The increasing integration of solar photovoltaic and wind energy resources into power systems is transforming the structure and operating characteristics of modern electrical grids. Although these renewable energy resources provide significant environmental and economic benefits, their high penetration introduces several technical challenges related to power-system stability. The intermittent nature of renewable generation, reduced contribution of conventional synchronous generators, lower system inertia, and the increasing dependence on power-electronic interfaces can adversely affect voltage and frequency stability, particularly under severe disturbances and rapidly changing operating conditions. This thesis investigates the impact of high penetration levels of solar and wind energy resources on power-system stability and evaluates appropriate measures for enhancing grid stability under different operating and disturbance conditions. A suitable power-system model is developed to represent conventional generation, renewable energy sources, transmission and distribution networks, and their associated control systems. Different renewable penetration levels and operating scenarios are considered, and the resulting effects on system voltage, frequency, power flows, transient response, and stability margins are analyzed. Particular attention is given to the dynamic characteristics of inverter-based renewable generation and its interaction with conventional synchronous generation. To improve system stability, different technical approaches, including appropriate renewable-energy control strategies, reactive-power support, energy-storage systems, and/or coordinated control of conventional and renewable resources, are investigated. The effectiveness of these approaches is evaluated by comparing system responses before and after their application under selected disturbances and operating conditions. The results provide an assessment of the stability limitations associated with high renewable penetration and demonstrate practical strategies for maintaining acceptable grid performance. The findings can contribute to the planning, operation, and control of power systems with increasing shares of solar and wind energy while maintaining adequate reliability and stability.
