Research On Power Balance Control And Phase Locked Loop Control For ISOP Connected Inverter System

The integration of power electronic system is an inevitable trend for the broader and deeper development of power electronic technology.The combined inverter system is one of the important branches.This article selects the Input-Series-Output-Parallel(ISOP)inverter as the research object.There are two main research goals: one is to achieve input voltage sharing(IVS)and output current sharing(OCS);the second is to realize the phase synchronization of output voltage of each module.In order to find suitable topology for the standardized module of the ISOP inverter,it is found out that a two-stage high-frequency isolation inverter structure should be used and the modeling method is indicated in detail.DC/DC converter adopts the voltage feedback control and DC/AC converter adopts the current feedback control.The independent control further improves the modularity of ISOP inverter.From the perspective of power balance,the relationship of ISOP inverter between IVS and OCS is analyzed,and It is found that IVS is related to active power sharing,and OCS is related to reactive power sharing.In order to realize the distributed control of ISOP inverter,the output voltage inverse-droop control is adopted here.The strategy is improved on the basis of the traditional droop control method and it realizes IVS and OCS of ISOP inverter according to the inverse-droop characteristics of the output voltage and frequency.Through the analysis of the inverter output impedance,the virtual impedance is introduced to realize the decoupling control of active power and reactive power,and the selection principle of the upwarping coefficient is given.The simulation results verify the effectiveness of the strategy.Regarding the power calculation used in the strategy,the power calculation method in DSP is elaborated,and the method of adjusting the output voltage frequency in DSP is also analyzed.In order to realize the synchronization of the output voltage of each module,a phase-locked loop(SOGI PLL)based on a second-order generalized integrator is designed.On this basis,it points out that each module should be softstarted first and slave module tracks the output voltage phase of the main module through the SOGI PLL and the output voltage synchronization reference bus.After the output voltage phase synchronization of each module is completed,the main module controls each module to complete the parallel through communication.The simulation results show that SOGI PLL has excellent adjustment speed and accuracy.