Abstract
The direct current (DC) microgrid requires a fast load shedding scheme that prevents instability and voltage collapse when the distributed energy resources are unable to meet the power demand. The load shedding scheme is also expected to prevent unnecessary service interruptions caused by over-shedding of loads. This paper proposes an adaptive voltage-based load shedding scheme utilizing voltage thresholds that are automatically adjusted depending on the rate of change of locally measured bus voltages. The performance of the proposed load shedding scheme is investigated and compared with that of the conventional voltage-based load shedding scheme, using a realistic and detailed study system, under various disturbances. The comprehensive simulation studies that are conducted using the PSCAD software indicate that the adaptive load shedding scheme (i) effectively maintains the DC microgrid power balance through fast and coordinated load shedding, (ii) prevents the DC bus voltages from falling below acceptable levels, (iii) ensures that the critical loads do not experience excessive steady-state voltage deviations, (iv) minimizes the durations and magnitudes of the temporary voltage drop caused by sudden disturbances, and (v) improves power supply reliability.
Highlights
The ever-increasing penetration of distributed energy resources (DERs) is fundamentally changing the operating principles of the modern power systems
The direct current (DC) microgrid is interfaced to the AC utility grid by a 1 MW gridtied converter (GTC) and a 750 V / 4.8 kV transformer at the node 701
An adaptive voltage-based load shedding scheme is proposed for the direct current microgrid
Summary
The ever-increasing penetration of distributed energy resources (DERs) is fundamentally changing the operating principles of the modern power systems. The timer-based load shedding [36] utilizes different time delays to prioritize non-critical loads and sheds a load whenever its voltage remains lower than a common threshold within a time period longer than the corresponding time delay. This scheme may lead to over-shedding issue when short delays are used. The existing non-communication based DC load shedding schemes have been comprehensively investigated and compared in [40] These schemes utilize fixed voltage/time thresholds, and either cause excessive bus voltage deviations or cause over-shedding of loads. The proposed adaptive DC load shedding strategy is inspired by the aforementioned AC load shedding strategies, but operates based on the variations of the DC microgrid bus voltages, and has significantly different operation requirements and constraints, e.g., higher speed requirement
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