Applied Mechanics and Materials Vols. 380-384

Abstract: t is a powerful guarantee for the safe and stable operation of the grid to detect and study its characteristics such as the active power, the reactive power, the flicker and the harmonic. Dewetron5000 system and its software can be used to collect and analyze the experimental data of power system without getting the corresponding conclusion quickly, directly and clearly. In view of the above questions, the software has been developed to test the power quality for wind farm into the grid, the collected data after being processed by the secondary can display the situations of power quality and power regulation clearly and fast. The software has a very important role on the development of the test standard and system for wind power grid.

Abstract: Owing to the fluctuating and the randomness of wind speed, the influences of large-scale wind power integration on the grid should not be ignored. The output fluctuation of wind farm has serious effect on power quality, causing the problems like voltage flicker and harmonic, it will pose a threat on the safe and stable operation of power grid. This paper mainly analyzed the influence mechanism of wind power integration on power quality and studied the detection method of power quality. The effectiveness of the proposed method was verified by the simulation of real operation data of a wind farm in Jilin Province. The method presented in this paper will provide a reference for the establishment of Chinas wind power testing system and has important engineering significance.

Abstract: To improve the stability and output voltage quality of inverter, an new repetitive control strategy for 400Hz Constant Voltage Constant Frequency (CVCF) inverter has been proposed . Based on active damping, this strategy damps the oscillations on the output LC filter of inverter under unload or light load. Using state-observer to weaken the impact of time delay in digital control, a 5.5 kW one-phase 400Hz inverter prototype by this strategy has been tested.The result shows that low THD (about 1.5%) with inductive loads and fast error convergence (2 fundamental periods) can be achieved by this strategy which can be demonstrated to be brief and effective.

Abstract: The leading phase operation of generator is an effective method to reduce voltage of the key point which is much high in valley load period. This paper reviews the history on leading phase of generator and introduces the current situation on stable monitoring of the generators leading phase capacity. Meanwhile, this paper proposes main restricted conditions of generator leading phase and analyzed in details. At last some experiments are performed for part generating sets with a capacity of 100MW above in one province and obtained the experiment results on voltage regulation through leading phase of synchronous generating sets.

Abstract: The principle of restraining the harmonic using the series reactors was introduced and the relationships between circuit condition and the harmonic current were analyzed in this paper.The considered problems in selecting the reactance rate were discussed. On the base of power quality test results at a certain region in China, a selection method of reactance rate of series reactors, rated voltage and capacity of a capacitor were put forward to realize the compensation for reactive power.

Abstract: The AC system strength at DC receiving-end exerts great influences on the voltage stability of power grid. The selected DC control modes and reactive power compensation mode should fit with the AC system strength at receiving end. This paper analyzes the influences of AC system strength at DC receiving-end on voltage stability of power grid from the point of mechanism, and conducts simulations based on Shandong power grid.

Abstract: In order to ensure the dynamic balance of power load and improve the accuracy of short-term load forecasting, this paper presents a method of short-term load forecasting for electric power based on DB wavelet and regression BP neural networks. In this method, we get the wavelet coefficients at different scales through series decomposing of wavelet decomposition to load sample, and each scale wavelet coefficients for threshold selection, and then trained adjusted wavelet coefficients by regression BP neural networks, reconstructed load sequence predicted date through inverse wavelet transform. Finally, the accuracy of this method is significantly higher than BP neural network by examples verification.

Abstract: According to the sensor failure possibly existing in engineering systems, the LMI approach is applied to design the passive fault-tolerant controller for a class of uncertain systems with state and control time-delay. The stable criterion of the sensor fault-tolerant system is given in LMIs to guarantee the closed-loop system to have robust stabilization and robust fault-tolerant capability basing on Lyapunov stability theory. A multi-state fault model is built to simulate the different fault types for sensor or other component fault. A numerical example of a heat treatment furnace is given to verify the effectiveness of the approach.

Abstract: This paper presents the thoughts about application of composite grid method to solve for current distribution of the dipole.It discusses the basic principle of the method and calculation steps, compares the calculated results with the normal method (FEM) of single set of grid computing , and summarizes the application process and development direction in the future.

Abstract: Based on the principle of electronic transformers, a new type of the power supply is designed, and the factors affecting the switching frequency are given. The feedback mechanism of the new power supply is analyzed in detail. Whats more, the pulse width modulation which controls switch tube adopts the RS flip-flop PWM. Finally based on the TL431, a 50W regulated power supply is design, which has a simple structure, small size, and low cost.