Introduction:
A three-phase full converter is a power electronic device that converts three-phase AC input voltage into a variable DC output voltage. It is commonly used in various industrial applications such as motor drives, battery charging systems, and power supplies. The converter consists of a set of semiconductor devices called Silicon Controlled Rectifiers (SCRs), which are used to control the flow of current and voltage.

Explanation:
The number of SCRs required in a three-phase full converter depends on the type of converter configuration used. There are two types of converter configurations:

1. Three-Phase Bridge Converter:
In a three-phase bridge converter, each phase of the input AC voltage is connected to a diode bridge rectifier. This configuration requires a total of six SCRs, with each phase requiring two SCRs. The SCRs are connected in an anti-parallel configuration with each diode of the bridge rectifier. The SCRs are controlled in pairs to achieve the desired output voltage.

2. Three-Phase Half-Bridge Converter:
In a three-phase half-bridge converter, each phase of the input AC voltage is connected to a single SCR and a diode. This configuration requires a total of nine SCRs, with each phase requiring three SCRs. The SCRs are connected in series with the diode to form a half-bridge configuration. The SCRs are controlled individually to achieve the desired output voltage.

Conclusion:
In conclusion, a three-phase full converter requires six SCRs in a three-phase bridge converter configuration and nine SCRs in a three-phase half-bridge converter configuration. The choice of converter configuration depends on various factors such as cost, power rating, and control requirements.