[TCML] Inverter dead times

["Herwig Roscher" <herwig.roscher@xxxxxx>]

Hello !

In order to understand inverters for SSTCs better, I've studied AN1045 of International
Rectifier and found in chapter "Full Bridge Inverter":

"...All the IGBTs should not be OFF at once during switching, since the power source
feeding the inverter continuously supplies current. It follows that a pair of IGBTs
should be turned ON a time delta t before turning OFF the other pair; time delta t
depends on turn-on and turn-off times associated to the devices (normally is some
hundreds of nanoseconds long). As a result, for a finite short time, a cross-conduction
of current takes place through the legs and the IGBTs must withstand it. During this
interval of time, the only harmless path for the reverse current is through a “free-
wheeling” diode and an IGBT..."

In chapter "Half-Bridge Inverter":

"...In this circuit, cross conduction must be accurately avoided. X1 and X2 must never be
ON at the same time. This is accomplished by switching X2 ON a time delta t after X1 is
switched OFF. Again, this blanking time depends on turn-on and turn-off times associated
to the devices.

There is *no* freewheeling current. D1 and D2 are protection diodes which ensure that V
EC is always well below the safety limit, in particular during switching transients. Very
low current diodes can therefore be used, provided they are fast enough..."

My questions:
1. Is it really advisable to tune full bridge inverters having a short shoot-through
time?
2. What is the correct design for the free-wheeling/protection diodes and could
suppressor diodes be used (very fast) ?
3. Need the IGBTs in a half-bridge inverter to have a V CES of 600 V, if the rail voltage
is 400 V dc ?

Looking forward to reading your comments,

Herwig
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