Test: Step Up Choppers - Electrical Engineering (EE) MCQ

Concept:

The output voltage of a step-up chopper is given by:

where, V_o = Output voltage 

V_in = Input voltage

D = Duty cycle

The duty cycle is given by:

T_ON is the pulse width of the output.

Calculation:

Given, V_o = 500 V

V_in = 220 V

T_off = 80 μs

Identification of DC-DC Converter:

• Buck converter: Inductor is connected in series with the combination of the capacitor and resistor.
• Boost converter: Inductor is connected in series with the supply voltage source.
• Buck-Boost converter: Inductor is connected in parallel to the supply voltage source.

Under steady-state operating conditions:

• The average voltage across the inductor is zero. V_L = 0
• The average current across the capacitor is zero. I_C = 0

Given DC-DC converter is a Boost converter with duty cycle ratio δ.

The voltage across the load is the same as the voltage across the capacitor.

Concept:

For a buck-boost converter,

Calculation:

Given that,

Source voltage (V_DC) = 32 V to 72 V

Output voltage, (V₀) = 48 V

For a buck-boost converter,

Where D is duty ratio

When V_DC = 32V,

Concept:

The circuit diagram of a boost converter is shown below.

Step Up or Boost converter is used to obtain the output voltage greater than the input voltage.

The relation between the output voltage and the input voltage is given by

Where D is the duty cycle of the chopper

Calculation:

Duty ratio = 50 % = 0.5

Input voltage (VS) = 25 V

Average output voltage (Vo) =

Formula:

Where, Vo is the output voltage

V_in is the input voltage

T_ON is the pulse width

Application:

Given,

V_in = 200 volts

T_ON = 200 µs

V₀ = 600 V

From equation (1),

or, 3T - 600 = T

Hence, T = 300 µs

If the Pulse width is half then, the new value of pulse width (T_ON') will be,

Hence,

Hence, the new value of output voltage (V_0') will be,

Concept:

When the switch is ON:

Applying KVL as per loop:

Calculation:

Concept: 

The output voltage of a step-up chopper is given by:

where,

V_o = Output voltage

V_S = Input voltage

D = Duty cycle

The duty cycle (D) is

where,

T_ON = Conducting period or pulse width in seconds

T_OFF = Non-conducting period in seconds.

T = Total conducting period = Pulse width.

T = T_ON + T_OFF

Calculation:

Given

 T_ON =150 μs

Vo =  500 V

VS = 200 V

T = 250 μs

Concept

At the edge of the continuous conduction, the value of inductance becomes minimum and such value of inductance is known as the critical inductance of the converter.

At the boundary of continuous conduction, I_L(min) = 0

Calculation of ΔI_L

When the switch is ON:

Putting this value in equation (i):

The value of the minimum inductance (Lmin) for continuous current for a boost converter is given by:

Concept:

The circuit diagram of a boost converter is shown below.

A step-up or Boost converter is used to obtain the output voltage greater than the input voltage.

The relation between the output voltage and the input voltage is given by

Where D is the duty cycle of the chopper

Calculation:

Input voltage (VS) = 100 V

Average output voltage (Vo) = 60 V

Concept:

The circuit diagram of the buck converter is shown below.

The waveforms of current flows through the resistor, inductor, and capacitor are shown below.

The waveforms of ripple current and voltage are shown below.

Calculation:

For buck converter, peak to peak ripple current is given by,