Abstract
This paper aims to present a new structure of the parallel Z-source inverters (ZSIs) for dual-input single-phase grid-connected photovoltaic (PV) systems. The ZSI is a single-stage buck-boost converter that uses an inductor-capacitor network between the inverter bridge and the PV string and follows the maximum power point by applying the shoot-through vector. Therefore, a DC/DC converter is no longer needed to track the maximum power point, and the cost and complexity of the power conditioning system (PCS) are reduced. For controlling the proposed PCS, a cascade control structure is employed in this paper. The inner current loop injects the maximum active power with unity power factor sinusoidal current to the grid. The outer capacitor voltage loop is applied to control capacitors voltages in the Z-source networks. Additionally, an enhanced dual-string maximum power point tracking (eDS-MPPT) method is proposed to find MPPs with minimum burden competitional. The eDS-MPPT does not need the PVs voltages measurements compared to other MPPT methods. The simulation results confirm the accuracy of the performance of the system.
Highlights
The use of renewable energies, especially solar energy, is increasing due to environmental problems caused by fossil fuels
Multiple photovoltaic (PV) strings are connected in parallel to make an array, and the PV array is connected through a DC/DC converter and an inverter as a power conditioning system (PCS) to the grid [8,9,10]
Two photovoltaic strings are connected to a 110 V, 50 Hz grid through the Z-source inverters (ZSIs)
Summary
The use of renewable energies, especially solar energy, is increasing due to environmental problems caused by fossil fuels. For commercial use of solar energy, reducing cost and system size and improving output power efficiency are among the significant challenges [1,2]. Photovoltaic systems are used in both standalone and grid-connected applications [3,4,5]. Two main structures of the grid-connected photovoltaic strings are shown in Figures 1 and 2 [6,7]. Multiple photovoltaic (PV) strings are connected in parallel to make an array, and the PV array is connected through a DC/DC converter and an inverter as a power conditioning system (PCS) to the grid [8,9,10].
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