Vol 88, No 6 (2017)

In modern technology, the protection of mechanical objects from vibrational effects is an important problem. The task of increasing the efficiency of a vibration–isolation system as applied to vehicles is discussed. Operator equations that describe the movement of a single-mass system for active vibration isolation with a controllable magnetorheological damper are presented. A mathematical model of a closed system with negative feedback with respect to the vibration acceleration of the protected object in the form of a block diagram is considered. A controller that provides a decrease in the vibration accelerations of the protected object within a certain frequency range to a preset level is created. The possibility of simplifying the controller without substantial losses in control quality is substantiated by comparing the dynamic characteristics of the system. On the basis of a computer simulation, the dynamic characteristics of the open- and closed-loop systems for a harmonic disturbance were investigated taking the mass of the vibroprotected object into account. The description of the developed experimental bench for investigating the dynamic characteristics of the vibration–isolation system is given. The frequency characteristics of the active vibration–isolation system were studied. Comparison of the calculated and experimental data testifies to the effectiveness of the developed models and the adopted assumptions. The possibility fundamentally improving the quality of a vibration–isolation system when using the created system is shown.

The method of selecting power semiconductor devices for group parallel connection on the basis of models developed on the basis of the measured electrical and thermal parameters and characteristics of certain devices are considered. Experimental data are obtained using the ADIP-6 test equipment. The electrical part of the model is constructed on the basis of the electrical parameters of the volt–ampere characteristic in a high-conductivity condition, and the thermal part is developed on the basis of the electrothermalanalogy method. The parameters of the thermal model are determined on the basis of the measured value of the thermal junction-to-case resistance in the steady-state thermal mode. The electrical and thermal parts of the model are connected through the temperature dependences of the volt–ampere characteristic parameters. A sample of ten power diodes is considered as an example, parallel connections consisting of two diodes are constructed of them, and the electrical and thermal processes are analyzed in this group using the simulation method for all possible combination of the diodes. The potentially reliable and unreliable diode combinations were specified on the basis of the simulation results. The temperature of the semiconductor structure is used as a criterion for determining reliability. A connection in which the temperature of the semiconductor structures of the devices included in the connection did not exceed the admissible limit value was considered as potentially reliable. Two connections, referred to as “potentially reliable” and “potentially unreliable” connections, are considered as an example.

The problem of eliminating rotor-position sensors in ac drives has been the focus of intense research for over two decades. Among the expected benefits of the solution to this problem are reduction of drive cost and size, as well as increased reliability. The methods developed for this purpose are usually called “methods of sensorless control.” It has been shown that sensorless-control methods for ac machines provide high efficiency at medium and high speeds. However, these methods are less efficient at lower speeds and control of the position at low and near-zero speeds is not possible. To overcome this limitation, methods of sensorless control based on the tracking the position of rotor asymmetries have been proposed. These methods measure the response of a machine to the high-frequency component of the excitation signal. One of the most attractive aspects of this method is the absence of limitations when operating at very low or near-zero speeds, which allows one to control the rotor position. This paper presents the results of theoretical and experimental studies of the method for determining inductances Ld and Lq in a synchronous reluctance machine (SynRM) using the injection of a high-frequency component into the stator voltage. This paper discusses the principles of this method and its application to the mathematical model of the SynRM and the M3AL 90LDA 4 engine produced by ABB Co. Determination of these parameters is necessary for the implementation of sensorless-motor-control systems.

The use of hydrogen energy sources is promising for the creation of ship electric-power systems. These sources have a number of significant advantages over conventional energy sources (diesel generators or turbine generators), such as the possibility to provide low-noise regimes of ship motion and creation of an airindependent shipboard power plant. Using hydrogen energy sources as components of electric-power systems along with conventional energy sources makes it possible to optimize the operation of diesel generators as regards minimum fuel consumption and provide a reserve of power. The article analyzes the structural variants of energy channels with hydrogen energy sources and current inverters providing parallel operation with diesel generators or turbine generators in ship ac electric-power plants. The problems of regulation and distribution of active and reactive powers between sources operating under a total load are considered. Comparative analysis of the generalized energy indicators and of the degree of distorting influence of energy channels with hydrogen energy sources on the voltage waveform of a ship electrical-power network in static operating modes is presented.

It is proposed to use a simple switched-reluctance electric machine that does not have windings or permanent magnets on a movable part to develop a linear reciprocating electric machine intended for use as an electric generator together with a free-piston internal-combustion engine. It is noted that one of the most difficult problems in the development of such a linear electric machine is the development of a control system. A sensorless control algorithm is considered. Information on the stator-phase inductance of the electric machine and its variation is used to determine the position of the movable part. For its estimation, probing voltage pulses of known duration are applied to the phase. The amplitude of the current pulses caused by them will be proportional to the phase inductance. A mathematical model of electromagnetic processes is used to test the efficiency of the proposed control algorithm and determine appropriate control parameters. Since stator phases have separate magnetic circuits and are not magnetically connected, the electromagnetic processes in each phase are considered independently. Model parameters are determined experimentally using an experimental prototype of the considered electric machine, for which the dependences of the phase flux linkage and the generated force on the phase current for different positions of the movable part are obtained. The results of the investigation of processes in the considered electric machine at different frequencies of the movable part are given. It is found that, at frequencies of the movable part close to the nominal frequency, the phase should be connected to the power supply even before the movable part reaches the extreme position. Control using probing pulses applied to the operating phase is impossible, because the level of these pulses does not reach the maximum value until the phase is switched on. In this case, it is necessary to use the probing pulses of another, nonoperating phase to determine the position of the movable part. Such an algorithm makes it possible to control a linear reciprocating switched-reluctance electric machine at both low and high frequencies of the movable part. The obtained results confirmed the correctness of the adopted approaches to the development of a sensorless control algorithm.

A significant number of low-oil circuit breakers are currently in operation. They are considered obsolete and inferior in their characteristics to more modern types of switches—vacuum and gas-insulated circuit breakers. When triggered, low-oil circuit breakers can serve as sources of considerable overvoltages, one of the causes of which is the current chopping that is connected with the arc-extinction mechanism in a dense environment. Current chopping usually occurs when small inductive currents are disconnected, for example, the no-load current of transformers and electric motors. When arc processes in circuit breakers are investigated, various methods are used, including adaptive ones (the “black box” method). This paper considers the possibility of using the arc model on the basis of the Mayr equation for studying the phenomena of current chopping and overvoltages that are generated by a low-oil circuit breaker. The features of constructing such a model are analyzed, and its structure, appearance, and description are presented. The model was constructed in the MATLAB software package. The case of the RLC-circuit disconnection from a source of a low-resistance EMF was considered taking the arc-extinction mechanism into account. This circuit simulated the switching off of an electric motor that was connected via a cable line. This article also presents s comparison of the experimental and calculated data.

Parallel operation of three-phase power transformers with different short-circuit voltages has been studied using a lab bench. The circuit diagram of the bench and experimentally measured vector diagrams of the currents in primary and secondary windings of the transformers have been presented. It has been found that, when the difference of short-circuit voltages of parallel operating transformers is more than 10%, both an arithmetic difference of currents and a great phase shift of secondary-phase voltages occur. As a result, one of the transformers becomes overloaded, while the other is underloaded. It has experimentally been found that the load current is determined by the geometrical sum of currents of secondary windings in transformers. It has been shown that one of the studied transformers works in the conversion mode and its currents are shifted by 180° with respect to the phase, which is the main reason for failure of the normal operational conditions of parallel transformers.