SiC based reconfigurable DC-DC integrated converter for EVs

The objective of the research is to develop and optimize an integrated converter prototype for 50 kW traction operation as boost converter and 6.6 kW charging operation as dual active bridge (DAB) converter. A scaled down prototype is first developed to verify the reconfigurable integrated converter operation and loss verification. The boost converter is operated in current interleaving mode to reduce the capacitor requirement. Phase shift modulation is adopted for DAB converter. The unique aspect of the design is to incorporate a hybrid high frequency integrated magnetics which can be operated as DC boost inductor and AC isolation transformer for dual active bridge converter. The magnetizing inductance of the hybrid high frequency integrated transformer is used for boost operation and the leakage inductance is used for the DAB converter operation. A model for finite element analysis (FEA) is developed to evaluate the leakage and magnetizing inductance for different winding and core configurations. Based on the leakage and magnetizing inductance, an analytical converter model is developed to predict the transformer current waveforms and output power. To achieve the highest efficiency for different operating conditions, a loss model is developed for efficiency optimization.

Due to the bidirectional power flow capability of DAB converter, it can be operated in both charging operation and traction operation. Since the integrated converter can drive the traction motor as both boost and DAB mode, they are designed independently for highest efficiency at light load and full load condition. For most integrated converter topologies presented in literature, extra mechanical or solid-state contactor is required for reconfiguration which adds cost and increases the volume of the converter. In the proposed integrated converter, reconfiguration between DAB and boost mode is achieved by switching the BMS contactors which are already available in EVs. However, the time required to reconfigure the converter between boost and DAB modes are high due to the mechanical contactors. A trapezoidal modulation scheme is developed to ensure seamless power flow during the mechanical contactor transition time. The modulation scheme ensures the reliability of the BMS contactor and prevents overshoots. Using targeted design approach based on consumer driving habits and drive cycle statistics, the topology provides a unique way to design and optimize independently EV efficiency for different torque-speed requirement.