Switching loss is in function of the switching frequency and switching energy associated for each transistor. The switching energy is related to the device current and voltage at the switching transient. Using the switching energy curve in the datasheet, as for example the one in LMG3522R030 datasheet, the total switching loss can be estimated.

Figure 3-1 Grid Voltage and Grid Current

Figure 3-3 Switching Losses: S3 and S4

Figure 3-2 Switching Losses: S1 and S2

In Figure 3-1, current and voltages on the switching node of the switching cell shown previously are shown. Note that both the current and the voltage are in phase, and as a result, involving an inverter operation of the switching cell. The switching losses of the four transistors are shown in Figure 3-2 and Figure 3-3. Note that switching losses are only present for half-electrical period. This means that half-period the switches are hard-switching and the other half-period the FETs are soft-switching. In average over full AC period AC losses are equal for all FETs. Additional investigations have been conducted and the switching losses in all the operational modes mentioned below are always the same, where with operating mode this is mean:

• Power Factor Corrector (PFC) power from the AC to the DC
• Inverter power from the DC to the grid.
• Capacitive and inductive compensators, when only reactive power is pushed or drained to the grid.