Transmission Line Modelling for Inverter-Fed Induction Machines

• Main Author: Jorks, Hai Van
• Format: Others
• Language: German; en
• Published: 2015
• Online Access: https://tuprints.ulb.tu-darmstadt.de/4405/1/Dissertation_Jorks_2015-02-16.pdf; Jorks, Hai Van <http://tuprints.ulb.tu-darmstadt.de/view/person/Jorks=3AHai_Van=3A=3A.html> (2015): Transmission Line Modelling for Inverter-Fed Induction Machines.Darmstadt, Technische Universität, [Ph.D. Thesis]

This thesis is focused on high-frequency (HF) modelling of inverter-fed induction machines.The common mode (CM) input impedance of an existing 240 kW induction machine is computed in the frequency range of 10 Hz - 1 MHz and the results are compared to measurements. Transmission line (TL) theory is used to provide a consistent relation between field and circuit approaches. In the analysis of electromagnetic fields, special attention is attributed to the modelling of eddy currents inside the core lamination. In order to investigate this effect thoroughly, two modelling approaches are compared. First, a 2D simulation approach, where iron core lamination effects are included by means of an equivalent material approximation. The second approach consists in fully three-dimensional (3D) analysis taking into account explicitly the eddy currents induced in the laminations. In order to provide the 3D reference solution, a specialized simulation tool has been developed. The tool is built upon an existing in-house finite element (FE) code, which employs vector basis functions of both, low and high, order. Another key feature of the code is the parallel processing on a cluster, which allows for large-scale simulations of the 3D motor models. The FE code has been adapted to the extraction of the impedance matrix, which is associated with the conductors in the motor cross-section. Even though, the number of conductors may be numerous, the code allows for very efficient extraction of the desired parameters while avoiding unnecessary computational overhead. All simulations are carried out in frequency domain. Still, a procedure to include the magnetic nonlinearity of the motor core material is discussed and implemented. The proposed method computes iteratively the inhomogeneous permeability distribution for a given low-frequency (LF) excitation. The material data are then used in the linear computations in the HF range. The FE code is also successfully used for the computation of the 3D fields in the end-region of an induction machine. Once again, efficient large-scale simulations are realised, whereas here, mesh elements of different types have been combined. The modelling approaches are presented, using the example of an inverter-fed induction machine. Nevertheless, they may be employed to obtain important HF parameters of other radial flux machine types as well.