Renan F. Bastos

An Intelligent Control System Used to Improve Energy Production From Alternative Sources With DC/DC Integration

A fuzzy P+I and a classical proportional-integral (PI) controllers for charging and discharging of a battery pack connected to a photovoltaic (PV) array are described. To maintain the PV array operating as close as possible to the maximum power point (MPP) a perturb and observe (P&O) algorithm along with a classical PI controller to regulate the terminal voltage of the PV array are also investigated. The power electronics interfaces used to keep the PV array operating close to the MPP and to manage the charging and discharging of the batteries are the step-up and bidirectional buck-boost converters. On the other hand, the interface to the grid consists of a voltage source inverter (VSI), which controls the power injected into the grid and regulates the DC-link voltage. The DC-link voltage is also controlled by a fuzzy P+I or classical PI controllers, which are used to promote the power balance between the DC-link and grid and to determine the amount of current and, consequently, power absorbed by or injected into the grid. Simulated and experimental results under different conditions are presented to demonstrate the effectiveness of the proposed approach.

Fuzzy positive feedback for islanding mode detection in distributed generation

This paper proposes a fuzzy voltage and frequency positive feedback (PF) for islanding detection in distributed generation system (DG). The proposed method is based on positive feedback in dq synchronous frame and the design methodology of the fuzzy detection is based on fuzzy inference rules. The main idea is to reduce the injection of disturbances at the point of common coupling (PCC) during the grid-connected operation. A comparison between the fuzzy algorithm and the classical methods are done. The simulation results demonstrate the effectiveness of the proposed approach.

Fuzzy secondary controller applied to autonomous operated AC microgrid

The present work addresses the AC microgrid control issue using hierarchical control structure and droop controllers for load sharing. Once the droop controllers impose an operation with frequency and voltage deviations, depending on the load and droop parameters, a hierarchical control structure must be added to change the droop controller operating points. The hierarchical controllers operate with local measurements and shared signals from communication links among the distributed generating systems connected to the microgrid. Depending on the size of the microgrid, the communication links can be economically unviable. This work proposes the development of a fuzzy secondary controller to AC microgrids to reduced the link communication dependency and using only local measurements. It is expected the deviations be fixed as happens with the conventional secondary controllers when the microgrid is operating as stand-alone mode, and can provide a certain amount of power to the connected utility bus operating as grid-connected mode.

Reduction of positive feedback gain on Anti-islanding method based on frequency

This paper presents a study to reduce the positive feedback gain in Anti-islanding detection methods based on frequency positive feedback. The main idea is to reduce the injection of disturbances at the point of common coupling (PCC) during the grid-connected operation. This proposal refers to the closed-loop frequency adjustment of the synchronization algorithm PLL (Phase Locked Loop). Firstly, is presented the anti-islanding method used in this work and introduced the controller design of the PLL algorithm for islanding detection. In order to evaluate the paper, simulation and experimental results are shown to support these statements.

Decentralized control for renewable DC Microgrid with composite energy storage system and UC voltage restoration connected to the grid

In this paper we propose a new decentralized control strategy applied to a DC Microgrid in order to manage the power delivery of storage devices into a common DC-link, avoiding high-bandwidth communication (HBC) between the storage devices (SD) and alternative sources. Batteries and Ultracapacitors (UC) are used as SD and the common DC-link is fed by alternative sources such as photovoltaic panels, wind turbines and fuel cells as well. The batteries are used to supply/absorb extra power in steady-state regime while the UC absorbs the power transients caused by variations on the power production or load connections. The proposed strategy uses as input for the batteries control only the DC-link voltage and state of charge (SOC), while for the UC only the DC-link voltage and UC terminal voltage are used to achieve the power sharing among the storage devices, equalization of the batteries and voltage restoration of the UC without HBC. The DC-link voltage is not restored in order to work as the sharing signal between storage devices. Additionally, the DC Microgrid is connected to the AC grid in order to deliver the extra power to the distributed system; however, the voltage variation on the DC-link does not affect the power quality of the produced energy. Simulated and experimental results are presented to demonstrate the feasibility of the proposed approach.

Torque control of a dc machine for wind turbine emulation

This paper presents an automated system applied to a dc machine used to the emulation of aerodynamic torque of a distributed generation power plant. The experimental arrangement proposed aims to avoid the wind turbine dependence of climatic variations. In order to evaluate the proposed approach, we presented a set of experimental results.

Three-phase VSI supplied by renewable energy sources and controlled in voltage and power modes for grid-tie operation

This paper presents a strategy to control the terminal voltage produced by the voltage source inverter (VSI) as well as, the power delivery or absorbed from the grid independently of the local load. The terminal voltage is controlled by means of double cascade PI controllers. The resonant controller is placed in parallel to the classical voltage PI to improve its performance. To enhance the resonant structure dynamic response, an adaptive resonant controller based on the modification of their coefficients is used. Additionally, the paper exhibits the reactive power control at the grid changing the voltage amplitude synthetized by the VSI, and the active power control by means of the management of the angle of displacement between the grid voltage and the VSI terminal voltage. To the power control operates adequately two controllers in decoupled mode of operation (one with faster dynamic response and other with slower time response) are employed. To prove all statements proposed in this paper a set of experimental results are presented.