Magnetic bearing with separate bias and control windings

Although magnetic bearing (MB) supports the target object without contact, enabling high-efficiency operation, its complex hardware and nonlinear characteristics make control system design challenging. Self-sensing is a signal-processing technique that estimates the position of a levitated object in a MB using current signals. However, conventional self-sensing MB with single winding, where the winding is used for both actuation and sensing, suffers from noise and interference. This paper investigates a self-sensing MB system with separate bias and control windings. The bias winding is used to estimate the air gap of the electromagnet, whereas the control winding is responsible for generating the electromagnetic force. First, a mathematical model of MB with separated windings is derived and compared with that of a conventional MB. The actuator gain and stiffness can be tuned effectively by appropriately adjusting the ratio between the bias and control windings. Furthermore, an electromechanical model and analysis of the proposed MB configuration are presented. In this design, the inductance of the control winding remains nearly constant regardless of the air gap, which facilitates the current control. Additionally, using fewer turns in the bias winding is recommended to improve the resolution of self-sensing and minimize the influence of current control on the bias winding. Finally, one DOF MB test rig was constructed and the concept of a self-sensing MB with separate bias and control winding are experimentally validated.