Design and Implementation of Grid Connected Solar PV Fed Multilevel Inverter

Abstract

In recent years, the efforts to spread the use of renewable energy resources like solar, wind etc. instead of pollutant fossil fuels and other forms have increased. The increment in energy demand is now forcing us to generate the power using these non-conventional sources. Most of the power across nation is generated by means of fossil-fuels resulting into huge amount of carbon emissions in the environment. This suggests the power producers to move towards the Green Power Technology. The usage of modern efficient photovoltaic solar cells has been featured as an alternative to energy and demand-side management. Among all the available non-conventional energy sources, solar photovoltaic (PV) system has several advantages such as clean energy and serves quite well in remote areas contributing towards significant share in power generation. Under this topic, a photovoltaic supported multilevel inverter are used to transfer the bulk solar power to the grid. Amongst the various topologies of multilevel inverter known, cascaded H-bridge configuration serves quite useful for this applications because of its flexible modular structure compatible with the power bus. The proposed scheme converts the dc power into high quality ac power for feeding into the grid. In this photovoltaic systems involve interfacing of power converters with PV array and utility grid. These power converters perform majorly two tasks. Firstly, they ensure the efficient utilization of PV array by extracting maximum power. Secondly, they provide sinusoidal output current to grid hence giving unity power factor operation. Implementation of MPPT is important because output power in solar PV system varies at different radiation intensities. Change in environmental conditions and position of earth with respect to sun causes variation in radiation level. Therefore, when interfacing solar PV system to the grid, the maximum power is extracted from the PV modules for efficient utilization of available solar energy. Now to ensure proper tracking of output voltage of inverter with grid voltage, phase locked loop is implemented extracting grid phase angle so as to synchronize inverter phase angle with grid phase angle. The dissertation work is carried out in two parts. First part deals with the optimization of PV module, a P&O based maximum power point tracking (MPPT) controller is used which enables the maximum power extraction under varying irradiation and temperature conditions using Boost Converter. Second part includes control and synchronisation algorithm for Multilevel Inverter in which a proportional integral controller structure along with Second Order Generalized Integrator Phase-Locked Loop (SOGI PLL) is designed to maintain constant grid voltage and frequency. The simulations are carried out in MAT- LAB SIMULINK Software and for hardware is implemented using dSPACE Advanced Controller.