Functional Safety of Electric Vehicles - Active Dischage of HV Capacitors

[Hrod_Wolf]

Hello everyone,

As I am discovering the active discharge, I wonder how it works for a DCDC converter. Can someone provide some links or basic litterature for me to understand the principle and some technical litterature to know it in-deph please ?

I aim to propose a strong safety strategy (Functional Safety Concept) in order to make sure that:
1- The active discharge operates properly
2- There is no interaction operating the active discharge while reacting to the DCDC internal failure.

Thank you in advance for your responses.

[f4eru]

There are many, many ways to make your device safe. It all depends on your architecture, objectives and budget....
A simple resistor may be enough.

[PartialDischarge]

I read some standard that recommends for example using resistors in parallel in case one of them fails open.
Usually active discharge circuits are commanded by a central control that send and On/off via an isolated dc/dc converter to the discharge circuit ( because usually the dc rails to be discharged are floating and the central control is not)
The discharge circuit is usually a string of mosfets of Jfets in cascode to meet the capacitor voltage and resistors are added to limit the current to a predefined level

[Hrod_Wolf]

I firstly want to understand the principle of the active discharge and how that works.
Secondly I’m interested in all readings you can suggest.
Thank you

[nctnico]

Also don't forget to have some kind of indicator to show there still are lethal voltages present. It has been a while but I vaguely recall LEDs and neon lamps being used in some of the high power supplies I have worked on a long time ago.

[NiHaoMike]

Also don't forget to have some kind of indicator to show there still are lethal voltages present. It has been a while but I vaguely recall LEDs and neon lamps being used in some of the high power supplies I have worked on a long time ago.

Blue LEDs work great for that, takes very little current to get a visible glow. One fail safe configuration would be to have two in series (at high voltage, if a LED fails open, it probably will change to failing shorted) then with a properly rated resistor or string of resistors to the voltage rail. Add a second one of those resistor/LED strings for redundancy.