A high-frequency pulsating dc link for electric vehicle drives with reduced losses

This paper proposes a motor drive suitable for electric vehicles (EVs) with notably reduced losses as compared to conventional drives. The proposed drive feeds the dc-link with a dynamically reconfigurable battery formed by cascaded half-bridges containing battery units. The reconfigurable battery concurrently forms a modular multilevel dc-link able to synthesize variable dc-link voltages, which can adjust the dc link voltage to run a motor to operate at the optimum load point or even to contribute to modulation and greatly reduce the switching loss of the main inverter—in this case a standard two-level three-phase inverter. Up to ⅔ switching actions are avoided in the main inverter, which can run at maximum duty cycle and fundamental-frequency commutation. The saved switching effort in the main inverter is shifted to the modular multilevel dc-link, but with much less loss due to the fractionized switching voltage and the use of field-effect transistors (FETs).At high drive speeds, the converter halves the total loss compared to a standard inverter only; at lower speeds and thus smaller modulation indices, the advantage is even more pronounced because of the dynamically lowered dc-link voltage. Other benefits include alleviated insulation stress for motor windings and direct battery balancing. The proposed motor drive is verified on a down-scaled setup with eight modules constituting the dc-link.