Research On Control Strategy Of Three-phase T-Type Three-Level Non-Isolated Grid-Connected Inverter

As the energy crisis continues to intensify,humans are increasingly aware of the importance of renewable energy,especially the use of solar photovoltaic technology.Photovoltaic power generation is currently the most used two-level and three-level technology.Compared with the two-level grid-connected inverter technology,the three-level switching tube terminal voltage is smaller,the output harmonic content is less,and the high voltage is large.It is especially widely used in power applications.However,the three-level control object is more and the control strategy is more complicated.Therefore,based on the comparison of many current three-level topologies,this paper studies the control strategy based on the T-type three-phase three-level topology.The content is as follows:The topology of common three-phase three-level grid-connected inverters is analyzed and compared in detail,and the advantages of T-type three-level grid-connected inverters in topology and control methods are summarized.On the basis of this topology,the three-level photovoltaic grid-connected inverter is mathematically modeled,and the commutation process in the operation of the three-level inverter is analyzed in detail,which is the basis for the subsequent control strategy..The two chapters explain the suppression of common mode leakage current and the imbalance of the midpoint potential on the DC side.For the common mode leakage current problem,the common mode leakage current simulation modeling is carried out,and the concept of common mode voltage is used.The common mode leakage current is reduced by reducing the amplitude of the common mode voltage.The seven-stage and five-segment simulation modeling is carried out by the traditional PI-SVPWM method,and the five-stage type can effectively suppress the common mode voltage.For the midpoint potential imbalance problem,the PI midpoint loop is added and the Matlab/Simulink simulation model is used to prove its effectiveness.On the basis of the traditional pulse width modulation strategy,in view of the contradiction between common mode leakage current and midpoint potential balance,the model predictive control algorithm is adopted in the fourth chapter to consider these two problems comprehensively.Compared with the traditional control technology,the control method is more flexible.By using the concept of the objective function,the objects to be controlled are uniformly added.By adjusting the weighting factor,the object can be flexibly and effectively controlled,and the modulator is not needed.The reference current and midpoint potential balance control have a faster dynamic response.Finally,through the Matlab/Simulink simulation model,it is verified that the model predictive control can achieve comprehensive control by adjusting the weighting factor for two major problems.