Electrical – Hard and Soft Chopping


I am controlling my BLDC (Brushless DC motor) controller with PWM technique by changing the duty cycle to reduce the power(current) in phase winding.
what is hard and soft chopping in PWM based controller(BLDC controller). Soft chopping is good PWM control technique compare to the hard one. But what is the concept of the both chopping and how to apply in the controller.

Best Answer

There are dual N type bridges which use the low side PWM to create the boost voltage for the high side driver gate. This reverses sides with direction.

Acceleration ramp on PWM control, limits current and thus controls torque.

Soft chopping reduces slew rate dI/dt and thus reduces EMI noise at the expense of driver VI*f power dissipation often reduced by passive CM and DM LLC filters . (common and differential mode dual winding with RF caps to CM gnd and differential)

Examine the timing diagrams in published designs to see how.