Ing. Miroslav Lev

This paper deals with the parameter identification of induction machine rotor and stator windings. These two magnetically coupled circuits are described and analyzed to explain the novel method that can identify the set of substitute parameters (not equivalent circuit parameters) which can be used for some analysis of transient processes in a stationary induction machine. The parameters are: inductive leakage factor, substitute rotor resistance, substitute rotor inductance, and substitute mutual inductance. The method belongs to the group of so-called off-line methods, i.e., it is performed on a machine in a standstill, and it assumes a star-connected induction motor. The correctness of the method is verified by calculation as well as by measurement. Moreover, the practical use of the method is shown in an example of how to determine the rotor winding temperature rise, and the results of the measurement on an induction motor with a power of 0.75 kW are presented. The method can be performed even when the rotor circuit is hidden inside the completely closed rotor construction, as in the case of a squirrel cage induction motor, i.e., without access to the rotor circuit.

Self reactance Xd in direct axis ’d’ and self reaktance Xq in quadrature axis ’q’ influence the load characteristics of the permanent magnet machine. Their calculation methods are known. All calculations should be verified by measurements. Measurement with AC variable voltage and frequency source applied on stator winding is correct when eddy currents do not exist. Other methods evaluate the DC current decay after initial direct current was applied on the stator winding. Accuracy of these methods is lowered because of the numerical evaluation of current decay curve. Another method performs the measurement on the machine loaded as a motor. The load angle  is measured by a machine set of four machines. The accuracy is lowered by higher harmonics induced in no load in the helping synchronous machine. The load angle can be also obtained by geometrical construction of the vector diagram. In this paper the evaluation of the generator steady state regime of the machine is used. The generator works with different loads consisting of capacitance, inductance or arbitrary impedance or resistance. When the generator transfers from no load to load regime the rotor is shifting and the load angle changes. This angle is measured. The newly proposed measurement methods are simple in special cases of loads. Results of measurements and their experimental verification are published in the paper.

Tento příspěvek podává podrobnější informaci o konkrétním hledání příčiny závady na spínacím přístroji, při kterém byla na katedře Elektrických pohonů a trakce Elektrotechnické fakulty ČVUT v Praze využita moderní metoda počítačové tomografie. Na závěr příspěvku je stručné seznámení s historií této metody.

This paper presents simulation and implementation of DC-DC converter. The converter is connected to a photovoltaic panel. The converter is intended for implementation of various Maximum Power Point Trackers (MPPT). There are described converters and used MPPT in this paper too. Input voltage of the converter is tens of volts and maximal input power is 200 W. This power corresponds to power of a photovoltaic panel. The converter was designed to be connected to an inverter. The inverter input voltage must be more than 400 V because it is connected to single-phase grid without using transformer. This voltage is produced by the DC-DC converter.

Switching of 3-phase inductive load produced current transient phenomena which are dangerous from the point of view of circuit protection. Amplitude of current in each phase conductor depends on the switching moment and actual mains voltage value. Minimisation of load current surge is possible by means of phase sequentional switching.

Switching of 3-phase inductive load produced current transient phenomena which are dangerous from the point of view of circuit protection. The aim is to present mathematical and physical model of synchronized switch, which enables to minimize current non-symmetry and current surge during load making operation. Obtained results are used for semiconductor switch control unit design. Simulations and experimental results are presented.

System "dSpace" application scope for drive control or diagnostics algorithm design and for electric machine simulation is presented in the paper

The paper deals with the problem switching of induction three phase load by means of electronic switch with mains inrush current surge depresion.

Operation principle of air-cored tubular linear induction motor is described in the paper. System of fundamental equations and its solution were derived. Mathematical model in software system MATLAB were developped for three-phase stator winding with 96 solenoidal coils. Rotor winding is created by the one short-circuit turn (tube).

Operatin mode of linear induction motor with cylindrical winding is described in the paper. Fundamental equation system and its solution were derived. Mathematical model was based on analytical design methods of self- and mutual inductances and their derivates in dependence on the rotor position. Speed- and acceleration courses in dependence on the rotor winding coil position are the solution result of the machine motion equation. Machine model was build for three-phase stator winding having 96 coils and for the rotor created by one short-circuit coil, in software cross-products MATLAB.

Each switching of 3-phase load with current transient phenomena is accompanied. Amplitude of current in each phase conductor related to switching moment and actual mains voltage value. Minimization of load current surge is possible by means of phase sequentional switching. The aim is to present mathematical and physical model of synchronized switch, which enable to minimize current non-symmetry and current surge during load making operation. Achieved results are presented.

Switching of induction three phase machine is connected with transient current peak. This peak depends a little on switching time. The transient current peak can be reduced by sequential terminals switching. The paper simulates transient current peaks using a mathematical model. In the experimental part of the paper the experiments are described and oscillograms are published.

Spínání třífázové induktivní zátěže je spojeno s proudovým přechodným dějem. Velikost přechodného děje závisí na okamžiku sepnutí zátěže ve vztahu k okamžitým hodnotám napětí v jednotlivých fázích napájecího napětí. Minimalizace proudového nárazu během přechodného děje lze dosáhnout sekvenčním spínáním jednotlivých svorek zátěže. Předmětem příspěvku je matematické modelování přechodných dějů a experimentální ověření výsledků matematického modelování na polovodičovém spínači, umožňujícím sekvenční spínání zátěže.

Článek pojednává o spínaných zdrojích a integraci tohoto tématu do výukových kurzů. Studenti se mohou dozvědět o výkonových měničích včetně jejich návrhu.

Příspěvek pojednává o pohonech používaných v současnosti u výtahové techniky a o pohonech nově zaváděných do výtahové techniky.