Brushless doubly-fed machine (BDFM) has advantages of brushless reliability and low frequency conversion capacity. It has a broad application prospect in AC speed regulation and direct drive wind power generation system. In this paper, winding arrangement and slot electromotive force star diagram of stator with different pole numbers are analyzed and studied comprehensively. When the number of slots per pole and phase is different, we get the winding wire insertion rule. These rules are of great significance for further design and application of multipole BDFM.

Virtual material model is an effective equivalent modelling technique to simplify and characterize the stiffness weakening effect of mechanical joints. In order to further improve the accuracy of virtual material model, the density and thickness parameters of virtual material model were optimized and modified by response surface method. The advantage of this method is that under the condition of maintaining the original surface characteristics of the joint, the micro-characteristics of the joint under certain pre-tightening conditions can be quantitatively characterized macroscopically, which makes the analysis results more close to the actual situation. The natural frequencies of the virtual material model before and after modification are compared with the experimental natural frequencies, and the validity of the method and the modified model are verified.

The stimulation wastewater is a kind of re-discharge wastewater produced by various operational measures according to the production needs, it has high viscosity and is difficult to treat. Based on the analysis of the viscosity characteristics of stimulation wastewater, the viscosity reduction experiments were carried out to evaluate the viscosity reduction effects of two measures. The experimental results show that the natural static viscosity reduction is easy and does not need to consume treatment agent. In the rapid viscosity reduction method, the organic structure can be destroyed by adjusting the pH value or adding oxidizing substances to meet the requirements of viscosity reduction. Among them, ozone has the advantages of fast viscosity reduction, good effect, appropriate amount of hydrogen peroxide, which can strengthen the viscosity reduction in wastewater and shorten the time of natural viscosity reduction. In summary, if enough time is available, static viscosity reduction is the appropriate method; if conditions are not available, natural static viscosity reduction and oxidative viscosity reduction are combined. Hydrogen peroxide is the preferred fast viscosity reducer, which can ensure the effect of viscosity reduction.

Lignin is a complex phenylpropanoid biopolymer conferring mechanical strength to plant cell walls. Biorefineries, along with pulp and paper industry, generate large quantities of lignin. Lignin valorization is an essential process for an advanced, sustainable, and economical biomass-based industry. In this study, for the first time nanostructured Fe 0 @Fe 3 O 4 was loaded on active carbon fiber (ACF) as an oxygen diffusion cathode to be used in a heterogeneous electro-Fenton (E-Fenton) oxidation system. This novel Fe 0 @Fe 3 O 4 /ACF composite cathode was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analysis, transmission electron microscopy (TEM). On the degradation of lignin in water, this heterogeneous E-Fenton system with the Fe 0 @Fe 3 O 4 /ACF cathode showed much higher activity than other E-Fenton systems with commercial zero valent iron powders (Fe 0 ) and Iron ions (Fe 3+ ) under same condition. On the basis of experimental results, we proposed a possible pathway of lignin degradation in this heterogeneous Fe 0 @Fe 3 O 4 /ACF E-Fenton process. This heterogeneous E-Fenton system is very promising to remove organic pollutants in water.

Brushless doubly fed machine (BDFM) is a new type of AC motor, which has the advantages of brushless reliability and low cost. The inductance parameters of this kind of motor are relatively complex, and the inductance parameters are the basis for motor performance analysis and high precision control. In this paper, the inductance parameters of the motor are calculated by finite element analysis method, along with the experimental prototype is developed to measure the inductance parameters. The correctness of the theoretical analysis is proved, which provides useful reference for the high precision control of BDFM.

Based on the lightning location data during 2009-2013 from China Meteorological Administration National-Lightning-Detection-Network (CMA LDN), this study analysed the temporal-spatial characteristics of the lightning in mainland China, and the results show: 1) Lightning detection systems used the Improved Performance through Combined Technology (IMPACT) method, which combined the direction finding (DF) and the time difference of arrival (TOA) technology. Among the four localization algorithms, the four-station method had the highest positioning accuracy, and its usage frequency also increased continuously, accounted for 50 %, up to 6000-10000 times by 2013. 2) Lightning activities showed clearly seasonal variation, and it had an increasing trend with a little inter-annual variation during the period of 2009 to 2013, which was mainly affected or restricted by ground temperature (rising from May every year, reaching its peak in August, and then gradually decreasing), potential water and convection in the atmosphere. 3) The negative cloud-to-ground (-CG) flashes were the absolute majority in China, positive cloud-to-ground (+CG) flashes accounted for 5.1 % of the total. Most of lightning currents ranged from -60 to +60kA. 4) The average lightning intensity of +CG and -CG flashes were 64.2kA and -40.28kA respectively. The positive lightning ratio is prominently high in December and January, most of which distributed in southern Anhui province, northern Jiangxi province, North Central Guangxi province, Yunnan province and West of Xinjiang Uygur Autonomous Region.