Research On Modular Three-phase Three-level Photovoltaic Grid-connected Inverter Unit

At present,non-renewable resources have been overused,and pollution problem is becoming increasingly serious.People pay more attention to the development and utilization of clean energy,and photovoltaic power generation is gradually recognized by people because of advantages.As the core power regulation device of the PV grid-connected system,grid-connected PV inverter is the focus of current research.this paper mainly studies the diode Neutral Point Clamped(NPC)three-phase three-level inverter and its strategy.Firstly,the research background of the topic and its significance are introduced,the current development of the three-level PV grid-connected inverter is explored,the advantages of inverter modularization are analyzed.The topology,working principle and control requirements of NPC three-level inverter are studied.The mathematical model of three-level inverter and SVPWM method are analyzed and deduced.Secondly,the different classification methods of PV grid-connected inverter are described.According to the working characteristics of photovoltaic cells,its mathematical model is built.On this basis,the MPPT control algorithm for photovoltaic cell array is studied,and three MPPT control methods are analyzed and compared.After selecting disturbance observation method as control algorithm,the deficiencies of disturbance observation are improved and the improved method is verified by simulation.The mathematical model of NPC three-level inverter is established,and double closed-loop gridconnected control strategy is studied.Finally,through theoretical analysis and simulation,a 10 k W experimental prototype with TMS320F28335 as the digital main control chip is designed,and the program design and debugging of the experimental equipment are completed on ccs8.0 software.The hardware circuit design of the system includes many aspects,such as the selection of IGBT,the calculation of capacitance and inductance parameters and the selection of components,the design of voltage and current signal sampling,and the design of synchronous signal generation circuit.The software part includes the main and interrupt program design.The interrupt program includes AD sampling subroutine,MPPT control subroutine and SVPWM signal generation subroutine.The software design adopts interrupt service mode to output SVPWM driving signal to realize three-phase inverter.The experimental platform is used for photovoltaic grid-connected experiment verification,and the output experimental waveform is collected and analyzed by oscilloscope.The topic has been progressively improved from theoretical analysis to simulation verification,and then to the demonstration of experimental results.This inverter unit can be followed by the study of three-phase unbalance and modular parallel operation research.