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.
Electrical – Hard and Soft Chopping
brushless-dc-motorpwm
Related Solutions
In theory, one could use a BLDC motor as a 3-winding (six-phase) stepper motor, controlling rotation speed by controlling the frequency with which the windings are driven. Indeed, for certain situations where would be using a motor at only a fraction of its rated power (e.g. because the cheapest motor one could get was much bigger than necessary) this approach will work fine. A major problem with this approach, however, is that when a motor is driven at a fixed speed, a reduction in mechanical output torque will not cause a corresponding reduction in current draw. Instead, it will cause a massive increase in the amount of heat dissipated by the motor. Although stepper motors are generally able to safely dissipate 100% of rated power as heat, BLDC motors generally aren't.
One might regard the situation as being vaguely analogous to regulating the speed of an automobile purely by using the clutch and brake pedals while the engine was always running at wide open throttle. True, one could for a little while make the car go any desired speed using just two of the three pedals (and if one was going uphill, one could do it with the clutch alone), but fuel economy would be dreadful, and unless one added a truly massive amount of extra cooling to the clutch it would be destroyed in minutes.
So, if I want the speed to remain at, say 3000rpm, and increase the thrust from, say 400g to 500g, I increase the current through the motor. I do this by increasing the PWM duty cycle. But, this means the speed will also increase from 3000rpm to a higher value, right? How can this be maintained then?
You would only want to increase the torque (thrust) if the mechanical load were threatening to slow the motor down - by increasing the PWM to counter that increase in load torque you are largely keeping the motor at constant speed. Remember a simple DC motor (even a brushless type) has a very clear torque-speed characteristic that means, for a given speed at a given torque, an increase in torque of \$x\$ will reduce the speed largely by \$x\$ also.
It's a not a perfectly linear relationship and changes entirely when field windings are implemented but it's fairly reliable: -
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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.