AN3095 datasheet(23/55 Pages) STMICROELECTRONICS

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AN3095

DC-AC converter

Doc ID 16555 Rev 3

23/55

Diode losses may be evaluated according to the following equations:

Equation 49

where

Equation 50

The resulting total losses for the single-phase inverter are calculated below:

Equation 51

resulting in 98% theoretical efficiency for the inverter stage. A simple modification of the

control strategy, together with a different choice of power devices, may improve the

efficiency and performance of the DC-AC stage. The modified circuit is shown in Figure 13.

Figure 13.

Conversion systems with modified DC-AC inverter

The low-side power devices, Z2 and Z4, are low-drop IGBTs switching at 50 Hz according to

grid polarity while the high-side devices are MOSFETs switching at high frequency with

pulse-width modulation. Compared to the standard topology, the main advantages are lower

conduction losses of both MOSFETs and low-drop IGBTs, absence of switching losses for

the low-side devices and, eventually, the possibility of using higher switching frequencies

with a reduction of reactive components size and cost and wider bandwidth for the control

loop.

The possible implementation of this solution may be based on the use of STW55NM60ND

for the high-side and STGW35NB60SD, connected in parallel to an external SiC diode, for

the low side. A gain in efficiency between of 0.5 % and 1 % may be measured with such an

implementation.

)

cos

(

diode

−

450

pk =

rr =

(

)

Pcond

off

Psw

diode

tot

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