05/03/2020

Inverter Interview Question Answer - 3


1
Whether the load current is drawn from the supply source in the modified series inverter?


Modified series Inverter
  • The capacitor supply 50% of the load current and the DC source supply 50% of the total load current therefore the load current is drawn not only form the supply source but also from the capacitor in the modified series inverter.


2
Which semi conductor switching device is used in the high frequency series inverter?


Inverter grade thyristors

3
What is meaning of the time sharing principle in the series inverter?


Time sharing Principle
  • The inverter can be operated at high frequency by using time sharing principle. 
  • The numbers of series inverters are operate in parallel in the time sharing inverter.


4
What is reason behind the name ‘Parallel’ inverter?


Parallel inverter
  • As the commutating capacitor is connected parallel to the supply source, it is called as parallel inverter.


5
Whether the output waveform of the parallel inverter is sinusoidal?


The output waveform of the parallel inverter is square wave.

6
Describe the function of the feedback diodes in the parallel inverter.


Function of feedback diodes
  • The function of the feedback diodes is to permit load reactive power fed back to the DC supply when the load is inductive.


7
Give reason : The feedback diodes are connected to midpoint instead of end point of the transformer winding in the parallel inverter


Feedback diodes connection
  • If the feedback diodes are connected to the end points of the transformer, the commutating energy is dissipated in the SCRs and diodes therefore the de – rating of the SCRs and diodes is done. 
  •  The efficiency of the parallel inverter can be increased by connecting feedback diodes to mid tap points.


8
Describe the advantages and disadvantages of the Parallel inverter.


Advantages
  • It is possible to generated sinusoidal waveform by using suitable filters. 
  • Simple forced commutation circuit

Disadvantages
  • It is useful only when load is constant.
  • Design for fixed voltage
  • The inverter is not useful for high power if the value of inductor and capacitor is fixed.


9
What is meaning of the 180 degree mode of inverter operation?


180 Mode Inverter Operation
  • The 180 degree operation of the inverter signifies that each semi conductor switch conducts for 180 degree.


10
When gate signal is applied in the 180 degree and 120 degree operation of the inverter?


  • The gate signal applied and removed for 60 degree interval of the output waveform in the 180 degree and 120 degree operation of the inverter.


11
How many semi conductor switches conduct at a time in the 180 degree operation of the inverter?


Three ( one from each leg or two from any one leg and one from other leg )

12
What is phase shift between two adjacent switches in the 180 degree operation of the inverter?


60 degree

13
What is meaning of the 120 degree mode of inverter operation?


120 Mode Inverter Operation
  • The 120 degree operation of the inverter signifies that each semi conductor switch conducts for 120 degree.


14
How many semi conductor switches conduct at a time in the 120 degree operation of the inverter?


Two ( one from positive leg and other from negative leg )

15
What is phase shift between two adjacent switches in the 120 degree operation of the inverter?


60 degree

16
Describe the main difference between 180 degree and 120 degree mode of operation in the inverter.


180 degree operation of inverter
  • Each semi conductor switch conducts for 180 degree operation.
  • Two switches are conducted from positive leg whereas one switches from negative leg and vice versa.
  • The rated output power of the inverter is 33.3% of the maximum power rating of the six semi conductor switches.

120 degree operation of inverter
  • Each semi conductor switch conducts for 180 degree operation.
  • One switch conducts from positive leg and one switch from negative leg.
  • The rated output power of the inverter is 28.9% of the maximum power rating of the six semi conductor switches.



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