Design and Experimental Validation of a Composite FRL-NFTISMC and BSC for DC-Bus Voltage Stabilization in CPL-Based DC Microgrids

Transportation electrification relies heavily on DC distribution networks powered by power electronics and the integration of various power electronic loads. These tightly regulated loads, known as constant power loads (CPLs), can destabilize the system when operating alongside source converters. This paper presents a novel hybrid controller to stabilize the DC bus voltage in the presence of CPLs in a DC-DC boost converter (DDBC) within DC microgrids. To achieve this, the DDBC's dynamic model is first transformed into Brunovsky's canonical form through feedback linearization, resolving the non-minimum phase issue and making the model more suitable for designing the proposed controller. Next, a robust control input is developed to ensure the convergence of all relevant states to their desired values while effectively managing disturbances and handling significant fluctuations in input voltage and load. The proposed controller combines a modified fast-reaching law-based nonsingular fast terminal integral sliding mode controller (FRL-NFTISMC) with a backstepping controller (BSC) to address the negative incremental impedance behavior of CPLs, a common cause of grid instability. Furthermore, the composite controller guarantees large-signal stability, verified through the Lyapunov stability theory. Finally, numerical simulations in MATLAB 2022b/Simulink demonstrate the controller's robustness under various conditions, outperforming existing nonsingular fast terminal sliding mode controller, conventional sliding mode controller, and proportional-integral (PI) controllers. Experimental results from an in-house hardware platform support the simulation findings and theoretical design, highlighting the controller's superior response speed and system resilience across different operating modes.