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?
We use a -ve voltage for turning off the mosfet to prevent any false turn on. the mosfet can turn on at 3.0V itself. So, if we turn off using 0V then there is a chance of false turn on. To prevent it we use -ve voltage
Team was absent, that is the reason for the delay.
You mentioned that VCC2 is +15V and VEE2 is -5V but what about their return points? Where is that connected? Are +15V and -5V two terminals of a single supply? or +15V and -5V are two different supplies with each having a return or GND terminals? There is a CLAMP pin available to avoid false turn ON, have you not used that?
Look at the image of the table. It is clearly written than VEE2 is the GND terminal or return point of VCC2 for M version. Looks like you cannot connect a negative supply to VEE2 it should be GND or 0V and use CLAMP terminal to avoid false turn ON.
M version can be used only for Unipolar power supplies. Kindly check all the attached images. Typical application circuit is also attached, have a look at it.
You cannot use bipolar supply with the M version of gate driver IC you are using. You can only use unipolar supply so VCC2 should be 15V and VEE2 should be GND point of 15V. Use CLAMP pin as shown in the typical application circuit to avoid false turn ON.
It is designed by electronics team. I can pass this information to the electronics team.
Will this bipolar supply in this M version will affect the rms current or heat generation?
Could you give me a rough idea, what would be the maximum possible heat generation if 61A current is passing through the mentioned MOSFET? [Ambient temp=25°C]
Yes it will affect since the driver circuit does not have return point connected anywhere, definitely the MOSFET will find it difficult to turn ON fully, the MOSFET is not turning ON fully and that is the reason the resistance between drain and source is quite high and hence the higher power dissipation resulting in higher temperature. If you still want to use bipolar supply then why not use E version gate driver? why experiment with M version? datasheet clearly says E version is designed for bipolar supply, if you notice in the attached image the E version has positive, negative as well as GND which is the return point of the bipolar supply which is missing in your case right now.
If 61A is passing then roughly power dissipation should be around 8 to 9 watts.
I have discussed with electronics team. A miscommunication happened. The gate driver they are using is UCC5350-Q1. Gate driver data sheet
And the mosfet model they are using is,MOSFET Data sjheet
Is the bipolar supply allowable in this gate driver? What would be the allowable max heat for this case?
Once again apologies for the inconvenience caused.
