Single-pulse PWM in a bridge inverter With single-pulse width modulation (one pulse per half-cycle) in a single-phase bridge inverter, the output (fundamental) frequency equals the frequency of which signal?

Introduction / Context:
Pulse width modulation (PWM) uses a low-frequency reference to shape the output fundamental and a high-frequency carrier to determine pulse placement or width. In single-pulse PWM, exactly one pulse is generated per half-cycle, and the fundamental frequency is set by the reference waveform used for modulation.

Given Data / Assumptions:

• Single-phase bridge inverter.
• Single-pulse PWM (one pulse per half-cycle).
• Low-frequency reference compared with high-frequency carrier or timing ramp.

Concept / Approach:

The output voltage is synthesized by switching the DC link according to comparisons between the reference and a carrier (or by timing logic). The fundamental component of the inverter output tracks the frequency of the reference (modulating) signal; the carrier frequency sets the switching frequency, not the fundamental power frequency delivered to the load.

Step-by-Step Solution:

Verification / Alternative check:

Fourier analysis of PWM waveforms shows the fundamental component frequency equals the reference frequency; sidebands and harmonics are clustered around multiples of the carrier and its intermodulations but do not alter the fundamental frequency selection.

Why Other Options Are Wrong:

• Carrier frequency (option b) determines switching ripple, not the delivered fundamental.
• Options c and d conflict with standard PWM principles.

Common Pitfalls:

Confusing switching frequency with output fundamental; increasing carrier frequency reduces ripple but does not change f_out.

Final Answer:

Reference (modulating) signal