Four-wire System Research Articles

IDENTIFICATION ERROR OF UNBALANCE VOLTAGE SOURCES IN POWER SUPPLY SYSTEMS BY THE DISTORTING NODAL CURRENT CRITERION

One of the properties of electrical energy, that causes significant economic losses for both suppliers and consumers of electricity, is voltage unbalance. The most universal criterion for identifying voltage unbalance sources is the nodal distorting current. The accuracy of its determination depends on the method of measurement organization and is characterized by the greatest error for the local approach. The reason for this lies in an approximate method for determining the equivalent circuits of consumers of electrical energy and their parameters when measuring the parameters of the network operation mode only at one point of common connection to the power supply system. Analysis of the influence of approximate equivalent circuits and their parameters on the determination of the nodal distorting current showed that adequate identification of the sources of voltage unbalance distortion is possible only in the reverse sequence. At the same time, it is difficult to accurately determine the error in calculating this criterion in real time measurements due to the presence of additional unknowns that are required for its calculation. Based on this, it is proposed to carry out an upper estimate of this error. This required the introduction of additional functions with the search for their maximum under the given constraints. In addition, the uncertainty associated with the non-zero value of the identification criterion for a non-asymmetric consumer of electricity was taken into account that led to the need to introduce a dead zone for it. As a result of the studies carried out, expressions were obtained for an upper estimate of the error in determining the criterion for identifying sources of voltage symmetry distortion in the reverse sequence and determining its dead zone in real time measurements in relation to three-phase three- and four-wire power supply systems.

Impedance Matching-Based Power Flow Analysis for UPQC in Three-Phase Four-Wire Systems

Different from the extant power flow analysis methods, this paper discusses the power flows for the unified power quality conditioner (UPQC) in three-phase four-wire systems from the point of view of impedance matching. To this end, combined with the designed control strategies, the establishing method of the UPQC impedance model is presented, and on this basis, the UPQC system can be equivalent to an adjustable impedance model. After that, a concept of impedance matching is introduced into this impedance model to study the operation principle for the UPQC system, i.e., how the system changes its operation states and power flow under the grid voltage variations through discussing the matching relationships among node impedances. In this way, the nodes of the series and parallel converter are matched into two sets of impedances in opposite directions, which mean that one converter operates in rectifier state to draw the energy and the other one operates in inverter state to transmit the energy. Consequently, no matter what grid voltages change, the system node impedances are dynamically matched to ensure that output equivalent impedances are always equal to load impedances, so as to realize impedance and power balances of the UPQC system. Finally, the correctness of the impedance matching-based power flow analysis is validated by the experimental results.

Experimental Validation of Photovoltaic System with Isolated Dual Inductor dc-dc Converter for Grid-Connected Application

Abstract This article presents a double inductor–based converter for a grid-connected photovoltaic (PV) system with the utilization of the battery bank. This converter used to give continuous power to the three-phase four-wire power distribution system from the PV array. In order to increase the low magnitude of the PV array output voltage into a high dc voltage required for the three-phase dc link, the proposed system offers two boost stages. The double inductor–based converter gives power to the load in both the switched ON and OFF conditions of the chopping switch over buck, boost, and Cuk converters utilized in the PV-coordinated grid-connected applications. The operations of the proposed double inductor–based converter sustained three-phase four-wire power distribution system are analyzed and presented. The digital simulation and hardware experimental prototype results are presented to examine the performance of the presented double boost converter fed to the three-phase four-wire power distribution system.

Implementation of a Multiobjective Control for Islanded Hybrid Microgrid

This article presents an implementation of a fast and accurate control strategy for a synchronous generator driven by a diesel engine and a two-stage solar photovoltaic (PV) with a battery storage-based microgrid (MG) system. This MG feeds active power from a solar PV array to the distribution network by operating it at its maximum power point (MPP). The MPP of the solar PV array is estimated by using an incremental conductance control. An adaptive control of volterra least mean square/fourth (VLMS/F) is applied to an islanded hybrid MG to control the power converter that is interconnecting dc sources to the ac system, to improve various power quality indices such as harmonics suppression, compensation of reactive power, balancing of output currents from the diesel generator set, and neutral current compensation in a three-phase four-wire system. The simulation and experimental investigations of the developed MG show the performance superiority of the VLMS/F control strategy over the conventional controls.

A Novel Switched-Capacitor Inverter with Reduced Capacitance and Balanced Neutral-Point Voltage

A novel three-phase switched-capacitor multilevel inverter (SCMLI) with reduced capacitance and balanced neutral-point voltage is proposed in this paper. Applying only one DC source, the three-phase seven-level topology possessing voltage-boosting capability is accomplished without the high-voltage stress of power switches. Owing to the inherent redundant switching states of the proposed topology, two charging approaches that can effectively limit the voltage ripples and path selection for capacitors can be realized. This provides the presented topology with reduced capacitance, balanced neutral-point voltage, good performance in not only the three-phase four-wire system but also the three-phase three-wire system, and low total harmonic distortion (THD) of the output voltage. A comprehensive comparison with previous SCMLIs in various aspects is conducted to validate the merits mentioned above. The simulation results accord with theoretical analyses, confirming the feasibility of the proposed three-phase SCMLI.

CPC-Based Minimizing of Balancing Compensators in Four-Wire Nonsinusoidal Asymmetrical Systems

The article presents the possibility of using the currents’ physical components (CPC) theory to generate the reference current of the active power filter (APF). The solution proposed by the authors is based on the cooperation of minimizing balancing compensators (MBC), which, due to their use in 4-wire systems, have been divided into two structures. The first compensator, which purpose is to minimize and balance the reactive current and the unbalanced current of the zero sequence, is built in the star system (STAR-MBC). The purpose of the second compensator, which operation occurs in the delta system (DELTA-MBC), is to minimize and balance the other two components, i.e., the unbalanced current of the negative sequence and the unbalanced current of the positive sequence. The two structures cooperating with each other significantly reduce the currents associated with the reactive elements, i.e., reactive current, and the unbalanced current. As mentioned, these currents are reduced but not compensated to zero or to the reference value. In order for the compensation and balancing to bring the preferable effect, an APF system should be included, which will cooperate with MBC compensators. This solution is presented in this publication. The control of the active part of the hybrid active power filter (HAPF), which was presented in the paper, consists of the reflection of the waveform of the nonsinusoidal active current. In this approach, no current shift in relation to voltage is obtained, but the waveforms of these quantities remain distorted. The reactive current is compensated and the unbalanced currents are balanced. The second definition of generating a reference current can also be used. Through this approach, the active current with a sinusoidal waveform is achieved. The second approach allows for an additional reduction of the three-phase RMS value of the load’s current. In both of these approaches, the active currents flowing through the lines will reflect the amplitude and phase asymmetry that is present in the supply voltage. The APF system will follow the changes in power or load conditions and generate the correct value for the reference current. The calculations presented in the article, as well as the current and voltage waveforms, were created as a result of the constructed mathematical models, which were used for theoretical illustrations. Calculations and waveforms were generated based on a script written in Matlab.

Dynamic Voltage Restorer Integrated with Photovoltaic-Thermoelectric Generator for Voltage Disturbances Compensation and Energy Saving in Three-Phase System

The dynamic voltage restorer (DVR) combined with a photovoltaic–thermoelectric generator (PV-TEG) system is proposed for voltage disturbance compensation in the three-phase four-wire distribution system. The PV-TEG hybrid energy source is used in the DVR system to improve the system ability for deep and long-period power quality disturbance compensation. In addition, the DVR will save grid energy consumption when the hybrid PV-TEG module generates sufficient power to meet the load demand. An enhanced variable factor adaptive fuzzy logic controller (VFAFLC)-based maximum power point tracking (MPPT) control scheme is proposed to extract the maximum possible power from the PV module. Since the PV and TEG combine a hybrid energy source for generating power, the DVR can work efficiently for the voltage sag/swell, outage compensation, and energy conservation mode with minimum energy storage facilities. The in-phase compensation method and the three-leg voltage source inverter (VSI) circuit are chosen in the present system for better voltage and/or power compensation. To confirm the effectiveness of the proposed hybrid PV-TEG integrated DVR system, a simulation-based investigation is carried out with four different operational modes with MATLAB software. The study results confirm that the proposed DVR system can compensate power quality disturbances of the three-phase load with less total harmonics distortion (THD) and will also work efficiently under energy conservation mode to save grid energy consumption. Moreover, the proposed VFAFLC-based control technique performs better to achieve the maximum power point (MPP) quickly and accurately, thereby improving the efficiency of the hybrid energy module.

Nyström Minimum Kernel Risk-Sensitive Loss Based Seamless Control of Grid-Tied PV-Hybrid Energy Storage System

This paper presents Nyström minimum kernel risk-sensitive loss (NysMKRSL) based control of a three-phase four-wire grid-tied dual-stage PV-hybrid energy storage system, under varying conditions such as irradiation variation, unbalanced load, and abnormal grid voltage. The Voltage Source Converter (VSC) control enables the system to perform multifunctional operations such as reactive power compensation, load balancing, power balancing, and harmonics elimination while maintaining Unity Power Factor (UPF). The proposed VSC control delivers more accurate weights with fewer oscillations, hence reducing overall losses and providing better stability to the system. The seamless control with the Hybrid Energy Storage System (HESS) facilitates the system’s grid-tied and isolated operation. The HESS includes the battery, fuel cell, and ultra-capacitor to accomplish the peak shaving, managing the disturbances of sudden and prolonged nature occurring due to load unbalancing and abnormal grid voltage. The DC link voltage is regulated by tuning the PI controller gains utilizing the Salp Swarm Optimization (SSO) algorithm to stabilize the system with minimum deviation from the reference voltage, during various simulated dynamic conditions. The optimized DC bus control generates the accurate loss component of current, which further enhances the performance of the proposed VSC control. The presented system was simulated in the MATLAB 2016a environment and performed satisfactorily as per IEEE 519 standards.

Flexible Control Strategy for Enhancing Power Injection Capability of Three-Phase Four-Wire Inverter During Asymmetrical Grid Faults

A three-phase four-wire inverter is highly suitable for low-voltage distributed grids owing to its zero sequence control; however, essential aspects of grid-following inverters during faults, such as the power oscillation control flexibility and power injection capability, are rarely discussed in detail. Thus, by introducing zero sequence instantaneous power into a four-wire system, this article proposes a flexible control strategy that enhances the power injection capability of the inverter in the photovoltaic generation system during asymmetrical grid faults. First, a generalized reference current generation with flexible control of positive, negative, zero sequence current (FPNZSC), and power oscillations is presented. Second, a maximum allowable power injection (MAPI) algorithm based on the actual value constraints of power oscillations and peak current is presented according to the requirement. The proposed MAPI-FPNZSC strategy further extends the existing fault ride through methods in three-wire inverter systems, which is also suitable for single line-to-ground and double line-to-ground faults and can be easily realized in the natural or stationary frame. The effectiveness of the proposed strategy is verified by comparing the provided three typical objectives with the traditional method, and tested in a real-time hardware-in-the loop experimental platform.

Three-Phase Four-Wire OPF-Based Collaborative Control of PV Inverter and ESS for Low-Voltage Distribution Networks With High Proportion PVs

The use of photovoltaic reactive power and energy storage active power can solve the problems of voltage violation, network loss, and three-phase unbalance caused by photovoltaic connection to low-voltage distribution networks. However, the three-phase four-wire structure of the low-voltage distribution network brings difficulties to power flow calculation. In order to achieve photovoltaic utilization through optimal power flow, a photovoltaic-energy storage collaborative control method for low-voltage distribution networks based on the optimal power flow of a three-phase four-wire system is proposed. Considering the amplitude and phase angle of voltage and current, a three-phase four-wire node admittance matrix was used to establish the network topology of the low-voltage distribution network. Also, to minimize the network loss, the three-phase unbalance and voltage deviation. a multi-objective optimization model based on three-phase four-wire network topology was established considering the voltage constraints, reverse power flow constraints and neutral line current constraints. Through improving the node admittance matrix and model convexity, the complexity of solving the problem is reduced. The CPLEX algorithm package was used to solve the problem. Based on a 21-bus three-phase four-wire low-voltage distribution network, a 24-h multi-period simulation was undertaken to verify the feasibility and effectiveness of the proposed scheme.

Research on harmonic current suppression of three-phase four-wire power conversion system

The harmonic current of the three-phase four-wire gridconnected power conversion system (PCS) will be increased due to gridside harmonics and neutral loop. To solve these problems, the three-phase four-wire I-type three-level converter is applied as the topology in this paper to study the harmonic current suppression of the grid-connected PCS. A compound control strategy with the proportional integral (PI) and repetitive controller in parallel is presented and the interaction between the parameters of the compound controller is analyzed. The comparative research is carried out from the theoretical perspective of model analysis, and a controller optimization scheme is proposed. Finally, under the grid and neutral current waveform quality of simulation and experiment, the correctness and effectiveness of the proposed scheme is verified.

Вибір системи живлення низьковольтних однофазних електроприймачів повітряних ліній напругою 220/380 В

Two-phase three-wire and single-phase two-wire branches from main three-phase lines are integral components of three-phase four-wire systems. Therefore, the aim of this work is to choose the optimal power supply system for single-phase electrical receivers depending on their power and branch length. The comparison of single-, two- and three-phase power supply systems of single-phase electric receivers is carried out and analytical expressions are obtained to determine power losses, phase voltage loss and wire cross section for allowable voltage loss at the same total active load power and its equal distribution between phases. Based on the obtained expressions, the total power losses, voltage loss in phase and neutral wires for different power supply systems are analyzed. In the transition from a three-phase four-wire power supply system of single-phase electric receivers to a single-phase two-wire or two-phase three-wire system with the same total load power and equal load phases with wire cross sections selected for allowable voltage loss, power loss and phase voltage with a corresponding decrease in their active resistance. It is shown that in some cases the use of single-phase and two-phase branches saves conductive materials in comparison with the three-phase linear branch, the cross section of which is inflated due to the need to ensure the condition of mechanical strength. The dependences of the limiting length of three-phase and single-phase overhead insulated lines, which corresponds to the allowable voltage loss, on the active load power are calculated. It is shown that the limiting length of three-phase linear branches significantly exceeds the limiting lengths of single-phase and two-phase branches at the same load power. The optimal version of the power supply system should be selected on the basis of technical and economic calculation depending on the load capacity, line length and allowable voltage loss.

Adaptive Balancing by Reactive Compensators of Three-Phase Linear Loads Supplied by Nonsinusoidal Voltage from Four-Wire Lines

A method of the design of an adaptive balancing reactive compensator in four-wire systems with linear loads and nonsinusoidal voltage is described in this article. The method of compensation is founded on the Currents’ Physical Components (CPC) – based power theory of three-phase systems with nonsinusoidal voltages and currents. The compensator is built of two sub-compensators of Y and  structure, respectively. The Y compensator reduces the reactive current and the zero sequence symmetrical component of the unbalanced current. The  compensator reduces the negative sequence symmetrical component of the unbalanced current. The positive sequence symmetrical component of the unbalanced current and the scattered current remain uncompensated. It is because shunt reactive compensators do not have any capability for that. Thyristor Switched Inductors (TSIs) enable the susceptance control of the compensator branches, referred to in the article as Thyristor Controlled Susceptance (TCS) branches. Periodic switching of thyristors in these branches causes the generation of harmonic currents, in particular the third-order harmonic. Moreover, in the presence of the supply voltage harmonics, a resonance of the equivalent capacitance of the compensator with the distribution system inductance can occur. These two harmful phenomena in the compensator suggested were reduced by the selection of a special structure of the TCS branches and their LC parameters. The presented method of the adaptive compensator synthesis was verified in the article with a numerical example and results of computer modeling of the load with an adaptive compensator.

Power Quality Improvement for Grid-connected PV System Based on Distribution Static Compensator with Fuzzy Logic Controller and UVT/ADALINE-based Least Mean Square Controller

This paper presents a novel method of power quality enrichment in a grid-connected photovoltaic (PV) system using a distribution static compensator (DSTATCOM). The paper consists of two-step control processes. In the primary step, a fuzzy logic controller (FLC) is employed in the DC-DC converter to extract the peak power point from the PV panel, where the FLC produces a switching signal for the DC-DC converter. In the secondary step, a unit vector template (UVT)/adaptive linear neuron (ADALINE)-based least mean square (LMS) controller is adopted in the DC-AC converter, i.e., voltage source converter (VSC). The input to this VSC is the boosted DC voltage, which originates from the PV panel as a result of DC-DC conversion. The VSC shunted with the power grid is known as a DSTATCOM, which can maintain the power quality in the distribution system. The UVT controller generates reference source currents from the grid voltages and DC-link voltages. The ADALINE-based LMS controller calculates the online weight according to the previous weights by the sensed load current. The UVT/ADALINE-based LMS controller of a DSTAT-COM performs several tasks such as maintaining the sinusoidal source current, achieving a unity power factor, and performing reactive power compensation. The reference current extracted from the UVT/ADALINE-based LMS controller is fed to the hysteresis current controller to obtain the desired switching signal for the VSC. A 100 kW solar PV system integrated into a three-phase four-wire distribution system through a four-leg VSC is designed in MATLAB/Simulink. The performances of the FLC and UVT/ADALINE-based LMS controllers are demonstrated under various irradiances as well as constant temperature and nonlinear loading conditions.

Impedance Modeling and Stability Analysis of Three-Phase Four-Leg Grid-Connected Inverter Considering Zero-Sequence

With the increasing applications of grid-connected voltage source converters, it is important to analyze the impedance characteristic of the grid-connected system to implement the stability analysis of the grid connection operation. Compared with the three-phase three-wire system, an additional zero-sequence path exists in the three-phase four-wire system. Therefore, it is necessary to consider the influence of the zero sequence when analyzing the stability of the system. In this paper, an impedance model including positive-sequence, negative-sequence and zero-sequence impedance of the three-phase four-leg grid-connected inverter is established. Through impedance characteristic analysis, the relationships between zero-sequence impedance and positive-sequence, negative-sequence impedance can be found which are decupled. Based on the developed zero-sequence impedance model, the main factors affecting the zero-sequence impedance model are revealed. Then, the system stability consisting of the grid and three-phase four-wire inverter is investigated, and the experimental results validate the theoretical analysis.

Application Features of Thyristor Regulators to Control the Light Flux in Industrial Fishing

To control the intensity of the light flux when fishing saury it is necessary to widely change the voltage of the lighting fishing equipment. It is reasonable to carry out this by controlling additionally installed thyristor regulators supplying individual symmetric three-phase groups of light sources that will ensure balanced loading of the synchronous generator stator windings. In this research the features of using a thyristor voltage regulator in a four-wire system of ship power supply are studied based on mathematical analysis, conclusions are made using computer modeling and the use of current limiting reactors is justified.

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.

A Comprehensive Study on Shunt Active Power Filters for Grid – Tied wind systems

The term power quality (PQ) has got major attention at the distribution side and consumer side in the recent years. Continuous rise of power electronic devices in grid-tied applications, uninterruptable power supplies (UPS) and motor drive applications etc, simplifies the control technology, and makes the system robust and flexible. But, these devices inject the current harmonics into the line which pollutes the electrical system. In addition, it draws more reactive power and creates the unbalance in the system. Initially, passive filtering techniques (inductors and capacitors) were used to lessen the PQ problems. Because of the lacking of the quality performance, the passive filter methods have been replaced with advanced power electronic topologies. Researchers, constantly investigates for better and cost effective solutions to improve system PQ. Shunt active power filter (SAPF) is one of the better solutions for enhancing the power quality by compensating the harmonic currents and other reactive power problems in the grid-tied system. In this paper, the basic structure of SAPF is briefly discussed along with the detailed control system functionalities. This paper provides a concise assessment on SAPF classifications, topologies and comparisons of single-phase, three-phase three-wire (3P3W) and four-wire (3P4W) systems. The features of all the configurations are provided along with their complications, so as to identify the better topology for specific application. The merits and demerits of these configurations are also discussed briefly.

Uniform carrier‐based PWM method for three‐phase three‐level three‐wire and four‐wire converter system with neutral‐point balancing

In this study, a simple carrier-based pulse-width modulation (CBPWM) method is proposed for a three-phase three-level neutral-point-clamped converter with neutral-point (NP) balancing, which can be applied to three-phase three-wire (TPTW) and three-phase four-wire (TPFW) converter systems simultaneously. First, the effect of each switching state for the NP potential in TPTW and TPFW systems is analysed in detail, and a newly NP control strategy by reconstructing the switching state and adjusting the corresponding duration time is deduced for all operation conditions, it only needs to add the offset voltage to the modulation reference voltage to guarantee the NP balance and is easy to implement. Then, under all operating conditions, the mathematical model of NP current is derived and analysed to evaluate the low-frequency voltage oscillation in the NP. Finally, the effectiveness and feasibility of the proposed CBPWM strategy are verified by the experimental results based on a 12 kVA laboratory prototype.

A Methodology for Power Quantities Calculation Applied to an FPGA-Based Smart-Energy Meter

A complete description of a field-programmable gate array (FPGA)-based smart energy meter is presented in this article. By implementing the power quantities definitions of the IEEE 1459–2010 Standard, a novel power quality analyzer capable of performing remote monitoring of electric power systems operating under sinusoidal, nonsinusoidal, balanced, and/or unbalanced conditions was developed. In order to ensure portability, the digital signal processing algorithms implemented on the FPGA device were entirely coded in hardware description languages, and all equations of them are fully described to be applied to any digital signal processing environment. These algorithms are completely defined as functions of the grid fundamental frequency, and by adjusting the sampling frequency, the adaptability of all modules developed is ensured. Experimental results were obtained using the developed platform in a three-phase four-wire system operating under several conditions, which were defined by the presence of harmonic components imposed by nonlinear loads and supply voltages, as well as by setting bidirectional power flow in distributed generation scenarios by employing a photovoltaic system. Real-time and parallel processes are validated as well.