Experimental Validation of Control Designs for Low-Loss Active Magnetic Bearings

Abstract

This paper ofiers experimental validation of several recently developed nonlinear control laws, derived from the theory of integrator backstepping, control Lyapunov functions (CLF), and dissipativity, by implementing them on a spacecraft reaction wheel that is suspended by a low-loss active magnetic bearing (AMB). The electromagnets of the AMB are constrained by a generalized complementary ∞ux constraint (GCFC). This constraint allows one to operate the AMB with a large bias ∞ux, to obtain a desired bearing stifiness and force slew-rate, or with a very small (or even zero) bias ∞ux for low-loss AMB operation. Experimental evidence is provided to illustrate the role of the ∞ux bias in the control design and highlight the singularity issues associated with zero- and very low-bias AMB operation. Speciflcally, the tradeofi between bearing stifiness, power consumption, and power dissipation as a function of the bias is verifled. Also, it is experimentally shown that the singularity issues present in the standard nonlinear backstepping control laws can be destabilizing in zero bias, and moreover, the newly developed CLF and passivity-based control laws efiectively eliminate the zero-bias singularity issues.