Robust Speed Control of Magnetic Drive-Trains with Low-Cost Drives

The paper presents a methodology to improve the operating robustness of low-cost magnetic drive-train (MDT) systems in which load-side sensing is not a preferred option for addressing pole-slipping and variable torsional stiffness issues. Firstly, through dynamically analysing the relative displacement angle between both sides of the MDT (resulting from the developed electromagnetic- and load-torque), the paper offers an operating criteria using the inertia ratio and electromagnetic- and load-torque excitations to prevent the MDT from pole-slipping. Subsequently, the relationship between controller parameters and dominant/resonant poles of closed-loop MDT control system, is discussed. It is shown that controller parameters for MDTs to accommodate a wide range of torsional stiffness variations can be determined from natural frequencies that are bounded by operating constraints. Using the presented principles, desired performance with respect to speed reference tracking and load-torque disturbance accommodation can be achieved by simply determining the natural frequency of the dominant poles. Simulation studies and experimental measurements on a custom MDT test facility are used to underpin the efficacy of the proposed analysis and design techniques.