Vol 87, No 1 (2016)

A mathematical model of a two-loop control system of a dc drive with a control unit realized on the basis of the widely used P and PI controllers was obtained. The optimized parameters of the system are the gain coefficients of the current and speed closed loops and coefficients of the integral components of the corresponding controllers. Two variants of optimization of the system structure and parameters are considered: (1) standard consecutive adjustment of the current and speed loops to the modulus optimum, which leads to a static control system with a P speed controller and a PI current controller; and (2) system adjustment to the modulus optimum as a united whole, which leads to an astatic system with a PI speed controller and a P current controller or without a current controller with proportional current feedback to the power converter input. The formulas for optimal values of adjustable parameters for both variants are obtained. It was shown for instance by simulation in Matlab–Simulink that the system adjusted in accordance with the second variant has better performance indices, such as offset, transient time, and overshooting at a changing set point and disturbance variable.

This paper outlines the effect of the switching frequency and the conducting relative duration of a power switch in an impulse convertor on the level of conductive emission by a feed circuit in a frequency range of from 0.15 to 30 MHz. Expansion was performed of the rectangular impulse at frequencies of 50 and 100 kHz in the Fourier series in an LTSpice simulated system. The results of this research allow us to determine the ability to reduce the level of the conductive emission using a lower switching frequency of the power switch. These results are confirmed by full-scale experiments. These experiments are based on imitation of the output block of the impulse convertor. Means of measurement were used that are restricted by GOST (State Standard) to large-scale experiments. It is shown that (1) it is necessary to choose the switching frequency, not only using gross geometry minimization of the device, skin effect, and magnetization reversal of the coil and transformer core, but taking into account of allowable emission level as well, and (2) it is necessary (in the case of nominal power) to provide an open state relative impulse duration close to 50% in the switching PWM convertor.

The double-ended travelling wave method of determination of location of a fault in electrical networks has significant errors due to changes in the propagation velocity of electromagnetic waves. We have developed a travelling wave method of improving the accuracy of location of a fault determination in power transmission lines that is based on navigation algorithms. The method is applicable to lines with branches. The distance to fault determination for the developed method is up to twice as accurate as the double-ended travelling wave location of a fault method. The accuracy of the developed method is less influenced by external factors (change of sag, soil resistance, the instantaneous value of the current at the fault time) than is the accuracy of the double-ended travelling wave location of a fault method. The proposed method allows reducing the errors in determining distance to the location of a fault, and its accuracy is less affected by external factors. The developed method can be incorporated into existing and prospective devices based on travelling wave methods of location of a fault determination.

To obtain the current pulses applied to the active load, the circuit breaking effect has been used in the primary winding of the pulse transformer. When the direct current voltage source is disconnected, the current of primary winding is reduced to zero, so that a current pulse is formed in the secondary winding of the pulse transformer that is transmitted into the load. A circuit of the inductive pulse generator operating on the basis of generalized switching laws was developed so as to increase the amplitude of current pulses in the active load and the corresponding power. The circuit contains a pulse transformer, the secondary winding of the pulse transformer is connected to the load, and an additional inductor is connected parallel to the primary winding of the pulse transformer. When the direct current voltage source is disconnected, the current of primary winding passes through zero and decreases to a negative value, which leads to a significant increase in the current pulse in the load. In accordance with the generalized law of commutation, the relationships for the calculation of the current jump of pulse transformer primary winding and a jump in the load current have been obtained. Using the state-space technique, mathematical models of the circuits mentioned above with linear active load have been developed. Theoretical and experimental studies have shown a significant increase in the current pulse value and its capacity in the active linear load when the inductive pulse generator has been used. The values of currents in inductive coils detected experimentally were practically the same as the calculated values.

A magnetogasdynamic model of a welding arc is presented. Numerical implementation of a model within the limits of an axisymmetrical task is constructed in the COMSOL Multiphysics program–computer system. The obtained results agree well with experimental data.

Methods to calculate the thermal processes and temperature of the most heated points of the tank and windings of a power transformer in conditions of flow of geomagnetically induced currents in grounded windings are developed. Dependences of additional loss in the tank and windings are obtained for a TRDN-63000/115/6.3/6.3 power transformer. It is shown that additional losses in power transformer windings are caused by the geomagnetically induced currents and depend on the first and nth harmonic components of magnetizing current, as well as on the load factor of a power transformer. The dependences of excess temperature of the most heated points of windings over ambient temperature on the geomagnetically induced current and load factor are determined. It is found that the excess temperature of the most heated point of winding over ambient temperature is also affected by the total additional loss of active power in the tank caused by the eddy currents at a geomagnetic storm. The acceptable load capacity of power transformers in geomagnetic storms with different intensities is determined in dependence on the ambient temperature. An increase in the load capacity of power transformers above set values in geomagnetic storms can lead to overheating of transformer windings and triggering of transformer gas protection, which will cause an electric power system to malfunction.