Fully controlled bridge converter feeding a highly inductive load (assume nearly constant DC load current) What is the typical input (source) current waveform drawn from the AC supply?

Introduction / Context:
A fully controlled bridge converter supplying a highly inductive load is a staple case in power electronics. With large inductance, the load current can be assumed nearly constant (continuous conduction). The question focuses on identifying the shape of the input (mains) current waveform under these conditions, which is essential for estimating harmonics, power factor, and filter requirements.

Given Data / Assumptions:

• Topology: single-phase fully controlled bridge (four SCRs) or an equivalent fully controlled bridge.
• Load: highly inductive, so i_load is approximately constant within a cycle.
• Continuous conduction, device drops and overlap neglected for concept.
• Freewheeling occurs inherently via the bridge commutations.

Concept / Approach:

When the bridge devices conduct, the source must supply approximately the constant DC load current. During the alternate half cycle, the current reverses direction in the supply (because a different pair of SCRs conducts), but its magnitude remains nearly the same while conducting. Between commutations, depending on control angle, the source current is zero. Thus, the input current is a sequence of flat-topped pulses rather than a sinusoid.

Step-by-Step Solution:

Verification / Alternative check:

Standard waveforms in converter texts show rectangular line current pulses for continuous-current operation with inductive loads. Harmonic analysis confirms significant odd harmonics typical of rectangular pulses.

Why Other Options Are Wrong:

Sinusoidal is incorrect because phase control and the DC load current flatten the conduction current. DC is impossible since the AC source enforces alternating polarity. Triangular would require linearly changing current, which contradicts the constant-current assumption due to large inductance.

Common Pitfalls:

Confusing the DC load current with AC source current; assuming any AC-fed circuit draws sinusoidal current; overlooking the effect of large inductance making the current during conduction nearly constant.

Final Answer:

Rectangular (pulsed, approximately constant magnitude during conduction)