Research On DC-DC Conversion Topology For Multi-branch Photovoltaic DC Collection

As a representative of new energy development and utilization technology,photovoltaic(PV)power generation has become the main force in the field of new energy development and utilization.Since PV power generation can meet grid-connected conditions after boosting,boost collection technology has become one of the key technologies in the field of PV power generation.The traditional AC boost collection technology has poor stability and low efficiency,which restricts the grid-connected absorption of PV power generation.With the development of DC transmission technology and power electronics technology,PV DC boost collection technology emerged as the times require,and it has become a research hotspot in the field of PV power generation.Aiming at the technical challenges of multi-branch PV DC collection system,this paper focuses on the research of DC-DC converter topology,which is the core link of the system.This paper first gives an overview of the multi-branch PV DC collection system,and analyzes its basic structure and technical difficulties.On this basis,the input independent output series(IIOS)type multiconverter units DC conversion topology is selected as the PV DC conversion topology and its power mismatch mechanism and existing solutions are analyzed and studied,which lays a theoretical foundation for the proposed new design scheme.Aiming at the future application scenario of distributed PV access to DC distribution network,this paper proposes a design scheme of IIOS PV DC converter with internal power balancing unit,and its topology,working principle,control strategy and small signal modeling and parameter design were analyzed in detail.The design scheme can fundamentally solve the power mismatch between converter units,and has excellent wide range operation capability.It is very suitable for distributed PV power generation where the fluctuation range of PV array output power is large.Aiming at the future application scenario of DC boosting collection for PV power station,this paper proposes a design scheme of IIOS PV DC collection system with embedded hybrid storage units,and its system architecture,working principle,operation control strategy,energy management strategy and the system parameter design are analyzed in detail.The design scheme combines the advantages of the PV-storage combination system and the IIOS-type DC conversion architecture.On the one hand,it can suppress the power mismatch between the arrays,maintain the ideal operating state of the collection system,and improve its adaptability to complex working conditions;On the other hand,it can realize system optimization control based on optical-storage coordination,and improve the grid-connected friendliness of PV DC power generation system.Based on theoretical analysis,the simulation experiments are carried out for the two design schemes proposed in this paper.The simulation results show that the two design schemes proposed in this paper have good operation characteristics and verify the correctness of theoretical analysis.In addition,a hardware experiment platform is built for the proposed design of PV DC converter,and its performance under power mismatch is verified by hardware experiments.The simulation and experimental results show that the two technical schemes proposed in this paper are correct and effective,and have potential value for the future application of PV DC collection system.