The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch...The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch, equations that are used to decide the lubricating oil flow and the number of oil films (i.e. the number of rotating and stationary plates) are deduced theoretically. Also key parameters are provided for the design of the hydraulic system. All these together provide the theoretical basis for the soft start design of the belt conveyor and references for the application of the oil film clutch in similar fields.展开更多
The mechanism of a hydro-viscous soft start is of great importance in the design of a hydro-viscous clutch and its control system. To explain the mechanism of a hydro-viscous soft start, the startup process of a belt ...The mechanism of a hydro-viscous soft start is of great importance in the design of a hydro-viscous clutch and its control system. To explain the mechanism of a hydro-viscous soft start, the startup process of a belt conveyor was numerically analyzed with the modified Reynolds equation, an energy equation and a temperature-viscosity equation. The effect of temperature and grooves of the friction disk surface on torque transfer and load capacity of the oil film have also been analyzed. The results show that 1) the grooves are the basis of forming dynamic pressure but they may reduce the capacity of torque transfer to a certain extent, 2) during the startup process, temperature has little effect on torque transfer and load capacity and the variation in load capacity of the oil film is very small, indicating that it is preferable to use the flow rate as a control object than the pressure of the feed cylinder. The results have been verified by an experiment.展开更多
全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的...全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。展开更多
The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electrom...The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.展开更多
文摘The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch, equations that are used to decide the lubricating oil flow and the number of oil films (i.e. the number of rotating and stationary plates) are deduced theoretically. Also key parameters are provided for the design of the hydraulic system. All these together provide the theoretical basis for the soft start design of the belt conveyor and references for the application of the oil film clutch in similar fields.
文摘The mechanism of a hydro-viscous soft start is of great importance in the design of a hydro-viscous clutch and its control system. To explain the mechanism of a hydro-viscous soft start, the startup process of a belt conveyor was numerically analyzed with the modified Reynolds equation, an energy equation and a temperature-viscosity equation. The effect of temperature and grooves of the friction disk surface on torque transfer and load capacity of the oil film have also been analyzed. The results show that 1) the grooves are the basis of forming dynamic pressure but they may reduce the capacity of torque transfer to a certain extent, 2) during the startup process, temperature has little effect on torque transfer and load capacity and the variation in load capacity of the oil film is very small, indicating that it is preferable to use the flow rate as a control object than the pressure of the feed cylinder. The results have been verified by an experiment.
文摘全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。
基金This work was supported in part by the National Key Research and Development Program of China under Grant 2017YFB0902904,in part by the Natural Science Foundation of Hubei Province under Grant 2016CFB448,and in part by the Shenzhen City Science and Technology Innovation Plan under Grant JCYJ20170306170937861,and in part by Wuhan City Science and Technology Program under Grant 2016070204020165.
文摘The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.
