New Publications are available for Power supply quality and harmonics
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New Publications are available now online for this publication.
Please follow the links to view the publication.Power quality analysis of PV system of summer and winter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0715
PV system has been rapidly developed in recent years, while it generates harmonics and there-phase unbalance for its grid-connected inverter, causing voltage fluctuations and flicker for its uncertain power output. Therefore, power quality is highlighted as an important parameter of the PV system. To study the actual power quality characteristics of PV system, a large-scale grid-connected BIPV power plant was investigated. This paper discussed power quality parameters defined by standards of PV system, and introduced the key structure of the BIPV system. Based on the field tests taken under different conditions in summer and winter, the paper explored the operating characteristics of the PV system on voltage harmonics, current harmonics, three-phase unbalance, voltage flicker, active and reactive power properties, etc. Results demonstrate the power quality characteristics and provide a reference for evaluation of similar PV systems. (4 pages)Evaluation of reactive power control concepts for PV inverters in low-voltage grids
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0892
The proportion of renewable energies in power generation has increased significantly in recent years according to the political aims. In low-voltage grids, these are mostly distributed intermittent generation systems such as photovoltaic systems that are connected through inverters to the grid. Thus, the distribution networks have to meet hitherto unfamiliar technical challenges. A temporary reversal of the power flow can cause overvoltage problems. Traditional voltage regulation strategies cannot solve this problem. Consequently, regenerative sources need to be turned off temporarily or on the long term the grid infrastructure has to be extended by the network operator. Therefore, the distributed generation has to take part in the voltage regulation. With the help of reactive power, which is generated by the solar inverters, power capability and voltage quality of the networks can be increased. Thus, grid extension can be delayed or even avoided in many times. This paper presents a new approach to the evaluation of reactive power control strategies. Different reactive power control concepts are simulated and evaluated concerning their efficiency, effectiveness and stability. (4 pages)Integration of demand side management, distributed generation, renewable energy sources and energy storages
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0784
The increasing number of renewable energy sources and distributed generators requires new strategies for the operation and management of the electricity grid in order to maintain or even to improve the power supply reliability and quality. In addition, liberalization of the grids leads to new management structures, in which trading of energy and power is becoming increasingly important. The interconnection of DG inevitably changes the characteristics of the system to which it is being connected, due to the fact that distribution systems were traditionally designed with the assumption of a passive network. The consequence of the integration of DG is that this assumption is no longer valid. There are a number of technical challenges that needs to be addressed. The main objective of this Task is to study how to achieve a better integration of flexible demand (Demand Response, Demand Side Management) with Distributed Generation, energy storages and Smart Grids. (4 pages)Incorporating harmonic limits into assessment of the hosting capacity of active networks
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0869
Harmonic emissions from converter-interfaced distributed generation connection can potentially lead to voltage distortion levels that are above applicable standards. The risk increases as greater connection volumes are facilitated by Active Network Management schemes. By incorporating harmonic limits into assessment of the hosting capacity of active networks, this paper demonstrates that by incorporating harmonic levels at the planning stage can prevent inadvertent restrictions on the integration of renewables. Other aspects considered include: the impact of active network controls on harmonic propagation and hosting capacity and the role of active harmonic mitigation methods. (4 pages)Development of voltage regulation method including voltage control by switching capacitors of customers in autonomous demand area power system
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0773
In 6.6kV power distribution system of Japan, the introduction of many distributed power generations (DGs) is expected. Under such circumstances, power flow congestion and voltage fluctuation on distribution lines caused by varied output of the DGs will occur. This will result in failure to maintain power quality and supply reliability by conventional power system management. Especially, in residential, commercial and industrial mixed area of Japan, the distribution system voltage will rise at the end of feeder because of reverse power flow by photovoltaic (PV) generations and capacitors (SC) for power factor control by 6.6kV customers. We have proposed a new power supply system referred to as the Autonomous Demand Area Power System (ADAPS). ADAPS may be in the loop formation, in addition to the conventional tree branch formation. We try to establish network technology and operation management technology of ADAPS, and identify its effectiveness. In this paper, we studied voltage regulation method by using Static Var Compensator (SVC), Step Voltage Regulator (SVR) and customer's SCs controlled to improve power factor and to regulate voltage at connection point as power distribution system in transition period from conventional system to ADAPS. (4 pages)Optimisation of HV/MV-transformer-voltage-control in distribution networks with a high proportion of distributed generation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0734
The power supply from many small decentralised power generation plants (DPG) is increasingly influencing the voltage quality in the distribution networks. The further expansion of the decentralized energy plants is expected to lead to a worsening of the situation. The need to further expand the German distribution network, a need forecast by the BDEW (the German Energy and Water Authority) has given rise to the necessity to look for fast, cheaper and innovative solutions to reduce the negative effects on the power supply of the power generation plants on the MV and LV network levels. Within the framework of a pilot project carried out by the LEW Verteilnetz GmbH, it was examined whether the maintenance of the voltage level in the MV network could be improved with the help of an optimised voltage regulator of the HV/MV transformer, at the same time remaining in the stipulated limits. The LEW Verteilnetz GmbH (LVN) is a regional network operator in Bavaria and a subsidiary of Lechwerke AG based in Augsburg. The network area of Lechwerke includes Bavarian-Swabia as well as parts of Upper Bavaria. (4 pages)The VSC-HVDC electric power quality analysis and research
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0766
New energy technology application will occupy more and more of the important position in the future of the electric power development. Traditional transmission mode has become the bottleneck which restricts the mass construction of the new energy electric power plant. The flexible DC transmission technology has more advantage than the traditional transmission technology in the application of new energy and distributed energy electric power system.This paper is based on study of electric power quality in VSC-HVDC and synthetically analyses on the electric power quality suppression.This paper expounds the conventional HVDC electric power quality characteristics. Analysis the application of VSC-HVDC to implications electric power quality after through comparing measure data between VSC-HVDC put operation and no put operation. On the basis of the analysis this paper put forward improving suggestions. (4 pages)Microgrids operation with micro dispersed generators and renewables
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0866
The biggest challenge in the contemporaneous world: maintain the supply of electric energy with reliability and quality. A lot of technological solutions, involving telecommunications, energy storage, dispersed generation (DG) with alternative sources and another usual electric generation, are in large scale implementation. Moreover, Microgrids (MG) concept is in large discussion in order to obtain better results in operation and management of this new distribution system. Local black start strategies are one of the most important implementation for that new kind of grid. In the first phase of the R&D project developed with CPFL, one Brazilian electric utility, inside of the environment of ANEEL, the Brazilian Regulatory Agency to the electric system, it was made a study concerning the technologies of distributed micro generators and connection requirements. Models and control strategies simulations have been done in order to reproduce the performance of this energy sources when connected in the grid during the practice tests. It was evaluated topologies with resistive loads, capacitive loads, and inductive/non-linear loads. These topologies are in parallel with the distribution utility grid using a special test bench able to synchronize the energy and power quality measurements of all devices. (4 pages)Study on the operational reliability of AC relay based on the impact from electric energy quality
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0697
In the power system there are variety of electric energy quality problems such as magnitude deviation, frequency deviation of the supply voltages and harmonic of them. As the exciting source, the voltage supplied by the power system has an important impact upon the operational performance of AC relay. In this paper, one sort of clap-type AC relays is chosen to study the impact from electric energy quality problems. First, Ansoft Maxwell 3D, based on the finite element method, is employed to create the 3D model of AC relay. Second, considering the magnitude deviation of the supply voltages, static suction characteristics of the chosen relay are calculated. Then, considering the magnitude deviation, frequency deviation and the distortion degree, series of simulations are done to obtain the dynamic characteristics of the clap-type AC relay. At last, based on the changes of electric energy quality parameters, the influence law about the operational reliability of the AC relay is given.Distributed generation in Austria
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0902
From a regulatory perspective the approach towards a higher share of Distributed Generation (DG) has to be balanced considering national energy policy as well as maintaining the quality of electricity supply, adapted network expansion concepts and related costs. The status and potential estimation was based on collection and analysis of the existing data. The pooling of DG to e.g. virtual power plants has been evaluated by investigating the current legal and market requirements. Concerning economic and climate change aspects a comparison of mini CHPs and centralised CCGT has been modelled. The influence of DG on voltage regulation, losses and reactive power has been analysed by means of a generic network model. (4 pages)Technical solution/recommendations for large penetration of DGS in KEPCO distribution network
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0790
The interconnection standards/guidelines have been designed to prevent unfavourable interconnection problems of the DG (Dispersed Generations). Therefore, in practice, unit or cumulative interconnection capacity for particular voltage levels have been be limited to maintain admissible power quality and reliability. Recently, the interconnection standard/guidelines in South Korea are revised at Feb. 2012. In this paper, we briefly introduce the revised version of the DG interconnection standard/guidelines in South Korea and technical solutions/recommendations for large penetration of DG in the KEPCO (Korea Electric Power Company) distribution network. (4 pages)Study on reliability for automatic transfer switching equipment
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0699
As the automatic transfer switching equipments (ATSE) are widely used on distribution line. They are mainly used to switch the load automatically and ensure the security and reliability of power supply. So, the reliability of ATSE is extremely important. This paper mainly includes: 1) to analyze the failure modes of ATSE; 2)to establish the reliability characteristic parameters of ATSE; 3) to discuss the test methods of reliability demonstration test in details.Dynamic system performance of renewable power generation units - useful and doubtful grid code requirements
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0805
To maintain system stability and functioning and to ensure the quality of supply, system operators are responsible to set up transparent and commonly valid requirements for the usage and connection to their relevant grids. Facing the increasingly high penetration of dispersed power generators the requirements have been continuously updated and revised by TSOs and DSOs according to the new challenges of its transforming traditional operation procedures in all European Member States over the last decade. Based on gathered experiences in many years the reasonable needs for specifically designed and more stringent requirements with respect to system management and control schemes of renewable energy systems (RES) have evolved. However the accurate definition of advanced requirements is still ongoing and manufacturers are subjected to a rather dynamic technical as well as legislative framework in this context. In fact, ENTSO-E is currently working on a first pan-European grid code. In some ways also DSOs are overcharged in choosing the most suitable solution with respect to their alternatives like reactive power contribution of RES. Hence the intention of this paper is to highlight the contemporary sophisticated requirements related to the dynamic performance of RES during system disturbances and their respective contribution to system recovery and voltage support. The investigation of the required capabilities shows for example that under specific system conditions and operation modes the intended support function of injecting reactive current during voltage dips may not lead to the anticipated but rather to unsolicited impacts on the system that even can contradict the intention of system recovery. The corresponding analysis is based on simulations performed in German wind farm certification procedures by using manufacturer-specific models that have been validated in accordance with German Technical Guideline TR4. (4 pages)Improving power quality in distribution feeders with high PV penetration through inverter controls
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0749
Voltage fluctuations caused cloud transients in distribution systems with a high level of distributed photovolaic systems is of concern to electric utility companies since this can lead to power quality issues. This article proposes a scheme that can minimize this problem by allowing grid-tie inverters to generate controllable amounts of reactive current in a way to neutralize the change in active current. Inverter oversizing is not required by the implementation of this method. The performance of this technique is verified through computer simulations using PSCAD software. (4 pages)Improved network analysis by using hourly meter values
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0736
This project, PAM (Project Area Measurement), will investigate how Smart metering data could be used to improve network analysis in order to optimize the asset management process and hopefully reduce the investment costs. The project is divided in these three parts: load profiles, power quality and network losses. (4 pages)The impact of large-scale PV on distribution grid operation and protection; and appropriate testing
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0742
The paper focuses on the impact grid-connected, largescale photovoltaic (PV) has on the power system operation (stability, availability, reliability) and protection philosophy. It assesses qualification methods and standards of particularly the utility-interactive equipment (grid inverters), which directly influences the security of supply and power quality of the grid. Advanced emulation of grid conditions, including hardware in the loop testing scenarios, are proposed for the testing and validation of such grid equipment under realistic conditions(including worst-case). This to ensure suitability of the equipment for grid application and stable and safe grid operation. (4 pages)Portable test platform for evaluating voltage dip immunity of industrial robots and components in the automotive industry
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0358
Power quality disturbances like voltage sags and harmonics are an important cause of many ill effects and economic losses in industrial productive processes. Among others problems, production down times, equipment malfunctions and/or destruction of devices and even quality defects in final products can be originated by voltage dips. Power quality surveys and electromechanical device testing are previous steps for achieving an effective mitigation solution. This paper discusses a power quality survey conducted in an automotive company. In addition, a portable test platform for evaluating voltage dip immunity of industrial robots and components is presented. The results obtained from this survey and the immunity test may be useful for improving the power quality of this type of installation [3,4,6]. (4 pages)Predictive control of a direct AC/AC matrix converter for power supply applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0228
The use of Model Predictive Control (MPC) is investigated for a three phase to three phase direct matrix converter with input and output LC filter for power supply applications. It allows generation of sinusoidal output voltages and input currents with low harmonic distortion. The work describes in details the design of the proposed finite states model predictive control in conjunction with a full load observer. The proposed matrix converter power supply produces unity input power factor and a perfect tracking of the sinusoidal output voltage, accurately following the imposed reference in the presence of a linear load. A simulation study is presented to validate the proposed control scheme. (6 pages)Effects of renewable distributed generation (RDG) on voltage dip mitigation in microgrids
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0099
Many countries are accepting the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC) in other to reduce the emission of carbon dioxide and other greenhouse gases. Renewable distributed generation (RDG) has become one of the most effective ways to reach this goal. It has been recognized as an alternative way of generating clean energy around the globe today. There has been an increase in the number of integrated RDG to the grid and also within the microgrids in other to support the power needed by the load during crisis. Current literature highlights voltage dips to be a serious problem, which has serious cost implication whenever they occur. One of the corrective methods has been mitigation through renewable distribution generation. This paper demonstrates how renewable distributed generation can be used to mitigate voltage dip as a result of faults from both the external grid and within the microgrid. (6 pages)Reduction of passive filtering in aerospace starter/generator systems using a multilevel converter with predictive current control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0250
The application of predictive current control to a multilevel converter is investigated in an aerospace starter-generator system. The use of a multilevel inverter with predictive current control enables the system to reduce the harmonic distortion in the current waveform when compared to a conventional Field Orientated Controller. It is important that the power converter is optimized to control the current harmonics as aerospace starter-generators are typically low inductance machines. Experimental results taken from a prototype inverter show a substantial reduction in THD is achieved using the proposed controller. (5 pages)Fault type classification in transmission line using STFT
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0130
Modern power supplies must provide reliable, high-quality power. Therefore, it is important that a transmission line fault be identified accurately, reliably and corrected as soon as possible. A method for classifying fault type based on short time Fourier transform (STFT) is provided in this paper. STFT is a means of signal processing in which a Fourier transform (FT) is performed by setting a window function with a constant size. This transformation is used to analyze transients in the power system. In order to verify the suggested algorithm, the transmission system is modeled by EMTP-RV and line faults are simulated in the transmission line. This paper analyzes characteristics of STFT by using simulation results from MATLAB and classifies line faults by fault type. The simulation results show that the suggested algorithm is effective and valid for detecting fault types during line faults. (5 pages)Voltage sag mitigation using a direct matrix converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0229
Conventional approaches for voltage sag mitigation relies on voltage source inverters (VSIs). The bulky DC link electrolytic capacitors used in VSIs are reported to be the reason behind majority of failures of these converters. Absence of these electrolytic capacitors in Matrix Converter(MC) makes it a more reliable and compact alternative than the VSIs. This paper reports the performance of MCs as a sag mitigating device for linear loads. (6 pages)Protection of domestic solar photovoltaic based microgrid
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0137
A large-scale implementation of distributed generation (DG) for households involves each house generating its energy from photovoltaic (PV) cells. This approach is particularly suitable in rural electrification projects where demand is relatively low and yet grid connection is costly. A meshed microgrid is an attractive solution for energy generation and sharing in domestic electrification projects. Solar PV systems located on different houses can be interconnected together into a meshed microgrid. This interconnection creates an integrated system that can be treated as a single DG. While they remain autonomous, the systems can operate as one microgrid. This approach provides a more reliable and robust grid as the systems can supplement each other. However, protection and control in a meshed power network setup is a challenge. This is because a meshed microgrid has more interconnections and interfaces compared to radial architecture power grid. This is further complicated by effects of DG on power quality, such as transients: voltage sags and swells, under and over-current faults amongst other difficulties. The challenges necessitate robust protection schemes supported by effective control and fault location identification facilities. This paper discusses implementation of islanded or grid-connected microgrids formed by solar systems installed in homes. The paper discusses microgrid protection, adaptive control and fault location identification. In grid-connected mode, power flow in microgrids is bi-directional. This characteristic rules out many of the traditional protection schemes based on current direction. Thus differential current protection scheme is the focus of this paper. In conclusion, this scheme overcomes many protection problems including the low fault current nature of conventional inverters. (6 pages)Comparison of 3- and 9-phase brushless PM drive systems for aerospace actuation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0249
Nearly all electric vehicles (EVs), hybrid electric vehicles (HEVs), more electric aircraft, electric ship propulsion and others power conversion industrial applications uses power electronic inverters to convert AC to DC or vis versa, as in the starter/generator machine system and generation/regeneration process of the traction motor. Also, it has become possible to integrate HEVs power electronics component in one package with one set of liquid cooling. Recently, compactness and reliability of the power conversion and generation system design in automotive, in particular, and in aerospace industries are growing with global necessity of shifting from conventional airborne emission vehicles and aircrafts to the green all electric ones. Therefore, an advanced technology in the area of energy storage, conversion and dc-link capacitors, which account for a major fraction of the volume, weight and also cost of the inverter, is demanded by the developer of HEVs and other industrial areas. In three-phase system a dc-link voltage source inverters (VSI) are fed via controlled or uncontrolled rectifier bridges from a main source. Here, a dc-link capacitor is usually used to maintain a stiff dc-link voltage across the VSI, and to perform other tasks, as in [1]. Such that, in this application, the dc-link capacitor deals with the main voltage fluctuation and provides a dc-link current ripple to suppress the generated electromagnetic interface (EMI) caused by pulsating current (ripple current) associated with the inverter switching. It is recognized in the literature [1-7] that for voltage stiff inverter the dc-link capacitor adequate selection, sizing and minimizing presents a major issue for improving electrical system compactness and utilization. Lai et al discusses the use of low-inductance high current film capacitor in a high-power dc-bus inverter for battery-powered traction motor drives [2]. Another discussion that shows merits of an advanced film capacitor technology over conventional electrolytic capacitor for dc-link applications was presented by Grinberg et al [3]. A dc-link capacitor minimization method via direct capacitor current control has been described by Gu and Nam [4]. Such that, the dc-link capacitor can be minimized by making the converter side dc-link current similar to the inverter side dc-link current waveform in a pulse width modulation (PWM) converter-inverter system. However, the dc-link capacitor reduction technique of Gu et al is not for stiff voltage-source inverter. A simple analytical expression for current stress on the dc-link capacitor caused by the load-side inverter of the voltage dc-link converter system is derived by Kolar and Round [1]. Conclusions have been obtained by some of the previous papers, which declare that the dc-link capacitor of practical systems usually determined by the effective capacitor current stress and not, for example, by a given maximum admissible value of the amplitude of the dc-link voltage ripple [1]. In Dahono paper [5], analysis and minimization of output current ripple of multiphase PWM inverters was presented. The minimization of this current ripple is achieved for three-phase PWM inverter by injecting a twenty-five percent third harmonic in the reference sinusoidal signal. Whilst, minimization of the output current ripple of a multiphase PWM inverters can not be attained and it will become unsymmetrical if harmonics are injected into the sinusoidal reference signal [5]. Also the paper discussed by Dahono mentioned that multiphase PWM inverters with number of phases equal to multiple of three will give better results than the one that is not a multiple of three, for example, if the number of phases is a multiple of three, the multiphase PWM inverter can be operated as several three-phase PWM inverters. As for the authors knowledge, no verification nor investigation of this claim have been found in depth in the literature. In the paper, 3-phase and 9-phase PWM inverter modules with different threeand nine-phase brushless permanent magnet (BLPM) machine configurations will be analysed in detail to show the adequate use of this configuration to either eliminate the need or significantly reduce the size of the dc-link capacitor that suppress the generated EMI caused by pulsating current associated with the inverter switching for stiff voltage-source inverter. In addition, different operating points on the general torque speed curve for different BLPM machine drive configurations will be investigated to give decision of the adequate and best machine drive configuration, in terms of improving power and torque capabilities with the minimization of output torque ripple, which can be practically implemented and used in many promising industrial areas. (2 pages)Equivalent capacity of the lower voltage ride through for wind farm from overcurrent protection in power collection lines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0075
Magnitude and duration of voltage sags are the most important two factors to the Lower Voltage Ride Through (LVRT) capacity of the wind generator. Since most voltage sags are caused by the system faults, and sag durations are controlled by the tripping time of overcurrent relay in power collection lines based on the sags' magnitude. The specification of the LVRT capacity of wind generator is introduced into the operation characteristics of the relay in power collection lines. The evaluation model of equivalent LVRT capacity to overcurrent protection is proposed in paper, and the equivalent LVRT capacities from zone I and zone II relay are quantified. Improvement measures are also proposed. (5 pages)AC distribution grid proposal to improve the power quality of the Line-B Metro System of Mexico City
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0350
A power quality diagnosis campaign was done for the Line B of the Mexico City underground system to understand and improve its behaviour. A comparative analysis of the results obtained during the campaign is presented describing a method to improve the power quality. The AC distribution of this underground system consists of a set of transformers and multipulse rectifiers; however, the harmonic content is highly dominant by the 6k±1 harmonic order and the harmonic distribution is poorly mitigated by the load-balanced arrangement. The field measurement work, the practical issues at the power quality campaign and a proposal to improve the harmonic performance are explained together with the field and estimated results obtained with measurements realized to the AC medium voltage grid of the Mexico City Line B. (6 pages)A fast synchronously rotating reference frame-based voltage sag detection under practical grid voltages for voltage sag compensation systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0348
A Fast synchronously rotating reference frame (FSRRF)- based voltage sag detection under practical grid voltages for voltage sag compensation systems is proposed in this paper. The proposed voltage sag detection is also based on abc-dq transformation as conventional synchronously rotating reference frame (CSRRF)-based voltage sag detection but adding of 2ω component eliminator (2ω component is generated by synchronously rotating reference frame-based transformation in unbalance voltage sag conditions) and dedicated band-stop filter (BSF) (to exclude the effect from harmonic voltages in practical grid voltages) then very fast voltage sag detection time under practical grid voltages condition is achieved. The computer software simulation and the experimentation are made to investigate and verify the operation of proposed voltage sag detection. The detection time of FSRRF-based voltage sag detection is around one eighth of CSRRF-based voltage sag detection in the case of single-phase voltage sag and around one fifth in the case of two-phase voltage sag. This voltage sag detection can be used in any voltage sag or interruption compensation systems to improve their performance. (5 pages)Application of a subharmonic protection relay
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0022
With the increased use of renewable wind energy, wind farms are being built in remote areas, often far from load centers. The required long transmission lines are often constructed with series capacitive compensation to electrically shorten the lines. Events in the transmission system can cause interactions between the series capacitors and the system's inherent impedance which can result in sub-synchronous resonance frequencies. Modern wind turbine systems use advanced electronic control and converter systems which can generate harmonics and inter harmonics. Mechanical system interactions (tower-to-blade) can also generate sub-harmonics. Wind generator speeds vary continuously depending on the availability of wind at any particular time. This particular operating characteristic of wind farms introduces the challenge of predicting when and how much harmonics and sub-harmonics are being introduced to the power system. Synchronous generators are often built with shaft torsional modes that are in the same range as system sub-synchronous resonance frequencies. These torsional modes can interact with transmission network resonances to produce damaging oscillations that can damage generators and transformers, and cause damage at points of common coupling in the electrical grid. This paper discusses an engineering process that can be followed for the application of a new sub-synchronous relay that provides protection for transmission lines, particularly those with serial compensation and wind farm interconnections, and how it can be used together with digital fault recorders to monitor the power system to determine the existence of sub-synchronous resonance phenomenon. Moreover, it gives the reader criteria to determine if the levels of SSR obtained by means of DFRs are considered critical. The paper goes further, providing possible settings for the sub-harmonic protection relay including the protection elements associated to sub-harmonics as well as providing overcurrent and other protection functions. (6 pages)STATCOM and UPQC: options to enhance fault-ride-through capability of a fixed speed wind generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0191
The enhancement of fault-ride through (FRT) capability of a Fixed Speed Induction Generator (FSIG) with the help of a Unified Power Quality Conditioner (UPQC) and STATCOM are examined in this paper. The FRT performance of these equipments are evaluated and compared in accordance with Irish Grid Code requirement. A simulation study carried out on a 2 MW wind turbine with varying power system parameters has shown that the application of a STATCOM can be economical for a stronger networks where as a UPQC seems to be the economical option when the FSIG is connected to a weaker network. (6 pages)Periodic injection of a second harmonic component with Fourier isolation for the detection of power islands
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0349
Distributed Generation (DG) systems include several technologies, many based on renewable energy sources. Due to the intermittent nature of many DG systems, it is necessary to include energy storage devices. This results in a multitude of DG units that require grid connection. Single phase power converters are necessary to achieve connection between domestic scale DG units and the grid. The majority of utility connection standards state that the DG unit must detect a loss of mains (LOM) event and stop feeding energy into the grid. This paper presents a laboratory setup that has been specifically designed to verify the adherence to grid connection standards. Multiple in-the-loop based LOM detection methods are presented, analysed and compared. A harmonic injection technique is introduced and its merits discussed. (5 pages)Regulated AC/DC/AC power supply using Scott transformer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0202
In today's industry, it is necessary to convert power for equipment used in environments where dissimilar voltages and frequencies are the norm. Static frequency converters or industrial power supplies are used for converting either 50Hz or 60Hz utility line power to 400Hz power. They are more efficient than motor-generator sets. In addition, they offer harmonic cancellation, power factor correction, phase conversion, voltage conversion with balanced, smooth, and controlled power output. Many varied applications in power electronics require sinusoidal outputs at frequency 400Hz. This paper describes the design, simulation and implementation of a power converter topology and control techniques for realizing sinusoidal output systems. A 150 KVA 3-phase power supply, whose line voltage and frequency are 440V and 60 Hz, is converted via a controlled rectifier to a dc voltage. Two center tapped transformer inverters shifted 90° in phase are used to convert the dc voltage to get two phase AC power supply which is converted via a Scott transformer to a three phase, whose line voltage and frequency are 440V and 400 Hz. A resonant filter is used to eliminate harmonics. Feedback signals from load voltage and dc link current are used to control the rectifier so as to maintain constant voltage at variable load conditions. The system is theoretically analyzed and experimentally verified. (6 pages)Superiority of decision tree classifier on complicated cases for power system protection
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0054
Diagnosis of power system faults requires identification and classification of voltage disturbances in power systems and smart grids. The objective of this approach is to develop state of art signal classification algorithms for classifying different types of power quality disturbances (faults) based on latest improvements in signal processing and pattern recognition techniques. This paper proposes a new solution for power system monitoring against all possible power quality issues. S-transform is used for analyzing distorted power signal. As a classifier, decision tree algorithm is used and its performance is compared to other classifiers. The proposed hybrid power system monitoring system is able to detect common power system disturbances such as voltage sag/swell/, flicker, DC component, electro-magnetic interference, harmonics, transients and blackouts. (6 pages)Detection of high impedance fault in MV distribution system
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0080
High impedance fault (HIF) exposes great hazard for personal safety and property security. High impedance fault (HIF) in MV distribution with restricted fault current cannot be detected and cleared by conventional over current relays. In this paper, an integrated scheme utilizing different features of HIF is presented. Various documented field data has been investigated and summarized to get the most distinctive features of HIF. Based on these features, a simulation model using arc thermal equation and random factor has been developed. The integrated scheme investigates into different scopes of the fault features ranging from transient high frequency, harmonic distortion to fundamental intermittent. EMTP (Electromagnetic Transients Program) simulation results show that the integrated scheme can detect most HIFs and discriminate HIF from other interference scenarios such as CT saturation, load nonlinearity and capacity transients. Therefore, this scheme achieves a better result with reliability and security. (6 pages)Demonstration of energy management system for smart grids
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0004
The increasing integration of distributed and renewable energy sources into the electrical power network presents challenges for the operation and management of the network. New techniques are required to ensure the effective management of the balance between supply and demand, and the proper maintenance of voltage stability and power quality in the network. A new energy management system, designed specifically for the management of smart grids, is described, and its operation in conjunction with energy storage systems is explored. Large scale demonstration systems have been implemented in order to study and prove the new techniques, the configurations and results of which are recorded. The experience gained from the demonstration systems will result in improvements to the new techniques and consequent benefits for the future management of electrical networks. (6 pages)Source voltage, frequency and impedance variation effects on the harmonics generated from a personal computer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0210
The penetration of harmonics in residential power system networks due to the widespread use of nonlinear loads such as Personal Computers (PCs) can cause severe problems including voltage and current distortion. Almost all residential customers are subjected to variations in the system voltage and frequency. Also, the source impedance is different for different customers depending on their distance from the utility transformers and distribution cabinets and the system loading. Hence, the purpose of this paper is to investigate the effects of the voltage amplitude, source impedance and system frequency on the harmonics produced by a single PC for variations within practical limits. Experimental measurements and computer simulations are performed to confirm the observations. (6 pages)Voltage unbalance protection VT and relay errors effect on unbalanced voltage detection; considerations for system relaying, stability and developments
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0069
In a power system network, an unbalanced voltage condition can occur due to various reasons. Excessive voltage unbalance has become an issue of concern in power quality at network level, leading to numerous problems. This calls for a stringent management of unbalanced. There are several codes of practice to advise and to enforce network operating conditions to keep system unbalance within specific limits. Analysis of system unbalance voltage and power system control is carried out through Voltage Transformers and protective relays. The accuracy of Voltage Transformers from primary to secondary varies according to the type (Class of VT). Also, the accuracy of Relays is of the concern to the same extent. This poses a limitation on detection of actual system unbalance. This study gives an overview of fundamentals of sequence components, unbalanced voltage definitions and use of different types of VTs and relays to analyse unbalanced voltage. This paper considers detection of low level voltage unbalance equivalent to maximum limits allowed in national grid codes in order to initiate system to generate tripping/alarm. This article endeavours to summarise deviational effect of accuracy levels of VT and relays. The study provides a reference of selection of VTs and Relays to detect known % unbalance in the system. Coverage has been extended to discuss mitigation techniques of voltage unbalance and deviational error minimisation. The emphasis is to initiate a thought process for requirement of improved methodologies to eliminate errors in analysing. Therefore this study aims in building a better power system. (7 pages)Examination of new current control methods for modern PMW controlled AC electric locomotives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0314
A railway electrification system supplies electrical energy to railway locomotives and multiple units. There are several different electrification systems in use throughout the world. The single-phase AC network systems are widespread (25 kV 50 Hz or 15 kV 16 2/3 Hz). The Hungarian system is 25 kV 50 Hz AC. This article is just dealing with the AC network supplied locomotives. Nowadays in our country the series wound DC traction motor driven locomotives are still widely used. These vehicles are equipped with diode or thyristor rectifier circuits that inject harmonics into the AC line and distort the line voltage. In our work we examined and compared current control methods that can be achieved by "network-friendly" locomotives connected to distorted line. We worked out a new current control strategy that possesses several advantages. The modern locomotives endeavour to consume sinusoidal current from the AC network, in phase with the network voltage fundamental. In generator mode these endeavour to supply back to the grid sinusoidal current in antiphase to the voltage fundamental. We compared current control methods with this "common" strategy. One of them can reduce the consumed root mean square (RMS) or fundamental current of a distorted line connected modern locomotive in motor mode. Other one can increase the generated RMS and fundamental current in generator mode. With these strategies the harmonic currents can be used for active power. Moreover it turned out that the harmonic content of the network can be reduced by the "new" strategies. For the study, we built a test system. We can model the line side converter of a modern locomotive DC-link frequency converter with the system. A common solution in locomotives is when several line-side converters feed two DC-links. In the test system we modelled these with one converter, while the motor-side voltage source inverters and the electric traction motors were taken into account as a controllable current source DC-link. (5 pages)High-efficiency UPS protection for it equipment
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0357
Double-conversion UPS are often the preferred choice for protecting critical loads, the typical example being IT equipment in data centres. While providing optimum protection, double-conversion UPS only provide limited efficiency. Some UPS feature a high-efficiency operating mode (so-called ECO mode) where the load is fed via the bypass path. Particularly, some Advanced ECO mode implementations combine efficiency with a very fast transfer to inverter when the utility voltage is going out of given tolerances. Traditionally, market adoption of these technologies has been limited, following concerns on exposure of the load to utility disturbances. This paper aims to clear these concerns by presenting experimental results from testing real IT equipment with UPS protection operating in Advanced ECO Mode. Particularly, the system has been exposed to common power quality events on the UPS input utility, while evaluating the residual effect on the IT equipment power supply. (6 pages)Protection and stability assessment in future distribution networks using PMUs
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0094
Phasor Measurement Units (PMUs) have the potential to play an essential role in power system monitoring and operation in the future, particularly for power systems incorporating increasing amounts of distributed generation (DG) and possibly systems operating in islanded mode in the future [1]. Their ability to directly measure and provide the voltage and current phasors at the PMU location offers numerous possibilities for ascertaining information relating to the state and health of the power system. Typical applications of PMUs in distribution networks include: state estimation, dynamic stability supervision, instability prediction and control, protection and fault location, and power quality monitoring [2]. (6 pages)Mitigation of voltage sags and voltage swells by dynamic voltage restorer
http://dl-live.theiet.org/content/conferences/10.1049/ic.2011.0047
Modern industrial processes are based on a large amount of electronic devices such as programmable logic controllers and adjustable speed drives. Unfortunately, electronic devices are sensitive to disturbances, and thus, industrial loads become less tolerant to power quality problems such as voltage sags, voltage swells, and harmonics. The dynamic voltage restorer (DVR) has become popular as a cost effective solution for the protection of sensitive loads from voltage sags and swells. This paper deals with modeling and simulation of a Dynamic Voltage Restore (DVR) for mitigation of voltage sags and voltage swells. The control of the compensation voltages in DVR based on d-q-0 algorithm is discussed. Effectiveness of proposed technique is investigated through computer simulation by using MATLAB/SIMULNK software.A brief analysis on bridgeless boost PFC converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0368
This paper presents bridgeless power factor correction circuits that achieve both high reliability and high efficiency. In electric equipments, using power factor correction (PFC) technology can in crease power factor, reduce harmonic pollution on grid and improve power utilization. Rectifier Bridge is commonly used to realize A C to DC conversion in PFC topology and PFC stage realizes power factor correction function. With power level's improving, the loss of bridge rectifier occupies a large proportion in the whole power stage loss. Bridgeless Boost PFC omits Rectifier Bridge by decreasing conduction loss and improves efficiency. This paper introduces the principle of operation including the control scheme and verified performance based on simulation and experimental results.Dynamic voltage restorer based on fuzzy logic control for voltage sag restoration
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0329
Power quality problems such as voltage sags are presently impor tant issues in the industrial field. The dynamic voltage restorer (DVR) is a series compensation device that mitigates voltage sag problems. Due to the nonlinearity of the D VR dynamic character istics, the compensating performance of the D VR is affected much by its control strategy. In this paper, fuzzy logic control is proposed to enhance the compensating performance of the transformer-less D VR. Recently new FL methods have been applied to Custom Pow er Devices, especially for active power filters. The operation of DVR is similar to that of active power filters in that both compensators must respond very fast on the request from abruptly changing ref erence signals. Simulation studies were conducted to show that the proposed fuzzy logic DVR control is very effective in damping the system oscillations and improving the compensating performances compared to the traditional PI control.Application of PI, fuzzy logic and ANN in improvement of power quality using UPQC
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0381
The unified power quality conditioner (UPQC) is being used as a universal active power conditioning device to mitigate both current and voltage harmonics at a distribution side of power system network. This paper emphasis enhancement of power quality by using UPQC with fuzzy logic controller (FLC) and Artificial Neural Network (ANN) controller wrt the conventional proportional-integral (PI) controller. The proposed FLC and ANN are capable of providing good static and dynamic performances compared to PID controller.Adaptive-hysteresis current controller based active power filter for power quality enhancement
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0325
This paper presents a shunt active power filter for power quality enhancement in terms of harmonics and reactive-power compensation due to the non-linear loads in the distribution network. The compensation approach uses calculation of real-power (p) losses only, which is simpler and different from the conventional p-q theory. The voltage source inverter based active filter switching pulses are generated from adaptive-Hysteresis Current Controller (HCC). This adaptive-HCC changes the hysteresis-bandwidth according to the instantaneous compensation current variation that is used to optimize the required switching frequency. This would improve the active power filter performances. The three-phase shunt active power filter system is investigated under both steady state and transient conditions with non-linear loads.SHAF for mitigation of current harmonics with p-q and Id-Iq control strategies using both PI and fuzzy controllers
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0389
Control strategies for extracting the three phase reference currents for shunt active power filters are compared, evaluating their performance under different source conditions with PI and Fuzzy Controllers in MATLAB/Simulink environment. The p-q control strategy is unable to yield an adequate solution when source voltages are not ideal. Extensive simulations are carried out with PI controller and also with Fuzzy controller for both p-q and Id-Iq control strategies under different main voltages. Extensive Simulations are carried out with PI as well as fuzzy controller for both p-q and Id-Iq control strategies by considering different voltage conditions and adequate results were presented. On owing Id Iq method with fuzzy logic controller gives away an out-standing performance under any voltage conditions (balanced and un-balanced) over remaining combinations.Modelling and power quality enhancement of induction motor with soft starter using synchronous reference frame theory
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0333
An This paper presents a method for obtaining the desired reference current for Voltage Source Inverter (VSI) of Shunt Active Filter fed Induction motor using Synchronous Reference Frame (SRF) theory. The modeling is based on the a-b-c stationary frame to 0-d-q rotating frame transformation of the ac system variables. The cur rents injected by the active filter are controlled in the synchronous orthogonal 0-d-q frame using a decoupled nonlinear control strategy. The reference harmonic components are extracted from the sensed nonlinear load currents by applying the synchronous reference frame method, where an AC voltage controller fed three-phase Induction motor is taken as the nonlinear load. To improve the performance of the PI controller, the feedback path to the integral term is introduced to compensate the winding up phenomenon due to integrator. The Phase Locked Loop (PLL) with PI filter is used for Synchronization, with much emphasis on minimizing delays. The results confirm the performances considered theoretically for the shunt active filter topology and to comply with IEEE 519 recommended harmonic standards.Performance analysis of three phase cascaded H-bridge multi level inverter for under voltage and over voltage conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0370
A Multilevel Inverter is a power electronic device built to synthesize a desired AC voltage from several levels of DC voltages. Nowadays, modern industrial devices are mostly based on electronic devices such as programmable logic controllers and electronic drives. The electronic devices are very sensitive to disturbances and become less tolerant to power quality problems such as under voltage and over voltage conditions. In general under voltage and over voltage conditions will occur more at source side. In this paper a closed loop Control system is designed using PI controller in order to maintain load voltage constant for under voltage and Over voltage conditions. The triggering pulses to Cascaded H-Bridge (CHB) MLI is given using multi carrier phase shifted technique and MATLAB simulations have been carried out.Performance improvement of i<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">d</sub>-i<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">q</sub> method based active filter using particle swarm optimization
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0382
At present the inevitable usage of large number of non-linear power electronic loads has raised severe electric power quality issues. Therefore, it is always desirable to get superior compensation capability by the active power filter (APF). In this paper Particle swarm optimization (PSO) technique is proposed to be employed in shunt APF and a comparative evaluation of the APF performance using conventional and PSO methods under ideal and distorted conditions of supply source is presented. The id iq method of reference filter current generation has been used here, as it yields better end result in compensating the harmonics and unbalance in source current under non-ideal mains conditions. Extensive MATLAB simulations are carried out in order to compare the APF responses. The results reveal that, PSO based APF yields more optimized result in terms of harmonics compensation capability as well as faster convergence to optimum solution.Comprehensive analysis of Z Source inverter topologies for photovoltaic systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0342
This paper investigates the performance of various topologies of Z Source Inverters and a new family of embedded Z Source Invert ers, examining them as a Power Conditioning System (PCS) for a three phase Photovoltaic (PV) System. The performance of PCS was analyzed considering the various conditions pertaining to the intermittent nature of solar. The results are comparatively analyzed so as to ensure the reliability of the PCS. All the models were simulated in MATLAB/SIMULINK and the performance of the same were inferred.Estimation of harmonic voltages using independent component analysis
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0364
Non-linear loads like the electric arc furnace and PWM inverters generate voltage harmonics on a large scale. Arc Furnaces generate even order harmonics and certain odd order harmonics not commonly present in other loads. Under such a situation application of conventional Independent Component Analysis (ICA) methods is not possible. So, certain modifications have to be incorporated to the existing ICA methods. Modified FastICA and JADE are the two ICA algorithms considered in this paper. Efficient Variant ICA (EFICA) has better accuracy than FICA in the presence of finite samples, but it is not attempted in this paper as performance is given more importance than accuracy. A simple five bus system with the electric arc furnace and the PWM inverter is investigated by applying the modified JADE and Fast ICA algorithms. The simulation results of the work point a compromise between accuracy and performance. This arises as the FastICA (or EFICA) collapse when only one independent component exists.