Common Mode Current Reduction in Traction Systems for Electric Vehicles

The market for fully electrified vehicles is expanding fast. The number of sources and loads that are connected to the vehicles traction voltage systems (TVS) are increasing and thus also the ElectroMagnetic Compatibility (EMC) requirements on these sources and loads. These requirements should make sure that neither function nor lifetime of any source or load is severely affected by another. The Common Mode (CM) and Differential Mode (DM) currents and voltages, generated by the modulation of the various power electronic converters, need to be covered by the requirements. In addition to this, requirements on both intentional and parasitic impedances, influential at frequencies up to at least 10 MHz, have to be compiled. This paper presents a theory for lowering the CM disturbances from the Electric Machine Drive (EMD) to the Electric machine (EM). When supplying zero output from the EMD, all phases are moved to the positive or negative pole, of the DC link in a 2-level converter, simultaneously, resulting in a common mode current. With a short intentional delay between the gate pulses, the common mode peak current and voltage derivative to the EM can be reduced.