Control of magnetic levitation systems with reduced steady-state power losses

In this paper, we address the problem of controlling a magnetic levitation system with reduced electric power losses. A general control/ biasing strategy is proposed which introduces a bias flux in the nonlinear control law, function of the mechanical states. The bias flux ensures the power losses converge to zero as the mechanical states converge to zero and a singularity-free control, without affecting the closed-loop stability. General conditions on the functional form of the bias are provided along with a design example of the control/biasing strategy. An experimental study illustrates that the proposed time-varying-bias controller yields a stabilization performance comparable to the constant-bias version of the controller, but with significantly less ohmic power losses.