Series connection of SCRs (high-voltage stacks) When SCRs are connected in series for higher blocking voltage, do they require both static and dynamic equalizing (stabilizing) circuits?

Introduction / Context:
Series-stacked SCRs are used to withstand higher voltages than a single device can block. Unequal device characteristics necessitate equalizing networks to avoid over-stressing any one device.

Given Data / Assumptions:

• Multiple SCRs in series across a high DC link.
• Device parameter tolerances (leakage, capacitances, recovery).
• Presence of both steady-state and transient conditions.

Concept / Approach:

Static equalization (typically via resistors) ensures near-uniform voltage sharing under steady DC conditions. Dynamic equalization (typically via RC snubbers) addresses non-uniform capacitive and recovery behavior during transients (turn-off, surges). Both are necessary for reliable operation.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer application notes recommend both networks for high-voltage stacks to prevent avalanche of a single device during surges.

Why Other Options Are Wrong:

Using only one type leaves the stack vulnerable either during steady DC (no resistors) or during switching transients (no snubbers).

Common Pitfalls:

Oversizing only the highest-leakage device or assuming identical parts always share stress evenly; ignoring temperature dependence of leakage.

Final Answer:

True