Vaclav Kus

The education of EMC -the strategy and teaching overview at the UWB

This contribution introduces the education of EMC at the University of West Bohemia in Pilsen (UWB). The phenomenon of Electromagnetic compatibility (EMC) has been taken into account almost at all faculties of electrical engineering in the Czech Republic. However there often are only partial mentions of EMC in frame of individual electrical engineering subjects and the education is focused on the one specific EMC area. At the Faculty of Electrical Engineering at the UWB we have paid attention to these questions in several special subjects in the bachelor and master studying programs. In this paper the education system of the Faculty of Electrical Engineering has been presented. The main attention has been given to the low frequency interference of power electronic converters.

Current harmonics of voltage-source active rectifier with random switching frequency

This paper presents the issue of current harmonics drawn from the grid by three-phase voltage-source active rectifiers when the switching frequency of the devices is random; it is not an integer multiple of the supply frequency (50 Hz). The first part compares the harmonic analysis calculations derived for the piecewise linearized simplified current waveform and the simulations in the random frequency case. The second part presents a comparison of the current harmonic analysis when the switching frequency is the integer multiple of the supply frequency and when it is not. The second part also shows a dependence of the current spectrums on the random switching frequencies. This paper verifies, that the same conclusions of the previous publications apply to both the switching frequency that is the integer multiple of the supply frequency and the random switching frequency.

Analysis of current drawn by the voltage-source active rectifier from the electricity network

This paper deals with analysis of the current drawn from the grid by the voltage-source active rectifier. These converters are designed and controlled so that the current drawn from the grid approaches sine wave and power factor approaches one. Analytical calculations of harmonic analysis of this current based on the Fourier series are performed on a simplified model. These analytical calculations of the simplified model are compared with simulations. It is proved that even when the simplified model is used; the results of the analytical calculations differ very little from simulations. Little effect of active rectifier load on the absolute values of the current harmonics is proved in this paper. Absence of characteristic harmonics produced by diode rectifier in the spectrum of the current and the effect of the switching frequency for the presence of new harmonic current are shown in simulations.

The torque ripple reduction at the drive with the switched reluctance motor

The torque ripple has an adverse impact on the life of the machine and other drive components (especially bearings, gearboxes, couplings, etc.) and also produces an unpleasant acoustic noise. The reduction of the torque ripple can be solved in several ways - to select different configurations of SRM (to increase the number of phases or use the machine with higher number of steps), a suitable choice of commutation angles (so that they mutually overlap) or minimize the torque ripple by torque regulator or by direct torque control. This paper summarizes the practical results.

Effect of dead times on the values of input current harmonics drawn from the grid by a voltage-source active rectifier

This paper presents an effect of dead times on values of an input current harmonics drawn from an electric grid by a voltage-source active rectifier. The first part shows a derivation of the effect on one pulse of the voltage and then the values of the current harmonics are derived. The main section discusses a description of voltage with the pulse width modulation with respect to the dead time. A voltage waveform at the input terminals of the inverter, its harmonic analysis, and calculations of the current harmonics values are derived. The last part shows simulations and comparison of the harmonic analysis of the current with and without dead times.

Simulation and measurement of angular vibration of induction machine via Hilbert transformation

This paper describes the utilization of the Hilbert transformation for the angular vibration measurement of an induction machine. When we use a very common incremental rotary encoder as a speed sensor, it is necessary to process very high frequencies. In this case, the Hilbert transformation is useful. In this paper, the background of the Hilbert transformation, the angular vibration simulation and the verification measurement are described.

DC link voltage ripple of voltage-source active rectifiers

The paper deals with the DC link voltage ripple of voltage-source active rectifiers switched by PWM. The DC link voltage is maintained constant by a converter control; it fluctuates around the desired value. Therefore the first part of the paper describes the influence of voltage-source active rectifier parameters on the DC link voltage ripple. The effects of capacitors, loads and switching frequencies on the DC link voltage ripple are investigated. Also the paper discusses the influence of the DC link voltage ripple on current harmonics drawn from the grid by voltage source active rectifiers. The harmonics in the input current spectrum appear around the switching frequency. The last section analyzes the deviations of the current harmonics caused by the DC link voltage ripple.

Influence of a dead time duration on the input current spectrum of voltage-source active rectifiers

The paper discusses the influence of a dead time duration on the input current spectrum of voltage-source active rectifiers. The main body shows the simulations of a three-phase voltage-source active rectifier with respects to the dead times. This section especially describes the figures which present the harmonics analysis of the input current and its dependence on the dead time duration. The last part of the paper discusses the Total harmonic distortion of the current and effect of the dead times on this comprehensive indicator of the distortion. The higher dead time duration causes additional harmonics and it mainly affects odd harmonics.

Ensuring the operation of electrical equipment during short-time voltage sags or power outage

This paper describes the situation of a modern electric drive (induction machine supplied from indirect frequency converter with voltage source inverter) in industry (paper mills, etc.), where a voltage sag can bring significant problems with long-time interruption of the production process. One method of operation is a direct increase of voltage in the DC-link of a frequency converter with a step-up converter during voltage sag. A transistor designed for braking is often used. It is used often present transistor designed for braking. The article presents the waveforms of voltages and currents in the circuit of an indirect frequency converter in the case of voltage sags without the intervention of a step-up converter. Then it presents waveforms with the use of a boost converter and its various control options.

The electric drive with indirect frequency converter and asynchronous motors with improved immunity against the supply voltage dips

This paper solves problematic of immunity against the voltage dips, of the power supply of the electric drive with induction motor supplied from the indirect frequency converter. There are demonstrated the several variants of adaptation of power circuits for achieving a higher immunity against the voltage dips of the power supply. First variant is using of the additional converter in DC-link. Second variant is using of the additional input converter. Third variant is using of active rectifier in place of common used non-controlled rectifier. The paper shows the results of measurement of first variant on laboratory.