EMI/Y-capacitor in inverter phase outputs?

Question

Is it good or even used practice to filter out common-mode EMI in 3-phase industrial inverter (IGBT) phase outputs using phase-to-earth Y-capacitors? High du/dt might limit the lifetime of such capacitor, can ceramic y-capacitors handle this if film capacitors are in problems? 1000-3000V/us was mentioned in film capacitor's datasheet of for example TDK B81123. Any reason to use the caps in the phase outputs from the IGBT protection point of view (suppress voltage spikes or ESD)?

Wasn't able to find any literature related to the issue. Also DC-link could be tied to earth using Y-caps, not much of that either.

Answer 1

In short: build a class-D amplifier. This requires an LC filter at the inverter output. The filter keeps switching noise internal to the unit, and away from the cabling and motor (a shielded cable/conduit is not necessarily required). As an added bonus, the inductance limits \$dI/dt\$, allowing the control circuit some time to respond to peak current or fault conditions. (You are designing in fault protection, right?)

Putting a capacitor at an unfiltered inverter output is likely to not only increase EMI by increasing peak current flow, but those peak currents may destroy the inverter itself as well. The capacitor may overheat, but clearly this is a secondary consideration.

In the event such application is required -- snubber capacitors in resonant inverters perhaps -- C0G type ceramic, or polypropylene film of suitable rating, are likely to have low enough losses to handle that service.

Answer 2

It is an option to put such caps at the inverter output to guide the common mode current to ground before it would go mainly over the motor bearings to ground (which is often a major lifetime issue for variable speed controlled drives).