Three phase pwm inverter for three phase motor

Hi all,

I am SKM400GB123D IGBT Modules to control Three phase motor using PWM sine patterns
IGBT Driver i am using is IR21362
Gate resistor is 3.3 Ohm.
1N4007 diode in parallel of gate resistor
Switching frequency is 5KHz
minimum Duty cycle time is 12uSec
maximum Duty cycle time is 120uSec
Dead time is 8uSec
Gate turn on voltage is 14V
Gate turn off voltage is 0V
This system have been prepared for 75KW motor load
I have tested this on 0.5W motor load
The system designed for input DC voltage 600VDC
I have tested this on 300VDC.
at this voltage motor works well as speed varies as i vary Duty cycles
But when i applied 600VDC as mentioned that the system designed for
the behavior is as

at start up motor works well but as i increased its duty cycle its speed increased and then
all three upper side IGBTs shorted and main fuse blown.

I am unable to understand that why upper three IGBTs shorted while half bridge should be completely shorted if there is dead time problem which i found at very early stage and i resolved it.

Please suggest me the solutions as early as possible

Thanks in advance

Do you observe the formula U/F=const. When you increase the voltage you must proportionally increase the frequency.