Research On PV Modular DC Boost Collection System And Control Strategy

With the global warming and environmental problems becoming increasingly prominent,countries around the world have increased the use and development of new energy sources.PV DC boost collection systems are one of the key technologies for large-scale PV power generation and grid integration.The system has the advantages of high voltage,large capacity,and high efficiency.Therefore,it is of great significance to study the topology and control strategy of PV DC boost collection system.This paper first introduces the research situation of current high-power PV DC-boost converters at home and abroad.Through the comparison of high-power,high-ratio and high-voltage DC-DC converter circuits,comprehensive consideration of conversion efficiency,application range,control difficulty and other factors Complete the topology evaluation and selection of high-power high-voltage DC boost converter.Subsequently,this paper proposes a topology and control strategy suitable for±30kV/1.5MW distributed PV DC boosting system and ±30kV/1MW centralized PV DC boosting system.The high-power DC boost converter is a Boost full-bridge isolated boost converter as a basic unit,which is composed of a combination of a front-stage parallel and a rear-stage series.This structure can satisfy the large-capacity,high-ratio DC boosting.The design requirements of the flow device and achieve the goal of power superposition at a constant voltage.After that,this paper studies the Modular Multilevel Converter(MMC)topology and control strategy suitable for grid connection of PV DC boost collection system.The basic principle of full-bridge MMC is analyzed,and the relationship between voltage and current between each bridge arm is analyzed in detail.The electromagnetic transient mathematical model of full-bridge MMC is established by coordinate axis transformation to design the control system of full-bridge MMC.Lay the theoretical foundation.The triangular carrier phase-shift modulation strategy is adopted as the modulation strategy of the full-bridge MMC.The closed-loop control of the full-bridge MMC is realized by triggering the control of the sub-modules.In order to realize the smooth start of the PV DC-boosting system,the multi-level converter is studied.Start control strategy for the serial/parallel system.Finally,this paper analyzes the fault ride-through capability of the PV DC boost collection system.Under the MATLAB/SIMULINK simulation platform,the simulation experiment of DC-side bipolar short-circuit fault and AC-side short-circuit fault of the system is carried out.The experimental analysis proves the MMC type.PV grid-connected inverters have relatively good fault ride-through capabilities.