Photovoltaic system with multilevel converter coupled to a compressed air energy storage system for grid integration.

Abstract

Electricity demand is continuously increasing and nations including South Africa, are looking to exploit renewable energy sources to augment conventional electricity generation. An analysis of electricity demand and supply, the electricity infrastructure and the status of renewable electricity including the progress and plans made thereof in South Africa were carried out. A review of the challenges affecting the bulk exploitation of renewable energy (RE) resources and its future prospects are discussed to determine the sustainability of these efforts. This research investigation focuses on a simulation model designed to harness the energy from the sun through a photovoltaic system. Based on empirical data of environmental conditions, a photovoltaic (PV) system model to generate 30 MW of electricity at Witkop substation, Polokwane (South Africa) was developed and to be fed into the grid. A maximum power point tracker (MPPT) control scheme is utilised to ensure that maximum power can be derived from the PV plant. A modular multi-level converter (MMLC) is utilised to convert the electricity generated by the PV system from direct current (DC) to alternative current (AC). The MMLC coupled to compressed air energy storage (CAES) stores the electricity generated during the day and injects it into the grid during peak periods of electricity demand. Mathematical models of the PV system, the MMLC, the CAES and the grid integration were developed, modelled and simulated to describe the electrical behaviour and to establish the ideal operational parameters of the various systems components. Furthermore, validation of the performance of the system components in the simulation model were carried out against manufacturers’ data sheets for similar studies and prototypes. The simulation model were used to combine all the system components effectively into the grid based on the electricity generation system configurations, electricity demand and the environmental conditions of the selected site. More importantly, this investigation seeks to increase the effort of development of PV generation models in the field of renewables when compared to other alternative energy sources such as wind energy generation.