Influence of MOSFET Scattering on Common Mode Cancellation in Phase Shifted Inverter Operation

A method to decrease Electromagnetic Interference (EMI) caused by semiconductor switching in redundant inverter topologies is to switch a high-side semiconductor of inverter one simultaneously to a low-side semiconductor of inverter two in order to destructively overlay the disturbances. This approach is particularly interesting for automotive steering systems, because of safety driven redundancy requirements two inverters are always available for a phase shifted operation. Laboratory tests on a sixphase demonstrator show up to 40 dB disturbance attenuation in the range of 20 kHz to 10 MHz. This paper investigates how MOSFETs scattering affects the disturbance cancellation. For this purpose, statistical evaluations of the most important influencing parameters and measurements of switching processes are presented.