cameroon gce advanced level 2025 power electronics 2
cameroon gce advanced level 2025 power electronics 2
3. Chopper
(Image of Figure 4, a chopper circuit with a DC source, switch K, diode D, inductor L, and motor M.)
In the circuit of Figure 4, the supply voltage of the series chopper is constant with a value of Vs=210V.
D is an ideal diode and K is a perfect switch.
The duty cycle ratio is α and the period is T which is equal to 0.1ms.
For t∈[0;αT], K is closed.
For t∈[αT;T], K is opened.
It is considered that the voltage at the terminals of the motor is equal to its emf E and E is proportional to the rotational speed of the motor: E=kn with k=5.25×10−2 V/(rev/min).
It is assumed that the current i varies linearly between the minimum and maximum values Imin and Imax.
a) Give the expression of i(t) for the interval
i. t∈[0;αT] (2 marks)
ii. i(t)∈[αT;T]. (2 marks)
b) Draw in synchronism the waveform of , , and for two periods. (7 marks)
c) Give the expression of the average load voltage in function of and . Deduce the relation between E, and . (4 marks)
d) Express the ripple current in function of , , L and T. (4 marks)
e) What value of that is maximum? Calculate the value of . (4 marks)
f) Calculate the value of to regulate the rotational speed to . (3 marks)
g) Express the average values of and . (4 marks)
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