Stefan Östlund

Sensorless rotor-position detection from zero to rated speed for an integrated PM synchronous motor drive

By integrating the motor, the converter and the control circuits of electrical drives into one casing several advantages are obtained. The drive becomes compact, the amount of wiring is significantly reduced, and the control of the inverter and the motor can be designed to better utilize their respective characteristics. The paper presents an integrated permanent magnet synchronous motor drive (IPMSM) using complete digital control. The control includes a simple sensorless estimation of the rotor position both at standstill and at rotation. The algorithm for the initial rotor position detection is based on the saliency of the rotor at no load and it provides both the location as well as the direction of the magnetization. At rotation the rotor position is estimated by a predictor-corrector-based observer. The integrated concept makes it simple to include accurate values of the machine parameters.

Design considerations for a medium frequency transformer in a line side power conversion system

Design considerations are presented for a medium frequency transformer in a line side power conversion system for electric railway traction. The system employs soft commutation in order to reduce switching losses and allow for high operating frequency of the transformer. Two different designs are evaluated; The first one is dry insulated and the second one is liquid-immersed. Calculations indicate that a 1 MVA transformer operating at 4 kHz could be realized with an active weight of below 150 kg for both dry and liquid-immersed transformer concepts. The transformers are modeled magnetically, electrically and thermally, and a geometric optimization procedure based on a cost function is applied to achieve an optimum design.

A three-phase soft-switched isolated AC/DC converter without auxiliary circuit

This paper describes an ac/dc converter system consisting of a voltage-source converter (VSC) with purely capacitive snubbers and a two-phase by three-phase cycloconverter, connected via a medium-frequency (MF) transformer. By alternately commutating the two converters, it is possible to achieve beneficial switching conditions for all semiconductor devices. A commutation and modulation algorithm is described, which allows for pulsewidth-modulation control of the output voltage while maintaining soft switching. Low-load operation of the converter is a potential difficulty because the load current may be insufficient for recharging the snubber capacitors of the VSC. However, if the cycloconverter is used to momentarily short circuit the transformer, a quasi-resonant commutation mode of the VSC can be achieved, making a fast and soft commutation of the VSC down to zero load possible, without an auxiliary circuit. Furthermore, the design and operation of a 40-kVA prototype converter system are described. The experimental results from the prototype clearly show the practical feasibility of the studied concept.

Active snubber circuit for source commutated converters utilizing the IGBT in the linear region

This paper describes a gate control method where an IGBT is controlled in its linear region by means of closed loop control in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

A primary-switched line-side converter using zero voltage switching

A new primary-switched AC/DC power converter and its modulation are presented. It employs a single- or three-phase transformer, with a matrix converter (primary) and a conventional two-level converter (secondary). This allows galvanic isolation at medium-frequency zero-voltage primary commutation and five line-side voltage levels. Two distinct modulation methods are explained in detail, and it is shown how a combination of these allows optimal operation in terms of efficiency and voltage harmonics. Measured waveforms on a 30-kW prototype confirm the expected performance.

Designing, Implementing and Maintaining a First Year Project Course in Electrical Engineering.

Being a modern electrical engineer does not only require state of the art skills in areas such as transfer and processing of information, electronics, systems engineering, and biomedical electrical engineering; it also requires generic engineering skills such as oral and written communication, team building, interpersonal skills, and the ability to take the responsibility of solving assigned tasks. In the development of a new electrical engineering curriculum, it was considered a challenge to introduce these generic engineering skills in a more applicable way. The approach described in this paper has been very successful in implementing and maintaining a challenging first year project based engineering course with a high level of training of generic engineering skills.

Switching Frequency Limit for Soft-Switching MF Transformer System for AC-fed Traction

The migration to line side power conversion topologies comprising a medium frequency transformer in AC-fed propulsion systems may reduce size and weight of the conversion system. The switching frequency is a crucial factor affecting the viability of such a conversion system. An increased switching frequency of a mutually commutated conversion system comprising a medium frequency transformer employing soft switching is verified by single pulse measurements. A test bench to characterize standard IGBT modules under soft switching has been build and loss measurements on a 3.3 kV IGBT module are presented for hard and soft switching. A loss model of the investigated topology is developed and the maximum switching frequency for a converter equipped with the investigated module is estimated for hard and soft switching

HVDC feeding with OPF and unit commitment for electric railways

In this paper a railway power system design based on an HVDC feeder is suggested. The converter stations between the public grid and the HVDC feeder can be sparsely distributed, in the range of 100 km or more, whereas the converters connecting the HVDC feeder to the catenary are distributed with a much closer spacing. The ratings of the catenary-connected ones can be lower than substation transformers or rotary converters, since the power conversion can be fully controlled. Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared to conventional systems, especially for cases with long catenary sections, and when there are substantial shares of regeneration from the trains.

Rail Power Supplies Going More Power Electronic [Technology Leaders]

In recent years, interest has risen in using electrified rail operations as an environmentally friendly and efficient way of producing passenger and freight services. New high-speed lines are being ...

Design and optimization procedure of a single-sided linear induction motor applied to an Articulated funiculator

The paper describes the design of a single-sided linear induction motor (SLIM) intended for an Articulated Funiculator (AF). A procedure is proposed where first an analytical design is carried out to obtain a preliminary geometry. The analytical design is based on approximate equivalent circuits under constrained conditions. In the second step a two-dimensional finite element method (2D-FEM) analysis is performed to validate the accuracy of the analytical models. The modification and optimization are conducted to acquire the best design.