Single Phase Full Wave Controlled Bridge Rectifier

[Physicist3]

Homework Statement

For a bridge rectifier (4 thyristor) feeding an RL load having infinite inductance (to assume constant current) and a 100 ohm resistance, calculate for firing angles of 90°, 120° & 150° the average DC voltage and current. The bridge supply is 200V RMS. Draw Waveforms of load voltage, thyristor currents & supply current.

Homework Equations

V_av = 2V_m/PI * Cos(α).

I_av = V_av/R

The Attempt at a Solution

90°

V_av = (sqrt(2) * 200)/PI * cos(90) = 0.0V

I_av = 0A

120°

V_av = (sqrt(2) * 200)/PI * cos(120) = -45.01V

I_av = -45.01/100 = 0.4501A

150°

V_av = (sqrt(2) * 200)/PI * cos(150) = -77.97V

I_av = -77.97/100 = 0.7797A

I understand how the waveforms for the voltage should be but in the book solutions, for 90° firing angle, it shows a positive current for each thyristor, whereas the average value calculated is 0.0A hence it would be suggested that there should be no current. Also, for the firing angles of 120 & 150, should the current be inverted in terms of the currents for 30 and 60 degrees where the current is the positive value of the values for 150 and 120 respectively?

 

[gneill]

I think you'll want to integrate over a period to find the average values. Perhaps you might begin by sketching the load voltage or current for one of the firing angle cases.