The Importance of Hot-Swap and Transient Suppression in HVDC Systems

Why is hot-swapping so important in DC systems? If you have only worked with AC systems, this question might baffle you. In an AC system, when you want to plug or unplug something you just do it, without thinking whether the main circuit breaker is on or off.

However, in DC systems it’s not that easy. If you simply try to unplug a DC-DC converter from a live circuit and the converter is not equipped with a hot-swap circuit, you have just turned your DC-DC converter into a very expensive, one-time welding machine.

If you want to be able to plug and unplug your converter without damaging it and the surrounding systems, you only have two options:

  1. Depower the whole system every time you need to plug in or unplug a converter
  2. Design a hot-swap circuit to allow you to plug and unplug the converter from a live circuit

Option 1 above is not always feasible, especially in larger systems powering a multitude of power electronic converters. Depowering the entire system just to reconfigure a small section can be very cumbersome: imagine for example a datacenter where you need to depower the whole system and lose all your computing capability every time you need to unplug a single blade. In these cases, option 2 is the best option. Historically, hot-swap circuits have been developed and deployed in 12 V and 48 V systems.  However, because of the continuous increase in power requirements in many applications, some designers are now investigating a transition to higher distribution voltages (380 Vdc being one of the most attractive). With this transition comes the need for hot-swapping capability at higher voltages. New approaches need to be explored since the severity of potential arcing events at 380 V is extremely higher than at 12 V and 48 V, and therefore the low voltage approach is not directly scalable.

To simplify the customer design effort, Vicor’s BCMs in a VIA package have been equipped with built-in hot swap circuitry tailored for the characteristics of the BCM. This integrated solution completely eliminates the requirement for a customer hot swap design and the need for external components. The integrated and optimized hot-swap feature guarantees smaller size, higher power density, and better overall performance than an external discrete solution, and significantly reduces the system design effort and build time.

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