Generally DC generators are classified according to the ways of excitation of their fields. There are three methods of excitation.
- Field coils excited by permanent magnets – Permanent magnet DC generators.
- Field coils excited by some external source – Separately excited DC generators.
- Field coils excited by the generator itself – Self excited DC generators.
How to control the output voltage for the different types of the dc generator and how to reverse the voltage polarity?