Unbalanced Load Conditions Research Articles

PENGARUH KETIDAKSEIMBANGAN BEBAN TERHADAP PROFIL JARINGAN TEGANGAN RENDAH

Load imbalance occurs due to unequal distribution of load in each phase, this can occur in low voltage network distribution lines, one of which occurs in the DS0588 transformer, Merdeka feeder, Denpasar. Based on the data obtained, the percentage of DS0588 transformer load unbalance is 14%. The DS0588 transformer is one of the transformers at the Merdeka Denpasar Feeder with a capacity of 160 kVA which is located on Jalan Badak Agung, Renon Denpasar. Load unbalance data obtained at PLN UP3 South Bali. The research was carried out by the method of redistribution of the load on each phase under unbalanced load conditions, so that the total load of the three phases is the same or close. The results obtained were that the percentage of unbalanced loads in unbalanced conditions was 14% and when balanced conditions decreased to 2.2%. The losses in the distribution network when the unbalanced condition is 25 kW and the balanced condition drops to 23.3 kW, this shows that the load imbalance has an effect on the low voltage network losses. The higher the load imbalance, the higher the losses incurred.

A Novel Prairie Dog-Based Meta-Heuristic Optimization Algorithm for Improved Control, Better Transient Response, and Power Quality Enhancement of Hybrid Microgrids.

The growing demand for electricity driven by population growth and industrialization is met by integrating hybrid renewable energy sources (HRESs) into the grid. HRES integration improves reliability, reduces losses, and addresses power quality issues for safe and effective microgrid (MG) operation, requiring efficient controllers. In this regard, this article proposes a prairie dog optimization (PDO) algorithm for the photovoltaic (PV)-, fuel cell (FC)-, and battery-based HRESs designed in MATLAB/Simulink architecture. The proposed PDO method optimally tunes the proportional integral (PI) controller gain parameters to achieve effective compensation of load demand and mitigation of PQ problems. The MG system has been applied to various intentional PQ issues such as swell, unbalanced load, oscillatory transient, and notch conditions to study the response of the proposed PDO controller. For evaluating the efficacy of the proposed PDO algorithm, the simulation results obtained are compared with those of earlier popular methodologies utilized in the current literature such as bee colony optimization (BCO), thermal exchange optimization, and PI techniques. A detailed analysis of the results found emphasizes the efficiency, robustness, and potential of the suggested PDO controller in significantly improving the overall system operation by minimizing the THD, improving the control of active and reactive power, enhancing the power factor, lowering the voltage deviation, and keeping the terminal voltage, DC-link voltage, grid voltage, and grid current almost constant in the event of PQ fault occurrence. As a result, the proposed PDO method paves the way for real-time employment in the MG system.

Power quality enhancement using a novel SAPF control scheme employing high selectivity filter

Abstract Severe issues such as degradation of power quality and efficiency have surfaced in past few years due to extensive use of power electronic converters for conversion and control in power system. The shunt active power filter (SAPF) has gained attention as a competent solution among researchers. However, most SAPF control schemes render ineffective results under non-ideal supply conditions. A novel single-phase p–q scheme based on high selectivity filter (HSF) for extraction of reference compensation currents is proposed in this paper. A three H-bridges (3HB) voltage source inverter (VSI) topology of SAPF is considered and its dc-link voltage is regulated using an Enhanced Bacterial foraging optimization (BFO) based PI controller. This topology along with the proposed SAPF control scheme can guarantee improved APF performance as each phase of the three-phase four-wire system can be controlled independently. Extensive investigations are carried out using MATLAB/Simulink simulations followed by real-time performance verification in Opal-RT Lab. The effectiveness is assessed in terms of current harmonics, excessive neutral current and current unbalance compensation. The results obtained with proposed scheme when compared with conventional three-phase and single-phase p–q schemes employing low-pass filters (LPF) yield remarkably superior results under ideal, distorted and unbalanced supply and unbalanced loading conditions.

A Novel Continuous Control Set Model Predictive Control for LC-Filtered Three-Phase Four-Wire Three-Level Voltage-Source Inverter

In this article, a novel continuous control set model predictive control (CCS–MPC) is proposed for an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -filtered three-phase three-level four-wire voltage-source inverter (3P-4W-3L-VSI). The proposed MPC algorithm provides independent control of each phase of the 3P-4W-3L-VSI under various unbalanced load conditions, which shows superior performance under unbalanced loads. Furthermore, different from conventional MPC methods, the CCS–MPC achieves fixed switching frequency, hence simplifying the design of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters. In addition, dc offsets are introduced to the proposed modulation to effectively balance the neutral-point voltage of the 3P-4W-3L-VSI. Experimental results are presented to verify the effectiveness of the proposed MPC algorithm.

Virtual Vector-Based Direct Power Control of a Three-Phase Coupled Inductor-Based Bipolar-Output Active Rectifier for More Electric Aircraft

Direct power control (DPC) has gained increasing attention in recent years as a simple and efficient control strategy for pulse width modulation (PWM) rectifiers. In this paper, the idea of DPC is introduced into the three-phase coupled inductor-based bipolar-output active rectifier (TCIBAR) for the first time, and a virtual vector-based direct power control (VVB-DPC) strategy is proposed for TCIBAR to realize the bipolar DC power supply for more electric aircraft (MEA). First, the mathematical model of the TCIBAR is deduced, and the basic principle of the classic DPC strategy is reviewed. On this basis, the limitations of the classic DPC strategy in TCIBAR control are analyzed. Second, a set of virtual vectors are derived to establish a novel virtual-vector switching table. Based on the virtual-vector switching table, the hysteresis power control of TCIBAR can be realized without affecting the DC-side neutral-point potential of TCIBAR. Finally, a neutral-point potential control method based on DPC architecture is studied and integrated into the VVB-DPC strategy to maintain the bipolar DC voltage balance of TCIBAR under unbalanced load conditions. The VVB-DPC strategy is experimentally studied on a TCIBAR prototype, and the experimental results verify the feasibility and effectiveness of the proposed strategy.

Neural Classification of Rotor Faults in Three-Phase Induction Motors using Electric Current Signals in the Frequency Domain

Three-phase induction motors are widely used in different applications in the industry due to their robustness, low cost, and reliability. Untimely identification and correct diagnosis of incipient faults reduce cost and improve the maintenance management of these machines. This paper explores a new method for robust classification of rotor failures in three-phase induction motors (MITs) connected directly to the electrical network, operating in a steady-state, under unbalanced voltages and load conditions. Through an innovative methodology, an analysis of the electrical current signals from 1 hp and 2 hp motors in the frequency domain was performed. Such analysis was applied in constructing input matrices for a Multilayer Perceptron Neural Network (MLPNN) to detect faults. Furthermore, this methodology proved to be robust because the samples of the failing and healthy motors include voltage unbalance conditions in the electrical supply and a significant variation in the load applied to the motor shaft. Such load variation was used for the detection of failures of 1, 2, and 4 broken bars consecutively on the rotor and in the condition of 2 broken bars and 2 other broken bars diametrically opposite. The results were promising and were obtained using 847 real samples from an experimental bench used to construct the neural model and its respective validation.

Design and modelling of three‐to‐five phase three‐limbed transformer

AbstractThis study presents a design study and modelling of three‐to‐five phase transformer with three‐limb magnetic core. The basics of phase transformation windings are discussed. The purpose of such winding is to produce at the secondary a balanced multiphase voltage system, from multiphase primary of different number of phases, without unbalance in the primary and secondary under load conditions. In order to overcome the imbalance due to the dispositions of the winding coils on the magnetic core, simulations using aided computer design are performed. Furthermore, this study presents a model of a three‐to‐five phase three‐limbed transformer, which is suitable for modelling the behaviour of this transformer at no‐load, under load, and under unbalance load conditions. This study is conducted by simulation and experimental tests.

Monitoring System for Levels of Voltage, Current, Temperature, Methane, and Hydrogen in IoT-Based Distribution Transformers

The distribution network is an integral part of electricity distribution, both technically and non-technically, which is very vulnerable to disturbances. This disturbance should be resolved as soon as possible so that it does not interfere with the performance of the electricity distribution and also damage the distribution transformer. In overcoming this disturbance, it can be done by using a safety device and a voltage breaker in each load area. The protection system in the distribution network must work quickly and immediately isolate abnormal conditions to prevent further damage and minimize blackouts. This disturbance should be resolved as soon as possible so that it does not interfere with the performance of the electricity distribution and also damage the distribution transformer. . The effects of this disturbance are changed in voltage, current, temperature, and gas levels in the distribution transformer. So we need a tool that can monitor the condition of the transformer. NodeMCU ESP8266 is a microcontroller that can connect to the internet network, which is used as the central control. The PZEEM-004T sensor is applied as a current and voltage reader. For gas measurement, the MQ-4 sensor is used to measure CH4 gas levels; the MQ-7 sensor is used to measure CO gas levels, and the MQ-8 sensor is used to measure H2 gas levels. The test results found that due to the unbalanced load conditions, there was an increase in temperature in the transformer, which resulted in changes in gas levels. Where from the test, it was found that the lowest gas content was CH4 reaching 113 PPM, CO went 21PPM, and H2 reaching 158PPM.

Modeling and Emulation of a Synchronous Generator Considering Unbalanced Load Conditions

Modeling and Emulation of a Synchronous Generator Considering Unbalanced Load Conditions

An Expanded Lyapunov-Function Based Control Strategy for Cascaded H-Bridge Multilevel Active Front-End Converters

Cascaded H-bridge multilevel (CHBML) active front-end (AFE) converters exhibit some enticing benefits, comprising high adaptability for numerous applications, such as tractions, solid-state transformers, electric vehicle charging stations, and medium and high power electric drives. Yet, when the CHBML- AFE is operating under an unbalanced load condition, it is crucial to utilize an advanced control technique to maintain system stability. In this research, a Lyapunov Function (LF)-based control approach is utilized for regulating a single-phase CHBML- AFE with LCL filter to achieve global asymptotic stability. A capacitor voltage feedback is introduced and added to the traditional LF-based control strategy to reduce the resonance of the LCL filter. Furthermore, the proportional-resonant (PR) control procedure is utilized to derive the grid current reference, offering improvement to the robustness of the current control design. A balanced DC voltage control method is also employed to suppress the unbalanced DC voltage conditions among CHBML- AFE cells. In addition, the transfer function of the reference grid current and the actual grid current is evaluated for the CHBML- AFE with LCL filter parameters and their eventual variations in the employed control technique. The effectiveness of this control strategy is validated utilizing simulation and experimental studies.

Stability Analysis and Control Design for Multiterminal HVDC Network With Power Flow Controller

The power flow control in high-voltage direct current (HVDC) grids can be improved by employing the interline dc power flow controller (IDCPFC). This article presents an improved control scheme using IDCPFC to balance power flow in the dc networks. In this work, a differential-mode transformer (DMT) is used in combination with a bidirectional buck converter to form a variable DMT. In comparison to the existing methods, the proposed system is scalable to higher voltages and powers, which makes it suitable for high-voltage dc transmission systems. Analysis of a small-signal model of the proposed method and design of compensator for improvement of transient behavior is performed. A simulation is performed with independent feed-forward and feedback control to show the effectiveness of the proposed method. The proposed method is also validated through a 600-W experimental prototype. The experimental results show that the current flow between lines is controlled for unbalance load conditions.

Numerical investigation of patellar instability during knee flexion due to an unbalanced medial retinaculum loading effect

Background and aimHealthy patellofemoral (PF) joint mechanics are critical to optimal knee joint function. Patella plays a vital role in distributing quadriceps load during the knee extension. Patellar tracking, not physiological tracking, causes an increase of strains in PF ligaments, peaks of localized stress of soft tissues and articular cartilage and bony parts, and knee pain; these problems lead to complications such as bone abnormalities and osteoarthritis. This research aimed to develop a Finite Element (FE) model to evaluate patellar instability due to the medial retinaculum asymmetric loading effect. MethodsA numerical model of the knee was obtained by matching nuclear magnetic resonance (MRI) for soft tissues and computerized tomography (CT) for bones, carried on a normal adult. Loading setup was chosen by using literature data. The intensity of the muscle forces was calculated by a static optimization taking into account ground reaction and knee flexion/extension during walking. The effect of patellar instability was obtained by gradually unbalancing this symmetry, one side was unloaded till 90 N, and the other loaded till 110 N. ResultsUnbalanced forces of 10 N acting on the retinaculum alone can produce a real difference in displacements of about 7 mm, and an increment of about 44% on patellar contact forces. ConclusionThis research demonstrated how an unbalanced forces acting on the retinaculum can produce significant patellar instability. Patellar instability starts at 25–30° of the knee flexion angle but tends to appear at 15° when the unbalanced muscular loading conditions are acting.

Optimal Control of BESS for Improved Grid Integration of the Hybrid DFIG/PV System Using Dual-Layer Adaptive Control

In view of the stochastic nature of wind and solar energy, maintaining quality power in grid-connected hybrid energy system is crucial for efficient energy utilization, especially in the presence of non-linear loads. This paper deals with the control and performance assessment of grid-integrated hybrid energy system that comprises of doubly fed induction generator (DFIG) and photovoltaic (PV) system including battery energy storage (BES) as a stand-by supply to meet utility and load demand. In order to maintain power balance and address various power quality issues encountered with hybrid renewable integration along the source and the grid/load end, a dual-layer variable-step size adaptive control is implemented for the grid-interfaced converter of the proposed system. The variable step-size based dual-layer least mean square (LMS) adaptive control functions by extracting weights of various control signals (stator and load current) where the step-size parameter adjusts according to the conditions that limit the maladjustment error and increase the rate of convergence. The DC-link voltage control realized by bidirectional BES control reduces the steady-state error and fluctuations in the voltage. An artificial bee colony (ABC) optimization is adopted for optimal gain tuning of the DC-link voltage controller as a result of which the battery performance and grid-side converter performance is enhanced with the increased power exchange to the grid. The system model is developed in MATLAB/Simulink and controller performance is evaluated for diverse operating conditions including steady-state, unbalanced non-linear load conditions, wind-speed and solar irradiation variation and specified grid power modes.

Design and Analysis of the Shunt Active Power Filter with the ε-NSRLMMN Adaptive Algorithm for Power Quality Improvement in the Distribution System

In this article, an adaptive normalized Sign Regression Least Mean Mixed Norm (ε-NSRLMMN) algorithm-based control technique is developed for the Shunt Active Power Filter (SAPF) to compensate for the grid current harmonics and reactive power under balanced and unbalanced loading conditions. The adaptive ε-NSRLMMN control algorithm improves power quality and makes the source current sinusoidal and power factor (PF) close to unity. It is used for load compensation in a three-phase distribution network. The fundamental active component is extracted from the distorted load current using an adaptive technique. This control algorithm has the advantages of improved convergence, better stability, lower harmonic distortion, less complexity and less steady-state error than the Sign regressor least mean mixed norm (SRLMMN), Least mean square (LMS) and least mean fourth (LMF). Adaptive ε-NSRLMMN is used for learning the fundamental active weight components of the load current. The parameters of the proposed algorithm are trained in real-time. A traditional PI controller has been used to regulate the dc-link voltage of the Voltage Source Converter (VSC). The performance of the proposed algorithm has been justified by simulation and experimental results.

Implementation of Unbalanced Thermoelectric Equivalent Circuit for Power Flow and Thermal Rating of Underground LV and MV Cables

This manuscript proposes a time-series temperature-dependent power flow method for unbalanced distribution networks consisting of underground cables. A thermal circuit model for unbalanced three-phase multi-core cables is developed to estimate the conductor temperature and resistance of Medium (MV) and Low Voltage (LV) distribution networks. More specifically, a novel approach is proposed to model and estimate the parameters of the three-phase thermal circuit of 3- or 4-core cables, using the results of Finite Element Method and Particle Swarm Optimization. The proposed approach is generic and can be accurately applied to any kind of 3- or 4-core cables buried in homogeneous or non-homogeneous soil. Furthermore, it is applicable in cases where one or more adjacent cables exist. Using the proposed approach, the conductor temperature of each core can be individually and precisely calculated even under unbalanced loading conditions. The proposed approach is expected to be an important tool for simulating unbalanced distribution networks and estimating the conductor temperatures. The proposed thermal circuit is validated using two 4-core LV and one 3-core MV cables buried in different depths in homogeneous or non-homogeneous soil. Time-series power flow for a whole year is performed in a 25-bus unbalanced LV network consisting of multicore underground cables.

Effects of Household Battery Systems on LV Residential Feeder Voltage Management

With the advancements of the battery energy storage systems (BESSs), reduction of their manufacturing costs and government subsidies, the BESS uptake is likely to increase rapidly in power distribution networks. This paper investigates the effects of residential BESSs on low-voltage (LV) networks using the actual household load profiles equipped with BESS and solar-photovoltaic (PV) systems. The electricity consumption data collected via smart meters (2200 households with PV/BESS, 1950 households with PV only and 1000 households without a PV or a BESS) at different solar-PV penetration levels and network types are used to simulate real network operating scenarios. A real LV distribution network in Australia is analysed in DIgSILENT PowerFactory under different scenarios, such as, customers with and without a solar-PV/BESS, with a solar-PV but without a BESS, and without a solar-PV, by using both the power flow and quasi-dynamic simulation studies under balanced and the unbalanced network loading conditions. According to the study, customers experience large voltage excursions from solar-PV power exports, which could be resolved by the household BESS, provided that the BESS charging is coordinated with the solar-PV production. Moreover, quasi-dynamic simulation shows that the BESS could reduce the violation of the over-voltage limit during the solar peak hours (midday) by lowering the worst-case feeder voltage by 3%. Finally, extreme-event (high solar PV generation scenario) simulation shows that the implementation of the BESS controller to facilitate charging BESS during afternoon solar-PV export may reduce the negative grid impact and will assist to avoid network upgrades.

Investigations on the Modulation Strategies for Performance Improvement of a Controlled Wind Energy System

The challenges faced in an isolated wind energy conversion system (WECS) are larger transient times, high steady-state error, and larger harmonic content. To overcome these issues, an adaptive voltage controller (AVC) along with the load current observer (LCO) could be the better proposition. However, the AVC and LCO, in conjunction with the conventional space vector pulse width modulation (SVPWM) technique to operate the three-phase inverter of WECS, would not be able to further improve these parameters. This paper proposes the use of the unified voltage SVPWM (UVSVPWM) technique along with the AVC and LCO, which could improve the transient behavior by about 30% as well as reduce the harmonic content of the load voltage and current by about 70% and 2%, respectively. This paper considers an isolated WECS connected to the linear load, which is operated under balanced as well as unbalanced load conditions. The proposed control technique is verified for both the balanced and unbalanced cases using MATLAB/Simulink.

An Improved Down-Scale Evaluation System for Capacitors Utilized in High-Power Three-Phase Inverters under Balanced and Unbalanced Load Conditions

The DC-link capacitors in an electronic power system are the main constraint of the power density and lifespan of the power converters. Evaluating the load life of capacitors working in severely adverse circumstances plays an important role in the design stages of the next-generation power converters. In this article, an improved evaluation system for the capacitors utilized in high-power three-phase voltage source inverters is proposed. The purpose of this article is to reproduce the same encountered stresses when a DC-link capacitor is used in a high-power inverter with pulse-width modulation. Hence, an improved down-scale evaluation system for the DC-link capacitors used in high-power three-phase inverter systems under balanced and unbalanced load conditions is proposed. Moreover, AC and DC analyses in the proposed evaluation system are conducted. The equivalent circuit and transfer functions are derived to verify the proposed evaluation system. Finally, a prototype system is constructed to facilitate the theoretical results as the verification.

Neural Network Controlled Solar PV Battery Powered Unified Power Quality Conditioner for Grid Connected Operation

The Unified Power Quality Conditioner (UPQC) is a technology that has successfully addressed power quality issues. In this paper, a photovoltaic system with battery storage powered Unified Power Quality Conditioner is presented. Total harmonic distortion of the grid current during extreme voltage sag and swell conditions is more than 5% when UPQC is controlled with synchronous reference frame theory (SRF) and instantaneous reactive power theory (PQ) control. The shunt active filter of the UPQC is controlled by the artificial neural network to overcome the above problem. The proposed artificial neural network controller helps to simplify the control complexity and mitigate power quality issues effectively. This study aims to use a neural network to control a shunt active filter of the UPQC to maximise the supply of active power loads and grid and also used to mitigate the harmonic problem due to non-linear loads in the grid. The performance of the model is tested under various case scenarios, including non-linear load conditions, unbalanced load conditions, and voltage sag and voltage swell conditions. The simulations were performed in MATLAB/Simulink software. The results showed excellent performance of the proposed approach and were compared with PQ and SRF control. The percent total harmonic distortion (%THD) of the grid current was measured and discussed for all cases. The results show that the %THD is within the acceptable limits of IEEE-519 (less than 5%) in all test case scenarios by the proposed controller.

A Finite Element Model for Investigating Unsteady-State Temperature Distribution and Thermomechanical Behavior of Underground Energy Piles

The underground energy geostructure represented by the energy pile is one of the key paths for the cooperative development of underground space and geothermal energy. Because of its advantages of low cost, high efficiency and no extra occupation of underground space, it has become a feasible alternative to the borehole heat exchanger. The change in the temperature field of the energy pile and its surrounding ground not only affects the geological environment but also influences the thermomechanical performance and the durability of the structure. However, the temporal and spatial unsteady-state temperature distribution of piles and surrounding rock under typical intermittent and unbalanced thermal load conditions is still unclear. In this paper, a finite element model was applied to analyze the unsteady-state temperature distribution, and the thermomechanical behavior of the energy pile group was developed and verified. The temperature field distribution of pile and surrounding rock under typical intermittent working and unbalanced thermal load conditions were determined. Moreover, the thermomechanical behavior characteristics of the energy pile group were investigated. Finally, the influences of pile layout on the thermomechanical behavior of the energy pile group were identified by designing six different scenarios. The results indicate that under typical intermittent operation conditions, the temperature of the energy pile and surrounding ground near the heat exchange pipe varies periodically. For areas with unbalanced cooling and heating loads, long-term operation of energy piles leads to thermal accumulation, and the maximum temperature of energy piles occurs in the first daily cycle. In summer/winter working conditions, the increase/decrease in pile temperature induces axial compression/tensile stress. When the pile group is partially used as the energy pile, the non-energy pile acts as the “anchor pile”, and it generates the added tensile stress.