Parts of Electric Drives:
1. Electrical motors and load
2. Power modulator
4. Control unit
5. Sensing unit.
Most commonly used electric drives are
DC motos – Shunt , Series. Compound and permanent magnet.
Induction Motors – Squirel cage , wound rotor and linear
Synchronous motor - Wound field and permanent magnet
Brushless Dc motors , stepper motors, and switched reluctance motors can be used.
It can classified as
1. Controlled rectifier (AC to DC converters)
2. Inverters (DC to AC converters)
3. AC voltage controllers (AC to AC converters)
4. DC choppers (DC to DC converters)
5. Cyclo converters (Frequency conversion)
Single Phase and Three Phase , 50Hz readily available in most locations.
Very low power drives fed from single phase source. Rest of the drives from three phase source.
Low and medium power motor are fet from 400v supply.
Higher rating , motors are fed from 3.3kv , 6.6 kv , 11kv.
Some drives are power from a battery , battery voltage may be 24v, 48v and 110v.
Sensing unit :
1. Speed sensing is required for implementation of closed loop speed control schemes.
2. Speed sensing by tachometers , high speed accuracies required digital tachometers are used.
3. Current sensing methods are
· Use of current sensor employing hall effect.
· Involves the use of a non-inductive resistance shunt in conjunction with an isolation amplifier which has an arrangement for an amplification and isolation bet power and control units.
Control Units :
· Control for power modulator is provided in the control unit.
· When semi conductor converts are used, the control unit will consist of firing circuits, which employ linear and digit integrated circuits and transistor and a up when sophisticated control is required.