Strange MOSFET gate signal of a brushless dc motor

Thread Starter

arman74

Joined Jul 1, 2017
30
Hi guys.
We are trying to drive a 350 watts 3 phase sensor BLDC(40v 9A) with 6 n channel mosfets. We are using irf2103 as gate drivers.We have driven the motor without load,but when we try them under load(it is a scooter motor) the motor generates weird sounds and the low side mosfets get very warm and then burn. At every step we pwm a high side and just make the low side on(no pwm). We checked the gate signal and we saw some strange signals at the high side gates. When we pwm on high side mosfets the pwm is on the gates,but before and after our pwm there are some ramp-pwm signal on the high side gates and we dont know what it is.Below is a pic of this problem.
I would be thankful if you help me:).

Yellow is the low side of one half bridge and the blue one is the gate signal of the other half bridge high side mosfet.
The same signal as the blue exist on the motor phase and boot strap capacitor.
 

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