Calculation of the voltage stability margin considering uncertainties in the load and limit of the generators

• Grant number: 23/09332-8
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: September 01, 2023
• End date: August 31, 2024
• Field of knowledge: Engineering - Electrical Engineering - Power Systems
• Principal Investigator: Rodrigo Andrade Ramos
• Grantee: Gustavo Gonçalves dos Santos
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Associated research grant: 18/20104-9 - Wide-area monitoring, dynamic security analysis and control of modern power system networks, AP.TEM

Abstract

The operational security of Electric Power Systems is needed to meet the growing electricity demand, respecting acceptable voltage levels and maintaining a constant frequency. In this context, power system operators are concerned with voltage stability. In fact, due to economic and environmental restrictions in recent decades, system devices have been close to their operating limits. Hence, power systems are more vulnerable to abrupt drops or rises in voltage magnitudes. In this context, voltage stability assessments, the scope of this research project, are essential for the system operator to be able to carry out preventive and emergency actions and avoid, for example, interruption situations and blackout occurrences. Currently, in stability assessments, one major challenge is considering generation and load uncertainties. The increase in generation from variable, intermittent, and uncontrollable natural sources, such as wind and solar energy, suppliers of active power, and, more recently, reactive power, makes it difficult to predict the power flow. Furthermore, system loading throughout the day is quite variable, as it depends on load levels (which, naturally, undergo continuous variations) and distributed generation, which is usually intermittent. Therefore, classical techniques for voltage stability analysis that assume an arbitrary load growth direction do not properly represent the uncertainties associated with the system load prediction. The innovative alternative proposed in this project is to represent load uncertainties using a hypercone model. In this model, as the load grows in an expected direction, the radius of the hypercone that characterizes the uncertainty associated with future loading also grows. The research challenge associated to this project is the development of an approach to consider the generator reactive power limits in this formulation. This post-doctoral proposal starts from this hypercone load uncertainty model but includes the maximum reactive supply capacity of the generating units in the stability analysis. A smooth formulation using a sigmoidal function will be used to evaluate the discontinuity issues in stability analyses caused by generator reactive power limits. Therefore, as long as the maximum loading point is adequately redefined for the power system model modified with the smooth formulation, it will be possible to employ the hypercone model to represent the load growth of the system. As a result, the uncertainties associated with the load growth direction and the reactive power limits of the generators will be considered simultaneously in the determination of the voltage stability margin. Finally, the equations developed for the hypercone model (modified to consider the generator reactive power limits) will be implemented in a computer and numerically solved for different test systems. Additionally, if the time restrictions allow, the project intends to assume confidence intervals for the maximum power transfer hypersurfaces to include uncertainties related to the power flow model, in order to develop a stochastic version of the proposed approach for the calculation of the voltage stability margin. (AU)