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This paper investigates and compares two popular combined winding configurations for bearingless machines, the multi-phase (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 paper 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 paper 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.

This paper studies the modeling and field-oriented control (FOC) for hysteresis motors, with the goal of achieving position control of hysteresis motors for servo applications. Hysteresis motors include a wide range of machines with solid cylindrical or ring-shaped steel rotors, which generate torque primarily via the magnetic hysteresis effect of the rotor material. Previously, hysteresis motors have been mainly used under open-loop operation. However, they are also attractive for position control in some special applications such as in-vacuum operation or when smooth running and high speed is required. In this paper, an equivalent circuit model for hysteresis motors that describes the motor's transient-time dynamics is introduced, and a state-space model for hysteresis motors is developed. This model is used to construct a rotor flux orientation observer for the FOC for hysteresis motors. Three methods for estimating the rotor field angle are introduced. The proposed FOC-based position control method was tested with three hysteresis motors, including two custom-made motors of different rotor materials and one off-the-shelf hysteresis motor. Experimental results show that position control for all three hysteresis motors can reach a bandwidth of 130 Hz with the proposed methods. To the authors’ best knowledge, this is the first experimental study on FOC and position control for hysteresis motors.

Alongside technical performance features, low system costs are the highest priority in the field of low-power electric drives. This makes adoption of magnetic bearing technologies difficult in applications with higher production volumes. Since published literature on cost-saving measures in this field is scarce, we present in this paper some ideas and stimuli using three selected examples: 1) a highly integrated hybrid bearing that provides active stabilization in 3 degrees of freedom (DOF); 2) a brushless permanent magnet motor with additional axial bearing capability; and 3) a bearingless flux-switching motor. We describe their particular designs and operational features, and compare the additional mechanical and electrical costs of these and similar systems with those of standard motor technologies. This paper concludes with a stability analysis of example 2), since it features passive permanent magnetic bearings, which are inherently only weakly attenuated.

For high-speed bearingless disk drives, certain topologies seem advantageous. The authors have published works on a bearingless disk drive for high speeds that is characterized by a slotless stator and a toroid winding set. Several different variations of this setup are imaginable. The ones which this paper focuses on are the variation of the number of phases, of the number of coils, and of the applied coil connection. A comparison of the constructed and tested setup with the possible variations is presented in the course of this paper.

This work presents the first prototype of a novel class of bearingless slice motors. It differs from other examples of this motor topology mainly by the absence of permanent magnets in the rotor. A homopolar permanent magnetic bias air gap field is generated by stator magnets and enables the passive stabilization of three degrees of freedom. The presented drive concept features special operational behavior distinguishing it from other state of the art bearingless drives. To proof the proper functionality of the novel design, a prototype motor is optimized and designed. Various measurements are conducted to verify the finite element simulation results and to prove the functionality of the drive and its nonlinear control scheme.

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.