Research On PV Grid-connected Inverter Based On Silicon Carbide MOSFET And Its Control Strategy

With the increasing shortage of energy,governments around the world attach great importance to the development and utilization of clean energy.Among them,solar photovoltaic power generation has bright prospects for development.Photovoltaic power generation system and power grid need to use inverter as interface equipment,so photovoltaic inverters are one of the hotspots of current research.In order to further improve the performance of inverters,it is an inevitable trend to apply SiC MOSFET with high frequency and high efficiency to inverters.However,the inherent switching oscillation of SiC MOSFET may endanger the safety of devices and the power quality of inverters.Based on this,an accurate model is established to provide guidance for the application of SiC MOSFET in grid-connected photovoltaic inverters.In addition,due to the introduction of SiC MOSFET devices,the improvement of switching frequency of photovoltaic inverters is very significant.Therefore,this paper studies the control strategy of inverter under high switching frequency,and proposes a constant frequency adaptive hysteresis control.In this paper,the 1.2 kV-SiC MOSFET of CCS050M12SM2 produced by Cree Company is taken as the research object.The characteristic curves of SiC MOSFET devices are obtained through double-pulse experiment,which provides a reference for verifying the reliability of the model.On this basis,the static characteristic model and the non-linear capacitance model of SiC MOSFET are established.Based on the conditions of different working areas,the mathematical equations of static characteristic parameters are derived.The mathematical model of parasitic capacitors is deduced in different ways.The hyperbolic tangent function is used to deal with C_gss nonlinearly.The Miller effect of C_gd is used to obtain the relationship between capacitance and voltage.The change trend of C_ds is described by the formula of piecewise fitting before and after inflection point.The control strategy of SiC grid-connected inverters with high switching frequency is discussed,the basic principle of hysteresis control is analyzed,and the relationship between the width of traditional hysteresis control loop and switching frequency is obtained.It is pointed out that the control precision of traditional hysteresis control will be reduced due to the restriction of switching frequency,and the switching frequency will fluctuate in a certain range.Based on this,this paper presents a variable loop width adaptive hysteresis control for LCL inverters.Considering the slope of reference current,a loop width calculation link is designed,so that the loop width can be adjusted in real time to achieve a constant switching frequency.This control method can achieve a very high precision current tracking effect in high frequency SiC inverters.The SiC three-phase photovoltaic grid-connected inverter system is constructed,and the inverter circuit and controller parameters are designed and calculated after the switching frequency is increased.Simulated in Saber environment,the proposed SiC MOSFET model is used in the inverter system.By comparing the switching oscillation waveforms of simulation and experiment,the accuracy and applicability of the model are verified.The current waveforms of simulation and experiment under different switching frequencies are compared and studied.The influence of switching oscillation on SiC inverters at high frequencies is analyzed.The design method of damped oscillation circuit is proposed.The damped effect is verified by simulation.