Herbert Grabner

A flux-based PMSM motor model using RBF interpolation for time-stepping simulations

This paper describes an advanced method of modeling synchronous machines, in particular interior permanent magnet (IPM) motors. The dynamic motor model considers magnetic saturation and the dependence of electrical, magnetic and mechanical quantities on the rotation angle, and can be integrated into multidisciplinary system simulations. A set of magnetic finite element method (FEM) solutions is used to set up the model based on radial basis function (RBF) interpolation. The presented motor model can be used to simulate any time-stepping cases, such as studies of field weakening control, sensorless motor control algorithms or short circuit behavior. No magnetic FEM simulation is needed at runtime. We demonstrate the functionality of our method using the example of a BLDC motor simulation with voltage block commutation. The model derivated results are in good accordance with our measurements.

Wide Air Gap and Large-Scale Bearingless Segment Motor With Six Stator Elements

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.

Nonlinear Feedback Control of a Bearingless Brushless DC Motor

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.

A study on systematic errors concerning rotor position estimation of PMSM based on back EMF voltage observation

Many published methods of rotor position estimation of permanent magnet synchronous machines (PMSM) for medium to high speed are based on the estimation of the back electromotive force (EMF) voltage. From a practical point of view and the demand of minimum complexity, a simple idealized motor model is used many times. Due to this simplification and to a change of coordinates, an observation error of the back EMF voltage occurs, which has, as a consequence, an effect on the estimated rotor position. This study describes an intelligent method of sensorless speed control of PMSM for the whole speed range, which is especially appropriate for pump- and fan-applications. A quite simple method of back EMF voltage observation was found and integrated into the control strategy. Furthermore, the mentioned systematic errors and their effects on the accuracy of the estimated rotor position are analyzed systematically and documented carefully. Theoretical results are verified by simulations and measurement results.

Modeling, Simulation, and Design of a Permanent-Magnet-Assisted Synchronous Reluctance Machine

We have designed a permanent-magnet-assisted synchronous reluctance machine (PMa-SynRM) for applications requiring robustness and cost-effectiveness. To keep costs low, we use ferrite magnets for magnetic excitation. To achieve an efficient torque behavior, we considered various design aspects in the development of the PMa-SynRM. Our PMa-SynRM features magnets placed in the stator only and not mounted on the rotor. This paper presents the modeling and simulation of the magnetic behavior and the geometric optimization of the PMa-SynRM. The rotor geometry was investigated in particular detail using 2- and 3-D finite-element simulations. We performed no-load and load measurements and applied system analysis to identify the torque characteristic.

Feedback control of a novel bearingless torque motor using an extended FOC method for PMSMs

In recent years, industrial demand for magnetically supported direct drives which operate without contact and feature high torque capacity has been growing. We present a novel design solution for a bearingless torque motor. The proposed configuration has a six-phase winding with concentrated coils in double star connection to minimize power electronics efforts. The six-phase winding system generates simultaneously both the actively controlled motor torque and the radial bearing forces for radial position control. The disk-shaped hollow shaft rotor carries 26 permanent magnets. To reduce system costs, tilting deflection and axial position of the rotor are stabilized passively by magnetic reluctance forces. We describe the mathematical model and an appropriate control for current and voltage drivers. Finally, we present a prototype motor.

Design of a Brushless Permanent-Magnet Synchronous Drive With a Purely Passively Suspended Rotor

This paper deals with the design and optimization of a permanent-magnet synchronous machine as a means of propulsion for a passively levitated rotation system. The strict conditions in terms of axial and radial stiffness and the limited construction space particularly affect the design process. Three-dimensional finite-element simulations were performed to obtain the most efficient drive that fulfills the constraints. Additionally, a passive magnetic bearing was designed, which is capable of compensating for gravitational and load forces in the axial direction and of stabilizing the rotor in the radial direction. The optimization process and the constructed prototype system are described, and the work concludes with measurements validating the accuracy of the simulations.

Design of a brushless permanent magnet synchronous drive with a merely passively suspended rotor

This paper deals with the design and optimization of a permanent magnet synchronous machine as propulsion of a passively levitated rotation system. Especially the strict conditions regarding the axial and radial stiffness as well as the limited construction space affect the design process significantly. 3D finite element simulations are used to obtain the most efficient drive that fulfills the constraints. Additionally, a passive magnetic bearing is designed, which is capable if compensating the gravitational and load force in axial direction and of stabilizing the rotor in radial direction. After the optimization process, the constructed prototype system is described. The work concludes with measurements validating the accuracy of the simulations.

Active position control of high speed drive systems

High speed drive systems are often described at an operating point above the critical speed. Therefore, the resonance frequencies have to be passed twice (start up / run down). In the worst case, the strong vibrations at critical speeds can lead to self-destruction. Unbalanced rotors are the main cause for the self-excited vibrations. Over the past years, the focus of investigations [1] was laid on the improvement of the operating characteristics by using passive elements to guarantee stability of the system. However, the transition through the critical speed is still an unwanted high mechanical strain. In this paper, an innovative concept for rotary drives will be presented, which is able to compensate excessive vibrations or deflections actively. A permanent magnet excited synchronous motor (PMSM), which is able to generate motor torque and radial force simultaneously [2], with a large air gap is used. The capability of generating a highly dynamic and active control variable for the rotor position opens up new opportunities for drive applications. In this work, many different technical disciplines are combined, creating a truly mechatronic product.

Modelling, simulation and design of a novel permanent magnetic reluctance machine

In permanent magnetic reluctance machines (PMRM), all magnets are usually situated in the rotor. Instead of mounting the magnets in the rotor, this electrical machine has only magnets placed in the stator. To obtain an efficient torque behaviour, magnetic flux barriers are used in the rotor of the PMRM. Due to these facts, this novel PMRM has some significant advantages compared to conventional synchronous machines with permanent magnetic excitation, e.g. using cheaper ferrite magnets instead of NdFeB-magnets to get a comparably power density. This paper deals with the modelling and simulation of the magnetic behaviour and the geometric optimization of the PMRM. Especially the rotor geometry was investigated in detail using two dimensional and three dimensional finite element (FE) simulations. The verifications were done between the simulations and the measurements on the real system.