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Microgrids must be able to restore voltage and frequency to their reference values during transient events; inverters are used as part of a microgrid's hierarchical control for maintaining power quality. Reviewed methods either do not allow for intuitive trade-off tuning between the objectives of synchronous state restoration, local reference tracking, and disturbance rejection, or do not consider all of these objectives. In this paper, we address all of these objectives for voltage restoration in droop-controlled inverter-based islanded micro-grids. By using distributed model predictive control (DMPC) in series with an unscented Kalman Filter (UKF), we design a secondary voltage controller to restore the voltage to the reference in finite time. The DMPC solves a reference tracking problem while rejecting reactive power disturbances in a noisy system. The method we present accounts for non-zero mean disturbances by design of a random-walk estimator. We validate the method's ability to restore the voltage in finite time via modeling a multi-node microgrid in Simulink.
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Performance of droop-controlled microgrids with heterogeneous inverter ratings
This paper characterizes synchronization perfor- mance and total transient power losses in droop-controlled microgrids with heterogeneously rated inverters. We consider frequency and voltage dynamics for a Kron-reduced network model with highly inductive lines in the presence of impulse disturbances. We quantify the total transient frequency and voltage deviations from synchrony and the associated total transient resistive losses through the L 2 norm of the system output. We derive closed-form expressions for this norm that depend on the heterogeneous droop gains and properties of the network. Our results indicate the importance of inertia in mitigating transient frequency deviations. We also show that if disturbances are uniform, the transient resistive losses are given by a monotonically decreasing function of the active power droop gains regardless of the network topology. Numerical examples further analyze these losses, revealing that they can be amplified by high droop gain heterogeneity. This relationship indicates that non-uniform power sharing requirements can limit performance.
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- Award ID(s):
- 1544771
- PAR ID:
- 10109810
- Date Published:
- Journal Name:
- European Control Conference (ECC19)
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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