Short-term Voltage Stability Analysis Using FRT Control Techniques In Grid-connected Photovoltaic Systems

Among the most suitable opportunities to satisfy energy requirements is to infiltrate renewable energy resources into the current electricity system.By integration of renewable distributed generators(DGs)for example solar systems,wind power turbines are very famous nowadays.Recently,solar energy is quite renowned because of the cost reduction of PV modules,advancement in technologies and also different countries are giving incentives in this area.But there are some drawbacks as well when large-scale integration of DGs to power system.One unease is power system reliability due to high penetration.Voltage stability is a top consideration.This thesis mainly focus on short-term voltage stability analysis in grid-integrated PV systems by considering low-voltage ride-through(LVRT)requirements as predefined by different countries.In the first part of thesis,a photovoltaic power system model is developed which is suitable for the short-term voltage stability analysis considering fault ride-through(FRT)control techniques.Solar cell model is designed.The intention is to ride-through the system during any fault or voltage dip in the grid side,the PV system should remain connected.In voltage stability analysis the main aim is to check the system performance under load injection during faults.Voltage stability is more related to load dynamics and therefore different load properties are to be considered in voltage stability analysis.In the second part of thesis,it will investigate photovoltaic system characteristic during integration to grid.The system performance when there is no fault or voltage dip.The developed strategies also perform maximum power point tracking(MPPT)function,which is implemented in the DC-DC converter.Also it will observe the photovoltaic(PV)system when there are different types of fault in the system i-e symmetrical and unsymmetrical faults.As the most dangerous faults are balance fault in the system.So a proper dynamic voltage support control techniques are formulated during these fault.The reference values of active and reactive currents in photovoltaic system during the whole process for FRT are formalized.The model assure current references and control designs to get low voltage ridethrough(LVRT).As the foremost concern is voltage stability analysis.In the last section of this work,to analysis the short-term voltage stability a proper load model is needed,so static load and dynamic load are formalized.Voltage instability is an essential consideration of the safety of the distribution system.As far as a significant proportion of photovoltaic is concerned,it's indeed necessary to better understand the impact of high PV generation on both static and dynamic factors of voltage stability in distribution networks.In order to examine the influences of the PV system on dynamic stability,dynamic distribution system model which include load and PV system,this study will discuss a three-phase induction motor(asynchronous)for different load conditions.Finally,a suitable test system for short-term voltage stability is developed including dynamic load induction motor(IM).Reference values for reactive current injection are derived and tested.For DC-link voltage control the method used is crow bar techniques which will reduce the accumulation of voltage during faults on the DC side of voltage source inverter(VSI).All simulations results are validated and analyzed using MATLAB/Simulink software.