Power Electronics and Power Systems
EE3C, Power Electronics and Power Systems
Task 1 (Marks: 20)
A three-phase 6-pulse diode rectifier, connected to a 3-phase AC supply, having a
voltage of 415 V (line-to-line RMS), a frequency of 50 Hz, and a per phase series
inductance of Ls = 5mH, feeds a static RL load.
Question 1
Draw the circuit diagram of the AC-DC diode converter.
[2]
Question 2
Implement this rectifier in Simulink. The diodes have a forward voltage drop of
1.0 V when conducting. Model the load as the series of a resistor R = 10 Ω and an
inductor L = 100 mH.
1. Show the diagram of the voltage across the load
[2]
2. Calculate the overlap angle according to the theory
[4]
3. Compare this overlap angle with that from the simulation.
[4]
Question 3
Using the circuit parameters of Question 2:
1. Discuss in maximum 2 sentences the advantages of reducing the
harmonic content of the output voltage by means of a low-pass filter.
[2]
2. Design the low-pass filter, with the order of your choice, for the case
indicated in Question 2
[3]
3. Use the Simulink model to compare the load voltage waveforms with
and without the filter.
[3]EE3C, Power Electronics and Power Systems, Dr P Tricoli
TURN OVER…
2/7
Task 2 (Marks: 40)
A three-phase 6-pulse, fully controlled thyristor rectifier supplies a static RL load, from
a three phase 415 V (line-to-line RMS), 50 Hz, AC supply having a per phase series
inductance of Ls = 2.5 mH.
Question 1
Draw the circuit diagram of the AC-DC thyristor converter.
[2]
Question 2
Implement this rectifier in Simulink. The thyristors have a forward voltage drop of
1.0 V when conducting. Model the load as the series of a resistor R and an
inductance L.
Investigate the following cases in the simulation study:
a) R = 50 Ω, L = 2 mH and Ls = 2.5 mH
b) R = 50 Ω, L = 200 mH and Ls = 2.5 mH
c) R = 10 Ω, L = 200 mH and Ls = 2.5 mH
d) R = 10 Ω, L = 200 mH and Ls = 10 mH
For all cases, the firing angle of thyristors has to be chosen to get an average voltage
of 500 V across the load.
In your report, you have to show and comment (maximum 2 sentences) the
following for all the cases:
1. the firing angles to achieve the desired load voltage;
[1+1+1+1]
2. the waveforms of the DC voltage across the load;
[2+2+2+2]
3. the values of the THD of the currents of the three phase AC supply;
[1+1+1+1]