Applied Mechanics and Materials Vol. 441

Abstract: An improved FTU-based matrix algorithm is presented for faults locating in complex distribution networks with multiple source multiple and faults. Firstly, the paper supposes the only power source and the positive direction according to the structural characteristics of the distribution system, and build the description matrix D which is based on the positive direction and the relevancy between different feeders. Based on the fault currents direction sent from the feeder terminal unit (FTU), we can set up the fault information vector F. Secondly, combined with the description matrix D, by searching the nonzero elements in the fault information vector F , we can establish the fault location vector L according to the fault locating criterion. Finally, by observing the elements in fault location vector L, we can find out the fault area location quickly. This algorithm can solve the problems of feeder terminal fault, circle net fault and multiple source multiple fault, all of which cannot be solved by other algorithm completely. And this method needs not matrix multiply or standardization. It's easy to build the description matrix D, which is very sparse and has good real-time and practicality. The criterion of this algorithm is proved to be effective by simulation in MATLAB environment.

Abstract: In this paper, we study a modified predictive direct power control scheme (P-DPC).This scheme which based on model predictive control (MPC) uses a discrete rectifier model to infer the predictive direct power control theme again, and selects the operating time of voltage vector and voltage vector to realize fixed switching frequency through setting the minimum power errors of each sampling period. This control scheme has a lower switching frequency compared to MP-DPC; and it is still simple and clear implemented in the stationary reference frame directly, meanwhile, it does not need PI controllers or voltage-oriented controllers compared to other developed control schemes. We make simulations using MATLAB. The result show the excellence of this novel predictive direct power control scheme through improving the switching frequency, current THD and active power and reactive power quality compared to MP-DPC and LUT-DPC.

Abstract: This article introduced the developmental status about networking of NC, discussed Internet-based project of network technique and topology structure, that used communicate controller to connect common NC machine tools to Internet and monitor long-distance；gave out the method to realize communicate controller that used MCU and RTL8019AS Ethernet controller chip.

Abstract: According to the existing layout design of gas valves in urban communities, we come up with a wireless monitoring system which is able to efficiently control gas valves in certain area when seismic events occur and introduce in detail the system terminal’s hardware and software design. This terminal has earth’s activity collection and valves mutual monitoring function in one, and realizes real-time collection of earth’s vibration. When it earthquakes, the wireless LAN can realize functions such as earthquakes sensing and safe disposal of valves. Through optimizing the wireless network, we can guarantee system overall safety and stable operation. This system’s low power consumption, strongly real-time, high flexibility indicate its broad application prospects.

Abstract: In order to improve the detection rate of intruders in coal mine disaster warning internet of things, and to solve the problem that the back propagate neural network (BPNN) is invalid when these initial weight and threshold values of BPNN are chosen impertinently, Genetic Algorithms (GA) s characteristic of getting whole optimization value was combined with BPNNs characteristic of getting local precision value with gradient method. After getting an approximation of whole optimization value of weight and threshold values of BPNN by GA, the approximation was used as first parameter of BPNN, to train (educate) the BPNN again (in other words, learning). The educated BPNN was used to recognize intruders in internet of things. Experiment results shown that this method was useful and applicable, and the detection right rate of intruders was above 95% for the KDD CUP 1999 data set.

Abstract: The paper introduces a high precision ultrasonic heat meter design based on time-difference method. It analyzes and researches the measure theory of time-difference ultrasonic heat meter, and presents a piecewise interpolation method to calculate the flow. With the low-power chip as the microcontroller, the system adopts high-precision time measurement chip TDC-GP21 for flow measurement as well as the temperature measurement. Compared with traditional heat meter, it is of low power consumption and high measurement precision, and the tests show that the results meet the heat meter industry standard second order accuracy.

Abstract: The measuring system of the tester is consisted of the downhole measuring tester and ground replaying system, structure and parameters of the tester has been designed, of the testing circuit

Abstract: A small level measurement system is designed by installing a compact capacitive level sensor in the small container. By analyzing the capacitive sensor structure, a sensor measurement circuit is designed with high sensitivity, measuring stability and good repeatability. Capacitance measurement circuit makes use of multiple harmonic oscillation principle. The microcomputer measures the oscillation frequency of the multivibrator, and calculates the liquid level height based on the monotonic function about the liquid level height and frequency.

Abstract: Ultrasonic ranging (UR) technology has being used widely in many industries around the world. This paper aims to design and manufacture an ultrasonic distance measuring system with lower price and higher accuracy. Based on the deep study of principle of ultrasonic ranging, we designed the general plan and detailed electrical circuits for the ultrasonic distance measuring system based on single chip microprocessor of AT89S52, including the transmitter module of ultrasonic wave, receiving module of ultrasonic wave, display module etc. Then, we compiled the relative driven programs for all modules. After that, we debugged the combined system of hardware and software system. At last, the experimental results show that the cost is about 300RMB for 3 prototypes, measuring rang is 0.16~1.5m with the accuracy of 0.001mm, which means the ranging system meets the design requirements of lower price and higher accuracy.

Abstract: Single probe and dual probes are always taken adopt to measure the material's thermal conductivity and thermal diffusivity. The measurement principle of the two kinds of probes is different and introduced in this article. Taken the material which has low thermal diffusivity for example, the single probe and dual probes are compared by the calculation accuracy and temperature response sensitivity. Numerical simulation results show that, under the same conditions, the thermal properties obtained by the dual probes are closer to the true value for the test material, but single probe has more sensitive at temperature response.