Ricardo Q. Machado

Operation of a Three-Phase Power Converter Connected to a Distribution System

This paper presents the operation of a distributed generation (DG) system driven by a dc-dc step-up converter and a dc-ac voltage source inverter (VSI) interfaced with the power grid. To create a stable mode when different kinds of loads are connected locally or when working under contingency, the step-up converter must regulate the dc link voltage, allowing the VSI to stabilize its terminal voltage. The power flow between the grid and the DG is controlled by applying a power/voltage method that regulates the amplitude and the displacement of the grid voltage synthesized by the DG, while a phase-locked loop algorithm is used to synchronize the grid and DG. Additionally, a set of simulations are performed independent of the load type or its work regime (whether it is connected to the grid). The effectiveness of the proposed method is evaluated by experimental results.

Methodology for placement of Dispersed Generation Systems by analyzing its Impacts in Distribution Networks

The Brazilian electric systems need the development of new researches and tools, in order to obtain a logic solution to maintain and improve the reliability and the quality of the power delivered to customers. The study of the appropriate connection of dispersed generation sources is an essential topic to be analyzed, since this process may provide positive impacts along the feeders. The main effects of the DG operation inside a distribution system model are here analyzed through the software DigSilent®, considering power losses and voltage levels. Moreover, a multi-objective methodology - Bellman-Zadeh algorithm and membership fuzzy functions - is used for evaluating quantitative and qualitative parameters. The main objective of the paper is finding the appropriate DG placement inside a distribution system model. It is important to observe that the methodology presented in this study can be applied to distribution system feeders to find in which feeder will be the most appropriate DG location, as well to any node inside a determined feeder providing a specific place for the appropriate DG site.

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.

Storage energy management with power quality concerns the analytic hierarchy process and the fuzzy logic

In view of current and foreseeable energy shortage and environmental scenario, the exploitation of renewable energy sources offer great potential to satisfy the energy lack and to decrease the dependence on fossil fuel, also reducing global warming caused by CO2 emissions. However, widespread implementation of these sources will be more attractive only if they operate together with energy storage technologies. Besides, an effective storage energy management is essential to deal with some mismatches among power quality, efficiency, costs and environmental constrains. This paper presents a methodology taking as basis the analytic hierarchy process and fuzzy multi-rules and multi-sets. By exploiting a multi-criteria decision making, this methodology evaluates the operation of energy storage systems such as: pumped hydro storage (PHS), compressed air energy storage (CAES), H2 storage, flywheel, super-capacitors, lithium-ion and NaS advanced batteries and VRB flow battery. The main objective of the study is to develop a multicriteria analysis to find the most appropriate energy storage system concerning a power quality priority. For this, the criteria in analysis are: efficiency, load management, technical maturity, costs, environment impacts and power quality. Considerations and results described in this paper are part of the Research & Development Program undertaken by the Federal University of Santa Maria, Brazil.

An electronic solution for the direct connection of a three-phase induction generator to a single-phase feeder

This paper proposes a solution for the direct connection of a three-phase induction generator to a single-phase feeder. This high power quality system is intended to be used in micro-hydro power plants applications with control of the water flow. It is employed to maintain the speed of the induction generator greater than its synchronous value. The difference between the generated power and the power consumed by the local load flows through the single-phase feeder. The power flow control is provided by a three-phase PWM inverter that additionally guarantees the local power quality. A system with good power quality must have sinusoidal and constant amplitude voltages, fixed frequency operation, balanced induction generator voltages and currents, harmonics and reactive power compensation. The paper describes the inverter control strategy, presents design criteria of the controllers, and shows experimental results.

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.

Neural classification of power quality disturbances: An application of the wavelet transform and principal component analysis

This paper proposes a different method of power quality disturbance classification combining discrete wavelet transform (DWT), principal component analysis (PCA) and neural networks. This method associates properties from the multiresolution-analysis (MRA) technique with standard deviation and average calculation to extract the discriminating features from distorted signals at different resolution levels. Subsequently, a PCA algorithm is used to reduce the feature space dimension by mapping the obtained feature set into a set of fewer independent elements. Then, a radial basis function network (RBF) is employed to perform the classification of disturbances. In order to evaluate the proposed method, classifications with and without the PCA algorithm are performed.

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.

Fuzzy secondary controller for autonomous stand-alone and grid-connected AC microgrid

The present paper addresses the AC microgrid control issue using the 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 generation systems connected to the microgrid. Depending on the geographical size of the microgrid, the communication links can be economically unviable. This paper thus proposes a fuzzy secondary controller for AC microgrids to reduce the link communication dependency by using only local measurements. The simulation results show that the deviations as happened with the conventional secondary controllers can be compensated when the microgrid is operating as stand-alone mode, and can provide a certain amount of power to the connected utility bus when 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.