Tonu Lehtla

Analytical and Experimental Investigation of Neutral Point Clamped Quasi-Impedance-Source Inverter

Analytical and Experimental Investigation of Neutral Point Clamped Quasi-Impedance-Source Inverter In this paper a new modification of a three-level neutral-point-clamped inverter is presented. The proposed topology combines the advantages of the three-level neutral-point-clamped full-bridge inverter with those of the quasi-impedance-source inverter. The neutral-point-clamped quasi-impedance-source inverter is especially suitable for renewable energy sources. The steady-state analysis of a neutral-point-clamped quasi-impedance-source inverter in the continuous conduction mode is presented. The presented models as well as deduced equations are verified by an experimental prototype.

Control of Ultracapacitors Energy Exchange

Ultracapacitors can store and also give out large energy pulses. That makes them perfectly suitable as short term energy storage devices in electrical vehicles. The usage of ultracapacitors prevents over sizing of the battery pack due to peak power demands. This paper introduces the basic concept of how ultracapacitors could be used in Tramways. The main purpose of the paper is to introduce one possible control-strategy of ultracapacitors energy exchange. With the energy exchange is meant the movement of energy form the ultracapacitors into distribution network and vice versa. Three different regulators, proportional (P), integration (I), and the combination of both (PI) are tested and compared to each other. Practical results are analyzed and compared with the simulation results.

Comparison of university level study methods and laboratory equipment for teaching of electrical drives

The paper deals with teaching problems on the university level. Integration of different study fields like mechatronics, electrical drives and industry automation is under discussion. The article compares different classical and modern study methods and laboratory equipment: classical lecture and laboratory courses, virtual Internet-based training and virtual laboratories, project-based learning by doing, self-made stands for experiments, standardized teaching laboratory systems, and industrial component-based laboratories

Cooling Methods for High-Power Electronic Systems

Cooling Methods for High-Power Electronic Systems Thermal management is a crucial step in the design of power electronic applications, especially railroad traction and automotive systems. Mass/size parameters, robustness and reliability of the power electronic system greatly depend on the cooling system type and performance. This paper presents an approximate parameter estimation of the thermal management system required as well as different commercially available cooling solutions. Advantages and drawbacks of different designs ranging from simple passive heatsinks to complex evaporative systems are discussed.

An improved interface converter for a medium-power wind-hydrogen system

This paper discusses problems related to more cost-effective operation of wind parks. A new rational solution of storing excess energy in the form of hydrogen is described. As hydrogen is produced by the electrolysis process, focus here is on electrolyser and wind turbine interconnections with relevant converter topologies and on the most feasible options.

Hardware-in-the-loop simulator of a flow control system for centrifugal pumps

A hardware-in-the-loop model of a centrifugal pump is proposed. The new simulator consists of the pump and pipeline imitators built on the basis of the variable speed drives connected via the programmable logical controller and Profibus communication components. The mathematical description of the flow maintenance represents a core of the simulation methodology. To study the system, a series of tests have been conducted that proved the designed system flexibility and accuracy in flow control imitation at the steady-state pumping mode.

Comparative analysis of electric drives met for vehicle propulsion

The paper concerns the analysis of the propulsion drives for the battery-fed electric vehicles. Proposed power and torque estimations help to compare different models of the drives in terms of their dynamic performance at start-up and braking, static stability on the road, energy consumption, and control suitability. Focus is on the assessment and verification of various motors from the viewpoint of their force, power, torque, and energy possibilities. The dimensioning procedures are performed, regenerative braking abilities, and types of electric drives met for propulsion are discussed. Several simulation estimates are presented and explained. Finally, an experimental setup used for the result verification is described.

Flexible Curricula for E-Learning of SME Staff in Electronic Engineering

Basing on a study of promoted innovative set-ups and practices in the industrial European SMEs, this paper describes a novel approach to curricula organisation that aims to facilitate and improve the quality and efficiency of in-service training, on-the-job training, and undergoing training provided in a workplace environment of electronic engineering. The purpose is to ground an educational model suitable for planning optimal training trajectories in the framework of the curricula arrangement in the context of SMEs. The focus concerns reevaluation of the curriculum design along with the strengthen role of e-learning basing on the conceptual models and structures.

Interlock delay time minimization and its impact on the high-voltage half-bridge DC/DC converter

In DC/DC power converters, as in many other applications with inverter circuits, the interlock delay time between IGBT switching on and off in the opposite inverter arms is used to avoid a short circuit in a DC link. It is suggested by several handbooks that 20% of the half period should be used. However, in some applications, e.g. power supplies with extended input voltage variations, much smaller interlock delay time must be used to ensure correct operation of the inverter. In this paper the interlock delay time minimization possibility is analyzed on an example of an existing experimental device based on 6.5 kV IGBTs. Moreover, the possible impact of interlock delay time minimization on the isolated DC/DC converter components, operability and efficiency is evaluated.

Analysis of capacitor-related mid-voltage point shift problems in high-voltage half-bridge DC/DC converters

Half-bridge topology is an attractive topology for many power electronics applications. It is simple and more cost-effective than other topologies. The new high-voltage IGBTs on the market enlarge the possibilities and add to the attractiveness of that topology, in particular in high voltage applications. However, despite the overall design simplicity, the designer must guard against a number of problems with this type of a converter. A major problem is in the staircase saturation of the isolation transformer core. One of the possible reasons is the mid-voltage point shift, which can be caused by the input capacitor mismatch. This paper analyses in detail how input capacitors influence the voltage unbalance in a high voltage half-bridge converter. In this project polypropylene capacitors were used. Thus special attention will be paid to polypropylene capacitors. Through analysis the maximal possible asymmetry between the input capacitors can be estimated. From the asymmetry the resulting mid-voltage point shift will be calculated and finally verified with simulations and measurements.