State and disturbance estimation with supertwisting sliding mode control for frequency regulation in hydrogen based microgrids

This study considers the use of an enhanced super-twisting sliding mode control (STSMC) scheme, via the incorporation of a hybrid extended state observer (ESO) and a higher order sliding mode observer (HOSMO) state estimation and disturbance observer (DO) based on exponential decay embedded via a tracking element in order to hasten the estimation of disturbance thus improving performance significantly. This scheme is employed to generate single and multiple control signals per agent based on the microgrid's presented components, such as energy storage devices and renewable energy sources (RESs) alongside the harness of a puma optimizer (PO) metaheuristics scheme to optimize each area regulator's performance. The sliding surface incorporated is chosen based on desired control objectives. Adjusting the constricted area frequency and reducing tie-line power transfer fluctuations are considered the primary goals for frequency regulation in a multi-area power system. Also, based on the presented simulations, adequate performance in terms of minimum chattering, low complexity, fast convergence, and adequate robustness has been achieved. Using various microgrid peripheral components, such as a multi-terminal soft open point (SOP) with a dedicated terminal for hydrogen energy storage, alongside the proposed enhanced STSMC, the frequency change and power transfer rate of change are maintained within the range of ×10^{- 6} values, substantially preserving proper performance compared to other simulated scenarios. In regard to the final simulated case involving SOP, the following has been achieved: steady state errors of 2.538 × 10^{- 6} Hz for ΔF₁, 3.125 × 10^{- 6} Hz for ΔF₂ and 1.920 × 10^{- 6} p.u for ΔP_tie alongside peak disturbance overshoot reduction in comparison to stochastic case of 99.580%, 99.605% and 99.771% for same mentioned elements respectively. Also, a reduction in peak disturbance undershoot of 95.589%, 99.547% and 99.573% respectively, has been achieved. Thus, the enhanced STSMC can effectively mitigate frequency fluctuations and tie-line power transfer abnormalities.