GATE Electrical Engineering Power Electronics Syllabus

Power Electronics syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Power Electronics in GATE Electrical Engineering, not a summary of it.

1. 1

   Static V-I characteristics and firing/gating circuits

   3 topics

   • Thyristor
   • MOSFET
   • IGBT
2. 2

   DC to DC conversion

   3 topics

   • Buck Converter
   • Boost Converter
   • Buck-Boost Converter
3. 3

   Single and three-phase configuration of uncontrolled rectifiers

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

4. 4

   Voltage and Current commutated Thyristor based converters

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

5. 5

   Bidirectional ac to dc voltage source converters

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

6. 6

   Magnitude and Phase of line current harmonics for uncontrolled and thyristor based converters

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

7. 7

   Power factor and Distortion Factor of ac to dc converters

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

8. 8

   Single-phase and three-phase voltage and current source inverters

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

9. 9

   Sinusoidal pulse width modulation

   overview

   Examined as a single unit within Power Electronics — no further topic split in the official outline.

Power Electronics flashcards for GATE Electrical Engineering

18 of 51 cards from the Power Electronics deck — real questions with worked answers.

1. What is a thyristor (SCR), and how many layers and junctions does it have?

   A thyristor (Silicon Controlled Rectifier) is a four-layer ($P\text{-}N\text{-}P\text{-}N$), three-junction ($J_1, J_2, J_3$), three-terminal (anode, cathode, gate) unidirectional power switch that conducts current in one direction once triggered.

2. List the three terminals of a thyristor (SCR).

   Anode (A), Cathode (K), and Gate (G).

3. What are the three modes of operation of a thyristor?

   Forward blocking mode (off), forward conduction mode (on), and reverse blocking mode (off).

4. How is a thyristor turned ON?

   By applying a positive gate current pulse $I_G$ while the device is forward biased (anode positive w.r.t. cathode). Once latched, it stays on even after the gate signal is removed.

5. What is the latching current $I_L$ of a thyristor?

   The minimum anode current required to keep the thyristor in the ON state immediately after it has been triggered and the gate signal removed. It is typically 2–3 times the holding current.

6. What is the holding current $I_H$ of a thyristor?

   The minimum anode current required to maintain conduction. If the anode current falls below $I_H$, the thyristor turns off. Generally $I_L > I_H$.

7. Why can a thyristor not be turned OFF by the gate?

   Because the regenerative (latching) action of the two internal coupled transistors ($\alpha_1 + \alpha_2 \geq 1$) keeps it conducting; the gate loses control once latched. It must be turned off by reducing anode current below $I_H$ (commutation).

8. State the two-transistor model condition for a thyristor to turn ON.

   The SCR latches when the sum of the common-base current gains satisfies $\alpha_1 + \alpha_2 \geq 1$.

9. What is the difference between natural (line) commutation and forced commutation of a thyristor?

   Natural/line commutation: the AC supply itself drives the anode current below $I_H$ (used in AC circuits/converters). Forced commutation: external L–C circuitry forces the current to zero in DC circuits (used in choppers/inverters).

10. Define the $\frac{di}{dt}$ rating of a thyristor.

    The maximum permissible rate of rise of anode current. Exceeding it causes local hot-spot heating near the gate-cathode junction (current cannot spread fast enough), damaging the device. A series inductor limits $\frac{di}{dt}$.

11. Define the $\frac{dv}{dt}$ rating of a thyristor and how it is protected.

    The maximum rate of rise of forward anode-cathode voltage; exceeding it causes false turn-on via junction capacitance charging current $i = C_j\frac{dv}{dt}$. Protected by a snubber (RC) circuit across the device.

12. What is a snubber circuit used with a thyristor?

    An $R\text{-}C$ network connected across the thyristor to limit $\frac{dv}{dt}$ and suppress voltage transients, preventing accidental (false) turn-on.

13. What is the typical V-I characteristic feature distinguishing thyristor forward conduction from forward blocking?

    In forward blocking, only small leakage current flows up to the forward breakover voltage $V_{BO}$; after triggering, the device switches to the low-voltage, high-current forward conduction branch. Higher gate current reduces the required $V_{BO}$.

14. What type of device is a MOSFET (in power electronics), and is it voltage- or current-controlled?

    A power MOSFET is a majority-carrier, voltage-controlled, three-terminal (gate, drain, source) unipolar device. It is controlled by gate-source voltage $V_{GS}$ and draws essentially zero steady-state gate current.

15. Name the three terminals of a MOSFET.

    Gate (G), Drain (D), and Source (S).

16. What is the threshold voltage $V_{th}$ (or $V_{GS(th)}$) of a MOSFET?

    The minimum gate-to-source voltage required to form a conducting channel and turn the MOSFET on. For an n-channel enhancement MOSFET, conduction begins when $V_{GS} > V_{th}$.

17. Why are power MOSFETs preferred for high-frequency switching applications?

    Because they are majority-carrier devices with no minority-carrier storage, giving very fast switching speeds and low switching losses; they switch at much higher frequencies than BJTs or thyristors.

18. What is $R_{DS(on)}$ in a power MOSFET and why does it matter?

    It is the drain-to-source on-state resistance. Conduction loss is $P_{cond} = I_D^{2} R_{DS(on)}$. A low $R_{DS(on)}$ reduces conduction losses; it increases with temperature (positive temperature coefficient).

See more Power Electronics flashcards →

Planning Power Electronics for GATE Electrical Engineering

Power Electronics (GATE Electrical Engineering) FAQ