In a three-phase bridge inverter, the gating (firing) signals for the three legs are phase-shifted to produce a three-phase output. What is the phase difference between the three sets of gate pulses?

Introduction / Context:
Three-phase bridge inverters synthesize three sinusoidal (or quasi-sinusoidal) phase voltages that are 120° apart. The gating scheme must reflect this separation to generate balanced three-phase outputs for motors or grids (via filters).

Given Data / Assumptions:

• Standard three-leg inverter topology.
• Balanced three-phase output desired.

Concept / Approach:
For a balanced three-phase system, phase voltages (or their fundamental components) must be separated by 120°. Thus, the switching functions (or their reference phases) are typically displaced by 120° to achieve the correct phase relationships.

Step-by-Step Solution:
1) Identify three legs: A, B, C.2) Apply modulation with phase shifts of 0°, 120°, and 240° (equivalently −120°).3) The fundamental components then have 120° displacement.
Verification / Alternative check:
Carrier-based PWM references for three-phase inverters use phase-shifted modulating waves by 120° to obtain a balanced set.
Why Other Options Are Wrong:

• 60°/240° alone do not represent the three mutual separations properly.
• “Any of the above” is incorrect; 120° is specific to three-phase balance.
• 90° would create four-phase relationships, not three-phase.

Common Pitfalls:

• Confusing electrical angle between line voltages and switching pattern details.
• Assuming 60° relates to six-step commutations; the phase relation remains 120°.

Final Answer:
120°.