Real-time control and power management for interconnected microgrids with self-healing capability / Shameem Ahmad

Shameem , Ahmad (2022) Real-time control and power management for interconnected microgrids with self-healing capability / Shameem Ahmad. PhD thesis, Universiti Malaya.

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Abstract

Compelled by economic and environmental factors, microgrid (MG) has emerged as pioneer small-scale power generation system. However, it is necessary to ensure reliable and resilient operation of the MGs to avoid power failure incidents, which is a challenging task. Connecting multiple MGs to form interconnected MGs can improve power distribution systems resiliency and reliability. However, there are challenges while interconnecting multiple MGs, like possibility of power imbalance between distributed generators (DGs) capacity and load demand, complexity in modeling MGs controllers, and uncertainty of balanced power sharing among multiple MGs. To address all these issues, in this thesis, real-time control and power management systems (PMSs) for two interconnected MGs are developed. Voltage source inverters (VSIs) are important elements of grid-connected single MG to integrate photovoltaic system with utility grid which require fast response, stable and robust controllers for efficient operation. In this thesis, three power control methods are modeled for PV VSI among which the first two are fuzzy logic controller (FLC) and proportional integral (PI) controller based direct power control (DPC) methods, while, the remainder is dq current control theory (CCT) based power control method without using phase-locked-loop (PLL) and Park transformation. In addition, to ensure balanced power flow from different sources to the loads for acquiring better power quality and stable operation of MG, real-time PMSs are developed for both grid-connected and islanded modes of MG’s operation by taking into account the maximum utilization of renewable energy sources, energy storage systems and prioritization of critical loads together. Further, to improve the reliability of power distribution system, intelligent interconnection methods (IIM) for interconnecting two MGs with self-healing and interconnection capability are proposed by considering the power imbalance between DGs generation capacity and load demands of all the MGs. Moreover, to ensure balanced power sharing among multiple MGs during self-healing and interconnected modes of operation, PMSs for individual MGs are developed. Finally, to ensure flexible and smooth transition of multiple MGs among various operation modes like grid-connected, islanded, interconnected and self-healing, a multi-layer control strategy (MLCS) is formed. The real-time simulations are carried out using real-time digital simulator (RTDS) to validate the performance of the proposed power controllers, PMS, IIMs, and MLCS. From the simulation results, it has been observed that the proposed power controllers have better reference power tracking time ranging from (0.03 s – 0.11 s) along with reduction in output power ripples and current total harmonic distortion (THD) which are ranged from 1.6 % to 2.492 %. Further, the results show that through the implementation of the proposed PMS, maximum use of renewable energy sources and energy storage systems are ensured in MG by maintaining balance between supply-demand. The results also demonstrate that the developed IIMs can interconnect two MGs successfully to operate in self-healing and interconnected modes while the PMSs ensure balanced power sharing among the MGs. The final simulation results confirmed that the two MGs can operate flexibly and transit from one operating mode to another smoothly by employing the proposed MLCS.

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