Abstract
For system planning of three-phase inverter-based islanded ac microgrids, the low frequency instability issue caused by interactions of inverter droop controllers is a major concern. When internal control information of procured commercial inverters is unknown, impedance-based small-signal stability criteria facilitate prediction of resonances in medium and high frequency ranges, but they usually assume the grid fundamental frequency as constant and thus they are incapable of analyzing the low-frequency oscillation of the fundamental frequency in islanded microgrids. Aiming at solving this issue, this paper proposes two stability analysis methods based on terminal characteristics of inverters and passive connection network including the dynamics of the fundamental frequency for analysis of low-frequency stability in islanded multiple-bus microgrids. Based on the Component Connection Method (CCM) to systematically separate inverters from the passive connection network, a general approach is developed to model the microgrid as a multiple-input-multiple-output (MIMO) negative feedback system in the common system d-q reference frame. By applying the generalized Nyquist stability criterion (GNC) to the return-ratio and return-difference matrices of the MIMO system model, the low-frequency stability related to the fundamental frequency can be analyzed using the measured terminal characteristics of inverters. Analysis and simulation of a 37-bus microgrid verify the effectiveness of the proposed stability analysis methods.
Original language | English |
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Article number | 9024129 |
Pages (from-to) | 3662-3676 |
Number of pages | 15 |
Journal | IEEE Transactions on Smart Grid |
Volume | 11 |
Issue number | 5 |
DOIs | |
State | Published - Sep 2020 |
Funding
Manuscript received November 10, 2018; revised May 11, 2019 and August 22, 2019; accepted November 3, 2019. Date of publication March 4, 2020; date of current version August 21, 2020. This work was supported by the Engineering Research Center Program of the National Science Foundation and the Department of Energy under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program. Paper no. TSG-01738-2018. (Corresponding author: Wenchao Cao.) Wenchao Cao is with Danfoss LLC, Tallahassee, FL 32310 USA (e-mail: [email protected]).
Keywords
- AC microgrids
- droop control
- impedance
- inverters
- small-signal stability
- terminal characteristics