This work proposes a distributed secondary level control strategy for dc microgrids, which achieves accurate and proportional power sharing and dc bus voltage deviation restoration based on voltage-shifting. In contrast to similar approaches, only one variable per converter is transmitted in the low-bandwidth communication link and with a simple integrator as the secondary level controller both objectives are achieved simultaneously. The information state shared between converters is a $\lambda$ factor that incorporates the converter output voltage and power information. The secondary control computes the average $\lambda$ locally and the controller generates an unique voltage-shifting term that modifies the converter output voltage reference. When all converters' $\lambda$ converge to the average value, both the power sharing correction and the dc bus voltage restoration are attained. The proposed technique suppresses the need for a complex control structure and large amount of converter variables. The proposed control is evaluated through PLECS simulation and it is validated in a 4.5 kw dc microgrid setup.

This paper proposes a secondary level control technique for dc microgrids, which achieves accurate power sharing through a distributed strategy whilst performing dc bus voltage restoration in a decentralized fashion. In order to attain proper power sharing, each power converter exchanges its output power information with neighboring converters through a low-bandwidth network at defined time intervals. A consensus-based algorithm is employed to process this information and modify the converter's droop coefficient, compensating droop mismatches and cable resistances and enabling power sharing. Restoration of the average dc bus voltage is realized locally with each converter compensating its own output voltage drop through an integrator. A comprehensive design procedure and performance and stability analysis, including communcation loss and substantial time delays are also provided. The strategy has shown to be robust to some communication failure scenarios and moderate communication delays. The proposed method is evaluated trough PLECS simulation and it is experimentally validated in a 4.5 kW dc microgrid setup.

A hybrid AC/DC microgrid combines the benefits of AC and DC power systems. It provides high efficiency and is compatible with conventional AC distribution network. This paper proposes a centralized energy management approach to perform coordinated control on a hybrid AC/DC microgrid as a single-controllable entity. The central controller relies on low-bandwidth communication channels and is aimed at achieving 1) proportional power sharing among energy storage units located in both DC and AC sides of the microgrid, 2) state-of-charge equalization of the energy storage units, 3) grid power flow control, 4) plug-and-play capability, and 5) operation in grid-connected and islanded modes through an interlinking utility interface converter. The state-of-charge equalization method guarantees uniform operation of the energy storage units during both charge and discharge modes considering typical operational transients. Finally, the proposed model-free approach is evaluated experimentally through a laboratory-scale hybrid AC/DC microgrid in different operational conditions in both grid-connected and islanded operating modes.

Different control strategies for microgrid applications have been developed in the last decade. In order to enhance flexibility, scalability and reliability, special attention has been given to control organisations based on distributed communication infrastructures. Among these strategies, the implementation of consensus protocol stands out to cooperatively steer multi-agent systems (i.e., distributed generators), which is justified by its benefits, such as plug and play capability and enhanced resilience against communication failures. However, as the consensus protocol has a long trajectory of development in different areas of knowledge including multidisciplinary subjects, it may be a challenge to collect all the relevant information for its application in an emerging field. Therefore, the main goal of this paper is to provide the fundamentals of multi-agent systems and consensus protocol to the electrical engineering community, and an overview of its application to control systems for microgrids. The fundamentals of consensus protocol herein cover the concepts, formulations, steady-state and stability analysis for leaderless and leader-following consensus problems, in both continuous- and discrete-time. The overview of the applications summarises the main contributions achieved with this technique in the literature concerning microgrids, as well as the associated challenges and trends.

Low-voltage dc distribution systems have gained significant attention over the last years, since they provide simpler and more efficient integration of distributed generators and storage devices, establishing a pathway to net zero energy buildings. In low-power units, transformerless utility interface is preferred to reduce footprint and losses. However, the lack of galvanic isolation introduces a common-mode (CM) path between the dc distribution bus and the utility service grounding, leading to the presence of high CM voltages at the dc bus feeders. The attenuation of the CM voltage reduces the touch voltage amplitude and leakage current, contributing to a safer environment. In this paper, a feed-forward active compensation of the CM voltage is proposed. It relies on utility voltage parameters, estimated by a phase locked loop, to generate a counter CM voltage; hence, it does not require previous knowledge of the system CM path model or the addition of voltage sensors. Experimental results show that this technique can attenuate the CM voltage to non-dangerous magnitudes without interfering with the microgrid differential mode behavior.

This paper proposes a modified version of the power-based control (MPBC) applied to microgrids (µGs) with multiple points of connection (i.e., utility grid itself or any other neighboring µG). Using the MPBC, single-phase distributed energy resources (DERs) arbitrarily connected between the phases share the amounts of balanced power, while the unbalanced and homopolar power are steered only to the line-to-neutral inverters. The control technique is based on a three-level hierarchical control using narrow bandwidth, low data rate communication that properly coordinates the DERs connected to three-phase four-wire µGs. The MPBC allows the DERs to steer power flow at any of the multiple points of common coupling of a multi-PCC dispatchable µG. The modified control proposed herein is evaluated through simulation results using MATLAB/SIMULINK considering a real urban distribution grid with typical operational elements and conditions. When compared to the original power-based control (PBC), results show that a meshed µG may reach power benchmarks with accommodation time 80% lower when applying MPBC. Moreover, it may also lead to significant power loss reduction (about of 5%) in some studied cases.