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International Review of Electrical Engineering - November 2011 - Vol. 6 N. 6 (Special Issue)

Special Issue on "Power Quality in Smart Grids"
Papers

Power Quality in Smart Grids
On Power Quality Study for a DC Microgrid with Real-Time Simulation Platform
Power Quality Behavior of Commercial Grade LED Lamps
A Low Voltage Smart Grid Control Strategy with Power Quality Issues
Apparent Power Definitions: a Comparison Study
Smart Microgeneration Systems for Power Quality Improvement
Improving Power Quality Using Power Electronic Transformer
A Novel Location Algorithm for Power Quality Disturbance Source Using Chain Table and Matrix Operation
Support Vector Regression and Rule Based Classifier Comparison for Automated Classification of Power Quality Disturbances
Are the Limits to Harmonic Voltages Given by International Standards on the Safe Side from the Viewpoint of Power Component Reliability?
Harmonic and Interharmonic Estimation Using Time-domain Quasi-synchronous Sampling Technique and Comb FIR Filter
Voltages Sensitivity Analysis in Radial Active Distribution Networks Using Novel Closed-Form Approximate Equations
A High-Efficiency AC PV-Module for High-Quality Connection to Modern Low-Voltage Distribution Grids
Adaptive Filter to Compute the Reference Current on Shunt Active Power Filters
Design and Analysis of a State-Feedback-Controlled Hybrid Active Power Filter
Experimental Validation of two Control Techniques Applied to a Three Phase Shunt Active Power Filter for Power Quality Improvement
An ANN Based Digital Controller with Three-Phase Shunt Active Power Filter for Power Quality Improvement

International Review of Electrical Engineering - Papers

Power Quality in Smart Grids
by Neville R. Watson

Vol. 6. n. 6, pp. 2684-2688

Abstract - Smart Grids is an initiative that many countries are devoting time and resources to due to the immense potential benefits. The technology Smart Grids employs has the potential to change the power quality customers see, both for the better and worse. This paper describes the main relations between Smart Grids technology and power quality It also discusses the barriers to Smart Grids and potentially new power quality challenges Smart Grids will present. The importance of having adequate standards is also highlighted if Smart Grids is to be successful.

Keywords: Power Quality, Smart Grids, Standards.

On Power Quality Study for a DC Microgrid with Real-Time Simulation Platform
by G. W. Chang, H. J. Su, H. J. Lu, K. K. Jen, C. H. Chung, J. Z. Wu

Vol. 6. n. 6, pp. 2689-2698

Abstract - A microgrid is a hybrid power system consists of several distributed generation resources and local loads, which provide the solution to supply premium power to remote or specific areas. However, some undesired effects are accompanied with their installations and operations, such as imbalance, voltage fluctuation, and harmonics, as well as inter-harmonics. To the aspect of voltage quality, the switching on and off of the distributed generation resources may cause power fluctuation, hence the associated power quality disturbances are produced and affect the connected power system. To the design of a hybrid power system such as an ac or dc microgrid, it is necessary to perform computer simulation for the planning and study. Before the actual system is built, all potential responses of the system should be known and then the design can be modified to avoid negative impacts to the system. This paper presents an application of the real-time simulation tool for power quality studies of the dc micro grid planning. Experiences of modeling a dc microgrid components are presented and simulation results are reported.

Keywords: Power Quality, Real-Time Simulation, DC Microgrid, Wind Turbine, Fuel Cell.

Power Quality Behavior of Commercial Grade LED Lamps
by M. Manana, A. Arroyo, L. M. Muniz, S. Perez, F. Delgado

Vol. 6. n. 6, pp. 2699-2703

Abstract - The utilization of LED technology in lighting applications has been increasing during the last several years. Parameters like efficiency, reliability, chromatic response and cost are important to consider this technology as a competitive one.LED technology involves power converters so overallPower Quality performance has to be analyzed in terms of emission and susceptibility. This paper reviews the Power Quality behavior of some commercial grade LED lamps and establishes a comparison with the long established incandescent lamp.

Keywords: Power Quality, LED Lamp, Flicker, Harmonics.

A Low Voltage Smart Grid Control Strategy with Power Quality Issues
by A. Bracale, P. Caramia, G. Carpinelli, S. Meo

Vol. 6. n. 6, pp. 2704-2712

Abstract - The paper deals with Smart Grids including renewable generation units, in particular concentrated photovoltaic systems and plug-in vehicles fleets. DG units and fleets are interfaced to the grid through static converters. Several services are performed thanks to the converters presence, with objectives aimed at meeting needs either internal or external to the Smart Grid. Optimization constrained problems are formulated and properly solved in order to perform the services in the best economical and technical way. Among the objectives to meet, the proposed optimal control strategy includes Power Quality issues such as the minimization of waveform distortions as well as the optimization of the voltage profile at fundamental frequency. A numerical application on a 30-bus low voltage Smart Grid test system gives evidence of the effectiveness of the proposed procedure.

Keywords: Smart Grid, Power Quality, Optimization model, Plug-in Vehicle, Photovoltaic cell-based systems.

Apparent Power Definitions: a Comparison Study
by Murat Erhan Balci, Alexander Eigeles Emanuel

Vol. 6. n. 6, pp. 27143-2722

Abstract - This paper examines the concept of apparent power: It advocates the idea that the apparent power quantifies an ideal situation that represents optimum energy flow conditions not only for the energy supplier, but for the consumers as well. Different apparent power definitions were evaluated based on the simulation of a typical power network that supplies linear and nonlinear loads. The effects of different methods of nonactive power compensation on the power factor, unbalance, harmonic distortion, motor power losses and converters voltage ripple are analyzed. It was concluded that the present apparent power definition needs improvement, a mathematical expression that will favor in equal measure the provider and the user of electric energy.

Keywords: Power Definitions, Power Quality, Harmonics, Unbalance, Standards.

Smart Microgeneration Systems for Power Quality Improvement
by S. Ferreira Pinto, J. Fernando Silva, Sérgio Lopes

Vol. 6. n. 6, pp. 2723-2735

Abstract - This paper proposes a Smart microgeneration system (SmartµG) to improve power quality, allowing reactive power compensation and high order harmonics mitigation. For comparison purposes an equivalent model of a conventional µG designed to comply with international standards is presented. A third order LCL filter is used in the connection to the LV grid to guarantee high order harmonics filtering. Linear and non-linear controllers are designed, and the obtained models are simulated in Matlab/Simulink, allowing the analysis and comparison of power quality parameters. The performance of both microgenerators is tested in a small LV grid model and some power quality indicators as the current and voltage Total Harmonic Distortion (THD), Power Factor (PF) and Displacement Factor (DF) are evaluated. The obtained results show that the proposed SmartµG allows a significant reduction of the grid current THD and a consequent reduction of the grid voltage THD, increasing the Power Factor and guaranteeing an overall power quality enhancement. Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved
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Keywords: Microgeneration, Power Quality, Smart Microgeneration.

Improving Power Quality Using Power Electronic Transformer
by Zhibing Wang, Kushan Yu, Xiaoxin Zhou

Vol. 6. n. 6, pp. 2736-2745

Abstract - Design and implementation of a mixed Power Electronic Transformer (PET), based on three-level converter and H-bridges, is presented herein, which is applied to Premium Power Park in Smart Distribution Network. As a new Custom Power Device (CPD), PET supplies a possible solution for mitigation of current harmonic, compensating reactive power, and supplying steady power source. In this paper, the detailed mathematical derivations, together with basic operating principles, are analyzed, and a compound control technology is used to Power Electronic Transformer, which considers the distortion of current, the quality of power supply, the stability of power system, and the reliability of equipments. Eventually the feasibility of Power Electronic Transformer is verified by simulation and experimental results.

Keywords: Custom Power Device, Power Electronic Transformer, Power Quality, Premium Power Park, Smart Distribution.

A Novel Location Algorithm for Power Quality Disturbance Source Using Chain Table and Matrix Operation
by Guoqing Weng, Youbing Zhang, Haibo He

Vol. 6. n. 6, pp. 2746-2753

Abstract - To determine the power quality disturbance (PQD) source in distribution network, a novel three-stage automatic location algorithm based on chain table and matrix operation is proposed. Firstly, fast pre-judgment of feeder sub-region of PQD is achieved according to chain table. Secondly, preliminary judgment of the PQD source is realized based on definition and operation of several critical describing matrices, which can be automatically generated with chain table and computer programming. Thirdly, accurate location algorithm is implemented using virtual power quality monitor(PQM) and extended matrices. A case study demonstrated that the proposed algorithm can realize location of PQD sources automatically and has many advantages such as small computational complexity and suitable for computer programming.

Keywords: Power Quality Disturbance(PQD), Location; Rooted Tree, Chain Table, Matrix Operation.

Support Vector Regression and Rule Based Classifier Comparison for Automated Classification of Power Quality Disturbances
by A. Mohamed, M. F. Faisal

Vol. 6. n. 6, pp. 2754-2761

Abstract - The ability to detect and classify all the types of power quality disturbances encrypted in a voltage signal is vital in the analyses of identifying the causes of such disturbances. In this paper, a comparative study is conducted using support vector regression (SVR) and rule based classifier (RBC) for automatically classifying power quality disturbances in a three-phase industrial power system. The S-transform is used to extract features of the power quality disturbances which are mostly non-stationary and comprise of multiple disturbances that coexist together for only a short duration in time. The performances of the SVR and the RBC were compared for their abilities in making prediction for the classes of power quality disturbances. The results for the analyses on 744 numbers of single and multiple voltage disturbances gave classification accuracies of 92.5% (SVR) and 100% (RBC), respectively. Copyright © 2011 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: : Power Quality, Disturbance Classification, S-transform, Support Vector Regression, Rule Based Classifier.

Are the Limits to Harmonic Voltages Given by International Standards on the Safe Side from the Viewpoint of Power Component Reliability?
by Giovanni Mazzanti

Vol. 6. n. 6, pp. 2762-2772

Abstract - Power quality disturbances in “Smart Grids” encompass harmonic distortion. International standards such as IEC 61000 or EN 50160 set limits to harmonic voltages in public networks. This paper investigates whether such limits are always “on the safe side” from the viewpoint of the reliability of power components, by employing a probabilistic life model for estimating some reliability parameters of power devices operating in distorted regime. The model accounts not only for a possible temperature rise due to distorted current, but also for the effects of harmonic voltages on component insulation life via peak, shape and rms factors of the distorted voltage. Reliability parameters are derived for typical LV and MV cables and capacitors by simulating the random variation of voltage harmonics according to the probabilistic limits given in EN 50160. The application – that considers the role played by the phase-shift between voltage harmonics and the fundamental - shows that even if harmonic distortion matches EN 50160 limits, component life and reliability may be reduced significantly with respect to rated sinusoidal operation. Furthermore, not only the peak, but also the shape factor of the distorted voltage plays a non-negligible role.

Keywords: Harmonic Distortion, Voltage Harmonics, Power Component Reliability, Insulation Ageing, Life Modeling.

Harmonic and Interharmonic Estimation Using Time-domain Quasi-synchronous Sampling Technique and Comb FIR Filter
by Feng Zhou, Chunyu Zhao, Zhenyu Huang, Dayue Chen

Vol. 6. n. 6, pp. 2773-2784

Abstract - A triple-stage signal processing technique is developed for harmonic and interharmonic estimations in power systems. Firstly, the fundamental period is evaluated accurately by the multi-rate narrow bandpass finite impulse response (FIR) filter and the zero-crossing method. The actual sampling sequence can then be reconstructed to a quasi-synchronous sampling one. Consequently, a comb FIR filter can be applied to separate harmonics and interharmonics. Secondly, interharmonics are evaluated by the windowed and interpolated fast Fourier transform method, of which, harmonic interference is eliminated from interharmonics by the comb FIR filter. Thirdly, harmonic parameters are determined directly from the discrete Fourier transform results after quasi-synchronization. Simulation results show that the present method has a high accuracy of measurement for harmonic and interharmonic estimations under the circumstances of noise interference. Finally, experimental results on a self-developed power quality analyzer have demonstrated the validity of both the algorithm and the simulation.

Keywords: Harmonic Analysis, Interharmonics, Power System Parameter Estimation, Synchronization, Comb Finite Impulse Response (FIR) Filter, Multi-Rate Signal Processing.

Voltages Sensitivity Analysis in Radial Active Distribution Networks Using Novel Closed-Form Approximate Equations
by S. Conti, S. A. Rizzo

Vol. 6. n. 6, pp. 2785-2795

Abstract - The paper presents a novel closed-form approximate analytical formulation to quantify node voltage variations due to changes in active and reactive power, i.e. voltage sensitivity coefficients, at MV active distribution networks nodes. This is achieved by firstly obtaining a new closed-form approximate equation for node voltages. The developed expressions allow to workout voltage sensitivity coefficients as derivatives of voltage with respect to active and reactive power, thus avoiding the need for gradient-type iterative methods, which would require high computational effort. Finally, the analytical expressions are applied to assess voltage sensitivity of a test MV distribution network by using various typical conductors type, length and section in presence of different load/generation conditions.

Keywords: Active Power Distribution Systems, Distributed Energy Resources, Power Quality, Voltage Sensitivity, Power Flow.

A High-Efficiency AC PV-Module for High-Quality Connection to Modern Low-Voltage Distribution Grids
by R. Carbone, A. Tomaselli

Vol. 6. n. 6, pp. 2796-2805

Abstract - The paper deals with the possibility to introduce an innovative Photovoltaic (PV) AC-module, which main characteristics seem to make it particularly interesting for using in modern low voltage (LV) distribution grids, as low-power distributed generator from renewables. The introduced AC PV-module is simply based on a conventional DC PV-module endowed by the following additional and innovative components: (i) a mini and distributed on-board energy storage system, (ii) a cascaded H-bridge multilevel inverter with line-frequency switching and (iii) a passive, single-axis solar tracker with negligible additional consumption of power and high reliability. Firstly, a certain number of rechargeable batteries are proposed to be connected in parallel to a specifically designed number of PV-cells of the module, basically according to a criterion of maximizing the PV-module generating energy. Once introduced and designed this mini, distributed, passive energy storage system, the on-board available DC voltage physical levels are separately utilized as input for a cascaded H-bridge multilevel inverter, that is proposed to be mounted on the backside of the PV-module. Its main advantages can be founded in a quasi-sinusoidal output voltage with no high frequency harmonics, with low THD and in very low switching losses; also voltage harmonics at the lower frequencies can be eliminated by a proper control strategy. Finally, an innovative on-board solar tracker is proposed to be used for rotating, from a minimum to a maximum angle, only the cells of the PV-module, avoiding to rotate also the PV-module container and its remaining heavy components. In this way, additional power consumptions for following the solar position are practically eliminated; furthermore, being all the solar tracker components encapsulated into the module container, all issues related to failures caused by negative actions of atmospheric agents (wind, dust, rain, important temperature variations …) on mechanical and electrical components are avoided and, so, reliability results highly improved. In order to avoid any additional sensor for evaluating solar position to be followed by cells of the PV-module, together with complex control systems and actuators, a simple “shadowing screen” is proposed to be mounted only on a single “pilot-cell” of the module able to continuously follow the solar position: if the sun is not optimally aligned with the “pilot-cell” (and with all the mechanically interlocked cells of the PV-module), a differential of shadows, projected on the two sides of the “pilot-cell”, occurs and it is utilized to actuate a motor that will rotate the “pilot-cell” (together with all the cells of the module) until it is optimally aligned with the sun.

Keywords: AC PV-Modules, Photovoltaics, Distributed Generation, Smart-Grids, Energy-Storage.

Adaptive Filter to Compute the Reference Current on Shunt Active Power Filters
by Johann F. Petit, Guillermo Robles, Hortensia Amarís

Vol. 6. n. 6, pp. 2806-2815

Abstract - In this paper a new Adaptive Notch-Kalman Filter (ANKF) is proposed to estimate harmonics and symmetrical components in distorted and unbalanced electrical signals. The new filter is an adaptive system that includes a Notch filter in cascade with a Kalman filter. The Kalman filter outputs are fed back to the Notch filter in a recursive process guaranteeing optimal signal parameters estimation and fast convergence without the use of a synchronization tool such as a phase-locked loop (PLL). The ANKF can be configured either for single-phase or three-phase applications and has two operation modes: normal mode and enhanced mode. The first one is a steady-state mode and guarantees the filter’s ability to suppress the undesired signal components. The second one is a transient mode which accelerates the filter convergence every time that it detects a change in the steady-state signal, so that the new steady-state signal can be obtained faster. The filter feasibility has been successfully tested on different waveforms, obtaining a good and fast response. In addition, the proposed filter has been used in an experimental setup to compute the current reference in a shunt active power filter.

Keywords: Active Power Filter, Power Quality, Signal estimation, Kalman Filter.

Design and Analysis of a State-Feedback-Controlled Hybrid Active Power Filter
by Leopold Herman, Igor Papič

Vol. 6. n. 6, pp. 2816-2824

Abstract - This paper deals with reactive-power compensation and harmonics elimination using a hybrid active-power filter. It proposes a state feedback-controlled hybrid filter as a combination of a three phase, two level, voltage-source converter connected in parallel with an inductor of a shunt, single tuned, passive filter. This topological structure greatly decreases the voltage and current stress over the elements of the active filter. Since the topology is composed of a single tuned branch, the control structure also has to ensure sufficient filtering at other harmonic frequencies. In this paper an integral, state-feedback, multi-loop controller is proposed. To design the controller a mathematical model of the proposed filter in state-space is developed first. The effectiveness of the hybrid active filter is demonstrated on a realistic industrial-network model by means of computer simulations.

Keywords: Harmonics, Hybrid Filters, Mathematical Modelling, Power Quality, State Feedback Control.

Experimental Validation of two Control Techniques Applied to a Three Phase Shunt Active Power Filter for Power Quality Improvement
by Mustapha Sarra, Jean-Paul Gaubert, Abdelmadjid Chaoui, Fateh Krim

Vol. 6. n. 6, pp. 2825-2836

Abstract - This paper presents the comparative evaluation of the performance of two control techniques to determine the reference current for a three phase shunt active power filter (APF) in order to improve the power quality and compensate reactive power required by nonlinear load. The first one is based on the use of classic PI controller and the second one is based on instantaneous power theory (p-q theory). Both control techniques are based on time domain, simulated with Matlab/Simulink and validated with an experimental test bench developed in the LAII laboratory, University of Poitiers. Various simulation and experimental results are presented under steady state and transient conditions with a comparison between the two control techniques.

Keywords: Active Filter, Harmonics, Converter Control, Power Conditioning, Power Quality, Voltage Source Inverters (VSI).

An ANN Based Digital Controller with Three-Phase Shunt Active Power Filter for Power Quality Improvement
by Sindhu M. R., Manjula G. Nair, T. N. P. Nambiar

Vol. 6. n. 6, pp. 2837-2845

Abstract - Active power filters are one of the established means of improving power quality in retrofit power systems. A three-phase shunt active power filter is designed to effectively compensate for the source current harmonics and reactive power requirement in a three-phase system with a non-linear load that draws a highly reactive, harmonic-rich current from the supply. This paper presents a shunt active power filter with artificial neural network based control. The ANN based controller selects the amount of harmonic current injection based on the percentage of harmonics present in the instantaneous source current. This proposed method is simple in structure, easy to adjust and adaptable to changing source/load variations. The effects of a three phase shunt active power filter based on ANN Controller on a test system are analyzed under varying load/source conditions. Simulation and experimental results show that the ANN based Active power filter is very adaptive to varying load/source conditions.

Keywords: Active Power Filter, ANN Based Digital Control, Harmonics Compensation, Reactive Power Compensation.