Hello,
Iam designing a four quadrant DC drive. The problem i am facing here is, speed control of DC motor. Check the schematic.
Iam using the PWM technique to control the speed. The mosfet used is STW7NA100. I think the problem is with the snubber. I have selected the R & C values arbitrarily. A reverse connected diode (MUR860) is also used across drain and source.
Result: Three mosfets dead.
How to calculate the snubber values?
Motor parameters:
KW - 0.75
RPM - 1500
Volts - 220V DC
Amps - 5A
Excitation: 220V DC & 0.4A.
Switching frequency: 500Hz. Duty cycle [0 - 90%]
Experiment conducted:
1. Initially 220V DC is applied to field
2. Slowly armature voltage is increased upto 80V and maintained constant at 80V.
3. A voltmeter connected across drain and source reeds 80V (Vds = snubber voltage)
4. When the duty cycle is changed, Vds crossed 100V. and the armature voltage dropped to 40V. Here the mosfets are being dead.
see this videohttp://youtu.be/PIb6ZQdza1w
Iam designing a four quadrant DC drive. The problem i am facing here is, speed control of DC motor. Check the schematic.
Iam using the PWM technique to control the speed. The mosfet used is STW7NA100. I think the problem is with the snubber. I have selected the R & C values arbitrarily. A reverse connected diode (MUR860) is also used across drain and source.
Result: Three mosfets dead.
How to calculate the snubber values?
Motor parameters:
KW - 0.75
RPM - 1500
Volts - 220V DC
Amps - 5A
Excitation: 220V DC & 0.4A.
Switching frequency: 500Hz. Duty cycle [0 - 90%]
Experiment conducted:
1. Initially 220V DC is applied to field
2. Slowly armature voltage is increased upto 80V and maintained constant at 80V.
3. A voltmeter connected across drain and source reeds 80V (Vds = snubber voltage)
4. When the duty cycle is changed, Vds crossed 100V. and the armature voltage dropped to 40V. Here the mosfets are being dead.
see this videohttp://youtu.be/PIb6ZQdza1w
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