[Solved] In 180-degree PWM inverter power supply: ...

56) In 180-degree PWM inverter power supply:

• Power devices are made 'ON' for 1/3 of the cycle.
• Power devices are made 'OFF' for 1/2 of the cycle.
• The phase voltage = 0.4714 V_supply
• Line voltage = V_supply
• Line voltage < V_supply

Choose the correct answer from the options given below:

1. 1. B, C and D only [Option ID = 3133]
2. 2. B and E only [Option ID = 3134]
3. 3. B, C and E only [Option ID = 3135]
4. 4. A, B and C only [Option ID = 3136]

Answer: 3

Solution

To solve this problem, we need to analyze the characteristics of a three-phase bridge inverter operating in its two standard modes: 

${180}^{\circ }$

 conduction and 

${120}^{\circ }$

 conduction.

Let's evaluate each statement based on these modes:

1. Analysis of 

${180}^{\circ }$

 Conduction Mode

In this mode, each power device (SCR/Transistor) conducts for 

${180}^{\circ }$

 of a 

${360}^{\circ }$

 cycle.

• Statement A: Power devices are ON for 

  $1\mathrm{/}3$

   cycle (

  ${120}^{\circ }$

  ). 

  $\to$

   False (It is 

  $1\mathrm{/}2$

   cycle).

• Statement B: Power devices are OFF for 

  $1\mathrm{/}2$

   cycle (

  ${180}^{\circ }$

  ). Since conduction is 

  ${180}^{\circ }$

  , the OFF time is also 

  ${180}^{\circ }$

   (

  $1\mathrm{/}2$

   cycle). 

  $\to$

   True.

• Statement C: The RMS Phase Voltage (

  $V_{ph}$

  ) calculation:
  The standard formula for RMS phase voltage in 

  ${180}^{\circ }$

   mode is 

  $V_{ph}=\frac{\sqrt{2}}{3}{V}_{supply}$

  .
  

  $V_{ph}=\frac{1.4142}{3}{V}_{supply}\approx \mathbf{0.4714}{\mathbf{V}}_{\mathbf{s}\mathbf{u}\mathbf{p}\mathbf{p}\mathbf{l}\mathbf{y}}$

  . 

  $\to$

   True.

• Statement D: Line voltage (

  $V_L$

  ) = 

  $V_{supply}$

  . 

  $\to$

   False (The peak line voltage is 

  $V_{supply}$

  , but the RMS value is different).

• Statement E: RMS Line voltage (

  $V_L$

  ) calculation:
  The standard formula is 

  $V_L=\sqrt{\frac{2}{3}}{V}_{supply}\approx 0.8165V_{supply}$

  .
  Since 

  $0.8165<1$

  , then Line voltage < . 

  $\to$

   True.

2. Analysis of 

${120}^{\circ }$

 Conduction Mode

In this mode, each power device conducts for 

${120}^{\circ }$

 (

$1\mathrm{/}3$

 cycle).

• Statement A would be True, but Statement C would be False because phase voltage in this mode is 

  $V_{supply}\mathrm{/}\sqrt{6}\approx 0.408V_{supply}$

  .

Conclusion

Based on the calculations above, statements B, C, and E are all true for the 

${180}^{\circ }$

 conduction mode of a three-phase inverter.

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