Analytical determination of the turn-to-turn capacitances for the prediction of voltage peaks in a PWM-fed motor winding
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ORIGINAL PAPER
Analytical determination of the turn‑to‑turn capacitances for the prediction of voltage peaks in a PWM‑fed motor winding Jan Ole Stockbrügger1 · Bernd Ponick1 Received: 30 March 2020 / Accepted: 4 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The number of inverter-fed motors is increasing due to the good controllability of the motor and the meanwhile low acquisition costs. The steep voltage slopes of the converters lead to an uneven voltage distribution along the winding and thus to voltage peaks between the conductors, which stresses the insulation. The voltage distribution can be predicted by means of equivalent circuit diagrams, which take into account the capacitive coupling between the conductors. This paper presents a novel approach for an analytical determination of the turn-to-turn capacitances, which, in addition to the geometry and the placement of the conductors, considers the influence of materials with different permittivities. The conductors are simulated by means of line charges discretely placed inside the electrodes and receptor points attached to the conductor surfaces. The capacitances are determined by means of the Maxwell capacitance matrix. The method is validated by means of FEM simulations for different geometries and materials. Keywords Turn-to-turn capacitance · Surge voltage distribution · Winding failure · Traction motor · Insulation stress
1 Introduction An electric machine fed by an inverter has to cope with impressed pulse voltages leading to harmonics of voltage and current, which cause additional oscillating torques and an increased noise level [1]. In order to reduce the negative effects mentioned above, converters with higher switching frequencies have been developed [2]. A high switching frequency of the power electronics is essential, especially for the realization of high-speed drives. An increase in the switching frequency requires a reduction in the switching times of the power semiconductors. Due to the low voltage rise time of the semiconductors, an uneven voltage distribution along the stator winding occurs, which can lead to voltage peaks between the conductors of the winding [3]. The insulation of the electrical machine can be heavily stressed by the voltage peaks and in the worst case, an insulation fault occurs [4]. In order to properly design the insulation, the voltage distribution along the winding must be known. It can be predicted with the help of detailed equivalent electrical * Jan Ole Stockbrügger [email protected]‑hannover.de 1
Institute for Drive Systems and Power Electronics, Leibniz University Hannover, Hannover, Germany
networks, which take into account not only the conductor inductances and resistances but also the capacitive coupling between the conductors [2, 5–9]. The capacitances between conductors are usually determined by means of FEM software [2, 4, 5, 7–9]. Several analytical approximations are based on the equation of a plate capacitance or the method of image charges. In [10], tw
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