级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会...级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会因馈入点电气距离较近而存在强相互作用关系。为明确级联型混合直流馈入系统中MMC-HVDC对LCC-HVDC系统强度的影响,提出考虑幅值和相位的MMC等效电流源的简化等效方法,基于所提MMC等效原理将级联型混合直流馈入系统等效成单馈入LCC-HVDC系统,分析等效单馈入系统的参数计算方法,并提出等效单馈入短路比评估指标。最后通过该指标分析归纳了不同控制方式、不同电气距离下等效单馈入系统的系统强度变化情况,即为MMC-HVDC对LCC-HVDC系统强度的影响规律。机理分析和基于PSCDAD/EMTDC、MATLAB的仿真结果表明,所提等效方法具有有效性且所提指标能很好地反应MMC-HVDC对LCC-HVDC系统强度的影响。展开更多
Automatic profiling control using a boom-type roadheader requires an understanding of horizontal and vertical swing angles of the cutting boom. In this study the vertical angle of the cutting boom is discussed. First,...Automatic profiling control using a boom-type roadheader requires an understanding of horizontal and vertical swing angles of the cutting boom. In this study the vertical angle of the cutting boom is discussed. First, a vertical swing detection model for the cutting boom is established. Then, a kinematic analysis of the vertical swing mechanism is made and formulae describing the geometrical relationship between the vertical swing of the cutting boom and the telescopic length of vertical hydraulic lift cylinders and vertical swing angle of the boom are presented. Various factors such as complexity of the calculation model, the difficulty of installing the sensor and the cost are compared for two methods. Finally, directly measuring the vertical swing angle of the cutting boom with a tilt sensor is decided to be the more simple and effective method. The detection sensitivity and the vertical cutting error of a tilt sensor are studied. Vibration tests on an EBZ160 roadheader were performed in a coal mine. The characteristic vibration frequencies are analyzed. A design of a vibration isolation mount for the tilt sensor is presented. It makes the detection device work more reliably under conditions where vibration is present and lays a foundation for the implementation of an automatic roadhead cutter. A tilt sensor is installed on an EBZ160 and an EBZ200, and experiments have been done in a coal mine. The re- suits show that the experimental result is favorable and achieves the goal of automatic control of the vertical swing of the cutting boom.展开更多
This study introduces the site selection and data processing of GNSS receiver calibration networks. According to the design requirements and relevant specifications, the authors investigate the observation conditions ...This study introduces the site selection and data processing of GNSS receiver calibration networks. According to the design requirements and relevant specifications, the authors investigate the observation conditions of the potential sites and collect the experimental GNSS observation data. TEQC is used to evaluate the data availability rate and multipath effects of the observation data to determine the appropriate site. After the construction and measurement of the calibration network, the baseline processing of the medium and long baseline network is conducted by GAMIT. The accuracy indexes including NRMS, difference between repeated baselines, and closure of independent observation loops all meet the specified criteria.展开更多
In this paper, we propose a pre-processing method for the detection of wire-rope signals. This is necessary because of the lack of processing methods that are currently employed. First, we investigated the one-dimensi...In this paper, we propose a pre-processing method for the detection of wire-rope signals. This is necessary because of the lack of processing methods that are currently employed. First, we investigated the one-dimensional discrete morphological and wavelet transform. Then, we developed a pre-processing model that is based on the morphological wavelet-filtering algorithm. We then proposed a modified morphology filtering algorithm. We also designed an experiment platform for wire-rope detection.Eight levels of localized flaws(LFs) and damage were formed in the wire-rope specimen. We performed a series of experimental studies, and the results show that the proposed method can effectively filter the drift signal. The signal-to-noise ratio of the new filtering algorithm was over 26 d B. The signal-to-noise ratio of the existing method is less than 15 d B, and the noise-signal ratio of the new filtering algorithm has improved by 73%. Based on our results, the filtering effect of the proposed method is better than that of the present method. This study has great significance and practical value in engineering applications.展开更多
文摘级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会因馈入点电气距离较近而存在强相互作用关系。为明确级联型混合直流馈入系统中MMC-HVDC对LCC-HVDC系统强度的影响,提出考虑幅值和相位的MMC等效电流源的简化等效方法,基于所提MMC等效原理将级联型混合直流馈入系统等效成单馈入LCC-HVDC系统,分析等效单馈入系统的参数计算方法,并提出等效单馈入短路比评估指标。最后通过该指标分析归纳了不同控制方式、不同电气距离下等效单馈入系统的系统强度变化情况,即为MMC-HVDC对LCC-HVDC系统强度的影响规律。机理分析和基于PSCDAD/EMTDC、MATLAB的仿真结果表明,所提等效方法具有有效性且所提指标能很好地反应MMC-HVDC对LCC-HVDC系统强度的影响。
基金support from China University of Mining and Technology (Beijing)Financial supports for this work provided by the National Hi-tech Research and Development Program of China (No.2008AA062201)
文摘Automatic profiling control using a boom-type roadheader requires an understanding of horizontal and vertical swing angles of the cutting boom. In this study the vertical angle of the cutting boom is discussed. First, a vertical swing detection model for the cutting boom is established. Then, a kinematic analysis of the vertical swing mechanism is made and formulae describing the geometrical relationship between the vertical swing of the cutting boom and the telescopic length of vertical hydraulic lift cylinders and vertical swing angle of the boom are presented. Various factors such as complexity of the calculation model, the difficulty of installing the sensor and the cost are compared for two methods. Finally, directly measuring the vertical swing angle of the cutting boom with a tilt sensor is decided to be the more simple and effective method. The detection sensitivity and the vertical cutting error of a tilt sensor are studied. Vibration tests on an EBZ160 roadheader were performed in a coal mine. The characteristic vibration frequencies are analyzed. A design of a vibration isolation mount for the tilt sensor is presented. It makes the detection device work more reliably under conditions where vibration is present and lays a foundation for the implementation of an automatic roadhead cutter. A tilt sensor is installed on an EBZ160 and an EBZ200, and experiments have been done in a coal mine. The re- suits show that the experimental result is favorable and achieves the goal of automatic control of the vertical swing of the cutting boom.
基金Supported by Project of National Natural Science Foundation of China(No.41772346)
文摘This study introduces the site selection and data processing of GNSS receiver calibration networks. According to the design requirements and relevant specifications, the authors investigate the observation conditions of the potential sites and collect the experimental GNSS observation data. TEQC is used to evaluate the data availability rate and multipath effects of the observation data to determine the appropriate site. After the construction and measurement of the calibration network, the baseline processing of the medium and long baseline network is conducted by GAMIT. The accuracy indexes including NRMS, difference between repeated baselines, and closure of independent observation loops all meet the specified criteria.
基金the National Natural Science Foundation of China (No. 51404276)the Fundamental Research Funds for the Central Universities (Nos. 2014QJ01 and 2015QJ04)
文摘In this paper, we propose a pre-processing method for the detection of wire-rope signals. This is necessary because of the lack of processing methods that are currently employed. First, we investigated the one-dimensional discrete morphological and wavelet transform. Then, we developed a pre-processing model that is based on the morphological wavelet-filtering algorithm. We then proposed a modified morphology filtering algorithm. We also designed an experiment platform for wire-rope detection.Eight levels of localized flaws(LFs) and damage were formed in the wire-rope specimen. We performed a series of experimental studies, and the results show that the proposed method can effectively filter the drift signal. The signal-to-noise ratio of the new filtering algorithm was over 26 d B. The signal-to-noise ratio of the existing method is less than 15 d B, and the noise-signal ratio of the new filtering algorithm has improved by 73%. Based on our results, the filtering effect of the proposed method is better than that of the present method. This study has great significance and practical value in engineering applications.
