Rotordynamics of Electrical Machines


Electrical machines as electromechanical energy converters are irreplaceable in almost all areas of technology. From micromotors and servomotors in models or vehicles to turbogenerators in nuclear power plants, they exist in all orders of magnitude. While electric motors are becoming increasingly important (especially in vehicle technology), generators (for example) are an indispensable part of worldwide energy production.

Research at the Department of Technical Dynamics focuses on mechanical vibration phenomena in electrical machines, taking multi-physical feedback into account. Building on previous research results, the aim is to provide and improve an uniform analytical approach for calculating the forces and torques between the stator and rotor of the machines. This can then be used to analyse the rotor dynamics of different machines. The focus is on both stationary operating conditions, where the stability of the rotor and any bifurcations in the solution behaviour are investigated, and on transient processes, such as driving through resonance and the associated Sommerfeld effect.


For the nonlinear rotordynamic analysis of electrical machines, a qualitative analytical description of the forces and torques generated by the magnetic field between stator and rotor is required. Especially their applicability limits and validity represent a current research aspect in the field. Existing models are to be reviewed and improved. New aspects of modelling concern the influence of saturation and the coupling between the electrical and mechanical subsystems.


The validation is made both numerically and on the basis of a model test bench (see experiment).

On the basis of the knowledge gained, systematic rotordynamic analyses are then carried out and also validated experimentally. This should lead to a deeper qualitative understanding of possible vibration problems, which can be used to improve the reliability and NVH aspects of the machines.

1. F. Boy, Modelling the Rotordynamics of Saturated Electrical Machines due to Unbalanced Magnetic Pull, Kassel University Press (2020)

2. F. Boy, H.Hetzler. A Co-Energy Based Approach to Model the Rotordynamics of Electrical Machines. Proceedings of the 10th International Conference on Rotor Dynamics – IFToMM 63, 2018, S. 190-204.

3. F. Boy, H. Hetzler. An Asymptotic Approximation of the Magnetic Field and Forces in Electrical Machines with Rotor Eccentricity. Electrical Engingeering 100 (2), 2018: S. 389-399.

4. F. Boy, H. Hetzler. The effect of field damping on rotordynamics of non-salient pole generators. Technische Mechanik 37 (2017): S.384-393.

5. F. Boy, H. Hetzler. On the electromechanical coupling in rotordynamics of electrical machines. Proc. Appl. Math. Mech., 17, 2017: S. 365–366.

6. F. Boy, H. Hetzler. Zur nichtlinearen elektromechanischen Interaktion in der Rotordynamik elektrischer Maschinen, 140. Norddeutsches Mechanikkoloquium, 01.07.2017.

7. F. Boy, H. Hetzler. Nonlinear electromechanical interactions in rotordynamics of electrical machines, 9th European Nonlinear Dynamics Conference  (2017)

8. F. Boy, H. Hetzler. On the rotordynamic stability of two-pole synchronous electric machinery considering different load cases. Proc. Appl. Math. Mech., 16, 2016: S. 265–266.

9. F. Boy, H. Hetzler, Ph. Schäfer. On the rotordynamic stability of synchronous electric machinery considering different load cases and operating conditions. Proc. ISMA 2016, 2016: S. 837 – 849.

10. F. Boy, H. Hetzler. Rotordynamics of Two-Pole Turbo Generators with Refined Modelling of the Unbalanced Magnetic Pull. Proc. Appl. Math. Mech., 15, 2015: S. 243 – 244.