5 March 2020

Inverter Interview Question Answer - 1


1
Describe the function of the Inverter.


Function of the Inverter
  • The function of the inverter is to convert fixed DC into variable voltage, variable frequency alternating supply.


2
Explain the term : DC link converter


DC link converter
  • It is a combination of the AC to DC converter and DC to AC converter. The input and output stage is AC whereas the intermediate stage is DC.
  • The DC link converter consists of rectifier at the input stage and inverter at the output stage. 
  • It is a two stage static frequency converter in which the alternating power at source frequency is rectified and filtered.
  • The output of the rectifier is fed to the input of the inverter which convert fixed DC into variable voltage, variable frequency alternating supply.


3
What should be input of the inverter?


It may be DC source, battery, fuel cell, solar cell or rectifier.

4
Which semi conductor device is used in the inverter circuit for the high power output?


Silicon controlled rectifier ( SCR )

5
Which semi conductor device is used in the inverter circuit for the low power output?


Semiconductor Devices
  • Bi – junction  transistor ( BJT )
  • Gate turn off thyristor  ( GTO )
  • MOS controlled thyristor ( MCT )
  • Metal oxide field effect transistor  ( MOSFET )


6
Which type of wave shape the output voltage of the ideal inverter consists of?


Sinusoidal

7
On which factor the output frequency of the inverter depends?


Switching time of the semiconductor device


8
Describe the different types of the inverter.


Types of inverter
According to output supply
  • Single phase
  • Three phase

According to input source
  • Voltage source
  • Current source

According to output waveform
  • Square wave
  • Pulse width modulation
  • Quasi square wave

According to commutating components connections
  • Series
  • Parallel

Bridge inverter : Half bridge and Full bridge
According to method of commutation
  • Line
  • Forced


9
What is meaning of the forced commutated inverter and line commutated inverter?


Forced commutated inverter
  • The inverter in which the SCR turns off by naturally zero is called as the naturally commutated inverter.

Line commutated inverter
  • The inverter in which the SCR turns off by forced commutation is called as the forced commutation inverter.


10
How many switching semiconductor devices are used in the single phase half bridge inverter?


Two

11
Explain the term : Cross conduction or shoot – through – fault 


Cross conduction ( shoot – through – fault )
  • The single phase half bridge inverter in which incoming and outgoing semiconductor switches conduct simultaneously for a short time is called as cross conduction or shoot – through – fault.

                                                                                          
12
Describe the effect of shoot – through – fault effect.


Effect of shoot – through – fault
  • The DC input supply is short circuited and both switching semiconductors are damaged.


13
How the cross conduction of the semi – conductor device is avoided?


Cross conduction
  • The cross conduction of the semi – conductor device is avoided by dead band or delay is introduced between the trailing edge of the base drive of the  outgoing semi – conductor device and leading edge of the base drive of the incoming semi – conductor device.  
  • The dead band should be longer time than that of the turn off time of the switching semiconductor devices.


14
How many switching semi – conductor devices conducts during dead band in the single phase half bridge inverter?


Not a single semi – conductor

15
How many switching semiconductor devices are used in the single phase full bridge inverter?


Four

16
What is meaning of the voltage source inverter and current source inverter?


Voltage source inverter
  • It is inverter in which the output voltage remains constant for a given type of load. 
  • The large capacitor is connected at the input side of the inverter.

Current source inverter
  • It is inverter in which the input current remains constant for a given type of load. 
  • The large inductor is connected in series with the supply source at the input side.


17
Describe the different method of voltage control of the single phase inverter.


Method of voltage control
External control
  • AC output voltage
  • DC input voltage

Internal control
  • Series parallel control

Pulse width modulation ( PWM ) control
  • Single PWM
  •  Multiple PWM
  •  Sinusoidal PWM


18
What is meaning of the pulse width modulation technique?


Pulse width modulation
  • It is technique in which the on and off time of the switching semiconductor is varied.


19
Describe the advantages and disadvantages of the PWM techniques.


Advantages
  • The output voltage can be control without any external components. 
  • Lower order harmonics are eliminated therefore the filter requirement is minimized whereas the higher order harmonics are easily filtered.

Disadvantages
  • The inverter grade SCRs requires which have low turn on and turn off time.



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