Power Electronics Cycloconverters - Power Electronics

What are Cycloconverters in Power Electronics?

Cycloconverter is a frequency changer which changes AC power from one frequency to AC power at another frequency and this process is called as AC-AC conversion. This cycloconverter is widely used in electric traction, AC motors which have variable speed and induction heating.

It attains frequency conversion in one stage and makes sure that the voltage and the frequencies are convenient. Additionally, commutation circuit’s usage is not required as it makes use of natural commutation. Power transfer within a cycloconverter will occur in two directions (bidirectional).

Main problem with cycloconverters is that while it is operating at small currents, inefficiencies can be created with dismissal delay and additionally, operations will be only smooth at frequencies that are not equal half frequency input values. This is true as cycloconverter is an AC- AC converter which is phase controlled. Thus, to provide the necessary AC output voltage, it should do a selection of the voltage input segments by applying line (natural) commutation. This describes why the output frequency is lower than the frequency input.

Harmonics in a cycloconverter will be majorly affected by methods of control, overlap effect, the number of pulses in a given cycle, operation mode and mode of conduction.

Cycloconverters are of 2 types

  • Step Up cycloconverter − Step Up cycloconverter make use of natural commutation and produces an output at higher frequency than that of the input.
  • Step Down cycloconverter − Step Down cycloconverter makes use of forced commutation and produces an output with a frequency lower than that of the input.

Cycloconverters can be further classified into three categories

  • Single phase to single-phase − Single phase to single-phase Cycloconverters will have two full wave converters which are connected back to back and when one converter is operating, the other one will be disabled and no current will pass through it.
  • Three-phase to single-phase − Three-phase to single-phase cycloconverter will be operating in four quadrants that is (+V, +I) and (−V, −I) being the rectification modes and (+V, −I) and (−V, +I) being the inversion modes.
  • Three-phase to three-phase − Three-phase to three-phase cycloconverter will be widely used in AC machine systems which operate on three phase induction and synchronous machines.

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