Broadband PLC （power line communication） technology is a main factor of the development of digital convergence in the indoor network. It uses the already existing power cable infrastructure for communication purpose...Broadband PLC （power line communication） technology is a main factor of the development of digital convergence in the indoor network. It uses the already existing power cable infrastructure for communication purposes. The EM （electromagnetic） field radiating from the cable could, however, disturb other communication systems, and thus should be evaluated. The MoM （method of moment） and the FEM （finite element method） have been studied to estimate the EVI field emitted from the power cable. However, the M oM is difficult to treat the dielectric material of the cable and the FEM is time consuming. This paperpresents a new approach to estimate the radiated EM fields caused by PLC sy stems from the CM current along the cable, based on the transmission line theory. The proposed model has the advantage of using the measured primary parameters of the cable. An experimental analysis of the EM radiation distribution is also presented. A comparison showed that the model results agree quite well with the measurements performed in this study.展开更多
Electric power systems usually cover large geographical areas and transmission facilities are continuously increasing. These power systems are exposed to different environmental conditions which may cause faults to oc...Electric power systems usually cover large geographical areas and transmission facilities are continuously increasing. These power systems are exposed to different environmental conditions which may cause faults to occur on the system. Different types of studies are usually done on electric power systems to determine how the system behaves before, during and after a fault condition. The behaviour of variables of interest such as currents, voltage, rotor angle and active and reactive power under fault conditions are studied and observed to help determine possible causes of faults in a power system. The objective of this paper is to investigate a fault that occurred on the 330 kV transmission line between Ruacana power station and Omburu sub-station, the fault caused all the generators at Ruacana power station to trip and consequently caused a blackout at the power station that lasted for 6 h. Preliminary findings showed that the observed fault was an earth fault but the exact type of earth fault was however not known at the time. This research investigation sets out to determine the exact fault that occurred; the most probable cause of the fault, and propose possible solutions to prevent reoccurrence of such a fault. The section of the power network in which the fault occurred was modelled using DigSilent Power Factory software tool, and transient fault analysis was carried out on the model for different fault conditions. Results obtained were then compared with data obtained from NamPower records to ascertain the type of fault.展开更多
Due to the coexistence and coupling of continuous variables and discrete events, the vehicle height adjustment process of electronic air suspension system can be regarded as a typical hybrid system. Therefore, the hyb...Due to the coexistence and coupling of continuous variables and discrete events, the vehicle height adjustment process of electronic air suspension system can be regarded as a typical hybrid system. Therefore, the hybrid system theory was applied to design a novel vehicle height control strategy in this paper. A nonlinear mechanism model of the vehicle height adjustment system was established based on vehicle system dynamics and thermodynamic theory for variable-mass gas charge/discharge system. In order to model both the continuous/discrete dynamics of vehicle height adjustment process and the on-off statuses switching of solenoid valves, the framework of mixed logical dynamical(MLD) modelling was used. On the basis of the vehicle height adjustment control strategy, the MLD model of the adjustment process was built by introducing auxiliary logical variables and auxiliary continuous variables. Then, the co-simulation of the nonlinear mechanism model and the MLD model was conducted based on the compiling of HYSDEL. The simulation and experimental results show that the proposed control strategy can not only adjust the vehicle height effectively, but also achieve the on-off statuses direct control of solenoid valves.展开更多
文摘Broadband PLC （power line communication） technology is a main factor of the development of digital convergence in the indoor network. It uses the already existing power cable infrastructure for communication purposes. The EM （electromagnetic） field radiating from the cable could, however, disturb other communication systems, and thus should be evaluated. The MoM （method of moment） and the FEM （finite element method） have been studied to estimate the EVI field emitted from the power cable. However, the M oM is difficult to treat the dielectric material of the cable and the FEM is time consuming. This paperpresents a new approach to estimate the radiated EM fields caused by PLC sy stems from the CM current along the cable, based on the transmission line theory. The proposed model has the advantage of using the measured primary parameters of the cable. An experimental analysis of the EM radiation distribution is also presented. A comparison showed that the model results agree quite well with the measurements performed in this study.
文摘Electric power systems usually cover large geographical areas and transmission facilities are continuously increasing. These power systems are exposed to different environmental conditions which may cause faults to occur on the system. Different types of studies are usually done on electric power systems to determine how the system behaves before, during and after a fault condition. The behaviour of variables of interest such as currents, voltage, rotor angle and active and reactive power under fault conditions are studied and observed to help determine possible causes of faults in a power system. The objective of this paper is to investigate a fault that occurred on the 330 kV transmission line between Ruacana power station and Omburu sub-station, the fault caused all the generators at Ruacana power station to trip and consequently caused a blackout at the power station that lasted for 6 h. Preliminary findings showed that the observed fault was an earth fault but the exact type of earth fault was however not known at the time. This research investigation sets out to determine the exact fault that occurred; the most probable cause of the fault, and propose possible solutions to prevent reoccurrence of such a fault. The section of the power network in which the fault occurred was modelled using DigSilent Power Factory software tool, and transient fault analysis was carried out on the model for different fault conditions. Results obtained were then compared with data obtained from NamPower records to ascertain the type of fault.
基金supported by the National Natural Science Foundation of China(Grant Nos.51375212 and 51105177)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20133227130001)the China Postdoctoral Science Foundation(Grant No.2014M551518)
文摘Due to the coexistence and coupling of continuous variables and discrete events, the vehicle height adjustment process of electronic air suspension system can be regarded as a typical hybrid system. Therefore, the hybrid system theory was applied to design a novel vehicle height control strategy in this paper. A nonlinear mechanism model of the vehicle height adjustment system was established based on vehicle system dynamics and thermodynamic theory for variable-mass gas charge/discharge system. In order to model both the continuous/discrete dynamics of vehicle height adjustment process and the on-off statuses switching of solenoid valves, the framework of mixed logical dynamical(MLD) modelling was used. On the basis of the vehicle height adjustment control strategy, the MLD model of the adjustment process was built by introducing auxiliary logical variables and auxiliary continuous variables. Then, the co-simulation of the nonlinear mechanism model and the MLD model was conducted based on the compiling of HYSDEL. The simulation and experimental results show that the proposed control strategy can not only adjust the vehicle height effectively, but also achieve the on-off statuses direct control of solenoid valves.
