Influence of the Configuration of the Load Cable on Switching Characteristics of IGBTs

Inhalt:
While the negative influence of long cables between an inverter and an AC motor on the motor has been investigated in literature the effect on the switching energy of the IGBTs is often not considered. This leads to a discrepancy between the expected losses derived from data sheet measurements with pure inductive load and the real application. This work focuses on evaluating the switching energy of IGBTs in a three-phase inverter depending on the geometry of the cable. The effects of different lengths of a shielded 4 core cable (up to 50 m) are investigated and compared with non-shielded cables. Critical paths of parasitic capacitive leakage currents are defined and evaluated by measurement. Additionally, the influence of different grounding concepts are discussed. The measurement results show, that especially the large capacitance between shield and phase leads to an increased turn-on current and therefore turn-on energy, while the turn-off energy is reduced. However, the overall switching energy increases with the length. Additionally, two significant effects within the switched current and voltage occur depending on cable length and current amplitude. A simulation model is able to investigate and explain these effects.