Synchronous motors are those that are locked to the supply frequency. Typically the rotor can be a permanent magnet or excited with DC via slip-rings. The stator provides the rotating field that moves the rotor as with an induction motor. It can be seen as an brushless alternator used as a motor. There needs to be some way to spin it up to speed. The phase is also locked to the supply, and can be adjusted to make the current lead or lag. Therefore it can behave as a large capacitor or inductor.

A synchronous ac alternator is similar to connecting conventional alternators in parallel. Though there is no mechanical connection, the shafts of two such generators in parallel are locked together. This is to do with connecting an AC generator in parallel with the grid. It is running at the same RPM, and in phase with the grid etc. The peaks of the sine wave outputs occur at the same instant. They can be used with wind generators and other standby power systems. The synchronized ac alternator supplies power when the drive torque is sufficient, otherwise it is just spinning around, like a synchronous motor. See the third link. It should be distinguished from an induction generator (also called an asynchronous generator), which is like an induction motor used as a generator, is not synchronous in shaft speed, and has some advantage in a wind generator as the "slip" is easier on gearbox wear. The induction brushless ac generator needs to be connected across an active supply, so can only supply a maximum related to perhaps one third of the rest of the "grid" size. See the third link. I have seen articles about using induction motors as generators by using capacitors between the output and windings - you can say a self excited induction generator. Maybe these have some application in home wind generators, despite inefficiencies?

A synchronous condenser - this is using a synchronous motor as a capacitor. There is no mechanical load, and it is adjusted to make the current lead the supply voltage, like a capacitor. Large ones are used to correct power factor in electrical supply grids. See the first link below.

Synchros (also Selsyn) are a special type of servo motor, something like a rotating transformer. There are normally two connected together. The receiver repeats the angle of the transmitter. If you twiddle the transmit synchro back and forth, or rotate it, the receiver synchro follows this movement. They were widely used in radar, and fire control systems to repeat the antenna or gun angles to the display area. See the second link below.

When an electric current is passed through a coil of wire, a magnetic field is produced (an electromagnet). Conversely, when a magnetic field is moved through a coil of wire, a voltage is induced in the wire. The induced voltage becomes a current when the electrons have some place to go such as into a battery or other load. Both of these actions take place in brushless alternators, motors and ac generators or dynamos. Voltage is generated when a coil of wire is moved through a magnetic field. It doesn’t matter whether the coil is moving or the magnetic field is moving. Either configuration works equally well and both are used separately or in combination depending on mechanical, electrical and other objectives. The old DC generators (dynamos) used a stationary field and rotating armature. Automotive alternators use the opposite configuration with a rotating field and stationary armature. In a Stamford alternator, both configurations are used in one machine.

A brushless alternator is part of the charging system of your car that produces electricity for many devices. A type of ac generator, the alternator transforms mechanical energy into electrical energy. Although your car's battery supplies some electricity, most of the electrical mechanisms within the vehicle, require the alternator's steady stream of power.

Alternating current (rather than direct current) gives the stamford alternator its name, because this is the type of electricity it creates. It's mainly a mechanical device, concealing a pulley, wheels, brushes and wires, which hooks to the crankshaft and runs to the battery. This way, the gasoline powers the engine to turn the crankshaft, which in turn connects to the alternator. The ac alternator converts that motion into current whenever the car is running. The resulting electricity operates the cooling fan, headlights, windshield wipers, radio, defogger, and air conditioning.

To be more specific, an alternator is very efficient at producing a constant, high voltage, even when the car is idle, because of how it works. The belt (from the crankshaft) connects to a pulley system, called the rotor, such that when the belt is turning, it moves magnets across a special surface, called a conductor. Moving magnets, in the stator, generate an electrostatic field, otherwise known as electricity. This alternating current is controlled by a voltage regulator to keep the voltage steady. Another part, called the diodes, convert alternating current into direct current that flows on to the battery and other components.

Even if your alternator dies or malfunctions, your car will run for a while directly off of the battery, until all the battery's power is sapped. Therefore, it is hard to tell when your alternator has problems. Sometimes a harsh noise, or intermittent headlights, will give it away. Check to make sure the belts on the alternator are not cracked, or improperly tightened, before you replace the entire thing. A rebuilt alternator can be a reliable, but less expensive, option if you need it repaired.

Certain of the foregoing and related objects are readily attained in a brushless alternator having a three-phase stator winding, consisting of at least one set of delta connected stator coils disposed in stator plates and surrounding the main field winding in the rotor. The rotor is disposed on a shaft rotatably supported within the housing of the alternator. An exciter and shaft-mounted rectifying means are provided for supplying DC voltage to the main winding of the rotor. The exciter field coil is wound spool-like on a core, with the field coil contained within an exciter stator attached to the alternator housing. The main winding in the rotor is wound spool-like on a core with the rotor having a cylindrical sleeve extending from one end and engaging and supporting the exciter armature in alignment with the exciter stator.

The exciter produces a three-phase AC voltage which is rectified by diodes mounted to and rotating with the alternator shaft. The rectified voltage is supplied to a main field winding disposed within the rotor mounted onto the shaft. This, in turn, provides a DC current flow in the main field winding, which is required for inducing the ac alternator output current, in a main armature winding. The exciter and main field windings are wrapped sequentially and annularly around their respective cores. The exciter armature is attached to and partially enclosed within a cylindrical flange extending outward from the rotor. The exciter field coil is disposed within and surrounded on its sides by the exciter armature.

A feedback circuit is provided within the ac generator in order to maintain output voltage during varying load and temperature conditions. Within the stator is a set of feedback coils in a three-phase delta connection. The output voltage from these coils is rectified and supplied to a voltage regulator, as shown in FIG. 3. When the battery voltage deviates beyond the working range, the voltage regulator compensates by supplying a correspondingly higher or lower DC voltage to the field coil in the exciter stator, as required. This, in turn, results in the desired change of output voltage.

An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. Most alternators use a rotating magnetic field but linear alternators are occasionally used. In principle, any AC generator can be called an alternator, but usually the word refers to small rotating machines driven by automotive and other internal combustion engines. Alternators in power stations driven by steam turbines are called turbo-alternators.

Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric current. The early machines were developed by pioneers such as Michael Faraday and Hippolyte Pixii.

Faraday developed the "rotating rectangle", whose operation was heteropolar - each active conductor passed successively through regions where the magnetic field was in opposite directions. The first public demonstration of a more robust "alternator system" took place in 1886. Large two-phase alternating current generators were built by a British electrician, J.E.H. Gordon, in 1882. Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 Hz. In 1891, Nikola Tesla patented a practical "high-frequency" alternator (which operated around 15 kHz). After 1891, polyphase alternators were introduced to supply currents of multiple differing phases. Later alternators were designed for varying alternating-current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors.

Construction

A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller brushless alternators may look like one unit but the two parts are readily identifiable on the large versions. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wear parts.

 Main alternator

The main ac alternator has a rotating field as described above and a stationary armature (power generation windings).

 Control system

Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.

 Automatic voltage regulator (AVR)

The AVR regulates the alternator's output voltage by varying the amount of current in the stationary exciter field coils. Automatic voltage control may be used where load current variations exceed the built-in ability of the generator to regulate itself. An automatic voltage control device "senses" changes in output voltage and causes a change in field resistance to keep output voltage constant.