This paper proposes an effective technique to control the power flow among different phases of a three-phase four-wire distribution power system by means of single-phase converters arbitrarily connected among the phases. The aim is to enhance the power quality at the point-of-common-coupling of a microgrid, improve voltage profile through the lines, and reduce the overall distribution losses. The technique is based on a master/slave organization where the distributed single-phase converters act as slave units driven by a centralized master controller. Active, reactive, and unbalance power terms are processed by the master controller and shared proportionally among distributed energy resources to achieve the compensation target at the point-of-common-coupling. The proposed control technique is evaluated in simulation considering the model of a real urban power distribution grid under non-sinusoidal and asymmetrical voltage conditions. The main results, concerning both steady-state and transient conditions, are finally reported and discussed

Abstract-In

This paper presents a simple and robust control technique for distributed energy resources (DERs) in micro-grids. The technique utilizes the full potential of DERs during grid-connected and islanded operating modes. In grid-connected mode, the control pursues quasi-optimum operation of the microgrid so as to reduce the distribution losses and voltage deviations while fully exploiting renewable energy sources. In islanded mode, it effectively manages any available energy source, including storage devices, to ensure a safe and smooth autonomous operation of the microgrid. In addition, prompt adaptation to variations of the generated and absorbed power is ensured in each operating condition. The proposed control can be implemented by an Information and Communication Technology architecture, which is inherently flexible and scalable, allows plug-and-play integration of distributed energy sources, and does not involve time-critical communications

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The presence of single-phase distributed generators unevenly injecting active power in three-phase microgrids may create undesired upstream current unbalance. Consequently, voltage asymmetry and even active power curtailment may occur in such networks with negative economic impact. Thus, this paper proposes an optimal multiobjective approach to regulate the active and reactive power delivered by distributed generators driven by a three-layer hierarchical control technique in low-voltage microgrids. This method does not require previous knowledge of network parameters. The multiobjective algorithm is implemented in the secondary level achieving optimal dispatch in terms of maximizing the active power generation, as well as minimizing the reactive power circulation and current unbalance. By the existence of a utility interface three-phase converter placed at the point-ofcommon-coupling, the proposed control can regulate the power circulating among the microgrid phases, and the microgrid structure can withstand grid-connected and islanded operating modes. The path for interphase power circulation through the DClink of the utility interface allows the multiobjective algorithm to achieve better results in terms of generation and compensation compared to the system without utility interface. The proposed method is assessed herein by computational simulations in a threephase four-wire microgrid under realistic operational conditions.

This paper formulates an optimization-based algorithm for the compensation of unwanted current terms by means of distributed electronic power converters, such as active power filters and grid-connected inverters. The compensation goal consists in achieving suitable load conformity factors, defined at the source side and within a feasible power region in terms of the power converter capability. Based on the measured load quantities and on a certain objective function, the algorithm tracks the expected source currents, which are thereupon used to calculate proper scaling coefficients and, therefore, the compensation current references. It improves the power quality at the point of common coupling and enables full exploitation of distributed energy resources, increasing their efficiency. The compensation is based on a decoupled current decomposition and on an optimization-based algorithm. In this paper, the strategy is applied to nonlinear and unbalanced three-phase four-wire circuit, under nonsinusoidal and asymmetrical voltage conditions. The steady-state and dynamic behaviors have been analyzed by theoretical, simulation, and experimental results. Furthermore, the proposed approach is also compared to other compensation strategies showing its effectiveness.

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 renewable energy sources. In islanded mode, it manages effectively any available energy source, including storage devices, to ensure a safe and smooth autonomous operation of the microgrid. Further, prompt adaptation to variations of the generated and absorbed power is ensured in each operating condition. The proposed control can be implemented by an ICT architecture which is inherently flexible and scalable, allows plug-and-play integration of distributed energy sources, and does not involve time-critical communications