Voltage Asymmetry Research Articles

Solar‐powered switched reluctance motor‐driven water pumping system with battery support

This work deals with the development of an efficient and reliable solar photovoltaic-fed water pump with a battery energy storage (BES). This system ensures a continuous and rated supply of water in all working conditions. A new control logic for BES is developed, which significantly improves the overall response of the system. The support of the battery as a backup source is obtained through a bidirectional DC-DC converter. Both the charging/discharging control and maximum power tracking of the solar panel are achieved through this bidirectional converter, whereas the voltage asymmetry compensation across split capacitors at DC link and motor drive controls are supervised by switched reluctance motor converter. The performance of the present scheme is examined through both simulated and experimental responses and is found adequate under all operational scenarios.

The use of energy routers to improve reliability of power supply to non-traction consumers

The purpose of the studies presented in the article was to determine the effectiveness of the use of energy routers (ER) in railway power supply systems to increase the uninterrupted power supply to non-traction consumers, reduce unbalance and nonsinusoidality, and reduce voltage dips in emergency modes. The research was carried out by means of computer modeling using the Matlab software system based on the developed models of power supply systems (PSS) equipped with ER with energy storage devices. The results obtained show that in standard circuits of PSS for linear consumers with short circuits in the supply network, voltage dips occur, the depth of which reaches 100%. The use of an ER and an energy storage device connected to DC buses allows maintaining voltage at consumer clamps near the nominal value in case of short circuits in the 10 kV feed line and 25 kV overhead contact system. The ER significantly limits the recharge of the short circuit location from the power storage. In addition, on the basis of the ER it is possible to provide the normative quality of electricity considering voltage deviations, asymmetry and harmonic distortions on the 0.4 kV buses of the substation that feeds non-traction consumers.

The most common violations of regulatory indicators of the quality of electric energy in electric networks

Work on ensuring the quality of electric energy in accordance with the requirements of GOST 32144-2013 is currently relevant and requires prompt and high-quality solutions. The article lists the main consumers of electric energy that negatively affect its quality, provides the results of measurements of electric energy quality indicators and the most common violations of regulatory requirements, analyzes the influence of voltage asymmetry on the operating conditions of electrical equipment. The basic formulas for calculating the asymmetry coefficients and ways to reduce the voltage asymmetry are proposed.

ТЕПЛОВА МОДЕЛЬ СИСТЕМИ «АСИНХРОННИЙ ГЕНЕРАТОР–АСИНХРОННИЙ ДВИГУН» ПРИ НЕСИМЕТРІЇ В ОБМОТКАХ СТАТОРА

Purpose. Development of the IG model for estimation of influence of variations of parameters of the generator on quality of process of self–excitation at definition of the basic and boundary operating modes and system of initial excitation at invariable parameters of the generator. Result. The article presents studies of the system "asynchronous generator-asynchronous motor" with parametric asymmetry to determine the quality of generated electricity in load modes of operation on a mathematical model. The assessment of the thermal state in steady-state conditions was carried out using an equivalent thermal equivalent circuit. Thermal transients were investigated when starting an asynchronous electric motor from an autonomous power source based on an asynchronous generator. On a thermal mathematical model, a study of the influence of the asymmetry of the output voltage and its deviation from the nominal value on the heating of the connected asynchronous motor was carried out. A regression model has been developed for studying the operating conditions of electricity consumers when powered by an asynchronous generator with an asymmetry of the stator windings. Practical value. The use of the obtained equations will make it possible to determine the most rational combination of factors affecting the heating of the stator windings of asynchronous machines, at which they will not overheat in excess of the maximum permissible temperature values of the corresponding insulation classes. Figures 9, tables 2, references 23.

Учёт несинусоидального/несимметричного режима работы электрической сети коммунально-бытового назначения при расчете уровня тока нулевого проводника

During the operation of 0.4 kV electric networks, asymmetry of currents and voltages is unavoidable. As is known, unbalanced operation of 0.4 kV networks is stemming from nonuniform distribution of loads between the phases. This results in that a fundamental frequency zero-sequence current will flow through the neutral conductor in a four-wire three-phase electric network. On the other hand, during balanced operation of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic, higher harmonic currents multiple to three are summed in the neutral conductor. Therefore, it is of relevance to analyze unbalanced operating conditions of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic. The article presents the characteristics of a municipal load for analyzing unbalanced/nonsinusoidal conditions of its operation. For carrying out full-valued assessment of unbalanced operating conditions of a four-wire electric network, a simulation model of a 0.4 kV network section containing a nonsinusoidal load is developed. It is shown that during unbalanced operation of an electric network containing electric loads with a nonlinear volt-ampere characteristic it is recommended to take into account zero-sequence current higher harmonic components that are not multiple to three. An algorithm for calculating the neutral conductor current harmonic component for determining the cable temperature rating is developed.

Аппаратные решения для энергосберегающих технологий управления объектами распределительных сетей на базе силовых полупроводниковых устройств

The article considers topical issues in development of energysaving technologies to optimize the control of distribution networks according to the criterion of minimum power losses. The technology consists in introducing new hardware to control the modes based on static devices. Based on the analysis of the existing hardware created to control the modes of distributio networks, the developed circuitry solutions of the power part and the control system of the multifunctional thyristor voltage transformer and hybrid thyristor capacitor are proposed. Their main technical characteristics and ways to reduce voltage asymmetry, limiting short circuit currents and regulating reactive power are det ermined. The use of software and hardware solutions was recommended for a wide range of energy conservation tasks, both in the electric power sector and at the level of industrial facilities

Efficiency of the balancing devices to power quality improve

Violation of the symmetrical mode of operation of the electric network causes a deterioration in the quality of electric energy and significantly reduces the reliability of the functioning of electrical equipment and elements of the electric network. A mathematical model of an electrical network with a grounded neutral is proposed аnd a software package that allows us to evaluate the level of voltage asymmetry of a three-phase system depending on the changing unbalanced load was created. The simulation and calculation of the studied parameters for various combinations of loads and the technical means of balancing the operating mode of the electric network (the balancing device – BD) is carried out. Programs for the Matlab graphic editor are compiled and diagrams of changes in electricity quality indicators are constructed. A numerical analysis is carried out and recommendations are given to determine the most appropriate place for connecting the BD in the electrical network to improve the quality of electricity based on the calculation made.

An Improved Control Technique for Grid Interactive 4-Phase SRM Driven Solar Powered WPS Using Three-Level Boost Converter

This article aims to develop a unique configuration of a solar-powered water pumping system (SPWPS), which ensures an uninterruptable water supply along with the earning possibility for the consumer. This water pumping system utilizing the switched reluctance motor drive, needs no current sensor on the motor side to run the system. The concept of integrating the grid to the SPWPS as an electrical energy storage device, provides assistance against the fluctuations in power, minimum electricity cost and earns from excess of photovoltaic power. An efficient control logic for grid-side voltage source converter is developed in this article. It has multiple intends like to regulate the desired dc-link voltage, to maintain the power quality and to improve the dynamic responses. This controller incorporates the second- and third-order generalized integrator-based filter for fundamental component extraction of grid voltage and has the benefits of both the filters. Moreover, the new control logic for dual output boost converter as a maximum power point tracking converter is also proposed in this article. It helps to simultaneously maximize the solar power as well as to nullify the voltage asymmetry across both dc-link split capacitors of a mid-point converter under all operating modes. The applicability of the developed arrangement with designed control logic is verified by experimental results.

Kompensacja reaktancyjna odbiornika liniowego w układach trójfazowych czteroprzewodowych zasilanych napięciem sinusoidalnym asymetrycznym w myśl teorii składowych fizycznych prądu (część 2)

Four-wire systems are the most common ones in everyday life. Electrical installations within the home, office, or industrial plant are mostly four-wire installations. Receivers connected to such a system are mainly single-phase loads, which from the power connection are an unbalanced three-phase load. Apart from, the load imbalance, the supply voltage also has some asymmetry. Voltage asymmetry, load imbalance, the design of reactance compensators are issues that were not simultaneously included in the power equation in fourwire systems. This article presents the mathematical fundamentals of the construction of reactance compensators operating in voltage asymmetry.

Control of electric locomotives with asynchronous electric motors under asymmetric operating conditions in Uzbekistan

The control of energy conversion processes in an alternating current electric traction drive with asynchronous (induction) motors under asymmetric operating conditions are considered in the paper and the ways to improve their efficiency are proposed. It was stated that asymmetric modes create asymmetry of currents in the AM phases, which negatively affects both the electrical and mechanical parts of electric traction drives. The analysis of electromagnetic processes in the complex asymmetry of currents and voltage in the circuits of electric traction drives allows creating an adaptive algorithm for electric locomotives control which allows increasing electric power indices and the system reliability.

Modeling of balancing transformers to determine the effectiveness of their application

One of the urgent problems is providing consumers of distribution electric networks with high-quality electricity. The most important indicators of the quality of electricity are the level and asymmetry of voltage, the deviation of which from the normative indicators leads to disruption of operation and a decrease in the service life of electrical equipment. If the standard indicators of electricity are not met, the consumer has the right to demand compensation from the electricity supply companies. For balance the voltage on the 0.4 kV side of the step-down substations, it is promising to use transformers with a balancing winding both in new construction and in their reconstruction. The problem of determining the effect of the use of transformers with a balancing winding is that the manufacturer does not provide the necessary parameters for them to ensure the calculation of the phase voltage level when connecting an asymmetric load. Also in existing software products, such as, for example, Matlab/Simulink, there are no ready-made mathematical models of the transformers under consideration. As a result, it is impossible to reliably assess the benefits of replacing conventional transformers with a balancing winding, when the task of a feasibility study for the reconstruction of a substation arises in order to ensure standard indicators of the quality of electricity and reduce electricity losses.

Mathematical description of commutation in multipulse rectification schemes with voltage asymmetry

Modern achievements in the field of construction of transformers and Converter technology allow creating integrated multipulse rectifier units that meet the currently increased requirements of electromagnetic compatibility between different consumers of electric energy and the network feeder. Current rectification carried out with the help of valve devices is closely related to commutation processes, the widespread use and distribution of which requires accurate consideration of the factors that determine them. One of the important questions is the degree of influence of the structural asymmetry of the transformer converter of the number of phases on the overlap angle and on the rectified voltage in the commutation zone. The paper offers a mathematical description of the steady-state process for solving a wide group of practical problems, including commutation periods for the case of converter asymmetry with an arbitrary number of ripples of the rectified voltage.

Low voltage ride through control strategy for MMC photovoltaic system based on model predictive control

Based on the photovoltaic (PV) grid-connected system with MMC, a low voltage ride through (LVRT) control strategy is proposed to overcome the problem of the voltage asymmetry drop in the power grid. On the AC side of the grid-connected system, limit the output current peak and output three-phase symmetrical current, analyze the circulating current component under grid-side asymmetric faults, and use multi-step model predictive control to suppress the circulating current and improve the suppression effect; On the DC side of the grid-connected system, according to the requirement of the inverter output current amplitude limit, the fixed power control is realized through MPC to maintain the AC-DC power balance. Analyze the stability of MPC algorithm, and improve the algorithm to increase its stability margin. The effectiveness and feasibility of the proposed control strategy are verified by the analysis of the RT-lab experimental platform.

Source-side low-frequency harmonic suppression method for matrix converter

ABSTRACT Matrix converters (MCs) with a two-phase load can be used to drive a symmetrically or independently controlled load. Because MCs do not have a large-capacity energy storage unit when a two-phase output voltage is independently controlled, the ripple in the output power is coupled with the source side. However, the conventional modulation strategy significantly increases the number of low-frequency harmonics in the source side. The harmonic content also increases with the increase in output voltage asymmetry. In this paper, a dual current decoupling control strategy is proposed based on a source-side negative-sequence regulator. This method can suppress the input low-frequency harmonic by tracking and reasonably configuring the pulsating power, thereby improving the source-side performance. Moreover, simulations and experimental results verify the effectiveness of the proposed control strategy.

Research on a Fundamental and Harmonic Detection Method Based on D-Q Rotating

The widespread use of power electronics in power systems has led to increasingly serious power quality problems in power systems. Active power filters play an important role in governing the harmonics of power systems. The fast and accurate detection of fundamental and harmonic currents in power systems is one of the key aspects of power filters to manage harmonics. In this paper, a new detection method for the fundamental or the nth harmonic component of the fundamental by presetting the frequency of the d-q conversion matrix is proposed. Analysis of simulation results shows that the detection method is not affected by the voltage distortion or asymmetry of the three-phase circuit, and that the results for fundamental and harmonic detection. The ability to accurately reflect changes in frequency and amplitude excursions.

Systematic method for studying single-electron transistors

We present a thorough classification of the electronic transport patterns of single-electron transistors (SETs) using a two-letter notation, based on the symmetry properties of SETs and a nondimensionalization procedure. We find five unique symmetry types of SETs: one symmetric and four asymmetric. For these types and the corresponding dimensionless transistor parameter sets, denoted by the two-letter scheme, we calculate and compare current–voltage curves, modulation curves, charge stability diagrams, and the average and standard deviation of the number of excess electrons on the transistor island. The simulation is performed using the mean of the recurrent solution method for the system of kinetic equations for the charge probability distribution function. On the basis of the simulation results, we analyze the properties of asymmetric SETs. We also consider the effect of asymmetry in the transistor bias voltage and show that this effect can be compensated by renormalization of the left and right junction capacitances. In addition, we propose a measurement technique that can be used to determine the voltage bias asymmetry ratio in real experiments. Finally, using the Bardeen approximation for the tunnel matrix element and the parallel-plate capacitor approximation, we estimate the geometric features of the tunnel junctions.

Control of Three-Phase Power Electronic Converter With Power Controllers in Stationary Frame

This article concentrates on a three-phase power converter control system that uses voltages and currents in a stationary reference frame. The advantages of such a control system include the lack of transformation between stationary and rotating reference frames and hence, there is no need for an extra algorithm such as a phase-locked loop for the grid voltage phase-angle determination, as the power components are the same in every coordinate system. The method proposed in this article uses proportional-resonant-integral controllers for tracking referenced Akagi's instantaneous power components, which contain intentional oscillations of double grid frequency. Thanks to that, the sinusoidal converter current is maintained despite the negative sequence component in grid voltage. Different targets for converter current asymmetry, from corresponding, through symmetrical, to opposite to voltage asymmetry may be achieved, depending on the operation mode and the demanded power. Moreover, the power limitation method allowing limitation of the phase-current amplitude even for unbalanced phase currents was applied.

Non-arc and non-interruption control scheme of phase commutation switch based on diode natural commutation

It is an effective way to balance three-phase loads by installing phase commutation switch(PCS) to automatically transfer single-phase load from heavy load phase to light load phase. A PCS with the circuit topology based on diode natural commutation is introduced. This PCS uses latching relay as switch element. The PCS control principle is studied under the ideal condition of three-phase voltage symmetry and pure resistance load. The influence of the load characteristics of the actual single-phase user and the three-phase voltage asymmetry on the PCS control is analyzed. Considering that the latching relay is not an ideal switch, the action parameters of the latching relay are tested. According to the actual situation of single-phase users and the batch test results of latching relays, a practical non-arc and non-interruption control scheme of the PCS is proposed. The control scheme is tested on a developed prototype of the PCS.

Synchronization System for Semiconductor Frequency Converters with a Power Supply Network

This article provides a detailed description of synchronization node operation based on the well-known method of a phase-locked loop. It is shown that the phase-locked loop method can be successfully applied in synchronization nodes of valve frequency converters provided that the amplitude of the reverse phase sequence does not exceed 20%. The dependence of the transient time of the measured variable voltage in the synchronization device is obtained depending on the level of asymmetry of the supply voltage, which was estimated by the amplitude of the voltage component of the reverse phase sequence. The dependence of the transition time on the amplitude of the reverse phase sequence is quadratic because of the need to reduce the uniform bandwidth of the second-order filter. The results of the refinement calculation of the metrological characteristics of the synchronization device with account for nonlinear distortions showed that, with the simultaneous presence of nonlinear distortions in the supply voltage curve and asymmetry of the supply voltage, the permissible level of the amplitude of the negative sequence voltage is limited to 10%.

Improving the optimal system of automated control over the level of electric power quality indicators in electric networks

This paper reports solving an important scientific task of minimizing the economic losses caused by the established deviation and the asymmetry of voltage in the distributing electrical networks with a rated voltage of 10 kV.It has been found that the existing systems of automated control over the mode parameters of distributing electrical networks do not fully take into consideration the multifunctional influence of symmetry-compensating devices at the level of electricity quality indicators.It has been proposed to use, as the criteria functions for the task on automated control over the electric power quality indicators, the functional dependences that assess the level of losses caused by the established deviation and asymmetry of voltage in electrical networks. That has made it possible, in contrast to existing control systems, to better account for the negative impact of the established deviation and asymmetry of voltages on the modes of electric network operation.We have determined the functional dependences between the input and output parameters of the control object (a distributing electric network with a voltage of 10 kV with a symmetry-compensating device), which formed the basis of the criteria functions for a multi-criteria optimization problem. The ultimate solution to the problem on a multi-criteria optimization based on a method of approaching a utopian point in the criteria space was derived by minimizing the Chebyshev distance from the utopian point to a Pareto-optimal set of solutions. Based on the obtained solution to the problem on a multi-criteria optimization, we have built an algorithm for determining the vector of optimum control.Computer simulation of the optimal automated control system for the power quality indicators in distributing electrical networks has been performed.Analysis of the simulation results has revealed that the automated control system proposed in this work, when compared with the existing ones, makes it possible to reduce the negative effect exerted by the above-the-norm values of the established deviation and asymmetry of voltage on the operation of electrical networks