Excitation in an alternator refers to the process of supplying direct current (DC) to the field windings of the rotor to produce the magnetic field required for electromagnetic induction. This magnetic field interacts with the stator windings to induce an alternating current (AC) output. The strength of the excitation current directly affects the magnetic field strength and hence controls the voltage generated by the alternator.

In modern systems, an automatic voltage regulator (AVR) adjusts the excitation current automatically to maintain stable output voltage despite varying load conditions.

A brushless alternator is a type of electrical generator that produces alternating current (AC) without the need for brushes and commutators.

• Rotor: Instead of using brushes and a commutator, a brushless alternator has a rotor with permanent magnets or electromagnets. These magnets generate a rotating magnetic field when electricity is supplied to them.
• Stator: The stator consists of coils of wire arranged around the rotor. As the magnetic field of the rotor rotates, it induces an alternating current in the stator windings through electromagnetic induction.
• Rectifier: The alternating current produced in the stator windings is then converted into direct current (DC) by a rectifier assembly, typically consisting of diodes. This DC is necessary for the excitation of the rotor's magnets.
• Excitation: The DC is fed to the rotor's electromagnets or permanent magnets, creating a steady magnetic field. This field interacts with the rotating magnetic field of the rotor, inducing a three-phase AC current in the stator windings.
• Output: The three-phase AC output from the stator windings is then available for use in powering electrical devices or for distribution in an electrical grid.