Auxiliary commutated chopper (Class-C/McMurray) peak capacitor current A voltage-fed auxiliary commutated chopper uses a commutation inductor L and capacitor C with input voltage V. What is the peak capacitor current during the resonant commutation interval?

Introduction / Context:
In auxiliary (forced) commutation of thyristor choppers, an LC network is charged and then resonated to apply a reverse current/voltage for turn-off. Estimating the peak commutating current is essential for rating the capacitor, inductor, and switching devices.

Given Data / Assumptions:

• Ideal resonant commutation: negligible resistance during the short commutation interval.
• Input (charging) voltage: V.
• Commutation components: inductor L and capacitor C.
• Natural resonant frequency: ω0 = 1 / √(L * C).

Concept / Approach:

For a series LC excited by a step of voltage, the characteristic impedance is Z0 = √(L / C). The resulting sinusoidal current has a peak value equal to the applied step divided by Z0, provided the capacitor is driven from V to resonate with L.

Step-by-Step Solution:

Verification / Alternative check:

Dimension check: √(C / L) has units of 1/Ω, so V * √(C / L) has units of ampere, consistent with current.

Why Other Options Are Wrong:

V / √(L * C) is voltage divided by 1/ω0, producing units of volt-second per henry (not a current); V * √(L / C) gives the inverse of the desired dependence; V * C / L has incorrect dimensions.

Common Pitfalls:

Confusing characteristic impedance Z0 = √(L/C) with the resonant frequency ω0; mixing up peak voltage and peak current formulas; neglecting damping, which only slightly reduces the peak in real circuits.

Final Answer:

V * √(C / L)