Local Electric System Research Articles

Variable Switching Frequency Control of Distributed Resources for Improved System Efficiency

This contribution explores the possibility of improving the global efficiency of three-phase inverter-based distributed resources (DR) embedded in low-voltage distribution feeders, by the adaptation of their switching frequency (SF) to the operation point of both the converter and local loads. The core of this proposal lies on the fact that in a good number of applications, in both service and residential sectors, the owner of the DR is also in charge of the losses caused in the local electric power system. This fact leaves room for a global optimization of the power losses, i.e., converter losses will be considered together with those losses caused by the current harmonics injected into the local grid. A dynamic adaptive SF frame of the DR is considered in this proposal to allow its operation beyond its rated frequency at light loads, subjected to the thermal constraints of the device. Simulation results obtained using PLECS software as well as an experimental validation of the method are included.

A compact nanogrid for home applications with a behaviour-tree-based central controller

This paper proposes a nanogrid for home applications. Compactness, rapid installation and minor changes to the existing equipment are among the basic concepts behind the proposed nanogrid. With this in mind, the authors designed the proposed nanogrid as a compact object. To this aim, the power electronic converters of a typical nanogrid are no longer distributed and placed close to peripherals; they now are grouped together. The electric wires of the local power distribution system connect the grouped converters to the distributed peripherals (e.g. photovoltaic panels, batteries storage systems, loads). As a benefit, when the proposed nanogrid is installed between the meter and the switchboard of an existing dwelling, no significant changes to local equipment, devices and electrical system are required.A central controller governs the proposed nanogrid. Such a controller ensures the power balancing, implementing the continuous controllers of all the power converters belonging to the proposed nanogrid. In addition, such a controller optimizes generation and demand, implementing a decisional process based on behavioural rules.In this paper, a behaviour tree models the behavioural rules. The behaviour tree serves the discrete controller to decide the operation point of the nanogrid. The behaviour tree drives the central controller to pursue strategic targets so as to ensure power supply continuity to critical loads, maximize the exploitation of renewable energy sources and minimize power flow at the point of delivery.This paper also illustrates a single-phase 1 kW prototype of the proposed nanogrid; the prototype is subject to four tests and conditions: black start, utility failure, utility restore and over generation. Besides the capability to pursue the strategic targets mentioned above, the experimental results also demonstrate the proposed nanogrid’s capability to adjust the current imported from the utility grid, to change from grid-connected mode to stand-alone mode and vice versa, to compensate for a surge of the DC bus voltage.

Determination of the optimum capacity of the photoelectric stations storage for increasing the balance reliability of local electric systems

In this work the actual task of increasing the balance reliability of local electrical systems (LES) is solved by establishing a drive within the limits of the balance sheet of a photovoltaic electric stations (PES). The law of distribution of generation of PES for a certain period of time of day during the year is analyzed. A mathematical model for generating PES in the form of Gaussian mixtures is proposed. The main characteristics of the probabilistic nature of solar power generation are obtained. The probability of covering the given loading schedule by generating the PES is determined for a certain time of day throughout the year. On the basis of certain probabilistic characteristics of the PES generation, the capacity of the drive is determined, which will increase the balance reliability of the LES.The probabilistic characteristics of both the process of generating electricity at the PES and the process of its consumption are precisely determined by a mathematical model based on the Gaussian mixture. On the basis of the received characteristics it is relatively easy to obtain the probability of covering the loading schedule with the source of renewable energy and to determine the probability of providing balance reliability in the local electrical system. It is expedient to estimate the probability of providing a loading schedule at hourly intervals on which the day is broken. This reduces the analysis errors that are caused by the natural conditions for generating electricity from renewable sources, and take into account the features of its consumption graphs.In this paper the capacity of the drive is determined based on the possibilities of accumulation of surplus electricity, at the peak generation time of the PES.

Reconciliation of photoelectric station generation schedule and local electrical system loading

Reconciliation of photoelectric station generation schedule and local electrical system loading

MODELING OF COMPATIBLE WORK OF DISTRIBUTED POWER SOURCES OF ELECTRIC POWER AND CENTRALISED POWER SUPPLY

Urgency of the research. Current trends of distributed generation development in Ukraine indicate a rapid generation in-crease from renewable energy plants. Most developed countries gradually refuse from the fossil fuels use and invest more and more to the “green” energy. Therefore, there is a need for a detailed study of the operation conditions of distributed energy sources due to their instability, as well as the processes that arise in distribution electric networks with diverse types of distributed energy sources. Target setting. In the producing process of power energy by distributed energy sources due to the increase in their num-ber, there are situations where several renewable sources of energy operate to only one system of buses. Thus, such distributive networks acquire the features of a local power system, which complicates the control process of such systems, and also there is a problem with the electricity supply of consumers. Actual scientific researches and issues analysis. The analysis of publications suggests that in literature more attention is paid to studying the operating modes of solar power plants, or small hydroelectric power plants. However, almost no attention was paid to the study of their cooperation work. Uninvestigated parts of general matters defining. Only a few works are devoted to the study of the cooperation of the diverce sources of distributed energy sources in the local electrical systems. That is why, their impact on power distribution networks and on the grid in general has not been studied extensively. The research objective. In this article was considered the influence of asynchronous generators on small hydroelectric power plants on the operation modes of distribution electrical networks, and were investigated the processes that are occurring in local power systems with different types of distributed energy sources. The statement of basic materials. Based on the research results, was developed a computer model of a such system in the PS CAD software environment. Two solar stations and one small hydroelectric power station with an asynchronous generator were connected to the power supply. It was shown the simulation of two modes of operation: a joint operation of a small hydroelectric power station, two solar power stations and a power supply center; a joint operation of a small hydroelectric pow-er plant, two solar power stations and a power supply disconnected. Conclusions. As a result of computer simulation, it is shown that by switching on a small hydroelectric power plant with an asynchronous generator in the case of an emergency shutdown of centralized power supply, it is possible to restore the work of solar power plants, and thus partially or completely restore the power supply of consumers.

Ontario's Auction Market for Financial Transmission Rights: An Analysis of its Efficiency

Financial transmission rights (FTR) are financial products that entitle their holder to receive a payment based on the degree of congestion in a transmission system. In many liberalized electricity markets, FTR are sold at auction by the local electricity system operator. This paper addresses several questions about the performance of FTR auctions in Ontario's restructured electricity market, including whether auction market clearing prices approximate realized payouts and whether there is any evidence that the competitiveness of auctions, as measured by the number of bidders, affects the forward market unbiasedness or informational efficiency of the auctions. The paper finds that the auction process is inefficient in the sense that market clearing prices are substantially and systematically lower than realized payouts, resulting in substantial transfers away from consumers. However, there is some evidence that the auction market is more efficient when there are three or more bidders.

Coupling of Wind Power Heating with High Energy-Consuming Industries to Increase Wind Power Consumption in Xinjiang, China

Numerous problems have emerged with the rapid development of wind power in Xinjiang. The predominant problem is the inhibition of the healthy development of the wind power industry by wind power curtailment in Xinjiang. In this study, wind power heating and high energy-consuming industries were coupled to increase wind power consumption in Xinjiang on the load side. The feasibility analysis of wind power heating in Dabancheng showed that the heating load characteristics coincide with the wind characteristics and the electric heating technology can fulfill the requirements for wind power heating. A business model innovation achieved a win–win situation. Furthermore, a wind power heating system was designed in Dabancheng, the boiler capacity and the heat storage capacity were calculated, and a heating system model with heat storage technology was established. Wind power heating with heat storage can improve the consumption of wind power and increase the local electric load and system adjustability. Furthermore, heating with curtailed wind power can save 2942 tons of standard coal as well as reduce 5172 tons of CO2, 2.9 tons of SO2, 22 tons of NOX, and 2 tons of soot emissions. Non-grid-connected distributed wind power was applied to the high energy-consuming coal chemical industry to reduce wind power curtailment, expand the consumption market, and reduce pollution. A multifunctional wind-photovoltaic complementary system with hydrogen energy storage coupled with traditional high energy-consuming coal chemical industry was established. The implementation plan using wind and solar energy to produce, store, and apply hydrogen energy was proven beneficial. Wind power consumption was improved on the load side. The wind power curtailment problem was reduced by increasing local load using the curtailed wind power to provide clean heat in Dabancheng and constructing the multifunctional wind–photovoltaic complementary system. This study will contribute to the healthy and sustainable development of the wind power industry in Xinjiang.

Optimization of the functioning of the renewable energy sources in the local electrical systems

Optimization of the functioning of the renewable energy sources in the local electrical systems

Determination of optimal power reserves for carrying balance reliability of local electric system

Determination of optimal power reserves for carrying balance reliability of local electric system

Shaping of PWM Converter Admittance for Stabilizing Local Electric Power Systems

This paper suggests the concept of shaping the pulsewidth-modulated (PWM) converter admittance. The analytic admittance matrix equation, which is derived from the small signal model of a PWM converter, is formulized. Based on the damping coefficient and the natural frequencies of phase-locked loop and dc voltage loop, the variations in admittance frequency responses are discussed. In addition, the frequency response can be adjusted through pole placement using the gain of the current controller. The controller gain for a stable operation is designed by detailed understanding of the frequency response shape. Furthermore, to stabilize the local electric power systems (EPSs) that invoke instability through the interaction between constant power load PWM converters, the admittance shaping loop is utilized for the distributed generator PWM converters. Through computer simulation and hardware experiments, the proposed shaping guidance can effectively stabilize local EPS.

Adaptive system for automatic stabilization of the power factor for electric drives of separation device by means of serially connected capacitors bank

A method for designing adaptive systems for automatic extremum search to stabilize the power factor of local electric power system of electric is considered. It consists in application of the serially connected capacitors compensating the reactive component of the total electric power of in parallel connected centrifugal machines usually called as an aggregate. Operation of the system just demands measuring voltage at the output of the static frequency converter for electric drives. The proposed control system is designed to stabilize the power factor close to unity in a case of alteration of parameters of a separation cascade or a single separation device in an aggregate. Such system can be operated continuously or connected occasionally depending on a technological situation. In addition, it totally excludes the phenomenon of overcompensation.

The impact of distributed power sources to the best of flow in electrical networks

Intensive implementing distributed generation sources from alternative energy sources leads to a situation where one feeder can connect several different types of distributed energy sources, including solar power plant and small hydropower plant. The system consists of distributed generation small-capacity power plants scattered throughout the energy system. They supply electricity to consumers in the near and in the case of excess energy can transfer its network centralized power. This paper discusses the reduction of active power losses in the local electrical systems that operate different types dispersed energy sources. The main goal is to develop a methodology for determining the point of power flow section the local electrical system of dispersed generation sources and develop a method for choosing the optimal place network disconnection criterion of active power losses. The article shows the computer model regime for local electricity system that allows to determined the place point of power flow section and calculated the power loss at section schemes in the respective nodes. The choice of multi sections is difficult optimization problems. It is proved that in the use of multiple distributed sources of energy in the local electrical system for optimum energy losses point of power flow section (several possible points of power flow section) is selected at the lower junction voltage. Regulation of power generated by small hydroelectric power plant affects the change point of power flow section local electric networks and reduces the active power losses in the local electrical system

Evaluation probabilistic characteristics of solar power generation in applications of intellectualization local electric systems

Growth of the share of renewable sources of energy in electric energy balance of the country is stipulated both by state preferences and certain reduction of the prices at the world market for the elements of such sources. Solar power plants are developing at a rapid pace. Some consumers start to construct plants of direct conversion of solar energy as a means to provide certain level of energy independence. These consumers leave the group of “passive” and join the group of “active” users and are able to influence the operation mode of local energy system.In new conditions the coordination of the work of active consumers, sources of distributed generation and distributive electric network is impossible without intellectualization of the process of generation, distribution and consumption on the level of local electric system , using Smart Grid technologies.Greater part of renewable sources of energy is represented by solar power plants (SPP). Their operation mode depends on natural conditions of the region, where they are located. That is why the problem of SPP stability estimation is important in the problem of covering the daily schedule of energy consumption. The aim of the research is to evaluate the probability of providing the consumption schedule by means of corresponding source on the base of statistic data.The authors try to solve the given problem, using EM algorithm. The authors could not select the law of SPP generation distribution, applying direct analysis of statistical data, that would satisfy the character of data change, it is suggested to divide the data into the series of mixtures, each of which would correspond to normal law. EM algorithm enables to select optimal, by the criterion of maximum of probability, amount of mixtures. By the values of characteristics of these mixtures the probabilities of emergence both of certain generation and consumed power could be obtained. To reduce the negative impact of random factors, characteristic for certain periods of the day, statistic data were considered by half hour periods of the day. As a result, the authors succeeded in determining the general coefficient of source stability. Probabilities of covering the possible load in determined period of the day are defined. It enables further to evaluate necessary volume of reserve and start-stop characteristics of energy sources that can be used as the reserve

Prospects of electric-energy cooperation between Russia and northeast Asian countries

The article shows trends in the development of interstate electrical connections and interconnections around the world and potential energy-economic effects of their creation. The current situation and problems of the functioning of the electric-power industry in northeast Asian countries, including eastern regions of Russia, China, Japan, the Republic of Korea, Mongolia, and the Democratic People’s Republic of Korea, and their potential role in formation of interstate power interconnection in the region has been analyzed. The potential directions and projects of transboundary power transmission between national and local electric energy systems of these countries have been shown. The role of renewable power sources (water, wind, and solar energy) in the development of interstate electrical connections and interconnections, including the Asian Super Grid interconnection, is analyzed.

Possible application of biohydrogen technologies as electricity sources in Indonesian remote areas

A prototype system for hydrogen gas production from a biological system of facultative fermentation has been applied for electricity power supply. The prototype was designed for application in remote or isolated areas in Indonesia. The fermentation system, which was designed to be as simple as possible, includes the preparation of the microbial seed, the substrate material, the vessel and other required equipment, gas capture and purification, a converter, and transportation. The model experiment in the field undergoes several modifications depending on the biomass sources in the actual location, i.e., some areas have agroforestry, sugarcane, soy sauce and palm sugar wastes. The light intensity and temperature followed the natural conditions. The results indicated that a cultivation scale of 5–25 L per substrate does not affect the result, i.e., a hydrogen production of approximately 60–70% of the total gas produced. The hydrogen gas produced was converted into electricity sources to power fans and house lamps. However, the hydrogen power is not yet sustainable due to the batch fermentation system, the biomass supply and the local electrical system, which is conventional (not a grid system). We propose to merge the electrical system in those areas, i.e., combining the source of electrical power from wind, solar, biomass, ocean current and fossil fuel-based generators. The model of the electricity pool system is important for Indonesia because, geographically, Indonesia consists of more than seventeen thousand islands, where the electricity supply remains unstable.

Discussion on General Solution of the Laplace Equation for Far Field Electric Potential

In this paper, the general solution of Laplace equation is presented，the electric potential yielded by local electric charge system in remote field is discussed. The result shows that the electric potential yielded can be expressed as the repeated addition of multiple molecules, local electric charge system can be replaced by multiple molecules located at the origin. By comparing the result with the general solution of Laplace equation, the physical meanings of all terms of the general solution are much clearer, the mathematical equation and the physical model are unified.

Investigation and evaluation of active frequency drifting methods in multiple grid-connected inverters

As the development of distributed generation goes on, more grid-connected inverters are being inevitably connected to the same local electrical power system and the perturbations exerted by each inverter for islanding detection might interfere with each other. The islanding detection principle of commonly used active frequency drift (AFD), sandia frequency drift and slip-mode frequency shift are comprehensively investigated and improved algorithms are proposed as well for better detection performance. Moreover, the interaction of these strategies applied in multiple-inverter systems especially with frequency measurement errors is systematically analysed. The corresponding detection performance is summarised, which can also serve as an effective guideline for designing AFD methods in multi-inverter systems. Finally, simulation and experimental results are provided to verify the islanding detection performance of these methods under multiple-inverter operation.

A European supergrid for renewable energy: local impacts and far-reaching challenges

This article assesses the impact of extensive deployment of indigenous and external renewable energy sources on a local electricity system (Sardinia Island) and discusses the main challenges faced by the European power grids in integrating high shares of renewable-based generation technologies. It presents the 2030 scenarios for the Sardinian power system and the results of steady-state analyses in extreme (renewable) generation and consumption conditions. These results are eventually combined with the assessment of key technology development trends to explain how this can affect the development of a European supergrid. In general, the article stresses that rendering the bulk-power system capable of accommodating high renewable energy penetration not only requires reinforcing the electricity highways but also demands carefully planning the architecture of and the interface with regional power systems.

Performance Evaluation of Active Islanding-Detection Algorithms in Distributed-Generation Photovoltaic Systems: Two Inverters Case

Grid-connected photovoltaic (PV) inverters employ an islanding-detection functionality in order to determine the status of the electrical grid. In fact, the inverter must be stopped once the islanding operating mode is detected according to standards and grid-code limits. Diverse islanding-detection algorithms have been proposed in literature to cope with this safety requirement. Among them, active methods based on the deliberate perturbation of the inverter behavior can minimize the so-called nondetection zone, which is a range of conditions in which the inverter does not recognize that it is operating in an undesired island. In most cases, the performances of these methods have been analyzed considering a highly dispersed generation scheme, where only one distributed-generation power system is connected to the local electrical power system (EPS). However, in some studies, it has been highlighted that if two or more PV inverters are connected to the same local EPS, their anti-islanding algorithms do not behave ideally and can fail in detecting the islanding condition. However, there is no systematic study that has investigated the overall capability of different anti-islanding methods employed on several inverters connected to the same EPS to detect islanding condition. This paper is a first attempt to carry out a systematic study of the performances of the most common active detection methods in a case of two inverters connected to the same EPS. In order to evaluate the global capability of the two systems to detect islanding condition, a new performance index is introduced and applied also to the case when the two inverters employ different anti-islanding algorithms.

Development of a computer algorithm for feedback controlled electrical nerve fiber stimulation

The purpose of this research is to develop an algorithm for a feedback controlled local electrical nerve fiber stimulation system which has the purpose to stop the repetitive firing in a particular region of the nervous system. The electrophysiological behavior of the neurons (under electrical currents) is modeled by Hodgkin–Huxley (HH) type nonlinear nerve fiber dynamics. The repetitive firing of in the modeled fiber is due to the deviations in the channel parameters, which is also called as bifurcation in the nonlinear systems theory. A washout filter is augmented to the HH dynamics and then the output of the filter is fed to the external current generator through a linear gain. This gain is computed by linear projective control theory. That is a linear output feedback control technique where the closed loop spectrum of the full state feedback closed loop is partially maintained. By obtaining a spectrum of eigenvalues with completely negative real parts the nerve fibers can be relaxed to the equilibrium point with or without a damped oscillation. The MATLAB script applying the theory of this work is provided at the end of this paper. A MATLAB–Simulink computer simulation is performed in order to verify the algorithm.