7-1 概论自从1851年出现了他励式直流电机和1860年出现了自励式直流电机以后,人们就在想如何按要求来改变它的输出功率和电压的大小问题。最先想到的就是在电枢回路或者励磁绕组回路串入一个可改变它的电阻值大小的电阻器来解决。由于电枢回路电流大,则所需可变电阻器容量大、消耗功率多 7-1 Introduction Since the isolated DC motor in 1851 and the self-excited DC motor in 1860, people were wondering how to change its output power and voltage requirements as required. The first thing that came to mind was that a series resistor in the armature circuit or the field winding circuit could be used to change the resistance of the circuit. As the armature circuit current is large, the required variable resistor capacity, power consumption and more