Power Frequency Converters
Power frequency converters take electrical input power at one frequency and voltage and provide electrical output power at a different frequency, and at a different or equal voltage. There are two basic types of power frequency converters: rotary (motor-generator set) and solid state. The major difference between the two is the method used to enact the frequency conversion. Either of these two types of power frequency converters is acceptable for most applications but there are a number of distinct differences in their capabilities and features. These differences may determine that one type of converter is better suited to a specific application. When in doubt, check with the product manufacturer. Rotary power frequency converters use input power to run a motor. The motor spins a generator, which produces the required output power. These converters can be categorized into belt driven, coupled inline, and single shaft. Belt driven converters consist of a motor, generator, belts, pulleys and control. The motor power is transferred to the generator via the belts and pulleys. The type of motors can be induction or synchronous. The use of induction motors can yield a low-cost, highly accurate output frequency. Synchronous motors provide even higher frequency accuracy but at a much higher cost. Coupled inline converters are similar to belt driven converters except that power is transferred from motor to generator via an inline coupling attached to the motor and generator shaft. Single shaft rotary power frequency converters have both the motor and generator rotors on the same shaft. Solid-state units convert the input AC power into DC, and then the DC into the required output power. These units have very few moving parts (usually only cooling fans) therefore they have lower requirements for preventive maintenance. The output stage of modern solid-state converter is an Insulate Gate Bipolar Transistor (IGBT) inverter. These types of power frequency converters use a microcontroller to generate the important features of the output waveforms, including the frequency and voltage, and to provide harmonic damping, and voltage compensation and regulation, among other features.
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