Linear Load Conditions Research Articles

Evaluating the Harmonic Effects on the Thermal Performance of a Power Transformer

Harmonics in the power grid contribute to increased power losses in both the core and windings of power transformers. These losses lead to abnormal rises in temperature causing overheating and reduce the efficiency of the transformer. If the losses and temperature exceed the values set during the design stage for linear load conditions, it can damage the transformer’s insulating materials and shorten its lifespan. To assess the thermal impact of power system harmonics on transformers under steady-state and transient conditions, the rated losses and harmonic losses of the transformer are calculated. These losses are then inputted into a developed thermal 3D finite element method (FEM) performance model to determine the temperature distribution of transformer components. The numerical results from the thermal model will be compared with data from a Hyundai test report and real measurements from Egypt’s Kureimat power plant, specifically a 750 MW combined cycle power plant. The thermal modeling is focused on a step-up (16.5/240 kV), 240 ± 4 × 2.5%, 180/240/300 MVA power transformer operating in ONAN, ONAF1, and ONAF2 modes. This paper shows that the developed model aligns closely with actual measurements and the HYUNDAI test report. The loss calculations reveal that the discrepancy in total losses, with and without accounting for harmonics, becomes more pronounced as the load increases. Using this model, the presence of grid harmonics results in a higher temperature distribution across transformer components, leading to an increase in the hot spot temperature.

Hybrid optimal-FOPID based UPQC for reducing harmonics and compensate load power in renewable energy sources grid connected system.

Integration of renewable energy sources (RES) to the grid in today's electrical system is being encouraged to meet the increase in demand of electrical power and also overcome the environmental related problems by reducing the usage of fossil fuels. Power Quality (PQ) is a critical problem that could have an effect on utilities and consumers. PQ issues in the modern electric power system were turned on by a linkage of RES, smart grid technologies and widespread usage of power electronics equipment. Unified Power Quality Conditioner (UPQC) is widely employed for solving issues with the distribution grid caused by anomalous voltage, current, or frequency. To enhance UPQC performance, Fractional Order Proportional Integral Derivative (FOPID) is developed; nevertheless, a number of tuning parameters restricts its performance. The best solution for the FOPID controller problem is found by using a Coati Optimization Algorithm (COA) and Osprey Optimization Algorithm (OOA) are combined to make a hybrid optimization CO-OA algorithm approach to mitigate these problems. This paper proposes an improved FOPID controller to reduce PQ problems while taking load power into account. In the suggested model, a RES is connected to the grid system to supply the necessary load demand during the PQ problems period. Through the use of an enhanced FOPID controller, both current and voltage PQ concerns are separately modified. The pulse signal of UPQC was done using the optimal controller, which analyzes the error value of reference value and actual value to generate pulses. The integrated design mitigates PQ issues in a system at non-linear load and linear load conditions. The proposed model provides THD of 12.15% and 0.82% at the sag period, 10.18% and 0.48% at the swell period, and 10.07% and 1.01% at the interruption period of non-linear load condition. A comparison between the FOPID controller and the traditional PI controller was additionally taken. The results showed that the recommended improved FOPID controller for UPQC has been successful in reducing the PQ challenges in the grid-connected RESs system.

Development of renewable energy fed three-level hybrid active filter for EV charging station load using Jaya grey wolf optimization

This work develops a hybrid active power filter (HAPF) in this article to operate in conjunction with the energy storage system (ESS), wind power generation system (WPGS), and solar energy system (SES). It employs three level shunt voltage source converters (VSC) connected to the DC-bus. Optimization of the gain values of the fractional-order proportional integral derivative controller (FOPIDC) and parameter values of the HAPF is achieved using the Jaya grey wolf hybrid algorithm (GWJA). The primary objectives of this study, aimed at enhancing power quality (PQ), include: (1) ensuring swift stabilization of DC link capacitor voltage (DCLCV); (2) reducing harmonics and improving power factor (PF); (3) maintaining satisfactory performance under different combinations of loads like EV charging load, non linear load and solar irradiation conditions. The proposed controller's performance is evaluated through three test scenarios featuring different load configurations and irradiation levels. Additionally, the HAPF is subjected to design using other optimization algorithms such as genetic algorithm (GA), particle swarm optimization (PSO), and ant colony optimization (ACO) to assess their respective contributions to PQ improvement.

Power quality disturbance mitigation in grid connected photovoltaic distributed generation with plug-in hybrid electric vehicle

In the last twenty years, electric vehicles have gained significant popularity in domestic transportation. The introduction of fast charging technology forecasts increased the use of plug-in hybrid electric vehicle and electric vehicles (PHEVs). Reduced total harmonic distortion (THD) is essential for a distributed power generation system during the electric vehicle (EV) power penetration. This paper develops a combined controller for synchronizing photovoltaic (PV) to the grid and bidirectional power transfer between EVs and the grid. With grid synchronization of PV power generation, this paper uses two control loops. One controls EV battery charging and the other mitigates power quality disturbances. On the grid connected converter, a multicarrier space vector pulse width modulation approach (12-switch, three-phase inverter) is used to mitigate power quality disturbances. A Simulink model for the PV-EV-grid setup has been developed, for evaluating voltage and current THD percentages under linear and non-linear and PHEV load conditions and finding that the THD values are well within the IEEE 519 standards.

Three Parts Modulation and Hybrid DC Capacitor Voltage Balancing for a Single-Phase Two-Leg Five-Level NPC Inverter

Capacitor voltage unbalance in NPC multilevel inverters is an inherent challenge and has a severe effect on five and higher-level inverters. Current modulation-based voltage balancing schemes for five-level NPC inverters require a high number of switching, especially at high modulation index operations. Moreover, hardware-based voltage balancing techniques come with a high component count. This paper proposes a unique three-part modulation technique combined with a hybrid voltage balancing approach to reduce switching losses and maintain voltage balancing. The modulation is composed of different carrier-based modulations, while the hybrid balancing scheme combines modulation-based and hardware-based balancing techniques. Comparative switching loss analysis demonstrates a reduction in inverter switching associated with the modulation. While the voltage unbalance characteristics of the modulation are determined considering linear loading conditions. Furthermore, balancing capacity analysis and switching loss reevaluation are used to justify the hybrid balancing performance. The concept verification use Matlab-Simulink simulation and hardware experiments on a five-level single-phase NPC inverter setup operated at different modulation index and power factor conditions.

Conventional and lightweight aggregate one-way reinforced concrete slabs subjected to fire and repeated loads: comparative experimental study

ABSTRACT This study presents experiments on nine one-way, reinforced concrete slabs with a slab weight reduction approach utilising lightweight expanded clay aggregate (LECA). All slabs’ sizes, steel reinforcing, and concrete mix composition were equal. They were subjected to the same repeated linear load and high-temperature conditions. The slabs were classified into three groups based on the presence of LECA. The main variables were the LECA ratio (0, 20, 40) % of coarse aggregate and the exposure temperatures (ambient, 400, 700) ℃. The repeated load was applied according to the ACI-19 code, 50% of the ultimate load for seven cycles. The results showed that the presence of LECA reduced flexural strength and fire resistance. The deflection of the slabs increased with the LECA. The most significant reduction in ultimate load capacity was approximately 35.1%, with a maximum increase in slab deflection of 37.2%. However, the stiffness decay was significant, about 50%.

The material deformation modes of monocrystalline gallium antimonide (GaSb) under nano-scratching

The deformation characteristics of GaSb are investigated by employing nano-scratch tests to understand the material removal mechanism during ultra-precision grinding. The nano-scratches are obtained by a cube-corner tip under the two linear normal load conditions (0–30 mN and 0–60 mN). The normal force/scratch distance-penetration depth curves and the characteristics of chips and cracks are analyzed to understand the transition mechanism of ductile to brittle removal. In addition, the maximum principal stress near the bottom of the scratch is calculated to analyze the deformation behavior. The results revealed that the deformation behavior of three zones of deformation is plastic deformation, the transition from plastic to brittle deformation, and brittle deformation, respectively. The change rate of stress is significant differences in the zone of brittle-ductile transition. The critical ratio between mean contact pressures and hardness in the transition region is determined as 0.39 and 0.21, respectively.

Adaptive Least Mean Square Controller for Power Quality Enhancement in Solar Photovoltaic System

The objective of the proposed work is to develop a Maximum Power Point Tracking (MPPT) controller and inverter controller by applying the adaptive least mean square (LMS) algorithm to control the total harmonics distortion of a solar photovoltaic system. The advantage of the adaptive LMS algorithm is given by its simplicity and reduced required computational time. The adaptive LMS algorithm is applied to modify the Perturb and Observe (P&O), MPPT controller. In this controller, the adaptive LMS algorithm is used to predict solar photovoltaic power. The adaptive LMS maximum power point tracking controller gives better optimal solutions with less steady error 0.7% (6 watts) and 0% peak overshot in power with the tradeoff being more settling time at 0.33 s. The development of the inverter control law is performed using the d-q frame theory. This helps to reduce the number of equations to build a control law. The load current, grid current and grid voltage are sensed and transformed into d and q components. This adaptive LMS control law is used to extract the reference grid currents and, later, to compare them with the actual grid currents. The result of this comparison is used to generate the switching gate pulses for the inverter switches. The proposed controllers are developed and implemented with a solar PV system in MATLAB Simulink. The total harmonics distortion in grid and load current (3.25% and 7%) and voltage (0%) is investigated under linear and non-linear load conditions with changes in solar irradiations. The analysis is performed by selecting step incremental values and sampling time.

Enhanced control method for voltage regulation of DSTATCOM based SEIG

Self-excited induction generator (SEIG)-based wind energy conversion systems (WECS) are very popular for feeding stand-alone loads in remote areas where there is no grid. SEIG needs adjustable reactive power to regulate terminal voltage and frequency. Usually, a combination of a distributed static compensator (DSTATCOM) and a fixed capacitor bank is used to meet this reactive power demand. DSTATCOM is the most suitable option for power quality compensation. The performance of DSTATCOM depends on its control algorithm that generates the proper switching signals for voltage source inverter (VSI). Many control algorithms have been proposed for DSTATCOM in the literature. Among them, the most frequently used algorithms are synchronous reference frame (SRF), instantaneous reactive power (IRP), and current synchronous detection (CSD) algorithms. An effective control algorithm must accurately estimate the amplitude of the terminal voltage without being affected by harmonics, DC-offset, and frequency variation. For this purpose, an enhanced phase locked loop (EPLL)-based CSD control algorithm is proposed to estimate the amplitudes of individual phase voltages, and to filter SEIG voltages in case of harmonics, DC offset, and frequency variation. The proposed algorithm has been tested under linear and nonlinear load conditions. The obtained results clearly demonstrate the effectiveness of the proposed EPLL-based CSD control algorithm.

Analysis of Levenberg Marquardt - ANN based reference current generation for control of shunt active power filter

Shunt active power filter (SAPF) is an inevitable solution that needs to be installed by industrial consumers to prevent the power quality issues due to the non-sinusoidal currents drawn by non-linear loads. SAPF provides harmonic current compensation and reactive power management to eliminate the current related power quality issues. Various reference current generation schemes such as d-q theory, instantaneous reactive power theory, discrete Fourier transform, PI controller, fuzzy logic etc. are reported. Artificial neural network (ANN) is an emerging concept in SAPF for reference current generation. In this paper, detailed analysis of Levenberg Marquardt–feedforward ANN based reference current generation scheme for the control of SAPF is presented. This paper mainly focuses on successful implementation of Levenberg Marquardt algorithm for training the feedforward ANN network for reference current generation with different non linear and unbalanced load condition. Performance analysis of Leven Marquardt – ANN based reference current generation for the control of SAPF under different operating condition is carried out in MATLAB/SIMULINK platform.

Fuzzy and ANFIS Controllers to Improve the Power Quality of Grid Connected PV System with Cascaded Multilevel Inverter

In this paper, A Cascaded Multi level Inverter (CMLI) interconnected with the 10 KW PV System, Boost Converter along with Cascaded Feed Forwarded Neural Network (CFFNN) MPPT Controller is proposed to improve the Power Quality (PQ) for Linear, Non-linear and unbalanced loading conditions and minimize the total Harmonic Distortion (THD). The CMLI Consists of Novel type 9-Level Inverter with Reduced number of switches, and is connected to Bridged type inverter as cascaded, to get the required amount of Output voltage which can be used for grid integration. For controlling the inverter the Current controller is much required to control the current and to synchronize the Phase lock loop (PLL) is important. Here a new Adoptive Neuro Fuzzy Interface System (ANFIS) Control tuned with PI Controller is used to advance the performance of the power quality of the system under various loading conditions and undesired oscillations and THD can be improved compared with Conventional PI Controller and Fuzzy-PI Controller, Load voltage and current waveforms are analyzed under IEEE 519. The system is developed in the MATLAB environment to check the dynamic PV performance with MPPT controller and the results are found satisfactory.

Harmonics resonance elimination technique using active static compensation circuit

The existence of nonlinear loads produces high distortion and low power factor in the power system that leads to get poor power quality. Resonance problem is occurred due to the power system inductances and the compensation capacitors which increases the harmonic distortion. Therefore, it is necessary to prevent the action of resonance even if conventional or modern methods are built to improve the power system quality. In this paper, active static compensation circuit is proposed and designed to have the features of improving power factor, reducing THD, and eliminating the harmonics resonance effect at the same time with different linear and nonlinear load conditions. These features have been performed based on a modified pulse width modulation technique to drive and control the proposed circuit. The originality designed point of this technique is to have ability to operate the active static compensation circuit as harmonics injector, power factor corrector and resonance eliminator at the same time. Simulation model results illustrate that the proposed circuit is effective for both steady-state and transient operations conditions. The THD of the supply voltage and current at firing angle (α=300) is reduced by 99% and 98.8% respectively. While the power factor is improved to stay around unity.

Evaluation and Analysis of Soft Computing Techniques for Grid Connected Photo Voltaic System to Enhance Power Quality Issues

The major problem in grid connected transmission and distribution networks are the power quality issues due to the unbalance loads. The power quality issues relate to the current and voltage based issues generated at the point of common coupling. Some of the current based power quality issues relate to reactive power extraction, poor zero voltage regulation, harmonics in the load currents undesired neutral current and power factor and. Several DSTATCOM compensation techniques has been introduced for compensation of reactive power and power quality issues in the three phase, four wire system. The proposed system focus on DSTATCOM soft computing techniques such as: Widrow–Hoff least mean square, vectorial filter, discrete adaptive filter and quasi Newton control algorithms. The proposed algorithms controlled the switches pulses to drive the voltage source converter section in the DSTATCOM network thereby mitigating power quality issues and reactive power generation in the grid connected photovoltaic system. The soft computing techniques has maintained constant DC bus capacitor voltage and common coupling voltage along with unity power factor, zero voltage regulation under linear and non-linear load conditions, eliminating the harmonics in the load currents. The proportional integral controller is used for error correction between the reference and capacitor voltage. The novel drift-free maximum power point technique has shown better results under varying temperature and irradiances conditions. The DSTATCOM soft computing techniques has been implemented and simulated in MATLAB/SIMULINK.

A fractional derivative-based numerical approach to rate-dependent stress–strain relationship for viscoelastic materials

Strain/stress-controlled loading, loading–unloading, loading-relaxation (or creep), and corresponding cyclic tests are essential for characterizing the viscoelastic materials' rate-dependent stress–strain relationship. A three-parameter model is proposed based on the basic definition of fractional derivative viscoelasticity and time-varying viscosity. This model is applied to many complex loading conditions. The solutions for three monocyclic loading conditions are given and then further generalized to arbitrary linear loading conditions, which are assumed to be first-order functions of time. The generalized solution for the arbitrary linear loading path is validated by modelling the mechanical response of cyclic loading–unloading and loading–relaxation (or creep) tests. Four sets of experimental data for polymer materials are employed to demonstrate the proposed fractional derivative model's efficiency. The results show that it can accurately model strain/ stress-controlled response under various loading conditions using only three parameters. The model is then implemented in numerical software to explore its capacity further, and the simulation results show that it also succeeds in simulating cyclic loading–unloading tests.

Improved finite control set model predictive control for distributed energy resource in islanded microgrid with fault-tolerance capability

In this paper, improved finite control set model predictive voltage control (FCS-MPVC) is proposed for the distributed energy resource (DER) in AC islanded microgrid (MG). Typically, AC MGs have two or more power electronic-based DERs, which have the ability to maintain a constant voltage at the point of common coupling (PCC) as well as perform power sharing among the DERs. Though linear controllers can achieve above-mentioned tasks, they have several restrictions such as slow transient response, poor disturbance rejection capability etc. The proposed control approach uses mathematical model of power converter to anticipate the voltage response for possible switching states in every sampling period. The proposed dual-objective cost function is designed to regulate the output voltage as well as load current under fault condition. Two-step horizon prediction technique reduces the switching frequency and computational burden of the designed algorithm. Performance of the proposed control technique is demonstrated through MATLAB/Simulink simulations for single distributed generator (DG) and AC MG under linear and non-linear loading conditions. The investigated work presents an excellent steady state performance, low computational overhead, better transient performance and robustness against parametric variations in contrast to classical controllers. Total harmonic distortion (THD) for linear and non-linear load is 0.89% and 1.4% respectively as illustrated in simulation results. Additionally, the three-phase symmetrical fault current has been successfully limited to the acceptable range.

Asymmetrical 17-Level Inverter Topology With Reduced Total Standing Voltage and Device Count

Voltage source Multilevel Inverters (MLIs) are vital components for medium voltage and high-power applications due to their advantages like modularity and better power quality. However, the number of components used is significant. In this paper, an improved asymmetrical multilevel inverter topology is proposed producing 17-levels output voltage utilizing two dc sources. The circuit is developed to reduce the number of isolated dc-sources used without reducing output levels. The circuit utilizes six two-quadrant switches, three four-quadrant switches and four capacitors. The capacitors are self-balancing and do not require extra attention, i.e. the control system is simple for the proposed MLI. Detailed analysis of the topology under linear and non-linear loading conditions is carried out. Comparison with other similar topologies shows that the proposed topology is superior in device count, power quality, Total Standing Voltage (TSV), and cost factor. The performance of the topology is validated for different load conditions through MATLAB/Simulink environment and the prototype developed in the laboratory. Furthermore, thermal analysis of the circuit is done, and the losses are calculated via PLECS software. The topology offers a total harmonic distortion (THD) of 4.79% in the output voltage, with all the lower order harmonics being less than 5% complying with the IEEE standards.

Measurement of Simplified Single- and Three-Phase Parameters for Harmonic Emission Assessment Based on IEEE 1459-2010

This article investigates the feasibility of using a simplified approach, based on the measurement of power ratio parameters, for harmonic emissions assessment at the point of common coupling (PCC). The proposed approach comes from the common concept of power factor correction and the definitions of the IEEE Std. 1459-2010, where line utilization and harmonic pollution levels are evaluated by means of ratios between the power quantities of the apparent power decomposition. In addition to the IEEE Std. 1459-2010 indicators, in this article, the behavior is studied of additional parameters that are conceptually similar to those defined by the IEEE Std. 1459-2010. The suitability of such parameters is discussed, for both single- and three-phase balanced/unbalanced cases, taking into account both their behavior in different scenarios and their effectiveness when the measurement uncertainty is taken into account. The study is supported by some simulation results that have been obtained on an IEEE benchmark power system, which allows reproducing linear and nonlinear load conditions, balanced and unbalanced operating conditions, and the presence of capacitors for power factor correction.

Regulation of Hybrid Micro Grid Under Transient Operations

In recent times, there has been a significant awareness in the installation of distributed generation comprising of renewable energy resources such as wind and solar. The proposed hybrid micro grid is seen as a promising solution to counteract the effect of intermittency of wind and solar radiations. In this paper, a hybrid AC/DC micro grid interfaced with voltage-frequency controller is proposed. The proposed distributed control scheme overcomes the drawback of single point failure and also it does not require any communication link which reduces the cost. This novel strategy suits well in sustaining voltage and frequency in islanded operation of micro grid, as well as in grid connected mode and in resynchronisation with utility grid. The controller also maintains total harmonic distortion within specified norms under different balanced/unbalanced linear and nonlinear loading conditions. The SPS tool has employed to verify the efficacy of proposed topology.

Comparative Study of FCS-MPC and PWM Control Techniques for Autonomous Four-Leg VSI

Finite control set model predictive control (FCS-MPC) is considered as a new control technique in the power electronics fields which do not require modulation stage. The absence of modulation stage results in operating under variable switching frequency which can affect the harmonic distortion of the output signal, the switching losses, filters design and so on. On the other hand, the linear controllers control the power converters with constant switching frequency by using modulators. In this paper, the overall performance of FCS-MPC is assessed by performing a comparative study with a linear controller based on scalar pulse width modulation (PWM). The control systems are applied on an autonomous four-leg voltage source inverter (VSI) with LC filter as part of an autonomous power supply system. The main purpose of the two control techniques is to control four-leg VSI to provide balanced load voltage with lower total harmonic distortion. The steady state performance of the two control techniques is tested under balanced, unbalanced, linear and nonlinear load conditions. Moreover, the effect of the load variations on the switching frequency of the FCS-MPC is discussed. Finally, the performances of the two control methods in tracking the reference voltage under transient conditions are analysed.

Mitigation of power quality issues for grid connected photo voltaic system using soft computing techniques

Now a days Alternating Current distribution and transmission systems are suffering from many power qualities issues, mainly due to the presence of complex equipment in the residential, commercial, industrial applications. Power quality issues in distribution systems are classified as current-based and voltage-based quality problems. Complex Power Devices and distribution static compensators (D-STATCOM) are used to compensate for current-based power issues. The number of current-based power quality problems are unbalanced currents, undesired power factor, increased neutral current, and poor voltage regulation. Therefore, depending upon the problem, the configuration of the DSTATCOM is selected in the practice. This paper focuses on the control algorithms: Lorentzian adaptive filter, discrete adaptive filter, neural network least mean square and quasi newton control algorithms, for controlling shunt compensator (D-STATCOM) for compensating power issues, reactive power, unity power factor and load balancing under linear and non-linear load conditions with zero voltage regulation by maintaining constant capacitor voltage (VDC) and eliminate harmonic currents at point of common coupling by proportional-integral controller. In the proposed system MPPT is obtained by DC converter and the power quality issues are further analyzed in the existence of harmonics either in the currents or voltages. The DSTATCOM-control algorithms based solar Photo Voltaic system is simulated in MATLAB along with SIMULINK.