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: TON/ TON + TOFF
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 – 180o 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:
- 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 – IH = IL = 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.
Vo = VS /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.