How to suppress circulating current when inverter components are connected in parallel

When paralleling IGBTs or diodes in frequency converters to increase current capacity, suppressing circulating current between devices is crucial. Circulating current can lead to uneven current distribution, additional losses, and even damage. Suppression measures include: selecting devices with matched parameters, and using modules from the same batch with good parameter consistency whenever possible. Optimize the symmetry of the layout, ensuring that the parasitic inductance (especially the emitter inductance) of each parallel branch is as consistent as possible, and adopt a symmetrical busbar design. Setting independent gate resistors for the gate drive of each device allows for fine-tuning of their respective switching speeds, but adjustments must be made carefully to prevent oscillations.

Sometimes, small inductors or ferrite beads are connected in series with the emitters of parallel devices to balance dynamic current, but this increases losses and complexity. For diodes, a small resistor can be connected in series with the anode to balance quiescent current. Drive signals must be synchronized and clean to avoid situations where one device is turned on while the other is not yet turned off due to differences in drive delay. Monitoring the temperature uniformity of parallel devices using an infrared thermal imager can indirectly assess the current sharing effect. Eintec's power modules and drive solutions consider the needs of parallel applications and provide technical guidance to help achieve stable and reliable parallel operation.