Variable bias current in magnetic bearings for enhanced control system performance and energy efficiency

Active Magnetic Bearings (AMBs) offer significant advantages for high-speed and high-precision applications due to their contactless operation, low mechanical wear, and active control capabilities. Conventional control strategies often rely on constant bias currents to linearize the electromagnetic force-current relationship. However, this approach increases energy consumption and introduces non-differentiability in the control inputs, which hinders flatness-based motion planning and reduces overall control performance. This paper proposes a variable bias current allocation strategy formulated as a multi-objective optimization problem. A complementarity function is used to nonlinearly distribute the electromagnetic forces across paired coils, while satisfying physical constraints and reducing energy consumption, without compromising dynamic performance. Experimental validation on an axial AMB test bench demonstrates significant reductions in steady-state power consumption compared to existing approaches. Beyond local performance gains, the proposed strategy ensures a continuous and differentiable force-current relationship. This regularity is essential for integration into a global control architecture combining flatness-based control, state observation, and trajectory planning. This architecture allows further enhancement of system dynamics through accurate trajectory tracking and robust disturbance rejection. The results highlight the dual benefit of the proposed approach: improved energy efficiency and compatibility with advanced AMB control frameworks, grounded in system physics rather than empirical tuning.