Research On Single Phase Buck-boost Common-grounded Z-source Inverter

In order to solve the contradiction between the current shortage of fossil energy and people’s increasing energy demand,renewable photovoltaic energy has received extensive attention and development,especially the non isolated photovoltaic system,which has the advantages of small volume,low cost and high efficiency,and will be widely used in the future.However,at present,there are still some deficiencies in the non isolated photovoltaic system.On the one hand,due to the resonant network formed by the parasitic capacitance of the photovoltaic panel,the output filter inductance and filter capacitance through the grounding circuit,it is easy to produce large leakage current,resulting in grid connected current distortion,electromagnetic interference and other problems,and even pose a threat to personal safety;On the other hand,due to the low voltage of a single photovoltaic panel,a high voltage rise circuit is required to meet the output voltage requirements.If more switches are used to realize the voltage rise and fall operation,it will often lead to large system loss and low efficiency;Similarly,by adding passive components to form the voltage lifting unit to realize the voltage lifting operation,it will lead to many circuit components,large volume and high cost.In the isolated inverter,in order to suppress the leakage current,reduce the number of components and improve the voltage boost,the following research has been carried out:Taking the non isolated inverter as the research object,this paper proposes a singlephase voltage raising and lowering double terminal common ground Z-source inverter,that is,three switch double terminal common ground Z-source inverter.It adopts the double terminal common ground structure,that is,the negative terminal of the input side is connected with the negative terminal of the output side,and the parasitic capacitance is bypassed to eliminate the leakage current.At the same time,the topology adopts a small number of components,so that the system has small volume,low cost and the topology realizes the voltage raising and lowering function,It has high voltage gain during boost operation.This paper introduces the structure of three switch two terminal common ground Zsource inverter in detail,expounds the working mode according to the switch sequence,analyzes two modulation modes,and designs the parameters of passive components.In addition,the closed-loop control modeling and grid connected control modeling of the circuit are carried out.Through the simulation and verification in Matlab / Simulink,it is confirmed that the topology has the ability of voltage rise and fall and grid connected power generation.Finally,based on DSP of TMS320F28335 and FPGA of xc6slx9,an experimental prototype of three switch two terminal common ground Z-source inverter is built,and the control circuit suitable for the main circuit is designed.Based on the experimental platform,the dynamic performance and steady-state performance of the topology under the conditions of step-up,step-down and grid connection are verified.The experimental results confirm the correctness of the theoretical analysis and the effectiveness of the topology.