FAULT-TOLERANT DESIGN AND ROBUST CONTROL OF MULTIPORT DC–DC CONVERTERS WITH REDUCED CURRENT RIPPLE FOR STANDALONE PV–BES SYSTEMS

Abstract

The increasing penetration of renewable energy systems, battery energy storage systems, and electric vehicles (EVs) has accelerated the demand for efficient, reliable, and fault-tolerant power electronic interfaces capable of handling multidirectional power flow with enhanced dynamic performance. In this context, multiport DC–DC converters have emerged as a promising solution for integrating photovoltaic (PV) sources, battery energy storage systems, and multiple DC loads within a unified power conversion framework. However, conventional converter architectures are often constrained by high current ripple, increased semiconductor stress, limited fault-tolerant capability, poor dynamic response under non-minimum phase (NMP) conditions, and reduced robustness against parameter uncertainties and operating disturbances. Furthermore, maintaining stable converter operation under varying source conditions, load dynamics, and semiconductor fault scenarios remains a significant challenge in modern EV and renewable energy applications. This thesis presents the modelling, analysis, design, and experimental validation of advanced non-isolated time-multiplexed multiport DC–DC converter architectures with fault-tolerant capability, reduced current ripple, soft-switching operation, and robust controller design for sustainable energy and light electric vehicle applications. Initially, a robust voltage-mode controlled time-multiplexed DC–DC multiport converter is investigated under non-minimum phase operating conditions. A systematic controllability analysis based on switched linear system (SLS) theory is carried out, and a robust PI controller is designed using the stability boundary locus method in conjunction with Kharitonov’s theorem to ensure stable closed-loop operation under structured uncertainties and external disturbances. The proposed controller effectively improves disturbance rejection capability, voltage regulation performance, and system robustness under varying source and load conditions. Subsequently, a tri-port fault-tolerant modular DC–DC converter with soft switching capability is developed to achieve improved efficiency, modularity, and reliability. The proposed topology incorporates switched-boost action with time multiplexed operation to regulate multiple output ports while enabling bidirectional v battery charging and discharging operation. The integration of zero-voltage switching (ZVS) and zero-current switching (ZCS) techniques significantly reduces switching losses and semiconductor stress. In addition, modular stackable architecture and closed-loop switching reconfiguration enable reliable fault-tolerant operation under open-circuit switch fault conditions. Detailed mathematical modelling and design analysis are carried out to characterize converter operation under various operating conditions. Further, a solar PV-fed fault-tolerant four-port DC–DC converter is presented for light electric vehicle applications. The proposed converter integrates PV source, battery energy storage system, medium-voltage DC load, and low-voltage auxiliary load within a single non-isolated multiport architecture. The interleaved structure and phase-shifted control strategy effectively reduce battery charging current ripple and improve current sharing capability while enhancing converter reliability. The converter employs maximum power point tracking (MPPT), switched-boost operation, and time-multiplexing control to achieve coordinated multiport power management and bidirectional power flow operation. Detailed analysis of current ripple characteristics and converter operation under healthy and fault conditions is presented. Finally, a comprehensive modelling and robust controller design framework for a non-isolated time-multiplexed multiport fault-tolerant (TMMFT) converter is developed considering parasitic elements and non-ideal operating conditions. Large signal, averaged, and small-signal models are derived for different operating states, and controllability analysis is carried out using graph-theoretic principles and switched linear system modelling. Robust controller synthesis based on the stability boundary locus approach and Kharitonov’s theorem is implemented to ensure stable operation under parameter uncertainties and open-circuit switch fault conditions. Sensitivity and complementary sensitivity analyses are carried out to validate robustness and disturbance rejection capability under healthy and faulty operating scenarios. The proposed converter topologies and control strategies are experimentally validated using laboratory-scale prototypes implemented with real-time digital control hardware. Experimental investigations confirm reduced current ripple, improved vi voltage regulation, enhanced fault-tolerant capability, robust dynamic performance, effective disturbance rejection, and reliable operation under varying operating conditions. The outcomes of this research establish the suitability of the proposed multiport converter architectures for next-generation renewable energy systems, battery energy storage systems, and electric vehicle charging applications requiring high efficiency, reliability, and operational resilience.