A single-phase full-bridge VSI is fed from a 48 V battery and delivers power to a resistive load of 10 Ω. Using square wave switching, verify1.RMS value of fundamental output voltage is 43.2 V.2.Power delivered by the fundamental component is 186.6 W.3.Total power delivered to the load is 230.4 W.Which of the statements are correct?

Correct Answer: D - 1, 2 and 3

Quick Concept Explanation

In 180° conduction, three devices conduct at a time and the fundamental output is higher; the floating star neutral can shift relative to the DC midpoint. Full-bridge square-wave total RMS voltage is 48 V, so total load power=48²/10=230.4 W. Fundamental RMS=4Vdc/(π√2)≈43.2 V and fundamental power≈43.2²/10=186.6 W.

Exam focus: Track pole voltage and load-neutral voltage separately. Common trap: Balanced load does not force the floating neutral to the DC midpoint at every switching state.

Statement-wise Verification

• Statement 1 - Correct.
  RMS value of fundamental output voltage is 43.2 V.
  Fundamental RMS=4Vdc/(π√2)≈43.2 V and fundamental power≈43.2²/10=186.6 W.
• Statement 2 - Correct.
  Power delivered by the fundamental component is 186.6 W.
  Fundamental RMS=4Vdc/(π√2)≈43.2 V and fundamental power≈43.2²/10=186.6 W.
• Statement 3 - Correct.
  Total power delivered to the load is 230.4 W.
  Full-bridge square-wave total RMS voltage is 48 V, so total load power=48²/10=230.4 W.

Core Concept

Three-phase voltage-source inverters can be operated with 120° or 180° conduction sequences. In 120° conduction, each switch is on for 120° and only two devices conduct at a time, leaving one phase disconnected for intervals. In 180° conduction, three devices conduct at a time and the fundamental output is higher; the floating star neutral can shift relative to the DC midpoint.

Formula / Key Relationship

Conduction duration: 120°→two switches at a time; 180°→three switches at a time.

Step-by-Step Check

Full-bridge square-wave total RMS voltage is 48 V, so total load power=48²/10=230.4 W. Fundamental RMS=4Vdc/(π√2)≈43.2 V and fundamental power≈43.2²/10=186.6 W.

Why the Other Options Are Wrong

Option A is incorrect because it omits correct statement(s) 3. Option B is incorrect because it omits correct statement(s) 1. Option C is incorrect because it omits correct statement(s) 2.

Exam Shortcut / Approach

Track pole voltage and load-neutral voltage separately.

Common Mistake

Balanced load does not force the floating neutral to the DC midpoint at every switching state.

Quick Revision

Square-Wave Fundamental and Load Power is linked with Single-Phase Full-Bridge VSI, Inverters and Power Electronics. Track pole voltage and load-neutral voltage separately.