits system nonlinearity rather than canceling it.

## Abstract

This paper deals with the output feedback stabilization problem of nonlinear multi-input multi-output systems having an uncertain input gain matrix. It is assumed that the system has a well-defined vector relative degree and that the zero dynamics is input-to-state stable. Based on the assumption that there exists a state feedback controller which globally asymptotically stabilizes the origin of the nominal closed-loop system, we present an output feedback stabilizer which recovers the stability of the nominal closed-loop system in the semi-global practical sense. Compared to previous results, we allow that the nominal system can have a nonlinear input gain matrix that is a function of state and this is done by modifying the structure of the disturbance observer-based robust output feedback controller. It is expected that the proposed controller can be well applied to the case when the system's nonlinearity is to be exploited rather than canceled.