E.A.A. Coelho

A State Equation Model of a Single-Phase Grid-Connected Inverter Using a Droop Control Scheme With Extra Phase Shift Control Action

This paper presents a state equation model of a single-phase pulsewidth modulation inverter connected to the grid, using frequency-active power and voltage-reactive power droops, including an extra phase shift loop. The influence of the control parameters on the systems behavior can be studied using the proposed state equation model, which was obtained from the small-signal analysis. The models results are compared with numerical simulations of the nonlinear system to verify their accuracy. Comparisons are also made with experimental data reported in the literature.

An electronic ballast with high power factor and low voltage stress

This paper presents a new configuration for an electronic ballast with high power factor for fluorescent lamps. The proposed ballast consists of the integration of a buck-boost converter, used as an input stage to correct the power factor and regulate the voltage on a dc bus, and a resonant half-bridge inverter to drive the lamp. The buck-boost converter operates at a constant frequency and constant duty cycle in a discontinuous conduction mode during all input cycles.

A proposal of Led Lamp Driver for universal input using Cuk converter

In recent years, light emitting diodes (LEDs) have become a viable alternative to conventional light sources. The LEDs are now approaching performance levels that make them attractive for use in several illumination applications. One of the main advantages of LEDs is their very long life that it is also related directly with the maintenance of the LED current, preventing the device overheating. To contribute with the advantages of the LEDs, the same ones need efficient drivers with optimized control circuitry. The main focus of this paper is to improve the LED driver characteristics using microcontrolled Cuk converter, therefore, greater durability and efficiency can be achieved and working for different nominal values of voltage, from an universal input voltage or battery. Mathematical analysis and experimental results are presented to the drive of an LED lamp of 11 W built with 10 power LEDs Creereg XLampreg XR-C.

A high power factor ballast using a single switch with both power stages integrated

This paper presents a high power factor electronic ballast used to startup fluorescent lamps employing a single power stage and a single-switch. This topology was obtained combining of a Boost converter and a new inverter topology with coupled inductors. The use of a single active switch reduces the number of components used in the control and power circuits. The equations used for designing the proposed reactor and for choosing the semiconductor devices are presented. A prototype operating at 50kHz was built and used to startup 40-W fluorescent lamps.

Review of Active and Reactive Power Sharing Strategies in Hierarchical Controlled Microgrids

Microgrids consist of multiple parallel-connected distributed generation (DG) units with coordinated control strategies, which are able to operate in both grid-connected and islanded modes. Microgrids are attracting considerable attention since they can alleviate the stress of main transmission systems, reduce feeder losses, and improve system power quality. When the islanded microgrids are concerned, it is important to maintain system stability and achieve load power sharing among the multiple parallel-connected DG units. However, the poor active and reactive power sharing problems due to the influence of impedance mismatch of the DG feeders and the different ratings of the DG units are inevitable when the conventional droop control scheme is adopted. Therefore, the adaptive/improved droop control, network-based control methods, and cost-based droop schemes are compared and summarized in this paper for active power sharing. Moreover, nonlinear and unbalanced loads could further affect the reactive power sharing when regulating the active power, and it is difficult to share the reactive power accurately only by using the enhanced virtual impedance method. Therefore, the hierarchical control strategies are utilized as supplements of the conventional droop controls and virtual impedance methods. The improved hierarchical control approaches such as the algorithms based on graph theory, multi-agent system, the gain scheduling method, and predictive control have been proposed to achieve proper reactive power sharing for islanded microgrids and eliminate the effect of the communication delays on hierarchical control. Finally, the future research trends on islanded microgrids are also discussed in this paper.

Stand-alone photovoltaic energy storage system with maximum power point tracking

This digests deals with the study of a stand-alone photovoltaic system, which is able to extract the maximum power from photovoltaic array for all solar intensity conditions and to provide output voltage regulation. The proposed system consists of a DC-DC converter in combination with battery energy storage in a simple structure. Operating principle and control strategy are described. Digital simulation is included, supporting the validity of the concept.

Differential-Evolution-Based Optimization of the Dynamic Response for Parallel Operation of Inverters With No Controller Interconnection

In this paper, the use of differential evolution (DE), a global search technique inspired by evolutionary theory, to find the parameters that are required to achieve optimum dynamic response of parallel operation of inverters with no interconnection among the controllers is proposed. Basically, in order to reach such a goal, the system is modeled in a certain way that the slopes of P- ω and Q -V curves are the parameters to be tuned. Such parameters, when properly tuned, result in systems eigenvalues located in positions that assure the systems stability and oscillation-free dynamic response with minimum settling time. This paper describes the modeling approach and provides an overview of the motivation for the optimization and a description of the DE technique. Simulation and experimental results are also presented, and they show the viability of the proposed method.

Proposal of a Soft-Switching Single-Phase Three-Level Rectifier

This paper is concerned with the study of a single-phase boost-type three-level rectifier. The converter is supposed to present high input power factor, low current harmonics, low total harmonic distortion, and simple control scheme. In order to minimize switching losses, a passive nondissipative snubber is associated with the aforementioned converter. The theoretical analysis, design procedure, and analytical results regarding a 1.2-kW prototype are presented to validate the proposal.

Small-Signal Analysis of the Microgrid Secondary Control Considering a Communication Time Delay

This paper presents a small-signal analysis of an islanded microgrid composed of two or more voltage-source inverters connected in parallel. The primary control of each inverter is integrated through an internal current and voltage loops using proportional resonant compensators, a virtual impedance, and an external power controller based on frequency and voltage droops. The frequency restoration function is implemented at the secondary control level, which executes a consensus algorithm that consists of a load-frequency control and a single time delay communication network. The consensus network consists of a time-invariant directed graph and the output power of each inverter is the information shared among the units, which is affected by the time delay. The proposed small-signal model is validated through simulation results and experimental results. A root locus analysis is presented that shows the behavior of the system considering control parameters and time delay variation.

Analysis of a soft-switched PFC boost converter using analog and digital control circuits

This work presents a comparison between analog and digital (PIC16c73a) control types applied to the boost converter with a nondissipative snubber. Both control types use the bang-bang hysteresis current waveshaping control technique in order to achieve a quasi-unity power factor. The analog control applied presented a high power factor (0.998), high efficiency (92.87%), and low harmonic distortion [total harmonic distortion of current (THDI =2.84% and total harmonic distortion of current (THDV) =2.83%]. The digital control presented a high power factor (0.990), high efficiency (92.46%), and low harmonic distortion (THDI=5.09% and THDV=2.84%).