AQG 324 and SiC Modules: When the Named Guideline Does Not Cover Your Device

EV & automotive · 3 min read · 18 cited facts

AQG 324 is the guideline automotive customers name when they ask whether a power module is qualified for a drive inverter. The ECPE working group behind it formed in June 2017 and released AQG 324 on 12 April 2018, building on the German LV 324. It defines characterisation, environmental and lifetime testing for power modules used in motor-vehicle converter units.

The released version focuses on silicon-based modules. Wide-bandgap coverage for SiC and GaN was scheduled for later versions. That leaves a sharp gap: if your drive inverter uses SiC modules, the guideline your customer names and the guideline that actually covers your device may not be the same document. Settling which document governs — and which annex revision — belongs in the contract, not in the test lab afterwards.

What the SiC annex asks for

A revised AQG 324 annex on SiC-based modules gives specific guidance on four stresses:

• Power cycling.
• High-temperature gate bias.
• High-temperature reverse bias.
• Dynamic reverse bias.

Each is a long hold at a fixed electrical condition rather than a short characterisation sweep. That is why the equipment question for module qualification is duration stability and per-device monitoring rather than peak capability — a rig that can hit an impressive transient but cannot hold a bias point flat for weeks is answering a question nobody asked.

The bus the module lives on

AQG 324 addresses modules for motor-vehicle converter units, and the DC windows those units see are set by the OEM voltage-class documents. For a drive inverter the relevant LV 123 classes are HV_2b and HV_3:

A caution on sourcing. LV 123 and LV 148 are OEM-confidential documents, and every published table — including this one — is a vendor or lab republication. Errors circulate: at least one vendor table prints the LV 148 lower unrestricted-operating bound as 24 V, and that figure is not correct; VDA 320 puts unrestricted 48 V operation at 36–52 V. Check the republication you are working from against the OEM revision your contract names.

What this means for the equipment

The annex stresses are endurance holds, so the supply's job is to hold a programmed condition without drift for the full duration and to watch every device individually — one failing module must not disturb the bias on the rest. The other requirement comes from the application itself: a drive regenerates, so the DC side of any inverter or module test has to sink as readily as it sources. That single requirement eliminates most unidirectional bench supplies before any other specification matters.