Design and Control of Grid Connected Photovoltaic System

Abstract

Renewable Energy Systems (RESs) are poised to address the concerns arising due to excessive usage of depleting fossil fuels and global warming. Among various renewable resources namely wind, solar, fuel cells, and hydro; solar energy is being harnessed prominently because it is freely available, does not involve moving parts, and can be placed near the load centers. However, the Photovoltaic (PV) source is characterized by intermittent output and wide operating range and therefore requires power converters or Power Conditioning Unit (PCU) for grid interconnection. From the viewpoint of easy maintenance and cost-effectiveness, the grid-tied structure can be advantageous for the PV system as they do not use batteries for energy storage. Different configurations of PCUs have been investigated for various RESs. The two-stage structure is generally used with PV systems having low and fluctuating output voltage. Such structure is usually operated utilizing a DC-DC converter to regulate the PV output voltage and maximize the output power, whereas the inversion process is achieved through an inverter. Traditionally, two-level Voltage Source Inverter (VSI) and Current Source Inverter (CSI) are widely used for grid integration. The VSI is a buck converter and requires an additional DC-DC boost converter to boost its DC-link voltage; while CSI is a boost converter and requires a DC-DC buck converter for buck operations. The impedance source inverters, which characterize single-stage power converters, provide voltage boost ability within the inversion stage. This group of PCUs is poised to be a viable option in comparison to the two-stage arrangement for low and fluctuating voltage sources. The Z-Source Inverter (ZSI) is a single-stage topology proposed to overcome the shortcomings of VSI and CSI. However, ZSI provides a boost in single-stage but is not a preferable candidate for PV as it takes discontinuous current from the source.