Difficulty: Easy
Correct Answer: 6 times the line frequency
Explanation:
Introduction / Context:Pulse frequency determines the ripple frequency in the DC output and the gating pattern of a 3-phase fully controlled rectifier. Understanding its relationship to mains frequency is crucial for filter design and control timing.
Given Data / Assumptions:
Concept / Approach:In a 3-phase 6-pulse bridge, a device is fired every 60 electrical degrees, resulting in six firing events each line cycle. Therefore, the pulse frequency f_p = 6 * f_line. This also sets the dominant DC ripple at 6f_line for continuous current operation.
Step-by-Step Solution:
Line cycle = 360°.One gate command every 60° → 6 pulses per cycle.Thus, f_pulses = 6 * f_line.Verification / Alternative check:
The converter is known as a '6-pulse' rectifier; harmonic spectra show ripple at 6f, 12f, 18f, etc.Why Other Options Are Wrong:
3f corresponds to a 3-pulse (half-controlled) system; 9f/12f do not match the standard 6-pulse bridge.Common Pitfalls:
Confusing device conduction angle (120°) with the firing interval (60°) and resultant pulse count.Final Answer:
6 times the line frequency
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