Test: Chopper- 2 - Electrical Engineering (EE) MCQ

The average value of load current

The maximum value of load current

Now, the average value of the voltage is

Also, 
or, 
or,
or, 

The output voltage,
V₀ = αV_s = 0.6 x 220 - 132 V
∴ Back emf

At no- load, N₁, = 1500 rpm and E_b1 = 220 V Now, E_b α N
∴ 
or, 
or, 

As the motor is running at 1710 rpm its back emf is
Since  therefore current flows in the reverse direction and hence second quadrant chopper will be used with the motor.
Now, 
= 230.8 volt
Also, V₀ = (1 - α) V_s
or, 230.8 = (1 - α) x 250
or, 1 - α = 0.9232 or α = 0.0768
or, α = 7.68% = 7.7%

For a four-quadrant chopper, the average voltage in all the four-modes is given by
V₀ = 2 V_s (α - 0.5)
The average curreni,

or, 
or,    α = 0.877
Since α > 0.5, the motor is operating undi
forward motorina mode.

For a type-A chopper, average output voltage





 

• Type-A chopper is also called “step-down chopper” as average output voltage V₀ is always less than the input dc voltage V_s.
• Type-B chopper is also called “step-up chopper” as load voltage 
which is more than source voltage Vs.
• Type-C chopper configuration is suitable for motoring and degenerative braking of dc motors.
• Type-D chopper characteristic is shown below

• DC choppers can be used in only dc drives.
• Output voltage from a chopper circuit depends only on duty cycle and is independent of load current.
Hence, statements 1 and 3 are not correct.

Given, V_s = 230 V
Load resistance, R_L = 10Ω   α = 0.4
When chopper is ON,
output voltage = (V_s - 2) volt
When chopper is OFF, output voltage = 0 volt
Average output voltage

Rms output voltage,


Power output delivered to load is

= 2079.364 Watt
Power input to chopper;

Chopper efficiency

Boost-regulator is a step-up chopper.
Output voltage,

or, 
or,