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This paper presents a power-based droop controller for distributed energy resources converters in dc microgrids that are connected to the utility ac grid by a grid-interface converter. Typically, when dc microgrids are interfaced to ac power systems, the microgrid dc bus voltage can be affected by fluctuations caused, for example, by background harmonics present in the ac systems or by fluctuating...
This paper introduces a power-based droop controller for parallel operation of distributed energy resources in dc microgrids. This controller achieves power flow control when the bus voltage is imposed by a grid-interface converter that links the microgrid to an upstream grid. In such a case, accurate load distribution is allowed regardless of cable impedances. On the other hand, the proposed controller...
This paper proposes a unified power-based droop control method for distributed energy resources in dc microgrids that can operate both in grid-connected and islanded mode. When the main grid is available, the bus voltage is regulated by the grid-interface ac/dc converter, while distributed energy resources operate as power controlled sources. During abnormal operation of the main grid (e.g., due to...
This paper presents the application of an online stability monitoring technique (MT) for droop controlled power converters in DC microgrids. This method is based on Middlebrook's loop-gain measurement technique, adapted to digitally controlled switched-mode power supplies (SMPS). In particular, the MT is used to evaluate the stability margin in control loops of droop-controlled distributed energy...
The paper describes a fully-dispatchable microgrid architecture that features i) the adoption of a master/slave power-based control in the central dispatcher to drive distributed power generators and ii) the connection of a suitable power converter equipped with energy storage, called Utility Interface, at the point of common coupling with the mains. Property i) ensures scalability and capability...
This paper proposes a technique for the power flow control of three-phase four-wire low-voltage power systems, that aims at compensating the reactive and unbalance current terms measured at the point of common coupling of microgrids. It is based on a master/slave control architecture where a grid-interactive inverter, installed at the point of coupling between utility and microgrid, acts as master...
This paper presents the comparison of three different fully digital, oversampled, large bandwidth inverter current controllers: a proportional integral controller, a predictive controller, and a non-linear hysteresis controller. The purpose is to determine which one allows to achieve the highest final performance when adopted as the inner current control loop in a microgrid utility interface converter...
This paper presents and analyzes experimentally an active microgrid architecture. The microgrid architecture is described and the employed control scheme reviewed, showing how the devised system is able to meet energy needs, ensure good power quality, and allow seamless transitions from grid-connected to islanded operation. Also, the proposed solution is briefly contextualized with respect to approaches...
Low-voltage grids are characterized by mainly resistive interconnection impedances, which cause grid voltage profiles to be influenced by active power flows, and, in particular, to be susceptible to overvoltage conditions at active nodes during periods of peak production. This paper describes an overvoltage control technique for low-voltage microgrids that aims to regulate the power injection from...
We present and evaluate a lightweight and effective approach for the management of prosumer communities through the synergistic control of the power electronic converters acting therein. These controllable elements are the utility interface (UI), installed at the point of common coupling with the electrical utility, and the energy gateways (EGs), interfacing distributed generation units and energy...
The paper presents a microgrid architecture and control allowing full dispatchability of the power generated by distributed energy sources. To this purpose, full advantage is taken of power control and energy storage capability of distributed generation units and of the Utility Interface, a grid-interactive power converter equipped with energy storage and located at the point of common coupling. A...
This paper presents a simple and robust control technique for distributed energy resources in microgrids. The technique utilizes the full potential of distributed energy resources, during grid connected and islanded operating modes. In grid-connected mode, the control pursues quasioptimum operation of the microgrid, so as to reduce distribution losses and voltage deviations while fully exploiting...
The paper presents a general control technique for Utility Interfaces acting in low-voltage microgrids. The Utility Interface (UI) is a three-phase power conversion unit, equipped with energy storage, which governs the interaction between the utility and the microgrid. It is in charge of several functions: in grid-connected operation, UI performs as a voltage-supporting unit and compensates for reactive...
A rapid prototyping methodology for digital controllers is presented in this paper. Its main application is in the development, debugging and test of microgrid inverter controllers. To fulfill the application requirements, these systems are characterized by complex multilayer architectures, extending from PWM and current control loops up to global optimization and high level communication functions...
Low-voltage microgrids can be seen as the basic tiles of the smart grid patchwork, owing to their capability to efficiently manage their distributed energy resources in aggregate form. They can support the grid in terms of demand response, power quality, ride through capability, etc., and at the same time they can ensure electrical continuity to the loads even in case of grid failure. This paper describes...
This paper proposes a simple and effective approach to control the distributed energy resources (DERs) in a low voltage microgrid so as to increase energy efficiency and hosting capacity of the microgrid itself, with the only requirement of narrowband communication among distributed loads and generators. More specifically, the control aims at taking full advantage of distributed renewable sources...
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