Abstract
To improve the efficiency of photovoltaic (PV) grid-tied systems and simplify the circuit structure, many pseudo DC-link inverters have been proposed by combining a sinusoidal pulse-width modulation (SPWM) controlled buck-boost converter and a low-frequency polarity unfolder. However, due to the non-ideal characteristics of power diodes, the voltage-gain of a buck-boost converter is limited. To meet the needs of grid-connected systems with low input voltage and 220 Vrms utility, this paper uses two two-switch buck-boost converters with coupled inductors to develop a transformer-less buck-boost grid-tied inverter with low leakage-current and high voltage-gain. The proposed inverter is charging on the primary side of the coupled inductor and discharging in series on the primary side and the secondary side so that the voltage-gain can be greatly increased. Furthermore, the utility line can be connected to the negative end of the PV array to suppress leakage current, and the unfolding circuit can be simplified to reduce the conduction losses. High-frequency switching is only performed in one metal-oxide-semiconductor field-effect transistor (MOSFET) in each mode, which can effectively improve conversion efficiency. A prototype was implemented to obtain experimental results and to prove the validity of the proposed circuit structure.
Highlights
In recent years, the amount of greenhouse gas emissions has risen rapidly along with the development of technology
For PV power generation systems powered in parallel with the mains, an inverter is required to convert the PV output voltage into an AC output, so that many scholars focus on the investigation of the circuit structure of inverters [1,2]
Many single-stage inverters derived from boost or buck-boost converters have been proposed [4,5,6], but they are restricted by the usage of two input sources or the wide-range changes in input voltage
Summary
The amount of greenhouse gas emissions has risen rapidly along with the development of technology. Except for increasing the number of components, increasing costs, and reducing reliability, the main shortcoming is lowering the system efficiency caused by multiple energy processing To overcome these problems, many single-stage inverters derived from boost or buck-boost converters have been proposed [4,5,6], but they are restricted by the usage of two input sources or the wide-range changes in input voltage. Based on the previous considerations, a transformer-less buck-boost grid-tied inverter with low leakage-current and high voltage-gain is proposed. The proposed inverter has the following features: Only single energy-processing is required, and high-frequency switching is only performed in one MOSFET in each mode, which can effectively improve efficiency; The inverter operates with the principle of boost or buck, so that part of the energy can be directly transmitted to improve efficiency; The proposed inverter is feasibility for PV grid-tied systems with wide-range voltage changes because of its step-up and step-down capabilities
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