直流电机控制系统英文翻译

直流电机控制系统英文翻译内容摘要：

a constantvoltage source. In a motor the relation between the . aE generated in the armature and terminal voltage tV is t a a aV E I R （ 18） where aI is now the armature current input. The generated . aE is now smaller than the terminal voltage tV , the armature current is in the opposite direction to that in a generator, and the electron magic torque is in the direction to sustain rotation of the armature. In shunt and separately excited motors the field flux is nearly constant. Consequently increased torque must be acpanied by a very nearly proportional increase in armature current and hence by a small decrease in counter . to allow this increased current through the small armature resistance. Since counter . is determined by flux and speed, the speed must drop slightly. Like the squirrelcage induction motor, the shunt motor is substantially a constantspeed motor having about 5% drop in speed from no load to full load. Starting torque and maximum torque are 8 limited by the armature current that can be mutated successfully. An outstanding advantage of the shunt motor is case of speed control. With a rheostat in the shuntfield circuit, the field current and flux per pole can be varied at will, and variation of flux causes the inverse variation of speed to maintain counter . approximately equal to the impressed terminal voltage. A maximum speed range of about 4 or 5 to I can be obtained by this method. The limitation again being mutating conditions. By variation of the impressed armature voltage, very speed ranges can be obtained. In the series motor, increase in load is acpanied by increase in the armature current and . and the stator field flux (provided the iron is not pletely saturated). Because flux increase with load, speed must drop in order to maintain the balance between impressed voltage and counter . Moreover, the increased in armature current caused by increased torque is varyingspeed motor with a markedly drooping speedload characteristic. For applications requiring heavy torque overloads, this characteristic is particularly advantageous because the corresponding power overloads are held to more reasonable values by the associated speed drops. Very favorable starting characteristics also result from the increase flux with increased armature current. In the pound motor the series field may be connected either cumulatively, so that its . adds to that of the shunt field, or differentially, so that it opposes. The differential connection is very rarely used. A cumulatively pounded motor has speedload characteristic intermediate between those of a shunt and a series motor, the drop of speed with load depending on the relative number of ampereturns in the shunt and series fields. It does not have disadvantage of very high lightload speed associated with a series motor, but it retains to a considerable degree the advantages of series excitation. The application advantages of . machines lie in the variety of performance characteristics offered by the possibilities of shunt, series and pound excitation. Some of these characteristics have been touched upon briefly in this article. Still greater possibilities exist if additional sets of brushes are added so that other voltages 9 can be obtained from the mutator. Thus the versatility of . machine system and their adaptability to control, both manual and automatic, are their outstanding features. A machines is made up of two basic ponents: － The stator which is the stationary part of the machine. It consists of the following elements: a yoke inside a frame。 excitation poles and winding。 mutating poles (poses) and winding。 end shield with ball or sliding bearings。 brushes and brush holders。 the terminal box. － The rotor which is the moving part of the machine. It is made up of a core mounted on the machine shaft. This core has uniformly spaced slots into which the armature winding is fitted. A mutator, and often a fan, is also located on the machine shaft. The frame is fixed to the floor by means of a bedplate and bolts. On low power machines the frame and yoke are one and the same ponents, through which the magic flux produced by the excitation poles closes. The frame and yoke are built of cast iron or cast steel or sometimes from welded steel plates. In lowpower and controlled rectifiersupplied machines the yoke is built up of thin (～ 1mm) laminated iron sheets. The yoke is usually mounted inside a nonferromagic frame (usually mad。