Danilo Iglesias Brandão

Power-Based Control of Low-Voltage Microgrids

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.

Dead-Beat Current Controller for Voltage-Source Converters With Improved Large-Signal Response

A digital dead-beat current controller for voltage source converters is presented in this paper. The control structure is specified in a digital hardware description language, synthesized, and deployed on a field-programmable gate array chip. By updating, with negligible computation delay, the duty cycle twice in a switching period, the reference current error is nulled in half a modulation period, so that the controllers small-signal bandwidth is maximized. In addition, due to a simple transient detection circuit, the large-signal response delay is reduced to a small fraction of the modulation period, which is determined by the chosen current signal oversampling rate. The controller can effectively support different voltage-source inverter applications, such as active filters, uninterruptible power supplies, microgrid distributed energy resource controllers, and dc-dc converter applications, including interface converters for renewable energy sources, laboratory battery chargers, and electronic welding machines.

Centralized Control of Distributed Single-Phase Inverters Arbitrarily Connected to Three-Phase Four-Wire Microgrids

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.

Inverter control strategy for DG systems based on the Conservative power theory

Considering that typical distributed generators are equipped with a switching power interface and most of them have a DC-AC converter, this paper deals with a multi task control strategy for distributed generation (DG) inverters. Such strategy simultaneously allows the DG systems to inject the available energy, as well as to work as a voltage drop compensator or an active power filter, mitigating load current disturbances and improving power quality. The main difference of the proposed methodology with respect to others in the literature is that the proposed control loops are based on the Conservative Power Theory decompositions. This provides decoupled power and current references for the inverter control, offering a very flexible, selective and powerful strategy for the DG control system. The paper also discusses the choice of the waveform reference for injecting/absorbing active power into/from the grid, and both sinusoidal and resistive current injection have been compared. Finally, simulation and experimental results are reported in order to validate the proposed functionalities of the DG control strategies.

Bidirectional floating interleaved buck-boost DC-DC converter applied to residential PV power systems

The main goal of this paper is to design and analyze a bidirectional floating interleaved DC-DC buck-boost converter applied to a residential photovoltaic (PV) power system with energy storage. The floating interleaved bidirectional converter produces a higher DC voltage gain compared to conventional converters, reducing the required number of series connections for the PV and battery modules. This paper provides a smallsignal model of this bidirectional DC-DC converter, and describes control strategies for the DC-DC and DC-AC converters applied in a typical residential PV power system. The papers shows a transitional control strategy from gridconnected to islanded operating modes, as well as the back connection with the boost/buck operating modes for the bidirectional DC-DC converter. The paper describes the DC link management and voltage control where the regulation techniques are demonstrated by analysis and simulation results showing a complete system operation. Experimental results validate the proposed inverter control scheme.

Development of a four phase floating interleaved boost converter for photovoltaic systems

This paper explores the advantages of the Floating Interleaved Boost Converter, particularly with regards to solar photovoltaic power systems. This converter offers improved efficiency and voltage gain, while having lower input current ripple than other DC-DC boost converters. An analog linear feedback controller was developed, and adapted for discrete control. Two Maximum Power Point Tracking methods were explored, and their performances were evaluated in simulation. An experimental prototype was developed and demonstrated. The results show that this is a promising converter topology with many potential benefits for solar power applications.

Optimized compensation based on linear programming applied to distributed electronic power processors

This paper proposes a linear algorithm to optimize the compensation of reactive power, harmonic distortion and unbalanced load applied to distributed electronic power processors, for example, active power filters and/or photovoltaic grid-connected inverters, especially when their power capacity is limited. The optimized compensation consists in achieve, in terms of power quality, the best performance indices, defined at the source side and inside of a feasible region. It improves the power quality at the point of common coupling and enables full exploitation of electronic power processors, increasing their efficiency. The optimized compensation is based on the orthogonal current decomposition (Conservative Power Theory) and on the linear programming (Simplex algorithm). The steady state and dynamic behaviors have been analyzed by theoretical and simulation results. Finally, experimental results are shown to validate the proposed optimized compensation approach.

Optimized Compensation of Unwanted Current Terms by AC Power Converters Under Generic Voltage 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.

Cooperative compensation of unwanted current terms in low-voltage microgrids by distributed power-based control

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 unit while the distributed energy resources act as slave units, allowing to fully exploit their available power capability. The proposed control technique ensures high power quality, smooth power exchange with the utility, and prompt and seamless transitions between grid-connected and islanded operation. The paper introduces the considered system architecture, overviews the power theory underpinning the control approach, and describes the proposed control technique. Finally, a real three-phase distribution system is considered as case study in simulation; the obtained performances in improving the overall power quality are reported and commented, in particular for what concerns the compensation of reactive and unbalance current terms under sinusoidal/symmetrical and nonsinusoidal/asymmetrical voltage conditions.

Single-phase synchronverter for residential PV power systems

Distributed energy sources, mainly from renewable energy, have been increasingly applied to commercial facilities and residences. The power control of the various distributed sources is a fundamental task and is being studied in several recent papers. Among the current works many have explained the use the so called synchronverter control strategy to regulate the active and reactive power flow for three-phase distributed generators. Nevertheless, none of them have addressed a proposal for single-phase synchronverter power systems. In this paper, a brief review of synchronverters is presented. Thereupon, it is proposed a single-phase synchronverter for residential distributed generators, such as photovoltaic power system. The proposed single-phase model is based on the conventional structure of the three-phase control model. Simulation results are shown in order to validate the single-phase synchronverter, including evaluating performance in the presence of power quality issues, such as voltage sag and grid harmonic distortion, in both grid-connected and islanded mode.