SiC MOSFET losses calculation equations

im_zg

Hi,

can you please share equations for SiC MOSFET Conduction and Switching Losses? Are they similar to the IGBT losses (Vce0, rce, Vf0, rf), https://www.koreascience.or.kr/article/CFKO201732568238441.pdf, page 4 and 6?

In my project, I am thinking of using six C2M0160120D SiC MOSFETs and I would like to calculate MOSFET and diode losses.

I am also trying to SpeedFit 2.0 Design Simulator, but I get an error of exceeding the maximum runtime of 120 seconds.

AAnders

Hello,

Thank you for your question. Unlike IGBTs, SiC MOSFETs do not exhibit a turn-on voltage knee. They are purely resistive, so the forward conduction loss is simply I^2*RDS(on). The value of RDS(on) can be found in the datasheet and varies with temperature and gate voltage. The conduction loss of the body diode of the SiC MOSFET is modeled similarly to the FWD diode that is often co-packaged with an IGBT (I*Vf0+I^2*Rf). The switching loss component of the losses can be estimated from the plots on the datasheet. However, we do recommend using SpeedFit for loss estimations as it will automatically factor in the effect of temperature and include the effect of different gate resistance values, bus voltages, and current levels.

Can you share the topology and operating conditions that you are trying to run on SpeedFit?

im_zg

Hi,

thank you for the reply. I assume the three-phase 2-level inverter SpeedFit model uses sinusoidal PWM. I would like to replicate the losses calculation as I would like to compare losses for different PWMs, for example, space vector, discontinuous, or any other PWM methods developed for research or academia.

In the datasheet for C2M0160120D, in Figure 23 only Eon and Eoff are given, and says FWD = C4D05120A. Can I assume FWD is C4D05120A? There is a difference between Forward Voltage; 1.4 for C4D05120A and 3.3 for C2M0160120D Reverse Diode.

When I look at the C4D05120A datasheet, it does not give Err (diode switching energy), but it says "Essentially No Switching Losses". Can I also assume there are no FWD switching losses, i.e. Err = 0 mJ?

For SpeedFit, I accidentally left the default value of the inductance for a three-phase 2-level DC/AC inverter. When changing it to real (project) value, it worked ok :)

AAnders

Hi,

Are you planning to add a parallel Schottky diode to the MOSFETs in your inverter? If so, then you can use the switching loss curves shown in Figure 23. However, if you are planning to just use the body diode for conduction during the dead time, the MOSFET switching losses, particularly Eon will be higher since it will include the reverse recovery of the body diode of the opposite device which is higher than the Schottky diodes that were used in the testing to create the curves in figure 23.

The Schottky diodes do not have reverse recovery charge in the typical sense, but they will exhibit a small amount of recovery charge as a result of the stored capacitive energy in the junction, which can be found in the datasheet.

SpeedFit currently does not support other modulation schemes. However, you can download our PLECS device models and create your own simulation employing any control scheme you wish to explore. The device models are available at https://www.wolfspeed.com/tools-and-support/power/ltspice-and-plecs-models

As a final note, you may be interested in looking at our C3M0160120D device. It is a newer generation than the part you mentioned which has several benefits including lower cost and gate drive compatibility with a broader portfolio of parts in case you want to test with other RDS_on value parts.

AAnders

Hello im_zg,

If the information here answers your question, may I request you to click on the "Close this discussion" link.