Research On Z-source Three-level Inverter And Its Grid-Connected Control Methods

As the interface device of the micro-grid,the inverter is the bridge of the energy transfer between the distributed energy resources,grid and loads.In recent years,with the wide application of renewable energy and the development of micro-grid technology,the research on the new topology of inverter and its grid-connected control methods has become a hot spot.The Z-source three-level inverter has smaller electromagnetic interference and lower output voltage harmonic distortion rate.It has both buck and boost ability,and no dead time is needed,so the efficiency of energy transfer can be improved.In this paper,the topology,modulation methods and grid-connected control strategies of Z-source three-level inverter are studied,and a new quasi-Z-source three-level inverter topology is proposed.Firstly,the topological structure and working principle of the traditional single Z-source NPC three-level inverter are introduced in detail,and its shortcomings are analyzed.On this basis,several improved Z-source NPC threelevel inverters are introduced,and the advantages and disadvantages of different topologies are analyzed and compared.It is found that the current topologies of the Z-source NPC three-level inverter have common drawbacks: large Z-source network capacitor voltage stress.Then,after the study of the principles of the Carrier-Based PWM modulation and the Space Vector PWM modulation of Z-source three-level inverter,as for the problems about traditional Z-source three-level inverter capacitor voltage stress is high and huge inrush current exists when start-up,this paper proposes a new quasi Z-source NPC three-level inverter topology,which can effectively reduce the Z-source network capacitor voltage stress and inhibit the start inrush current.The working principle of the new quasi Z-source NPC three-level inverter is introduced in detail,the value formula of inductance and capacitance parameter of the new quasi Z-source network is deduced.The software simulation platform of the new quasi Z-source NPC three-level inverter is built for verification.Finally,the grid-connected control methods of the new quasi-Z-source NPC three-level inverter is studied.Three inverter control methods,including PQ control,V/f control and droop control,are applied to the reduced capacitor voltage quasi Z-source NPC three-level inverter proposed in this paper.The theory of the three control methods is analyzed respectively,and the gridconnected control system of quasi Z-source NPC three-level inverter is constructed,and a simulation model is built in Matlab/Simulink software environment for verification.Simulation results show that the new quasi Zsource NPC three-level inverter is suitable for the three traditional inverter control methods and can be applied in the micro-grid.