Torque and Current Ripple Analysis in Integrated DC-DC Boost Chargers Based on SynRMs and WR-SMs

The automotive industry is increasing the voltage level of electric vehicles from 400 V to 800 V to reduce charging time without increasing the current levels. The vehicle wiring and the connectors that link the external DC fast charger to the internal battery impose limits on the maximum charging current for thermal, mechanical, and reliability reasons. Despite the presence of 800 V vehicles in the market, only a small portion of charging stations across Europe currently support this higher voltage level. Consequently, electric vehicles must be inherently compatible with 400 V DC charging stations, albeit with a slight increase in both the cost and weight of the powertrain components. The solution outlined in this study involves reconfiguring the electric motor and the three-phase inverter into a DC/DC boost converter to adapt the high-voltage battery to the voltage level of the off-board charger. During the charging process, several constraints should be considered from both the machine's and the off-board charger's point of view. These aspects include the generation of a zero-mean torque independent of the rotor position and minimizing the output current ripple of the off-board charger and the torque ripple. The analysis presented in the paper considers synchronous machines without permanent magnets, such as synchronous reluctance machines and wound-rotor synchronous machines.