Communications - Scientific Letters of the University of Zilina, 1999 (vol. 1), issue 3
Articles
Determination of Induction Motor Efficiency Using Non-Linear Programming
Ladislav Janoušek, Valéria Hrabovcová
Communications - Scientific Letters of the University of Zilina 1999, 1(3):4-12 | DOI: 10.26552/com.C.1999.3.4-12 
This paper deals with determination of induction motor efficiency, as one of the qualitative indexes of machine operation, by means of acalculation and measurement during its operation. The possibilities of the efficiency calculation are described and it is explained that the simplest method for the efficiency determination is a calculation from a steady state equivalent circuit of the machine. This method is improved by an optimization of the induction machine equivalent circuit parameters based on the measured quantities during steady state operation of the machine. Optimization utilises non-linear programming.
Sensorless control of synchronous motor drive with forced dynamics
Ján Vittek, Slavomír Seman, Daniel Vaňko
Communications - Scientific Letters of the University of Zilina 1999, 1(3):13-22 | DOI: 10.26552/com.C.1999.3.13-22
Acontrol method for electric drives employing synchronous motors with forced closed-loop dynamics is presented. The prescribed response to the reference speed demand can be chosen as direct acceleration control, linear first order and second order speed response. In addition to this, the angle between the stator current and magnetic flux vectors can be mutually maintained perpendicular. The drive control system also contains a set of two observers for estimation of rotor speed and the load torque. The experimental results obtained for direct acceleration, first order dynamic and second order dynamic indicate good agreement with the theoretical. The...
Mathematical model of two parallel synchronous motors supplied from current type frequency converter
Byambaa Sergelen, Jiří Pavelka, Petr Tušla
Communications - Scientific Letters of the University of Zilina 1999, 1(3):23-28 | DOI: 10.26552/com.C.1999.3.23-28
The contribution describes the mathematical model of electrical drive composed of two parallel synchronous motors. Besides the equations there is mentioned block scheme in MATLAB and simulation results of the starting of two synchronous motors supplied from network. The next stage of research work will be to create the mathematical model of synchronous motors supplied from one current type frequency converter.
Ciphering systems based on the error - correcting coding techniques
Mária Franeková, Peter Nagy
Communications - Scientific Letters of the University of Zilina 1999, 1(3):29-34 | DOI: 10.26552/com.C.1999.3.29-34
This paper remarks on the possibility of the ciphering algorithm use based on the standard encoding techniques from the linear error - correcting coding area. The quality of deciphering algorithms is determined for (n, k) Hamming codes and the valid code word lengths are recommended for practical use. The presented principle can be generalised for another type of the algebraic codes.
NFO speed control of induction motor without using shaft encoder
Petr Kadaník
Communications - Scientific Letters of the University of Zilina 1999, 1(3):35-40 | DOI: 10.26552/com.C.1999.3.35-40
This article focuses on the design and analysis of a speed-sensorless vector control of induction motor based upon a Natural Field Orientation (NFO). This method allows high-dynamic vector control of PWM VSI fed induction motor. The main merit of NFO is given by no requirement on any speed or position sensor. The presence of a tacho-generator or optical shaft encoder is commonly undesirable. These transducers significantly increase the costs and reduce the reliability and robustness of the overall system. The NFO method doesn't employ computationally extensive algorithms such as Model Reference Adaptive System or methods based on Kalman filter. Simulation...
Contribution to solution of pressure losses of heat exchanger
Blanka Paulinyová, Daniela Zvarková, Marián Mikulík
Communications - Scientific Letters of the University of Zilina 1999, 1(3):41-48 | DOI: 10.26552/com.C.1999.3.41-48
This paper tells deals withe the calculation of pressure losses of heat exchangers and its individual parts. Local and length pressure losses in circular sections and also sections of different shape are dealt with. There are different alternatives of tubular heat exchangers connection. Liquid and gaseous heat carrying agents and various coolants can be used. It is possible to dimension pumps or ventilators by this calculation. Operation and investing charges also depend on that.
The measurement of close hydrostatik circuit by LabView
Peter Kriššák, Igor Strážovec, Jozef Božek
Communications - Scientific Letters of the University of Zilina 1999, 1(3):49-55 | DOI: 10.26552/com.C.1999.3.49-55
In most cases, the personal computer (PC) can emulate traditional measurement and automation control instruments in industry, no matter which departments use it. The PC's extensive capabilities enable to create personalized, flexible systems with more possible implementations than traditional tools. Once a system is created, it is easy to change it for different applications without buying new equipment. In this paper, a computer based measurement system of close hydrostatic circuit and its static and dynamic characteristics acquired by application of LabView graphical programming software is presented.
Cash lfow analysis of river cargo ship projected for possibility of pushing towage
Jana Novomeská, Peter Patek
Communications - Scientific Letters of the University of Zilina 1999, 1(3):56-65 | DOI: 10.26552/com.C.1999.3.56-65
This work deals with river cargo ship analysis of effectiveness relating to technical parameters of single navigation and in configuration with barges DE. Input comes from the propulsion conception for reachable speeds for ACF of the ship analysis during the ordering for a specific relation. Evaluated are results of rate of turnover and final ACF of the vessel, as well as analyses of a group of vessels by specific freight rates independent of the building price of the ship.