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.

This paper presents a simple and robust control technique for distributed energy resources (DERs) in microgrids. 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.

Ln recent years, the concept of decentralising power generation through the deployment of distributed generators (DGs) has been widely accepted and applied, driven by the growing market of renewable energy sources. These DGs are normally equipped with a switching power interface, acting as front end with the grid. This paper proposes a multi‐task control strategy for distributed generation systems that simultaneously allows the DG to inject the available energy, as well as to work as a voltage drop compensator or as an active power filter, mitigating load current disturbances and improving power quality of the grid. The main contribution of the proposed system, with respect to other solutions in the literature, is that the proposed control loops are based on the Conservative Power Theory decompositions. This choice provides decoupled power and current references for the inverter control, offering a very flexible, selective and powerful control strategy for the DG. The paper also discusses the choice of the current waveform for injecting/absorbing active power into/from the grid, and both sinusoidal and resistive references have been compared in terms of damping capability. Finally, simulation and experimental results are provided in order to validate the proposed functionalities of the DG control system.

Electric grid codes are expected to change in near future to accommodate an increased number of distributed generation units in the distribution power system without impairing its power quality. It is desired that the generators remain connected during voltage sags and provide ancillary services, such as voltage and reactive power control, ensuring the operational stability of the power system. This paper explores how the existing strategies for active and reactive power injection impact the operation of grid-tied inverters in terms of required power, current flowing and reduction of active power delivery during the voltage sags. Such inputs are relevant to properly size converters for operation under fault events. In addition, this paper contributes to devise ${1}$ ) constant peak current control, ${2}$ ) constant active current control and ${3}$ ) constant average active power control strategies for three-phase four-wire grid-tied inverters considering the natural (abc) reference frame. The design and implementation of the investigated power injection strategies are discussed, and their effectiveness and technical viability are analyzed through dynamic computational simulations under symmetrical/asymmetrical voltage sags, and variation of the short-circuit ratio.

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.

The Primary Goal of this article is to discuss the development of intelligent controls for a power electronic inverter capable of interfacing a photovoltaic (PV)-based unit to the utility grid. The inverter is designed as a single-phase, full-bridge converter operating at 120 V, 60 Hz ac. The control functionalities of the inverter are defined under the perspective of the Smart Grid Initiative (SGI) of the U.S. Department of Energy and substantiated via case studies in this article as the ability to supply real and reactive power to local loads, supply real and reactive power to other utility loads up to the rated capacity of the inverter, provide voltage support at the point of common coupling (PCC), store energy in a lead-acid battery bank, and enable the provision of control options to the consumer based on near real-time electricity information obtained from the utility through advanced metering devices.