Three-phase Unit Research Articles

EVALUATION OF EFFICIENCY OF OIL DISPLACEMENT BY WATER AND GAS AT VARIOUS MODES

The purpose of the work is to analyze in detail the efficiency of oil displacement by various agents, such as water and gas, at different modes. During the study, various methods and technologies aimed at increasing oil recovery were considered, and the effect of various parameters on the efficiency of the process was studied.Particular attention was paid to the method of water-gas impact (HBV) using pump-ejector systems (PES), which provides a triple impact on oil formations by simultaneous or alternate injection of water and gas.Theoretical and experimental methods were used to conduct the study. The beginning of the work was the study and analysis of scientific sources on the issue of assessing the effectiveness of oil displacement. Further, laboratory tests were carried out to assess the effectiveness of oil displacement by various agents. Experimental studies were carried out on a two-phase and three-phase filtration unit. The main parameter measured was the coefficient of oil displacement by water and separation gas. The effectiveness of the impact of various modes of water and gas exposure was studied: alternating (cyclic) injection of water and gas with different cyclicity, simultaneous injection of water and gas, as well as injection of a fine water and gas mixture.Based on the results of the work, it was concluded that the degree of influence of wetting processes on the final displacement result is a critical factor. The following main points can be distinguished:- final value of oil displacement coefficient depends on selection of displacement agent;- in case of water and gas impact, the sequence of water and gas injection is of great importance;- the efficiency of oil displacement is highly dependent on the absolute permeability of the reservoir, as well as on the injection mode (sequential, simultaneous, cyclic).The results of the experiments can be useful for predicting the development of oil fields and choosing optimal methods for increasing oil recovery.The uniqueness of this article lies in the study of the possibilities of using multithreaded ejectors to increase the efficiency of hydrocarbon production.

Designing a Multi-Output Power Supply for Multi-Electrode Arc Welding

Multi-output power converters using different architectures can have significant efficiency advantages. This paper proposes a multi-output welding power supply that is based on the middle DC converter distributed architecture. This machine includes two converter groups, and each group comprises a three-phase rectifier unit, a full-bridge converter unit, a HF (high frequency) transformer, a rectifier unit, and a chopper converter unit. Among these units, the three-phase rectifier unit, full-bridge converter unit, HF transformer, and rectifier unit convert three-phase AC voltage into a low voltage, and the chopper converter unit converts the low voltage into the required current. The welding power supply can output four DC and two AC currents. This paper also analyzes the stability of the welding power supply. Finally, a prototype is designed and verified through experiments, and the maximum output of the prototype is 300 A. The experimental results show that the converter can output different DC and AC currents according to the requirement, the multiple outputs are independent of the others, and the output phase and value are independently adjustable. After verification, the proposed multi-output welding power supply can output steady current according to the requirement.

Expert knowledge based proportional resonant controller for three phase inverter under abnormal grid conditions

ABSTRACT Integration of photovoltaic (PV) power to the grid is achieved using three-phase inverters with high-quality current waveforms. The new grid codes impose a limit on the total harmonic distortion (THD) value of the inverter’s current waveforms. Due to simple structure and ease of design, proportional integral (PI) controllers are the most widely adopted methods to control three-phase grid-connected inverters; however under abnormal grid conditions, PI controllers may suffer from instability problems. To address the aforementioned problem, this article proposes an expert knowledge-based proportional resonant (PR) control for the integration of PV power to the grid under abnormal grid conditions. The proposed control method adjusts the control parameters based on rules generated from expert knowledge. Initially, parameters of the proposed control methods are optimized using particle swarm optimization (PSO) method. The proposed control is tested with a 100 kW grid-tied three-phase inverter unit under normal and abnormal grid conditions and its performance are compared with PI and fixed gain PR control methods. Moreover, the proposed control is tested experimentally with a scaled down 300 W grid-tied inverter lab prototype module. From the simulation and experimental results, it is verified that the proposed adaptive PR control technique is capable of providing low THD in the injected current under abnormal grid conditions compared with fixed gained PR controllers.

Modular Vector Control of Multi-Three-Phase Permanent Magnet Synchronous Motors

Recent developments in power electronics are making the multiphase machines a competitive alternative to the conventional three-phase counterparts. Due to their fault-tolerant features, multiphase drives represent a robust technology in high-power/high-current, safety-critical applications. Besides, their introduction to transportation electrification is gaining importance. Among the multiphase solutions, the multi-three-phase machines are receiving a lot of attention by the industry since they use the well-consolidated three-phase technology, thus reducing the design time and also the cost. Therefore, this article proposes a modular vector control scheme for multi-three-phase permanent magnet synchronous motors. The proposed solution uses a modular modeling approach for the independent and decoupled torque control of each three-phase unit, allowing the implementation of torque-sharing strategies among the three-phase sets of the machine. The developed modular control has been validated on a nine-phase permanent magnet machine.

Three-phase optimal power flow for networked microgrids based on semidefinite programming convex relaxation

Many autonomous microgrids have high penetration of distributed generation (DG) units. Optimal power flow (OPF) is necessary for the optimal dispatch of such networked microgrids (NMGs). Existing convex relaxation methods for three-phase OPF are only applicable to radial networks, not meshed networks. To overcome this limitation, we develop a semidefinite programming (SDP) convex relaxation model, which can be applied to meshed networks and also includes a model of three-phase DG units and on-load voltage regulators with different connection types. The proposed model has higher accuracy than other existing convex relaxation models and the SDP model effectively solves the OPF problem for three-phase meshed networks with satisfactory accuracy, as validated by real 6-bus, 9-bus, and 30-bus NMGs and the IEEE 123-bus test cases. In the SDP model, the convex symmetric-component of the three-phase DG model is shown to be more accurate than three-phase DG that is modelled as three single-phase DG units in three-phase unbalanced OPF. The optimal control variables obtained from the convex relaxation optimization can be used for both the final optimal dispatch strategy and the initial value of non-convex OPF to obtain the globally optimal solution efficiently.

A Dynamic Model for Six-Degree-of-Freedom Bearingless Linear Motor Systems

This article develops a dynamic model for six-degree-of-freedom bearingless linear motor systems by means of lumped-element modeling. A four-sided motor system, containing eight three-phase motor units fed by their own inverters, is considered as an example system, but the modeling approach can be applied to other motor systems as well. The mechanical subsystem of the model comprises the rigid-body dynamics. The electromagnetic subsystem governs the electrical dynamics of the motor units and the production of the resultant electromagnetic force and its associated torque. In order to model the unbalanced magnetic torque due to tilting of the mover, the motor units are spatially discretized into a number of identical submotor models having a uniform air gap. The submotor models of each motor unit are electrically connected in series, i.e., they share the same current, but their flux linkages and forces differ in tilted positions. The electromagnetic subsystem can be parameterized based on simple static two-dimensional finite-element method computations at a range of uniform air-gap and current values. The developed model is validated through a comparison between the time-domain simulation results and the experimental results. The model can be applied to time-domain simulations, real-time control system development, and various analyses of the system.

Оцінювання точності вимірювання електричної енергії вузлом комерційного обліку

The method for evaluation of the electricity metering accuracy by a three-phase commercial accounting unit in a reduced load mode is proposed. The method enables to determine the incomplete calculating of electricity by one or several phases in the case of a decrease in the load level of current transformers to values at which the permissible error is not standardized for a given accuracy class, or the operation of the electric energy meter of a transformer connection is in the dead mode. This is typical during downtime of production equipment at night, on weekends and holidays, when only the territory lighting of the enterprise, video surveillance, burglar alarms etc. are functioning. The method makes it possible to evaluate the relationship between the measured value and the phase currents using a fuzzy function. The measured value is the relative deviation of the readings of the transformer connection meter from the actual energy values, which are estimated from the readings of the direct connection meter. To estimate the parameters of the approximating dependences for the boundary real functions, which determine such a fuzzy function, it is necessary: to obtain samples of the measured value for each measuring channel when the current of the corresponding phase changes within the limits that correspond to the reduced load mode; for each of the samples, using the theory of fuzzy sets, estimate the boundaries of fuzzy intervals characterizing the measurement result; the boundaries of the obtained fuzzy intervals for fixed values of currents of a certain phase are approximated by functions representing the sum of two exponentials, as a result of which fuzzy functions are obtained that characterize the accounting uncertainty for each phase; estimate the boundaries of the desired fuzzy function, which determines the uncertainty in the measurement of electricity in three phases, as the root of the sum of the corresponding boundaries squares of the fuzzy functions, which show the accounting uncertainties for each phase. It was found that in the reduced load mode the incomplete counting of active energy over one measuring channel of the transformer connection meter of accuracy class 0.5 S can reach 3 %. The use of the method will make it possible to improve the accuracy of financial calculations between suppliers and consumers of electricity.

Modular Stator Flux and Torque Control of Multi-Three-Phase Induction Motor Drives

The recent advancements of power electronics are encouraging the development of the multiphase drives in both transport electrification and energy production applications. Among the multiphase solutions, the “multi-three-phase” drives are gaining impressive attention from the industry since they can be configured as multiple three-phase units operating in parallel. In this way, the three-phase technologies can be used, leading to a significant reduction in the costs and design time. Although the multi-three-phase drives possess natural modularity in terms of both machine winding and power converter, few control solutions able to implement a modular regulation of the torque are available in the literature. Therefore, this article proposes a control scheme implementing an independent regulation of the stator flux amplitude and torque contribution belonging to each winding set of a multi-three-phase induction machine. The proposed control solution can manage the voltage and current constraints introduced by each inverter unit. Besides, torque-sharing strategies among the three-phase sets of the machine can be implemented. Experimental results are provided for a modular power converter feeding a 12-phase induction machine with a quadruple-three-phase configuration, thus demonstrating the effectiveness of the proposed solution.

Novel High-Frequency Isolated Cascade PV Inverter Topology Based on Multibus DC Collection

This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.

Decoupled and Modular Torque Control of Multi-Three-Phase Induction Motor Drives

In recent years, the development of multi-three-phase drives for both energy production and transportation electrification has gained growing attention. An essential feature of the multi-three-phase drives is their modularity since they can be configured as three-phase units operating in parallel and with a modular control scheme. The so-called multi-stator modeling approach represents a suitable solution for the implementation of modular control strategies able to deal with several three-phase units. Nevertheless, the use of the multi-stator approach leads to relevant coupling terms in the resulting set of equations. To solve this issue, a new decoupling transformation for the decoupled torque control of multi-three-phase induction motor drives is proposed. The experimental validation has been carried out with a modular power converter feeding a 12-phase induction machine prototype (10 kW, 6000 r/min) using a quadruple three-phase stator winding configuration.

Физико-химические основы методологий определения остаточного срока службы витковой изоляции обмоток силовых трансформаторов по её степени полимеризации в Российской Федерации и за рубежом

The advantages of the method adopted in the Russian Federation for determining the degree of polymerization of power transformer windings according to the Standard of the organization Public joint stock company Russian networks № 34.01-23.1-001-2017 Scope and standards for testing electrical equipment, before the IEC 60450 standard are shown. Differences in the construction of kinetic regularities of power transformers windings insulation destruction adopted in the Russian Federation and according to the recommendations of SIGRE are presented and discussed. Physical and chemical mechanisms of power transformers windings insulation degradation are described. The combination of these mechanisms leads to the fact that the process of coil insulation degradation under various loads of power transformers, which determine the average temperature of their operation, is described kinetically by a family of semi-logarithmic anamorphoses. In a specific example, samples of windings turn insulation selected from a three-phase unit transformer of type TDC-125000/110, the results of kinetic model calculations of residual service life of power transformers winding insulation according to the recommendations of CIGRE differ in risk of the transformer damage due to the degradation of the winding insulation ( P v ≤ 400) from similar results obtained on the basis of the real kinetics of insulation degradation in operation at 40 - 60 % less. The latter is important, since the actual period for replacing a power transformer from project development to commissioning may be 2-2,5 years.

Determination of Optimal Q-V Droop Controller Parameters for Three-Phase Modular UPS System Based on Genetic Algorithm (GA)

This paper presents an optimized reactive power-voltage (Q-V) droop controller parameters for three-phase modular uninterruptible power supply (UPS) based on genetic algorithm (GA). The main objective of this paper is to minimize the voltage regulation error when there are changes in loads. In addition to select the control parameters carefully to promote the performance of the system against disturbances. This is substantial to attain power sharing between different UPS units to balance sudden disturbances that happen when there are changes in loads. We propose a discrete proportional-integral controller which compares the output voltage with the reference value given by the droop control loops then generates suitable voltage vector signal to pulse-width modulation (PWM) inverter. The fitness function for the optimization problem is formulated by considering the sum of square errors in voltage. This fitness function converges to local minima during the iterative operation of the genetic algorithm. Thus, the optimal parameters of the voltage droop control can be discovered with great probability. Simulation of two parallel-connected three-phase UPS units are carried out using MATLAB/SIMULINK R2018a. Comparison between the conventional trial and error tuning methods and GA optimization is performed. The results show that GA succeeded to minimize the output voltage root mean square error (RMSE) and to enhance the power sharing capability when there is variation in loads.

Optimal inverter based distributed generation units control strategy to improve voltage profiles in unbalanced distribution networks

Recently, the penetration of distributed generation (DG) at distribution level has grown significantly. Unfortunately, this has brought some unexpected power quality problems such as voltage unbalance. To reduce the voltage quality problems deteriorated by unbalanced features, a transformed multi-objective optimal power flow (OPF) model is built to optimise the active and reactive power outputs of three-phase micro-turbine generator units. A stricter measurement of voltage unbalance definition is employed which can replace the traditional voltage unbalance definition since it is able to hugely increase the computing efficiency. Another constraint model is also proposed considering the zero sequence effects for three phases and four wire parts of the whole system. The performance of the presented OPF models with different constraints has been evaluated by the IEEE 13-node and 123-node test cases. These simulation results demonstrate that by the proposed OPF objective function, the new combination of constraints could be exploited to achieve better network performance.

Power Sharing Method Based on Droop Control for Three-Phase UPS Systems

The main objective of this paper is to improve the power sharing capability and to achieve synchronization between three-phase Uninterruptible power supply (UPS) units in the presence of load interruption. This paper presents a droop-controlled scheme in such a way that the computation of the instantaneous value of the active power and the reactive power are taken as feedback signals to the frequency and voltage restoration control system. The restored frequency and voltage are introduced to voltage controller circuit, which produces a suitable control signal to sinusoidal pulse width modulation circuit (SPWM). Thus producing a suitable trigger pulses to the inverter gate in order to guarantee synchronization between three-phase UPS units. Simulation of two UPS units with the same ratings (4 KW) are carried out using MATLAB. The results show the effectiveness of the proposed control system in achieving synchronization and improving the power sharing capability in the presence of load interruption. Keywords: Uninterruptible power supply; power sharing; parallel operation; droop control . DOI : 10.7176/JETP/9-4-02 Publication date : April 30 th 2019

On the emergence of negative effective density and modulus in 2-phase phononic crystals

In this paper we report metamaterial properties including negative and singular effective properties for what would traditionally be considered non locally resonant 2-phase phononic unit cells. The negative effective material properties reported here occur well below the homogenization limit and are, therefore, acceptable descriptions of overall behavior. The material property combinations which make this possible were first revealed by a novel level set based topology optimization process which we describe. The optimization process revealed that a 2-phase unit cell in which one of the phases is simultaneously lighter and stiffer than the other results in dynamic behavior which has all the attendant characteristics of a locally resonant composite including negative effective properties far below the homogenization limit. We investigate this further using the Craig–Bampton decomposition and clarify that these properties emerge through an interplay between the fundamental internal modeshape of the unit cell and a rigid body mode. Through explicit numerical calculations on 1-D, 2-phase unit cells, we show that negative effective properties only appear for the specific material property combination mentioned above. Furthermore, we provide a proof which supports this conclusion. The concept is also shown to hold for 2-D unit cells where we show that an appropriately designed hexagonal unit cell made of 2 material phases exhibits negative effective shear modulus and density in an appropriate frequency regime in which it also exhibits negative refraction. As in the 1-D case, we show that the homogenized description in the 2-D case is rigorous as well. An important conclusion of this paper is that the class of unit cells expected to result in negative properties can be expanded beyond the classic unit cell (three-phase unit cells with an explicit locally resonant phase) to include topologically simpler 2-phase unit cells as well.

Diagnostics and an on-load operation algorithm of high-speed voltage regulators

Diagnostics methods are considered of single- and three-phase high-speed switching units, such as of the PC and PNOA series, mounted on 35- to 330-kV power transformers. The diagnostics is carried out using a multichannel digital oscilloscope without opening the contactor tank and draining the dielectric liquid from it. Algorithms for automated determination of working capacity of switching devices are presented. It is revealed that the developed algorithms make it possible to shorten the time for preparing and obtaining the oscillograms of currents and automatic processing of measured values, automate the determination of working capacity of switching devices, record the diagnosing results in print, and create a database in digital form.

Security-constrained optimal energy management system for three-phase residential microgrids

This paper presents a mixed-integer linear programming (MILP) model for the optimal energy management of residential microgrids, modeled as unbalanced, three-phase, electrical distribution system (EDS). Initially, the problem is formulated as a mixed-integer nonlinear programming (MINLP) problem. Then, a set of linear approximations and equivalent mathematical representations are used to obtain a precise MILP model. The proposed formulation considers three-phase generation units (GU), single-phase photovoltaic (PV) resources, and single-phase energy storage systems (ESS), as well as load management. The aim of the proposed model is to minimize the final operational costs of the microgrid while considering operational constraints of the EDS and an unexpected outage of the main grid through a security-constrained set of equations. The optimal solution of the MILP model is found using commercial convex optimization solvers. The proposed model was tested in a residential, three-phase EDS. Results show that the proposed linearizations and approximations produce accurate solutions when compared with a nonlinear three-phase OPF formulation, with an error in the objective function near to 2% and a maximum error in the voltage near to 1%. Efficiency and flexibility of the proposed methodology are also discussed.

Measurements for validation of manufacturer’s white-box transformer models

The transformer manufacturers make use of electromagnetic transient calculations by detailed white-box models to ensure that the transformer will withstand the lightning impulse test during the factory acceptance test. In principle, such models could be used in general electromagnetic transient simulation of overvoltages in the system. One of the objectives of CIGRE JWG A2/C4.52 is to assess the accuracy of the manufacturer’s white-box models in the context of general transient overvoltages that can occur in the system. As part of this activity, extensive measurements have been performed on two three-winding transformers: one three-phase unit and one single-phase unit. The measurements involved voltage transfer between external terminals and from external terminals to three points in the regulating winding. The measurements were performed with alternative points of voltage excitation, grounding conditions and alternative tap settings, giving 64 cases for each transformer. Some admittance measurements were also performed. This paper gives an overview of the measurements that were performed, the measurement procedure, and some initial results. The voltage transfer measurements were mostly performed in the frequency domain and transferred to the time domain via rational function approximation and recursive convolutions. That way, voltage transfer functions have been generated for well-defined excitations, e.g. the standard 1.2/50 µs voltage wave. In addition, initial results for black-box modeling of the three-phase unit is shown. The measurements are currently being used within CIGRE JWG A2/C4.52 for benchmarking of white-box models.

Decentralized Method for Load Sharing and Power Management in a Hybrid Single/Three-Phase-Islanded Microgrid Consisting of Hybrid Source PV/Battery Units

This paper proposes a new decentralized power management and load sharing method for a photovoltaic (PV)-based, hybrid single/three-phase-islanded microgrid consisting of various PV units, battery units, and hybrid PV/battery units. The proposed method is not limited to the systems with separate PV and battery units, and power flow among different phases is performed automatically through three-phase units. The proposed method takes into account the available PV power and battery conditions of the units to share the load among them. To cover all possible conditions of the microgrid, the operation of each unit is divided into five states in single-phase units and seven states in three-phase units and modified active power-frequency droop functions are used according to operating states. The frequency level is used as trigger for switching between the states. Efficacy of the proposed method in different load, PV generation and battery conditions is validated experimentally in a microgrid lab prototype consisting of one three-phase unit and two single-phase units.

Control Of Utility Interfaces In Low-voltage Microgrids

This paper presents a general control technique for utility interactive inverters in low-voltage microgrids. The Utility Interface (UI) is a three-phase power conversion unit, equipped with energy storage, which governs the interaction between the utility grid and the microgrid. The UI is in charge of several functions: in grid-connected operation, it performs as a voltage-supporting unit and compensates the reactive power, unbalance, and distortion caused by loads, whereas in islanded operation, it performs as a voltage- forming unit and sets the voltage and frequency for the entire microgrid. Moreover, the UI ensures seamless transitions from grid-connected to islanded operation and actively decouples the microgrid and the mains. Finally, the UI can perform as a centralized microgrid controller for distributed energy resources. The UI is therefore a crucial component, which needs to be analyzed carefully to ensure safe and reliable operation for the microgrid. This paper discusses a control approach that provides all required functionalities and ensures proper microgrid operation even in case of non- intentional islanding or severe load transients. The experimental results show the behavior of the system in different scenarios.