Assertion–Reason on inverter output control by PWM Assertion (A): The output voltage of an inverter can be effectively controlled using pulse-width modulation (PWM). Reason (R): In a current-source inverter (CSI), the input current is constant.

Introduction / Context:
PWM is the predominant technique for controlling inverter output magnitude and waveform quality, particularly in voltage-source inverters (VSIs). Separately, current-source inverters aim to keep the DC input current nearly constant using a large series inductor.

Given Data / Assumptions:

• PWM varies pulse widths or switching patterns to adjust the fundamental output and reduce harmonics.
• CSI employs a stiff current source at its input.

Concept / Approach:
Statement A: True. By modulating pulse widths (sinusoidal PWM, space-vector PWM), an inverter’s fundamental RMS output can be linearly controlled while managing harmonic content.
Statement R: True in principle for CSIs; a large DC-side inductance imposes quasi-constant input current. However, that constancy does not explain why PWM controls an inverter’s output—the explanation pertains to switching pattern control rather than current-source characteristics.

Step-by-Step Solution:
Accept A as true: PWM directly sets effective output voltage waveform.Accept R as true: CSI design targets nearly constant input current.Causality check: R does not logically explain A, so choose “both true, but R not the explanation”.

Verification / Alternative check:
Control textbooks treat PWM as an inverter modulation method independent of whether the DC link is voltage- or current-fed; CSI constant current is a separate design feature.

Why Other Options Are Wrong:

• (a) would require R to explain the PWM principle, which it does not.
• (c), (d), (e) contradict established inverter theory.

Common Pitfalls:

• Conflating VSI and CSI control methods; PWM control of voltage does not depend on a CSI’s constant-current input.

Final Answer:
Both A and R correct but R is not correct explanation of A