The current stress of transistors and diodes of a 3-phase inverter is dependent on the modulation index M and the phase shift between voltage and current. In case of a high modulation index, and voltage and current approximately in phase (energy flow from DC source to AC motor), the transistor experiences high current stress and the diode low current stress. In case of a 180 degree phase shift (energy flow from AC motor to DC source), it is just the opposite: high stress for the diode and low stress for the transistor. In case of a 90 degree phase shift (no real power flow), diode and transistor current stress are independent from the modulation index. In the case of a very low modulation index, the on- and off-times become approximately equal, resulting in equal current stress for diode and transistor. This is then independent from the phase-shift.

• Drag the red points on the voltage and current curve to change the modulation index and phase shift between voltage and current.
• Click the check boxes to switch between the transistor curve iT(t) and diode curve iD(t).