| With the depletion of non-renewable energy and the rapid development of renewable energy,organic combination of distributed new energy and microgrid technology is gradually changing the traditional structure of power grid,photovoltaic/storage microgrid,which includes photovoltaic power generation system and energy storage system,has broad prospects in distributed microgrid field.In a new type of 1500 VDC photovoltaic energy storage system,high voltage multilevel inverters and isolated bidirectional DC/DC converters with high power density and high efficiency have become the research hotspots.In this dissertation,the photovoltaic energy storage system is taken as the research object and high voltage multilevel inverters and isolated bidirectional DC/DC converters are mainly studied.Firstly,the significance of photovoltaic power generation,the research status of photovoltaic energy storage system and its key technical issues are introduced in this dissertation.Then,aiming at the topology of highefficiency isolated bidirectional DC/DC converters in photovoltaic energy storage system,a two-stage bidirectional DC/DC converter and its parameter design procedure is presented in this dissertation.Meanwhile,the working principle of LLC-SRC resonant converter under LLC operation and SRC operation is analyzed and its parameters are designed which is verified by simulation and experiment results.Aiming at the topology of high voltage photovoltaic inverters in photovoltaic energy storage system,a novel modulation method for ANPC five-level topology is proposed.The circuit topology of ANPC five-level inverter and eight current flow states and their effects are analyzed in this dissertation.A complete state machine for ANPC five-level inverters is established together with sixteen reliable switching states and PD-SPWM.At last,the advantages of the PD-SPWM and the state machine for ANPC five-level inverter are verified by simulation and experiment results. |
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