Elmano Margato

Rise time reduction in high-voltage pulse transformers using auxiliary windings

Today high-voltage pulses are reaching more fields of application. High-voltage pulse transformers are often used in association with high-voltage pulse generating circuits to further increase the pulse output voltage level. However, because of the transformer parasitic elements involved, the transformer is the critical device in shaping the rising characteristics of the output pulse. One of the techniques usually adopted to decrease the leakage inductance of the transformer adds two auxiliary windings to the transformer. If properly used, these auxiliary windings reduce the leakage flux and, therefore, the leakage inductance. As a result the pulse rise time is reduced. In this paper, a mathematical model is used to describe the observed behavior of a transformer operating with auxiliary windings, based on the theory of electromagnetic coupled circuits. The model is discussed regarding the experimental results obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab/Simulink with the measured transformer parameters.

A new method to build a high-voltage pulse supply using only semiconductor switches for plasma-immersion ion implantation

Abstract A new method to obtain high voltage (kV) pulses suitable for a plasma immersion ion implantation (PIII) facility is presented. The circuit proposed is based on a step-up transformer with a constant flux reset clamp circuit that takes advantage of the low duty ratio required to reduce the voltage stress on all semiconductor switches. An initial prototype was assembled with 800-V semiconductor switches for an output pulse of −5 kV, 5-μs pulse width and 10-kHz pulse frequency. Theoretical and experimental results are presented and discussed.

Pulse Shape Improvement in Core-Type High-Voltage Pulse Transformers With Auxiliary Windings

High-voltage pulsed power technologies are rapidly emerging as a key to efficient and flexible use of electrical power for many industrial applications. One of the most important elements in high-voltage pulse-generating circuit technology is the transformer, generally used to further increase the pulse output voltage level. However, its nonideal behavior has significant influence on the output pulse shape. The most attractive winding configuration for high-voltage, the core-type transformer with primary and secondary on different core legs, is seldom used in pulsed applications, because of its weak magnetic coupling between windings, which would result in a slow-rising output voltage pulse. This paper shows that auxiliary windings, suitably positioned and connected, provide a dramatic improvement in the pulse rise time in core-type high-voltage pulse transformers. The paper derives a mathematical model and uses it to describe the observed behavior of the transformer with auxiliary windings. It discusses experimental results, obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab and taking into account the measured transformer parameters

Predictive optimal matrix converter control for a Dynamic Voltage Restorer with flywheel energy storage

This paper presents a predictive optimal matrix converter controller for a flywheel energy storage system used as dynamic voltage restorer (DVR). The flywheel energy storage device is based on a steel seamless tube mounted as a vertical axis flywheel to store kinetic energy. The motor/generator is a permanent magnet synchronous machine driven by the AC-AC matrix converter. The matrix control method uses a discrete-time model of the converter system to predict the expected values of the input and output currents for all the 27 possible vectors generated by the matrix converter. An optimal controller minimizes control errors using a weighted cost functional. The flywheel and control process was tested as a DVR to mitigate voltage sags and swells. Simulation results show that the DVR is able to compensate the critical load voltage without delays, voltage undershoots or overshoots, overcoming the input/output coupling of matrix converters.

Self-Excited Induction Generator for Micro-Hydro Plants Using Water Current Turbines Type

A study of a micro-hydro run-of-the-river project using a squirrel cage induction generator is presented. A water current turbine, propeller type, is considered. A three-phase voltage source inverter is used to establish with deadbeat control on the AC side, the required currents to excite the generator. A DC control loop with PI controller is used to maintain the DC bus voltage constant with rotor speed. The control strategy is developed using the field orientation technique which is provided by a digital signal processor (DSP). The proposed model and adopted control strategy are validated both by numerical simulation and experimental results from a laboratory prototype

Modern technologies for experimental education in industrial electronics and electric drives

This paper describes the methods used by the teaching group of power electronics and electrical drives of Electrical Engineering and Automation Department of Instituto Superior de Engenharia de Lisboa (Portugal) to increase the effectiveness of experimental training in the areas of industrial electronics and electric drives. It is well known that the interest of new students for electrical engineering courses has decreased, all over the world, and some proactive actions have to be done by engineering schools in order to increase their attractiveness. The approaches followed by this teaching group were intended to improve the student enrollment and to develop sustained competences in the electrical engineer profile by a fair balance between didactic tools and industrial equipment. A judicious introduction of industrial material in laboratory work can be both stimulating as well as a valuable link to the real world. The versatility and moderate cost of modern integrated power electronics modules, the capacities of modeling and control dedicated software, modern digital signal processors and also the judicious use of industry grade equipment, opened new challenges in experimental training. This set of equipment allows to build a variety of configurable open systems, with more or less complexity, that can be explored at different levels of power electronics and electrical drives, from the power stage to the control functions, as exemplified in this paper

Predictive Optimal Control of Unity-Power-Factor Matrix Converters used in Field Oriented Controlled Induction Motor Drives

This paper presents predictive optimal control applied to field oriented controlled induction machine drives employing a matrix converter with input current control and near unity input power factor. The method uses a discrete-time model of the converter system to predict the future values of the output and input currents for all the 27 possible output voltage vectors generated by the matrix converter. The optimal controller minimizes output current (allowing the establishment of field oriented control) and input current errors using a cost functional with adequate weights. The performance of the proposed predictive control is validated by numerical simulations, which are also compared to Venturini modulation.

Analysis of a modular generator for high-voltage, high-frequency pulsed applications, using low voltage semiconductors (<1kV) and series connected step-up (1:10) transformers

This article discusses the operation of a modular generator topology, which has been developed for high-frequency (kHz), high-voltage (kV) pulsed applications. The proposed generator uses individual modules, each one consisting of a pulse circuit based on a modified forward converter, which takes advantage of the required low duty cycle to operate with a low voltage clamp reset circuit for the step-up transformer. This reduces the maximum voltage on the semiconductor devices of both primary and secondary transformer sides. The secondary winding of each step-up transformer is series connected, delivering a fraction of the total voltage. Each individual pulsed module is supplied via an isolation transformer. The assembled modular laboratorial prototype, with three 5 kV modules, 800 V semiconductor switches, and 1:10 step-up transformers, has 80% efficiency, and is capable of delivering, into resistive loads, -15 kV1 A pulses with 5 micros width, 10 kHz repetition rate, with less than 1 micros pulse rise time. Experimental results for resistive loads are presented and discussed.

Dynamic behavior of two power supplies for FFC NMR relaxometers

The main power supply of a FFC NMR relaxometer can be based on different topologies. Its design has been done having as a basic reference the parameters of a magnet specially designed and optimized, and the magnet current that is needed to achieve a magnetic induction of 0.2 T. Due to the particularities of this magnet, the FFC power supplies must have characteristics that are not fulfilled by the most common commercial power supplies, as FFC NMR power sources generally behave as current sources that should be able to drive cycling currents with slew rates lower than 3 A/ms. In this paper, the design and dynamic characteristics of two solutions for the power supply are presented and assessed. One solution uses an additional auxiliary power supply that is replaced by a capacitor in the other solution. To guarantee the required current slew rates, the possibility of using resistors to dissipate the energy stored in the magnet is also discussed. In addition, the performance of both topologies is also presented with attention to the fact that the resistance of the magnet is not constant..

Technical and economic analysis of a micro hydro plant — a case study

The hydro power plants with generated power less than 10 MW are becoming more attractive considering both technical - economic aspects and environmental issues. The profits obtained with electrical energy production using this renewable primary energy source come from economic savings in the case of self consumption or financial incomes when electrical energy is delivered to the utility and sold. Additionally, this type of energy production is environmentally friendly, contributes toward gas emission and global warming reductions and can be used to regulate the watercourses. This paper presents an overview of available technical solutions to be used in micro-hydro power plants and proposes suitable equipment for a particular solution, based on average values of water fall and water flow. An economic analysis of the considered power plant is also presented.