Research On Grid-Connected Techniques For Multi-Module Of Input-Series-Output-Parallel Inverter System

Since humans began to focus on the development and utilization of wind energy and solar energy,this will put forward higher requirements for grid-connected inverter used in distributed power system,there is no doubt that the difficulty of designing a single inverter is greatly increased.Input Series Output Parallel(ISOP)inverter system is very suitable for high input voltage and high current power conversion applications.If we apply this inverter system topology into grid-connected application,we can build a large volume grid-connected-inverter-system using multiple standard inverter modules with small volume,which can improve system reliability and convenience the designers.The key issue of researching ISOP inverter system is to guarantee input voltage sharing(IVS)and output current sharing(OCS)among the constituent modules.This paper researches the grid-connected technology of multi-module ISOP inverter system.Firstly,the main topology of ISOP grid-connected inverter system is selected and optimized,the inductance of the LCL filter is reduced which decreases both the volume and the weight of the system.Next,the control variables of ISOP grid-connected inverter system is screened.We found that feedback of inverter side inductor current can not only suppress the resonant peak caused by the LCL filter,but also can indirectly guarantee the high power factor of grid current.At the same time,this paper gives the compound control method to realize power balance of each module.A power balance strategy for ISOP inverter system under distributed control architecture,with control loops dispersed into each module is shown.And modules communicate with buses.Then a detailed implementation to fulfill the redundancy is given,which bypasses the fault module by using switches.As for the new module,both the voltage loop and current loop control is necessary.Voltage loop control mode works before inverter system is connected with grid,current loop control take place of voltage loop control after connected with grid.On the basis of theoretical analysis,an ISOP inverter system consisting of three inverter modules is fabricated,both simulation and experimental results are presented to verify the effectiveness as well as the validity of the proposed compound control and the redundancy scheme.