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SarkariResultOutBMS · 2024

Previous Year Question

A quasi-square wave operation of single-phase PWM inverter is obtained using voltage cancellation method by combining
  1. Square wave and unipolar sinusoidal PWM switching schemes
  2. Square wave and bipolar sinusoidal PWM switching schemes
  3. Unipolar and bipolar sinusoidal PWM switching schemes
  4. None of the above

Correct answer: A

Explanation

Quasi-square-wave operation is produced by combining two square-wave bridge outputs with a controllable phase displacement. Their overlapping portions add while displaced portions cancel, allowing the fundamental output to be adjusted and selected low-order harmonics to be reduced.

Formula

vout = vbridge1 − vbridge2 with phase displacement

Step-by-step solution

Voltage Cancellation Method explanatory diagram

Correct Answer

A — Square wave and unipolar sinusoidal PWM switching schemes

Concept and Reasoning

Quasi-square-wave operation is produced by combining two square-wave bridge outputs with a controllable phase displacement. Their overlapping portions add while displaced portions cancel, allowing the fundamental output to be adjusted and selected low-order harmonics to be reduced.

Calculation / Key Relation

vout = vbridge1 − vbridge2 with phase displacement

Exam Takeaway

Voltage cancellation uses phase-shifted square waves.

Common Mistake

Do not confuse quasi-square operation with sinusoidal carrier-based PWM.

Common mistake

Do not confuse quasi-square operation with sinusoidal carrier-based PWM.

Exam tip

Voltage cancellation uses phase-shifted square waves.

Quick method

Voltage cancellation uses phase-shifted square waves.