An Integrated Power Conversion System for Electric Traction and V2G Operation in Electric Vehicles With a Small Film Capacitor

An integrated power conversion system is proposed for electric vehicles (EVs), which consists of a dual active bridge (DAB) dc-dc converter cascaded by a three-phase four-leg (TPFL) dc-ac converter. The integrated power conversion system can realize both vehicle-to-grid (V2G) operation and traction operation for EVs. The large capacitor is avoided in the dc link of the proposed power conversion system. Instead, an active snubber with a small film capacitor is connected to the dc link to suppress the voltage oscillation, which is induced by the removal of the large dc-link capacitor. By designing the phase-shifting control for the primary H-bridge of DAB, a high-frequency pulsating dc-link voltage with zero portions is generated. Setting switching actions of the secondary H-bridge of DAB and TPFL during zero portions of the dc link, the zero-voltage-switching (ZVS) operation is achieved, and the system efficiency can be improved consequently. Therefore, the fixed-switch-moment control strategies, namely, the finite-set model-predictive-control (FS-MPC) and switch-table direct-torque-control (ST-DTC), are proposed to regulate TPFL for V2G operation mode and traction operation mode, respectively. Detailed analysis of different switch states within one half operating cycle is presented. Both simulation and experiment are conducted to verify the effectiveness of the proposed system and control schemes.