chopper circuits(power electronics)

Object

To study the chopper circuit through simulation

Apparatus used

Computer

Theory and formula used

Let f be the frequency of switching of transistor switch, V_s is the DC source voltage: R L and E be the load resistance, inductance, and the back EMF of a DC machine (The battery voltage for a battery load) load respectively.

When transistor is ON (Mode 1)

V_o=V_s

When transistor is OFF but the chopper is in continuous current conduction mode (Mode 3)

Mode 1 (Calculation of maximum current in the discontinuous current mode)

Mode 2 (Calculation of maximum turn on time for discontinuous conduction)

Where :

At the boundary of continuous and discontinuous current mode

just at giving

At

Simplifying the equation:

Putting frequency f = 1/T

For L=1mH,R=0.5Ω,f=500 Hz and V_s=250V

Expressions for Discontinuous Current Conduction Mode

For Discontinuous Current Conduction Mode for ON period of transistor using Eq.1

At t = 0, i=I₂

At t=T_on, I = I₁ =

At t=T_on,

For OFF period transistor using Eq.2

At t=T_on, I = I₁ while I = I₂ at t=T

Therefore,

Substituting the value of I₂ in the expression of I₁

Similarly substituting the value of I₁ in the expression for I₂