Sliding mode control in load frequency regulation: A comprehensive review on theory, variants, and implementation in isolated microgrids

Significant issues for load frequency control (LFC) arise from the increasing insertion of renewable energy sources into power systems, especially in low-inertia isolated microgrids. This work presents the first thorough and organized analysis devoted solely to the wide spectrum of sliding mode control (SMC) methods as a reliable remedy for this issue. From traditional linear and integral SMC to more sophisticated techniques like fractional-order, terminal, higher-order, adaptive, disturbance observer-based, and artificial intelligence-based controllers, the paper carefully investigates a wide range of SMC types. A unified analytical framework is provided for each variant, which includes the derivation of control law, system-level architecture, and a critical evaluation of its suitability for isolated microgrids. Another important contribution is a thorough comparative analysis that assesses the control performance, main benefits, and implementation difficulties of each type of SMC provided in detailed tables. Although SMC provides a strong and adaptable equipment for guaranteeing frequency stability, the assessment indicates that there are still some unexplored research prospects. Future research should concentrate on improving chattering suppression further, building decentralized schemes suited for future smart grids, along with creating advanced hybrid and data-driven SMC schemes.