Question

how to increase the RPM of a dc motor​

Answer 1

Explanation:

To increase the torque ... that a bit harder. All you can do, electrically (as you can do it mechanically via gears), is to reduce the source impedance to maximise the current that can be delivered for a given stator impedance. To keep RPM constant keep voltage constant.....

Answer 2

Answer:

Increasing the speed can be achieved by increasing the supply frequency as the speed and frequency are directly proportional; however, there are two constraints. The first is the saturation of the magnetic circuit, but this issue can be significantly avoided by keeping the V/f ratio constant.