I have a quick question for you guys and gals.
I have built a circuit that can control a Brushless DC motor called an Electronic Speed controller. I was told that I should put snubbers on each phase. I will attach the circuit below. The problem is, I don't know how to calculate the values for these RC snubbers that were recommended.
When I run the motor in open loop (I don't want to add my code for closed loop commutation yet until I fix this problem) and I attach the oscilloscope to one of the phase leads of the motor with respect to the ground of the circuit, I see high spikes in the PWM waveform. I am driving the highside Nchannel MOSFETS with PWM while leaving the lowside MOSFETS completely on or off so that I can control the current, torque, and speed of the motor. Every time the voltage goes high in the PWM signal, there is a significant spike which I am assuming is from the inductive kick of the electromagnetic stators of the motor. I was told that snubbers would solve this.
I kept damaging motors over time and other components. So my question is, how do I calculate the values of the snubber components...?
...or do I just play around with the values and/or RC time constant and view the waveform on the oscilloscope until I reduce the spiking completely or to a bearable minimum?
I only showed the section of the circuit I thought was relevant but if you need me to upload more let me know. I have RC snubbers (R8, C15; R9, C16; R10, C17) on each of the 3 phases but I don't know what values to use or even know how to come up with these values. So if anyone could guide me in the right direction I would be thankful.
Thanks for any help,
Michael Walden
I have built a circuit that can control a Brushless DC motor called an Electronic Speed controller. I was told that I should put snubbers on each phase. I will attach the circuit below. The problem is, I don't know how to calculate the values for these RC snubbers that were recommended.
When I run the motor in open loop (I don't want to add my code for closed loop commutation yet until I fix this problem) and I attach the oscilloscope to one of the phase leads of the motor with respect to the ground of the circuit, I see high spikes in the PWM waveform. I am driving the highside Nchannel MOSFETS with PWM while leaving the lowside MOSFETS completely on or off so that I can control the current, torque, and speed of the motor. Every time the voltage goes high in the PWM signal, there is a significant spike which I am assuming is from the inductive kick of the electromagnetic stators of the motor. I was told that snubbers would solve this.
I kept damaging motors over time and other components. So my question is, how do I calculate the values of the snubber components...?
...or do I just play around with the values and/or RC time constant and view the waveform on the oscilloscope until I reduce the spiking completely or to a bearable minimum?
I only showed the section of the circuit I thought was relevant but if you need me to upload more let me know. I have RC snubbers (R8, C15; R9, C16; R10, C17) on each of the 3 phases but I don't know what values to use or even know how to come up with these values. So if anyone could guide me in the right direction I would be thankful.
Thanks for any help,
Michael Walden
Attachments

152.4 KB Views: 76
Last edited: