Applied Mechanics and Materials Vols. 380-384

Abstract: By measuring the current-voltage (I-V) characteristics in the temperature range of 100 K to 300 K, mechanisms of the forward tunneling current and the reverse leakage current of GaN-based blue light emitting diodes are analyzed. For the forward current, both the temperature-independent current slope and an ideality factor larger than 2 are typical features of the defect-assisted tunneling mechanism. For the reverse leakage current, the linear relationship between I and (V+V_bi)^1/2 indicates a hopping conduction mechanism at low bias, while the power law I-V relationship suggests that the space charge limited current dominates the reverse leakage current at high bias.

Abstract: The frequency response analysis (FRA) is a effective diagnostic method in monitoring the deformation of transformer winding. This paper uses the current sweep-sequency source as the excitation to replace the voltage source in the traditional method.And the frequency response curves can be drawn from the current signal rather than the voltage signal.It can be judged whether there is deformation in the transform winding by comparing the frequency response curves.The method can realize the on-line monitoring and diagnosis for the transformers whose neutral points is grounded directly. The Research Background The safety of transform is the necessary condition for power system operation. As the increasing of power system capacity,the short-circuit current will be bigger than before.Therefore, transformer will take more risk of winding deformation.

Abstract: As demand for data rate continues to increase, new problem of LVDS start to come out, such as signal integrity. Those problems are primarily caused by frequency-dependent loss in transmission line. The purpose of pre-emphasis is to apply intentional overdriving to the signal and get it back to the original signal with the proper weight, thereby compensating for the ISI from the nearby data symbol. In order to avoid over-emphasis we propose a programmable pre-emphasis adapting to different situation, and finish the prototype which can improve the transmission bandwidth more effectively, achieving high-speed data transmission.

Abstract: When the Distributed Generation (DG) access to the distribution network, it will have great impact on the distribution network. In order to reduce the impact, through the research of distribution network accessed with DG, I summarize a set of feasible operation scheme, which can improve the security and economy of distribution network. In this paper, IEEE33 notes distribution network is used as an example. I build the model of distribution network with SIMULINK. By changing the capacity and location, I study the impacts on voltage of distribution network. On the basis of a large number of simulation examples and experimental data, I summarize several principles we should comply with.

Abstract: In this paper, starting from the active network loss formulas and wind characteristics, it is pointed out the reactive power loss and reactive flow is the major impact of wind power integration on power system loss. The reactive power loss formulas of box-type transformer, main step-up transformer, wind farm collector line and connecting grid line are analyzed. Next the reactive power loss of transformer and transmission line is described in detail. Then put forward the loss reduction measures that installing SVC on the low voltage side of the main step-up transformer and making the doubly-fed wind generators send out some reactive power at an allowed power factor. Use the case of Gansu Qiaodong wind farm to verify the effectiveness of the proposed measures.

Abstract: Base on the existing disadvantages of the conventional three-stage charging method, the paper provided a intelligent and dynamic Charging ideal with a fuzzy control ideal based on J. A. Mas 's law and the characteristics of lead-acid battery charging. A fuzzy controller design achieved according to the empirical data of charging control and the systems hardware and software realized with PIC6014 microcontroller as the core. Experiments show: The intelligent and dynamic charging systems based on fuzzy control enable the charging current to achieve real-time changes according to the acceptable current size of the battery, enhanced the energy efficiency and avoid over-charge and less-charge effectively, realized efficient, fast and safe charging.

Abstract: The technology of large-scale wind power connected to grid is a key technology in the application of wind power. However, the large-scale wind power will cause the negative effect on the voltage of grid. So, the regulation of reactive power is necessary, which can stabilize the voltage level of the grid. The doubly-fed induction generators (DFIG) themselves own the ability of providing reactive power. Considering the reactive power demand when the power grid is operating, and then rationally allocating static and dynamic reactive power compensation equipment, the operational efficiency can be improved. The particle analyzes the reactive power limit of DFIG, considering the limit of stator and rotor. In this way, the reactive power compensation capacity of DFIG is used first, the use of reactive power compensation equipments are greatly reduced, so the economy of the wind farm is obviously improved.

Abstract: DC-bus voltage is affected by fluctuations of load and grid impact, threating the safe operation of the system. According to the instantaneous active power balance, a power feedforward control strategy was proposed to reduce the DC voltage fluctuations. In this strategy, the load active power was directly fed-forward to the grid-side given instantaneous active power node through a constructed load state feedforward channel, which avoided the slower process of indirect power adjustment through outer voltage loop. So, the system response speed was greatly accelerated, the DC-bus voltage fluctuation was inhibited effectively, and the dynamic performance of the system had improved. Test results demonstrate the effectiveness of the proposed strategy.

Abstract: Traditional current strategy based on dq transformation used in three-phase PWM voltage source rectifier (VSR) has some shortcomings, such as dynamic response slow and DC voltage fluctuation. According to the problems, firstly this paper established discrete mathematical model of VSR, derived predictive current control strategies for VSR. Secondly, design a dual-closed-loop controller with current inner loop and voltage outer loop for the system. Finally, experimental researches are done. The results show that the three-phase PWM voltage source rectifier based on predictive current control in stabilizing DC voltage, control the AC current, etc, it has good steady-state and dynamic performance. The control method is simple, easy to implement, and has a certain practical value.

Abstract: An Amorphous IGZO (a-IGZO) TFTs pixel driving circuit and row driving circuit for AMOLED are proposed. The pixel driving circuit is composed of four a-IGZO TFTs and one capacitor (4T-1C), which effectively compensates the threshold-voltage-shift (ΔV_th1V) of the drive TFT, and shift registers, NAND gates and inverters constitute the row driving circuit. To verify the effect of the proposed circuit, simulation using H-spice was performed, and results prove that the presented circuit can be applied to monochromatic 2-inches QVGA AMOLED.