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The Design and Analysis of a Two-Stage PV Converter with Quasi-Z Source Inverter

The single-phase photovoltaic (PV) systems are being widely researched due to several environmental and financial advantages. The PV converters are implemented either in single stage of two-stage topologies according to intermediate dc bus requirements. In the two-stage topologies, the recent researches are based on transformerless structures to eliminate bulky and lossy transformer isolation. Therefore, several methods including stray current grounding have been proposed in the literature to obtain isolation without the use of transformer. This paper proposes a two-stage PV converter with quasi Z-source (qZS) inverter in the second stage. The first stage of PV converter is comprised by a conventional boost converter that the maximum power point tracking (MPPT) controller is improved with integral regulator addition to incremental conductance algorithm. The MPPT efficiency of improved system is measured as 98.8% regarding to the designed controller. In addition to its efficiency, MPPT controller stabilized the intermediate dc bus voltage against the various irradiation values applied to PV plant. The qZS network is designed to ensure continuous conduction mode (CCM) operation considering shoot-through and non-shoot-through states. The switching control of H-bridge inverter is realized by the designed grid tracking controller that samples grid voltage as a reference input and decomposes to detect phase, frequency, and amplitude values. The power factor of inverter output is measured at 0.988 and total harmonic distortion (THD) ratios of current and voltage waveforms are at 1.71 %.