Applied Mechanics and Materials Vol. 740

Abstract: Voltage sag is the major power quality problem and receives wide attention. Although wavelet analysis works well for detecting voltage sag features, the existence of noise can reduce the advantages of wavelet method or even make it ineffective. To solve the problem, the paper uses multi-scale wavelet information by multiplying the results of several scales, and then searches the local maxima from the product to find the transition moment of voltage sag. The proposed method can suppress the noise and improve the accuracy for detecting voltage sag features. Simulation result validates the effectiveness of the proposed method.

Abstract: Proton Exchange Membrane Fuel Cell (PEMFC) is established for the numerical simulation computation by using the MATLAB/SIMULINK, By changing the different working conditions, The proton exchange membrane fuel cell output performance is analyzed .Data show that the hydrogen pressure, oxygen pressure, current density, temperature, has certain influence on voltage and power distribution of PEMFC, For PEMFC to normal and stable work, according to the above conditions should be obtained the optimal value, thus ensuring optimal output performance of PEMFC.

Abstract: SVPWM is widely used in power electronic transformation system for it has high voltage utilization ratio and small THD. The InfineonXMC4500 MCU is used as the control core in the lithium battery charge and discharge control system which has three-phase SVPWM rectifier/inverter circuit topology. The mathematical model of the system, the circuit structure, control strategy and software process are introduced in the paper, through the test the results verify the validity of the system.

Abstract: With the maturity of GPS technology and the decrease of GPS module cost, which is becoming more and more widely. This paper designed the SCT90C516 micro-computer as the control core of GPS positioning system, Consisted by GPS module, independent keys and LCD display, serial communication interface and on STC micro-computer modules. Aiming at tracking the objective in the outdoor environment. And it can be used in smart clothes, vehicle positioning and tracking to protect wild animals.

Abstract: This system uses the MSP430F6638 and FPGA as the core, includes full bridge rectifier circuit, power factor correction circuit, Boost/Buck circuit and sample circuit. According to the sampling voltage and current value, The FPGA adjusts PWM wave duty ratio of power factor correction chip UC3854, completing single phase AC/DC conversion circuit with a voltage outer closed-loop and current inner closed-loop and active power factor correction (APFC). Test shows that the output voltage can stable in a setting value, with amplitude range ±0.05V, and when load’s impedance changes, this circuit can keep a small voltage adjustment rate and load adjustment rate. We use electronic parameter measurement device to measure the efficiency of AC/DC converter in a specified condition (voltage input Us=24V, current output Io=2A, voltage output Uo=36V), result demonstrates it’s a relatively ideal value. At the same time, under the control of UC3854, the power factor of alternating current input is 0.9734.And when we set the range of power factor between 0.8~1.0, The circuit can automatically adjust the power factor to track the set value.

Abstract: The nearest level modulation (NLM) is commonly used in the multi-level multi-module converter (MMC), which need to convert the fractional part of the input sine wave to the digital signal (DPWM). However, the narrow pulse width of digital signal , the frequent change of the digital signal and the frequent instability of output are caused by the sensitive fractional portion of the input, which push Multilevel converter into the position where it has to operate in high frequency and be unstable. In order to solve the problem mentioned above, this paper provides a way called hysteresis comparison to meet the control requirements of precision, adopting the comparison between the fractional part and triangular carrier wave. The approach this study provides is called hysteresis comparison which not only can ensure the stability of the output of the digital signal but also can be able to obtain better digital pulse width by adjusting hysteresis threshold trigger. At the same time, it could ensure the stability and pulse width of the output by means of reducing the frequency of the digital output. The feasibility of this approach has been certified by the simulation of field-programmable gate array (FPGA). Apparently, the actual results show that this method can optimize the control of HVDC Flexible.

Abstract: The accuracy of model becomes increasingly demanding in the simulation system with the development of supercapacitor. The traditional methods of parameters identification in supercapacitor modeling are very complicated. This paper presents an easy and new method by the Simulink tool. The experimental data for the identification of the model parameters was obtained through the constant charge-discharge experiments. Then the variable capacitor of the supercapacitor equivalent circuit model was modeled in Simscape Language, so parameters directly got with Parameter estimation in Sumulink. Simulation results were presented and compared experimental data. And the result showed that the new method was not only speeded the identification of parameters, but also improved the modeling precision up to 98%.

Abstract: For multi_level multi_module in the flexible HVDC converter (MMC) module capacitor control algorithm is commonly based on nearest voltage level modulation (NLM), this algorithm requires the decimal part of the input sine wave for analog-to-digital conversion by digital signal (digital pulse modulation, referred to as DPWM),in the choice of hysteretic DPWM control signal is better, if the input triangle carrier wave frequency selection is not good, in each digital signal level will cause the output frequency of DPWM is not stable, some DPWM frequency is too high, and some DPWM has no output. In order to solve this problem, to meet the requirements of control precision, the carrier frequency change DPWM triangular wave, the output ideal control signal, the output control signal is analyzed, put forward how to carry out DPWM frequency selection. Through the simulation certified the feasibility of this method, the control method of downloading to the field programmable gate array (FPGA) chip, the results of the actual control operation show that this method can optimize the control of flexible HVDC.

Abstract: Coal mine roadway advanced detector, including the transmitting and receiving devices, is a kind of geophysical instrument used in coal mine roadway advanced detection based on the dynamic and directional electric field excitation method. The transmitting device emits dual frequency modulated square wave current into the excavation face and the receiving device receives potential difference of coal and rock medium generated by induced polarization, of which the frequency selection circuit is to filter the interference of the harmonics of the signal and other frequency components. The paper derived expressions of emission current. Considering the actual working conditions, the paper proposed the design requirements of the frequency selection circuit and the scheme of a controller to control multiple frequency selection filter circuits. The paper completed the design of the control circuit consisting of a microcontroller and analog switch MAX313 and the band-pass filter circuit consisting of universal active filter UAF42. According to the circuit simulation and the analysis of the data with software of multisim, it proves the design of circuit meets the requirements.

Abstract: The crop growth cabinet control system mainly consists of color touch screen interface operating system and control system. They communicate with each other through the RS485 module. The control system’s control core is ATmega128L single chip microcomputer, and operating system interface uses Cortex_M3 as the kernel of 32-bit processor STM32F103VC, and adopts μC/GUI to write human-machine interface which real-time monitors crop growth environmental parameters in the cabinet, and by setting various parameters to simulate the plant a variety of ecological environment.