Quote:
Originally Posted by zbrozek
Well, I expect the current in the motor to rise while its leads are connected to the rail, to fall when it's freewheeling, and to fall precipitously when its leads are both shorted to ground.
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A wise person once told me "Data is always better than speculation"
Your data is showing you what the motor current is doing.
During the off portion of the PWM period,
the CIM leads are shorted. See attached sketch, taken from the Black Jag User's Manual. When the leads are shorted, the current continues to flow through the CIM coil due to the coil inductance.
The Jag switches at 15KHz; that's a 67 μs period. At 20% duty cycle, that's 13 μs "on" and 53 μs "off". During the "on" portion, the voltage is applied and the current builds up. During the "off" portion, the CIM leads are shorted and the current continues to flow but decays. That's what your data is showing.
Do you have access to equipment to test the CIM's coil inductance? If so, would you be willing to do that? Then we could crunch the numbers and show that the inductance is high enough to store sufficient energy to maintain current flow during the off portion.