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This paper investigates a Yagi antenna with circular polarization (CP) at the end-fire direction based on normal-mode helix. It consists of a right-handed center-fed helical dipole and two parasitic helixes with the same direction of rotation. The parameters of the driven helix are optimized to realize circular polarization and quasi-uniform radiation in the plane normal to the helix axis. The coupling between the driven and parasitic helixes is utilized to achieve a unidirectional radiation. It is found that an end-fire beam with CP is obtained by carefully choosing the parameters of the parasitic helix and the spacing between them. Simulation results show that the final optimized antenna achieves a gain of 6.4 dBic and front-to-back ratio of 8.1 dB at 1 GHz.

In order to achieve a clean, efficient energy utilize, effectively alleviate the increasingly serious energy crisis and environmental pollution. The paper builds a typical microgrid composed of inverters-based on multi-micro-generators and adopts the master/slaver control strategy, that is, electric vehicle charging and discharging system acts the master control source, while wind turbines, photovoltaic and storage system act as slaver control source. Using PSCAD software to establish its dynamic simulation model and study the control strategy and dynamic operating characteristics of the electric vehicle charging and discharging and the microgrid under grid-connected mode, isolated mode and their transition mode to achieve smooth operation and ensure grid security, stability. Finally, it has been demonstrated that the feasibility of the control strategy.

With the development of economy and industry, increasing demand for electric energy and reserves shortage of non-renewable energy become contradictory focus. Meanwhile, climatic problems like global warming are becoming increasingly prominent. Developing new energy sources to replace conventional ones, becomes the best solution of energy and climatic problems. Wind energy is recognized as an ideal renewable energy form due to its merits such as extensive distribution, low cost and mature technology. This paper introduces a reliability evaluation method for distribution system containing wind turbines as distributed generation. Firstly, we sample wind speed per hour by a fitting function of distribution. Then, piecewise function is used to calculate output of each unit. This method takes random energy output of wind power generator into account. By using time varying output and load model, we can simulate the actual situation of distribution system. Also, correlation of wind turbines is introduced into the evaluation. We use correction matrix to modify obtained wind speed sequence. By this correction, the sampled wind speeds of different units could avoid having great differences. This paper use RBTS system to test the method mentioned above. Result shows that because wind sequence reaches median of the vector after correction, system reliability indices have deteriorated.

This paper presents a new method for distribution evaluation based on Monte Carlo simulation and minimal path. Firstly, a simplification model is constructed according to switches using for disconnecting the failure component. Then the failure element and failure duration time is simulated with Monte Carlo Method. Using section topology matrix finds which fault type each section belongs to. Thus, the fault type of every load point is obtained. Finally, failure occurrence times and failure duration time of each load points are counted. Thereby, the basic reliability indices of the distribution system could be calculated.

According to strong proponent of energy conservation and emission reduction, the development of new energy vehicles has been upgraded to the national strategic level in "Twelfth Five-Year Plan" period, and it becomes the main theme of Chinese automobile industry. And the planning of electric vehicle battery-switch station (BBS) has a great impact on the popularisation of electric vehicle and the security of power system. For reasonably planning of the location and sizing of the BBS, an optimization planning cost model and a new demand model of battery-switch station are proposed. This demand model is based on analysis of customers' characteristics. And in the optimization cost model, the objective function includes such variables as network loss cost, building cost and running cost of a particular battery-switch station, electrovalence and so on. Its constraints include the acceptable load power of the power system, the demand of electric vehicles, and the limitation of service territory of the BBS and so on. Finally, a practical example is carried out to demonstrate the performance of the demand model and the planning method.

Extended equal area criterion method (EEAC) is always applied for transient stability analysis of large scale power system. The coherency identification of generators clusters after accidents is on the basis of EEAC Method, and the coherency identification of generators clusters used to take the complex power angle method as the criterion, which consume a lot of time and possess a relatively inefficient. A new approach to the coherency identification of generators clusters based on wide area measurement system is proposed in this paper, which utilize the ratio of accelerated kinetic energy to distribute the critical machines clusters. The concept of the ratio of accelerated kinetic energy and related algorithm are described in detail in this paper. Take the power grid of He Bei province in China as a calculation example to illustrate the feasibility and advancement of this approach.

An integrated indices system for urban power grid security assessment is proposed, which includes five kinds of indices such as capability of supplying power safely, static voltage security, topological vulnerability, transient security and risk indices. The indices system can scientifically and fully reflect the security level of power grid and provide a quantitative base for the establishment of emergency management technology and measures. The traditional indices and methods for power system security assessment are improved and some indices are first proposed such as "number of lost components after N-K contingencies" and "the largest power supply region index". Based on utility theory and considering effects of external environment on failure probability of lines, risk indices are constructed including "overload risk index", "low voltage risk index", "voltage collapse risk index" and "angle instability risk index". Power System Security Assessment Indices Calculation and Analysis Software is developed, which provides an accessorial and practical tool for power system plan and operation. At last, one urban power grid is used as a research example and the results show effectiveness of the indices system and practicability of the software.

Combined with the actual situation of 10 kV distribution network of electric power supplier in Beijing city, based on collecting amount of statistic information, this paper calculate and analyze the operation status of the distribution grid. Set up subjection function and evaluate modeling from the rate of load, loss and the N-1 check of the voltage level of grid node aspects, and get the subjection value and "good" or "bad" expectation in fuzzy method. These results are rational evaluation for the supply capability of the medium voltage distribution grid in the city. Considering all kinds of factors, present the comprehensive and quantitative evaluation index of the electric network was got through setting up appraise index collection, matrix of judgment level collection and suited operators. The evaluation index provides basis for the construction of the network structure programming, and costing program of distribution