Frequency drive-variable or (VFD) that its main purpose is to control the speed of the engines, alternating current. This drives in addition to the application to control the speed of the drives can be used at low speeds, the characteristic curve of torque-speed is very desirable similar machine, the DC found, and in many applications can be using this method, engines, DC engines, si Cage, the squirrel replaced.

one of the important parameters in determining the speed of the engines, alternating current., the frequency of the input voltage to it is that drives the variable frequency is also based on the same work. Since that change frequency reactance induction motor also changes. drive, should the voltage of the sync frequency setting.

more drives, variable frequency to adjust the frequency, the prime power input, a direct current conversion work, and then again to make it alternate with the frequency of the desired him back. That drive for power conversion DC to DC from what way to a large extent to producer, date of production and the size of the motor that the drive should control it does depend on. the voltage output usually in the form of a square, which is for engines, in case of a particular problem does not cause, however, some manufacturers use a single additional waveforms, stair, and brought them up to shape of the sine wave gets closer.