Applied Mechanics and Materials Vols. 291-294

Abstract: The quasi-Z-source inverter (qZSI) has some unique advantages and is suitable for renewable energy sources such as solar and wind generation system. In order to make the inverter have the ride-through ability and the current into the grid symmetrical when unbalanced grid faults occur, the topology of qZSI with super capacitor substituting the low voltage capacitor and the unbalance control strategy were proposed. With a super capacitor the system can balance and smooth the power between the generation unit and grid, also the current injected into the grid can be symmetrical through the unbalance control method. The circuit of the new topology and the mathematical model of the three-phase converter under grid voltage unbalance conditions have been analyzed. And then, closed-loop control scheme for the proposed system is used to control the power flow of generation unit, grid and super capacitor in this system, also unbalance control strategies in positive (dq) + and negative (dq) – reference frames have been implemented in the grid-connected qZSI system to make the current into the grid symmetrical during the grid fault. The operating mode during unbalanced grid fault is simulated in MATLAB/Simulink, and the simulation results are presented to verify the theoretical analysis and the control scheme.

Abstract: In this article, a design of smart home control system which based on wireless transmission technology was presented. Through WIFI and 3G technology, users can monitor the equipments of their homes in everywhere. With WIFI’s ADHOC characteristics, equipments can be added or reduced easily. The high data transmission speed capability of WIFI and 3G makes the video monitor become possible. Both UDP and TCP protocol are used, thereinto, the UDP protocol is used to transmit video data, while the TCP protocol is used to transmit the data with security requirements. In order to save cost, Lwip protocol stack have been used to implement the requirements of this design.

Abstract: After an analysis on the shielding failure trip of accidents of two kinds of tower type for JG and ZGUT in 220kA transmission line in Jiujiang,the main causes of shielding failure trip on the JG and ZGUT type tower which the protection angle of middle phase jumper of JG type tower and middle phase wire of ZGUT type tower are too large were summarized.The measures to prevent the JG and ZGUT type tower from shielding failure were proposed in which TH-lightning rod above cross arm of suspension point of the Jumper string of JG ype tower and the middle phase conductor of ZGUT type tower were reasonably installed.The measures prove to be an effective way.

Abstract: The article deals with the problem of the optimal development of urban power supply systems. The article offers various methodological approaches to discovering weak points of the existing power networks, as well as most effective ways of pinpoint actions in the situation of shortage of information and funding.

Abstract: This paper expounds the hardware and software system design for the transformer temperature measurement based on optical fiber grating. According to the linear relationship between the Bragg grating center wavelength and temperature, the FBG-T-01 optical fiber sensors constitute a sensor array through the WDM principles. And the tunable release-pearl ROM cavity (F-P) filtering demodulation method is used for wavelength detection. On the basis, the polynomial fitting algorithm for peak is proposed. The software system could find anomaly problem of transformer winding problem timely. The measurement point temperature and the temperature rise rate both are the criterions to judging transformer winding temperature normal or not. The experimental results show that optical fiber grating temperature measuring system is accurate and stable. It can perform the transformer temperature measurement task favourably.

Abstract: Dynamic economic emission dispatch (DEED) is an important optimization task for power plants. The problem is a highly constrained multi-objective optimization problem involving conflicting objectives with both equality and inequality constraints. This paper introduces two objective functions of DEED model: the lowest generation cost and the smallest carbon emissions with power balance constraints, unit output constraints and unit ramp rate limits. Then the paper presents a multi-objective hybrid evolutionary algorithm (MHEA) to solve the DEED model. The MHEA is a hybrid optimization algorithm based on orthogonal initialization, improved differential operation with migration strategy, parameter adaptive control, multi-objective selection strategy and analytic hierarchy process based fuzzy technique (AFT). Numerical results of one test system demonstrate the capabilities of the proposed approach. Compared with other classical methods, the proposed approach gets better result.

Abstract: Parameters identification of excitation system plays a key role for the power system stability analysis. In this paper, a small population-based particle swarm optimization (SPPSO) approach is used to acquire excitation system on-line model quickly and accurately. In the proposed approaches, three operations are introduced to improve the performance of the algorithm, namely mutation operation, DE-acceleration operation and migration operation. Furthermore, the BPA-FV practical model and the PMU data are adopted. The simulation results of the model obtained by SPPSO have been compared with that of the model obtained by other approach in literature and our reformulations. The SPPSO algorithm shows better performance on the convergence as well as computation time and effort.

Abstract: With the characteristic of line loss volatility, a research of line loss rate prediction was imperatively carried out. Considering the optimization ability of heuristic algorithm and the regression ability of support vector machine, a heuristic algorithm-support vector machine model is constructed. Case study shows that, compared with other heuristic algorithms’, the search efficiency and speed of genetic algorithm are good, and the prediction model is with high accuracy.

Abstract: Several blackouts happened in a worldwide area, it exposures the vulnerability of continual increment of power system scale. The weak link has a strengthening effect on the spread of the accelerated failure, and leads to the occurrence of cascading failures, it's a serious threat to the security and stability of the grid. Based on the existing researches, the article proposes a new structure vulnerability evaluation model based on improved electrical betweenness, and verifies the rationality and effectiveness of this model by the analysis of the IEEE-39 node system.

Abstract: Based on the full analysis of prior benefit estimation methods of pumped storage power station, from the perspective of pumped storage power station participating in actual operation, itemized analysis on the main dynamic benefits of pumped storage power station and further study of quantitative calculation methods of all the benefits have been down in this paper. When calculating emergency reserve benefit, it introduces a new method of quantitative evaluation of dynamic benefits in a accident, whose core is calculating the curves of load rising in two situations, which are with and without pumped storage units’ participation. With this method, three specific indicators for the evaluation of emergency reserve benefit can be achieved, namely the lack of supply of power consumption, the lack of electricity and accident duration difference. The calculation of black start benefit should be taken into account some of the cost compensation as a black start power. These studies can necessarily promote the healthy development of the pumped storage power station.