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Analysis and Assessment of Soft-Switching Inverters for SiC-based Traction Drive in Electric Vehicles

Circuit topology
Fig.1. Two soft-switching topology candidates, the ARCP and 6S with coupling inductor.
  Whether using soft-switching inverter topology for low-voltage high-current traction drive inverter remains unclear. In this paper, four widely accepted topology candidates, including two-level inverter (2-L), three-level T-type inverter (T2), auxiliary resonant commutation pole inverter (ARCP), and six-switch inverter with coupling inductor (6S), are select-ed and investigated for a 200-kW SiC-based traction inverter. Considering voltage stress of switching positions, three SiC device candidates with different characteristics are chosen from the current market.

  Firstly, the system specifications as well as component candidates are intro-duced. The power devices, including one from UnitedSiC due to its high switching energy but low conduction resistance for soft-switching, and another one from Microsemi because of it well overall performances for hard-switching, are narrowed down from original 50+ devices on the market. Moreover, two capacitor candidates, which are CeraLink and Film capacitors, are con-sidered for DC-link capacitor.

  Secondly, the mechanism of topology candidates is discussed in detail in or-der to identify key parameters for power loss calculation. Based on different voltage stress of different switching positions and calculated current components in auxiliary branch, the loss dis-tribution of soft-switching topologies can be analyzed. Since the switching-on loss is greatly eliminated, combining the generated conduction loss in auxiliary branch, the conduction loss is dominant in soft-switching inverters and the conduction loss is direct proportional to the output current.

  In conclusion, the final comparisons for four topology candidates are shown under 20 kHz and 100 kHz, using CeraLink and Film capacitor as DC-Link capacitor. It is clear that the performance of soft-switching inverters largely depends on the power device technology or characteristics. By using the latest device such as Microsemi one for 2-L inverter, the efficien-cy improvement by using soft-switching inverter is always less than 0.2%, while having higher cost and volume.

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