Research On T-type Three Level Grid-connected Inverter Based On Model Predictive Control

With the continuous development of industrialization,power consumption and energy consumption are increasing,while the storage of non renewable energy is decreasing,so the comprehensive utilization of renewable energy seems to be more and more important.Solar power generation and wind power generation are key renewable energy.Grid connected inverter is the equipment that connects DC generator equipment to power grid.It determines whether DC generator equipment can connect to power grid safely,stably,reliably and efficiently,and plays a vital role in grid connection.The traditional two-level grid connected inverter has the disadvantages of many harmonic current components,high switching frequency and electromagnetic interference,which can not be used in high voltage and high power areas.Because of these shortcomings,there are three-level grid connected inverter,but the three-level grid connected inverter has more switching devices and more complex control.In order to improve the efficiency and reliability of the three-level grid connected inverter,it is necessary to develop a scientific design scheme for its control system.Therefore,the control technology of T-type three-level grid connected inverter is studied in this paper.Firstly,this paper introduces the traditional three-level inverter topology,analyzes and compares the advantages and disadvantages of different topologies.On this premise,the T-type three-level inverter topology is formulated.After comparison,it is found that this inverter topology has the following characteristics: lower cost and less power consumption.Secondly,by analyzing the mathematical model of T-type three-level inverter,the mathematical model of T-type inverter is established in αβ coordinate system and abc coordinate system.Secondly,the control technology of T-type three-level inverter is analyzed,and the model predictive control technology is deeply studied.The algorithm of finite control set model predictive control(FCS-MPC)has attracted the attention of many scholars in this field.The finite control set model predictive control makes full use of the discretization characteristics of power electronic converters and takes into account the finite switching states of power electronic converters(the converters have specific switching combinations)Function)evaluates the prediction results of each behavior(switch combination),and selects the switch combination which can satisfy the minimum cost function to control the power electronic converter.It also has the advantage of no modulator.On the basis of this control technology,the predictive model and cost function of T-type three-level inverter are established,and the problems of time delay and large amount of calculation in traditional model predictive control technology are studied,and the solutions are proposed.Then this paper analyzes the basic problems of T-type three-level inverter when the power grid is unbalanced.Because in the irrational power grid state,the traditional PLL can not accurately phase-locked,so this paper uses the decoupling double synchronous reference frame PLL to decouple the negative sequence voltage component on the positive sequence component,so as to ensure the accurate synchronization of the power grid In order to solve the problem that the phase-locked effect is not ideal when the grid voltage contains a large number of high-order harmonics,a second-order generalized integrator quadrature signal generator(SOGI-QSG)is added before the positive and negative sequence decoupling of DDSRF-PLL to eliminate the influence of harmonics on the phase-locked loop.Finally The simulation model is built in matlabgsimulink,and the system is verified in ideal power grid and non ideal power grid.The simulation results show that the model predictive control algorithm designed in this paper can make the grid current track the reference current well in ideal power grid,on the other hand,it can also control the balance of neutral point potential well.At the same time,in non ideal power grid,this method can be used In order to ensure the balance of grid current,it also has good steady-state performance and dynamic performance.On the basis of simulation,the physical platform is designed and built.On the power electronics experimental platform,a 5k W grid connected inverter prototype with DSP28335 as the main control chip is designed.According to the experimental results,it can be found that this control policy plays an effective role.