cameroon gce A level 2024 power electronics 2
cameroon gce A level 2024 power electronics 2
SECTION A: COMPULSORY
1. SINGLE PHASE FULL WAVE CONTROLLED RECTIFICATION
A single phase, full wave rectifier bridge is connected to a 220V, 50HZ network through a transformer having a
transformation ration of 0.5. The rectifier supplies a 1500 resistor R in scries with a thyristor having a firing angle of a –
30°.The voltage at the secondary of the transformer is given by the expression V2 (t) –^V2msintol
d) Calculate:
i. The effective value of the voltage at the secondary of the transformer.
| ii. | The times t » and t2 when conduction starts and stops respectively. The effective values of the load voltage and current |
| 1.1. For a non inductive load (R, E) avec L=0 a) Sketch the waveforms of v( t9) and Ri ( 9 ) |
b) Calculate the reverse voltage across the diodes D| and D2
c) Knowing that the duration of conduction of the diode is 150°, determine the value of the emf E
d) Calculate the value of R to limit the current circulating in the diodes to 36A
1.2.We now assume that the load is inductive (E–0) with L high enough to make the conduction continuous
e) Sketch the waveforms v (
| i9 ), 1 ( »9 ), im ( 9 ), io2 ( 9 ) f) Calculate the average and effective value of the voltage v |
1.3.The load is now complete (RLE) with R–2.4£2, E ~–30.2V and L is high enough to make the load current i
constant
g) We assume that the average value of the load voltageVav = 74.3V, determine the average current 1JV(4 marks)
h) The voltage drop of the diodes is V 0 = 0.7–K).02iD, calculate the power dissipated by the diodes (4 marks)
A) The load L is a purely resistive R
a) Briefly describe the functioning of the circuit diagram in figure 3
b) Sketch the waveforms of VL, II, VTHI by indicating the period of conduction of each thyristor and
diodes
c) Determine the expression of the effective current in the load in terms of R, a, and V where V is the
effective value of v
d) Deduce the expression of the power transmitted to R
e) V= 220V, R=20Q, Calculate the power for a = 0, a = n
