Ef510 Assignment 1 2024

POWER ELECTRONICS – EF510
ASSIGNMENT 1 AND 2
DATE DUE: 16th JUNE, 2024.
ASSIGNMENT ONE
QUESTION ONE
The single-phase half-wave rectifier of Figure 1 has a freewheeling diode and a ripple free
average load current of 𝐼𝑎 . (a) Draw the waveforms for the currents in 𝐷1 , 𝐷𝑚 , and the
transformer primary; (b) express the primary current in Fourier series; and (c) determine the
input PF and HF of the input current at the rectifier input. Assume a transformer turns ratio of
unity.
Figure 1.
QUESTION TWO
The battery voltage in the Figure 2 is 𝐸 = 12𝑉 and its capacity is 100 𝑊ℎ. The average charging
current should be 𝐼𝑑𝑐 = 50 𝐴 . The primary input voltage is 𝑉𝑝 = 120𝑉 , 60Hz, and the
transformer has a turns ratio ℎ = 2: 1. Calculate (a) the conduction angle δ of the diode, (b) the
current limiting resistor R, (c) the power rating 𝑃𝑅 of R, (d) the charging time h in hours, (e) the
rectifier efficiency η, (f) the peak inverse voltage PIV of the diode.
Figure 2.
1
QUESTION THREE
The three-phase full-wave rectifier has a load of L = 2.5 mH, R = 5 Ω, and E = 20 V. The line-to-
line input voltage is 𝑉𝑎𝑏 = 208 𝑉 , 60 Hz. ). (a) Use any suitable software to plot the
instantaneous output current 𝑖0 . (b) Determine (1) the steady-state load current 𝐼0 at ωt = π/3, (2)
the average diode current 𝐼𝐷(𝑎𝑣 ) , (3) the rms diode current 𝐼𝐷(𝑟𝑚𝑠 ) , and (4) the rms output current
𝐼0(𝑟𝑚𝑠 ) .
QUESTION FOUR
The three-phase bridge rectifier has an RL load and is supplied from a Y-connected supply. (a)
Use the method of Fourier series to obtain expressions for the output voltage 𝑣0 (𝑡) and load
current 𝑖0 (𝑡). (b) If peak phase voltage is 𝑉𝑚 = 170 𝑉 at 60 Hz and the load resistance is R =
200 Ω, determine the load inductance L to limit the ripple current to 2% of the average value 𝐼𝑑𝑐 .
QUESTION FIVE
The LC filter is used to reduce the ripple content of the output voltage for a six-phase star
rectifier. The load resistance is R = 20 Ω, load inductance is L = 7.5 mH, and source frequency is
60 Hz. Determine the filter parameters L and C so that the ripple factor of the output voltage is
3%.
ASSIGNMENT TWO
QUESTION ONE
For the 12-pulse thyristor rectifier shown in Figure 1 the output current is ripple free with
constant value of 1000 A and the thyristor firing angle 𝛼 = 60°. Calculate: (a) The active power
drawn by the load, (b) The reactive power drawn by the load, (c) The power factor of the rectifier,
(d) The rms value of the input line current, (e) The THD% of the input line current, and (f) The
peak value of the input line current.
Figure 1.
2
QUESTION TWO
A single-phase full-bridge fully controlled thyristor rectifier has a RLE load. The following
specifications are given: 𝑉𝑖 = 230 2𝑠𝑖𝑛 100𝜋𝑡 , 𝑅 = 4 Ω, 𝐿 = 40 𝑚𝐻, 𝐸 = 80𝑉, and firing
angle 𝛼 = 30°. Use Fourier Series to calculate the following:
(a) The average output current.
(b) The rms output current.
(c) The power delivered to source E.
(d) The input power factor
Verify the theoretical results with simulation results.
QUESTION THREE
A 3-phase full converter is fed from 3-phase, 230 V, 50 Hz supply having per-phase source
inductance of 4 mH. The load current is 10 A ripple free.
(a) Calculate the voltage drop in dc output voltage due to source inductance.
(b) If dc output voltage is 210 V, calculate the firing angle and the overlap period .
(c) In case the bridge is made to operate as a 1ine commutated inverter with dc voltage of 210 V,
calculate the firing angle for the same load current.
QUESTION FOUR
A single-phase bidirectional ac voltage controller delivers a load power of 50 kW with an
efficiency and power factor of 0.9 and 0.85 respectively. The input voltage is 230 V, 50 Hz.
Determine the maximum possible ratings of (a) average and rms thyristor currents and (b)
repetitive voltage of the thyristors.
QUESTION FIVE
A three-phase full-wave (or bidirectional) controller (star connected) has a Y-connected
resistive load.. For 0 ≤ 𝛼 < 60°, show that the rms output voltage for Y-connected load is given
by
1 2
1 𝜋 𝛼 𝑠𝑖𝑛2𝛼
𝑉𝑜 = 6𝑉𝑠 − +
𝜋 6 4 8
QUESTION SIX
The three-phase full-wave ac voltage controller (star connected) is used to control the power
from a 2400-V, 60-Hz, ac source into a delta-connected resistive load. The maximum desired
output power is 150 kW. Calculate (a) the maximum rms current rating of thyristors 𝐼𝑅𝑀 , (b) the
maximum average current rating of thyristors 𝐼𝐴𝑀 , and (c) the peak value of thyristor voltage 𝑉𝑝 .
Verify the theoretical results with simulation results.
QUESTION SEVEN
A single-phase to single-phase bridge-type cycloconverter is fed from 230 V, 50 Hz source and
has a load R = 20 Ω. Output frequency is one-fifth of input frequency. For a firing angle delay
of 45°, calculate (a) rms value of output voltage (b) rms current for each converter (c) rms
current of each thyristor and (d) input power factor.
Derive the expression for rms output voltage for this cycloconverter.
3
QUESTION EIGHT
1
Cycloconverter circuit of Figure 2 used for obtaining on output frequency 𝑓𝑜 = 3 × source
'frequency 𝑓𝑠 . Turns ratio from primary to upper secondary is 1/1 and to lower secondary is 1/n.
Derive expression for the rms value of output voltage for firing angle 𝛼. For 𝑉𝑠 = 230𝑉, 50 Hz;
n = 3; 𝑅 = 20 Ω and 𝛼 = 45°, find the load power.
Figure 2.

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POWER ELECTRONICS – EF510

DATE DUE: 16th JUNE, 2024.

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