Question

Explain cycloconverter and its types.

Answer 1

Cycloconverter:

Cycloconverter is an AC to AC converter which converts input AC into variable AC. It changes frequency. Basically, there are two types of cycloconverter one is step up cycloconverter and second is step down cycloconverter. Step up cycloconverter converts lower input AC frequency to higher output AC frequency. Step down cycloconverter converts higher input AC frequency to lower output AC frequency. Cycloconverter is useful for both variable and fixed output frequency means cycloconverter is useful for changing fixed input frequency to variable output frequency and it is also useful for changing variable input frequency to fixed output frequency. In cycloconverter, there is no need for DC link. Cycloconverter inherently have voltage control feature. Cycloconverter is a one stage conversion device. Cycloconver is a one stage frequency changer. Cycloconverter is used for any power factor. Cycloconverter allows power flow in any direction.

Types of cycloconverter:

• Step up cycloconverter:
  

In step-up cycloconverter lower input AC frequency is converted to higher output AC frequency. Step up cycloconverter requires forced commutation.

• Step down cycloconverter:
  

In step down cycloconverter higher input frequency is converted to lower output frequency.

Single phase to single phase cycloconverter:

Midpoint cycloconverter and bridge type cycloconverter are the two configurations.

• Mid-point configuration:
In mid-point type cycloconverter there is one single phase transformer whose secondary winding is mid-tap. And it consists of four thyristors as shown in the figure. The four thyristors are connected in two single phase fully controlled bridge configuration connected in opposite direction.

• Bridge configuration:
  
There are two groups of converters in bridge converter one is positive group converter and second is negative group converter. Each group has four thyristors. These bridge groups are fully controlled and the input to them is single phase AC. The two bridge should conduct alternately otherwise shortcircuit will produce at the input. P-converter is for the positive half cycle and N-converter is for the negative half cycle.

Three phase to single phase cycloconverter:

The figure shows three phase to single phase cycloconverter.

 

Three phase to three phase cycloconverter:

The figure shows three phase to three phase cycloconverter.

Applications of cycloconverter:

• Cycloconverter is used for induction heating.
  
• SVC (static VAR compensator).
  
• Wind generator.
  
• AC motor speed control.
  
• Electric traction application.

Advantages of cycloconverter:

• Cycloconverter can be used for both fixed and variable frequency output.
• Cycloconverter can be used with any power factor.
• Useful for large power drives.

Disadvantages of cycloconverter:

• So many thyristors are required in cycloconverter.