Power section of a DC drive....






Power section of a DC drive consisting of power handling components can take any of the following shapes.

-single phase semicontrolled

-single phase fully controlled

-three phase semicontrolled

-three phase fully controlled

By ‘Semicontrol’ and ‘Full Control’ we mean the type of control we have over the power controlling devices, i.e. thyristors or diodes. In semicontrolled type, in a three phase configuration, only half of the devices have control over the current flowing through them. The sketch below shows that three out of six current carrying devices are diodes and three are thyristors. Seventh component across the +ve and -ve terminals is a diode and called FREEWHEELING diode. It is necessary to freewheel the energy in the inductance of the motor. With all six devices under control of gate pulses, the electronic circuit has total control over the motor current. This configuration is also known as 6 pulse configuration.





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Block Diagram



Ramp Circuit


Speed Amplifier


Current Amplifier


 Firing Circuit


Power Circuit


Types of DC drives 



 Checking Thyristor


Voltage feedback Vs Tacho feedback


Current Limit


Constant HP & constant Torque


Field Weakening


Using CRO 



Motor runs at full speed


Fuses Blow


Hunting in speed


Motor gives jerks


Belts vibrate


Speed control not satisfactory 



Speed drops on load


Motor overheats


Sparking on commutator


DC drives and Power Factor


Your comments and suggestions 


Drive stops all of a sudden 


Motor not able to drive the load


DC to DC isolation


 Motor or Drive?