Power Electronics Masterclass: The Definitive Guide to IGBT Selection & System Reliability

Selecting an IGBT for a motor drive is not merely about matching voltage and current ratings; it is about managing the kinetic energy of the system. In the context of Variable Frequency Drives (VFDs) and servo inverters, the IGBT stands as the guardian between the DC link and the inductive load, mediating power flows that can fluctuate from zero to overload in milliseconds.

The “Golden Rule” of drive design is balancing efficiency against electromagnetic noise (EMI). A device with an ultra-fast turn-on time (t_r) might reduce switching losses (E_on), but if the resulting dv/dt exceeds 5kV/μs, it risks destroying the motor’s winding insulation and bearing grease. The engineer’s task is to find the “sweet spot” where thermal performance and motor longevity coexist.

The Safety Net: Short Circuit Withstand Time (t_SC)

In the unpredictable environment of an industrial factory floor, a short circuit—whether due to a cable fault or a stalled motor—is a matter of “when,” not “if.” Unlike solar inverters, motor drives require IGBTs with a guaranteed Short Circuit Withstand Time (t_SC), typically 10μs.

This parameter is non-negotiable. As detailed in our breakdown of failure modes, the chip must survive the immense heat of a direct bus short long enough for the gate driver’s DESAT protection to intervene. Standard “high-efficiency” chips often sacrifice this robustness for speed, making them unsuitable for heavy-duty drives.

The Long Cable Dilemma: V_CE(peak) Management

When the distance between the drive and the motor exceeds 10 meters, physics fights back. The transmission line effect creates voltage reflections that can double the DC bus voltage at the motor terminals.

According to ABB’s technical guides on drive installation, managing this requires a holistic approach: selecting IGBTs with softer switching characteristics, implementing proper output filtering (dV/dt filters), and ensuring the module’s Reverse Bias Safe Operating Area (RBSOA) can handle the repetitive voltage spikes typical of long-cable installations.

This masterclass series walks you through these critical selection criteria, moving beyond the first page of the datasheet to the curves that define real-world reliability.