機(jī)械專業(yè)外文翻譯----直流電動機(jī)調(diào)速控制-wenkub
2023-05-19 00:26:38 本頁面
【正文】 due to mentator ripple. References ID(1999)From robust control to adaptive Eng Prac 7:1113–1124 U,Ljung L(1999)Closedloop identification revisited. Automatica 35:1215–1241 168。 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 the 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 systems, ., 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 available 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 drives can regenerate if the rotor shaft is driven faster than speed of the rotating field. The advent of lowcost variablefrequency supplies from thyristor inverters have brought about considerable changes in the use of induction motors in variable speed drives. Eddy current braking can be applied to any machine, simply by mounting a copper or aluminum disc on the shaft and rotating it in a magic field. The problem of removing the heat generated is severe in large system as the temperature of the shaft, bearings, and motor will be raised if prolonged braking is a
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