Nonlinear H∞ control

This paper discusses various aspects of developments concerning the robust H_∞ problem for continuous-time nonlinear systems. In the state feedback case, the problem can be solved in the framework of dissipative systems, and the associated storage functions solve the PDI in the viscosity sense. The main problem is then one of controller synthesis. In the output feedback case, the information state concept provides the appropriate framework. The solution is expressed in terms of a PDE for the information state (filter), and an infinite dimensional PDE or dissipation-type PDI for the value function (control). The attendant mathematical issues are discussed