Design And Implementation Of Two-stage Photovoltaic Grid-connected System Based On SiC MOSFET

Due to the rapid economic development,traditional energy exhaustion and environmental pollution,renewable energy are getting more attention,especially the development and utilization of solar photovoltaic(PV)power generation.Among them,Distributed PV power generation has gradually become one of the important branches,and it is also the most potential form of PV power generation at present.Distributed photovoltaic power generation systems generally adopt a two-stage structure,that is,the step-up converter and the inverter are cascaded.IGBT are widely used in traditional photovoltaic grid connected power generation system,but the current tailing effect of IGBT limits the switching speed and increases the switching loss,which makes it impossible to further improve the power density and efficiency of the topology.The new wide bandgap semiconductor device Si C MOSFET has the advantages of high temperature resistance,high frequency and high power density.Under the same working condition,using Si C MOSFET to replace IGBT is beneficial to improve the efficiency and power density of photovoltaic grid-connected system topology.In addition,the traditional MPPT control algorithm often fails to track due to sudden changes in the external environment,resulting in power loss.Therefore,this paper studies the design and control of the two-stage three-phase grid-connected photovoltaic system based on Si C MOSFETFirstly,based on the mathematical model of PV cells applied in engineering,the mathematical model and output characteristics of the PV array under uniform and partial shading conditions(PSCs)were analyzed.Especially,a mathematical model of PV array was established for the working conditions of PSCs.Furthermore,the existing MPPT is classified.the reasons for the tracking failure of traditional MPPT algorithm are analyzed,and the advantages of intelligent algorithms are pointed out.Secondly,based on the SiC MOSFET data provided by Infineon’s official website,the static and dynamic characteristics of the Si C MOSFET are analyzed,and the design requirements of its drive circuit are summarized.On this basis,an experimental device for Boost converter based on Si C MOSFET was designed and built.Then,based on the nonlinear control parameters of the tangent trigonometric function,an Improved Grey Wolf Optimizer(IGWO)maximum power tracking algorithm is proposed and applied to the Boost converter.Meanwhile,it is compared with P&O,PSO,SSA and GWO algorithms.The validity of the proposed IGWO algorithm is verified by simulation and experiment.Finally,a two-stage three-phase PV grid-connected power generation system based on Si C MOSFET was built.First,redesign the LCL filter of the existing three-phase inverter experimental prototype,and design the corresponding inverter control loop parameters.The switching frequency of the system is designed at 40 k Hz.In the two-stage three-phase PV grid connected system grid connected experiment,the Boost inverter adopts P&O algorithm and IGWO algorithm as MPPT control strategy respectively,and the inverter adopts double closed-loop control strategy.The IGWO performs better in the experiment comparison,with the advantages of high tracking accuracy,less harmonic content of grid connected current and high efficiency.