Adam Gozdowiak, Piotr Kisielewski and Ludwik Antal
The computation of accidental energizing of an off-line turbogenerator has been conducted. Inadvertent energizing of a turbogenerator has become a particular issue in a power plant. The investigated case is three phase energizing. Great emphasis is placed on physical phenomena occurring in the rotor. The results of computations allow one to indicate the risks of damages of construction elements and can confirm the limits of the values set in dedicated protection devices.
Krzysztof Dmitruk, Marek Korzeniewski and Andrzej Sikorski
Frequency based methods developed to detect an islanding condition in modern power grid structures have been discussed. The condition may occur in power grid lines to which additional energy sources with power electronic converters have been connected such as solar panels or wind turbines. It is a hazardous operating state for grid workers and devices connected to the islanded part of the grid. Such a state results from the inability to control amplitude and frequency of basic harmonic of the grid voltage. An islanding problem in a power grid with additional small energy sources has been discussed. A basic passive and active islanding detection method have been presented and compared with known frequency based algorithms, namely active frequency drift and active frequency drift with a positive feedback algorithm. Finally, a laboratory test of the proposed islanding detection methods in a three- -phase grid with an AC-DC converter has been conducted. To demonstrate differences between the tested methods, total harmonic distortion injected into the output converter current and detection time of islanding state have been measured.
Application of a state space controller for two-mass system has been examined. However, the classical version of the controller was modified in order to improve properties of the whole system. For this purpose fuzzy model was implemented as an adaptation element for the parameters. The theoretical description of the control structure, numerical tests and experimental results (using dSPACE1103 card) have been presented.
The parametric-active compensation of earth leakage currents which minimalized virtual capacitance current in ships of IT-type network has been discussed. The protection is based on automatic compensation of leakage earth currents. The protection system is governed by a controller. The results of simulation tests have been presented. The parametric-active compensation of earth leakage currents which minimalized virtual capacitance current in ships with IT-type network has been discussed.
Ludwik Zając, Mariusz Malinowski, Sebastian Styński and Marek Jasiński
A new high instantaneous power impulse converter (HIPIC) with a switched capacitor unit has been presented. HIPIC generates very short impulses (hundreds of microseconds) of instantaneous power in megawatt range while the average power is much lower (tens of kilowatts). The presented topology is composed of step-down converters, an H-bridge converter and a switched capacitor, adjusted with a new current control. It allows one to achieve the output current impulses with very short rising and falling times and strict peak current control with low ripples.
Jan Vittek, Lukas Gorel, Vladimir Vavrus and Lubos Struharnansky
Position tracking systems for AC drives offering high robustness to external load torques have been presented. A triple-loop cascade control structure was employed where the inner loop is a stator current control loop and the middle loop is a speed control loop based on the forced dynamic control and respecting vector control principles. Two alternative outer position control loop designs both of which respect prescribed dynamics and settling time of position have been developed. The former system prescribes also time constant of the speed control loop while the latter one respects time constant of speed control system developed independently. To enhance the tracking abilities of both control systems the dynamic lag pre-compensator has been included. Case studies of the both position control systems for time near-optimal control and energy near-optimal control have been presented. The tracking performances of the designed control systems were assessed based on comparisons of the experimental responses with the simulated responses of the ideal closed-loop system.
Measuring instruments, measurement methods, and an exemplary analysis of the impact of chosen operating stages of the converter drive on the power supply network have been presented. The measurements of electrical and mechanical parameters in drive systems used in industry are complex. The task is difficult due to the necessity of connecting a measuring instrument into electric circuits of an active facility with the use of only short non-operational periods of the device. However, a well-chosen model of a drive system allows the multivariate research of the impact of drive parameters and a control algorithm used on voltage and current harmonic content and performance of the system, and therefore on a simulation analysis of the impact of the drive on the power supply network.
The compensation and detection analysis of rotor faults in a sensorless induction motor drive system with an additional rotor resistance estimator has been conducted and the influence of the rotor faults on the properties of such system has been examined. The rotor flux vector and rotor speed have been reconstructed by the MRASCC estimator. The drive was tested for various conditions. Simulation tests were performed in the direct field oriented control (DFOC) structure realized in the MATLAB/Simulink software.
An equivalent sliding mode control method of an induction motor speed has been discussed. The control signal consists of two parts: a continuous and discontinuous one. Very good dynamical response of the drive system has been obtained, which however changes influenced by external and parametric disturbances occurring under various operation conditions. In order to ensure identical dynamic performance of the speed transients and system robustness during the switching line reaching phase, regardless of external and parametric disturbances, the time-varying switching line is proposed. The simulation results have been validated by experimental tests of the induction motor drive system.
Andrzej Gałecki, Lech Grzesiak, Barłomiej Ufnalski, Arkadiusz Kaszewski and Marek Michalczuk
The paper presents a linear-quadratic current controller with damped oscillatory terms designed for three-phase grid-tie voltage source converters used in SMES systems and operated under distorted grid voltage conditions. Special emphasis is placed on a synthesis of an anti-windup mechanism to prevent wind-up derived from the oscillatory terms by the use of a new active damping loop based on a simple moving average method. As a consequence, the current feedback gain may be increased without unwanted overshoot and overruns, and performance of the system can be improved.