Application Of Nonlinear Loads Research Articles

IIR filter-based compensator with modified feedback repetitive control scheme of voltage source inverter for nonlinear load applications

IIR filter-based compensator with modified feedback repetitive control scheme of voltage source inverter for nonlinear load applications

Hybrid One-Cycle-PI Control Algorithm for Shunt Active Power Filter in Mitigating Harmonic Currents

The quality of current waveforms, such as the presence of the harmonic components at the point of common coupling of various consumers, deteriorated due to the nonlinear load applications. Hence, a Shunt Active Power Filter (SAPF) is used to mitigate harmonic pollution in an electrical network. The heart of the SAPF operation is the current control technique. The choice of current control techniques significantly impacts the SAPF performance. As a result, a Hybrid One-Cycle-PI Control (HOCPIC) is proposed to work as a single-phase SAPF's current controller. The HOCPIC utilises a Proportional-Integral (PI) controller to minimise the error signal. As a result, the THD value of the supply current is reduced to 3.20% using the SAPF-based HOCPIC compared to 3.99% when using the SAPF-based OCC. The result proves that the SAPF-based HOCPIC performs better in compensating harmonic currents than the SAPF-based OCC.

Harmonics Mitigation Using MMC Based UPFC and Particle Swarm Optimization

The application of non-linear loads in the power electronic device causes serious harmonic issues in the power system since it has the intrinsic property of retrieving harmonic current and reactive power from Alternating Current (AC) supply that leads to voltage instability. To maintain a reliable power flow in the power system, an innovative Unified Power Flow Converter (UPFC) is utilized in this proposed approach. The conventional series converter is replaced with the Modular Multilevel Converter (MMC) that improves the power handling capability and achieves higher modular level with minimized distortions. The shunt compensator assists in minimizing the voltage fluctuations and maximizing the voltage stability under different load constraints. The Direct Quadrature (DQ) theory is utilized in this study to separate the harmonic components by generating reference frame current. The Proportional Integral (PI) controller aids in maintaining the direct current potential difference in the constant mode whereas the Pulse Width Modulation (PWM) generator helps in delivering optimized output to the MMC. The gain parameters of PI controller are optimized with the aid of employing Particle Swarm Optimization (PSO). The entire work is validated using MATLAB simulink and the obtained outcomes proves that this new UPFC is highly beneficial in minimizing the distortions with reduced Total Harmonic Distortion (THD) of 2.21%.

Power quality improvement in PV-grid system using hybrid lion-GH algorithm based custom power device

Voltage distortions, flicker and unbalances are the major synchronisation problems in grid connected photovoltaic system leading to power quality issues. Also, sudden changes of load, application of nonlinear loads and switching conditions causes power quality issues. To overcome these problems, the proposed grid connected PV system is implemented with a custom power device (unified power quality conditioner). The photovoltaic system is designed and implemented by mathematical model approach, and a maximum power point tracing-based (MPPT) dc-dc converter is used to extract maximum power from the solar system. The reference signal required for series and shunt converter of unified power quality conditioner (UPQC) is controlled with optimisation techniques. An MPPT-based boost converter is implemented with PV system to improve the efficiency in such a way that the duty cycle required for boost converter and parameters of PI controller are tuned effectively with an implementation of novel hybrid MPPT technique, i.e., hybrid connection of LOA-GH algorithm. This proposed system is to be implemented and tested in MATLAB/Simulink and results are to be verified with different controllers.

Effects of harmonic induction on metallic pipeline caused by overhead power lines

The industrial standards for dealing with the pipeline AC induction issue have been well established, and the limits for preventing the metallic pipeline from the AC induction have been specified. However, these standards only focus on 50/60 Hz induction. The noticeable harmonic induction on pipelines has been revealed by various field measurements and theoretical analysis with the rapidly increased application of nonlinear loads and devices in power systems. The harmonics are always considered a steady-state phenomenon. The major concerns of the pipeline AC induction in steady-state include touch voltage and pipeline corrosion. The limits for dealing with harmonic induction may not be the same as those for 50/60 Hz induction because both touch voltage and pipeline corrosion are frequency dependent. In this study, the AC induction limits for harmonics are investigated and proposed through analysis, simulations, and experiments. The results show that the AC induction limits for an individual harmonic are slightly stricter than or comparable with those for to the 50/60 Hz ones. However, the accumulative induction effect due to multiple frequencies, which is the practical case, is much more severe than that due to an individual frequency. A case study using field measurement suggests that the harmonic induction effect on the pipeline should be included in the AC induction coordination assessment.

Hybrid generalised power theory for power quality enhancement

This study proposes an advanced technique based on a hybrid generalised power theory (HGPT) decoupled approach for achieving enhanced power quality (PQ) in a solar-battery system. An 11-level reduced switch inverter (11-RSI) is proposed with reduced complexity to increase the voltage level and facilitate a one-way operation. On view to the simplicity in topology and to obtain maximum power operation, a modified perturb and observe-based maximum power algorithm is adopted. To avail better power management in the proposed microgrid (MG) system, a battery energy storage device is integrated with an appropriate control strategy. Moreover, an LCL filter is integrated in between the grid and 11-RSI, to filter the unwanted current harmonics and protect the system during any transient conditions. To test the robustness of HGPT during any non-linear load applications, various test cases have been formulated and investigated under different situations like change in solar irradiance, and battery charging and discharging conditions through Matlab environment, and compared with the conventional PQ control-based MG results.

A Comparative Study Of Harmonic Reduction Technique For Non-Linear Load Applications

A Comparative Study Of Harmonic Reduction Technique For Non-Linear Load Applications

Single Tuned Harmonic Shunt Passive Filter Design for Suppressing Dominant Odd Order Harmonics in order to Improve Energy Efficiency

Power quality refers to the provision of the clean and stable electrical power supplies with least interruptions of current and voltage However, power quality problems arise due to the application of nonlinear loads with end user devices. Electrical installations majorly suffer from adverse effects of harmonic currents and voltages. Though, this problem has been decades long and pattern of investigation for the researchers but due to evolution of semiconductor technology, it has become burning issue with reference to the power system loads. Therefore, it becomes necessary to mitigate these harmonics for the safe operation of electrical appliances. Thus, harmonic passive filters are cost effective and easy to implement. In this work, the mitigation of current harmonics has been accomplished through single tuned Shunt Harmonic Passive Filter (SHPF). Furthermore, the application of six pulse multiplication converter technique ensures the mitigation of dominant 3rd harmonic currents and reduction of succeeding 5th and 7th harmonic currents. Furthermore, shunt operation of single tuned harmonic passive filter enables the current to follow the low impedance path. Consequently, the current harmonic distortion becomes less than 5 % according to allowable IEEE 519 -1992 standards. This reduction in harmonic distortion not only reduces the losses incurred in the system but it also improves the energy efficiency of the electrical Power Distribution System (PDS).

Overview of power quality analysis and control technology for the smart grid

With the wide application of non-linear loads and the large-scale access of distributed energy generations based on power electronics equipments, power quality problems in the distribution network are increasingly serious with new characteristics. Further in-depth research is of great significance in theory and practice. This paper provides an overview of power quality analysis, compensators, and control technologies under the new situation of smart grid. It focuses on the topologies and control methods for power quality conditioners, especially new characteristics of power quality and applicable control technologies in microgrids and distributed power plants. Finally, trends and prospects of power quality control technology are introduced, which is important to achieve security and efficient operation of the smart grid.

Derating of transformers under non‐linear load current and non‐sinusoidal voltage – an overview

The increasing application of non-linear loads in power system causes additional losses in transformers resulting in premature damage. Manufactures and users of transformers realise the importance of this phenomenon and it is vital to adopt a procedure to prevent it thereby enhancing the reliability of power system. To achieve this, the most common method is derating of transformers. This paper intends to review derating of transformers under non-sinusoidal operation, for which all available approaches are classified into four major methods including IEEE recommended, analytical, experimental and finite elements based method. For each method, the fundamental theory, significant factors related to derating, test techniques as well as advantages and disadvantages are discussed. The methods are then evaluated and compared with each other from different points of view. Moreover, the overall trend of a more precise derating method is suggested. This review clarifies the research areas which require attention in the future to advance the subject.

Harmonic and Reactive Power Compensation of Grid Connected Photovoltaic System

Abstract Distributed Generation (DG) is predicted to play an important role in the electric power system in near future. It is widely accepted that photo voltaic generation is currently attracting attention to meet users’ need in the distributed generation market. In order to investigate the ability of photo voltaic (PV) units in distribution systems, their efficient modeling is required. This paper presents a dynamic model of a PV generation system. The increasing application of nonlinear loads may cause distribution system power quality issues. In order to utilize distributed generation (DG) unit interfacing converters to actively compensate harmonics, this paper proposes an enhanced control approach. In this paper, synchronous reference frame strategy has been chosen and a grid connected photo voltaic generation system (PVG) can send the active power to the grid, compensate harmonics and absorb the reactive power that the local loads generated. The converter controller models are implemented in the MATLAB / SIMULINK. The performance of the implemented PV model is studied with an isolated load. Synchronous reference frame strategy is used to generate current reference for compensation and conventional PI controllers are used for control. The strategy utilizes co-ordinate transformations to separate the reactive and harmonic content in the load current. The design of the closed loop controllers is kept simple by modelling them as first order systems. The simulation studies showed good results with the reactive current compensation giving almost ideal result of near unity power factor and harmonic currents getting compensated to a larger extent.

The Research Status and Development Trend of Active Power Filter

Power quality is getting worse with the extensive application of nonlinear loads, and active power filter technology is the effective way to settle the problem. This paper introduces the basic theory and the sorts of active power filters at first. Then the key technologies of active power filter are discussed in detail. Finally, based on some problems about current situation of active power filters, the directions of its development are analyzed in this paper.

Active Harmonic Filtering Using Current-Controlled, Grid-Connected DG Units With Closed-Loop Power Control

The increasing application of nonlinear loads may cause distribution system power quality issues. In order to utilize distributed generation (DG) unit interfacing converters to actively compensate harmonics, this paper proposes an enhanced current control approach, which seamlessly integrates system harmonic mitigation capabilities with the primary DG power generation function. As the proposed current controller has two well-decoupled control branches to independently control fundamental and harmonic DG currents, local nonlinear load harmonic current detection and distribution system harmonic voltage detection are not necessary for the proposed harmonic compensation method. Moreover, a closed-loop power control scheme is employed to directly derive the fundamental current reference without using any phase-locked loops (PLL). The proposed power control scheme effectively eliminates the impacts of steady-state fundamental current tracking errors in the DG units. Thus, an accurate power control is realized even when the harmonic compensation functions are activated. In addition, this paper also briefly discusses the performance of the proposed method when DG unit is connected to a grid with frequency deviation. Simulated and experimental results from a single-phase DG unit validate the correctness of the proposed methods.

Digital-Controlled Single-Phase Transformer-Based Inverter for Non-Linear Load Applications

The paper presents a new digital-controlled single-phase transformer-based inverter for non-linear load applications. A capacitive full-bridge circuit is added to provide instant current under non-linear load condition and thereby reducing the harmonics significantly to meet the required harmonic standard, IEEE 519-1992, even under non-linear load condition. The redundant capacity, cost, size and weight of line frequency transformer can therefore be dramatically reduced. Moreover, a new integrated controller for inverter control is proposed to eliminate both DC current component and steady state error even under heavy load condition. The proposed integrated controller consists of a Proportional (P) controller acts as voltage controller, DC offset canceller, an RMS compensator and non-linear load compensator.

Comparison of Power System Harmonic Prediction

Abstract Due to the advance in technology nowadays the application of nonlinear load is very demanding. The nonlinear loads that consist of power electronics devices in many applications may leads to power quality problems, and one of the major problems in power quality is harmonics. Active filter is a common tool has been used for harmonic mitigation, however the active filter use digital signal processing (DSP) to calculate the harmonic information which cause time delay between measured and injected harmonic that can results in failure to fully cancel the harmonics. This paper presents the concept, method and function of adaptive filters using Least Mean Square (LMS) and Recursive Least Square (RLS) to predict real time harmonics that may use in active filter to compensate for the time delay caused by the process of acquiring harmonic information. The results shown that the RLS and NLMS algorithms present a better performance than LMS and the mean square error (MSE) in general is increased when the harmonic order numbers that construct the signal increases.

Performance and Scalability of MJ Sequentially Fired Pulse Forming Networks for Linear and Nonlinear Loads

The principal advantages of the sequentially fired pulse forming network (SFPFN) over its passive analog are its utility in both linear and nonlinear load applications. Operation of the SFPFN consists of charging multiple capacitor banks to different voltage levels and sequentially firing these banks into the load at appropriate times. The load characteristics and the desired pulse attributes determine the module charge voltage and sequential firing schedule. This paper describes the pulsed power system and computer control system design of a 750-kJ SFPFN. Typical experimental results in the case of a linear load are presented and compared with simulations, and pulse-shaping capabilities are demonstrated. Scaling considerations are discussed in the case of increasing the SFPFN energy capacity to 7.5 MJ. The SFPFN uses a computer-controlled field programmable gate array to initiate the trigger signal for each module's output switch. The use of a computer-controlled firing circuit provides an opportunity to incorporate real-time load monitoring and feedback to select the optimal firing times and durations based on dynamic load conditions. The incorporation of feedback during a pulse sequence also allows for the firing sequence to be halted in the event of a fault or other potentially harmful event. The charging controller features a computer monitoring and control system to allow a single power supply to charge multiple capacitor modules by an array of switching relays, even though each module may be charged to a different voltage. In linear load testing, the SFPFN provided a relatively constant current pulse to a resistive load. Pulse-shaping capabilities are demonstrated by varying the charge voltage of individual banks prior to a firing sequence. Future applications of the SFPFN include powering a helical launcher

Implementation of a double AC/DC/AC converter with power factor correction (pfc) for nonlinear load applications

Implementation of a double AC/DC/AC converter with power factor correction (pfc) for nonlinear load applications