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High-performance switching devices like SiC MOSFETs introduce high-frequency ringing and overvoltage transients at motor terminals, leading to uneven voltage distribution across windings. In SiC-driven motors, the first coil and initial turns experience significant overvoltage stress, increasing the risk of insulation degradation and inter-turn faults. This study proposes an analog circuit to mitigate overvoltage stress. The circuit detects high dv/dt in the first coil and adaptively inserts a ceramic capacitor via a GaN switch, forming a low-impedance path for high-frequency currents. This diverts part of the transient energy to the second coil, reducing stress on the first coil and promoting uniform voltage distribution. The GaN switch remains closed to sustain the high-frequency current path through the capacitor, adapting to different operating conditions and cable lengths. The circuit was prototyped and experimentally validated on a 2hp induction motor driven by a SiC inverter, demonstrating its effectiveness in mitigating overvoltage stress. This compact solution enhances the reliability of SiC-driven motor systems by addressing uneven high-frequency voltage distribution.
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Smart Coils for Mitigation of Motor Reflected Overvoltage Fed by SiC Drives
High dv/dt from the emerging SiC variable-frequency drives can easily induce overvoltage across the motor stator winding terminals, especially for long-cable-connected and high-voltage motor-drive systems. Due to the fast switching speed and surge impedance mismatch between cables and motors, this overvoltage can be two times or even higher than the DC-bus voltage of the inverter, resulting in motor insulation degradation or irreversible breakdown. The most common solution to mitigate such overvoltage is to install a dv/dt or a sinewave filter at the output of the drive, which decreases the efficiency and power density of the system. Among different stator coils, the first one (close to the drive side) is the most susceptible to insulation breakdown since it experiences higher overvoltage than the others due to the nonlinear distribution of the reflected surge voltages. In this paper, an innovative high-efficiency ultracompact mitigation solution is introduced, which is a tiny auxiliary circuit embedded inside the motor stator (or at the motor terminal box), specifically across the first few coils of each phase (i.e., smart coils). The proposed smart coil circuit effectively mitigates the surge overvoltage, which can be scalable to any type of motor-drive systems, regardless of cable length and semiconductor rise time. The proposed solution can dramatically improve the reliability, efficiency, and power density of motor-drive systems.
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- Award ID(s):
- 2135544
- PAR ID:
- 10473166
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 978-1-6654-7539-6
- Page Range / eLocation ID:
- 1429 to 1436
- Format(s):
- Medium: X
- Location:
- Orlando, FL, USA
- Sponsoring Org:
- National Science Foundation
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