Deterioration Of Power Quality Research Articles

Power Sharing in Hybrid Microgrids Using a Harmonic-Based Multidimensional Droop

Droop-based control strategies are generally used in hybrid microgrids (HMGs) for voltage and frequency regulation in the dc and ac microgrids (MGs). The control of interlinking converters (ICs) that connect ac and dc MGs plays a vital role in the stability and efficiency of HMGs. However, conventional P-V droops for the dc side may not be effective due to line resistances and local nature of voltage. Also, conventional Q-V droops for the ac side may result in circulating power and current among parallel ICs diminishing their performance. In this paper, dc voltage harmonic frequencies are employed to create a global variable in the dc side of HMGs and to introduce an efficient droop control strategy for the dc MG without deteriorating power quality. Accordingly, accurate active power sharing is achieved and circulating power is eliminated. In addition, a three-dimensional (3-D) droop is suggested for voltage control at the ac MG using virtual impedances. Thus, proper reactive power sharing is accomplished among parallel ICs, while circulating currents are suppressed as well. The optimal gains of the 3-D droop are determined via an optimization problem. The efficacy of the proposed method is evaluated by examining it on a typical HMG in different situations.

An Efficient Hybrid AC Metro Power Supply System Integrating PV With Grid

Metro is integral to the urban rail transit with the expansion of the city. Due to the tremendous power consuming of the traction load which is generally considered to be megawatt class, the attendant problems concerning energy-saving and emission-reduction cannot be neglected. An approach wherein the photovoltaic plants are connected into the metro traction power supply system to provide electrical energy is proposed in this paper. Given the deterioration of power quality brought about by PV connection, the photovoltaic inverter adopts output reactive power control method.

Estimation of Consumers’ Responsibility to Power Quality Deterioration

Estimation of Consumers’ Responsibility to Power Quality Deterioration

Improved control strategy of TFAPF in active distribution networks

In order to solve the deterioration of power quality caused by power electronic devices in active distribution networks, it is necessary to improve the three-phase four-wire active power filters (TFAPF) control strategy. This study adopts the non-harmonic detection and proposes an improved control strategy of TFAPF based on the multi-model principle. Firstly, the mathematical model of TFAPF in the stationary coordinate system is established by replacing the network side current and the DC bus voltage directly as the state variables. Secondly, TFAPF in active distribution networks requires the power fluctuation and fast dynamic response, the proposed control strategy of TFAPF in the stationary coordinate system is applied, namely proportional integral, vector resonant and repetitive control composite controller as the current loop controller of TFAPF with a fast dynamic response, high accuracy and small amount of calculation, provide guarantee for the power quality in active distribution networks. Finally, the feasibility of the proposed control strategy is verified by simulation.

Harmonics and Mitigation Techniques Through Advanced Control in Grid-Connected Renewable Energy Sources: A Review

With more renewable energy based distributed generation (DG) units connected to utility power grids, deterioration of power quality at the point of common coupling (PCC) becomes a major concern. There are two types of harmonics associated with DG units, and together they may cause excessive harmonic distortion at the PCC. The first type of harmonics is generated by power electronic devices in DG units such as photovoltaic systems, which contains high-frequency harmonic components at multiples of the carrier frequency of the DG interfacing inverter. Such harmonics are first reviewed in this paper, and the potential operational effect at the system level due to LCL or LC filters installed at the inverter output to mitigate such harmonics are discussed. The second type of harmonics is generated by other nonlinear local, PCC, and utility loads in the system, which are common type of harmonics at multiples of the power grid frequency, 50/60 Hz. Harmonic mitigation for such harmonics achieved through advanced control of the DG interfacing inverter operated as a power quality conditioner are reviewed and summarized. This systematic review can facilitate better understanding of harmonics associated with renewable energy based DG units and provide guidelines on advanced control schemes to realize ancillary harmonic compensation service through DG interfacing inverters.

An Interline Dynamic Voltage Restorer Using Neutral-Point-Clamped (NPC) Multilevel Converter

Because of increased number of sensitive loads and automated processes in industry, need for high quality power is nowadays inevitable. Deteriorated power quality my result in huge financial losses and also decreases the productivity. The power electronic based solutions for improving power quality have become more common in the recent years. One of these solutions is to use the Dynamic Voltage Restorer (DVR), which is a series-connected voltage compensator. Interline DVR (IDVR) is a special structure, in which two DVRs share a DC-link. These two DVRs are installed in two independent distribution feeders which may have two different voltage levels. In this paper, a new structure for IDVR is proposed. The proposed DVR is based on the multilevel converters. Therefore, we call it as Multilevel Converter based IDVR (MLC-IDVR). Because of using multilevel converter, the quality of voltage waveform in the proposed structure is improved in comparison with the conventional IDVR. Also, it is more suitable for higher voltage applications. The performance of the proposed MLC-IDVR is verified by simulation results carried out by PSCAD/EMTDC software.

Integrating ultra‐fast charging stations within the power grids of smart cities: a review

Plug-in electric vehicles (PEVs) have become a key factor driving towards smart cities, which allow for higher energy efficiency and lower environmental impact across urban sectors. Industry vision for future PEV includes the ability to recharge a vehicle at a speed comparable to traditional gas refuelling, i.e. <3 min. per vehicle. Such a technology, referred to as ultra-fast charging (UFC), has drawn much interest from research and industry. However, UFC poses unprecedented challenges to existing electricity supply infrastructure due to its large power density, impulsive, and stochastic load characteristics. Planning the locations and electric capacities of UFC stations is critical to preventing detrimental impacts. In particular, efforts must be made of mitigate grid asset depreciation, grid instabilities, and deteriorated power quality. The authors first review planning methods for conventional charging stations. Next, they discuss outlooks for UFC planning solutions by drawing an analogy with renewable energy (RE) source planning. This analogy is based on the similar power density and stochastic characteristics of RE and UFC. While this study mainly focuses on UFC planning from the power grid perspective, other urban aspects, including traffic flow and end-user behaviour, are examined for feasible UFC integration within smart cities.

Modeling of three-phase electric motor operation by the MATLAB system with deteriorated power quality in the 0.38 kV distribution networks

One of the main operation modes that characterizes power quality in distribution networks is asymmetry of three-phase voltage system. Operation of an induction motor (IM) with disturbed voltage symmetry in the supply network can not be considered as a rated one. The system of voltages applied to the stator winding of IM under these conditions contains positive- and negative-sequence components. This worsens the performance characteristics of IM essentially. In order to balance the 0.38 kV network operation and enhance the efficiency of the three-phase electric motor operation it is suggested to use a special balancing unit (BU) that minimizes the negative-sequence components of current and voltage. The operation modes of the obtained system “supply source – induction motor – balancing unit” are simulated within the MATLAB software package of applied programs, which allows one to assess the impact of low quality of power on the operating characteristics of the electric motor and the efficiency of the balancing unit to increase the “durability” of the motor under the asymmetrical power consumption.

翌日PV発電出力における10秒単位変動の信頼区間推定

Photovoltaic (PV) power generation systems have gained much attention against a background of energy and environmental problems. However, the output of PV system depends on climate conditions. Therefore, a mass introduction of PV results in the power quality deterioration in the distribution system. To overcome the difficulty, it is effective to introduce Low Voltage Regulator (LVR) to the distribution system. However, the application of LVR brings a new problem, i.e., a control delay for activating the tap after detecting the fluctuation. With this background, to provide more useful predictive information in advance, this paper deals with a novel prediction interval estimation method of 10 second PV fluctuation with two-dimensional kernel density estimation. We also carry out the prediction by using several different methods for comparison, e.g., the conventional method with one-dimensional kernel density estimation and the application of various smoothing methods to this conventional method. Finally, some numerical results, which demonstrate the effectiveness of the proposed method on the basis of several indexes, are also presented.

Power quality aspects of solar power – results from CIGRE JWG C4/C6.29

The increasing use of solar power connected to the public grid and the associated concern for deteriorating power quality triggered the formation of a joint working group with the aim to describe a ...

Particle swarm optimization algorithm for simultaneous optimal placement and sizing of shunt active power conditioner (APC) and shunt capacitor in harmonic distorted distribution system

Due to development of distribution systems and increase in electricity demand, the use of capacitor banks increases. From the other point of view, nonlinear loads generate and inject considerable harmonic currents into power system. Under this condition if capacitor banks are not properly selected and placed in the power system, they could amplify and propagate these harmonics and deteriorate power quality to unacceptable levels. With attention of disadvantages of passive filters, such as occurring resonance, nowadays the usage of this type of harmonic compensator is restricted. On the other side, one of parallel multi-function compensating devices which are recently used in distribution system to mitigate voltage sag and harmonic distortion, performs power factor correction, and improves the overall power quality as active power conditioner (APC). Therefore, the utilization of APC in harmonic distorted system can affect and change the optimal location and size of shunt capacitor bank under harmonic distortion condition. This paper presents an optimization algorithm for improvement of power quality using simultaneous optimal placement and sizing of APC and shunt capacitor banks in radial distribution networks in the presence of voltage and current harmonics. The algorithm is based on particle swarm optimization (PSO). The objective function includes the cost of power losses, energy losses and those of the capacitor banks and APCs.

A DFIG Islanding Detection Scheme Based on Reactive Power Infusion

A lot of research has been done on photovoltaic (the “PV”) power system islanding detection in recent years. As a comparison, much less attention has been paid to islanding in wind turbines. Meanwhile, wind turbines can work in islanding conditions for quite a long period, which can be harmful to equipments and cause safety hazards. This paper presents and examines a double fed introduction generation (the “DFIG”) islanding detection scheme based on feedback of reactive power and frequency and uses a trigger signal of reactive power infusion which can be obtained by dividing the voltage total harmonic distortion (the "THD") by the voltage THD of last cycle to avoid the deterioration of power quality. This DFIG islanding detection scheme uses feedback of reactive power current loop to amplify the frequency differences in islanding and normal conditions. Simulation results show that the DFIG islanding detection scheme is effective.

Теоретичне обгрунтування методів реалізації вимог нормативної бази з якості електроенергії

. У наш час важко уявити собі своє життя без електрики. У квартирі, заміському будинку, офісі від наявності та якості електроенергії залежить все. На жаль, коли електроенергію стабільно подається в наші будинки і квартири, це ще не означає, що розрахункові параметри електроенергії саме такі, які необхідні для живлення побутової техніки та різних електроприладів, від яких безпосередньо залежить якість нашого життя, а іноді і саме життя. У даній роботі проведено аналіз проблематики дослідження та контролю якості електроенергії у мережах постачання споживачів. Поставлено головні задачі, які полягають у встановленні причин погіршення якості електроенергії та визначенні місця появи негативного процесу у мережі. Виходячи із класифікації видів навантажень та споживання ними електроенергії, запропоновані розвиток методики виконання вимірювань показників якості електроенергії та нові показники, що дозволять отримати додаткову інформацію для розв’язання вказаних задач.

Influence analyses of harmonics on distribution system in consideration of non-linear loads and estimation of harmonic source

AbstractRecently, non-linear loads have diversified and increased. It results in deterioration of power quality on a distribution system, since the equipment, which includes the non-linear loads, generates harmonics. The harmonics cause not only deterioration of power quality but also further various problems. Nowadays, the state of harmonics is becoming evident by the recent researches. However, since the harmonic analysis by using a detailed model of distribution system is too difficult, the analysis is carried out by a simplified model. In this paper, the authors construct an analytical distribution system model in consideration of the non-linear loads with the harmonic sources based on the practical data. Moreover, the influence analyses of harmonics are carried out by using this model. In addition, the authors estimate the harmonic sources in the simplified distribution system.

A Double-Resistive Active Power Filter System to Attenuate Harmonic Voltages of a Radial Power Distribution Feeder

Harmonic propagation between power-factor correction capacitors and system inductors seriously deteriorates power quality in a radial power distribution feeder. Installation of a resistive active power filter (RAPF) at the end bus only suppresses harmonic propagation, not attenuates harmonic voltages. This paper proposes a double-resistive active power filter (D-RAPF) system consisting of a terminal-RAPF and an attenuation-RAPF for each individual harmonic. The terminal-RAPF operating as the characteristic impedance of the feeder is installed at the end bus to suppress harmonic propagation at all harmonic frequencies. The attenuation-RAPF, whose control gain can be set according to the requirements of the harmonic voltage distortion limit, is installed at a specific position for each individual harmonic to attenuate the corresponding harmonic voltages. The D-RAPF system not only suppresses harmonic propagation and attenuates harmonic voltages more effectively, but also has the same rated power capacity as the RAPF. However, both the harmonic damping performance and the rated power capacity must be considered to choose the D-RAPF system or the RAPF when a harmonic current source exists at a position between the attenuation-RAPF and the terminal-RAPF. Simulation and experiment results verify the theoretical analysis and demonstrate the effectiveness of the D-RAPF system.

Accurate SFS Parameter Design Criterion for Inverter-Based Distributed Generation

The Sandia frequency-shift method, among all frequency-based active islanding detection methods (IDMs), is one of the most effective methods for inverter based distributed generators (DGs). The nondetection zone (NDZ) of the Sandia frequency shift (SFS) highly depends on its design parameters. If the design parameters are not properly tuned, they may result in failure of the method or deterioration of the system power quality (PQ) through injection of a high amount of harmonics. The main objective of this paper is to propose a new algorithm for SFS method parameter determination, which would add precision to the previous parameter design criterion. In this paper, also a new formula for multi-DG applications is proposed which results in optimally setting of all SFS parameters to eliminate NDZ. Using the new criterion, the negative impact of the conventional criterion on PQ is reduced, and the efficiency of the SFS IDM is increased. The simulation results show that the proposed algorithm results in more accurate detection of the islanding phenomenon in the shortest possible time. All of the simulations and NDZ analysis are carried out in the MATLAB environment.

Performance evaluation of composite filter for power quality improvement of electric arc furnace distribution network

Abstract Electric arc furnace (EAF) is one of the responsible cause for deteriorating power quality in the distribution network by, introducing harmonics, propagating voltage flicker and causing unbalance in voltages and currents. This paper presents performance evaluation of composite filter (CF) for power quality improvement of EAF distribution network. The performance of CF is evaluated in terms of harmonic and voltage flicker mitigation capability of CF. The composite filter is consisting of a shunt LC passive filter connected with a lower rated voltage source PWM converter based series active power filter (SAPF). Performance of the composite filter (CF) is compared and analyzed with that of passive filter to improve power quality at point of common coupling (PCC). Simulation for a typical EAF distribution network along with the PF and the CF filter has been carried out to validate the performance. The simulations have been carried out in MATLAB environment using SIMULINK and power system block set toolboxes.

On the matters of increasing the dependability of first stage pumping stations power supply

First stage pumping stations are first category power consumers that usually have back-up power supply. Additionally, the engine room of the pumping station is equipped with synchronous or asynchronous high-voltage motors that in transient states may create unforeseen problems in the power supply system not only within the station, but beyond. The dependability of plant and equipment is defined by many factors, e.g. start-up procedures, stopping-down, operational changes, equipment shutdown. [6]. The primary factors that reflect the impact of the transient states are mechanical overload, voltage slumps in load centers, voltage slumps in switchgear busbars, etc. The value of voltage slump associated with start-up of high-voltage synchronous motors that does not last more than 30 seconds is neglected, though the impact of start-up voltage slump is a negative factor that affects adjacent consumers on the grid [7]. The dependability of the power supply system has an effect not only on pump station operation, but also on the service life of the facility’s electrical equipment. An undependable power supply system can also contribute to higher electric loss and deterioration of power quality. Improving the dependability of power supply systems of the considered facilities requires first and foremost specific tasks to be solved. To that effect, this article specifies and analyzes primary causes of faults in first stage irrigation pumping plants. The authors clarify the dynamic stability of high-voltage synchronous motors and its dependence on short interruptions of power supply. They also analyze the impact of start-up currents of synchronous motors on the operation of pumping units and electrical equipment in general. The article substantiates the efficiency of soft starters (SSs) in start-up procedures of high-voltage synchronous motors of pumping units of irrigation pumping stations. The article also establishes the inefficiency of frequency converters in pumping units of irrigation pumping stations using specific examples. It was found that automatic transfer equipment in the considered facility does not ensure the speed of operation required for fault recovery and negation of water hammers in pumping units. The article sets forth the tasks and possible solutions related to improving the dependability of power supply systems of first stage irrigation pumping plants.

Application of Soft-constrained Differential Games Theory to Robust Load Frequency Control

The high penetration of renewable energy sources in power systems will deteriorate power quality and affect frequency stability. This issue is more severe in a small-capacity area or island power system that is weakly linked to the main grid. For the deviations of frequency and tie-line power exchange in power systems with multi-source generation units, we proposed a new robust control strategy based on linear quadratic soft-constrained differential games theory to reduce the influence from variations of wind farms output. The results of simulation testify its effect and robustness.

Real time simulation and experimental validation of active power filter operation and control

Nonlinear loads inject harmonics into electric power systems distribution network, which deteriorate power quality and affect the sensitivity of connected electronic equipment. Shunt active power filter (APF) is an important piece of depolluting equipment that is used in power systems to cancel current harmonics, compensate reactive power and balance supply loads. In this paper an APF setup is studied and analyzed using RT-Lab real-time simulator and controller. A simple control method is used to extract the harmonic contents of the supply currents. The pulse width modulation (PWM) technique is therefore applied to command the power switches to generate the reference current for the APF. Experimental results validate the real time model and the control method is used to properly compute and track the reference current, results show efficient filtering of the load harmonics and load balancing is also successfully achieved.