FOUR QUADRANTS IN MOTOR OPERATIONS

 

CIRCUIT DIAGRAM

Four quadrants motor operation of any drives or DC motor means that the machine operates in four quadrants.

TYPES OF MOTOR OPERATION IN EACH QUADRANT.

FORWARD MOTORING - QUADRANT I

In this mode of operation

• The applied voltage (Va) is positive and greater than the back emf (Ea) of the motor and therefore a positive current flow into the motor.
• Motor will receive electric supply from source and convert it into mechanical energy to rotate the mechanical load.
• Both current and voltage are positive, the power becomes positive. 
• The speed and torque are also positive in this quadrant. 
• The motor rotates in forward direction.

FORWARD BRAKING - QUADRANT II

In this mode of operation

• The motor runs in forward direction and the induced emf (Ea) continues to be positive. But the supplied voltage (Va) is suddenly reduced to a value which is less than the back emf.
• The current will reverse direction. This negative torque reverses the direction of energy flow.
• Load torque and motor torque are in opposite direction, the combined effect will cause to reduce the speed of the motor and hence back emf (motor emf is directly proportional to the speed) falls again below the applied voltage value.
• Both current and voltage become positive and the motor settle down to first quadrant again.
• The process by which the mechanical energy of the motor is returned to the supply is called as regenerative braking.

REVERSE MOTORING - QUADRANT III

• The third quadrant operation of the motor in which both motor voltage and current are negative. Thus the power is positive, i.e., the power is supplied from source to load.
• Reverse polarity of the supply, the motor starts rotating in a counterclockwise direction (or reverse to normal operation). The torque and speed are negative. 
• The operation of this quadrant is similar to the first quadrant, but only difference is the direction of rotation. 
• The magnitude of voltage to the motor decides the appropriate speed in reverse direction 
• Motor movements produced are counterclockwise.

REVERSE BRAKING - QUADRANT IV

• This is the quadrant-4 mode of operation in which motor voltage is still negative and its armature current is positive.This mode of operation is similar to the second quadrant operation and once again the regeneration occurs whenever the back emf is more than the negative supply voltage. 
• Hence the torque will be positive which opposes the load torque, thus the speed of the motor will be reduced during reverse  operation of the motor. ‘This mode of operation is mostly used for plugging in order to stop the motor rapidly. During plugging, the armature terminals are suddenly reversed, which causes the back emf to force an armature current to flow in reverse direction.
• Now the effective voltage across the motor becomes 2V (as V+ Eb). A braking resistor in series with the motor has to be connected to limit this current. Braking by plugging gives greater torque and more rapid stop, but the current drawn from the supply and energy stored in mechanical parts must be dissipated in resistance.