We are using MOSFET based air cooled Inverter for EV car. Maximum current rating is 425A. MOSFET allowed temp=100°C Total MOSFETs=42. Total arms=6, Number of MOSFET in one arm=7
The loss values are found out using Altair PSIM. Thermal simulation is done using Ansys icepak.
There are two operating points 1) 30 min run with 175A
2) 30 sec run with 425A.
Loss corresponding to 425A is not able to withstand for 30sec.
We have done one physical testing at 375A and ran for 30sec, temp reached is 94°C but for me in simulation it gave 140°C in 10 sec. Simulated loss value for 425A is 25.8W per switch
We’re trying to understand:
Is a loss of 25.8 W per MOSFET realistic or acceptable for this device?
Why is there such a large discrepancy between test results and simulation?
Datasheet says max Id current of 366A at Vgs 10V and temperature 25 degree celcius. At 100 degree celcius it reduces to 259A and with Vgs 6V at 100 degree celcius it further reduces to 216A. These are the continues current limitations. The current that you are mentioning of 375A and 425A, are they continues current or switching current? When you say single arm with 7 switches, how are these switches arranged? series or parallel?
375A and 425A are rms current. (Consider 425A only. because 425A is the peak current drawn from controller). And 7 switches are in parallel connection. So current through one single switch is 425/7=60.71A.
25.8 watts loss is quite high for ~61A through each MOSFET even at 95 degree celcius. How much is the gate drive voltage? and what is the Vds voltage during conduction?
I need to look at your circuit, the voltages applied to the driver, with Vds I meant the voltage dropped across the drain and source terminals when the MOSFET is conducting 61A.
I am trying to find out if your MOSFET is fully conducting or not. If it is not fully conducting then the resistance between drain and source can increase resulting in higher power dissipation across drain and source. As per the driver you have shared what voltage is connected to pins VCC2 and VEE2 and is there any other passive circuitry involved externally before driving the gate of the MOSFET?
Vcc2=15V, Vee2= -5V.
Before gate driver decoupling capacitor circuit is there.
There are 3 boards are there. MOSFETs are in power board, Gate driver board (it contains capacitor bank also) and control board.
The datasheet shows two different packages for UCC5350, kindly check the attached image and confirm which one is yours. It will be great if you can measure and let me know the voltage across drain, source terminals and gate, source terminals while the MOSFET is conducting 61A. Any specific reason for using -5V on VEE2?
