Optimized nonlinear control for solid state transformer based electric locomotives with hybrid energy backup

Abstract

Transportation sector demands innovative drive technologies for emission reduction with solid state transformers (SSTs) integration offering potential advancements. The transition from conventional transformers to SSTs is driven by the necessity for en hanced control capabilities and the alleviation of weight, volume and losses constraints. The proposed system integrates single phase AC input, transformed by sequential AC to DC and DC to DC converters whose output is fed to a DC bus which contains com bined output of battery and supercapacitor. By comparing the effectiveness of three different controllers: Proportional Integral, Sliding Mode Control, and Super Twisting Sliding Mode Control. The STSMC outperforms the other controllers for its capability to stabilize current and handle load fluctuations making it the preferred controller for locomotive performance. The gains of the controllers are optimized using an improved gray wolf optimization technique, ensuring efficient operation under varying conditions. Additionally, an integrated energy management system monitors the SoC of batteries and super capacitors, ensuring sustained load operation by switching to grid power for recharging when SoC falls below a predefined threshold. Stability analysis using Lyapunov stability criteria ensures robustness of the control strategy under dynamic operating conditions. Computational analysis validates STSMC as the best controller. To validate the proposed control strategy, a scaled down prototype is implemented, and processor in loop simulations are conducted, affirming the viability of the con troller design. This research contributes in advancing electric locomotive technology, offering insights into optimizing railway transportation systems for efficiency, reliability and system resilience.