Single-phase Loads Research Articles

Smart load balancing system for 3-phase 4 wire distribution system

In 3-phase 4 wire distribution system, imbalance phenomena arise because of disproportionate distribution of single-phase loads among 3-phases. To address this issue, distribution system requires equitable load sharing in each phase. In this paper, we proposed an intelligent system which can sense the loading in each phase and distribute the load proportionately in each phase of 3-phase 4-wire distribution system. In our proposed hardware, AI based micro-controller is used to sense the least loaded phase and gives command to relay module to connect the load to the least loaded phase whenever any new load is connected to the line. The load on each phase can be monitored in real-time with the help of IoT based data communication. The results of the proposed work shows that whenever any new load is connected to any phase, it automatically gets connected to the least loaded phase. This work is effective in balancing of load in each phase of 3-phase 4-wire distribution system.

Phase Balance Optimization of Customers and Electric Vehicles in a Real Low Voltage Electricity Distribution Network

Abstract Phase unbalance is a common issue encountered in LV electricity distribution networks, caused by uneven allocation of single-phase loads among phases. This paper analyses a part of a real LV distribution network, situated in Bosnia and Herzegovina. The impact of single-phase customers and single-phase charging of electric vehicles was analysed. To reduce unbalance and improve the voltage profiles, Phase Balance Optimization in DIgSILENT PowerFactory software was performed in six scenarios with different customer and electric vehicle unbalance. The goal was to find a method with the least number of changes in the customer and electric vehicle phase connection that fits within defined limits of voltage variations and voltage unbalance of a European norm for power quality (EN 50160). Results showed that all analysed scenarios were improved, with reference to voltage variation and voltage unbalance values, and were found acceptable by the limits from standard EN 50160.

Development of a web-based single-phase load monitoring and auditing system

<span lang="EN-US">In a developing nation like Nigeria, the conventional load monitoring and billing system has proved to be tedious, time-consuming, expensive, and prone to human error over the years. Therefore, this creates the need for an efficient system that can assist the Utility to monitor the energy consumption trend of the customers remotely. This work developed a web-based single-phase load monitoring and auditing system using NodeMCU (ESP8266) microcontroller, PZEM-004T sensor, and liquid crystal display (LCD) module for the hardware unit and Blynk internet of things (IoT) platform for the software unit. The system design was implemented around the ESP8266 microcontroller with relevant design models, and standard power and energy equations programmed into the microcontroller in the Arduino integrated development environment. The developed system was load tested to examine its performance and determine its reading error. The hardware and software units of the system operated satisfactorily when tested. The reading accuracy for current and voltage measured by the device were ±0.2% and ±0.4%, respectively, giving a reading error of ±0.8% for power measurement. The developed system is suitable for residential, commercial, and similar applications where the energy usage trend of some small loads is required for management purposes.</span>

A Grid-Connected Solar PV/Wind Turbine Based Hybrid Energy System Using ANFIS Controller for Hybrid Series Active Power Filter to Improve the Power Quality

The current needs of more nonlinear loads and the frequent usage of single-phase loads in three-phase system drastically create power quality issues in the grid-connected system. As a consequence, it creates an undesirable power quality issue (PQI) in the form of a change in the nature of voltage and current magnitude and waveforms in the power system. The voltage-related PQI leads to a huge disturbance in the system when compared with the current-related PQI. The hybrid series active power filter provides grids with the required voltage in series and suppresses the voltage-related harmonics caused by grid-connected nonlinear loads. The present work deals with an adaptive neurofuzzy inference system controller for the generation of a reference voltage signal that uses a reduced active filter rating. The simulation study was done in the MATLAB 2020b/Simulink environment and the experimental effectiveness of the proposed ANFIS controller was compared with that of a conventional controller. In the grid-connected system, this system prevents voltage quality problems such as voltage sag, flickering, voltage swell, neutral currents, and reactive power. The renewable energy sources interfaced into the DC-link minimize short and long voltage challenges so that they improve the overall performance of the system. In accordance with IEEE standard 519-1992, a prototype model was proved to demonstrate that the power delivery system works effectively under different conditions and reduces the total harmonic distortion by approximately 30%, which is less than the 5% acceptable limit.

Phase-changing control for three-phase four-wire back-to-back VSC based soft open points

The increasing integration of intermittent single-phase distributed renewable generation (DRG) and varying single-phase loads exacerbates the issues of imbalance either between feeders or between three phases in the low-voltage active distribution networks (LV-ADNs). Soft open points (SOPs), which can be utilised to regulate power flow between the connected feeders, can be recognised as a solution to both unbalanced situations, as they can realise load balancing between feeders and have the potential to compensate for unbalanced phase power flows. In this paper, the three-phase four-wire back-to-back VSC (3P4WB2B- VSC) is applied as the topology of the SOPs. Based on this, a phase-changing (PC) control is proposed. It is designed for mitigating (1) the issue of load imbalance between feeders and (2) the phase imbalance in the heavily loaded feeder in LVADNs. The model of 3P4W-B2B-VSC based SOPs under the PC control is built and simulated in Matlab/Simulink. Presented results demonstrate the practicability of the 3P4W-B2B-VSC based SOP and the effectiveness of the phase-changing control in mitigating unbalanced network usage.

DC-Link Current Minimization Control for Current Source Converter-Based Solid-State Transformer

This article proposes a fast predictive control method and a small dc-link inductor to minimize the dc-link current in current-source converter (CSC) based solid-state transformer. The dc-link current minimization can significantly reduce power loss and improve efficiency. The challenge of this problem is on improving both steady-state and dynamic performance. PI control methods and large dc-link inductors are conventionally used in the CSC but have limited dynamic performance. A model predictive control (MPC) method is proposed to achieve switching-cycle-level settling time, and the dc-link inductor is sized for 40% ripple to enable fast current change. Importantly, this article also proposes to minimize the dc-link current by varying the current even within a line cycle under single-phase load to improve the steady-state performance, in contrast with the reduction to a constant value in the literature. The proposed MPC features a constant switching frequency without weighting factors. The MPC does not have a high computational burden and is implemented in a regular digital controller for a prototype of soft-switching solid-state transformer (S4T) with reduced conduction loss. The effectiveness of the proposed method has been experimentally verified on the SiC S4T prototype during steady-state and dynamics under different multiport power flow conditions up to 2 kV peak. The dc-link current in the experiments is close to the minimum current with a short zero-vector duration, which further verifies the performance of the proposed method.

Photovoltaic Energy Conversion System Integrated Into Unbalanced Distribution Electrical Networks Through Hardware in the Loop

In this article, a real-time, hardware in the loop (HIL) and experimental photovoltaic energy conversion system (PVECS) integrated into unbalanced distribution electrical networks is presented. Commonly, the three-phase voltages are not balanced, because the input–output of single-phase loads in low and medium voltage networks. In this context, the photovoltaic (PV) systems integration under the dq0-Frame control operation scheme, tend to generate current deformations. In contrast, a new control technique for PVECS interconnection is validated in a HIL scheme, even in the presence of unbalanced voltage. This new technique is considered simple and easy to implement, since it consists of a single PI control loop, guaranteeing reliable operation under unbalances voltage events. Thus, preserving favorable characteristics, such as: 1) always balanced currents; 2) low harmonic distortion; 3) unit power factor; and 4) Compliance with the rules of the network code. The PVECS effectiveness is assessed by complete mathematical model, the simulation results are evaluated using MATLAB-Simulink (MATLAB r2018, Mathworks, Natick, MA, USA), and the experimental results are validated with a small-scale prototype operating in a HIL environment and the real-time simulator Opal-RT Technologies (Montreal, QC, Canada); integrating a power capacity of 15 kW in distribution networks.

Parameter Determination of Coupled and Decoupled Admittance Matrix Methods of the Norton Equivalent Model for an Air Extractor

Context: Studies carried out in low voltage networks have explored the modeling of linear single-phase loads (such as motors) and non-linear ones (such as those based on power electronics). However, induction motors exhibit non-linear characteristics between voltage and current due to the saturation of their magnetic parts. Therefore, it is necessary to study induction motors in the frequency domain with a model that allows reviewing the characteristic nonlinearity of their voltage-current interaction. Methodology: This article presents the frequency domain modeling of a single-phase induction motor used as a silent air extractor (127 V, 60 Hz, 66 W), which presents a capacitive behavior (fp = 0,93 in leading) and harmonic distortion due to a third-order component (7,0%) when fed with a pure sinusoidal voltage of 127 V. Results: This work establishes the parameters of two approaches to the Norton equivalent model (coupled and decoupled admittance matrix) which are used to estimate the distorted current signal and the values ​​of consumed active and non-active power. The results show comparisons errors of P, Q, THDi, and NRMSE indices of less than 7, 4, 14, and 3%, respectively. Conclusions: The parameters of the Norton equivalent model estimated for the single-phase induction motor allow calculating the current signal with a high degree of precision. This signal exhibits nonlinear characteristics and a capacitive behavior due to the permanent presence of a capacitor aiding the start and operation of the engine.

Модель совместной работы системы тягового и внешнего электроснабжения

Purpose: To improve record accuracy of external power supply network influence on the operation of traction power supply systems of industrial frequency AC. The article shows that existing mathematical models of traction and external power supply joint operation have sounding limitations. These limitations almost exclude the possibility of their practical use. At the same time, when projecting a new electrification, it is required to choose the most efficient external power supply scheme. At the exploitation of existing electrified sections, the necessity arises to assess equalizing current value during repairs in external power supply networks and to adopt a decision on changing power supply and sectioning schemes. Corresponding model is required to solve these tasks. Methods: Analysis of existing mathematical models and computer programs for joint calculation for traction and external power supply networks. Development of three-phase PU-generator models on the basis of EMF source behind an inductive resistance, development of three-phase and single-phase load models. Results: The article presents a description of a mathematical model implied to study the joint operation of 25 kV AC traction power supply systems and 110-750 kV power supply systems. The principles of building the model of three-phase and single-phase PU-generators on EMF source basis behind inductive resistance as well as the models of three-phase and single-phase loads are considered. Based on the given mathematical expressions, a computer model has been developed that allows analyzing the joint operation of three-phase external power supply networks and single-phase traction ones. The model is implemented in MATLAB-Simulink software package. Using this computer model, the influence of power flows through 110–330 kV network of Karelenergo and “FSK EAS” Public Companies on equalizing currents in the traction network of Knyazhaya — Idel section of Oktyabrskaya railway was analyzed. Practical importance: The reliability raise for traction power supply system operation at the expense of precise calculation of equalizing currents. Energy loss reduction in a traction network in account of traction network optimal power supply scheme choice.

Voltage control of standalone photovoltaic – electrolyzer- fuel cell-battery energy system

Abstract The study investigates the implementation of novel Neuro-Fuzzy controllers to maintain the power quality for standalone Photovoltaic (PV)-Electrolyzer-Fuel Cell- Battery based power generation systems. Standalone solar based power generation systems are widely becoming popular particularly in the remote areas with no connectivity to a grid. There are challenges to maintain the power output to meet the demand in these standalone systems because of the random nature of solar irradiances, variation of load and no irradiance during night time. The battery bank is required to store the excess energy for use later when required. The battery bank is integrated into a standalone system through a bidirectional DC to DC converter. However, large batteries are costly and require maintenance. Hence, electrolyzer and fuel cell are also integrated with respective DC to DC converters to make a cost effective operation. Small size battery bank is used to stabilize dc-link voltage during transients due to slow dynamics of electrolyzer and fuel cells. The maximum power point tracking (MPPT) device and perturbed and observed algorithm is used for the PV system to operate at maximum utilization. In this paper Neuro-Fuzzy controller based novel controllers are implemented to inverter and DC to DC converters for supplying quality power to both three phase and single phase loads at AC load bus. The presented results are examined through hardware-in-loop on the platform of OPAL-RT to investigate the proposed controllers in all the possible scenarios of a 1 MW standalone system. Results show that the proposed controllers improve the power quality and eliminate the frequency oscillations from the system voltage.

OPTIMAL PULSE WIDTH MODULATION IN THE ELECTRIC DRIVE CONTROL SYSTEM

The process of pulse width modulation (PWM) in the converter - electric motor system is considered. It is noted that the main task of pulse-width modulation of the voltage generated by the electron-key converter in the converter - electric motor system is to reduce current pulsations during the modulation period. It is proved that the dynamic process of changing the current in an electric machine on the PWM period can be approximated by an R, L-filter. It is established that the most important task of PWM is to minimize the current modulation error in the electric motor. The analysis of possible criteria for assessing the quality of the modulation process in electric drive control systems is carried out. It is shown that as an optimality criterion for assessing the quality of modulation in a converter - electric motor system, it is advisable to use an integral quadratic criterion of relative error, called local current dispersion, as well as the average value of local current dispersion over the period of the modulating function, called integral current dispersion. The process of single-phase modulation on a single-phase load is considered. Analytical estimates of the load current dispersion for this process are obtained. A condition, under which the current dispersion takes a minimum value, is recorded. The efficiency of pulse-width modulation optimization by the criterion of current dispersion is investigated. The average dispersion of currents in the load with a centrally symmetric arrangement of pulses on the modulation interval is taken as the base value of the dispersion. An expression that allows us to evaluate the efficiency of optimizing the current dispersion, taking into account the increment of the center of the modulation interval, is obtained. The dependence illustrating the efficiency of optimization by the criterion of pulse displacement relative to the center of the PWM interval on the relative frequency of modulation at different amplitudes of the modulating voltage is constructed. An expression is obtained for estimating the average value of the local current dispersion over the half-period of the modulating function.

Novel proposal for the analysis of technical losses in medium-voltage feeders from single-phase and three-phase load flow data

This work proposes a novel methodology for acquiring real data for load flow studies applied to the estimation of technical losses in three-phase unbalanced networks with renewable energy sources. A load flow analysis comprising an equivalent single-phase network is presented using real data under balanced conditions. In order to perform a three-phase load flow, it is mandatory to obtain electrical data from the three-phase network. However, there are no methodologies available in the literature for this purpose so far. In this sense, data collected from the application of the introduced approach in simulation tests were used to determine the technical losses in real three-phase feeders. From the results obtained in the single-phase analysis, one can identify the branches with the highest losses. The study could also be used as a benchmark project for reducing the losses by up to 94 MW in the region of Sobral, Brazil. From the results obtained in the three-phase analysis, it is possible to reduce the load imbalance in the real feeders while allowing the connection of renewable sources, resulting in a reduction of 73.32% in the percent losses, corresponding to US$ 2,315.21/month. Therefore, the data confirm that the analysis of technical losses and border measurements leads to satisfactory results, whereas the proposed method becomes an effective tool for distinct studies of the electricity sector. This approach is more accurate than the typical single-phase methodology, since it takes into account the load imbalance and the penetration level of distributed generation. Analysis of Electrical Networks (ANAREDE) and Network Analysis and Planning Studies of Power Distribution Systems (INTERPLAN) software were used to validate the three-phase analysis.

Strategy for compensation of unbalanced powers in LV residential distribution networks using distributed single-phase battery systems

Unbalanced powers, due to high penetration of single-phase PV rooftop systems and loads into a low voltage residential distribution system, can result in large neutral current and neutral to ground voltage rise. This paper proposes a distributed cooperative dynamic power balancing control strategy to mitigate the unbalanced powers using single-phase battery storage systems distributed in the low voltage residential distribution system. First, a distributed clustering algorithm is used to aggregate the battery storage systems connected to the same phase into the same cluster. Within each cluster, a distributed average grid power calculation algorithm calculates the average grid power exchanged with the corresponding phase. Then, the proposed distributed cooperative dynamic power balancing control strategy is applied to balance the unbalanced powers using the single-phase battery systems at the given bus while minimizing the power exchanged with the grid. The battery systems’ charge/discharge constraints, power constraints and willingness of the battery systems’ owners to participate in the power balancing control strategy are considered. Performance of the proposed strategy is verified using Real-Time Digital Simulator (RTDS).

수용가의 단상부하에 의한 전력계통 불평형 개선 연구

Electricity companies supply high-quality three-phase equilibrium power to capacity. However, a single phase load of the acceptor results in an amorphous power system. In design and construction, the single-phase load is distributed equally to each phase to minimize the inequality, but inequality is inevitable due to the different time zones of use of many unspecified loads. In the acceptance area, a separate single-phase transformer is installed to supply single-phase power to minimize three-phase inequality, but installation costs and installation spaces such as single-phase transformers and special high-pressure breakers are required. To improve this irrationality, this paper aims to supply single-phase power by introducing an open△ inverse connection method to the transformer tertiary side. The second side of the three-wheel transformer supplies three-phase equilibrium power, and the third side supplies single-phase power by open△reverse connections. Compared to the single-phase power supply method by a single-phase transformer, the quantity and loss of cables on the high-pressure and low-pressure sides are the same, and special high-pressure breakers and single-phase transformers are not required. This is in accordance with the government

Development of an algorithm for symmetrizing loads in networks of 0,4 kV at a distributed load along a line

PURPOSE. Consider the problem of unbalance of loads in electrical 0.4 kV networks, causing additional losses of electricity. Particular attention should be paid to networks with predominantly single-phase loads distributed along 0.4 kV lines. (rural electrical networks). To analyze the methods of balancing voltages and loads, both at the stage of designing electrical networks, and during their operation. Keep in mind that even with a properly designed electrical network with a uniform distribution of single-phase loads by phases during operation, due to the random nature of connecting new loads, including short-term connections, (for example, new household electrical receivers), current loads become asymmetric. Particular attention is paid to the issue of balancing load currents by switching them from the most loaded phases to the least loaded ones. Such switching is carried out on power transmission towers using the experience of operating personnel. To develop an algorithm for balancing current loads with the maximum exclusion of the human factor during balancing, using the readings of smart electricity meters as input data. The main idea of the algorithm is the calculation of modes for possible switching.METHODS. An algorithm that uses preliminary calculations of possible phase switching. When calculating the modes, the Newton-Raphson method was used, implemented by Matlab program.RESULTS. The article describes the relevance of the topic, considers the effect of asymmetry on the operation of electrical network elements.CONCLUSION. Calculations substantiating the main provisions of the phase switching optimization algorithm for balancing current loads are presented.

전기철도 급전계통 부하불평형에 대한 실험적 고찰

The domestic AC railway power supply system uses a scott transformer with two single-phase transformers T-connected for resolving the unbalance on the AC 3-phase power supply side. However, when single-phase M-phase and T-phase railway vehicles on the secondary side of the scott transformer exist as single-phase loads with different capacity, unbalance of current on the power supply side occurs.<BR>In this paper, In this paper, simulations were performed according to theoretical considerations and experiments were performed using a prototype simulator. The current unbalance on the power supply system was investigated when there was an impedance deviation between the windings of the Scott transformer and electric railway vehicles with different capacities were present on the secondary side catenary. The average error rate of the calculated value obtained through the formula and the simulation result value was within 1.68%, confirming that the implementation of railway power supply system modeling was confirmed. Also, it was confirmed that the impedance difference between the Scott transformer windings and the M-phase and T-phase load capacity unbalance cause unbalance in the current flowing in the power system.

Network performance evaluation of smart distribution systems using smart meters with TCP/IP communication protocol

The escalating significance of system reliability and resilience is transforming the planning and operation of contemporary distribution systems. To accomplish self-healing against power outages, advanced emerging technologies and devices such as smart meters are being deployed in the distribution systems. This work attempts to evaluate the performance of the smart distribution networks, where the communication protocol TCP/IP integrated with smart meters plays an essential responsibility. TCP/IP as a communication protocol has been used to send the data to the real world from simulation and receive it back into the simulation without losing data. Two-level control architecture has been proposed. The model has been designed using MATLAB/SIMULINK. To achieve it, the model consists of two LV distribution networks falling under one substation. Thus, two local controllers and one master controller have been modeled. Different single-phase loads (like domestic loads, colony loads having several houses, VIPs loads, shop loads, hospital loads, school loads, college loads, etc.) have been modeled as an amalgamation that has constant impedance and constant power loads. To simulate the functionalities of controllers, different case scenarios such as overcurrent protection, power theft, no shutdown of essential loads (like hospitals, VIPs), available power loss, and phase unbalancing in 42 residential loads altogether in two different areas have been studied and validated with real-time simulator through OPAL-RT.

Exploiting the Moth–Flame Optimization Algorithm for Optimal Load Management of the University Campus: A Viable Approach in the Academia Sector

Unbalanced load condition is one of the major issues of all commercial, industrial and residential sectors. Unbalanced load means that, when different loads are distributed on a three-phase four-wire system, unequal currents pass through the three phases. Due to it, a heavy current flows in the neutral wire, which not only adds the losses, but also puts constraints on three phases’ loads. In this paper, we have presented a practical approach for load balancing. First, we have considered the existing three-phase load system where the supply is a three-phase unbalanced supply. Before balancing the load, it is necessary to compensate the current in neutral wire. A nature-inspired moth–flame optimization (MFO) algorithm is used to propose a scheme for balancing of current in neutral wire. The information of a distributed single-phase load was used to balance the currents in a three-phase system. The feeder phase and load profiles of each single-phase load are used to reconfigure the network using an optimization process. By balancing the current of three phases, the current of the neutral conductor in substation transformers was reduced to almost zero.

Stability analysis of Three-phase Grid-Connected inverter under the weak grids with asymmetrical grid impedance by LTP theory in time domain

The Grid-connected inverter (GCI) often operates in the weak grid with asymmetrical grid impedance due to the unbalanced and single-phase loads. However, the time-periodic dynamic behavior effect of the Phase-Locked Loop (PLL) on the GCI operating in an asymmetrical system is not investigated in the time domain. This paper explores the influence of the asymmetrical grid impedance on the stability of the weak grid with GCI. Firstly, GCI's complete harmonic state-space (HSS) model considering PLL under the asymmetrical network is established. Secondly, in view of the developed HSS model, the predominant parameters are determined through the eigenvalues of the system state matrix, along with the participation factors. Afterward, with eigenvalue locus analysis, the stability boundaries of the system's critical parameters involving the current reference, current controller, and PLL controller are determined under different grid impedance asymmetrical indexes. It is found that the stability region of system parameters is narrowed with increasing impedance asymmetrical index. Lastly, simulations and experiments are carried out to verify the effectiveness of the proposed HSS model and the theoretical analysis results.Index terms— Grid-connected inverter, asymmetrical grid impedance, Phase Lock Loop, harmonic state-space model, stability boundaries, participation factors.

Three-phase Active Tracking AC-AC Voltage Regulator based on Buck Converter with an Efficient Hybrid Control Technique

This study proposes a switch-mode three-phase active tracking AC-AC voltage regulator based on the buck converter. The regulator topology incorporates a moderate number of components with less complexity and high efficiency. An efficient hybrid control technique, based on a closed-loop PID controller that is supported with a new designed feedforward controller, is proposed for the regulator control different to the similar studies in the literature. The hybrid control technique augments the response of active tracking of the reference output phase voltages to achieve an improved quality close to sine-wave output phase voltages for either the input AC phase voltages that are ideal pure sine-wave or include various harmonics. The regulator topology has a modular structure for independent control of each output phase. So, the regulator can help to achieve close to sine-wave output phase voltages to supply a balanced/unbalanced wye-connected three-phase load or independent single-phase loads. The presented three-phase regulator and the control technique are tested with simulation and experimental studies. The laboratory set-up of the regulator is designed for 2.2 kW output power, 0-300 Vp input phase voltages (50 Hz), and 0-200 Vp output phase voltages. The results demonstrated that the proposed switch-mode three-phase buck-type active tracking voltage regulator can provide the desired AC phase voltages with less than 5% THD (total harmonic distortion) and low harmonics for different operating conditions.