Addressing Instability Issues in Microgrids Caused By Constant Power Loads Using Energy Storage Systems

Renewable energy sources, the most reasonable fuel-shift taken over the naturally limited conventional fuels, necessarily deal with the self-functional microgrid system rather than the traditional grid distribution system. The study shows that the microgrid system, a comparatively low-powered system, experiences the challenge of instability due to the constant power load (CPL) from many electronic devices such as inverter-based systems. In this dissertation, as a methodical approach to mitigate the instability complication, AC microgrid stability is thoroughly investigated for each and every considerable parameter of the system. Furthermore, a specific loading limit is depicted by evaluating the stability margin from the small signal analysis of the microgrid scheme. After demonstrating all cases regarding the instability problem, the storage-based virtual impedance power compensation method is introduced to restore the system stability and literally extend the loading limit of the microgrid system. Here, a PID controller is implemented to maintain the constant terminal voltage of CPL via current injection method from storage. Since the system is highly nonlinear by nature, advanced nonlinear control techniques, such as Sliding Mode Control and Lyapunov Redesign Control technique, are implemented to control the entire nonlinear system. Robustness, noise rejection, and frequency variation are scrutinized rigorously in a virtual platform such as Matlab/Simulink with appreciable aftermaths. After that, a comparative analysis is presented between SMC and LRC controller robustness by varying CPL power. From this analysis, it is evident that Lyapunov redesign controller performs better than the previous one in retaining microgrid stability for dense CPL-loaded conditions. Finally, to ensure a robust storage system, Hybrid Energy Storage System is introduced and its advantages are discussed as extended research work

Integral sliding-mode controller for maximum power point tracking in the grid-connected photovoltaic systems

The output power generated in the photovoltaic modules depends both on the solar radiation and the temperature of the solar cells. To maximize the efficiency of the system, it is required to monitor the maximum power point of the photovoltaic system. For this purpose, monitoring the maximum power point (MPPT) of photovoltaic systems should be as quick and accurately as possible for increasing energy production, which ultimately increases the cost-efficiency of the photovoltaic system. This paper proposes a new approach for MPPT) using the concept of the integral sliding mode controller (ISMC) to ensure fast and precise monitoring of the peak power. The performance of the ISMC is significantly influenced by the choice of the sliding surface. To assess the reliability ISMC control, the results have been compared with those of a PI controller. The results obtained are used to evaluate the performance of the ISMC strategy under different climatic conditions. Finally, the effectiveness of the proposed solution is confirmed using simulations in PSIM tools and experimental results were used to evaluate the effectiveness of the proposed approach