| Energy storage systems of batteries are widely used in various fields.The structure of conventional centralized charger limits the scalability of the energy storage system,while the structure of distributed charger has good scalability and is thus endowed with high reliability.To satisfy the demand for a flexible and expandable structure,a distributed equalization and charging system based on the DC bus is proposed.The DC bus and the bidirectional DC converter m odule are used to achieve the balance function between distributed charging and equalization among battery packs.In this paper,starting from the basic module of the system,the bidirectional DC converter,the converter design and control method are studi ed,and on this basis,a control scheme of the equalization mode of the distributed equalization and charging system is proposed.The bidirectional DC converter adopts a full-bridge push-pull topology.The principle of the converter’s bidirectional operation is analyzed separately,and the different working modes of the converter are obtained,and the relationship between voltage and current is obtained,which provides a basis for the modeling of the converter circuit.In boost operation,the converter is essentially a current-type push-pull converter.The inherent turn-off voltage spikes of push-pull switches increase the stress of the switches and reduce the converter efficiency.Aiming at this shortcoming,a novel naturally-clamping modulation method without auxiliary or snubber circuits is proposed for realizing the soft switching of push-pull switches,and on this basis,an improved method to accomplish soft switching of all full-bridge switches is proposed,to reduce the stress of the full-bridge switches and improve overall efficiency.The key magnetic components of the converter are designed,and the circuit modeling and control loop design of the converter bidirectional operations are completed on this basis.A closed-loop simulation model is built,and the rationality of the control parameters is verified through simulation.Feasibility of the proposed modulation methods are validated as well.Based on the bidirectional DC converter prototype,an experimental platform for the function verification of the converter is constructed.The experimental results show that the converter can work efficiently in the buck charging mode;in the boost mode,the two proposed control methods can suppress the turn-off voltage spike of the push-pull switches,and realization of soft switching of the full-bridge switches is consistent with theoretical design.The minimal system experimental platform built on the basis of two converter modules verifies that the system can achieve energy transfer between batteries by means of bidirectional DC converters.In order to realize the equalization function of the distributed equalization and charging system,through the analysis of the control structure and functions of the system,a comprehensive control scheme of the system in equalization operation is designed to realize the shunt between the battery modules according to the battery energy state,and the power balance problem of the DC bus is analyzed in this scenario. |
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