Why Module Selection Deserves Care

The IGBT module is the most consequential component in a power converter. It sets the voltage class, the losses, the heatsink size and, in many cases, the reliability of the whole product. Choosing the wrong module late in a project costs time and money, which is why a structured selection process pays for itself. This guide walks through a repeatable method for selecting a Semikron module, using the SEMITRANS, SEMiX and SEMITRANS 3+ platforms as the candidate set.

Step 1: Fix the Voltage Class

Start with the DC bus, not the nominal AC voltage. A 380 to 480 V AC drive rectifies to roughly 560 to 680 V, and switching overshoot adds more, so a 1200 V module provides the necessary margin. A 690 V system moves to 1700 V, and a low-voltage battery supply can use a 600 V module. Include the switching overshoot in the calculation, because the device must survive the peak, not the average, and leave at least fifteen percent margin between the worst-case peak and the blocking voltage.

Overshoot and Margin

The commutation-loop inductance and the switching speed set the overshoot. A module with a low internal inductance, such as SEMiX or SEMITRANS 3+, reduces it, but the DC-link layout and the busbar still matter. Measure the overshoot at the module terminals during validation, because the bus measurement hides the peak the device actually sees.

Step 2: Set the Current and the Topology

Continuous current plus overload current sets the current rating. A motor drive may draw 150 percent of rated current for several seconds during acceleration, and welding equipment draws large repetitive pulses. Choose a module whose rated current covers the worst case at the expected case temperature, then verify the junction temperature with the thermal path. The topology follows the circuit: the half-bridge builds a three-phase inverter, the chopper builds a boost or brake stage, and the common-emitter builds a buck or boost converter. The SEMITRANS family covers all three.

Switching Frequency

Switching frequency is the next filter. Below about 15 kHz, conduction loss dominates and a low saturation-voltage device is efficient. Above 15 kHz, switching loss grows quickly, so a fast chip generation such as the IGBT 7 in SEMITRANS 3+ becomes attractive, and a three-level topology can reduce the loss further by halving the voltage step across each device.

Step 3: Choose the Platform and Package

The platform follows the mechanical and thermal needs. SEMITRANS 3 and SEMITRANS 2 give the broadest range in the proven 62 mm and 34 mm housings. SEMiX gives a low 17 mm profile with separated terminals and a driver on top, for a dense inverter. SEMITRANS 3+ gives the latest chip and the highest current in the classic footprint. Check the gate driver pairing, because a matched Semikron SKYPER or SKHI driver keeps the gate loop short and the protection proven. The BeiLuo FAE team helps finalise the choice and validate it on the bench.