Applied Mechanics and Materials Vol. 441

Abstract: Analyze the characteristic quantity difference between the transformer sympathetic inrush current and the internal fault current inside it depending on the Hilbert-huang transform and extract the new type Hilbert-huang criterion for the recognition of the sympathetic inrush current according to the transformed wave form features. Set up the transformer simulating models through PACAD for the sympathetic inrush current and internal fault current to extract their IMF component; identify the sympathetic inrush current and the internal fault current based on HHT criterion; verify whether HHT criterion can identify the sympathetic inrush current wave form and the transformer internal fault current correctly. The criterion has targeted feature with self-adaption ability.

Abstract: This article put forward with "DG optimization of the distribution network benefit " to measure the operating economy of distribution network containing DG and build an economic analysis model. Based on flow calculation, this model analysis the economic of distributed network with DG fully consider the various factors that have an impact on the economic of distribution network, such as line losses, transformer losses, electricity price and DG itself variable costs .Through the flow calculation and analysis, the feasibility of the model is validated.

Abstract: According to the problems emerged in the coalmine power system, such as poor reliability and lagging protection technology principles, this paper proposed some advices about the construction of the intelligent coalmine power system. Using SCADA system and GIS to locate the fault and recovery it; using Differential protection and intelligent monitoring terminal to guarantee the reliability of the coalmine power system; using Panoramic Data Platform to monitor the coalmine power system; using a series of auxiliary equipment to realize the automatic regulation and control of the coalmine power system.

Abstract: As microgrid is a significant part in the development of smart grid, researches focusing on operation efficiency, intelligent control and smooth transition with the main distribution network are very important in advancing micro-grid technology. This paper studies multi-microgrid control strategy based on IP and MAS and divided microgrid to three levels which are important, less important and unimportant. Then simulation experiments are designed to realize seamless transition between connected mode and island mode, intelligent management of microgrid by priority when the output power of main grid decrease.

Abstract: With conventional droop control, parallel operation of distributed generations (DG) in microgrid would lead to unbalanced power sharing. In this paper, inherent limitation of conventional droop control is analyzed. Analysis results show that different converter output impedance and line impedance make the power sharing unbalanced. In order to weaken or eliminate impedance difference from point of common coupling (PCC) to DGs, virtual impedance is introduced. By the introduction of designed virtual impedance, a novel droop control strategy with impedance compensation is proposed in this paper. Simulation results are presented from a two converters parallel-connected microgrid, showing the effectiveness of the droop control with impedance compensation. Simulation results show that DGs with proposed approach can allocate the power equally, and work stably in grid-connected mode, island mode and progress of reconnection to grid.

Abstract: Based on analysis of the equivalent circuit mathematics model of helical Exploding Magnetic Generator of Frequency (EMGF), this paper discussed the influence in time and frequency domain on the load current by inductance variation which include number of turns, and expansion velocity.

Abstract: A permanent magnet bias axial magnetic bearing (PAMB) is introduced, the configuration and operation principle are analyzed; The equivalent magnetic circuit is established, the math expression of axial suspension force and some equations for carrying capacity, current stiffness and displacement stiffness are deduced; The parameters of the proposed prototype are also given. The magnetic field simulation is performed by using the Finite Element software. The theory analysis and the simulation results show that the presented PAMB has smaller volume, the control is easier; the parameters design is feasible and exact.

Abstract: With the rapid growth in the size of Henan grid, in the context of UHV networking, Henan power grid operation is facing a more complex mechanism and operating characteristics. Risks affecting the security and stability will be more subtle. There are more and more problems in frequency oscillation. The power system has much more generators and dimension after interconnection. Small signal stability analyzing eigenvalue complex and longer, which greatly reduces the work efficiency. This paper which based on Henan power system stability diagnostic platform developed technology based on multi-band parallel algorithm for small signal stability analysis. The analysis of the small signal stability eigenvalue calculation is assigned to a different platform computing nodes simultaneously. Then this method is applied to Henan grid in the year of 2012. The results show that the small signal stability algorithm which based on the multi-band can ensure the correctness of calculations. Simultaneously, calculation time is greatly reduced and the work efficiency is improved. The practice has a strong role in the promotion.

Abstract: With the higher penetrations of wind and photovoltaic power in system, the randomness of its outputs adds amounts of uncertainty to system generation planning and scheduling. This paper formulates a day-ahead power economic dispatch model based on the uncertainty information of wind and photovoltaic power prediction obtained by prediction interval of power with a certain probability. The costs of spinning reserve and interruptible load regarded as spinning reserve are also taken into consideration. The proposed model is solved by Cplex. Finally, the simulation example of system composed of 10-units proves the validity of the model.

Abstract: Photovoltaic (PV) power systems are widely used today, so its useful to study how to make the PV maximum power output. In this paper a novel approach based on Support Vector Machine (SVM) for maximum power point tracking (MPPT) of PV systems is presented. The output power characteristics of PV cells vary with solar irradiation and temperature, so the controllers inputs is the level of solar radiation and ambient temperature of the PV module, and the voltage at maximum power point (MPP) is the output. Results show that the proposed MPPT controller based on SVM is sensitive to environmental changes and has high efficiency and less Mean Square Error (MSE).