Experimental Assessment of High Frequency Bearing Currents in an Induction Motor Driven by a SiC Inverter

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 (dv/dt). The CM voltage leads to machine leakage currents as well as bearing currents such as electric discharge machining (EDM) type current and capacitive-type (dv/dt) 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.INDEX TERMS Motor bearing, bearing current, SIC MOSFET, motor drive, common mode voltage, fastswitching.

Impact of High Switching Speed and High Switching Frequency of Wide-Bandgap Motor Drives on Electric Machines

“…Fig. 23 shows the schematic diagram of the CM voltage/current path in the inverter-cable-motor system [18]. In Fig.…”

“…The motor winding overvoltage can incept partial discharges that progressively yield to the degradation of polyamide-imide and polyester coating of motor coils [17]. The high voltage slew rate (high dv/dt) due to fast-switching and the high switching frequency increases the capacitive-type bearing current and affect the electric discharge machining (EDM) bearing current [18]. These bearing currents are the root cause of bearing degradation and failure.…”

On the Application of Extended Grounded Slot Electrodes to Reduce Noncirculating Bearing Currents

“…1. According to the above mentioned, it is not enough to apply electrostatic shields in the core-area only, as it was done in, i.e., [15] and [19]. In that case, the parasitic current is still able to reach the rotor and harm the bearing, albeit with a smaller amplitude.…”

Review of Traction System, Energy Efficiency and Electrical Design of Automated Guided Vehicles in Automotive Industry

“…In this section, possible interactions between common mode currents created by inverter and EMC/EMI related problems of an AGV is discussed briefly. Common mode currents (CMC) induced by common-mode voltages of inverter and its effect on bearing failures have been studied extensively in industrial applications and recently realized as a design and application problem in electric vehicles [62][63][64][65][66][67][68][69][70][71].…”

“…Measurement of shaft voltages by measurement instruments like in [51] is the practical way to evaluate the risks of bearing currents and potential EMI risks as well. Detailed analysis and solution proposals on CMC are studied in [62][63][64][65][66][67][68][69][70][71].…”