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While wide bandgap (WBG) switches have revolutionized power electronics and motor-drive systems, the high dv/dt associated with these fast-switching semiconductors can easily induce reflected high-frequency overvoltage spikes on motor stator terminals. The shorter rise time of the voltage pulses confines the cable length between the inverter and the motor in practice to avoid overvoltage across the motor stator windings. Even with shorter cables, voltage spikes from variable-speed drives can still cause premature insulation failure and reduce the remaining useful lifetime of the motors. While effective, conventional methods such as dv/dt passive filters or active gate drivers are usually bulky and/or inefficient. To address this problem, an overvoltage mitigation solution, named “Smart Coil,” is introduced in this article. The smart coil circuit is installed in parallel with the first coil of each motor phase, which typically experiences the highest reflected overvoltage. Upon detection of overvoltage, the proposed ultracompact smart coil circuit, located at the motor junction box, is activated to limit voltage stress across the coils. Since the smart coil is connected in parallel with the first coil, it only needs to process very low pulsed power during the overvoltage transients. Therefore, it has high efficiency and an ultracompact footprint while effectively mitigating voltage spikes. The proposed smart coil circuit can be easily scaled for various motor-drive systems regardless of the cable length or rise time of the switching devices. Simulation and experimental test results are provided to verify the effectiveness of the proposed method.
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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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