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 POWER ELECTRONICS – PAGE 13

Numerical Problems – Full Wave Controlled Rectifier

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Problem 1

A single phase full wave controlled rectifier has V_m = 250 V and firing angle α = 60°. Find the average output voltage.

Solution

V_avg = (V_m / π) (1 + cos α)

cos 60° = 0.5

V_avg = (250 / π)(1 + 0.5)

= (250 / 3.1416) × 1.5 = 79.58 × 1.5 = 119.37 V

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Problem 2

Input RMS voltage = 230 V. Firing angle α = 90°. Find average output voltage.

Solution

Convert RMS to Peak:

V_m = √2 × 230 = 325 V

cos 90° = 0

V_avg = (325 / π)(1 + 0)

= 325 / 3.1416 = 103.47 V

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Problem 3

For what firing angle will the average output voltage become zero?

Solution

From formula:

(1 + cos α) = 0

cos α = −1

α = 180°

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Problem 4 (Bridge Type)

For a fully controlled bridge rectifier, V_m = 300 V, α = 60°. Find V_avg.

Solution

V_avg = (2V_m / π) cos α

cos 60° = 0.5

V_avg = (2 × 300 / π)(0.5)

= (600 / 3.1416) × 0.5 = 190.98 × 0.5 = 95.49 V

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GATE / PSU Focus Points

• Always identify midpoint or bridge type
• Check whether RMS or Peak is given
• Remember: Full wave gives double output of half wave
• Bridge formula differs from midpoint formula