8/18/2019 Assignment5-2015

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CONCORDIA UNIVERSITY

DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

Power Electronics (I) ELEC-433/6411

Assignment #5: HVDC and AC controller

Due date: December 8, 2015, at 6:00 PM in the mailbox of Dr. Lopes (EV5.175).

1) 

The elementary 6-pulse HVDC system shown below is used to connect 2 ac systems of

different frequencies. The line resistance is equal to 1.2Ω. The line inductance can beneglected in this study. Both ac systems are rated at 25 kV and are to be represented by ideal

ac sources. The frequency at the left-hand side is 60 Hz and at the right-hand side is 50 Hz.

The HVDC terminals are implemented with “valves” of the T1901N SCR from Infineon that

presents:  I TAVMax = 2.1 kA, VDRMax/RRMax = 8 kV and t q (minimum reverse blocking, or turn-off, time) = 550 us. A) For power flowing from the left- to the right-hand side, what would

be the minimum extinction angle (γ min) one could use safely, without risking commutation

failures? For the following calculations, consider that an extinction angle of 2 γ min is used inthe inverter terminal. B) What is the maximum active power that could be transmitted in the

system in this case? C) Compute (Q3φ), the reactive power absorbed by both converters,

rectifier and inverter, for this condition. D) What should be the frequencies of the tuned

filters in the DC and AC sides of the converters, rectifier and inverter? E) How many SCRswould one need in series to withstand the voltage imposed in each “valve of SCRs?”

2) 

Consider a 6-pulse (∆-connected) TCR connected to a transmission line by means of a 500kVLL /18 kVLL coupling transformer. A) What should be the value of the required inductances

so that the three-phase TCR can absorb a maximum of 60 MVAr? B) How much reactive

power would it absorb when the firing angle of the thyristors is 150°? C) Draw the followingwaveforms for α = 120°: (i) line voltage in the output of the transformer, (ii) voltage across

one inductor, (iii) voltage across the antiparallel thyristors and (iv) current through the

inductor. Hint: consider the KVL for one “phase of the three-phase TCR.” Now assume that2 three-phase Y-connected TSCs, rated at 30 MVA each, are placed in parallel with the TCR,

in the secondary of the coupling transformer. D) What should be the value of the

capacitances of each element of the TSCs? E) Assuming that the TSC was previously in

service (Vcap not zero), draw the following waveforms when the thyristors of the TSC arenot being fired: (i) voltage across one phase of the TSC (input voltage), (ii) voltage across

one capacitor, (iii) voltage across the antiparallel thyristors. Identify the maximum voltage

across the thyristors. Recall that the thyristors should be rated to withstand this voltage level.Hint: consider the KVL for one “phase of the three-phase TSC.”

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