Control of drive trains incorporating magnetic gears

This is a thesis about the control of magnetic gears. A decade ago (2001) the first modern prototype magnetic gear box was constructed using rare earth magnets (NdFeB). Magnetic gear boxes have some desirable properties not found in their mechanical gear box counterparts, these include: contact-less torque transmission, lubrication-free, reduced noise and vibration, and non-destructive torque overload capability. Hitherto, no detailed investigation or analysis has been conducted on the effects of using a magnetic gear box in place of a mechanical gear box. As will be demonstrated in this thesis, magnetic gears possess a number of undesirable properties which must be given due consideration when designing speed and position controllers. In particular, unlike mechanical gear boxes, magnetic gear boxes have extremely low torsional rigidity. Furthermore, the torque transfer characteristic is fundamentally nonlinear and magnetic gear boxes have the potential to ‘slip’. On the one hand, ‘slipping’ is a great benefit as a non-destructive ‘torque fuse’; but on the other, this represents a consequential loss of control. This thesis examines the control issues that arise through the use of a specially constructed magnetic coupling integrated into an experimental test rig. The development of a linearized mathematical model of the experimental magnetic coupling is used to derive optimized classical controllers for speed and position, demonstrating outstanding theoretical and experimental results. To compensate for the possibility of ‘slip’, a methodology is presented for the detection and recovery from what is defined as ‘pole-slip’ in a magnetic coupling. To avert ‘pole-slip’, a model predictive control (MPC) scheme is developed that prevents over-torque pole-slipping. Feedback linearization is considered for a nonlinear model of the magnetic coupling and nonlinear control laws and state transformations are derived to produce perfect linearization, for both speed and position control, over the entire operating range of the experimental magnetic coupling.