High Power Density and Overcurrent Protection Challenges in the Design of a Three-Phase Voltage Source Inverter for Motor Drive Applications
The voltage source inverter (VSI) is certainly the most popular topology used in dc to ac power conversion. Virtually every commercial electric motor is driven by a VSI. There is a need for smaller and more efficient drives in high performance applications that is dictating unprecedented power density requirements on airborne motor drive systems. In reply to this need, higher switching frequencies are being sought and new switching devices like Silicon Carbide (SiC) JFETs have emerged. Although faster switching rates favor a reduction in the size of passive components and alleviate the current ripple in the inverter, a penalty is paid on switching losses. Owing to their low switching energy profile, SiC JFETs stand as promising candidates in high switching frequency environments. Their normally-on nature, however, raises a level of discomfort among designers due to the added complexities in the gate drive circuitry and the increased risk of dc bus shoot-through faults in voltage source inverters. Despite of these challenges the use of SiC JFETs continues proliferating in high power density applications. In an effort to study the new challenges introduced by this trend a 2 kW IGBT-based three-phase voltage source inverter operating at 65 kHz was designed, built, and tested. In addition a novel overcurrent protection residing in the inverter dc link is proposed in response to the concern of using normally-on devices in voltage source inverters. Successful hardware validation of both the VSI and the overcurrent protection circuit is supported with experimental results.