Adaptive Time Delay Strategy for Reliable Load Shedding in the Direct-Current Microgrid

This paper proposes a practical and reliable decentralized load shedding strategy to protect the integrity of the direct-current (DC) microgrid. The proposed strategy utilizes time delays that automatically adapt to the DC microgrid operating conditions through continuous evaluation of the bus voltage variations, without depending on remote communication. It is evaluated in comparison with the conventional timer-based load shedding strategy. The studies are performed in the PSCAD software environment, on a detailed model of a DC microgrid that contains various types of loads and distributed energy resources. The results of the investigations show that the proposed adaptive time delay strategy (i) effectively restores the balance between the power demand and supply in the DC microgrid by quickly shedding the necessary amount of loads, (ii) is able to prioritize the non-critical loads by coordinating the load shedding steps based on a pre-determined order, (iii) prevents the steady-state values of the DC microgrid voltages from falling below a predetermined lower limit, (iv) significantly limits the voltage sags caused by power deficit in the microgrid, (v) is highly expandable and is able to coordinate a large number of load shedding steps, and (vi) improves the reliability of the electrical power provided to the DC microgrid loads, by avoiding inessential load shedding.