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Medium voltage three-level wind power converter is a good choice for the next generation 10-MW wind turbine. However, since switching frequency of medium voltage semiconductor device is strictly limited, harmonic current is hard to depress, especially for LCL type wind power converter. This paper presents an effective way to eliminate resonance current under low switching frequency. Active damping strategy, instead of passive damping, is adopted here. Detailed system model is built, which shows the converter harmonic terminal voltage, generated by the PWM section, introduces considerable the resonance harmonic current. To guarantee system stability, a negative proportion gain is used in the active damping feedback loop. According to the system model, a low pass filter is also adopted in the converter current feed-back loop, where harmonic current depression performance is greatly improved. Experimental results validate the theoretical analysis.

LCL filter is widely used in grid connected converters for good harmonic mitigation performance. However, resonance poles of LCL filter challenge the system stability, especially in digital controlled system. Various active damping approaches have been proposed to solve the resonance issue, where the capacitor current based active damping control is an attractive option. In this paper, system stability with capacitor current based active damping control is analyzed with the consideration of digital control delay. A design principle for the active damping compensator is proposed in this paper, where maximum stability margin can be reached for active damping loop. It is shown that capacitor current feedback control with negative proportion gain, instead of positive gain, presents much better performance with considerable control delay. Simulative and experimental results validate the proposed control method.

In the field of the fabrication of micro- and nano-spheres, the phenomenon of Plateau-Rayleigh instability has drawn more and more attention. This surface tension-driven instability in two immiscible fluids can be used to generate uniformly size micro- and nano-spheres by imposing an external mechanical excitation. In this article, we mainly adopt numerical simulation method to study the effects of wavelength, viscosity and surface tension on Plateau-Rayleigh instability. In addition, a micro-spheres generation system based on controlling the breakup process of the co-flowing jet is studied. The numerical results show that the current method can efficiently control the size of the micro-spheres from a variety of fluids. Also, the effects of amplitude and frequency of the excitation during the fabrication process on the size of micro-spheres are investigated.

Panoramic stereo spherical vision system can simultaneously realize panoramic stitching and three-dimensional ranging. Its multi-channel image acquisition system is located in 3D space through the mechanical encapsulation. In this paper, an effective calibration method is explored to solve the problem of slight errors generated by the encapsulation structure installation and manufacturing. More importantly, the errors are difficult to measure, which leads the optical axes of lenses are not parallel. This paper uses a fine-tuning method of focused laser spot detection to solve the problem by analyzing the encapsulation structure and imaging model of the system. And its image processing algorithms and calibration process are described. The final experimental results confirm it is indeed feasible to this method.

This paper reports a new method for controlling micro- and nano-droplets by the aid of heat. Computational fluid dynamics (CFD) simulation results suggest this technique is capable of conveniently controlling the droplets sizes down to several micrometers or even nanometers. This pilot research offers the possibility of fabricating micro-droplet with specific size and without changing the fluid. Three factors are studied, including the temperature of continuous phase, the temperature of discrete phase and the temperature gradient on the orifice. The results show that heat transfer between the two phases is fast as characteristic length is in micron level. Increase in temperature can lead to the increase of the droplet radius, wherein the effect of the continuous phase temperature is the most significant.

AgI nanoparticle has been reported to exhibit size-dependent properties. In the paper, we reported the use of combinations of surfactants, such as AOT, SDS, PVP and TWEEN20, to control the AgI synthesis. AgI nanoparticles can be obtained with different sizes. Measured and confirmed by DLS and TEM, the nanoparticles can be massively and evenly prepared with the sizes less than 20nm. The post-processing of extraction for the nanoparticles is relatively simple and environmentally friendly. Further experimental results demonstrate that the stability of the nanoparticles is greatly dependent on the formula of the surfactant compositions. The method presented here is a potential high-throughput technique that could be applied to synthesize many other nanoparticles.

This paper reports a microfluidic reactor for synthesizing micro- and nano-droplets using fluid shearing instability of immiscible flow in microchannels. Three factors, flow rate between the two inputs, spout geometry and surface tension are numerically studied. Based on the simulation, a device with the optimal parameters was fabricated and tested. Both computational fluid dynamics (CFD) simulation results and experimental results suggested that this technique is capable of conveniently controlling the droplets sizes from hundreds of micrometers down to several micrometers or even nanometers. This pilot research offers a proof-of-concept demonstration using instabilities in the microchannels to synthesize large quantity of microdroplets. Although the microdroplets in this study were formed by DI water containing Tween20 and silicon oil, the design with modification could be applied for synthesis of other types of micro- and nano-droplets.

Equipment Battlefield damage repair (BDR) sequence is an important content in the equipment maintenance support decision-making in wartime. If not handled correctly, time, man-hours, parts, and resources will be wasted and opportunities to get back in the fight will be missed. The influence factors of equipment BDR sequence were analyzed considering the requirements of equipment maintenance support decision-making. The model of equipment battlefield damage repair sequence was established based on the theory and method of multiple attribute decision-making (MADM). The results of a case study showed that the method is feasible and effective.