A Single-Stage Non-Isolated Buck-Boost Inverter

The inverter is the key link in the photovoltaic power generation system.However,due to the influence of environmental factors on the solar cells,the output voltage fluctuates greatly,which makes it difficult to cope with voltage-source bridge inverters commonly used in small and medium-sized photovoltaic power generation systems.Although some inverter topologies with buck-boost capability have been proposed to help solve the problem of voltage fluctuations,most of them have the disadvantages of having a circuit structure containing a transformer or requiring a large-capacity electrolytic capacitor.In view of the above problems,this paper proposes a new single-stage non-isolated Buck-Boost inverter.The inverter structure does not contain electrolytic capacitors.The system has a small size,long life,and high reliability;the inverter output voltage can be Lower than the input voltage,it can also be higher than the input voltage,suitable for applications where the input voltage wide range fluctuations;In addition the inverter also has a low cost,simple structure,high power density,short circuit and open circuit protection is simple,resistance to the input side low frequency ripple Strong ability and other advantages.First of all,this paper studies two kinds of working modes of the new single-stage non-isolated Buck-Boost inverter--inductive current continuous mode(CCM)and inductor current discontinuous mode(DCM),and analyzes the circuit operation in two modes in detail.principle.Then this paper studies the modulation methods under two working modes,analyzes the steady-state relationship of the circuit,and discusses its buck-boost characteristic.Then this paper establishes the mathematical model of a new single-stage non-isolated Buck-Boost inverter with load operation in both CCM and DCM modes,deduces the control-to-output transfer function and designs a PR regulator accordingly.The simulation of the input voltage abrupt change and load switching shows that the closed-loop system meets the stability,accuracy and rapidity at the same time.In this paper,the mathematical model of the new single-stage non-isolated Buck-Boost inverter connected to the grid is established.The quasi-PR regulator is selected to perform closed-loop control.Simulation results show that the inverter has good grid-connected performance.Finally,a 200 W experimental prototype was built in this paper.The experimental results proved the correctness of theoretical analysis and simulation.