Power Management and Control Strategies in Hybrid AC/DC Microgrids

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The future trend of the power system is to ensure reliable, flexible, affordable and efficient power supply for customers with lower emissions. Conventional AC or DC microgrid suffers from increased losses and lower efficiency due to several AC-DC and DC-AC conversions. Therefore, hybrid microgrid (HMG) is getting popular to meet the growing penetration of modern DC loads and renewable energy sources with DC outputs into the existing AC power systems. The main objective of this dissertation is to develop and implement improved power management and control strategy to improve the performance of the hybrid microgrid. The first study proposes an improved power management and control coordination strategy for an autonomous HMG. The HMG considered in this part consists of multiple AC and DC sub-microgrids (SMGs) with different voltage levels. The hierarchical coordination of power management and control strategy for the autonomous HMG is introduced and analyzed. The designed system incorporates both the primary and secondary control levels to ensure a seamless and accurate transfer of power among the SMGs. A new technique for transferring power with a focus on the secondary control level is presented. The second study proposed in this thesis is a novel approach of distributed coordination control for multiple SMGs within the HMG. The traditional control method for power flow management among AC and DC SMGs is based on the proportional power-sharing principle. The proposed method suggests a distributed control system that ensures total controllability for the parallel interlinking converters (ILCs). It overcomes the total dependency on a specific variable for power exchange. The proposed method not only enables control of the power flow between SMGs but also ensures the continuity of power transfer in the event of a single SMG failure. The third study in this work focuses on coordinating the control and power management strategy for the multiple parallel ILCs that link the AC and DC SMGs together. The proposed new approach aims to manage the power flow across the HMG while regulating the voltage and frequency for the SMGs as part of the process. The main objective of the proposed method is to keep the HMG in autonomous operation with active power proportionally shared among its ILCs and distributed sources. The presented outer control loop is a modified arrangement that could not only ensure accurate power-sharing but also suppresses the circulating current at the DC side.
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