Variable Speed:

Self Excited Induction Generator (SEIG) Small systems of electricity generation are often stand alone applications, remote network of electricity supply, using widely fluctuating energy sources like wind and water for their source of energy. Generator fixed speed induction is not suitable for such applications. Generators at variable speed induction need some form of self excitation and packaging powerful to make practical use of their output voltage frequency and unregulated.
Operation Self excitation is obtained by connecting the capacitors to the terminals of the stator of the generator. When driven by an external prime mover, a small current is induced in the stator coils as flux due to residual magnetism in the cutting rotor windings and this current charges the capacitors. As the rotor turns, the flux cutting the stator windings will change in the direction opposite the orientation of the remanent magnetic field rotates with the rotor.

The current induced in this case is in the opposite direction and will tend to discharge capacitors. At the same time freed from the charge that the capacitors tend to reinforce the current increase in flow in the machine. As the rotor continues to turn induced emf and current in the stator windings will continue to rise until equilibrium is reached, according to the saturation of magnetic circuit in the machine. At this point the operating voltage and current will continue to oscillate at a given value peak and the frequency determined by the characteristics of the machine, the air gap, the slip, the calculation and choice of capacitor sizes .

The combination of these factors sets maximum and minimum speed range over which self-excitation occurs. The sheet of operation is generally low and the frequency variation depends on the speed range of operation.
If the generator is overloaded, the voltage will drop quickly provide a measure of the construction of self-protection.
Control Operating at variable speed induction generator needs a converter to adapt the output frequency variable generator fixed frequency of application or grid electricity. During operation of the controllable factor only available in a generator self-excited induction influence the output is the input mechanical mover, so that the system is not suitable for control of effective feedback.

Provide adjustable output voltage and frequency, external AC / DC / AC are required. A bridge with three diodes phase is used to correct the output current generator providing a current link three-phase thyristor inverter that converts energy from DC to link the required voltage and frequency.

DC generators (dynamos) Current (DC) Generator:
The field of stationary AC generator described above can be modified to provide unidirectional current by replacing the rings to slide on the rotor shaft of a collector adapted to reverse the connection to the coil each half cycle that passes Driver alternate north and south magnetic poles. However, power will be a series of half sine pulse, as the waveform from a rectifier as shown below.
Ripple output voltage can be minimized by using multi-plans.
The construction of a DC generator is very similar to the construction of a DC motor.
The rotor consists of an electromagnet to provide the excitement on the field. Current on the rotor is derived from the stator or in the case of large generators, from a separate excitation in rotation on the rotor shaft as well. Connection through the rotor is a switch so that the direction of current in the direction of the stator windings changes as the rotor poles crossing between northern and southern parts of the stator poles. The rotor is very low compared with the current in the stator windings and most of the heat is dissipated in the structure more massive stator.

In self-excited machines, when starting from rest, the current to start the electrical work is based on the small residual magnetism that exists in electro and around the magnetic circuit.

Automotive Alternators Generator automobile is a machine for variable speed AC issuing a fixed dc output.

Generator is a typical self excited alternating current machine. Using a generator rather than a DC generator using a switch and its potential reliability problems can be avoided. However, the current is required for all loads in the vehicle including the battery and, furthermore, the DC output voltage should be constant regardless of engine speed or load current. The charging system must include a rectifier to convert AC to DC and a regulator to maintain the tension generated within the independent design of the motor speed.

The rotor is driven by the engine and provides excitement on the field. Its speed is directly related to engine speed and depends on the ratios of the transmission or the drive pulleys. The output current is taken by the stator.

Automotive alternators are generally three phase machines to enable a compact design and at the same time, reducing the current in the stator windings by spreading it among three sets of windings. This also gives a reduction of the ripple voltage potential after correction.

Construction:

The rotor is a rotor claw pole in which both ends of the shape of the rotor north and south poles of an electromagnet. The "claws" extend them effectively produce parts in the north and south poles crossing poles of the stator. The rotor current energizing the electromagnet is supplied by the stator windings through three diodes auxiliary remedy before passing through two slip rings to a single rotor coil.
Moving magnetic field associated with the poles of the rotor causes a current to flow through the stator windings as the password field on the conductors of the stator.
The phase current produced by the alternator is rectified in a full wave, bridge circuit diode to produce a DC output. The EMF generator is directly proportional to the alternator (or engine) speed. The alternator is however designed to provide full voltage, typically 14.2 volts for a nominal 12 volt battery lead, at idling speed and maintain output voltage constant at that level that the engine increases speed.

Voltage Regulator:

To prevent the battery from being overloaded voltage DC output must be maintained below 14.2 volts maximum charge voltage specified for the battery. The function of the regulator senses the output voltage of the alternator and if it is greater than the voltage of 14.2 volts reference provided by a Zener diode, it interrupts the current field (rotor) coil . Not a current field of alternator voltage starts to fall. When the alternator voltage falls below the reference voltage, the current will be supplied to the field coil once again maintaining the output voltage at the desired level.

The rotor thus receives a pulsed DC on the speed range of engine operation, smoothed somewhat by the rotor winding inductance. Alternative designs to monitor the current load on the generator and provide a feedback mechanism using modulated pulse width to control the stator current to provide constant output voltage regardless of load.