直流電機(jī)速度控制中英文翻譯‘-文庫吧資料
2024-11-08 23:20本頁面
【正文】 Even if the load torque is removed ,the motor must provide sufficient torque to overe the viscous friction effect of the bearings. Other forms of regulator also provide output power。 A temperature regulator must maintain the temperature of, say, an oven constant despite the heat loss in the oven. A voltage regulator must also maintain must output voltage constant despite variation in the load current. For any system to provide an output, ., speed, temperature, voltage, etc, an error signal must exist under steadystate conditions. Electrical Braking In many speed control system, ., rolling mills mine winders, etc., the load has to be frequently brought to a standstill and reversed. The rate at which the speed reduces following a reduced speed demand is dependent on the stored energy and the braking system used. A small speed control system (sometimes known as a velodyne) can employ mechanical braking, but this is not feasible with large speed controllers since it is difficult and costly to remove the heat generated. The various methods of electrical braking avaiable are: (1) Regenerative braking. (2) Eddy current braking. (3) Dynamic braking. (4) Reverse current braking(plugging). Regenerative braking is the best method, though not necessarily the most economic. The stored energy in the load is converted into electrical energy by the work motor(acting temporarily as a generator) and is returned to the power supply system. The supply system thus acts as a “sink” into which the unwanted energy is delivered. Providing the supply system has adequate capacity, the consequent rise in terminal voltage will be small during the short periods of regeneration. In the WardLeonard method of speed control of DC motors, regenerative braking is inherent, but thyristor drives have to be arranged to invert to regenerate. Induction motor driver can regenerate if the rotor shaft is driven faster than speed of the rotating field. The advent of lowcost variable variablefrequency supplies from thyristor inve
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