Pedro G. Barbosa

Boost current multilevel inverter and its application on single-phase grid-connected photovoltaic systems

This work presents a novel current multilevel (CML) inverter topology, named boost CML inverter, and its application on energy processing of single-phase grid-connected photovoltaic (PV) systems. The structure allows a high power factor operation of a PV system, injecting a quasi-sinusoidal current into the grid, with virtually no displacement in relation to the line voltage at the point of common coupling among the PV system and the loads. The major appeals of using the CML technique are the balanced current sharing among semiconductor switches and the decrease of the current slope in the circuit devices, with a consequent reduction of conducted and radiated electromagnetic interference (EMI). The CML technique also allows adapting or minimizing current waveforms harmonic content. System description, mathematical approach, and design guidelines are presented, providing an overview of the new topology. In order to validate the proposed concepts, experimental measurements, made in a small-scale laboratory prototype, are also presented. The obtained results evidence the feasibility of the application of this new topology on singlephase grid-connected PV systems.

Analysis of voltage droop control method for dc microgrids with Simulink: Modelling and simulation

This work presents a performance study of a dc microgrid when it is used a voltage droop technique to regulated the grid voltage and to control the load sharing between different sources. A small model of a dc microgrid comprising microsources and loads was implemented in the Simulink/Matlab environment. Some aspects about centralized (master-slave) and descentralized (voltage droop) control strategies as well as the procedures to design the controllers, with and without droop control, are presented and discussed. Simulation results obtained with the digital model of the dc microgrid with three microsources will be presented to validate the effectiveness of the voltage droop strategy, applied to proportional and proportional-integral controllers, to regulate the microgrid voltage.

A study of shunt active power filter based on modular multilevel converter (MMC)

This paper presents a study of a shunt active power filter based on the modular multilevel converter (MMC) topology. The current controller of the shunt active power filter uses a PI-MRI (PI with multi reference frame integrators) technique to assure that the APF current tracks the reference signal. It is also investigated the performance of the method of selection and classification used to choose and to control which submodule (SM) of the MMC will become active. Simulation results will be used to evaluate and to demonstrate the behavior of MMC as active power filter.

Integrated bidirectional single-phase vehicle-to-grid interface with active power filter capability

This work proposes and describes the integration of a bidirectional grid interface, capable to simultaneously operate as an active power filter and a battery charger (or a power generator), to the on-board power electronics of an electric vehicle. The integration of additional functions to electric vehicles is a very desirable feature, since it can result on cost reduction (in comparison to the separated implementation of the integrated functions). Simulation results based on a small-scale system provide evidence of the feasibility of the proposed concepts.

Comparative analysis of current and voltage-controlled photovoltaic Maximum Power Point tracking

Maximum Power Point tracking (MPPT) in photovoltaic (PV) systems may be achieved by controlling either the voltage or current of the PV device. There is no consensus in the technical literature about how is the best choice. This paper provides a comparative analysis performance among current and voltage control using two different MPPT strategies: the perturb and observe (P&O) and the incremental conductance techniques.

Harmonic analysis of the power distribution Neutral-to-Earth Voltage (NEV) test case using four-wire three-phase harmonic current injection method

This work presents several harmonic analyses using the Four-Wire Three-Phase Harmonic Current Injection Method (FHCIM) to simulate the Power Distribution Neutral-to-Earth Voltage (NEV) Test Case. FHCIM is a fast and reliable Newton-Raphson multi-frequency power flow methodology to simulate unbalanced three-phase electric power systems with explicit representation of the network characteristics and components, including the harmonic couplings of non-linear loads as well as neutral conductors and groundings. The NEV test case is a radial distribution network in which the neutral voltages and currents present an important role due the system unbalances, grounding impedances and neutral conductors. Harmonic distortion on real networks, are due to the proliferation of non-linear loads, and can affect both neutral-to-earth voltage levels and neutral currents. Therefore, a digital tool for harmonic analysis is becoming very important for planning studies of electrical power systems. Simulations of the original NEV test case with unbalanced 3rd harmonic loads, as well as a modified case with non-linear loads, represented by SVCs, were carried out with the purpose of investigating the presence of a wide harmonic propagation spectrum.

A single-phase single-stage, high power factor grid-connected PV system, with maximum power point tracking

This paper proposes a single-phase, grid connected non-isolated, very compact photovoltaic (PV) processing system, which is able to inject a low-distortion current into the grid while tracks the maximum power point (MPPT) of the PV array. The arrangement is based on a buck full-bridge inverter, whose switches are gated to provide an almost sinusoidal current into the grid keeping the PV panels voltage near constant, using what is known as the simplest method of MPPT available to date. The concept is validated by a comprehensive set of theoretical equations and digital simulation results concerning a 720W PV power injected to a 127V, 60 Hz line grid. A solar radiation step response case is considered to prove the feasibility of the idea. The small number of components of the complete system confers to it a great efficiency and reliability.

Fault Current Limiter Based on Resonant Circuit Controlled by Power Semiconductor Devices

This work presents a resonant fault current limiter (FCL) controlled by power semiconductor devices. Initially the operation of two ideal resonant circuit topologies as fault current limiter are discussed. The analysis of these circuits is used to derive an alternative topology to the fault current limiter based on the connection of a series and a parallel resonant circuit. Digital models are implemented in the SimPowerSystem/Matlab simulation package to investigate the performance of the proposed FCL to protect transmission and distribution electric networks against short circuit currents. Transfer functions of the linear limiter models are used to identify the effect of each element of the FCL over its stability and its transient response. The developed analysis will be used to derive modifications in the FCL topology in such a way to improve their dynamic response.

Simultaneous active power filter and G2V (or V2G) operation of EV on-board power electronics

This work proposes the application of a battery or plug-in electric vehicle on-board power electronics on the mitigation of possible residential electricity network power quality problems simultaneously to its use as a battery charger or a power generator. The integration of additional functions to an electric vehicle is a very desirable feature, since it can result on cost reduction (in comparison to the separated implementation of the integrated functions). Simulation results provide evidence of the feasibility of the proposed system and concepts.

Analysis of non-linear adaptive voltage droop control method applied to a grid connected DC microgrid

Currently, the standards of reliability and power quality indicate a new design of the Electric Power Systems (EPS), in which the model of centralized generation gives way to the Distributed Generation (DG). One way to achieve the integration of sources in DG is using DC microgrids, since renewable energy sources can be integrated into systems using DC as well as energy storage and UPS, eliminating conversion stages. The voltage control in these systems is of paramount importance. Therefore, this paper proposes the use of a methodology for nonlinear control associated with the concept of voltage droop control in a grid-connected DC microgrid. Simulation results are presented and the behavior of the system is analyzed.