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Managing power sharing between islanded microgrids adds additional capability to existing Smart Grid configurations enabling otherwise isolated microgrids to share power. In geographies where population centers are widely dispersed and particularly, in countries that lack a robust and effective grid, these technologies enable growth in consumption and improved supply security when isolated microgrids are interconnected with feeder lines to shared loads. The challenge is to effectively control this power sharing capability in an environment where microgrid performance is substantially load dependent and where the interconnection capabilities between microgrids often grows organically to meet demand. The proposed control has advantages over other methods since it does not require communication capabilities between the interconnected microgrids and does not require knowledge of feeder line models. This paper addresses a proposed control system design for these systems that has a hierarchical structure to manage power sharing among distributed generation (DG), low voltage AC islanded microgrids with unbalanced loads. The proposed control consists of three parts. First, an active power (P) – frequency (f) droop control and a reactive power (Q) – voltage (V) droop control (P/f and Q/V) are used to enable the active and reactive power sharing between two interconnected DGs. Since this droop control is unable to share unbalanced power effectively, a negative phase sequence virtual impedance control is added as a second control to regulate the distribution of unbalanced power. Third, an unbalanced power and small signal frequency droop control is added to adjust the impedance value (L_v) in the negative phase sequence virtual impedance control to force the negative sequence current to reach the steady state operating point achieving unbalanced power sharing. The proposed control scheme is theoretically designed the effectiveness of this proposed control scheme is evaluated through simulation studies. The impact of both the feeder line model and the unbalanced load on power sharing effectiveness are investigated.
Malcolm W Daniels
Primary Advisor's Department
Stander Symposium poster
"Control of Unbalanced Power Sharing in Islanded AC Microgrid with Balanced and Unbalanced Loads" (2019). Stander Symposium Posters. 1734.