Analysis of Impact of Design Solutions of an Electric Machine with Permanent Magnets for Bearing Voltages with Inverter Power Supply

Abstract

The aim of the article is to present a new idea of limiting the bearing voltage in electric machines with permanent magnets through the use of a shielding winding placed in stator slot wedges. The first part of the article is dedicated to the mechanisms of generating bearing voltages when the machine is supplied from the mains and from a power electronic converter. Additionally, some methods of counteracting these phenomena were described. Next, multivariant simulation tests were carried out based on the two-dimensional field model of a synchronous machine with permanent magnets. The tests were run in order to determine the internal capacitances of the machine, on which the level of bearing voltages depends. Based on these results, the optimal variant of the design solution ensuring the limitation of the bearing voltage to a safe level was selected. Using the model of a two-level converter and based on the equivalent diagram of the internal capacitances of the machine, the influence of the proposed shielding winding on the bearing voltage was estimated.

Research on Analysis and Suppression Methods of the Bearing Current for Electric Vehicle Motor Driven by SiC Inverter

“…In order to better evaluate the impact of bearing voltage on bearing electric corrosion, the zone in Figure 6 where V b ≥ 1.1 V b * is defined as the bearing electric corrosion danger zone. According to Equation ( 6), the expressions of ω d_min and ω d_max of, respectively, the lower and upper frequency points in this zone are as follows: (11) In order to avoid the risk of bearing corrosion, the selection of switching frequency should try to avoid the danger zone between d min and d max in Figure 6. However, the selection of switching frequency is determined by many factors, such as efficiency, volume, power density, electromagnetic interference performance, etc.…”

“…Correspondingly, the curve of Vb also chan quency in Figure 6. According to Equations ( 7)- (11), the theoretical calcula each frequency point at the curve in Figure 6 are shown in Table 6 by using mon-mode filter. In order to attenuate the V b by at least half of the reference bearing voltage V b *, according to Equation ( 6), the Equation ( 13) can be obtained:…”

“…Correspondingly, the curve of V b also changes with frequency in Figure 6. According to Equations ( 7)- (11), the theoretical calculation results of each frequency point at the curve in Figure 6 are shown in Table 6 by using a 13 mH commonmode filter. The experimental waveforms are shown in Figure 12.…”

“…From current research, it could be summarized that the suppression of the motor bearing current can be addressed from three aspects, including the bearing reinforcement, the capacitive coupling paths within the motor, and the source of common-mode voltage. Conductive grease bearings and ceramic bearings have been applied to suppress bearing current [11]. Conductive grease bearings create a conductive channel inside the bearing, bypassing the bearing oil film, making it difficult to establish a stable bearing voltage, which prevents the discharge of the bearing oil film.…”

Influence of the Shielding Winding on the Bearing Voltage in a Permanent Magnet Synchronous Machine

“…The aim of the article is to present the idea of limiting bearing voltages in electric machines, particularly in synchronous machines with permanent magnets placed inside the rotor. The research presented in the article is a continuation of the publication [17], in which the authors conducted a detailed analysis of the impact of machine design solutions on parasitic capacitances. It was limited to the simulation of two-dimensional models, and the subject of the research was the comparison of, among other things, the shape of the stator slot opening, the number of shielding wires used in the slot opening space and the demonstration of their influence on parasitic capacitances and bearing voltages.…”