Question

Your supervisor suggests the article entitled “Design and implementation of firing circuits for single-phase converter” by T. Sen and P. K. Bhattacharya, International Journal of Computer and Electrical Engineering, vol. 3, no. 3, June 2011. The article is uploaded in your e-learning. Read the article and answer the following questions. 1- We can see that some types of Power Electronic Switches are introduced in the article’s introduction section. What are they? Can you briefly tell their different application levels and the benefit of each one? 2- Based on the article, there are two conditions under which a thyrsitor conducts current. What are those?

Answer 1

1. Thyristors or SCRs : Used as a switching device in the medium and large power levels starting from few kilowatts to several
mega watts at voltage levels of few hundred to several kilovolt levels. Cheaper than IGBTs and can function at very high voltages comapred to IGBTs, hence a better choice for line commutated converters.

Bipolar Junction Transistors (BJTs): Better voltage gain and very fast switching characteristics compared to SCRs, but uses are limited to medium power levels at few hundred volts.

Metal Oxide Semiconductor Field Effect Transistors (MOSFETs): Fast switching characteristics compared to SCRs, but uses are limited to medium power levels at few hundred volts. They operate at lower power and draws no current.

Insulated Gate Bipolar Transistors (IGBTs) : High voltage capability, low ON-resistance, ease of drive, relatively fast switching speeds and combined with zero gate drive current makes it a good choice for moderate speed, high voltage applications.

2.Thyristor conducts current if

i) The Anode is at higher voltage than the Cathode i.e. V_AK >0

ii) The Gate is at higher voltage than the Cathode i.e. V_GK>0