Alin Grama

Power factor correction circuit with a new modified SEPIC converter

This paper presents a new topology for a SEPIC converter used in power factor correction circuits. The conventional SEPIC converter was primarily designed to provide a nonpulsating input current, operating with both inductors in continuous current mode and only DC-DC conversion was considered. The modified SEPIC converter is designed to operate as an AC-DC converter and can be viewed as a cascade of a modified boost converter and a buck-boost converter. The boost converter operates in discontinuous current mode, while the buck-boost converter operates in continuous current mode. Since a high power factor is naturally achieved in this way, a simple feedback control technique is needed in order to regulate the output voltage. The paper also presents a calculus method for the power factor and total harmonic distortion factor for the proposed converter.

Supercapacitor modelling using experimental measurements

Supercapacitors are components for energy storage, dedicated for applications where both energy and power density are needed. Even if their energy density is ten times lower than the energy density of batteries, supercapacitors offer new alternatives for applications where energy storage is needed. We have done an experimental bench and we have measured the voltage across a supercapacitor in a constant current charge/discharge cycle. Using these measurements and a mathematical algorithm we have proposed an electrical model for the supercapacitor, and we have determined the parameters of the model also.

Design of a plasma generator based on E power amplifier and impedance matching

The paper presents the design key issues for a plasma generation method. A Class E Power Amplifier is used to generate plasma at 13.56MHz with a variable load implemented with an air coil and a variable capacitor. Class E amplifier represents a mean of high efficiency power amplification. Ideal amplifiers reach 100% efficiency and by proper filtering and tuning even the real circuit efficiency can be only 5% lower. By measuring the input impedance of the matching network the resistance, the voltage and the power of the plasma torch can be estimated. In order to do that, two matching networks were designed; the first one is partially compensated and the second is completely compensated. The problems that can appear at a capacitive tuning in air and Argon atmosphere are also presented. Finally, the steps needed to design the plasma generator with class E power amplifier and air coils are described.

Direct Digital Frequency Synthesis implemented on a FPGA chip

In applications where very precisely frequencies and fast switching speed are required the best solution consists in a DDFS circuit. This solution is very attractive in all digital systems because this architecture can provide fast tuning speed and coherent phase. In this paper a direct digital frequency synthesizer implemented on a FPGA (field programmable gate array) chip is presented. Comparatively with other component types (e.g. microprocessor), FPGA chips permit higher speeds for specific applications. The architecture used for DDFS circuit is a classic DDFS, described in the first paragraph of this paper, and short reports of the implementation are presented to underline the advantages of FPGA. This kind of circuit is easy to be implemented on a programmable gate array, and uses only a few resources of the device.

Simulink test bench for a hybrid battery-supercapacitor power system

This paper presents a test bench for a hybrid power system composed of a Lithium-ion rechargeable battery and a supercapacitor. Using this test-bench the parameters and the functionality of the entire hybrid power system can be estimated. The purpose of the paper is to test the behavior of the complete system during high load variations. In a power system the advantage of battery storage consists in high charge/discharge efficiency with the condition that the charging/discharging cycles are carefully controlled. The high power demand in many applications with short power surges increases the battery stress, drastically affecting its life time and capacity. A method to reduce this stress is proposed in the paper by using a supercapacitor connected in parallel with the battery. A comparison between the proposed system and one using only a Lithium-ion battery is conducted and the results are presented.

Experimental determination of Equivalent Series Resistance of a supercapacitor

The synergy between batteries and capacitors has been growing, to the point where supercapacitos may soon be almost as indispensable to portable electricity as batteries are now. One very important parameter of a supercapacitor is the Equivalent Series Resistance (ESR). The energy that can be stored in a supercapacitor depends on ESR, so we intend to measure that parameter. Our tests were made on a 350F supercapacitor, 14V, produced by Econd Ltd. We have two methods: the first consist in evaluating ESR by constant current discharge, and the second method consists in a dynamic discharge cycle at a constant current. After measurements and some mathematical evaluations a real value of ESR is proposed.

Simulation and design of a Class E power amplifier

Class E switching-mode tuned power amplifier offers high efficiency at high frequencies. Class E power amplifier concept, introduced by Sokal, is not defined by a special topology. The most simple topology for class E power amplifier consists in a single switch device that operate at carrier frequency of the output signal and a load network that must extract only a single spectral frequency component. The load network consists in a capacitor shunting the switch device and a series-tuned output circuit. To derive the basic equations for class E amplifier we use Fourier series techniques. These equations are implemented in Matlab with a friendly interface. This implementation and this interface can be a very useful tool for students that are interested in class E operation and also a good tool for class E circuit design. In this paper you can find a description of class E power amplifier with functional equations.

Fuel consumption reduction of a diesel-electric power generator

Generating electricity using renewable energy sources is a very actual problem. In this paper, Auxiliary Power Units (APU) is modeled using Matlab/Simulink resources. First, a diesel engine with governor was implemented to generate mechanical power. The rotational shaft was coupled at a synchronous machine used for generation of electrical power. A three-phase dynamic load is connected at generator. The load was modeled likewise electrical consumption profile for a greenhouse during a day. The novelty of our work consists in possibility of the diesel engine to adjust the mechanical power over the electric load, so the fuel consumption is significantly decreased. The paper describes the diesel engine with governor, and the synchronous machine implementation, and the fuel consumption reduction is also underlined.

Analysis and simulation of LCLR converters

In the last decades, induction heating systems have gained ground not only in fields such as industrial applications for heating, training or melting metal, but also in home appliances, such as those for cooking. The following work proposes to design a system, which will be able to heat metal using induction heating. The power transfer process will be optimized by limiting or even eliminating switching losses using techniques such as zero current/voltage switching and by designing a class D series-parallel LCLR resonant circuit, which operates at the resonant frequency. The intent of this presentation is to present the details of a LCLR converter, that ca be used in induction heating applications. The paper will present a simulation and a design method for such type of converters, with an extended analysis of the output stage that can be assimilated like a LCLR circuit.

Educational matlab tool for simulating of forward converters

The intent of this paper is to present the detail of a Matlab platform used for simulation and modeling of forward converter. The forward converter is also studied via a comprehensive analysis with operation equations of the circuit. An alternative to use the circuit-oriented simulators for study of these circuits operating is to describe the circuit and the controller by means of differential and algebraic equations. The advantage of using this Matlab platform consists in the possibility to easy modify the equations parameters which describe the functionality of the converters and which are in general behind the simulators.