| Frequency Changer |
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Traditionally, these devices were built out of electromechanical components such as Motor-generator sets or Rotary Converter s. But with the advent of Solid State electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a Rectifier stage (producing Direct Current ) which is then Inverted to produce ac of the desired frequency. The inverter may use Thyristor s or IGBT s. If voltage conversion is desired, a Transformer will usually be included in either the ac input or output circuitry and this transformer may also provide galvanic isolation between the input and output ac circuits. A Battery may also be added to the dc circuitry to improve the converter's ''ride-through'' of brief outages in the input power. Frequency changers vary in Power-handling capability from a few Watt s to megawatts. APPLICATIONS Aside from the obvious application of converting bulk amounts of power from one distribution standard to another, frequency changers are also used to control the speed and the torque of the AC Motors . In this application, the most typical frequency converter topology is the three-phase two-level voltage source inverter. The phase voltages are controlled using the power semiconductor switches and Pulse Width Modulation ( PWM ). Semiconductor switching devices and anti-parallel connected freewheeling Diode s form a bridge, which can connect each motor phase to the positive or negative dc-link potential. The PWM changes the connections of the phases between the positive and the negative dc-link potentials so that the fundamental wave voltage has the desired frequency and amplitude. The motor reacts primarily to the fundamental voltage and filters out the effects of the harmonic voltages. Frequency changers are typically used to control the speed of pumps and fans. In many applications significant energy savings are achieved. The most demanding application areas are found on the industrial processing lines, where the control accuracy requirements can be very high. ALTERNATE USES Frequency converter may also refer to a much-lower-powered circuit that converts Radio Frequency Signals at one Frequency to another Frequency . The circuit usually consists of a Local Oscillator and Frequency Mixer . SEE ALSO |
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