Showing papers in "Automation of electric power systems in 2010"

Development and Challenges of Distributed Generation,the Micro-grid and Smart Distribution System

Abstract: The basic concepts and development trend of distributed generation(DG),the micro-grid and smart distribution system are described.In particular,the influence of DG and micro-grid on the smart distribution system is analyzed from the point of view of the large-scale access of distributed energy resources.DG supplies users with green power from various locally available renewable energy resources,but large-scale interconnected operation of DG in the distribution system may give rise to security and operation problems.Micro-grid technology provides an interface to the interconnection of various DGs by means of structures at different levels,which is the most efficient way for the operation of DG.On the other hand,the smart distribution system makes it possible to realize flexible access to DG and safe,reliable,and optimal operation of the entire power system by effectively managing the micro-grids.Based on an analysis of the relationship between the three,suggestions about the idea and technical means are given for implementing the smart distribution system.

Cyber Physical Power Systems: Architecture,Implementation Techniques and Challenges

Abstract: To implement the objective of smart grids, it is essential to introduce the state of the art computing, communication and sensing technologies, and seamlessly integrate them with the power system. The cyber physical system (CPS) is an emerging but highly important research area concerning the deep integration of physical and information systems. In this work, based on the concept of the CPS and taking into account the characteristics of power systems, the cyber physical power system (CPPS) is proposed. The concept, main functionalities and technical characteristics of the CPS are first introduced. The architecture and major components of the CPPS are then illustrated. Next, some important techniques for developing the CPPS are clarified. Finally, several important research problems associated with the CPPS, including the theoretical foundation, system modelling, simulation algorithms, security assessment, reliability assessment, system design and planning as well as system operation, and the standardization of CPPS, are presented.

Power System Stochastic Economic Dispatch Considering Uncertain Outputs from Plug-in Electric Vehicles and Wind Generators

Abstract: A stochastic economic dispatch model,which can take into account the uncertain outputs of plug-in electric vehicles (PEVs) and wind generators,is developed. A simulation based approach is first employed to study the probability distributions of the charge/discharge behaviors of PEVs. The probability distribution of the wind power output is next derived based on the assumption that the wind speed follows the Rayleigh distribution. The mathematical expectations of the generation costs of wind generators and vehicle to grid (V2G) power sources are then derived analytically. The feasibility and efficiency of the developed stochastic economic dispatch model is demonstrated with the IEEE 118-bus test system.

Power Characteristics of Jiuquan Wind Power Base

Abstract: Jiuquan Wind Power Base (JQWPB) is the first 10 GW-level pilot wind power base in the world, whose construction is the first successful attempt to exploit wind energy in large scale and far away from the load center. By using the gauged wind resources data and the recent energy management system (EMS) operating data from the dispatching department, an analysis is made of the characteristics of wind power resources, and investigations are performed on the power characteristics of wind turbine generator, wind farm, wind farm cluster and the entire JQWPB. By comparing the wind power characteristics in different time scales, it has been found that the output power of the JQWPB has clear relevance to long time scale and is obviously complementary for short time scale. Also treated is the effect of wind power characteristics on power grid stability, peak load regulation and frequency control.

Nearest Level Modulation for Modular Multilevel Converters in HVDC Transmission

Abstract: This paper describes the circuit configuration and operation mechanism of MMCThe comparisons of some modulation methods for MMC show that NLM is the best for MMC in high-power high-voltage applications,such as high voltage direct current(HVDC)transmissionThe NLM method for MMC is proposed,and the formulas to calculate the fundamental and harmonic components are givenThe variations of the fundamental component and the voltage THD with the number of voltage levels and the amplitude of modulation wave are exhibitedThe system performance will be deteriorated in the over modulation range,which need to be avoidedSimulation results obtained with PSCAD/EMTDC are consistent with the theoretical resultsBoth the calculation and simulation results show that the output voltage of NLM based MMC is a good approximation to the modulation wave and has low harmonic contents in a wide operation range

Information Platform of Smart Grid Based on Cloud Computing

Abstract: The future development trend of electric power grid is strong and smart grid, and information platform is strong support for the construction of smart grid. In order to make full use of computing resources, and to better satisfy the need of smart grid for reliable storage and effective management of overall information, an construction method for information platform of smart grid based on cloud computing is proposed. In addition, based on the analysis of feasibility, advantages and problems of the new method, the architecture of information platform is given. Furthermore, considering the characteristics of condition monitoring of smart grid, the cloud computing platform based on Hadoop for condition monitoring of smart grid is proposed. To implement reliable storage and fast parallel processing of massive data, such crucial problems as virtualization, distributed storage and parallel programming model of MapReduce have further been researched.

Cloud Computing:Implementing an Essential Computing Platform for Future Power Systems

Abstract: Because of the continuous expansion of modern power systems,ever increasing computation and data processing capabilities are demanded for power system analysis. The existing computing platform of power systems,however,cannot meet these computational requirements. Given this background,an advanced power system computing platform based on cloud computing is developed. The basic concepts and main technical characteristics of cloud computing are introduced first. The cloud computing is then comprehensively compared with another large-scale distributed computing technology,namely grid computing. From aspects of the hardware components,system architecture and software technology,the implementation of power system cloud computing is presented in details. The potential applications of cloud computing in a number of areas,including power system security assessment,power flow and optimal power flow computation,system restoration,system monitoring and control,scheduling and reliability assessment,are clarified. Several important research problems to be resolved are finally discussed.

A Method for Electric Vehicle Charging Infrastructure Planning

Abstract: Electric vehicle has received more and more extensive attention,which is one of the major development directions of motor vehicles using new energy sourcesThe construction of charging infrastructure is an important prerequisite for the advancement of electric vehiclesDifferent from substation planning and gas station planning,the planning of electric vehicle charging infrastructure has its own distinct characteristicsThe development stages of electric vehicle charging infrastructure is proposed,which can be divided into 3 stages,the demonstration stage,public promotional stage and commercial utilization stageAnd the characteristics of each stage are studiedThe optimization model of charge mode choices is also proposed,and the charging demand of each changing methods can be forecasted based on this modelThe principle,process and model of planning for charging infrastructure are proposed,together with the interval-distance ratio,charge capacity redundancy and charging power redundancyCase studies are given to show that the proposed planning method is adaptive

The Impact of AMI on the Future Power System

Abstract: As an important component of the smart grid,the advanced metering infrastructure(AMI)will trigger profound changes in the future power system.In this paper,the definition,functions and some issues closely related to AMI,such as the electricity pricing mechanism,renewable sources of energy generation and consumer energy storage devices,are studied.The influence of AMI on future power system is discussed and the AMI and customer power information gathering system are compared.Finally,suggestions are made for research on and construction of AMI in China.

Design of Circulating Current Suppressing Controllers for Modular Multilevel Converter

Abstract: A circulating current suppressing controller(CCSC)is designed to eliminate the inner balancing currents in modular multilevel converter(MMC)The CCSC uses the inner mathematical model of MMC through a double fundamental frequency negative sequence rotational frame to decompose the three-phase alternative circulating currents to two DC componentsThe designed CCSC can minimize the distortion degree of the arm current significantly such that the arm current can closely approximate the fundamental sine waveSimulation results based on PSCAD/EMTDC show that the CCSC can suppress the inner circulating current of MMC efficiently without increasing the arm reactanceIt is also shown that this additional controller doesn't affect the AC side dynamics of MMC

Analysis on Capacity of Wind Power Integrated into Liaoning Power Grid Based on Power Balance

Abstract: The maximum installed capacity of wind power integrated into a certain power grid is the most important concern for the power company at the wind power planning stage. Based on the characteristics of power source and load in Liaoning power system,the possible problems in adjusting supply and load with wind farms in operation is analysed. By considering spinning reserve capacity during peak load time and thermal power plants running at minimum capacity during valley load time,the calculation method to determine the maximum installed capacity of wind power integrated is put forward,and the formula for calculation is summarized. The maximum installed capacity of wind power integrated in each year of 2010,2012,2015 and 2020 is given. It is pointed out that the acceptable capacity is less than the planned capacity. At last,the specific measures to increase the capacity of wind power are proposed.

Application of Hybrid Energy Storage System of Super-capacitors and Batteries in a Microgrid

Abstract: Because of the uncertainties and significant fluctuations of both power generation and consumption in a microgrid, the lead-acid battery energy storage system (BESS) endures too large fluctuations in battery charge and discharge currents to maintain the battery lifetime. This paper presents a hybrid energy storage system composed of super-capacitors and batteries. The mathematical model is given and its small signal stability criteria is also derived. Based on the topology of the hybrid energy storage system, the multi-hysteresis control strategy is adopted to improve the flexibility and practicability of the energy storage. Comparing the hybrid energy storage system with the BESS, it can be concluded that because of the high power density of the super-capacitor and the optimized control of the bi-directional DC/DC converter, some advantages can be attained. These include higher capacity usage rate and reduction of maintenance interruptions and operation costs. Both the simulation and experimental results verify the excellent performance of the proposed hybrid energy storage system.

An Agent Organization Theory and Its Application to Wide Area Backup Protection

Abstract: A novel formal representation of agent organization is proposed which gives a theoretical basis for multi-Agent system.Then,based on the requirement analysis of wide-area backup protection(WABP),a WABP algorithm is given.This algorithm uses the expert system combined with Bayesian network for fault diagnosis.Three architectures for the WABP system are compared and analyzed,and as the result,the regional integrated architecture is chosen.The organization structure of the WABP system is studied.The designs of core regional decision Agent are given,including the working process,the uniform interfaces and its relation graph of member-role-capability.The test results illustrate the rationality of the model,and provide a reference for the engineering development of WABP systems.

Mechanism and Modelling Approach to Low-carbon Power Dispatch

Abstract: The introduction of various low-carbon factors will impose significant constraints on traditional power dispatch. In a carbon-constrained world, apart from security and economy, which are the most important targets in traditional power dispatch mechanisms, more attention should be paid to the reduction of CO2 emission in power system operation. A new mechanism is proposed for lower-carbon power dispatch that takes a comprehensive consideration of security, economy and CO2 emission reduction. The background and definition of lower-carbon power dispatch mechanism are analyzed and the characteristics of lower-carbon power sources are defined. The relations between power generation and CO2 emission of various power plants are formulated and divided into three categories, the near-zero emission power sources, normal fossil fuel-based power plants, and carbon capture power plants. On this basis, a preliminary model is presented to formulate a lower-carbon power dispatch mechanism that takes into account the low-carbon power techniques, cost and emission constraints. The impact of the introduction of various low-carbon factors on the optimum power generation schedule is analyzed with examples.

Questionnaire Survey and Analysis of Natural Disaster Defense Techniques of Power Grids in China

Abstract: A questionnaire survey is carried out in ten grid and province graded power companies on the issues such as natural disaster type threatening power grids in China,the characteristic of natural disasters impacting power grids,existing defense techniques for natural disasters,difficulties and problems in disaster defense,and the demand for disasters defense techniques etcAt the same time,results of the survey are analyzedThe content and conclusion of the survey are valuable to research on relative fieldsBased on the survey and analysis,it is set forth that there should be further research on issues including the integrated information platform,acquisition and storage of external information of power grids,probability model of the power equipments'failures caused by disasters,analysis and warning for disasters'threatening safety of the power grid,self-adaptive control and decision-making techniques,and life lines project of handling extreme natural disasters,which will boost the power grid's capability to withstand natural disasters

Annotation for FEP and DSP in Terms of Trajectory Section Eigenvalues

Abstract: For any complex model, an equivalent model of a complex system can be found by using piecewise time-invariant linear system models derived along disturbed trajectories resulting from simulation studies. The method of trajectory section eigenvalues has the same assumptions used for numerical integration, namely that the system is time-invariant linearized in and only in a single simulation step. Therefore, in each integration step, not only the energy margin of the trajectory section can be analyzed by using a static extended equal-area criterion (EEAC) method, but also the oscillation damping and instantaneous frequency of the trajectories section can be observed with the analysis of equilibrium point eigenvalues, regarding the unbalanced power and kinetic energy in the section as the initial disturbance. The complete disturbed trajectory forms a uniform basis for large and small disturbance stability analysis. Section eigenvalues can reflect the effect of complex factors of the oscillation characteristics, and EEAC can reflect the essence of the complicated influence on synchronous stability. Introducing the concept of "sequences of trajectory section eigenvalues at the virtual equilibrium point", the influence of section kinetic energy on the pole-slip instability can be taken into account, in association with the two mechanisms of pole-slip instability and oscillatory instability. The oscillation damping and instantaneous frequency of far end point (FEP) and dynamic saddle point (DSP) are analyzed and the essential relations of large disturbance instability and small disturbance instability are revealed.

Development Purposes,Orientations and Prospects of Microgrid in China

Abstract: Proceeding from the background of energy use and power system construction in China,the development purposes of the microgrid are expounded in view of six aspects,namely,the distributed power access,regenerative energy utilization,rural electrification,user demands for power quality,power system disaster fighting capability as well as the relationship with the smart grid.This paper holds that the compatibility,flexibility,customization,economy,and autonomy should be taken as the development orientations of the microgrid and points out that in the strategic frame of building a strong smart grid,the microgrid has broad prospects for technological development and application in China.

Solution of Active Power Dispatch and Control Scheme for Interconnected Power Grids with Large-scale Wind Power Integration

Abstract: As wind farm has been and will be massively integrated into power backbone grid, power system dispatch and control is confronted with new challenges. The active power dispatch mode for interconnected power grids with large-scale wind power integration is analyzed, and it is concluded that the conventional local balance mode in a provincial grids can no longer resist large-scale wind power fluctuations. Then a centralized control mode of reallocating all generation resources of whole interconnected power grids is presented. And the characteristics of the proposed mode are analyzed, including active power balance method, active power control mainstay, resources allocation, interchange power, security constraint and data communication. Furthermore, to adapt to the current availability of dispatch system and technology foundation in China, a new solution is presented, which takes centralized control mode as goal and hierarchical coordinative control mode as transition.

Study on Dynamic Equivalence Model of Wind Farms with Wind Turbine Driven Doubly Fed Induction Generator

Abstract: For a large-scale wind farm with wind turbine driven doubly fed induction generator (DFIG), a new equivalent modeling method is proposed This method uses the DFIG pitch control action as the grouping rule of wind turbines By extracting eigenvectors that reflect pitch control action, it is used as input of support vector machine (SVM) The wind turbines are dynamically grouped, and the same group wind turbines are aggregated The calculating methods of equivalent model parameters are provided Thus a wind farm model represented by three equivalent wind turbines is obtained Compared with the traditional equivalent modeling methods, the results show that the proposed three-machine equivalent model more accurately describes the dynamic characteristics of a wind farm at the grid connection point

Strategy of Large Power System Coping with Accession of Microgrid with High Penetration

Abstract: The impact of microgrid accession with high penetration on the large power system security and stability,power quality and dispatching operations is analyzed.The problems are discussed including principle of interaction between large power system and microgrid,optimal planning,operation strategy,relay protection and pattern of electrical market.The key problems arisen from the massive microgrid accession to the large power system are defined.The framework structure and main contents of strategies of large power system coping with microgrid accession are proposed.

Energy Management System of Renewable Stand-alone Energy Power Generation System in an Island

Abstract: The shortage of energy restricts the economical development of the remote areas and islands where the grid extension is expensive and difficult. Moreover,fuel price has been increasing drastically over the past decades,as a result,stand-alone renewable energy hybrid power generation stations have become a solution to solve the energy shortage difficulties in those areas. Hybrid energy power generation becomes more popular all over the world. A renewable energy hybrid power generation system including wind energy,solar energy and wave energy,was established in Dangan Island,Zhuhai City by Guangzhou Institute of Energy Conversion,Chinese Academy of Sciences,and is supplying power for the residents in the island. A desalination plant in the system is standing by as a load,which will be switched on when the power is excess,or when there is a shortage for fresh water supplies. The excess power can be used to desalinate sea water to supply fresh water for the island. An energy management system of hybrid energy power generation based on a main-subordinate unit is designed to manage energy more effectively. This system samples the voltage and the current signal of battery,assesses the status of the battery,controls the energy flow,and sends massages to the persons concerned by a GSM module (TC35i). The running results show that the energy management system increases the utilization of renewable energy,and extends the service life of the batteries. It also provides a reliable guarantee for the efficient and stable operation of the stand-alone system.

A Multi-round Negotiation Model for Bilateral Contracting Considering Spot Price Risks in Electricity Market Environment

Abstract: Bilateral contracting represents an efficient approach for hedging the price risks in electricity spot markets. The existing research work on bilateral contracts has been concentrated on the effects of bilateral contracts on mitigating the electricity price risks and market power abuse,and less attention has been given to the forming mechanism of bilateral contracts. Given this background,a systematic multi-round bilateral negotiation framework,through which a generation company and a distribution one can reach a mutually beneficial and risk tolerable forward bilateral contract,is developed. Under this framework,the generation and distribution companies respond rationally to a stream of bilateral offers/counter-offers considering their respective benefits while accounting for the risks incurred by the price uncertainty in the spot electricity market. Each negotiating party can choose its own definition of the benefit and risk,and the expected utility is employed to describe the risk in this work. The concession factor is utilized to illustrate the negotiation strategy of the participants. The reservation expected utility and reservation expected profit are included in this framework so as to model the tolerable limits of the risk and the benefit. Finally,a numerical example is served for demonstrating the essential feature of the developed multi-round bilateral negotiating framework.

Disturbance Source Location of Forced Power Oscillation Using Energy Functions

Abstract: The power system forced power oscillation will be excited by the continuous cyclical small power disturbances.Its steady-state response during resonance is very similar to the response of the traditional weak damping low frequency oscillation.The energy conversion characteristics of the forced power oscillation in a linear system during the steady-state resonance is analyzed firstly using energy functions with the linear equations of motion of the rotor.Using this energy conversion theory,the difference between these two kinds of oscillations is obtained.Then,basic principles to identify the disturbance source of the forced power oscillation by energy function of linear system are proposed with a two-machine system.Finally,based on the structure preserving model of multi-machine power systems,the energy function is extended to the key branches and buses,which is useful to online identify the direction or location of the disturbance source of the forced power oscillation by simply using the network dynamic information.The simulation results of both the 4-machine 2-area system and the New England 10-machine 39-bus system indicate the feasibility and validity of the proposed method.

A New Current Differential Protection Principle for HVDC Transmission Lines

Abstract: A new current differential protection (CDP) principle for HVDC transmission lines is proposed in this paper by analyzing the fault characteristics of DC transmission line. Based on the distributed parameter model, the current at any point of transmission line can be calculated with the voltages and currents measured at local and remote convert stations. When a fault occurs on HVDC line, the sum of the current calculated with each station’s data depends on fault current and can reach maximum at the fault point. When no fault occurs or a fault occurs beyond HVDC line, the sum of the current is small (it is near to zero in theory). According to this feature, CDP can be implemented. Compared with traveling wave protection, CDP can effectively identify inner or external fault and can work in all fault process, and it features high reliability, lower sample frequency and simple algorithm. Compared with the traditional CDP used in HVDC line, it is independent of the distributed capacitance over the long transmission line, therefore it can operate well in the transient process and has high speed. The simulation results show that the method can identify inner or external fault reliably and rapidly.

A Classifying and Synthesizing Method of Power Consumer Industry Based on the Daily Load Profile

Abstract: The aggregate load online modeling with daily load profile has two key points to be solved,one is the appropriate classification and effective synthesis of customers' daily load profiles,the other is the industry composition ratio of the daily load profile in substations. Applying the theory of fuzzy C means clustering and pattern recognition,the authors propose a new method for consumer industry classification and synthesis with daily load profile of the power consumer. First,the customers are classified and selected on the basis of the active power in order to obtain the synthetical daily load curve of the industry. Then,the eigen-value parameters are obtained,by which the synthetical characteristics of the industry can be described and the results of classification and synthesis can be tested. Actual application shows that the method is clear in concept,convenient and practical.

A Coherence Identifying Method Based on Linearization at Non-equilibrium Point

Abstract: A coherence identifying method based on the linearized model for power systems at the non-equilibrium point is proposed,which can take into account the impact of faults. The theoretical derivation of the linearization at the non-equilibrium point is presented and the general laws of the dynamic characteristics of power systems at the non-equilibrium point are obtained. Two novel coherence identifying algorithms for power systems are designed and tested on the 4-generator 11-bus system and the IEEE 39-bus system,respectively. Through a comparison with the time domain transient simulation results,the efficiency of the algorithms is proved. Finally,the merits of this method as well as its possible applications in future are pointed out.

Thought About Protection of Distributed Generation and Microgrid

Abstract: The strategies of protection for distributed generation(DG) and microgrid are analyzed in macroscopic view.The research objects and research methods of protection for DG are analyzed.Based on the current achievements,four strategies of protection for DG are summarized and compared.The protection for AC microgrid is analyzed in the view of whether it depends on communication or not,and a thought of establishing microgrid switch station is presented.The feasibility of DC microgrid is analyzed.The size of DC microgrid is proposed,and the main points of protection for DC microgrid are discussed.At last,based on the grid topology,the connection strategies of DG and microgrid are proposed.

VSC-HVDC System Based on Modular Multilevel Converters

Abstract: This paper researches the application of a novel MMC in the VSC-HVDC system.First,the mathematic model of MMC system is established.Then fast PWM control for MMC system,the balance control for the DC voltages of modules,and methods to reduce switching frequency are proposed.As the system-level control,the nonlinear controller for VSC-HVDC system based on MMCs is designed.It includes decoupling control of active power and reactive power,and the constant DC voltage control.By simulation with software PSCAD/EMTDC,the feasibility and effectiveness of the proposed model and control are verified.

Black-start Decision-making in Smart Grids Using Multi-attribute Group Eigenvalue Method

Abstract: A black-start decision support system is an important component of a smart grid.Up to now,research work on the decision-making of black-start strategies is mainly focused on individual decision-making methods,and no research work is reported on group decision-making ones.In practice,black-start decision-making is usually made by several decision makers,such as power dispatchers/domain experts,rather than by an individual one.Hence,it appears necessary to investigate the application of the group decision-making method to the development of optimal black-start strategies.Given this background,a group eigenvalue method is presented for the black-start decision-making.The positive eigenvectors associated with the maximal positive eigenvalue can be obtained with the application of the Perron-Frobenius theorem,and then the integrated evaluating value of the ideal black-start decision-making expert can be attained.The power method in the numerical algebra is employed to deal with the optimization problem associated with the group black-start decision-making.Finally,a numerical example is served for demonstrating the reasonableness and effectiveness of the developed method.It is demonstrated by case studies that the inherent shortcoming of the individual decision-making methods in evaluating black-start strategies could be overcome at least to some extent.

Development Status and Perspective of Marine Energy Conversion Systems

Abstract: Ocean contains abundant energies,such as wave energy,tidal energy,tidal current energy and ocean thermal energy,which are clean and renewable By utilizing the marine energies,the energy structure and the environment can be improved Since the exploration of the ocean energy brings a lot of benefits,it is encouraged by the government around the world The development of the ocean energy conversion systems in the past decades is reviewed,and the effect and perspective of utilization of marine energies are also discussed