Fernando L. M. Antunes

A Three-Phase High-Frequency Semicontrolled Rectifier for PM WECS

This paper proposes the use of a three-phase high-frequency semicontrolled rectifier for wind energy conversion systems based on permanent magnet generators. The main advantages of the topology are: simplicity, since all active switches are connected to a common point, robustness, as short-circuit through a leg is not possible, and high efficiency due to reduced number of elements. As a disadvantage, higher but acceptable total harmonic distortion of the generator currents results. The complete operation of the converter and theoretical analysis are presented. Additionally, a single-phase pulsewidth modulation inverter is also employed in the grid connection. Experimental results on 5-kW prototype are presented and discussed.

LCL filter design for grid-connected NPC inverters in offshore wind turbines

This paper deals with the analysis, design and optimization of a LCL filter topology to connect a 7MW NPC inverter to the grid. Following the requirements based on the IEEE 519-1992 recommendation and the German Guideline VDEW, simulation results were evaluated in order to access the performance of the proposed filter and the quality of the current injected into the grid.

Application of a generalized current multilevel cell to current-source inverters

In this paper, a new cell which lends itself as a generic current multilevel one is applied to current-source inverters with output current harmonics minimization and without the use of high-frequency modulation. In this cell, inductors acting as current sources ensure equal current division among switches. DC current balance in the inductors is achieved, also, without closed-loop control. It is also shown that, while, for the five-level structure it is easy to find a proper control strategy, for higher levels, it is necessary to use numerical simulation programs to find out a proper switching strategy. Simulation and experimental results are included to show the performance of the new cell for high-power applications.

An artificial neural network-based real time maximum power tracking controller for connecting a PV system to the grid

This work deals with the application of a neural network-based controller for tracking the point of maximum power of a photovoltaic (PV) system interconnected to the utility grid. The neural network is used to identify, in real time, the voltage for maximum output power of the system. The controller, through the information supplied by the neural network, generates a control signal that will be applied to a DC/DC (boost) converter in such a way to take the voltage of the system to a value which guarantees the operation of the PV system at maximum power. The boost converter duty-cycle is generated by a PI controller based on the information supplied by the neural network. In order to connect the PV system to the electric distribution system a three-phase voltage source inverter (VSI) is used operating with optimized sinusoidal PWM strategy with harmonics elimination at the output voltage up to the 17/sup th/ harmonic. The inverter uses IGBT as power switches, and is microcontroller operated.

A High Step-Up DC-DC Converter Based on Three-State Switching Cell

A new non-isolated boost converter with high voltage gain is proposed on this work. This converter is suitable for applications with a high voltage gain between the input and the output. In this converter, for a given duty cycle, the output to input voltage ratio can be raised by adding transformer turns. Another important feature of this converter is the lower blocking voltage across the controlled switches compared to similar circuits, which allows the utilization of MOSFETs switches with lower conduction resistances RDS(on). In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1 kW assembled prototype

A Generalized High Voltage Gain Boost Converter Based on Three-State Switching Cell

A new non-isolated step-up converter with high voltage gain is proposed on this work. It is suitable for applications with a high voltage gain between the input and the output. In this converter, the output to input voltage ratio, for a given duty cycle, can be raised adding transformer turns ratio. Another important feature of this converter is the lower blocking voltage across the controlled switches compared to similar circuits, which allows the utilization of switches with low on-resistance RDS(on) MOSFETs. In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1 kW laboratory prototype

Junction Temperature Estimation for High Power Light-Emitting Diodes

The understanding of the thermal properties of a high power LEDs is essential in order to achieve the highest optical performance of the device without sacrificing its reliability. In addition to that, the good thermal management is also a key factor to avoid thermal induced variation of the photometric / colorimetric properties of power LEDs, such as variation of relative light output or the spectrum. This paper proposes a methodology to estimate junction temperature of high power LEDs. This method allows discarding the influence of the intrinsic series resistance of the LED electric model in 1-V curve, avoiding, as a consequence measurement errors.

Low cost self-oscillating ZVS-CV driver for power LEDs

This paper presents a self-oscillating zero-voltage-switching clamped-voltage (ZVS-CV) power electronics driver for LED strings. A simplified mathematical model of LED has been obtained and used to characterize the series resonant converter for the power LED driver. For a large voltage at the input, this converter does not need a current sensor to stabilize the average current through the LED string. By using the proposed converter the effects of the LED manufacturing tolerances and temperature drifts almost has no influence on the LED string average current, and this is analyzed with the application of the LED electrical model. The simplification of the control design, and of the converter, reduces the component number and the cost. The prototype utilizes a low cost series saturable transformer to drive the bipolar transistors (BJTpsilas). The saturable transformer is a component of the self-oscillating drives and determines the switching frequency of the resonant converter. Analytical results are verified by laboratory experiment.

Soft-switching interleaved boost converter with high voltage gain

In this paper a soft-switching interleaved boost converter with high voltage gain is presented. The high voltage gain converter is far suitable for applications where a high step-up voltage is required, as in some renewable energy systems, which use, for example, photovoltaic panels and/or fuel cells. Besides, in order to guarantee small switching losses and, consequently, a high efficiency, a non- dissipative soft-switching cell with auxiliary commutation circuit is used. Thus, a large step-up voltage, low switching stress, small switching losses, and high efficiency are expected from this topology. In order to verify its effectiveness, experimental waveforms from the high voltage gain converter operating with hard-switching and soft-switching are compared. Also, waveforms from the soft-switching cell are presented and analyzed. Theoretical analysis, operation principle and topology details are also presented and studied.

A transformerless single phase on-line UPS with 110 V/220 V input output voltage

In this paper, it is proposed a new nonisolated UPS system configuration that allows the bypass circuit operation even if the input voltage is different from the output voltage. The UPS system is composed by an AC-DC/DC-DC three level boost rectifier/converter combined with a double half bridge inverter. This topology allows the reduction of some parameters that are commonly discussed in the nonisolated UPS systems such as size and cost, compared with others isolated UPS configurations for the same purpose. Also, the efficiency are improved due to reduced number of switches and batteries, as well as no low frequency isolation transformer is required to realize bypass operation because of the common neutral connection. Both stages of the proposed circuit operate in high frequency, using a passive nondissipative snubber circuit in the boost converter and IGBTs switches in the double half bridge inverter, with low conduction losses, low tail current and low switching losses. A simple and well-known control strategy is used. Principle of operation and experimental results for a 2.6 kVA laboratory prototype are presented to demonstrate UPS performance.