POWER ELECTRONIC CONVERTERS FOR INTERFACING TO DC MICROGRID

Abstract

With rapid depletion of fossil fuel reserves and widespread environmental concerns, the global adoption of renewable energy sources is being highly encouraged. Solar energy is one of the most prominent renewable energy sources and offers numerous advantages. However, the adoption of photovoltaic (PV) systems in different applications is primarily limited due to high intermittency. Furthermore, conventional string PV system is highly susceptible to partial shading conditions while also witnessing poor reliability, poor robustness, and single point failure. Conversely, module level PV system (MLPS) offers highly flexible architecture with superior power utilization, reliability and robustness under different operating conditions while also achieving smooth system operation during the outage of a section due to bypassing provided by the diode. MLPS also utilizes distributed power generation controllers for evacuating maximum power from each panel. However, the integration of individual low voltage PV panel with high voltage DC microgrid is a major challenge in MLPS and requires high gain module level interfacing converter (MLIC) and multi-input module interfacing converter (MMIC). The lack of topological viability of conventional boost converter for MLIC due to its inability to operate at high gain with high efficiency prompted extensive research on the family of high gain DC/DC converters. This thesis focusses on investigating different novel high gain DC/DC converter topologies for MLIC and MMIC to integrate MLPS with DC microgrid. Comprehensive literature review of different DC/DC converter topologies and their comparative study is presented to affirm the viability of proposed converter topologies for MLIC and MMIC. The thesis viii presents modeling, steady state analysis, design methodology and loss distribution of proposed current-fed high gain isolated interfacing converter (CF-HGIIC) topology for MLIC and investigates its simulated performance on MATLAB Simulink environment and further through experimental investigation on the developed hardware prototype. Moreover, modified CF-HGIIC (MCF-HGIIC) topology for MLIC offering notable topological improvements over CF-HGIIC is proposed in the thesis and its modeling and steady-state analysis has been carried out. The simulated and experimental performance of MCF-HGIIC has also been investigated. The thesis also presents the novel multi-input CF-HGIIC (MI CF-HGIIC) topology for MMIC and discusses its modeling, steady-state analysis, and simulated performance. The system integration of MLPS with DC microgrid for different system architectures of MLPS utilizing proposed converter topologies has been discussed in the thesis while also exploring several applications of MLPS. The concept and challenges of dynamic shading and the failure of conventional MPPT controller to track such fast dynamics has been discussed. Different power generation control algorithms offering features like flexible power generation capability and fast dynamical response during dynamic shading conditions are also discussed to enhance the overall system performance under various operating conditions. The performance of different system architectures under diverse operating conditions such as source perturbations are evaluated using MATLAB Simulink environment to validate the efficacy of system and its salient features viz, modularity, robustness, plug-and-play operation etc. Moreover, the experimental performance of system under various source perturbations and the effectiveness of proposed converter in integrating MLPS with DC microgrid are also investigated in the thesis.