A Novel Isolated Nearly-pure Sine Wave Inverter for Single-phase Grid-tied PV Systems

A new isolated converter is proposed in this paper for 5 kW grid-tied single-phase PV systems, producing nearly sinusoidal output. The proposed converter consists of interleaved SEPIC and Ćuk converter stages, while the PWM inverter converting from dc to ac in conventional PV systems has been completely eliminated. Instead, the duty ratios of the dc-dc stages is continually varied, and the SEPIC stage is used to construct the positive half cycle of output voltage, while the Ćuk converter is operated to construct the negative half cycle of output voltage. Operating these converters in tandem and summing their output leads to the construction of a nearly pure sinusoidal wave at the converter output with minimal total harmonic distortion. This leads to the reduction of output side filters, increasing the power density and reducing cost. Furthermore, the converter effectively has two devices operating at high frequency and one switch operating at line frequency during each half cycle of output voltage. Thus, switching and conduction losses are reduced. This allows for reduction of heat sink requirement, thereby further increasing power density as well. The operation of the converter has been verified through simulation in MATLAB Simulink, and the results are discussed to further justify the converter.