Unbalanced Nonlinear Load Research Articles

Harmonics Assessment of Distribution Transformer with Photovoltaic Integration and Unbalanced Loads

Harmonic distortion is one of the monumental power quality problems in an electrical power system. It frequently originated from non-linear loads generating non-sinusoidal steady state waveforms, which may lead to various undesirable effects on distribution transformers such as increased losses, overheating and lifetime reduction. In previous works, the harmonic current contributions from non-linear loads from consumers have been appointed as the main contributor of harmonic issues in the distribution transformers. However, since the integrations of renewable energy as a distributed generation (DG) have exponentially increasing in recent years, the impact of solar photovoltaic (PV) system implementation into distribution system on amplifying additional harmonic contents also needs to be addressed. Therefore, this paper conducts a comparative analysis of voltage and current harmonic profiles within the distribution transformer in three-phase distribution network and three-phase grid-connected photovoltaic (GCPV) system, with both subjected to supply unbalanced non-linear loads. The simulation is carried out using MATLAB Simulink 2021a software and the results are compared according to standards. As a result, the distribution transformer in the GCPV system is proven to contain higher levels of voltage and current harmonic distortion compared to a normal distribution grid.

Three-phase four wire shunt active power filter based on Simplified Backstepping technique for DC voltage control

This work presents a simulation of Three-Phase Four-Wire Shunt Active Power Filter (SAPF) destined to suppress harmonic currents generated by nonlinear loads. The SAPF guarantee also the compensation for unbalanced nonlinear load currents, reactive power and harmonic neutral current. The identification method is based on the synchronous reference frame. In order to have good performances of DC voltage control, simplified Backstepping control for three-Phase four-Wire (SAPF) system is proposed. Complete simulation of the resultant active filtering system validates the efficiency of the proposed simplified Backstepping control law over to the traditional control with PI controller.

Power Quality Improvement on 11kV/440V Distribution System using DSTATCOM

At the PCC and source side, current and voltage harmonics are compensated by utilizing a distribution static compensator. In this work, we also compensated for voltage control and reactive power correction. An improved reference current switching signal is suggested using a synchronous reference frame control technique. The analysis is done on an 11kV/440V three-phase four-wire unbalanced nonlinear load distribution system. The DC link voltage and harmonic reduction of the suggested distribution system performance is compared with the PI and fuzzy logic controllers. Harmonic distortion is reduced, and reactive power is successfully compensated with the suggested method. These simulation results are obtained by MATLAB/SIMULINK software.

Voltage Quality Factor for Networks Supplying Unbalanced Nonlinear Loads.

While the common term for describing the harmonic content and the unbalanced loading of the three-phase supply is power quality, it is actually the quality of the voltage that is being addressed in most cases. The power supply system can only control the quality of the voltage; it has no control over the currents that particular loads might draw. Therefore, the standards in the power quality area are devoted to maintaining the voltage within certain limits. In this paper, a voltage quality factor, designated VQF, is suggested that integrally assesses the voltage quality of a given three phase supply from the two aspects mentioned above.

Comparative analysis of control techniques using a PV-based SAPF integrated grid system to enhance power quality

The deterioration of power quality due to the increased adoption of Power Electronic Switching Devices is a major concern for electrical engineers. In addition to industrial loads, household loads cause numerous disturbances on the utility side, such as sags, ripples, flickers, and harmonics. It is possible to create power quality problems in a system or to have them arise due to a faulty consumer. This paper implements a renewable energy system with a Shunt Active Power Filter (SAPF) that injects PV energy into a power grid in the presence of nonlinear loads and under various load conditions to maintain power quality and improve power grid capacity. The Perturb and Observe (P&O) algorithm adjusts boost converter duty cycles to track the Maximum Power Point (MPP). The boost converter output is connected to the grid via a SAPF. The effectiveness of SAPF in reducing total harmonic distortion has been investigated using various reference current generation strategies of control methods and improved maximum power factor. The voltage source inverter switches are controlled through hysteresis current control. Moreover, this paper explains how to regulate the dc link capacitor of a three-phase SAPF with PI, fuzzy, and Adaptive Fuzzy Neuro Inference System (ANFIS) controllers to enhance power quality and compensate for reactive power and harmonic current caused by nonlinear loads. This system is developed under balanced and unbalanced nonlinear loads in MATLAB-Simulink. Furthermore, SRF-based reference current generation techniques with ANFIS controller to achieve better performance tested for control performance in proto-type hardware model to validate the proposed performance of this system.

A Device for Decreasing Loss in Electric Networks Containing Unbalanced Nonlinear Load

Matters concerned with controlling the operating modes of low-voltage electric networks are discussed. Thus, 0.4 kV electric networks are characterized by significant emission of additional current sequences generated by unbalanced nonlinear load. A versatile compensating device filtering additional power flows caused by unproductive fundamental and higher harmonic current components is proposed as a technical means minimizing the undesirable consequences of additional current load. A method and calculation software were developed, using which the operating mode of a 0.4 kV electric network section was studied with the possibility to incorporate a simulation model of the proposed device. The compensating device parameters are calculated proceeding from the unbalanced power consumption in the network section considered. By using the MATLAB software package, time diagrams visualizing the variation of the studied indicators have been obtained. The economic efficiency of the proposed versatile device for decreasing electric energy loss has been estimated.

A variable step size robust normalized least mean absolute third‐based control scheme for a grid‐tied multifunctional photovoltaic system

SummaryThis paper develops a variable step size robust normalized least mean absolute third (VSSRNLMAT)‐based control scheme for a three‐phase grid‐tied multifunctional photovoltaic system (GTMPVS). The GTMPVS delivers PV power to grid‐connected loads and feeds excess power to the grid through a voltage source converter (VSC) when PV power is available. It enhances power quality (PQ) by mitigating current harmonics and compensating for an unbalanced load and reactive power simultaneously. The proposed control scheme accurately extracts the fundamental active and reactive weight components of nonlinear load current. The power exchange at the grid side occurs with balanced and sinusoidal grid currents. During the absence of PV power, the VSC continues its operation as a distribution static compensator (DSTATCOM), thus increasing the effective utilization of the power electronic switches employed in the VSC. The GTMPVS model is created in MATLAB/Simulink. The response of GTMPVS is observed under steady‐state and dynamic operating conditions while feeding power to a nonlinear load. The dynamic operating conditions are created by a change in solar irradiation and an unbalanced nonlinear load. Further, the proposed VSSRNLMAT control scheme is compared with some of the other adaptive filtering‐based control schemes, including least mean square (LMS), least mean fourth (LMF), least mean absolute third (LMAT), and normalized LMAT (NLMAT) in terms of convergence, oscillations, mean square deviation (MSD), computational complexity, and grid current total harmonic distortion (THD). It is found that the VSSRNLMAT control scheme offers THD of grid current as per IEEE‐519 standard. The proposed control scheme is implemented to operate the laboratory‐developed GTMPVS to verify the simulation results.

A Proposed Supercapacitor Integrated with an Active Power Filter for Improving the Performance of a Wind Generation System under Nonlinear Unbalanced Loading and Faults

This study proposes the integration of a supercapacitor (SC) with the DC link of a three-phase four-wire active power filter (APF) by using an interfaced three-level bidirectional buck-boost converter controlled by the fuzzy control approach. APF is a flexible alternating current transmission system (FACTS) device that enhances power quality in the electrical network by reducing the load current harmonics and compensating the reactive power. Regulating the DC voltage of the APF’s DC link and absorbing fluctuations in compensated reactive power during disturbances are the major objectives of the integration of an SC circuit to APF. The studied model is a wind farm of Gabal El-Zeit with a total capacity of 580 MW, connected to unbalanced nonlinear loads. The Gabal El-Zeit wind farm is divided into three projects with a capacity of 240 MW, 220 MW, and 120 MW. The model is simulated by the MATLAB/SIMULINK program, and the effectiveness of the proposed methodology is proved by applying different types of faults such as single-line-to-ground, double-line-to-ground, and three-line-to-ground faults. In addition, an additional SC circuit with a two-level converter is connected to the generators coupled to the wind turbines to enhance the performance of the wind farm during disturbances. The results show that SC-integrated APF can reduce the harmonic distortion and compensate the reactive power for high or low inductive loads. Also, it can regulate the DC voltage and absorb the fluctuations in the reactive power during faults. Finally, the performance and the stability of the overall electric system are improved.

A Hybrid Microgrid Operated by PV Wind and Diesel Generator with Advanced Control Strategy

All for a local area that gets its power from a solitary diesel generator (DG), this examination presents an efficient power energy choice for a microgrid. A twin feed enlistment generator draws power from a sun oriented photovoltaic (PV) cluster and the breeze to run this microgrid's electrical gear (DFIG). Two voltage source converters (VSCs) are sequentially coupled on the rotor side of the DFIG and share a DC transport that at last prompts the photovoltaic modules. Likewise associated with a similar DC transport as the DFIG stator is a bidirectional buck/help DC converter and a battery energy capacity (BES) to retain any overflow power. Most extreme energy collecting from the breeze and sun is accomplished by regulation of the bidirectional buck/help DC converter and the rotor side VSC. A changed form of the irritate and notice (P&O) technique is introduced for of expanding the energy result of a PV framework. Endeavors are being made to change VSC on the heap side to further develop DG's eco-friendliness. The ideal fuel-use reference DG power result may now be resolved utilizing a new, more broad methodology. Using the Sim Power Systems toolbox in MATLAB, we model and simulate many scenarios, including fluctuating wind speeds, fluctuating insolation, the impact of fluctuating load conditions on a bidirectional converter, and an unbalanced nonlinear load linked at the point of common coupling (PCC). Finding sinusoidal and balanced DG and DFIG stator currents.

Field Programmable Gate Array-Based Execution on a Distributed Energy Resource Supported Electrical Distribution System for Enhanced Power Quality with Optimal Active Power Flow Control

This paper explains the experimental study of a distributed energy resource (DER) integrated three-phase, three-wire electrical distribution system (EDS) under power quality (PQ) and optimal active power flow control (OAPFC). In this research, a back-to-back connected two-level VSI (BTB-TVSI) based distribution static compensator (DSTATCOM) for unbalanced non-linear load is designed. The aim is to provide better OAPFC in EDS with shunt compensation to maintain a round-the-clock quality power supply for end users. The improved neural network-based adaptive least mean square (ALMS) control algorithms are employed for DSTATCOM. The ALMS control strategy is realized using the SPARTAN-6 field programmable gate array (FPGA) evaluation kit. This research involves the comparative study of a two-level voltage source inverter (VSI) and a BTB-TVSI in terms of their OAPFC capability and robustness in mitigating power quality (PQ) against source current disturbances, low power factor (PF), poor voltage regulation, unbalanced voltage at the point of common coupling (PCC), high switching stress, and issues in the EDS operation. The experimental results demonstrate that the BTB-TVSI using an ALMS controller is able to achieve better dynamic performance and lower total harmonic distortion (THD) under selected/permissible limits in comparison to a conventional VSI.

Control of ILC in an Autonomous AC–DC Hybrid Microgrid With Unbalanced Nonlinear AC Loads

This article presents a multiobjective control scheme for a bidirectional interlinking converter (ILC) of renewable energy based ac–dc hybrid microgrid. The prime focus of the power management algorithm is to feed the ac loads, and dc loads from ac source, and photovoltaic battery energy storage (BES), respectively. The second objective is to utilize the solar power to maximum capacity, by feeding it to dc load, BES, and ac load, in the given order of priority. The ac and dc subgrids operate independently, while supporting each other in case of overloading/underloading, thus reducing the amount of power reserve required in each, and eliminating the need of dump loads. The ANFIS-MN-based power quality control is integrated in order to ensure the total harmonics distortion of ac source current remains below 5% as per IEEE 519 standard, irrespective of the nature of load connected. In addition, the ILC control prevents any negative sequence currents from entering the ac source, even if there is any open circuit fault leading to unbalanced loading on the three phases. The performance of ANFIS-MN-based ILC control is demonstrated to be superior when compared with the conventional and contemporary techniques under different scenarios.

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 real-time validation of PI and Fuzzy Logic tuned photovoltaic integrated DSTATCOM to improve power quality.

Power loss and malfunctioning of equipment due to current and voltage harmonics produced by nonlinear loads are major concerns for both power suppliers and consumers. This paper employs DSTATCOM to mitigate these harmonic distortions in distribution systems. DSTATCOM is a current controlled voltage source PWM converter with passive components. It supplies compensating current that eliminates current harmonics and provides reactive power compensation thereby providing a smooth source current. The performance of DSTATCOM is controlled using proportional integral and fuzzy logic-based control (FLC) schemes to improve power quality at dynamic loading. As the penetration of photovoltaic (PV) systems in energy production is significant, the power quality issues for PV-integrated systems have also been investigated. The maximum power point for a PV array is tracked using perturb and observe and FLC methods. The complete system is simulated in MATLAB and extensively investigated for a large range of balanced and unbalanced nonlinear load conditions. The simulation results are validated in real time through the hardware in loop (HIL) test bench using Opal-RT controller. The proposed PV-integrated DSTATCOM with FLC yields better performance in terms of DC link voltage settling time, total harmonics distortion, and smooth source current as compared to other schemes.

Increasing Green Energy Penetration and Efficient Utilization Through a Finite Control Set Model Predictive-based Virtual Inductance Droop Control

As global energy demand hikes up, the search is to provide adequate penetration of green energy to the power grid to solve this threat of energy crisis and preserve the globe from pollution. Thus, this paper proposes an inverter control algorithm in the form of a finite control set model predictive-based virtual inductance droop voltage control strategy for a hybrid microgrid structure, which will provide a more effective platform for high penetration and efficient utilization of green energy. The new control algorithm as tabled in this paper considers the following aspects: DC voltage control, enhancement of reactive power issues with conventional control, fast dynamic response to AC load voltage regulation under balanced, unbalanced, and unbalanced non-linear loads, and power quality delivery in an autonomous hybrid microgrid system. To verify the performance of the proposed control method, simulation models are built under various operating modes of load variations and source unavailability. When analyzed, the findings show the control method's great efficacy to achieve desirable efficiency of green energy utilization and its greater accommodation into the microgrid. Additionally, it alleviates pressure on conventional generation and the utility system, avoiding the need for expensive grid improvements.

Implementation of ANN Controller Based UPQC Integrated with Microgrid

This study discusses how to increase power quality by integrating a unified power quality conditioner (UPQC) with a grid-connected microgrid for clean and efficient power generation. An Artificial Neural Network (ANN) controller for a voltage source converter-based UPQC is proposed to minimize the system’s cost and complexity by eliminating mathematical operations such as a-b-c to d-q-0 translation and the need for costly controllers such as DSPs and FPGAs. In this study, nonlinear unbalanced loads and harmonic supply voltage are used to assess the performance of PV-battery-UPQC using an ANN-based controller. Problems with voltage, such as sag and swell, are also considered. This work uses an ANN control system trained with the Levenberg-Marquardt backpropagation technique to provide effective reference signals and maintain the required dc-link capacitor voltage. In MATLAB/Simulink software, simulations of PV-battery-UPQC employing SRF-based control and ANN-control approaches are performed. The findings revealed that the proposed approach performed better, as presented in this paper. Furthermore, the influence of synchronous reference frame (SRF) and ANN controller-based UPQC on supply currents and the dc-link capacitor voltage response is studied. To demonstrate the superiority of the suggested controller, a comparison of percent THD in load voltage and supply current utilizing SRF-based control and ANN control methods is shown.

Utility intertie multi‐photovoltaic‐inverters‐based microgrid control for solar rooftop

The solar photovoltaic (PV)-based microgrid is one of the most ideal renewable energy resources. This paper presents a utility grid intertie multi-PV-inverter-based microgrid (MG) control for the solar rooftop application. The main and ancillary voltage source converters (VSCs) DC links are assimilated with PV arrays of independent maximum power point tracking (MPPT) algorithms for the economical and efficacious single-stage configuration. At the point of common coupling (PCC), parallel VSCs arrangement increases the MG's power rating with distinctive local loads. In normal circumstances, the current control methodology is employed by the main VSC under the grid-interactive mode. Conversely, in some grid contingency conditions under the isolated mode, its control transfers to the voltage control, which regulates the frequency and the voltage at PCC and acts like a grid-forming inverter. The ancillary VSC operation is implemented with the current control algorithm. The main VSC supplies the active power towards the grid and accomplishes the load requirement, whereas the ancillary VSC retains its load demand in a grid-interactive mode and also regulates the load requirement in an islanded mode of operation. The utilization of feed-forward components for PV arrays powers in the VSCs current control techniques improves the MG dynamic performance. The seamless mode transfer performance of the main VSC is implemented via a power electronics switch. The MATLAB software is used to model a microgrid and its performance is analysed via RT-LAB in real time through the OPAL-RT (OP4510) controller for various scenarios, that is, varying solar insolation, load alterations and unbalanced non-linear loads. The utilization of the modified Kwong's algorithm-based current control enhances the power quality such as harmonics current elimination and improvement in the power factor. The voltage profile of PCC voltages is enhanced via using a modified Kwong's algorithm-based filter in the voltage controller. The modified Kwong's algorithm has fast convergence, reduces misadjustments and gives very good performance compared to the least-mean-square (LMS) and Kwong's approaches. The total harmonic distortion (THD) of grid currents and PCC voltages THD in an isolated mode is found according to the limits of the IEEE-519 standard.

Grid integrated solar energy transfer system with a two‐layer complex coefficient filter‐based control

In this paper, a novel control strategy for grid-integrated solar energy transfer system (SETS) is proposed which enhances the grid power quality along with active power injection. Some of the conventional grid synchronization controls face problems due to imperfect estimation of fundamental active load current during both grid-side and load-side disturbances. The proposed two-layer multiple-complex coefficient filter control improves the performance of SETS by accurately estimating the fundamental active load current at adverse operating conditions. One layer extracts the fundamental positive sequence of the sensed three-phase grid voltages and derives the unit in-phase voltage templates for grid currents reference generation to achieve unity power factor operation. The second layer evaluates the average active fundamental component of the load currents, and finally derives the reference amplitude of three-phase grid currents. The two-stage SETS consists of a quadratic boost DC-DC converter to extract the maximum solar array power forming an interface between PV array and inverter. It also provides high voltage gain and decreases the length of the PV array string while maintaining a low DC-link voltage ripple, extending the service life of the SETS. The effect of a nonlinear unbalanced load is nullified and therefore the grid current's waveform quality is maintained in compliance with the IEEE-519 standard during the dynamic operating conditions. The SETS provides sinusoidal, balanced, and steady grid currents at unity power factor withstanding adverse operating conditions such as distorted grid voltages, varying irradiance and varying unbalanced nonlinear load currents. Due to its flexibility to operate in such adverse conditions, the proposed control based SETS is suitable for grid-connected applications. Simulations are carried out in MATLAB/Simulink and results validate the performance of the SETS. The hardware prototype of the proposed SETS is developed and rigorously tested under various operating conditions to validate the proposed claims.

A Cascaded Generalized Integral Control for Multiobjective Grid-Connected Solar Energy Transfer System

A cascaded generalized integral control algorithm is presented in this article for a solar energy transfer system (SETS), connected to the grid. The control algorithm introduces a two part fundamental component extraction such as, primary harmonics filter with higher order harmonic reduction and dc-offset rejection, and secondary fine fundamental component tuning with fractional order and lower harmonics rejection property. This SETS transfers electrical energy converted from solar radiant energy, efficiently to the three-phase distribution grid. The two-stage system consists of a boost type dc–dc converter on the primary side. Moreover, the incremental conductance algorithm-based operation of the boost converter ensures maximum power output from the photovoltaic (PV) array. This system is designed to meet load demands and feeds remaining power to the grid. It mitigates the reactive power and harmonics requirements of the load at any irradiance level, and thereby keeps the balanced sinusoidal grid currents, in-phase with the respective grid voltages. As the PV array power and load power are varying, performance of SETS with adverse operating conditions is validated in this work. A prototype is developed and tested under varying irradiance conditions as well as nonlinear unbalanced load. The steady-state and dynamic behaviors of the system during transient operating conditions are expressed to substantiate the acceptability of the control technique for multiobjective grid-connected SETS.

Multimode Robust Control for Reconfigurable Microgrid With Dynamic and EV Loads

This article deals with the control and implementation of a multiobjective reconfigurable microgrid with electric vehicles (EVs), dynamic loads [induction motor (IM)], and home loads. This microgrid is reconfigurable in an islanded and the grid-connected modes with a robust synchronization control. For EVs, the microgrid provides the charging facility, and for home and dynamic loads, the microgrid balances and regulates the point of common coupling (PCC) voltage and frequency in an islanded mode. Usually, in an islanded mode of microgrid, the PCC voltage and frequency are regulated under the sudden start of an IM load, EV charging, and unbalanced nonlinear loads condition. An improved-diffusion proportionate affine projection sign-based control algorithm is used for voltage source converter to regulate the voltage and frequency of the islanded mode of microgrid and also improving power quality. Moreover, the robust grid synchronization control is also introduced in the microgrid control strategy to connect it to the grid/diesel generator set with a seamless mode of transition. The performance of the microgrid is demonstrated through simulated results obtained in the MATLAB/Simulink, and test results are taken from the experimental prototype, which is realized in the laboratory.

Seven levels fuzzy rule-based controller for modified shunt active line conditioner

ABSTRACT This paper presents a seven levels inverter (MLI) used as 3Φ Modified Shunt Active Line Conditioner (MSALC) providing features of low harmonic distortion (low THD) and low Harmonic Current Ratio Factor (HCRF), reduced switching losses, suppressing harmonic currents, compensation of reactive power, enhancement of power factor, balancing load current under unbalanced non-linear load and distorted voltage conditions. It employs Self Tuning Filters (STF) for ideal (reference) current generation. Fuzzy Rule-Based (FRB) current controller generates switching patterns or sequence for Electrical potential source inverter. MATLAB fuzzy logic trainer toolbox is used for stimulating the proposed system. The effectiveness of the presented MSALC is desirable to suppress harmonics which is proved from the simulation results validated by experimental prototype hardware using the THD and HCRF values obtained which is not yet reported in other Shunt Active Line Conditioner (SALC) for various types of loads under both steady state and dynamic load conditions.