Diagram

Draw the block diagram of conventional scherbius system


Name The Applications Of Stator Voltage Control.
 Fan
 Pump drives (where torque demand reduces with speed)

Define Inverters.
An inverter is defined as converter that converts DC into AC
Applications Of Variable Frequency AC Drive.
 Speed control of AC Fans,induction motors,pumps
 In food processing industry for mixers,slicers
 Mining Industry for reheat furnances
 Machine tools,lathes,grinders

Power Modulators Used for v/f control of three phase induction motor.
 Phase controlled converters
 Uncontrolled or bridge rectifier using diodes along with chopper
Advantage Of v/f speed control of induction motor.
 Smooth speed control
 Small input current and improved power factor at low frequency start
 Higher starting torque for low case resistance
 Good efficiency at all speed
 Speed below and above rated are possible





Block Diagram of Speed control scheme of slip ring induction motor.

How is speed control achieved by v/f control in 3 phase induction motor
The ac input with constant V and f is given to a converter which converts it to dc.It is
then given to an inverter whose output is a variable voltage variable frequency ac supply
Thus proper values of V and f can be selected so as to keep V/f ratio constant to obtain
the speed control of induction motor

Slip power recovery schemes

In the rotor resistance control the slip power in rotor is water as I2R losses.The scheme in
which the slip power in the rotor circuit is recovered and either feedback to the ac supply or
used to drive other machines