Switching losses are another form of power loss related to the energy lost in turning on/off the MOSFETs. These losses are directly proportional to the time needed to fully slew the drain-to-source voltage and the switching frequency of the MOSFET.

The equation for switching loss during FOC commutation is calculated using the formula:

In 12V automotive systems the conduction losses dominate the total power consumption so switching losses are not the focus point. However, with automotive manufacturers moving towards 48V EV/hybrid systems, the switching losses become a more dominant player in the total losses. This trend in the market shift has led to more engineers optimizing the switching behavior to reduce total power consumption.

The key parameter of focus is the time taken to slew the MOSFET to and from the battery voltage. By reducing the slew time ( $\frac{Voltage}{T_{rise/fall}}$ ), MOSFETs can be switched more efficiently. Reduction in slew time is achieved by increasing the gate current of the motor driver, resulting in a faster slew rate. Figure 2-2 shows the impact of slew rate on switching loss.

Figure 2-2 Switching Losses 12V vs 48V