A switching control strategy for magnetic bearings with a state-dependent bias

In this paper, we address the problem of controlling an active magnetic bearing (AMB) with reduced ohmic power loss. We consider an AMB system operated with only a single, opposing electromagnet active at any given time. A switching strategy is first described for the AMB mode of operation. A control/biasing strategy is then proposed which introduces a smart bias flux in the nonlinear control law. The bias is smart in the sense that it is a function of the rotor states, and varies on-line in a manner that reduces AMB power losses and avoids control singularities, without affecting the closed-loop stability. General conditions on the functional form of the bias are provided along with a specific bias design. A simulation study illustrates the performance of the proposed smart-bias controller in comparison to a standard, fixed-bias controller.