Abstract
This paper proposes a distributed predictive secondary control strategy to share imbalance in three-phase, three-wire isolated AC Microgrids. The control is based on a novel approach where the imbalance sharing among distributed generators is controlled through the control of single-phase reactive power. The main characteristic of the proposed methodology is the inclusion of an objective function and dynamic models as constraints in the formulation. The controller relies on local measurements and information from neighboring distributed generators, and it performs the desired control action based on a constrained cost function minimization. The proposed distributed model predictive control scheme has several advantages over solutions based on virtual impedance loops or based on the inclusion of extra power converters for managing single-phase reactive power among distributed generators. In fact, with the proposed technique the sharing of imbalance is performed directly in terms of single-phase reactive power and without the need for adding extra power converters into the microgrid. Contrary to almost all reported works in this area, the proposed approach enables the control of various microgrid parameters within predefined bands, providing a more flexible control system. Extensive simulation and Hardware in the Loop studies verify the performance of the proposed control scheme. Moreover, the controller’s scalability and a comparison study, in terms of performance, with the virtual impedance approach were carried out.
Highlights
M ICROGRIDS (MGs) represent an attractive solution in many applications, such as terrestrial, naval or aerospace electrical grids, due to their controllability, capability to include Distributed Generators (DGs) and flexibility [1]
Model Predictive Control (MPC) is emerging as a useful control strategy in the microgrids community [7]–[9] because it is a multi-variable constrained control scheme, which obtains a real-time solution at each sample instant
The results show that the Distributed MPC (DMPC) is robust against communication delays, and the delay affects the overshoot and the settling time of the consensus variables: the single phase reactive power is slightly affected when two unbalanced loads are connected simultaneously at different points in the MG at t = 30s, and the active power consensus is the variable most affected by delays
Summary
M ICROGRIDS (MGs) represent an attractive solution in many applications, such as terrestrial, naval or aerospace electrical grids, due to their controllability, capability to include Distributed Generators (DGs) and flexibility [1]. This proposal avoids the use of virtual impedance loops; it does not require additional converters in the MG In this case, contrary to the reported MPC-based methods for imbalance sharing, the proposed control algorithm achieves a global solution via consensus objectives which do not require an extensive computational burden (thanks to the distributed approach). (i) To the best of our knowledge, this is the first paper to propose a DMPC control scheme for unbalanced MGs. The proposal improves the sharing of imbalances among DG phases in AC MGs, avoiding the use of virtual impedance loops (as this methodology has many drawbacks [29]) and without the need for adding additional power converters to the MG.
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