half bridge problem class c chopper problem

Thread Starter


Joined May 28, 2009

Help needed! Okay now i am working on controlling a DC motor (prime mover) connected to the 3 phase syn motor so as to control the frequency. Alright, currently i can control the dc motor speed without any problem like the speed of 3000rpm or 1500rpm with the class c chopper(pwm) but whenever i turn on the variable load connected to the syn motor like 0 to 400ohm, immediately the dc motor slow down and the mosfet at the low side shall break down as shown in the picture. I am not sure what is the cause of the problem. Is it the back emf but i did connect the resistor to dissapate the back emf? The dc motor is draw approximately 230V 2-4A and my mosfet(IXTN36N50) rating is 500V 36A, driver is ir2110 and operating at 4khz (too slow?), dead time for pwm is 4us. Even without changing the pwm signal duty cycle leaving it constant like 92%, the dc motor is still able to run but whenever load is applied to the synchronous generator, the low side mosfet still fails and breakdown.Is it the mosfet rating isn't enough?