Firing frequency in a three-phase series inverter In a three-phase series inverter, the relationship between the firing frequency of the switches and the output (fundamental) frequency is:

Introduction / Context:
Series inverters commutate current through resonant elements. In three-phase versions, multiple switching events per electrical cycle are required to synthesize the three-phase waveform.

Given Data / Assumptions:

• Three-phase series inverter with six switch operations per cycle to create line-to-line steps.
• Idealized commutation; focus on event counting per fundamental period.

Concept / Approach:
A three-phase bridge involves six sequential switching intervals in one electrical period (each 60°), analogous to six-pulse operation. Thus, the gating (firing) events happen six times during each output fundamental cycle.

Step-by-Step Solution:
Three-phase synthesis → six equal segments per 360°.Each segment requires a firing event → six firings per cycle.Therefore, firing frequency = 6 * f_out.

Verification / Alternative check:
Waveform diagrams for three-phase inverters show six commutations per period, matching the six-step concept.

Why Other Options Are Wrong:
Equal/Twice/Thrice: Underestimates the number of commutations needed for three-phase stepped synthesis.

Common Pitfalls:
Confusing PWM carrier frequency with fundamental commutation count; here we refer to fundamental firing events.

Final Answer:
six times the output frequency