Showing papers presented at "European Conference on Power Electronics and Applications in 1999"

Asymmetric Multilevel Converter for High Resolution Voltage Phasor Generation

Abstract: Recent publications on so called multilevel inverters deal with series connected cells, mainly developed for the increase of the output-voltage magnitude, in order to meet the classical design levels of medium size motors in the lower megawatt power range [1], [2], [3], [4]. In all well-known multilevel topologies, generally a regular or symmetric voltage share over all partial sources has been chosen, with as main goal a better use of the individual silicon devices regarding the possible blocking properties. The definition of the resulting output voltage has generally been sufficient due to the high number of series connected cells. In the proposed solution, the main efforts are set to the aspect of getting a higher resolution of the voltage phasor, in relation with the use of motors with strongly reduced leakage inductances. Together with the specification of a limited current harmonic content, even the frequency of the fundamental component is an important parameter. One application field will be the variable speed drives for ultra-speed kinetic energy storage.

DC-DC Converters for Two-Quadrant Operation with Controlled Output Voltage

Abstract: A DC-DC converter is proposed with new modulation schemes for a voltage-controlled output. The DC-DC converter is designed for a reversible current in order to feed DC current motors or four quadrant converters, which need a galvanic separation from a DC source. The output voltage is stabilized while the load current can change rapidly. The new modulation method reduces the losses by 50%. Experimental tests have been made on a 20kW prototype.

Design of an integrated electromagnetic levitation and guidance system for SwissMetro

Abstract: Electromagnetic levitated and guided systems are commonly used in the field of people transport vehicles, tool machines frictionless bearings and conveyor systems. In the case of low speed people transport vehicles, the electromagnetic levitation offers the advantage of a very silent motion and of a reduced maintenance of the rail. In the world there are actually two working low speed systems: the Japanese HSST ([1], [2]) and the English BAMS (Birmingham Airport MagLev System [3]). In both these magnetically levitated trains the guidance force needed to keep the vehicles on the track is obtained with the levitation electromagnets, thanks to particular shapes of the rails and to a clever placement of the electromagnets with respect to the rails ([4]). This paper shows a simple magnetic model for the study of the levitation and guidance forces produced by an electromagnet coupled with an iron rail. The rail and electromagnet shapes taken into consideration in this paper can better refer to the Japanese HSST than to the English BAMS. This paper will also deals with the study of the guidance force in the case of a vertical position control. The study shows that the guidance force can be stronger than in an open loop study.

Optimization of a servo motor for an industrial robot application

Abstract: A permanent magnet synchronous machine has been optimized for an industrial robot application. The optimization was made with respect to material cost, considering the demands of the application. In the optimization, drive cycle information was utilised, and the effect of the inertia of the machine was considered. A simple magnetic equivalent circuit was used to calculate the no load flux, and the finite element method was used for the calculation of torque ripple and induced voltage. Root mean square values for the speed and the torque profiles of the drive cycle was used for the calculation of the iron and copper losses. The optimization yielded a smaller and less expensive machine, compared to the machine presently used in the application. The active length was reduced by 35 %, the inertia of the active part of the machine was reduced by 56 %, and the material cost of the active part of the machine was reduced by 30 %. The new machine has a novel design of the rotor and a simple magnet geometry. FEM calculations indicate that the machine has a high torque ripple, and it is assumed that this can be compensated for by current profiling. A prototype has been built and measurements show a very good agreement with finite element calculation results. The prototype has, due to an error in the manufacturing of the magnets, slightly inferior thermal properties to fulfil the demands of the drive cycle.

Low cost sensorless position detection for brushless DC motor

Abstract: This paper describes a low cost sensorless position detection scheme for a brushless DC motor. This method is based on interruption of the 3 phase-currents and reading the back-EMF. The hardware for measuring the back-EMF is very simple. The method is possible thanks to the flexibility of the modern DSP. The proposed scheme shows how it is possible to get rotor position information with a good accuracy (5°). This precision allows a sinusoidal alimentation. The method takes information about the rotor in a few microseconds ( 100 μs) and when it wants. That means it is robust and does not need to wait a back-EMF zero crossing. The goal of this paper is to prove that sensorless sinusoidal alimentation with a very limited number of components is also possible in a wide speed range. The paper presents the method as well as a wide range of experimental results showing the feasibility and the robustness of the proposed method with 2 different brushless DC motors. The speed range starts at about 1% and stops higher than 100% of the nominal speed

Three-Phase Unity Power Factor AC/DC Converter with Dual Isolated DC/DC Converter for a Battery Charger

Abstract: In this article the development and realization of a 8 kW battery charger with Power Factor Correction (PFC) is described The converter consists of two parts: The first part is an AC/DC converter based on a “VIENNA” topology with a controlled output voltage of 700V and midpoint connection [1],[2] The second part consists of two DC/DC converters with galvanic isolation and parallel outputs The output current and voltage can be controlled in the ranges 0-28A and 0-280V

Parameter Design of a state-variable controller for PWM Voltage Source converters connected to the grid

Abstract: Controlled pulse-width modulated (PWM) voltage source converters (VSC’s) are increasingly used in power systems for active filtering of line current harmonics and reactive power compensation. In this paper the parameter design of a state variable controller to determine the instantaneous switching pattern of the converter switches for optimal dynamic system performance is discussed. To this end the mathematical model of a system encompassing a three phase system grid and a VSC converter controlled by a state variable controller is developed. The space vector approach is used. Simulation results confirm the theoretical expectations.

Serial connected active voltage clamping

Abstract: The new post project for uranium enrichment SILVA needs specific power converters. The LETC laboratory of the C.E.A. in Pierrelatte has been studying these since 5 years. The aim of this laboratory consists in developing high voltage solid-state converters using a large number of small standard solidstate components (MOSFETs, IGBTs, thyristors and diodes) connected in series. In these associations, voltage balancement system are not used, but the voltage is limited on each stage in its safety area by clamping protection. This paper describes different voltage clamping systems, active clamping technique and their association in series.