Ing. Tomáš Košťál, Ph.D.

This paper presents an assessment of Solid State Transformer (SST) topologies from the usability in energy applications point of view. SSTs are nowadays at the center of researchers’ attention mainly due to reducing size and weight of traction transformers in railway vehicles. Our contribution aims to use the SST as a cornerstone of an Energy Router that should replace a typical distribution substation with a classical transformer. After a general overview of SST topologies classification an overview of design guidelines for key SST components (ferrite cores for medium frequency (MF) transformers, semicon-ductors and high voltage capacitors) is presented for two topologies that seem to be promising for energy applications: classical three-stage SST and two-stage SST with a low voltage DC link and galvanic insulation in the first stage. These two topologies are then compared from an economical point of view based on acquisition cost of key components in order to evaluate whether the technology has matured to be used commercially.

This paper presents a new, computationally modest on-line identification method for the simultaneous estimation of the rotor resistance and magnetizing inductance of an induction machine suitable for electric drives that use an indirect field-oriented control strategy (IFOC), and their control hardware is equipped with a resource-constrained microcontroller. Such drives can be found both in the manufacturing industry and railway traction vehicles in the thousands, having either older control hardware that cannot cope with computationally excessive identification methods or being in cost-sensitive applications, thus being equipped with a low-cost microcontroller. IFOC is a very common control strategy for such drives due to its good dynamic properties and comparatively simple implementation. However, it is sensitive to inaccuracies of rotor resistance and magnetizing inductance. These two parameters change during the operation of the drive, being influenced by the temperature, frequency, and saturation of the magnetic circuit. Improper values of parameters in the controller can degrade the performance of IFOC, resulting in slower acceleration or unnecessary oversaturation of the machine. Respecting these changes can therefore bring significant benefits such as the good dynamic properties of the drive, which can shorten operations in the manufacturing industry or travel times of vehicles. A number of on-line identification methods for monitoring the parameter changes have been published so far, but the majority of them are demanding on microcontroller time or its memory. The proposed method, on the contrary, is comparatively simple and thus easy for implementation with low requirements to the microcontroller.

One of the main challenges of current electric grid not only in the Czech republic is the integration of an increasing number of small and often unpredictable power sources, especially renewable ones. Transition to so called smart grids which should be an answer to this problem includes almost all components of electrical grid. This means that in the future there will be also some smart replacement of a distribution transformer. A device called energy router contains a power part - so called solid state transformer (SST) which could be such a replacement of the distribution transformer. This paper presents how such a device could be carried out and how control of electric power in the SST could be performed.

MMC is popular converter topology due to benefits such as low harmonic content, absence of filter or low capacity of the capacitors needed, to be mentioned among others. This paper presents general workflow for calculating the optimal value of MMC submodule capacity. The analysis is done for basic harmonic component based on energy flow.

Induction machines are backbone of industrial drives with higher power as well as traction vehicles. The modern drive with induction machine is a complex system that needs to calculate the control algorithms in short time, perform the given task and communicate with its neighbourhood. The recent development in the field of control hardware brings the possible transition from drive specific microcontrollers to Systems on Chip (SoC) incorporating the Field Programmable Field Arrays (FPGA). This new flexibility and computational power that is offered by such systems can be used for improving dynamic properties and efficiency of the drive. This paper shows that such an improvement can be achieved with the help of parameter identification evaluated on a 15 kW particular induction machine.

This paper explains the term energy router with help of the similarity between the energy network and internet. Their main differences are discussed as well. Furteher, all main parts of energy router - power electronics module, communication module and intelligent network module - are described. The solution of the power electronics module (Solid State Transformer) is described in detail. The other part of the paper deals with the power flow control. The components of the intelligent network are introduced in the end of the paper.

This paper concerns a modular pulse width modulation (PWM) modulator that is suitable for polyphase multilevel inverters. The modulator is implemented in a field programmable gate array (FPGA) with a softcore microprocessor controlling it. Further it presents experiments with a five level flying capacitor multilevel inverter and the proposed modulator.

This paper describes a modular approach of the design and implementation to the Field Programmable Gate Array (FPGA) based modulator suitable for two or multilevel power inverters. Such a modulator can be used in various types of controllers of the electric drives or traction computers where FPGA or System on Chip (SoC) are used which is current trend in high performance electric drives. It describes the advantages of such a system and some basic facts about FPGAs and the obstacles connected with the digital implementation of PWM. Further it contemplates the cases when processor – FPGA tandem of the controller is realised with a soft-processor, with a hardware processor core on a SoC or with two discrete devices.

This paper concerns usage of an on-line parameter identification method for optimization of power consumption of fan drives with induction machines in air handling units (AHU) of heat, ventilation and air conditioning (HVAC) systems of buildings. Variable frequency drives (VFD) are nowadays a key manner for lowering the consumption of HVAC system in off-peak times. However their controllers don't respect the changes of machine parameters during the operation. Proposed method can enhance the control algorithm of VFD with induction machine to optimize its efficiency. Further it can be implemented also on existing installations as it uses only standard components of the drive.

Many buzzwords concerning the problematic of energy production and its effective (smart) utilization in industry as well as in households – like Smart Grid, Big Data, Industry 4.0, Energy Router, Green Energy etc. – are often used in many different meanings or even only for making one’s idea more attractive. Nevertheless, their definitions aren’t united or they don’t express the essence in their entirely. The aim of this paper isn’t to define some of the buzzwords; however, it tries to explain what is really a so called energy router and why is it spoken about in the context of existing and to the near future planned system of electrification in the central Europe. Some kinds of energy storage are integral to the modern grid. The short overview of energy storage devices is presented at the end. This text should make the understanding of the problematic in wider extent easier.

One of the key parts of the frequency converter that can influence its efficiency and other properties is the PWM generator. Sinusoidal PWM (SPWM) generators are widely used solution of their realization especially if a field programmable gate array (FPGA) is used instead of more traditional microcontrollers or digital signal processors (DSP). This paper deals with a comparison between two different attitudes to an SPWM modulator realization in FPGA – a static and a reconfigurable. It describes the SPWM principles and crucial problems and then present two solutions. Finally the selected solutions are compared based on total harmonic distortion (THD) and usage of FPGA resources.

Induction machines are nowadays used also in electric drives with high demands on dynamic properties. However their control strategies usually need a mathematical model of the machine with a set of parameters. Obtaining of these parameters can be done by laboratory procedures but in-field procedures are more favorable due to potential savings in time and financial costs. This paper proposes an off-line parameter identification method that is suitable for self-commissioning of an electric drive in cases when machine and converter comes from different producers. The method is carried out entirely by means of a standard power inverter only by impressed stator voltages.

Popular control strategies of the induction machines such as field oriented control (FOC) or direct torque control (DTC) can be characterized by usage of the mathematical model of the machine they control. For proper operation of these methods, certain parameters of the model have to be obtained with suitable accuracy. However, the machine parameters change also during its operation. Deployment of the incorrect parameters can lead to lowering of the control performance. Rotor resistance of the machine has been identified as a one of the crucial parameters with a significant influence. This article concerns the influence of the rotor resistance in a manner of simulation and how it changes with the respect to temperature.

Precise control methods of the electric drives with induction machines like field oriented control (FOC) or direct torque control (DTC) need an accurate model of the machine the control. Certain parameters of the model have to be obtained with sufficient accuracy before the drive can be put into operation. This article concerns an offline parameter identification method that is suitable for on-site drive commissioning as it does all the necessary measurements only with the means of the power converter of the drive.

This paper concerns the influence of the incorrect parameter values of the mathematical model of the induction machine to power consumption of the electric drive in case of Filed Oriented Control (FOC). With the exception of stator resistance parameters for the model are not directly measurable and their values can change during the operation of the drive. One of the representations of mathematical model is presented and the influence of the wrong value of the rotor resistance is shown. Methods of obtaining the parameters are summarized and their benefits are presented compared to traditional laboratory tests. Online parameter identification methods are promising to allow the controller of the drive to respect the rotor resistance change and thus lower the power consumption of the drive.

Field oriented control (FOC) became nowadays probably the most popular control method of electric drives with induction machines. For it's proper operation, knowledge of certain machine parameters is needed, otherwise the performance of the control can be significantly lowered. Thus there is a demand for methods of parameter identification methods that can observe required parameters of the machine before the start of the drive. This article concerns an offline parameter identification method that is suitable for on-site drive commissioning, that is nowadays very often needed, as drives and converter may come from different producers. This method does not need any special equipment so it could be realized in industrial applications with no additional cost.

This paper carries out analysis of possible switching processes for voltage balancing of flying capacitors of the flying capacitor multilevel inverter. After short description of the FCMI principle, state diagrams and two stage modulation algorithm for generating the switching pulses are explained. Then a theoretical analysis of switching with 1C, 2C and 3C transitions is given with its effect to voltage balancing of flying capacitors. Conclusions of this analysis are then confirmed with measurements made on a laboratory model of five-level flying capacitor multilevel inverter.

Paper concerns verification of some of the models used for signal propagation in urban areas. After introduction, which briefly covers the historical evolution of mobile communication, it shortly describes Okumura - Hata, Ikegami and COST231 – Walfish prediction models in urban areas and their usage. Furthermore it deals with problematics of practical measurements with a hand-held device and suitable applications for this purpose. Finally it presents a comparison of measurement at 900 MHz and model prediction for Dejvice district of Prague.

Demand for environmentally friendly production of electricity lead to an unprecedented growth of usage of renewable power sources in recent years. Specific properties of some of these are that they produce DC voltage or voltage with a variable frequency. These types of sources are nowadays connected to grid via static semiconductor converters, which have some drawbacks. Among the largest of them is considered the generation of harmonics. Usage of multilevel inverters can improve this issue significantly. Among the other benefits of their usage could be found the possibility of grid connection without transformers. A multilevel converter can be used as an active filter in systems with renewables as well and its advantages could be used for long distance DC transmissions (HVDC) between large renewable power sources and centers as well.

This article concerns the application of an FPGA with a softcore processor system as a modulator for three-level flying capacitor inverter. It describes the advantages of such a system and some basic facts about FPGAs and the obstacles connected with the digital implementation of PWM modulator compared to the analog one. Furthermore it deals with individual blocks of the modulator structure and presents also the possibility of creating the user interface with classic PC monitor and keyboard within the same FPGA chip. Finally, it presents the the verification of the functionality of such a converter.

On 16 March 2011 M. Efmertová and O. Starý, vice-dean of FEE CTU in Prague have written a letter to George J. Klír (USA)1 containing an offer, that Laboratory for History of Electrotechnics (LHE), established by them the same year, could take over the Archive of Antonín Svoboda (1907-1908)2 and other documents, that have been collected and organized by G. J. Klír. This offer has been accepted, which contributed to successful establishment of Archive of A. Svoboda under LHE. Nowadays materials gathered for the archive are being assorted, labelled, organized and digitized. These operations are carried out by M. Efmertová and J.Mikeš with participation of students under LHE SOS practical training and students of History of science and technology seminar.

This paper deals with historical evolution of power electronic devices and converters from the very first beginnings of the mercury-arc rectifiers to the multilevel converters as the most recent technology. Various devices used for converters are described, both vacuum and semiconductor. Paper mentions not only historical dates and periods but also parameters and properties specific for the devices as well as their applications.

This paper aims to summarize the development of the devices with the rectifying properties and devices usable for power converters. Except the history, there are described also the parameters and their specific properties, these properties are also discussed from the time point of view. Further, the semiconductor converters are mentioned. The historical overview is focused on the multilevel converters in more details because the multilevel converters belong to very progressive converters topologies nowadays and they are the only one suitable for high power applications.

This article concerns practical problems with realization of the rotation speed control system of a DC motor with a microcontroller and a four-quadrant converter. It describes the obstacles in precise signal generating, speed measurement and control loop tuning. Every section discusses several possibilities of carrying out the task and concludes with the most suitable solution. Practical examples are given for PIC18F452 microcontroller, but most of the facts described in this article can be applied also on plenty of other devices. The main point of this article is to show, that even for a microcontroller, which seems to have comparatively many resources, its ultimate limitations can be easily reached even within a relatively uncomplicated task.