Research On Modular High-Gain Bidirectional DC/DC Converter

With the vigorous development of new energy technologies,DC/DC converters have broad prospects in various fields such as DC microgrids,energy storage systems and electric vehicles.The performance requirements for DC/DC converters are becoming increasingly demanding,with high voltage gain,wide operating range,low current ripple,bidirectional energy flow and high modular scalability being research hotspots.Through the analysis and study of existing non-isolated high-gain DC/DC converters,series capacitor DC/DC converter with good scalability is selected for the design and research of a modular high-gain bidirectional DC/DC converter(MHGBDC)in this paper.MHGBDC has the advantages of high voltage gain,bidirectional energy flow,low current ripple and fast dynamic response,but also has some issues.On one hand,whether using traditional average phase-shift or 180° phase-shift control methods,MHGBDC only has high voltage gain and selfcurrent sharing characteristics in a specific duty cycle range.Uneven current distribution among phases has adverse effects on the selection and design of inductors and the stable operation of the converter,and also increases system losses.On the other hand,existing research has not fully exploited the highly modular advantage of MHGBDC,and the operating mode is single and cannot adjust the operating conditions according to the input/output voltage,which limits the operating range of the converter.To broaden the current sharing operating range of MHGBDC,a current sharing strategy based on 180° phase-shift control method is proposed in this paper that does not require additional current sensors and auxiliary circuits.Firstly,taking four-phase MHGBDC as the analysis object,the duty cycle of each phase is adjusted based on the principle of charge conservation to achieve phase current sharing and the unification of voltage gain expressions over the entire duty cycle range.Then,the current sharing strategy is extended to N-phase MHGBDC,and a general expression for the duty cycle of each phase during current sharing operation is given.To broaden the operating range of MHGBDC,a redundant operation strategy is proposed in this paper that can adjust the number of sub-modules according to the actual operating conditions of the system.Firstly,the switching control method of the sub-modules is given.Then,the four operating conditions of four-phase MHGBDC are analyzed,and the independent operating conditions are connected through the proposed operating strategy,and switches the operating conditions according to the system demand,so that the system has a wider voltage regulation range and current-carrying range without changing the circuit structure.Combined with the topology structure and the proposed control strategy,the working modes and main characteristics of the converter are analyzed in this paper.Then,the closedloop control system is designed based on small signal modeling and transfer function derivation.To better verify the correctness of the theoretical analysis,simulation models and experimental prototypes are further constructed.Through simulation analysis and prototype experiments,the feasibility and effectiveness of the proposed strategies are further verified.