Abstract
Compared with silicon (Si) IGBTs, silicon carbide (SiC) MOSFETs have much faster switching speeds and high switching frequency operation capability, enabling compact and high-efficiency motor drive systems. However, the increased switching speed and frequency also cause increased-level of common-mode (CM) voltage with higher slew rates ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ). The CM voltage leads to machine leakage currents as well as bearing currents such as electric discharge machining (EDM) type current and capacitive-type ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ) current. These bearing currents can cause degradation or failure of motor bearings. In order to investigate the impact of SiC motor drives on the motor bearing currents, in this paper, the mechanism and modelling of bearing currents are analyzed first. Then, a direct measurement method is used to assess the bearing currents in the induction motor driven by the SiC converter. In the experiment, the number of EDM current events is counted and the amplitude of the capacitive-type of current is also examined under various switching speeds and frequencies of SiC devices. Furthermore, the bearing currents are also extensively tested under various bearing temperatures, motor speeds and dc-link voltages. The correlations between the bearing currents and various factors have been revealed in this paper.
Highlights
High-performance AC variable speed motor drive systems have been used in many applications such as industrial automation for energy saving and electrified transportation
Albeit the benefits brought by silicon carbide (SiC) devices for motor drives, there are increased reliability concerns regarding their negative impacts on motors such as the accelerated degradation of motor winding insulation and bearings due to the high dv/dt and high switching frequency [4]
This paper aims to provide a timely investigation and useful reference for the impact of high-frequency SiC converters on motor bearings
Summary
High-performance AC variable speed motor drive systems have been used in many applications such as industrial automation for energy saving and electrified transportation (road, air, rail and marine). SiC converters with high switching frequencies are preferred for driving motors with high fundamental frequencies (e.g., >1 kHz), where high speed and a large number of poles are adopted for the purpose of reducing motor size and weight. SiC inverters can achieve a switching frequency of 100 kHz and an output voltage slew rate (dv/dt) of 20 kV/μs, which is much higher than those from existing Si IGBT based inverters. The high-frequency common-mode (CM) voltage from SiC converters causes increased level of motor bearing currents, a main cause for bearing degradation and failure [5].
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