Interview Questions and Answer for Power Electronics Design Engineer:

In this tutorial we are going to learn about Interview Questions and Answer for Power Electronics Design Engineer:

Question 1 – What is Power Electronics?

Answer – Power Electronic deal with how to control and convert power (Electric energy) into one form to another and how to utilize of power at high efficiency.

Question 2 – What is firing angle?

Answer – The angle between the zero crossings of the input voltage and instant SCR is fired is called as delay or fire angle.

Question 3 – What is duty cycle?

Answer – It is the ratio of the ON time of the chopper to total time period of the chopper is called duty cycle.  Duty Cycle: T_ON/ T_ON + T_OFF

 Question 4 – What is latching current in SCR?

Answer –  It is minimum current required to latch (Turn ON) the SCR from forward blocking state to forward conduction state.

Question 5 – What is Thyristor?

Answer –A thyristor is a four layer semiconductor device , It is consist of two PN junction connected back to back PNPN, The most common Thyristor is the silicon controlled rectifier (SCR) . Thyristor are used in Motor speed control , pressure control system and liquid level regulations.

Question 6 – What is Snubber circuit?

Answer – The Snubber circuit is used for DV/DT protection of the SCR, It is series combination of a resistor and capacitor parallel with SCR.

Question 7 – What is difference between traic and thyristor?

Answer – A thyristor is also known as SCR is unidirectional device, Its normal operation it pass current in one direction only. A Triac is a bidirectional device, It will pass current in both direction, so that it used to switch alternating current.

Question 8 – What is minimum gate current required to turn on SCR?

Answer –Triggering current required at gate to turn on SCR.

Question 9 – What is use of SCR?

Answer – SCR is current controlled voltage blocking switch.

Question 10 – How many layers in DIAC?

Answer – 5 Layers in DIAC.

Question 11 – What is use of Traic?

Answer – It is used for switch in flood light and industrial heating.

Question 12 – How connect freewheeling diode with load?

Answer – Freewheeling diode connect with load in Parallel.

Question 13 – When maximum power loss in SCR?

Answer –During the raise time maximum power loss in SCR.

 Question 14 – What is use of cyclo – converter?

Answer – It is also known as Frequency Changer, It converts input power at one frequency to output power at another frequency with one stage converter.

Question 15 – What is period of maximum conduction of SCR?

Answer – 180^o angle

Question 16 – What is behaving of forward blocking mode of SCR?

Answer – It is behaving like Capacitor at forward blocking mode of SCR.

Question 17 – What is commutation in SCR?

Answer – It can use for input power factor is improved, It is also prevents the output voltage from becoming negative, Load current waveform is improved.

Question 18 – What is AC voltage controller?

Answer – This device can converts fixed alternating voltage to a variable voltage without change in frequency.

Question 19 – What is inverter?

Answer – A device which converts DC power into AC power at desired output voltage and frequency is called s inverter.

 Question 20 – What is Circuit turn OFF time?

Answer – A time during which a reverse voltage is applied across the thyristor during its commutation process.

Question 21 – What is Chopper & Its types?

Answer – It is equivalent to the transformer in ac circuit. It is static switch used to get the variable DC voltage from a constant DC voltage.

Two types of DC chopper:

1. Step – Up Chopper 2. Step – Down Chopper

Question 22 – What is Power diode & Signal diode?

Answer – Power Diode – The voltage, current and power rating is higher, Power diodes operate at high speed.

Signal diode – The voltage, current and power rating is lower, Power diodes operate at higher switching speed.

Question 23 – Why mostly use IGBT?

• Answer – The insulated gate bipolar transistor is easy to turn ON and OFF.
• Lower switching losses
• Smaller snubber circuit required.

Question 24 – For high frequency application what we prefer Mosfet or IGBT?

Answer – For high frequency application mosfet is best choice because mosfet has low switching loss as compare with IGBT.

Question 25 – How many types topology of SMPS?

Answer – Main topology of SMPS – 1.Buck, 2. Boost, Buck-boost,. Fly back topology.

Question 26 – What are the advantage of PWM technique for voltage control?

• Answer –The output voltage control with method can be obtained without any additional components.

Question 27 – What are the application of current source inverter?

• Answer – Speed control of AC motor.
• Induction heating
• Synchronous motor starting

Question 28 – What is meaning of series inverter?

Answer – A inverter in which the commutating elements connected in series with load.  

Question 29 – What are two method of control in AC voltage controller?

Answer – 1. ON OFF control and 2. Phase control.

Question 30 – How many junctions in SCR?

Answer – 3 junctions in SCR.

Question 31 – If latching current of SCR is 18mA then how much holding current?

Answer – I_H = I_L = 18/3 = 8mA

Question 32 – Is DIAC have gate terminal?

Answer – NO DIAC doesn’t have gate terminal.

Question 33 – What is used to protect a thyristor from high di/dt conditions?

Answer – Inductor does not allow sudden change in current through it.

Question 34 – A boost regulator has an input voltage of 5V and the average output voltage of 15V. then what is duty cycle ?

Answer – Boost regulator is step up chopper.

V_o = V_S /1-ὰ = 15 = 5/1- ὰ = 2/3

Question 35 – If 4 thyristor rated 200V in series, The operating voltage of the string is 600V then what is drafting factor?

Answer – String Efficiency = 600/4×200 = 0.75

DRF = 1-0.75 = 0.25

Question 35 – What is the waveform for input and output voltage in DC chopper?

Answer – Continues and Discontinues mode

Question 36 – How can protect the thyristor from over voltages?

Answer – By using of voltage clamping protect the thyristor from over voltages.

Question 37 – What is Buck topology?

Answer – This is also called step down technology and output voltage is lesser than input voltage is called Buck topology.

Question 38 – What is Boost topology?

Answer – This is also called step UP technology and output voltage is higher than input voltage is called Buck topology.

Question 39 – What is Buck-Boost topology?

Answer – In this technique we can get both condition step up or step down as per requirement.

Question 40 – What is fly-back topology?

Answer – Fly-back topology working on transformer when switch off then it release the energy from primary to secondary winding , It is use in AC to DC and DC to DC.