Overview
Motor drives are the backbone of industrial automation, and they are also one of the most demanding applications for a power module. A variable-speed drive must convert a DC bus into three-phase AC at a switching frequency high enough for smooth torque, while keeping losses, acoustic noise and EMI under control. A Semikron SEMITRANS or SEMiX half-bridge module integrates the two switches and their inverse diodes in a low-inductance package, so six modules form a complete three-phase inverter, and the module sets the voltage class, the losses and the heatsink size for the whole drive.
Choosing the Module for the Drive
The first decision is the voltage class. Industrial drives running from a 380-480 V AC line use a boosted DC bus above 600 V, so a 1200 V module such as the SKM453GB12E7 provides the necessary margin. A 690 V system moves to 1700 V, where the SKM803GB17E7 provides the blocking capacity. For a compact servo axis, the low-profile SEMiX platform lets the gate driver sit directly on top of the module, which keeps the commutation loop short and the inverter dense. The half-bridge circuit is the building block, so the same electrical approach scales from a small axis to a large drive by changing the module size and current rating.
Switching Frequency and Losses
The switching frequency sets a trade-off between torque ripple, acoustic noise, magnetics size and switching loss. 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+ and a matching CAL7 diode become valuable. A three-level topology further reduces the switching loss by halving the voltage step across each device, which is where the multi-level capability of SEMITRANS 3+ helps.
The Power Stage Layout
At the heart of any drive is the commutation loop formed by the DC-link capacitor and the switching devices. Every centimetre of that loop adds inductance, so the module and the capacitor should sit as close together as the layout allows, with a laminated busbar where possible. The low internal inductance of the SEMiX and SEMITRANS 3+ designs keeps the turn-off overshoot low, but the external busbar still sets the result. A matched Semikron SKYPER gate driver provides the isolation, the short-circuit protection and the soft shutdown, and mounting it close to the module keeps the gate loop small.
Thermal Design
The module thermal resistance, the interface material and the heatsink together set the junction temperature. Estimate the conduction and switching losses at the actual operating point, then confirm the junction temperature at the worst-case ambient and load. A 175 degree junction rating, as on SEMITRANS 3+, allows a smaller heatsink or a higher current for the same cooling, which is valuable in a compact drive. The BeiLuo FAE team runs the loss estimate and checks the thermal path.
Working With BeiLuo
Because Semikron covers the module, the gate driver and the thermal interface from one authorized channel, a drive manufacturer can build the whole power stage from one supplier with coordinated parts and one import documentation set. Send the bus voltage, the current, the switching frequency and the ambient for a matched recommendation with stock and lead time.