Bearingless motors and active magnetic bearings work completely contactless and wearless. With these properties, hermetically sealed and lubricant-free rotating systems for various applications can be designed. It is possible to stabilize three degrees of freedom by reluctance forces when a permanent-magnet excited rotor disc is used. Hence, only the remaining three degrees of freedom are actively controlled. A subtype of this constructional design called bearingless slice motor is the bearingless segment motor. This paper comprises the design process of a bearingless segment motor with five equal stator elements and concentrated windings. Finite-element simulations are applied to maximize the bearing forces and the motor torque per ampere and minimize the reluctance forces. However, the mathematical model of the system is nonlinear, therefore, an appropriate nonlinear control scheme has to be applied to put the system into operation. The introduction of a prototype, together with first measurements, completes the paper.

The demands on bearingless drive configurations concerning performance as well as costs are high. The proposed bearingless brushless DC motor consists of five concentrated coils in a symmetrical arrangement, which generate radial forces and motor torque simultaneously in interaction with a permanent-magnet-excited disk-shaped rotor. Additionally, tilting deflection and the axial position of the rotor are stabilized passively by means of magnetic reluctance forces. Thus, system costs can be reduced significantly compared to a conventional bearingless motor setup, which actively stabilizes all 6 DOF. Due to the nonlinearity of the plant, the use of linear control design methods alone is not suitable for achieving a high operation performance. This paper introduces a novel radial position and motor torque control algorithm for a bearingless brushless DC motor based on the theory of feedback linearization. Thereby, the combined model of translatory and rotatory dynamics can be split into independent linear systems by means of a nonlinear change of system coordinates and a static-state feedback. Experimental results demonstrate the effectiveness of the proposed approach.

Several processes in chemical, pharmaceutical, biotechnology, and semiconductor industry require contactless levitation and rotation through a hermetically closed chamber wall. This paper presents a novel concept that combines crucial advantages such as high acceleration capability, large air gap, and a compact motor setup. The basic idea is to separate a homopolar bearing unit axially from a multipolar drive unit on two different height levels. Hence, the proposed concept is denominated as ldquomagnetically levitated two-level motor.rdquo In this paper, the bearing and drive functionalities are explained in detail and design guidelines are given based on analytic equations and electromagnetic 3-D simulations. Furthermore, the influence of nonidealities such as saturation and coupling effects is evaluated and included in the design. Finally, extensive measurements on an experimental prototype exemplify the design considerations and prove the excellent performance of the new concept.

This article investigates and compares two popular combined winding configurations for bearingless machines, the multiphase (MP) and dual-purpose no-voltage (DPNV) windings. Each of these winding configurations has the ability to independently create suspension force and drive torque using the same stator coils. The article develops analogous bearingless motor force and torque models, space vector equivalent circuits, and a current regulation architecture for each combined winding approach. A comprehensive comparison is made between the two combined winding topologies by using these analogous models and through an experimental study. It is shown that, from a motor design perspective, these combined winding topologies are equivalent for certain design conditions, but that each winding places very different demands upon the drive power electronics. The article concludes that the optimal choice of winding configuration depends on the machine parameters and the expected loading and drive cycle. When compared in terms of total current stress exerted on the bearingless drive, the MP winding is preferred when over half of the coil current is used to produce torque rather than force. In terms of the drive's volt-ampere rating, the DPNV winding is shown to be advantageous for high operating speeds and low torque values.

The nonlinear radial forces relationship regarding phase currents and rotor angle demands a nonlinear control structure for bearingless motors. Most state-of-the-art control algorithms of bearingless motors are based on the assumption of linear current to force/torque relationship, and only the nonlinear relationship to the rotor angle is taken into account. However, in some types of bearingless motors, especially in motors with reluctance-type rotor, suspension forces are quadratic functions of the phase currents, which means that, in addition to linear terms, quadratic terms also contribute significantly to force generation. In this paper a novel control structure is presented, which allows controlling a bearingless motors featuring significant nonlinear current to force/torque relationship. DSP implementable solution was found by numeric solution followed by the 2nd order Taylor approximation. To check the functionality the suggested control structure was implemented with a bearingless flux-switching 12/10 motor.

In recent years, the demand for high purity spinning processes has been growing in certain industry branches, such as the semiconductor, biotechnological, pharmaceutical, and chemical industry. Therefore, the cleanness specifications have been tightened, and hermetically sealed process chambers are preferred. This paper presents an advantageous solution for such an application featuring a large scale, wide air gap, and a high accelerating bearingless segment motor. Bearingless slice motors allow complete magnetic levitation in combination with a very compact and economic design. The disc-shaped rotor holds permanent magnets generating magnetic flux in the air gap. Hence, three degrees of freedom are passively stabilized by reluctance forces. Thus, only the radial rotor position and the rotor angle have to be controlled actively. The announced bearingless segment motor is a subtype of the bearingless slice motor, featuring separate independent stator elements. This leads to a reduction of stator iron, cost, and weight and, in addition, leaves space for sensors and electronics enabling a very compact system design.