Test: Power Electronics- 4 - Electrical Engineering (EE) MCQ

Advantage of freewheeling diode

1. It prevents the output voltage from becoming negative

2. System efficiency is improved because energy stored in L is transferred to load R through FD.

3. Load current waveform is more smooth.

4. It reduces the reactive power demand of the converter.

5. It improves the displacement factor.

6. It improves distortion factor.

7. It improves the input PF.

PIV = V_m + E = 220√2 + 80 = 3 91.13 V

Single phase full wave half controlled bridge converter feeds an Inductive load. The two SCRs in the converter are connected to a common dc bus. The converter has to have freewheeling diode because the converter does not provide for freewheeling for high value of triggering angles

Voltage regulation = 
for single phase full converter bridge

due to source inductance effect 

Where μ is overlapping angle and α is firing angle
for α = 0, V₀ =  and

Voltage regulation

the average output voltage for single phase with a freewheeling diode

The average output current 

120 × 3.14 = 600 cos 30° - 3140 Ls

376.8 = 519.61 – 3140 Ls

-142.82 = -3140 Ls

Ls = 45.48 mH

Average value of output voltage

Average value of output current 
R.M.S value of diode current  
Load power = V_oI_o = 198.17 × 13.21 = 2617.83 W

Input power = V_sI_s cos ϕ

220 × 13.21 cos ϕ = 2617.83

cos ϕ = 0.9

Concept
R.M.S value of output voltage is


Calculation

The load current is Ripple free

∴ Ior = 197.32/15 = 13.15 A

Pdc = VoIo = 148.63 × 9.91 = 1472.93 W

Pac = VorIor = 197.32 × 13.15 = 2595.46 W

Rectification efficiency = 

Conduction diagram

From the conduction diagram the thyrsistor conduct for (π – α) radian while the diodes conducts for (π + α) radians. Since the load current is constant.

= 0.845