Interconnection of solar power to the grid through the power plant auxiliary system.

Abstract

In this thesis, an improved mathematical model based on classical equations and control approach for the photovoltaic system is developed and implemented using a pulse width modulation as the interfacing. The functionality of the developed model with the inclusion of a maximum power point tracking is verified against the generic model in Power Factory library which is constrained by assumptions, such as: no maximum power point tracking and uses static generator as the interfacing converter but gives an acceptable basic understanding of photovoltaic operation. The new improved mathematical model characterizes the solar cell with sufficient degree of precision with a percentage error of 0.03% measured in comparison with experimental data. The developed photovoltaic system under established control fulfils the operational requirements for a grid-connected photovoltaic system according to the South African Grid Code. Based on the developed mathematical model, various studies are performed, such as: steady-state and transient analysis to ascertain the impact of photovoltaic system integration with the power station reticulation system. The effects are analyzed with the photovoltaic system connected on the 11 kV bus bar which is the closest point to the generator to simulate an extreme circumstance. Case studies to demonstrate the photovoltaic effect on the reticulation system are evaluated for voltage stability and local generator behavior. Apparent features of the photovoltaic system such as the rapid power variation due to atmospheric changes (irradiance and temperature), tripping the photovoltaic system and simulating an electrical fault are implemented with various photovoltaic penetration levels. The results provided practical insight on the feasibility of interconnecting photovoltaic system to power station auxiliary network. Results illustrated at steady state the benefits of the generation capacity to be reduced relatively to photovoltaic penetration level and reactive power control which assist in supporting voltage during voltage dips at the point of connection and lastly the photovoltaic inverter presented the ability to limits/control fault current to about 1.5 p.u. which is lower than the 4 - 10 p.u. fault current typically caused by rotating machines. Transient studies discovered that the changes in atmospheric conditions do not impose stability threats but increased photovoltaic penetration level will increases the risk of generator becoming unstable during abnormal situations.