Nonlinear Load Conditions Research Articles

Power Quality Enhancement in Grid-Connected PV/Wind/Battery Using UPQC: Atom Search Optimization

Nowadays, the integration of hybrid renewable energy system (HRES) in grid connected load system are encouraged to increase reliability and reduce losses. The HRES system is connected to the grid system to meet required load demand and the integrated design creates the power quality (PQ) issues in the system due to non-linear load, critical load and unbalanced load conditions. Hence, in this paper, atom search optimization (ASO) with unified power quality conditioner (UPQC) is designed to solve the PQ issues in HRES system. The main objective of the work is the mitigation of PQ issues and compensate load demand in HRES system. The PQ issue problems are solved with the help of UPQC device in the system. The UPQC performance is increased by introducing fractional order proportional integral derivative (FOPID) with ASO based controller in series and shunt active power filter to mitigate PQ issues of current and voltage. Initially, HRES is designed with photovoltaic (PV) system, wind turbine (WT) and battery energy storage system (BESS) which connected with the load system. To analysis the presentation of the proposed controller structure, the non-linear load is connected with the system to create PQ issues in the system. The PQ issues are mitigated and load demand is reimbursed with the assistance of HRES system. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed. Three different cases are used to validate the performance of the proposed method such as Sag, Swell, and disturbances. Additionally, total harmonic distortion (THD) is analysed. The proposed method is compared with existing methods of proportional integral (PI) controller, gravitational search algorithm (GSA), biogeography based optimisation (BBO), grey wolf optimization (GWO), extended search algorithm (ESA), random forest algorithm (RFA) and genetic algorithm (GA).

Solar Powered Unmanned Aerial Vehicle With Active Output Filter Under Non-Linear Load Conditions

This paper presents a new electric powertrain for solar powered unmanned aerial vehicle (UAV). The proposed system structure is based on the development of the power supply system for both the Solong and Zyphyr aircraft models. The proposed UAV model incorporates the Zyphry UAV use of an AC line feeder instead of DC power lines to power the propellers. The proposed powertrain includes solar panels, an energy management system based on lithium sulfide battery, inverter, AC bus-line and active output filter (AOF). AOF topology is composed of a high switching frequency H-bridge inverter with a reduced size LC filter. The utilization of AOF system reduces the size and weight of the power transmission system and significantly improves its conversion efficiency by introducing an emulated series resistance with the H-bridge stage to ensure high quality pure sinusoidal waveform of the line voltage. This emulated series resistance produces an injected voltage across it to diminish unwanted harmonics created from the non-linear load. A simulation model and experimental setup are created to simulate the proposed system and the system is tested under non-linear load condition with closed-loop feed-back control strategy. The obtained simulation and experimental results demonstrate that high-quality sinusoidal line voltage waveforms can be obtained using the active resistance compensation technique with total harmonic distortion factor less than 3%. Moreover, power losses analysis and conversion efficiency calculation of the proposed system are performed and compared with that of the conventional three-phase PWM inverter, which proved that the power losses are reduced by 31%.

Synchronous Reference Frame with Finite Impulse Response Filter for Operation of Single-phase Shunt Active Power Filter

Power Quality (PQ) has been recognized as one of the main issues in electricity supply worldwide after the invention of nonlinear load. In 2017, PQ problem leads to significant economic losses in the Pan European region. Therefore, Active Power Filter has been developed during the past two decades to improve the harmonic compensation, reactive power, and voltage balance. In this research, the evaluation of the Synchronous Reference Frame (SRF) method is done under nonlinear load condition. The objective of this research is to modify the harmonic extraction algorithm based on SRF concepts for the application of single-phase shunt active power filter (SAPF) in harmonics mitigation and evaluate the performance of it. The performance of the SAPF that used SRF is evaluated and verified using MATLAB/Simulink. Besides that, the proposed SRF will be benchmarked with several existing techniques. The results are verified using MATLAB/Simulink with the aid of Powergui in the SimPower System block. Powergui has a built in Fast Fourier Transform (FFT) analysis tool that could perform harmonic analysis. With the aid of this tool, the Total Harmonic Distortion (THD) value can be viewed in the block. This research does achieve the THD value of the power system keeps under the limit set by IEEE standard 519.

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.

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.

Grid Integration of Renewable Energy Sources using GA Technique for Improving Power Quality

Hybrid Renewable energy sources (HRES) are rapidly increasingly compared to the traditional system since they are less effective to the environment and meet the huge demand required by the utilities. In the proposed paper the modelling, control and design analysis is implemented with PV, wind and battery as an energy storing device. The grid-interfacing inverter is regulated with a single-stage, three-phase RES-based distributed generation (DG) system. A genetic algorithm (GA) based shunt active power filter (SHAPF) is used to mitigate the power quality issues under nonlinear and unbalanced load conditions. The DG is grid-connected through a current-controlled –voltage source inverter (CC-VSI) via a DC link capacitor. Here the VSI is utilized to transfer the power from DG to the point of common coupling (PCC), SAPF to compensate for load current harmonics, under distorted supply voltage conditions, reactive power demand and load current imbalance. Both of these functions are important either individually or concurrently. As a result, the proposed controller regulates the power flow, controls it and acts as a SHAPF or does both at the same time. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed.

Mathematical Morphology-Based Artificial Technique for Renewable Power Application

This paper suggests a combined novel control strategy for DFIG based wind power systems (WPS) under both nonlinear and unbalanced load conditions. The combined control approach is designed by coordinating the machine side converter (MSC) and the load side converter (LSC) control approaches. The proposed MSC control approach is designed by using a model predictive control (MPC) approach to generate appropriate real and reactive power. The MSC controller selects an appropriate rotor voltage vector by using a minimized optimization cost function for the converter operation. It shows its superiority by eliminating the requirement of transformation, switching table, and the PWM techniques. The proposed MSC reduces the cost, complexity, and computational burden of the WPS. On the other hand, the LSC control approach is designed by using a mathematical morphological technique (MMT) for appropriate DC component extraction. Due to the appropriate DC-component extraction, the WPS can compensate the harmonics during both steady and dynamic states. Further, the LSC controller also provides active power filter operation even under the shutdown of WPS condition. To verify the applicability of coordinated control operation, the WPS-based microgrid system is tested under various test conditions. The proposed WPS is designed by using a MATLAB/Simulink software.

Power quality disturbance analysis using data-driven EMD-SVM hybrid approach

In the modern electrical power system network (EPSN), the power quality disturbances (PSDs) are the serious issue for the power engineer to maintain the uninterrupted and reliable power supply. Generally, PQDs are generated due to non-linear loading conditions, perturb loading and other occurrences such as transient, harmonics, sag, swell and interruptions. These problems of PQDs effect the power demand mapping problem, which effect the reliability and stability of the EPSN operating condition. In this study, a novel approach for PQDs diagnosis (PQDD) is proposed, which includes real-time data generation, data pre-processing, feature extraction, feature selection, intelligent model development for PQDD. Data decomposition approach of EMD is utilized to generate the feature vector of IMFs. These features are utilized as an input variables to the intelligent classifiers. In this study, PQDD is analyzed based on SVM method and obtained results are compared with conventional AI method of LVQ-NN. The results represent the higher acceptability of the proposed approach with diagnosis accuracy of 99.98% (training phase), 93.11% (testing phase) for SVM and 92.56% (training phase) and 91.0% (testing phase) for LVQ-NN based PQDD method.

Photovoltaic‐battery powered grid connected system using multi‐structural adaptive circular noise estimation control

The intermittent nature of renewable energy sources results in an interruptible and inadequate power. The integration of the battery energy storage to renewable energy sources provides reliable and continuous power to the loads. Further, the high penetration of renewable energy sources raises the power quality problems in the grid. This work deals with performance improvement of PV-battery energy storage based energy conversion system achieved through implementing a multi-structural adaptive circular noise estimation control for its grid connected mode. The control is developed for the grid side voltage source converter, which provides the power quality improvement and automated transition from grid connected mode to standalone mode or vice-versa. It provides multi-functional features such as harmonics extraction, DC offset elimination, and power quality improvement in PV-battery energy storage based energy conversion system even at nonlinear loading condition in grid connected mode. In standalone mode, the amplitude and waveform of load voltage are controlled sinusoidal by the voltage control. Performance of PV-battery energy storage based energy conversion system is studied to validate the acceptability of these controls according to the IEEE-519 standard.

Performance Comparison of DSTATCOM with PI and PSO-PI Controller under Nonlinear Load Condition

Performance Comparison of DSTATCOM with PI and PSO-PI Controller under Nonlinear Load Condition

Grid integration of Photovoltaic System Interfaced with Artificial Intelligence based Modified Universal Power Quality conditioning system

Unified Power Quality Compensators (UPQC) in load side utility system is not able to fully suppress harmonies in power grid and distortion in the interface system. To enhance the operation of the UPQC, a Fuzzy based Modified Universal power quality conditioning system (Fuzzy-MUPQCS) is developed. Modified Universal power quality conditioning system (MUPQCS) is a combination of two active filters in series and one active filter in shunt. A 3φ voltage source inverter is also used to maintain a common DC link capacitor voltage through Photo voltaic (PV) system connected to a utility grid. Highest Power Point Tracking (HPPT) algorithm is mainly used to pull out the maximum amount of power in the PV system. In this paper, Proportional integral controller based MUPQCS (PI- MUPQCS) and Fuzzy-MUPQCS are used to analyse the load voltage and load current distortion, THD analysis, power factor measurement, grid voltage and grid current distortion in the three phase system under nonlinear load conditions. The execution of the MUPQCS based 3φ system and the controllers are simulated using Matlab /Simulink model.

Design and analysis of Levenberg–Marquardt‐based adaptive SOGI

This study presents the design and analysis of an adaptive second-order generalised integrator (SOGI) technique for controlling voltage source inverter in a three-phase three-wire distribution system. The function of the proposed shunt active power filter involves compensation of reactive power for power factor correction, harmonic elimination, load balancing, voltage regulation under non-linear load condition. In this study, an effective approach for load compensation is proposed by designing an adaptive SOGI trained using Levenberg–Marquardt technique and compared with conventional techniques which ensure smooth operation under normal and distorted grid condition. An experimental setup is developed and its performance is analysed during different loading conditions. The experimental results are in line with the expected simulation results. Experimental and simulation results are verified and analysed using Bode plot.

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.

Generalized IDA-PBC Control Using Enhanced Decoupled Power Sharing for Parallel Distributed Generators in Standalone Microgrids

The development of an advanced modular control strategy for distributed generation-based islanded MicroGrids (MGs) is proposed in this article. This control strategy aims at achieving robust performances and accurate load power sharing in spite of system architecture. This strategy is based on the interconnection and damping assignment passivity-based control (IDA-PBC), which provides sufficient conditions to ensure the system modularity and stability. The design methodology of the proposed method is declined into three important steps. The whole system is modeled using the port-controlled Hamiltonian (PCH) formalism, the Hamiltonian function is minimized to synthesize the corresponding control laws, and finally, the stability of the synthesized control laws is verified. In this work, the Hamiltonian function is augmented with an enhanced decoupled droop (E2D) control in order to guarantee the stability of the whole system and ensure accurate power sharing when multiple DG units are interconnected. The effectiveness and modularity of the proposed modular IDA-PBC control with the E2D technique are evaluated and compared with a recent control strategy using an inner proportional-integral control with a decoupled droop technique. Experimental results and discussions are provided under resistive-inductive and nonlinear loading conditions.

Effect of Soil–Structure Interaction on Nonlinear Dynamic Response of Reinforced Concrete Structures

Investigating the nonlinear dynamic response of reinforced concrete (RC) structures is of significant importance in understanding the expected behavior of these structures under dynamic loading. This becomes more crucial during the design of new or the assessment of the existing RC structures that are located in seismically active areas. The numerical simulation of this problem through the use of detailed 3D modeling is still a subject that has not been investigated thoroughly due to the significant challenges related to numerical instabilities and excessive computational demand, especially when the soil–structure interaction (SSI) phenomenon is accounted for. This study aims at presenting a nonlinear simulation tool to investigate this numerically cumbersome problem in order to provide further inside into the SSI effect on RC structures under nonlinear dynamic loading conditions. A detailed 3D numerical model of full-scale RC structures considering the SSI effect through modeling the nonlinear frame and soil domain is performed and discussed herein. The constructed models are subjected to dynamic loading conditions and an elaborate investigation is presented considering different type of structures, material properties of soil domains and depths. The RC structures and the soil domains are modeled through 8-noded hexahedral isoparametric elements, where the steel bar reinforcement of concrete is modeled as embedded beam and truss finite elements. The Ramberg–Osgood constitutive law was used for modeling the soil domain. It was shown that the SSI effect can significantly increase the flexibility of the system, altering the nonlinear dynamic response of the RC frames causing local damages that are not observed when the fixed-base model is analyzed. Furthermore, it was found that the structures founded on soft soil developed larger base-shear compared to the fixed-base model which is attributed to resonance phenomena connected to the SSI effect and the imposed accelerograms.

MMLSTOGI based control for suppression of current harmonics in PV‐tied grid

In a photovoltaic array (PVA) tied grid system, PVA and the grid are connected at AC bus (ACB) to feed the power to the grid and the load connected locally at the ACB. The photovoltaic energy conversion system (PVECS) requires an improved dynamic controller to control the grid voltage harmonics under variable solar power and nonlinear unbalanced load conditions. The conventional filtering controllers are unable to remove the sub-harmonics and DC-offset in the input signal. Moreover, their attenuation for the dominant lower order harmonics is unsatisfactory for unbalanced loading conditions and highly nonlinear loads. A MMLSTOGI (mixed multi-level second and third order generalized integrator) based control is used in this work. It effectively mitigates the dominant lower-order harmonics and the DC-offset of load currents and extracts their in-phase and quadrature-phase fundamental components (FCs). The PVA is connected at ACB through interfacing voltage source converter (VSC). The DC-link voltage is ascertained by generating its reference value using an incremental conductance (InC) based maximum power point tracking. The PVA power is feed-forwarded in the control to enhance the dynamics of the system. The control is validated on a developed model in MATLAB SIMULINK background, and using a developed prototype.

Analysis of SOGI-ROGI for synchronization and shunt active filtering under distorted grid condition

This paper presents an interesting application of two different generalized integrators connected in a cascade configuration. A Second-Order Generalized Integrator (SOGI) and a Reduced-Order Generalized Integrator (ROGI) controller have been considered to cascade. The designed controller is applied to filter distortions in the grid voltage to generate a synchronizing signal as well as estimate the fundamental component of load current. Thus, their combination can achieve synchronization as well as find application in the improvement of the power quality of the distribution grid. In addition, the performance of SOGI-ROGI with the frequency locked loop (FLL) under frequency variations has been improved. Extensive simulation and hardware results are presented to illustrate the actions of designed controller under normal and distorted grid conditions. Results under highly distorted grid and non-linear loading conditions are presented vis-à-vis simple generalized integrators considered independently.

Study of the Mechanics of Spatial Elastoplastic Strain and Fracture of Weld Joints of Austenite Steels

The results of calculated–experimental and numerical studies of the relative strain intensity factors in the case of semi-elliptical inclined surface cracks in the weld joints of 12Kh18N10T austenite stainless steels with the assumption of redistribution of strain and initial residual stresses under nonlinear boundary loading conditions are presented. A parametric equation for the determination of the relative strain intensity factors in the case of semi-elliptical inclined surface cracks is given. This new parametric equation allows one to evaluate the comparative survivability of the local zones of details and construction in the bulk weld joint upon elastoplastic static and low-cycle loading.

A hybrid voltage‐current compensator using a synchronous reference frame technique for grid‐connected microgrid under nonlinear load conditions

A hybrid <scp>voltage‐current</scp> compensator using a synchronous reference frame technique for <scp>grid‐connected</scp> microgrid under nonlinear load conditions

Harmonic and unbalanced voltage compensation with VOC‐based three‐phase four‐leg inverters in islanded microgrids

This study proposes a novel method that combines sliding mode control (SMC) and virtual oscillator control (VOC) to eliminate voltage harmonics and unbalance caused by non-linear and unbalanced loads in a three-phase low-voltage microgrid. The conventional VOC is modified to fit the three-phase four-leg inverter systems and a novel SMC control is designed using the high-pass filter technique and linearised super twist algorithm. The proposed control method can keep the voltage harmonics and unbalance at the point of common coupling within the IEEE standard limits, under heavily non-linear and unbalanced load conditions. The validity of the proposed method is verified by both offline simulations in Matlab/Simulink and Control Hardware-in-the Loop simulations using an OPAL-RT platform.