• Issue 1,2009 Table of Contents
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    • >名家主持:分布式发电对大电网的影响
    • Reserch of load modelling for distributed generation planning


      Abstract (45) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:Increasing the penetration level of Distributed Generation (DG) into the distribution system is a new ehallenge for traditional electric power systems. Although it is generally recognised that DG has the potential of reducing energy losses in power systems, inappropriate modelling can lead to a misleading predictions for power loss reduction in DG planning. This paper presents an investigation into the impact of load models on the calculation of energy loss, and proposes detailed modelling of load in DG planning, where load is divided into three categories: residential, industrial and commercial. A comparative study of real and reactive power losses for various load models and load levels is carried out using the methodology proposed in this paper. A sample power system is adopted to analyse the system performance under various DG scenarios and at various load levels. Simulation results indicate that load models can significantly affect the load losses calculation in DG planning.

    • Investigation of islanding detection strategies for PV grid-connected converters


      Abstract (91) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:Islanding detection is an essential function for most grid-connected converters, especially PV grid-connected converters. The passive islanding detection methods have large none detection zone. The active islanding detection strategies are proposed to improve the detection ability. However, they introduce perturbations in the converters output, contributing to poor power quality. This paper analyzes the working principle and parameters selection rules for frequency shift and phase shift islanding detection techniques. The algorisms optimization and the multi-converter operation performance are also investigated. It provides basic islanding detection guidance for PV grid-connected converters.

    • Novel excltation system of synchronous generator


      Abstract (86) HTML (0) PDF 0.00 Byte (3) Comment (0) Favorites

      Abstract:In order to improve transient stability of power system at present, this paper presents a novel excitation system based on full controlled devices rectifier. It can damp oscillation by two channels, DC excitation and exchanging reactive with generator terminal, and it can be equaled to STATCOM and A. C. exciter. Simulation results of Multi-machine power system with PSASP show that the novel excitation systern can quickly damp power oscillation and maintain well voltage characteristics of generator terminal. , and have the better dynamic performance than traditional excitation system.

    • Artificial intelligence technique applied in distributed generation system


      Abstract (70) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:This paper gives a brief description of the key problems which need to be cautiously considered existing in both the isolated operation mode and the grid-connected operation mode for distributed generation (DG). Some advanced artificial intelligence techniques are adopted to solve those problems as effecfive tools. The application situation and research status of multi-agent system, artificial neural network, genetic algorithm and fuzzy logic in distributed generation system home and abroad are summarized detailedly. The existing problems and solving thoughts of each artificial intelligence technique are analyzed. Finally, a networked coordinated control system scheme for distribution systems with DGs is developed, which is based on the power line carrier communication (PLC) technique and multi-agent technique.

    • Investigation of the influence of microgrids high large penetration ratios on power network stability


      Abstract (135) HTML (0) PDF 0.00 Byte (17) Comment (0) Favorites

      Abstract:The penetration of microgrids modifies the character of energy flow direction in power systems, which has a great impact on power networks stability. The influence of the microgrids penetration ratio on voltage variety and power angle stability is analyzed in this paper. ,Numerical simulation is carried out with an EPRI 36 bus test system, and the allowable maximum penetration ratio is obtained. The factors that affect the penetration ratio are investigated. The studies in this paper provide evidences for the optimal energy matching of DG in microgrids and improvement of the stability and reliability of the power system connected microgfids.

    • >科学研究
    • Generalized voltage collapse index for long transmission network


      Abstract (49) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:A generalized voltage collapse index(GVCI) is derived which represents the distance to voltage collapse in terms of loading margin to maximum loading for long radial transmission system (or overhead/submarine cables) having substantial capacitive impedance. GVCI is an instantaneous value used to initiate the relay for control and protection by employing a set of local measurement provided by Phasor Measurement Unit (PMU). The effectiveness of the proposed GVCI is tested on a simple two-bus double circuit line and the effects of On-Load Tap Changers (OLTC) operation on voltage collapse have been analyzed analytically by extending the GVCI formulation to incorporate settings of OLTC. The proposed GVCI is compared with L-index for voltage collapse conditions. Finally, a possible application of the proposed index on remotely located wind farms is discussed.

    • Novel network based traveling wave location algorithm with information fusion


      Abstract (77) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:A novel network based traveling wave fault location algorithm is presented in this paper. With analyzing the relationship of the initial traveling wave arrival times recorded by fault location devices in the whole grid, the complex transmission network can be simplified into a radial network by using the shortest path principle, through which the initial traveling wave arrival times recorded at remote substations are converted into the times at the two terminals of the fault line. By deleting the invalid convertedtimes and fusing all. the valid converted-times, the whole power grid based fault location is realized. The novel algorithm can effectively solve the problem of location failure, which is caused by any fault location device fault, startup failure or time recording error. Simulation results show that the algorithm is with high precision and robustness, and the fault distance error is no more than 100 m.

    • Direct solution of optimal power flow considering small-signal stability constraints


      Abstract (57) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:In order to limit power system operation in the critical range of static stable stability, a group of small-signal stability constraints as inequality constraints in the traditional optimal power flow model are added, and the optimal power flow mathematical model considering small-signal stability constraints is established in this paper. The critical eigenvalues real value of the system matrix as small-signal stability index is applied to form a constraint function, then the small-signal stability constraints is transformed by Cayley transformation, spectral function and Smoothing Newton-Type Method. The large scale nonlinear system is thus convenienced to calculate with matrix eigenvalues directly. By using in a WSCC 3 machines 9 buses system, this method effectiveness are verified.

    • Research on a new unsymmetrical PWM technique for large capacity inverter


      Abstract (119) HTML (0) PDF 0.00 Byte (20) Comment (0) Favorites

      Abstract:A new unsymmetrical PWM technique is introduced in this paper, which is particularly applied to high-power inverter control in flexible AC transmission systems (FACTS). The proposed pulse pattern possesses only half-wave inverse symmetry, but its quarter-wave symmetry is absent, the freedom degree of switching angles is doubled, the specific harmonics are thus controlled by their amplitudes and phase angles. In the lower switching frequency, the technique is designed for use in an active power filter. The good performance of this technique in harmonics compensation is verified by the simulation of a parallel compensator using Simplorer.

    • Update and analysis of economic current density for medium and low voltage copper cables


      Abstract (139) HTML (0) PDF 0.00 Byte (14) Comment (0) Favorites

      Abstract:The ever-increasing copper price in the past several years has led to a significant increase of the cost of copper cables, and the economic section has hence decreased. Thus, whether the economic secfion obtained from past data could still meet the current carrying capacity is becoming a matter to be investigated. The recent cost data associated with medium and low voltage copper cables are collected and handled, and then as the basis for updating the economic current density data in this paper. To facilitate the use of the economic current density data, a cable type parameter is introduced. In addition, the stability and accuracy of the updated economic current density data are verified by using actual data.

    • Analysis of generation companies'''' optimal bidding strategy considering risks of contract market and day-ahead market


      Abstract (119) HTML (0) PDF 0.00 Byte (4) Comment (0) Favorites

      Abstract:Through the historical price data's processing, the uncertainty factor in the day ahead market and the contract market to the lognormal distribution is simulated in this paper. The revenue functions of the power generation companies are obtained. And the bidding model considering contract is established. Due to the relevance of the two market revenue, Gumbel Copula function is chosen and applied to the risk measure of power market. The CVaR is calculated with the Monte Carlo Simulation method. The obtained optimal bidding strategy of power generation companies is: the power generation companies with better risk tendency will put very small part of electricity into the contract market, they prefer a high bidding strategy ; while power generation companies with risk avoiding will increase the quantities of the electricity in the contract market, and they prefer a low bidding strategy.

    • Design and implementation of power market simulation platform based on JAVA


      Abstract (65) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:Design and implementation of power market simulation platform are presented in this paper. Based on the uniform SQL database, the simulation platform is designed and developed using JAVA 2. The modularized structure system and the visual graph interface are employed. This platform is constructed using the console and operation platforms with C/S(Client/Server) structure. Experimental parameters can be modified flexibly, the experiment process can be monitored precisely, and statistic graph can also be generated dynamically. This platform is applied in theory analysis for design and evaluation of power market system. It analyzes Time-of-Use Electricity Pricing Policy's influence on economic interests of power-generating enterprises and users business strategy in present. The action and effects mechanism of Time-of-Use Electricity Pricin~ Policy is r~v~|,~d

    • >技术应用
    • Instantaneous reactive power theory based improved harmonic current detecting method and its digital low-pass filter optimized design


      Abstract (120) HTML (0) PDF 0.00 Byte (19) Comment (0) Favorites

      Abstract:In response to the application of active power filter, an improved ip - iq algorithm for harmonic and fundamental reactive current detection based on instantaneous reactive power theory has been presented in this paper. The improved method can decrease the complex mathematical transformation and can be directly used in harmonic currents and fundamental current detection for three-phase three-wire, three-phase four-wire and single-phase distribution systems. A new dual-filter method of series filter technology is proposed, based on the series of average filter and Elliptic filter considering the advantage and disadvantage of FIR filter and IIR filter. Simulation results show that the proposed detection method is with real-time, high precision and easy implementation and application in distribution systems.

    • Real-time detection of short duration voltage variation based on model maximum and singularity of wavelet transform


      Abstract (51) HTML (0) PDF 0.00 Byte (3) Comment (0) Favorites

      Abstract:The detection method of short duration voltage variations with wavelet transform is introduced, relations between wavelet transform model maximum and original signals singularity and the wavelet transform based noise elimination principium with fixed threshold are analyzed in this paper. The real-time detecting process of short duration voltage variations is proposed, and simulations are carfled out. Results show that the proposed method can eliminate noise influence, and detect the times of short duration voltage variations accurately and efficiently.

    • RFID mobile inspection system for low voltage distribution network


      Abstract (77) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:Taking into account the management status of distribution networks and the characteristics and advantages of Radio Frequency Identification (RFID) technology, the construction blue print andsystem structure for distribution network inspection system are presentd in this paper. Aplication results show that the mobile inspection system extends mangement information system to outdoor work fields, it can effectively eliminate time delay and error rate of traditional manual operation and information transmission, and it can improve the on-site operation efficiency & convenient and reliability.

    • Analysis and treatment for inner surface iron oxide in boiler connecting pipes


      Abstract (85) HTML (0) PDF 0.00 Byte (2) Comment (0) Favorites

      Abstract:The iron oxide exists at the inner surface of heating surfance connecting pipes in Kaifeng power plant 2 ×600 MW units. The iron oxide microstruture is anlyzed in this paper, the PBR and expansion coefficient of FeO, Fe3O4 and Fe2O3 are compared, and the reason of the iron oxide is obtained. It is verifled that H2SO4 pickling is an effective method to clean iron oxide.

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