| The application and development of non-isolated inverters in photovoltaic systems are limited by their own leakage current problems.This paper takes single-phase non-isolated inverters as the research object,and explains the advantages and problems of traditional voltage-type and current-type circuit topologies that can suppress leakage current,as well as the advantages and problems of current buck-boost topology that can suppress leakage current..The current circuit topology that can suppress leakage current has problems such as adding more additional devices,limited buck-boosting capabilities,and relatively complex topology and modulation.In response to the above problems,this paper proposes a single-phase inverter topology that can suppress leakage current by symmetrically designing the traditional SEPIC circuit and cascading it with the bridge circuit.This topology does not add additional switching devices and is a non-common ground topology,with small inductor and capacitor parameters,no electrolytic capacitor,simple modulation,and can achieve up-down voltage inverter output.This article first introduces the working principle of the proposed inverter.There are two working modes,namely the one-way flow mode of the middle inductor current and the two-way flow mode of the middle inductor current,which are controlled by non-linear PWM modulation and SPWM modulation respectively.The buck-boost capabilities of the two working modes are analyzed separately,and theoretical calculations show that both modes can achieve buck-boost inverter.Then the common-mode loop of the circuit is analyzed and modeled,and the expression of common-mode voltage and current is given,which theoretically shows its ability to suppress leakage current.After that,the circuit is mathematically analyzed and modeled,and the closed-loop regulator is designed.In this paper,the topology is simulated and analyzed,and the open-loop simulation waveform,the simulation waveform with the input voltage disturbance and load disturbance added in the closed-loop,and the grid-connected simulation waveform are given.Finally,the software and hardware design of the experimental platform was carried out,and an experimental platform based on DSPTMS320F2812 was built.Through experiments,the relevant waveforms of the inverter under open-loop and closed-loop disturbances and grid-connected operation are given,which proves its buck-boost capability and can suppress the leakage current in the system.The correctness of the theoretical analysis is verified through experiments. |
