Study On Modular Control Of Input-series Output-parallel Inverter System

In high-power applications,the voltage and current stress of power semiconductor devices are usually beyond the existing available ratings,which increase the difficulty of power conversion system development.The electrical stress on each converter can be reduced significantly by choosing the structure of modular converter system.The modular structure brings many benefits such as short development cycle,high power density,low cost and easy maintenance.As one configuration of the modular converter system,Input-Series Output-Parallel(ISOP)inverter system can be a good solution for high-input-voltage and large-output-current applications.In order to ensure the proper operation of the ISOP system,input voltage sharing(IVS)and output current sharing(OCS)among the modules are required.Two modular control strategies are proposed in this paper to improve the modularity and reliability for ISOP inverter system.The main parts of this dissertation are as follows:1.The first part focuses on the research of modular control strategy of ISOP inverter system.The disadvantages of existing control strategies of ISOP inverter system are analyzed.It can be concluded that common interconnection part exists resulting in lower reliability and lower modularity of system.Therefore,a fully modular control strategy based on positive output-voltage-amplitude gradient is proposed.The control strategy not only ensures the input voltage sharing of ISOP system,but also avoids the mutual connection among modules,thus truly realizing the modularity design and improving the reliability of input-series system.The operation principle and stability analysis are explored.Simulation results verify the correctness of proposed strategy.2.Without losing modularity,the active power inverse-droop control is proposed in the second part.The IVS and OCS can be achieved without sensing the input voltage of the modules and the cost and volume of ISOP inverter system can be reduced because the input voltage sensors are eliminated.The operational principle of the active power inverse-droop control is introduced and the detailed system design is presented based on the proposed control scheme.The stability analysis and the guide line for power sharing loop design are also provided.At last,simulation results verify the effectiveness of the proposed control strategy.3.In the third part,a two-module ISOP inverter system is fabricated and tested in the laboratory and the experimental results verify the correctness of two modular control strategies based on positive output-voltage-amplitude gradient and active power inverse-droop method.