20-08-2013, 02:52 PM
Choose Your IGBTs Correctly for Solar Inverter Applications
Choose Your IGBTs.pdf (Size: 503.33 KB / Downloads: 105)
Given the many varieties of advanced power
devices available, choosing the right power
device for an application can be a daunting
task. For solar inverter applications, it is well
known that insulated-gate bipolar transistors
(IGBTs) offer benefits compared to other types of power
devices, like high-current-carrying capability, gate control
using voltage instead of current and the ability to match the
co-pack diode with the IGBT.
IGBT Technology
An IGBT is basically a bipolar
junction transistor (BJT) with a
metal oxide semiconductor gate
structure. This allows the gate of
the IGBT to be controlled like a
MOSFET using voltage instead of
current. Being a BJT, an IGBT has
higher current-handling capabil-
ity than a MOSFET.
An IGBT is also a minority
carrier device like a BJT, mean-
ing that the speed at which the
IGBT turns off is determined
by how fast the minority carrier
recombines.
High- and Low-Side IGBTs
Let’s assume a 1.5-kW solar inverter is being designed
with a 230-Vac output. Which IGBT shown in the table will
give the lowest power dissipation at 20 kHz? Fig. 4 shows
the breakdown of power dissipation of the IGBTs switching
at 20 kHz as discussed earlier. One can see that the ultrafast
planar IGBT has the lowest total power dissipation com-
pared to the other two planar IGBTs.
This is obviously due to the fact that at 20 kHz, switch-
ing loss becomes a very important component to the
total power dissipation of the IGBT. As can be seen, the
standard-speed IGBT has the lowest conduction loss, but
its highest switching loss makes the device unsuitable for
the high-side IGBTs.