EPE Journal Volume 01-2 
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EPE Journal Volume 01-2 - Editorial
EPE Journal Volume 01-2 - Papers



 EPE Journal Volume 01-2 - Editorial 

Another step forward in the Enertronics World  [Details]
By P. Ferraris

The Editorial of the EPE Journal Volume 1 N°2, "Another step forward in the Enertronics World", written by Prof. Paolo Ferraris, the Conference Chairman of EPE '91.


 EPE Journal Volume 01-2 - Papers 

30 Years Space Vectors, 20 Years Field Orientation, 10 Years Digital Signal Processing with Controlled AC-Drives, a Review (Part 2)  [Details]
By W. Leonhard

The dynamic interactions of AC-machines are far more complex than those of DC-machines and important quantities are not directly measurable. This has given rise to considerable difficulties in designing high performance AC-drive controls. About 20 years ago, they were overcome by the emergence of new methods of control, using moving frames of reference determined by the angular position of flux waves, hence called field orientation. Their application requires extensive on-line signal processing that can only be realised economically with microprocessors or special digital hardware.

The paper presents a review of this evolution, which has matured in less than 2 decades from research studies to a universally accepted method for controlling AC-machines. The method of field orientation has proved to be well adaptable to all types of power converters and AC-machines; modifications and extensions to include self-tuning and adaptive features are possible. It now seems to be generally accepted that field orientation in one of its many forms is the most promising control method for high performance AC-drives.

Part I of this paper can be read in EPE Journal Volume 1991-1.

The Double-Fed Induction Motor - Both stator and rotor voltages controlled by cycloconverters  [Details]
By D. Lecocq; P. Lataire; W. Wymeersch

In high power industrial applications such as steel rolling mills, drives must have excellent dynamic performances in a wide speed range. Field-weakening control for constant power operation must be applied above base speed. Also armature reaction is highly recommended because the armature reaction leads to a motor power factor drop and, if left unremedied, to the need of a heavier motor and a largersize converter.

Okuyama et al (1978) proved that a cycloconverter-fed synchronous drive is well adapted to these requirements. Armature reaction compensation can in this case be performed by a compensation winding in quadrature with the main field winding. This solution needs a special purpose synchronous motor with two field windings in quadrature, which is thus expensive.

As a three-phase winding is magnetically equivalent to a two-phase winding, armature reaction compensation is also possible in a double fed slip-ring asynchronous motor drive. If both stator and rotor are fed by a cycloconverter, the resulting drive has four degrees of freedom (amplitude and frequency of the stator and rotor voltages) that can be used to control the speed, stator flux, power factor and slip independently even during transient operation, if an appropriate control i.e. vector control is used. Figure 1 shows a general scheme of the proposed drive, suitable for high power applications.

GTO and Duality - For a better matching of phase controlled converters and power network  [Details]
By P. Ladoux, Y. Cheron; H. Foch
The thyristor has long been the only controlled component allowing to switch high power (MW). Mostly used in rectifier structures, the thyristor is now challenged by by the GTO that provides blocking capability. Using the duality and soft commutation concepts, the authors propose "new" topologies for turn-off and turn-on controlled rectifiers, as well as some series and parallel assemblies. The AC- and DC-side performances of these rectifiers are then exposed with the aid of the elementary commutation cell concept. The problems related to the implementation of such turn-off controlled rectifiers are finally discussed.

Protecting IGBTs against Short Circuit  [Details]
By G. Castino

Insulated Gate Bipolar Transistors (IGBTs) with the most rugged intrinsic short circuit performance generally have high saturation voltage and high operating losses, and vica versa.
This application note demonstrates that IGBTs with even modest intrinsic short-circuit capability can be fully protected against short circuit, allowing the most efficient, cost effective IGBTs to be used, without compromising ruggedness of the overall system.

Microcontroller-Based, Multi-Mode 3-Level Pulse-Width Modulator  [Details]
By B. Velaerts; P. Mathys

The 3-level voltage inverter is an efficient solution for high power variable speed drives, as it combines high voltage capabilities (due to GTOs in series) and significant reduction of losses and/or switching frequency (due to the intermediate level leading to lower voltage harmonics). This paper shows how the subharmonic and precalculated 3-level pulse-width modulation methods, used to control the inverter, can be implemented by a fully programmed modulator. The subharmonic modulation uses modulating and carrier waves to generate the commutations orders for the inverter. In addition to the classical bipolar 2-level and unipolar 3-level methods, our laboratory has developed a new "dipolar" 3-level subharmonic modulation, which is described in the paper. The precalculated moduylation, also presented, is based on optimized waveforms stored in EPROM, and reproduced in real-time by the modulator. Concerning the implementation of these modulations, a new sampling control method for the subharmonic modulation, and an original way to store the optimal angles of the precalculated modulation are explained. The implementation of the passage from one modulation mode to another is studied, introducing an efficient and simple method of transition. The prototype of the modulator is based on the 8097 micorcontroller from Intel, programmed in C-language.

Appropriate Pulse Width Modulation for a Three-Phase PWM AC-to-DC Converter  [Details]
By M. Weinhold

Research in the field of power devices has led to the development of power semiconductors that allow high switching frequencies. Especially the IGBT (Insulated Gate Biploar Transistor) is suitable for three-phase ac-to-dc converters in the medium power range (1 kW - 100 kW).

Because of the high switching frequencies the harmonic contents of the line-side converter voltages can be kept small, which results in reduced line-side reactors compared to conventional converter systems.

For full exploitation of the capability of the new devices appropriate pulse width modulation (PWM) is necessary.

This paper studies the reasons for line current distortion caused by a three-phase ac-to-dc converter in order to conclude the requirements for appropriate PWM schemes.

Quality criteria for the selection of the best PWM schemes are presented. The quality criteria are then applied under consideration of minimum switching state time of the converter valves.

Power Electronics and the Electricity Network - Will the evolution of those two techniques be compatible  [Details]
By H. Balériaux; G. Maggetto

The influence of power electronics equipment, generators of synchrounous and asynchrounous harmonics (high frequency noise) on the electricity network and its drawbacks for the customers are well known. Solutions do exist. On the network side, it is possible to configure it in a way that makes the internal impedance at the connection point low (fault current at any point higher than or equal to ten times the rated current). A judicious choice of the coupling of the power transformers will help too. On the side of power electronics equipment the situation is very complicated because it results from non-linear effects and from dynamic operating conditions. This leads into the creation and the superposition of harmonics being whole multiples of the supply frequency, harmonics not being whole multiples of the supply frequency, subharmonics, i.e. harmonics lower than rated network frequency, as well as d.c. components. The reduction of the harmonic level or the suppression of harmonic orders can theoretically be achieved by a due control technique but the end result depends strongly of the converter structure and the commutation speed of the semiconductor components. Furthermore the situation is made more difficult because of the associate L-C networks for protection purpose. One last possibility, and for many years it was the only possible one, is the interposition of low pass filter, and, or, more costly band stop filters; the last ones should be more and more considered as an emergency solution. We can reflect on the future evolution of these two fields - electricity distribution and power electronics - both having a major advantage in living together and developping in a harmonious way. This is what this paper is all about.