Bidirectional DC-DC Converters And Second-Order Ripple Suppression Schemes For Single-Phase Charging For Electric Vehicles

As an important part of the rapid development of the global new energy industry,the hybrid energy sources electric vehicles(HESEVs)are in a leading position in terms of both the performance of the vehicles themselves and the utilization rate of energy sources.The hybrid energy sources system(HESS)for EVs mainly includes battery pack and super-capacitor bank,onboard bi-directional DC-DC converters and hybrid energy sources management system(HESMS).Due to its low energy density and voltage level,the super-capacitor bank has a large range of terminal voltage during its charging and discharging processes.At the same time,in the process of providing power for EVs for a long time,the terminal voltage variation range of the battery is also large.Therefore,the onboard bidirectional DC-DC converters with wide voltage gain is needed to serve as the power interface between the hybrid energy sources and the onboard DC bus.Additionally,in the process of single-phase Pulse Width Modulation(PWM)rectification charging for EV battery pack,there is second-order ripple voltage on the on-board DC bus voltage,thus introducing second-order ripple component into the charging voltage and current of the battery,thereby resulting in the serious heating and the reducing life of the battery.Therefore,it is of great academic and practical significance to study the onboard wide voltage gain bidirectional DC-DC converters and to suppress the second-order ripple component of the onboard DC bus voltage and battery charging voltage and current.Firstly,two wide voltage gain bidirectional DC-DC converters,based on the switched-quasi-Z-source and the switched-capacitor,are proposed in this paper.The switched-quasi-Z-source networks and switched-capacitor unit make the proposed converters have obvious performance advantages,not only in the voltage gains,but also in the voltage stresses across the power switches.The operating principles,static performance and small signal dynamic models of the proposed DC-DC converters are analyzed in detail in this paper.Finally,the experimental results obtained from the scale-down prototypes validate the characteristics and the theoretical analysis of the proposed converters.Finally,in order to suppress the second-order ripple component in the on-board DC bus voltage,as well as in the battery charging voltage and current,during the single-phase PWM rectification charging for EV battery pack,this paper makes full use of the existing super-capacitor bank and the switched-quasi-Z-source/switched-capacitor bidirectional DC-DC converter connected to it in the HESS as the energy storage unit(ESU)and the auxiliary converter.Two second-order ripple active suppression schemes for capacitive energy storage on the onboard DC bus are proposed in this paper.The principles of the proposed ripple suppression schemes are also analyzed in detail in this paper.Finally,the correctness and effectiveness of the proposed schemes is verified by the experimental results on the 400 W scale-down prototype of the single-phase PWM rectification charging system for the battery pack.