The effect of circuit parasitic impedance on the performance of IGBTs in voltage source inverters

In order to reduce power losses and increase system power density, IGBT switching speeds in industrial motor drives continue to increase. These fast switching speeds, combined with high switching frequencies, have increased the interaction between the IGBT and the parasitic circuit impedance. This paper describes the switching behavior of fast switching IGBTs in the presence of parasitic circuit impedance. The sources of the parasitic impedance are identified and include the IGBT chip, power device packaging, physical circuit layout and motor load. The interaction between the power devices and circuit parasitic capacitance is shown to cause output voltage distortion that affects the volt-seconds applied to the motor. Analysis of the current paths and voltage distortion levels is performed as a function of the inverter switching state to predict the IGBT switching behavior. It is also found that parasitic capacitance contributes to an increase in the IGBT power loss and a change in the power loss distribution between the IGBT and diode in a power module.