Research On Design And Optimization Of Muti-Module Interleaved Grid-Connected Photovoltaic Inverter System

With the increasing scarcity of fossil energy,renewable energy has developed rapidly,such as photovoltaics.As the key component of photovoltaic system,grid-connected inverter system will determine the quality of electricity in the scenario,where lots of photovoltaic systems are connected with grid in the future.The optimization for the performance of photovoltaic gridconnected inverters has become a research focus for scholars.Especially with the development of the new generation power semiconductor devices,the switching frequency will be increased greatly,which causes the common-mode voltage problems of high-power inverters to get lots of attention.This thesis takes the multi-module interleaved inverter as the object,researches the related technologies of the grid-connected inverter system,and further optimizes the commonmode voltage,circulating current and other difficult issues,mainly including the following:First,three key control technologies of grid-connected inverter system are studied.Based on the orientation of grid voltage,the vector control strategy is the main control strategy for the system.Digital phase-locked loop and island detection strategy are to provide reliable phase information for the system.SVPWM is used to connect the control strategy and hardware.This thesis introduces the above technologies in detail,and makes some simplification according to the engineering application.Then,a prototype of 1200 k VA three-module interleaved inverter system was developed.In terms of power hardware,control hardware and control software,their design schemes are introduced in detail.A grid-connected experiment platform was built to test the relevant technologies and indicators of the prototype.With simulation and experiment results,a comprehensive analysis of the prototype’s performance is carried out,including the performance of startup,power factor,and THD of output current.Finally,the modulation methods of the interleaved inverter system are further optimized.A view of system synthesis vector is proposed.Using this view,the suppression of common-mode voltage for the interleaved SVPWM is analyzed in detail.Combined with the mathematical method of double Fourier,the suppression of harmonic is also analyzed quantitativelyu.A zero common-mode voltage PWM is analyzed,which can suppress the common-mode voltage to 0,and solves the common-mode voltage problems from its source.On this basis,an optimized modulation method is proposed,which inherits the advantages of the above two methods at the same time,and could further suppress the zero-sequence circulation current,which has greater value in practical.Finally,simulations and experiments are used to compare and verify the above modulation methods and related conclusions.The corresponding DSP configuration scheme is also given.