Variable structure control for parabolic evolution equations
  In this paper it is considered a class of infinite-dimensional control systems in a variational setting. By using a Faedo-Galerkin method, a sequence of approximating finite dimensional controlled differential equations is defined. On each of these systems a variable structure control is applied to constrain the motion on a specified surface. Under some growth assumptions the convergence of these approximations to an ideal sliding state for the infinite-dimensional system is shown. Results are then applied to the Neumann boundary control of a parabolic evolution equation. 
Laura Levaggi