The word compulsator is the shortened form of "compensated pulsed alternator". It is basically an alternator built for generating short pulses instead of continuous alternating current.

According to the Faraday's Law, the magnitude of the voltage generated in a loop of conductor is proportional the the rate of change of the magnetic flux through the loop. An ordinary alternator with an armature rotating in an uniform magnetic field thus produces a sinusoidal voltage.

Typically the compulsator's flywheel (with an attached armature coil) is spun up with an external power source, and at the correct moment, the field coil is energized and the switch connects the armature to the load. With a large magnetic field strength and a low-impedance armature with many turns and high rotational velocity, this results in a lot of power dumped into the load in a short time.

A typical compulsator and alternator both have a rotating armature coil for voltage generation, a switch to connect the said armature to a load and a static field coil for generating the magnetic field. The compulsator differs from an alternator in that is has also a special static compensating coil.

The compensating coil has an important job in making the armature coil low-impedance. Without it, an armature coil with a large number of turns would have a significant self-inductance, limiting the rise time of the current pulse produced. A basic compensating coil has the same shape as the armature coil, but is mounted outside the rotor. It's kind of like an mirror image of the armature coil, connected in series with it but with reverse polarity. When the coils are lined up, their inductances cancel each other out (at least to an extent). This makes possible for the output current to ramp up very quickly - otherwise the circuit would exhibit a reverse EMF proportional to the rate of change of the current.

What's the compulsator useful for then? Well, basically anything that requires a fast pulse of energy. This includes railguns, EMP generation, lasers and much more. Of course, a sufficiently large capacitor bank can supply similar pulses of energy too, but the compulsator's high power density and the ability to supply energy to it straight through a shaft from a prime mover like a diesel engine makes it extremely competitive in mobile applications.

For more information, look up US patents #4200831: Compensated Pulsed Alternator and #4935708: High Energy Pulse Forming Generator.